The Roberts Mountains Formation, 

a regional stratigraphic study with 

emphasis on rugose coral distribution 

GEOLOGICAL SURVEY PROFESSIONAL PAPER 973 

The Roberts Mountains Forn1ation, 

a regional stratigraphic study with 

emphasis on rugose coral distribution 

B1' CHARLES W. MERRIAM and EowiN H. McKEE 

Tl7ith a section on Conodonts, b_rv JOHN W. HUDDLE 

GEOLOGICAL SURVEY PROFESSIONAL PAPER 973 

A study of stratigraph_v, facies, and 

coral distribution in the 1niddle Paleozoic 

(Silurian and De·uonian) limestone belt of 

the central and southwestern Great Basin 

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON: 1976 
UNITED STATES DEPARTMENT OF THE INTERIOR 

THOMAS S. KLEPPE, Serretm)' 

GEOLOGICAL SURVEY 

V. E. :McKelvey, Director 

Library of Congress Cataloging in Publication Data 

Merriam, Charles Warren, 1905-

The Roberts Mountains Formation. 

(Geological Survey Professional Paper 973) 

Bibliography: p. 43-45. 

Includes index. 

Supt. of Docs. no.: I 19.16:973 

1. Geology, Stratigraphic-Silurian. 2. Geology, Stratigraphic-Devonian. 3. Rugosa. 

California. I. McKee, Edwin H., joint author. II. Huddle, John Warfield, 1907-

United States Geological Survey Professional Paper 973. 

QE66l.M45 551. 7'3'0979 

4. Geology-Nevada. 5. Geologyjoint author. III. Title. IV. Series: 

76-608307 

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

Washington, D.C. 20402 

Stock Number 024-001-02893-0 
CONTENTS 

Page 

i\bstract -------------------------------------------------- 1 

Introduction ---------------------------------------------- 1 

Purpose and scope of investigation _____________________ _ 

i\cknowledgments _____________________________________ _ 

History of investigation _______________________________ _ 

Paleontologic zoning of the Great Basin Silurian and Lower 

Devonian _______________________________________________ _ 

Scarcity of reefs or bioherms in the Roberts Mountains Formation _________________________________________________ _ 

Distribution of Great Basin Silurian limestone and dolomite 

belts and the regional dolomite problem _________________ _ 

Geographic distribution of Silurian limestones _____________ _ 

Roberts Mountains Formation of the Roberts Mountains, Nev __ 

Type section _________________________________________ _ 

2 

2 

3 

4 

4 

6 

7 

7 

9 

Stratigraphic relations to underlying and overlying 

formations -------------------------------------- 9 

Facies changes from limestone to dolomite __________ 10 

Stratigraphic paleontology of the type section____________ 10 

Fossils of units 1 and 2 ____________________________ 10 

Fossils of unit 3 ___________________________________ _ 10 

Age of the Roberts Mountains Formation of the type 

section------------------------------------------ 10 

Roberts Mountains Formation of the northern Simpson Park 

Mountains ------------------------------------------ 11 

Geologic setting________________________________________ 11 

Coal Canyon area ______________________________________ 11 

Coal Canyon fault zone ____________________________ 11 

Physical stratigraphy of the Pine Hill section________ 12 

Stratigraphic paleontology and age of Roberts Mountains Formation at Pine HilL_____________________ 13 

Fossils collected within the Coal Canyon fault zone __ 14 

Physical stratigraphy of the Pyramid Hill section ____ 14 

Problem ofthe Silurian-Devonian boundary at Pyramid 

Hill _ _ _ _ _ __ _ _ _ _ _ ___ _ _ _ _ _ _ _ __ ____ __ _ _ _ _ ____ _ _ __ __ 15 

Roberts Mountains Formation, Tuscarora Mountains _______ _ 

Physical stratigraphy ofthe Bootstrap Hill section _____ _ 

Stratigraphic paleontology of the Bootstrap Hill section __ 

i\ge of the Roberts Mountains Formation at Bootstrap 

15 

16 

16 

Hill __ _ _ _ _ __ _ _ _ _ _ _ _ _ _ _ ______ _ _ __ __ __ _ _ ____ _ _ __ ____ _ _ 17 

Roberts Mountains Formation of the northern Monitor Range 

Physical stratigraphy _________________________________ _ 

Stratigraphic paleontology and age of the Roberts Moun18 

18 

tains Formation at Copenhagen Canyon ______________ 18 

Roberts Mountains Formation at Brock Canyon, Monitor 

Range -------------------------------------------------- 19 

Roberts Mountains Formation at Dobbin Summit, Monitor 

Range -------------------------------------------------- 19 

Roberts Mountains Formation at Bare Mountain ____________ 20 

20 

22 

Roberts Mountains Formation of the northern Toquima 

Range --------------------------------------------------

Petes Canyon window----------------------------------

Ikes Canyon window ---------------------------------- 22 

June Canyon sequence ---------------------------- 22 

Roberts Mountains Formation of the northern 

Toquima Range-Continued 

Ikes Canyon window 

Page 

Mill Canyon sequence------------------------------ 22 

August Canyon sequence -------------------------- 23 

Northumberland window ------------------------------ 23 

Roberts Mountains Formation in the Toiyabe Range __________ 23 

Callaghan window ------------------------------------ 24 

Dry Creek area---------------------------------------- 24 

Point of Rocks and Straight Canyon ____________________ 24 

Pablo Canyon area ------------------------------------ 25 

Roberts Mountains Formation in the Shoshone Mountains ____ 25 

Silurian and Lower Devonian limestones of the northern In yo 

Mountains, Calif __ _ _ _ _ __ _ __ _ ___ ___ _ _ ____ __ _ _ __ __ _ _ __ 25 

Mazourka Canyon ------------------------------------ 25 

Vaughn Gulch Limestone -------------------------- 25 

Physical stratigraphy -------------------------- 25 

Stratigraphic paleontology ______________________ 26 

i\ge ------------------------------------------ 27 

Sunday Canyon Formation ------------------------ 28 

i\ge ________________________________ ------ ____ 28 

The Silurian-Devonian boundary in central Nevada __________ 28 

i\n appraisal of stratigraphic and age values of rugose corals and 

associated fossils, with description of previously unknown 

key Rugosa ____ -------------------------------------- 29 

Rugose corals of special stratigraphic value ______________ 29 

Silurian nondissepimented Rugosa------------------ 29 

Family Kodonophyllidae ________________________ 29 

Subfamily Kodonophyllinae Merriam ________ 30 

Subfamily Mycophyllinae Hill ______________ 30 

Family Streptelasmatidae Nicholson __________ 30 

Family Stauriidae Edwards and Haime __________ 31 

Family Tryplasmatidae Etheridge ______________ 31 

Family Pycnostylidae Stumm __________________ 31 

Compact cerioid Pycnostylidae of Silurian limestone 

facies ------------------------------------------ 32 

Dissepimented Rugosa of the Great Basin Silurian 

limestone facies ______________________________ 32 

Family Spongophyllidae Dybowski ______________ 32 

Family Endophyllidae Torley __________________ 34 

Family Chonophyllidae Holmes ________________ 36 

Family Kyphophyllidae Wedekind ______________ 36 

Family Calostylidae Roemer-------------------- 37 

Family Lykophyllidae __________________________ 37 

Fossils associated with rugose corals in Great Basin Silurian limestones _ _ ____ _ __ _ __ ___ _ _ _ ____ __ _ _ ___ ___ _ _ 37 

Dasycladacean algae as indicators of the Silurian ____ 38 

Conodonts of the Roberts Mountains Formation by 

John W. Huddle -------------------------------- 38 

Locality register of major fossil localities in the Roberts Mountains Formation and correlative strata -------------------- 39 

Selected references ____________________________ ------------ 43 

Index ---~------------------------------------------------ 47 

III 
IV CONTENTS 

ILLUSTRATIONS 

[Plates follow index] 

PLATE 1. Stylopleura and Pycnostylus. 

2. Stylopleura and Pycnostylus. 

3. Fletcheria and Tryplasma. 

4. Mucophyllum and Kodonophyllum. 

5. Tonkinaria, Kyphophyllum, Kodonophyllum, and Brachyelasma. 

6. Spongophyllum, Carlinastraea, and Australophyllum. 

7. Carlinastraea, Chonophyllum, and Calostylis? 

8. Carlinastraea and A ustralophyllum. 

9. Kyphophyllum and Chonophyllum. 

10. Verticillopora, Cladopora, Favosites, Kyphophyllum, Ketophyllum, and Hercynella. 

11. Verticillopora, Kozlowskiellina, H omoeospira, Dicoelosia, Plectatrypa?, and Gypidula. 

12. Coelospira, Fardenia, Kozlowskiellina, Conchidium, Cyathophylloides, Brachyelasma, and lycophyllid. 

Page 

FIGURE 1. Index map of part of Great Basin showing distribution of the Roberts Mountains Formation and correlative formations in 

the intermediate limestone belt in Nevada and California -------------------------------------------------------- 8 

2. Geologic map of the Coal Canyon area, northern Simpson Park Mountains _____________________________________________ 12 

3. Sketch map of the northern Toquima Range showing Paleozoic sequences that contain Silurian rock in separate thrust sheets __ 21 

TABLES 

Page 

TABLE 1. Characteristic fossils of the Great Basin Silurian coral zones --------------------------------------------------------- 5 

2. Occurrence chart of conodont species collected from Silurian and Lower Devonian formations in central Nevada __________ 40 
THE ROBERTS MOUNTAINS FORMATION, 

STRATIGRAPHIC STUDY WITH EMPHASIS 

CORAL DISTRIBUTION 

A REGIONAL 

ON RUGOSE 

By CHARLES W. MERRIAM and EDWIN H. McKEE 

ABSTRACT 

A large part ofthe Silurian and the base of the Devonian Systems 

are represented in the central and southwestern Great Basin by 

limestones of the Roberts Mountains and the Vaughn Gulch Formations. In Silurian time the Great Basin region was inundated by 

northward-trending shelf seaways of three wide facies belts: the 

eastern regional dolomite belt which bordered the ancient land mass 

on the east, the intermediate limestone belt here dealt with, and on 

the west, a chert-shale-graywacke belt with some volcanic rocks that 

extends into the Pacific Border province, best represented in southeastern Alaska. Studies of rugose corals show that each of the three 

belts has distinctive corals and associated fossils not yet found in the 

other belts; biofacies differences greatly complicate geologic correlation across the facies boundaries. 

The Roberts Mountains Formation, mainly limestone, calcareous 

shale, and some dolomitic limestone, is widely distributed in the 

central Great Basin, where it has been mapped from the Tuscarora 

Mountains on the north to the Toquima and Toiyabe Ranges on the 

south and west. It is known to be present as far north as southcentral Idaho but has been little studied in this region. The Vaughn 

Gulch Limestone and its lateral shaly graptolitic facies, the Sunday 

Canyon Formation, occur to the southwest in the Inyo Mountains. 

Thick eastern regional dolomite facies rocks such as the Lone Mountain Dolomite and the Laketown Dolomite come into close proximity 

to, or intertongue with, limestone of the middle belt in a few areas 

such as the Roberts Mountains, Bare Mountain near Beatty,, Nev., 

and the Inyo Mountains. In a number of places such as in the Tuscarora Mountains, the Simpson Park Mountains, the Roberts Mowntains, 

the Monitor Range, and the Toquima Range, the Roberts Mountains 

limestone has been subdivided into additional lithologic units given 

new formational names. These include the Windmill Limestone of 

Johnson, the McMonnigal Limestone, and the Wenban Limestone. 

The names Masket Shale and GatecliffFormation were used by Kay 

for rocks in the Toquima and Toiyabe Ranges that closely resemble 

parts of the Roberts Mountains Formation elsewhere. In most areas 

the basal part of the formation is a black cherty limestone or dolomite followed upward by calcareous shaly laminated and platy limestone that bears graptolites. The upper part consists of thin-bedded 

laminated limestone and slabby thicker bedded allogenic limestone 

. and dolomitic limestone yielding corals, brachiopods, and calcareous 

algae as well as graptolites. 

The Silurian-Devonian boundary lies within this upper interval. 

This boundary, defined on the basis of graptolites in the standard 

time scale, is more than 100 m lower than that based on rugose 

corals and calcareous algae that uses as reference the well-known 

section in Gotland, Sweden. 

INTRODUCTION 

The name Roberts Mountains Formation applies to 

limestones, mostly argillaceous, and some dolomitic 

marine strata occupying a northerly oriented linear 

belt within the central and west-central Great Basin. 

Diverse fossil assemblages from many localities indicate that in the time-stratigraphic sense this formation 

probably makes up much of the Silurian and the bottom of the Devonian Systems as represented in the 

Great Basin of the western United States. The 

Silurian-Devonian boundary lies· within the upper or 

even upper middle part of the formation. A reexamination of field relations of the fossil-bearing strata and a 

review of fossil comparisons with those of standard 

columns for the Silurian and Devonian Systems indicates that the standard time scale based on graptolites 

includes rocks in the Great Basin that are somewhat 

older than rugose corals would suggest. 

The Roberts Mountains Formation is bordered on 

the east by dolomite that prevails throughout the 

east-central and eastern Great Basin. On the west, 

where the boundary is theoretical, the limestones are 

inferred to grade into shale, graywacke, coarse argillaceous rocks, volcanic rocks, and subordinate limestone of the Pacific border province (Merriam, 1973a). 

Paleogeographically, three subparallel northwardtrending depositional facies belts are definable where 

the southwest Cordilleran geosynclinal seaways of 

middle Paleozoic (Silurian and Devonian) time crossed 

what is today the Great Basin. From east to west these 

belts are: the eastern dolomite belt, the intermediate 

limestone belt, and the western or Pacific Border 

graywacke belt. The transition from the dolomite to 

limestone belt passes through the classical facies of 

platform margin carbonate deposition. Limestones of 

the intermediate limestone belt persist to the southwest margin of the Great Basin, where they are represented by the Vaughn Gulch Limestone in the northern lnyo Mountains, Calif. 

As rugose corals are among the diagnostic fossils of 

the Roberts Mountains Formation, this study was inspired by the need for dependable stratigraphic sequences in deformed Great Basin Paleozoic rocks to 

1 
2 ROBERTS MOUNTAINS FORMATION, REGIONAL STUDY 

be used in conjunction with Rugosa and their stratigraphic ranges. Studies of Great Basin rugose corals 

and associated fossils have demonstrated marked biofacies differences between the three facies belts that 

make difficult interbelt paleontologic correlation. 

PURPOSE AND SCOPE OF INVESTIGATION 

In Silurian and Devonian limestone areas of the 

central and southwest Great Basin, geologic mapping 

within the past 10 years necessitates restudy and redefinition of the Roberts Mountains Formation and 

correlative units, including those of contiguous dolomite areas. J\mo_ng- primary objectives, this effort entails search for realistic vertical and lateral formation 

bq~ndaries which reflect depositional facies relations. 

The physical stratigraphydepends upon refinement of 

geologic mapping and paleontologic correlation as 

background, and the biostratigraphy presented here 

leans heavily upon zonation of the Great Basin Silurian and Devonian by means of corals and associated 

megafossils (Merriam, 1973a, b, c; 197 4). In this coral 

work, the Gotland, Sweden, Silurian yardstick is the 

primary standard of comparison and geologic correlation. In some sections a wide gap exists between the 

accepted Silurian-Devonian boundary as determined 

by the graptolite and conodont specialists and the 

placement of the boundary by the coral specialist. For 

example, the Monograptus uniformis Zone at the base 

of the Devonian falls as low as the middle part of the 

Silurian delimited by means of corals. Explanations 

are sought for these discrepancies. 

The systematic and descriptive paleontology of many 

rugose corals listed in this report is treated in recent 

works (Merriam, 1973a, b). A paleontologic appendix 

covers stratigraphically relevant but undescribed 

megafossils and evaluates certain little-known rugose 

coral groups, calcareous algae, and conodonts for age 

determination, correlation, and biostratigraphy. As no 

megafossils were found by the geologists who mapped 

many exposures of the Roberts Mountains Formation, 

age designations of these structurally and stratigraphically isolated beds are based on conodont studies. 

Twelve plates illustrate some of the distinctive 

megafossils of this formation. 

A detailed report by T. E. Mullens (unpub. data, 

1975) covers comparative lithology, sedimentology, 

and petrology of the Roberts Mountains Formation and 

its economic potential as a gold-bearing formation. 

Briefly touched upon herein are the complex environmental and geochemical aspects of the multifaceted dolomite problem bearing upon the complete 

change from marine limestone to pervasive diagenetic 

dolomite passing into the eastern dolomite belt. 

In recent years the Roberts Mountains Formation 

has assumed economic importance as host rock for the 

Cortez and Carlin gold ores of central Nevada. As a 

result, the known extent of the formation has been 

intensively explored and prospected. Some economic 

aspects of ore search, geochemistry, and geophysical 

prospecting are treated in other reports (T. E. Mullens, 

unpub. data, 1975). 

ACKNOWLEDGMENTS 

Geologic mapping used in this report includes results of D. C. Ross in the northern In yo Mountains, 

Calif., Harold Masursky and Jonathan C. Matti in the 

northern Simpson Park Mountains, and J. H. Stewart 

in the central Toiyabe Range and Shoshone Mountains, Nev. Efforts by these geologists toward clarifying geologic structure and stratigraphy have been 

most helpful. Detailed geologic mapping in the southern Tuscarora Mountains, Nev., by J. G. Evans, sheds 

new light on the source beds of earlier fossil collections 

made in the Bootstrap mine area before large-scale topographic maps made accurate field location possible. 

These especially well preserved silicified fossils collected by R. J. Roberts and associates near the 

Bootstrap mine in the years 1954 to 1958 first demonstrated the northward continuation of the Roberts 

Mountains Formation beyond the Humboldt River 

Valley. Rugose corals in Coal Canyon, Simpson Park 

Mountains, were first collected by R. J. Roberts; at a 

later time, Silurian and Devonian coral collections by 

J. G. Johnson and A. J. Boucot were contributed for use 

in this study. Collections of corals by Leland Cress at 

Maggie Creek, Tuscarora Mountains, revealed the 

presence of Silurian and Early Devonian corals in this 

area. A well-preserved colonial rugose coral from the 

Sunday Canyon Formation in Mazourka Canyon collected by C. H. Stevens of San Jose State University is 

ackno-wledged with thanks. Jonathan C. Matti made 

many helpful suggestions on the manuscript and reviewed the conodont section. 

Graptolite identifications accompanying this report 

are the work of W. B. N. Berry. 

Many detailed stratigraphic sections have been 

measured across the Roberts Mountains Formation 

throughout its known extent by T. E. Mullens. Lithologic data from these sections have been employed in 

the present report, especially at Bootstrap Hill in the 

Tuscarora Mountains. 

J. W. Miller ably assisted Merriam in detailed geologic mapping of the Coal Canyon area and other parts 

of the northern Simpson Park Mountains. In the Toquima Range all the detailed geologic mapping providing the basis for stratigraphic conclusions in that area 

is the work of E. H. McKee. Earlier geologic mapping 
INTRODUCTION 3 

of parts of that range was done by Kay and Crawford 

(1964). 

All fossil photographs are the work of Kenji 

Sakamoto. 

HISTORY OF INVESTIGATION 

Silurian limestones were first studied in the Roberts 

Mountains by Merriam while he searched for the base 

of the Devonian System in that area (Merriam, 1940, 

p. 11). On the northwest side of Roberts Creek Mountain, the lowest beds in the Nevada Formation identified in 1940 contain the Acrospirifer kobehana fauna 

of Early Devonian age and appeared at that time to 

conformably overlie massive dolomites identified as 

the Lone Mountain Dolomite of supposedly, but as yet 

unestablished, Silurian or perhaps Early Devonian 

age. Comparison with the Lone Mountain type section 

18 miles (29 km) to the south revealed significant 

lithologic differences. Whereas no limestone is present 

in the Upper Ordovician or Silurian at Lone Mountain, 

beneath the Lone Mountain Dolomite at Roberts Creek 

Mountain is a thick fossiliferous Silurian sequence of 

limestones and some dolomite named at that time the 

Roberts Mountains Formation by Merriam (1940). 

This unit occupied the stratigraphic interval between 

the underlying limestone and dolomite of the Hanson 

Creek Formation and the blocky light-gray dolomite 

interpreted by Merriam (1940) as the higher part of the 

Lone Mountain Dolomite. Comparison of the sections 

at Lone Mountain and Roberts Creek Mountain led to 

extension by Merriam (1940) of the name Roberts 

Mountains Formation to the dark dolomite beneath 

the type Lone Mountain Dolomite in accord with the 

view that this was a dolomite facies of the Roberts 

Mountains Formation. Later mapping in the Roberts 

Mountains by Winterer and Murphy (1960) clearly 

demonstrated the lateral equivalence by the intertonguing of the Roberts Mountains Formation and the 

Lone Mountain Dolomite. In a recent study of the stratigraphy and paleontology of the Lone Mountain 

Dolomite at Lone Mountain (Merriam, 1973b), the 

dark dolomite previously referred to as dolomitic 

Roberts Mountains Formation has been redesignated 

as part of the Lone Mountain Dolomite because it was 

considered desirable to retain the formational term 

Roberts Mountains for a predominantly limestone ·unit 

only. 

Above the type section of the Roberts Mountains 

Formation, at Roberts Creek Mountain, the saccharoidal Lone Mountain dolomites have yielded no fossils; 

the possibility remains that the uppermost part of this 

thick dolomite sequence may correlate with the finer 

textured Beacon Peak Dolomite Member of the Nevada 

Formation. 

Reconnaissance geology of the northern Monitor 

Range by Merriam and Anderson (1942) made known a 

southerly extension of the Roberts Mountains Formation. In Copenhagen Canyon, for example, the Silurian 

and Lower Devonian were found to be represented by 

thinly laminated calcareous shaly rocks carrying graptolite faunas and thicker graded beds of bioclastic 

limestone. Kay and Crawford (1964) recognized the occurrence of the Roberts Mountains Formation (called 

by them the :Masket Shale) farther southwest in the 

Toquima Range, where various limestone and argillaceous limestones occupy parts of several separately 

mappable thrust plates. More recent detailed mqppin_g, 

in that area by McKee (1976) sheds ad~ittonal light 

upon the facies, paleontology, and,, corr.elation of the 

Roberts Mountains Formation in the Toquima Range. 

Northwest of the type area, the Roberts Mountains 

Formation was extended into the northern Simpson 

P&rk Mountains by R. J. Roberts and associates during 

reconnaissance geologic mapping of northern Eureka 

County in 19t)4-58. Knowledge of these rocks was 

further advanced by Winterer and Murphy (1960) and 

Johnson (1965'1. R. J. Roberts and associates extended 

the distribution of the Roberts Mountains Formation 

northward into the Tuscarora Mountains and Elko 

County during the Eureka County mapping program. 

Since 1967, parts of the southern Tuscarora Mountains 

near Carlin, Nev., have been mapped in detail by the 

U.S. Geological Survey. Where the formation is locally 

gold bearing, 1nuch has been learned of the complex 

structure and stratigraphy; geochemical and geophysical investigations have been carried out by economic 

geologists in connection with drilling exploration beyond the currently productive belt. 

Ge'ologic mapping of the Cortez quadrangle by Gilluly and Masursky (1965) and the Mount Lewis area 

by Gilluly and Gates (1965) extended the known occurrence of the Roberts Mountains Formation into the 

Cortez Mountains and northern Shoshone Range. The 

formation has subsequently become economically important as a gold ore host in that vicinity. 

In 1968 the economic potential of the Roberts Mountains Formation as a source of gold in north-central 

Nevada became sufficiently evident to justify a special 

study by the U.S. Geological Survey. The lithologic and 

stratigraphic aspects of this study were undertaken by 

T. E. Mullens, who worked with quadrangle m~pping 

parties and geochemists in economically pf;'orpising 

areas. Mulle~s ha? carried ol1t detailed sectiop'II)easuremeht and studies' of sedimentary petrology in many 

areas, including those where mapping:was in progress 

(Mullens, unpub. data, 1975). 

Mapping of the Horse Creek Valley quadrangle in 

the northern Simpson Park Mountains by Har,Q.ld 
4 ROBERTS MOUNTAINS FORMATION, REGIONAL STUDY 

Masursky, begun about 1960, carried eastward the 

geology begun by Gilluly and Masursky in the adjoining Cortez quadrangle (1965). A progress map was 

transmitted by Masursky in 1971 for the use of the 

writers in conjunction with the Paleozoic stratigraphy. 

As the Horse Creek Valley quadrangle includes the 

Coal Canyon section, first fully described by Johnson 

(1965) and probably the best reference section for the 

Roberts Mountains Formation, parts of it have been 

remapped in more detail by Merriam and Miller, a 

work still in progress. 

Interest in southwestern Great Basin Silurian limestones as correlatives of the Roberts Mountains Formation developed in 1946 with geologic mapping of the 

Cerro Gordo mining district, Inyo Mountains, Calif. 

(Merriam, 1963). At that time it became evident that 

westward and northward, the Hidden Valley Dolomite 

(McAllister, 1952) changed to limestone. Section 

measurement, reconnaissance geologic mapping, and 

fossil collecting were begun in 1947 at Mazourka Canyon, where the coral genera and calcareous algae of 

these Inyo Silurian beds were found to be closely allied 

to those of the central Great Basin. Subsequently, Ross 

(1963, 1966) carried out the refinements of detailed 

geologic mapping of the northern Inyo areas. A northward change of Silurian limestone into shale facies is 

demonstrated by the Ross mapping. 

The underlying paleontologic motivation for this 

study of Silurian limestone dates from the discovery by 

Merriam of well-preserved Rugosa in the Roberts 

Mountains in 1933, and in the northern Inyo Mountains about 1946. As general worldwide knowledge of 

Silurian Rugosa progressed rapidly, coral studies leading to a provisional Great Basin Silurian coral zonation were initiated by Merriam (1963), providing, together with brachiopod studies, much of the paleontologic support for this contribution. Further incentive 

came with the brachiopod investigations of J. G. 

Johnson and A. J. Boucot, who introduced European 

comparisons, and with investigations by W. B. N. 

Berry of graptolites of Great Basin Silurian and Devonian rocks. Conodont studies by Gilbert Klapper coordinated with field studies of M. A. Murphy added a 

wealth of information about the Silurian and Devonian 

of central Nevada. The most modern discussion of the 

formation is the study by Matti, Murphy, and Finney 

(1975). 

PALEONTOLOGIC ZONING OF THE GREAT 

BASIN SILURIAN AND LOWER DEVONIAN 

Rugose corals provide a useful means of stratigraphic zonation in the Great Basin Silurian and Devonian limestone facies. These fossils; common in 

nearly all the bioclastic limestones, are generally well 

preserved and represent several genera known in the 

Silurian of Gotland, Sweden; England; eastern Europ·e; 

and Australia. Graptolites, the primary basis for subdividing the world Silurian System, are abundant in 

rocks of the lower part of the Great Basin Silurian and 

occur at many places well into the Devonian. Great 

Basin Silurian and Devonian brachiopods are well represented, and much has been done to tie their occurrences and stratigraphic ranges to mapped areas and 

measured sections. The large dasycladacean algae of 

the genus Verticillopora are especially useful in Great 

Basin Silurian strata. Verticillopora ranges upward 

from Great Basin Silurian coral zone B through zone E, 

apparently reaching a peak of development in coral 

zone D (see below). 

Conodonts are found through much of the Silurian 

and Devonian limestone of this province and are currently being coordinated with age determinations 

based on associated megafossils. 

Study of the stratigraphic distribution of Silurian 

Rugosa in correlative and overlapping reference sections throughout the Great Basin makes possible a 

hypothetical fivefold zonation based on the ranges of 

species and genera. Provisional zones are designated 

by capital letters A through E in ascending stratigraphic order. Gaps in the coral record within a single 

reference section are filled in correlative sections to 

complete the overlapping composite zonal scheme. No 

more than three coral zones have been recognized 

within any one reference column; further collecting is 

expected to eliminate some of these local gaps. 

The five coral zones ranging in age from Early to 

Late Silurian are: 

Age 

Late Silurian1 

Middle Silurian 

Early Silurian 

Coral zone 

E 

D 

c 

B 

A 

SCARCITY OF REEFS 

OR BIOHERMS IN THE 

ROBERTS MOUNTAINS FORMATION 

Reef and biohermal structures occur in Silurian 

marine limestone and dolomite rich in calcareous algae, stromatoporoids, crinoids, and corals in many 

areas throughout the world (Lowenstam, 1949). These 

structures are parts of the Niagaran Series of the 

Great Lakes and the Gotland of Sweden (Manten, 

1 Age designation based on comparison with the Gotland, Sweden, Rugosa. Coral zone E 

contains rocks of Lower Devonian age based on the occurrence of Monograptus uniform is, 

the accepted index for lowermost Devonian in the Great Basin. 
SCARCITY OF REEFS OR BIOHERMS 5 

TABLE !.-Characteristic fossils of Great Basin Silurian coral zones 

Geologic age 

Late 

Coral 

zone Rugose corals 

Silurian1 ______ E ______ Stylopleura nevadensis Merriam 

Stylopleura berthiaumi Merriam 

M ucophyllum oliveri Merriam 

Kodonophyllum mulleri Merriam 

Rhizophyllum cf. R. enorme 

Middle 

(Oliver) 

Rhizophyllum sp. D Oliver 

Chonophyllum simpsoni Merriam 

Australophyllum (Toquima-phyllum) 

johnsoni Merriam 

Carlinastraea tuscaroraensis 

Merriam 

Kyphophyllum nevadensis Merriam 

Kyphophyllum sp. c Salairophyllum? sp.2 

D ______ Brachyelasma sp. 

Stylopleura berthiaumi Merriam 

Tonkinaria simpsoni Merriam 

Tryplasma duncanae Merriam 

Carlinastraea tuscaroraensis 

Merriam 

Silurian ______ C ______ Tryplasma newfarmeri Merriam 

Denayphyllum denayensis Merriam 

Entelophylloides (Prohexagonaria) 

occidentalis Merriam 

Tabulate corals Brachiopods 

Orthostrophia sp. 

Schellwienella? sp. 

Barrandella? sp. 

Sicorhyncha? sp. 

Rhynchospirina sp. 

Plectatrypa? sp. 

Atrypa sp. 

Meristella sp. 

Kozlowskiellina sp. f 

Dicoelosia sp. r 

Gypidula sp. r 

H omoeospira sp. r 

Atrypa sp. 

Kozlowskiellina sp. f 

Dasycladacean algae 

Verticillopora annulata 

Rezak 

V erticillopora cf. V. 

annulata Rezak 

V erticillopora annulata 

Rezak 

Verticillopora cf. V. 

annulata Rezak 

B______ Streptelasmid corals (small) 

Brachyelasma sp. B 

Ryderophyllum ubehebensis 

Merriam 

Halysites (Cystihalysites) magnitubus 

Buehler 

V erticillopora sp. 

Pycnactis sp. K 

Petrozium mcallisteri Merriam 

Early 

Silurian ______ A ______ Rhegmaphyllum sp. h 

Dalmanophyllum sp. A 

Palaeocyclus porpita subsp. 

mcallisteri Merriam 

Cladopora sp. 

Heliolites sp. 

Halysites sp. 

Rhabdocyclus sp. d 

Cyathophylloides fergusoni 

Merriam 

Arachnophyllum kayi Merriam 

N eomphyma crawfordi Merriam 

Dicoelosia sp. 

Dalmanella sp. 

Atrypa sp. 

1 Age designation based on comparison with the Gotland, Sweden Rugosa. Coral zone E contains rocks of Lower Devonian age based on the occurrence of Monograptus uniform is, ·the 

accepted index for lowermost Devonian in the Great Basin. 2Salairophy/lum? from uncertain stratigraphic horizon at Coal Canyon, Simpson Park Mountains, Nev. Probably from coral zone E. 

1971). The Roberts Mountains Formation, however, 

shows little evidence of reefal structure, or even of 

minor bioherms having initial bottom relief. In most 

places, the lower part of the formation is thin and consists of evenly laminated fine-grained argillaceous 

limestone with no reeflike characteristics. The upper 

part of the formation contains thin- to medium-bedded 

bioclastic limestone as well as fine-grained thin laminated beds. These rock types represent a facies that 

must have formed at a moderate depth of water. Corals, calcareous algae, and brachiopods, mostly fragmental, are fairly abundant in parts of the formation, 

but they have not developed into reeflike structures; 

indeed, in most places the fossils have been transported with other calcareous debris as debris flows. 

At Coal Canyon, Simpson Park Mountains, depositional breccias may mark the vicinity of small patch 

reefs or bioherrns, but no inclined reef-marginal beds 

or reef core rock was found. Some limestone strata of 

the upper Roberts Mountains Formation in the Roberts 

Mountains rich in corals and other benthonic_ organisms appear to represent beds and banks of very 

low bottom relief, but many are thick allodapic beds 

deposited in basins or on a gentle slope at greater 

depths than reef formation and below wave base. 

Stromatoporoids contributed much of the material 

toward the building of reefs in the Niagaran of Illinois 

(Lowenstam, 1949) and in the Silurian of Gotland, 

Sweden (Manten, 1971). In the coral-rich Roberts 

Mountains Formation limestones, stromatoporoids, 

though present, apparently were not important as reef 

builders. 
6 ROBERTS MOUNTAINS FORMATION, REGIONAL STUDY 

DISTRIBUTION OF GREAT BASIN 

SILURIAN LIMESTONE AND 

DOLOMITE BELTS AND THE REGIONAL 

DOLOMITE PROBLEM 

Areal distribution of Great Basin Silurian carbonate 

rocks in contrasting lithologic belts such as the intermediate limestone and eastern dolomite belts leads to 

paleogeographic speculation and review of the multifaceted unsolved problems of the origin of marine 

dolomite. It is not a purpose of this report to enter into 

the complexities of geochemical and metasomatic 

change. Dolomites of the eastern belt certainly fall in 

the category of regional dolomite of diagenetic origin 

as contrasted with localized hydrothermal or metamorphic dolomites. In several mining districts of this 

province, the hydrothermal type locally forms very 

large bodies that may easily be confused with the 

diagenetic type (Hewett, 1931, p. 57-68). Nonetheless, 

some interpretation is appropriate in explaining the 

discrete lithologic and paleogeographic boundary zone 

separating the eastern dolomite from the intermediate 

limestone belt within which the Roberts Mountains 

Formation is found. 

In relation to regional dolomites of vast extent like 

the eastern dolomite belt, we may seek explanation of 

its lateral boundaries from various fields of study including paleogeography, paleobiology, geochemistry, 

marine environment and the sources of magnesium introduced to produce the double carbonate mineral 

dolomite. We may ask: how or why does proximity to 

the subdued Silurian land mass on the east favor 

diagenetic dolomitization while offshore limestones 

remain normal marine limestone? 

The dolomite question has been reviewed by many 

workers, including Van Tuyl (1916a, b), Steidtmann 

(1911, 1917), Skeats (1918), Fairbridge (1957), and, 

more recently many authors represented in Pray and 

Murray (eds. 1965), Bathurst (1971), and Hsu and 

Schneider (1973). Beyond doubt, the Laketown and 

Lone Mountain Dolomites, like the Niagaran of the 

continental interior-nearly continuous dolomites that 

cover thousands of square miles and are locally more 

than a thousand feet thick-fall into a regional category. 

It has long been known that the amount of regional 

dolomite increases downward through the geologic systems from Holocene to Precambrian (Fairbridge, 1957) 

and (Daly, 1907, 1909). The Silurian is one of the systems containing much continuous regional dolomite in 

North America, as in the Great Basin and the continental interior. 

Ulrich and Schuchert (1902) were perhaps the first 

to note that certain extensive regional dolomites border upon ancient shorelines. In the Great Basin Silurian, the regional dolomite belt lies between the old 

subdued landmass on the east and the intermediate 

limestone on the west. Farther west the Pacific border 

graywacke belt, through its extent from northern 

California to Alaska, is not known to include dolomite 

of the diagenetic type. Fossil and lithologic evidence 

indicates that the Silurian eastern dolomite and the 

intermediate limestone both represent shallow marine 

environments, possibly with some deepening where 

limestones appear, especially the allogenic graded 

types, and further deepening into graptolitic finegrained and laminated beds. The western limit of 

dolomite, here the Lone Mountain Dolomite, was the 

western limit of reef development that migrated westward by normal landward carbonate accumulation typical of all large carbonate-producing regions. The generally regressive series of carbonate rocks that were 

deposited in the Great Basin during the lower and 

middle Paleozoic are strong evidence for the landward 

accumulation of carbonate sediment (and hence retreat 

of the sea) produced in the shallow shelf seas. Very 

extensive tidal flats and mud shoals behind or east of 

the Lone Mountain reef are the present site of the regional dolomites we see today. 

Studies of rugose corals suggest that the Lone Mountain and Laketown Dolomites contain marine faunas 

differing in biofacies from those of limestones in the 

Roberts Mountains Formation (Merriam, 1973a). This 

does not, however, imply that the dolomite facies was 

initially deposited as dolomite sediment by direct 

chemical precipitation. Other ecological factors must 

be sought: for example, differences of water temperature, depth, salinity, and food supply. Fossils are locally abundant in the dolomites, but unless silicified 

early, that is, prior to dolomitization, they are destroyed by dolomitic recrystallization. Among the factors to be considered is the proximity to the shoreline, 

where extensive mudflats were doubtless very broadly 

exposed at low tide to bring about diurnal evaporative 

concentration to produce brines. Percolation of the 

magnesium-rich brine into the carbonate sediments 

may have taken place by reflux action seaward from 

the mudflats as suggested by Adams and Rhodes (1960) 

or by capillary transfer through the sediments as 

suggested by Friedman and Sanders (1967). Another 

theory suggests that drainage from the landmass on 

the east introduced additional magnesium as well as 

calcium to become available for the additive process of 

dolomitization. Movement of the carbonate-bearing 

ground water upward through the nearshore mudbanks probably was facilitated by evaporation across 

the banks and the subsequent pumping action created 

by this system (Hsii and Siegenthaler, 1969, and Hsii 

and Schneider, 1973). Westward toward the boundary 
THE ROBERTS MOUNTAINS, NEVADA 7 

zone between the eastern dolomite belt and the intermediate limestone belt, the magnesium calcium ratio 

became too low for dolomitization because of the absence of shallow water evaporative sites and less extensive tidal mudflats. 

It is possible that the organic community that populated the nearshore fiats (now the dolomitic belt) produced proportionally more high-magnesium calcite or 

even some dolomite by their biochemical processes, 

thereby fixing a large amount of magnesium into the 

system. In slightly deeper water with greater circulation, a different assemblage of organisms produced 

mainly calcite, and limestone was the carbonate deposited. Sediments in this region were not dolomitized because magnesium was not available. 

Concentration of brine magnesium carbonate by 

evaporation at low tide on mudflats as a major factor in 

the dolomitization process has been studied by a 

number of investigators under a theory involving supratidal mudflats to which marine waters are added 

only occasionally during exceptionally high springtides 

and heavy storms. Greater concentration of magnesium in the brines comes about by evaporation and by 

the solutions percolating downward and seaward (reflux) to bring about metasomatic dolomitization of underlying carbonate muds and sands already containing 

magnesium in organically secreted calcite matrices. In 

such evaporative environments, gypsum and other 

salines should also be represented. Within the past 10 

years, penecontemporaneous dolomites attributed to 

supratidal environments have been found in the Persian Gulf (Illing and others, 1965, Hsii and Schneider, 

1973, DeGroot, 1973), in the Netherlands Antilles 

(Deffeyes and others, 1965). These discoveries illustrate the local hydraulics and geochemistry of contemporary dolomite formation on a fairly large scale, but 

they do not appear to provide the entire key to resolving the problem of vast regional dolomites like those of 

the Great Basin Silurian. 

In reality, dolomitization on a regional scale as in 

the eastern Great Basin is probably the product of all 

the mechanisms suggested. Addition of magnesium 

concentrated by evaporative processes on the inshore 

tidal fiats, magnesium-rich solute introduced from the 

land drainage as well as crystalline dolomite clastic 

debris introduced from exposed and eroding dolomite 

formations (for example, the Ordovician Bighorn 

Dolomite), and redistribution of magnesium taken 

from sea water by organisms and deposited as high 

magnesium calcite must all be significant factors. 

GEOGRAPHIC DISTRIBUTION OF 

SILURIAN LIMESTONES 

Strata of the Silurian intermediate limestone belt 

are known over a distance of about 325 miles (525 km) 

in a south-southwesterly direction from the Tuscarora 

Mountains of Elko County, northern Nevada, to the 

northern Inyo Mountains, southeastern California 

(fig. 1 ). The width of the slightly sinuous limestone 

band can only be estimated, but in most places, it is 

more than 50 miles (80 km) wide and may exceed 90 

miles (145 km) before passing entirely into the western, predominantly shale-graywacke facies. Whereas 

the west boundary is inferred at this time because of 

lack of exposures and subsurface geologic data, the 

east boundary can be delimited within much narrower 

limits of error in many places, as, for example, at 

Roberts Creek Mountain, Bare Mountain near Beatty, 

Nev., and the Inyo Mountains, Calif., where the limestones and dolomites either intertongue, are interbedded, or crop out within a few miles of each other. 

The intermediate limestone belt has been mapped and 

studied in detail in the Roberts Creek Mountains, the . 

northern Simpson Park Mountains and Cortez Mountains, the Copenhagen Canyon area of the Monitor 

Range, the northern Toquima Range, and the northern 

Inyo Range. Outcrop areas where the geologic mapping 

is of a reconnaissance nature, or where the stratigraphic work has been confined to section measurement, are the Bootstrap mine area of the Tuscarora 

Mountains, Swales Mountain in the Independence 

Range, the Carlin Mine and Maggie Creek area in the 

Tuscarora Mountains, parts of the northern Monitor 

Range, and the Wall and Pablo Canyon area of the 

Toiyabe Range. A number of widely separated outcrop 

areas of these limestones have been identified and sections measured, but additional mapping or stratigraphic paleontology is needed. These areas include 

the Mount Callaghan area of the Toiyabe Range; the 

Ravenswood area of the Shoshone Range; areas near 

Reeds and Dry Canyons, Toiyabe Range; Dobbin 

Summit, Monitor Range; the Northumberland area of 

the Toquima Range; Bare Mountain area near Beatty; 

and occurrences north of Wells near Antelope Peak. A 

comprehensive documented stratigraphic summary of 

these localities and others is presented in T. E. Mullens 

(unpub. data, 1975). 

ROBERTS MOUNTAINS FORMATION OF 

THE ROBERTS MOUNTAINS, NEV. 

In the Roberts Mountains, the Roberts Mountains 

Formation is exposed over a large area on the west and 

northwest side of Roberts Creek Mountain, the type 

area of the formation. Other outcrops occur near the 

north edge of the range between Willow aand Birch 

Creeks. 

The Roberts Mountains Formation in its type area 

includes a variety of dark-gray to bluish-gray lime-
8 ROBERTS MOUNTAINS FORMATION, REGIONAL STUDY 

42" 

1 Western 

I Graywacke 

Shale 

1 Belt 

I IDAHO 

----'- ----------

I 

Limestone / 

Belt +2J/ 

I l~ I 1 71• Lone Mountain 

/ 21 ~~ureka 

.lAustin 14 +2~xyoke Canyon 

I .t·6 .7 ~~I OEiy 

I 11fes1o~28 Rab~it Hill 

I Canyon•• 1 Dobbin Summit 

: •• 2 tf 

j"anhattan0 I Eastern 

I 1 Dolomite 

z c::: 

~ .-,! >I> 

~,::c 

I Ibex 

Hills 

EXPLANATION 

Roberts Mountains Formation and correlative formations 

+ Fossil localities of stratigraphic importan:e with regard to the 

Roberts Mountains Formation 

1. Roberts Mountains Formation, type section. Roberts Creek 

Mountain, Roberts Mountains. 

2. Roberts Mountains Formation, reference section. Coal 

Canyon, northern Simpson Park Range. 

3. Roberts Mountains Formation. North pediment slopes of 

northern Simpson Park Range. 

4. Roberts Mountains Formation. Cortez Mountains. 

S. Roberts Mountains Formation. Goat Peak, Shoshone Mountains. 

6. Roberts Mountains Formation. Dry Creek area, Toiyabe Range. 

7. Roberts Mountains Formation. Petes Canyon window, 

Toquima Range. 

8. Roberts Mountains Formation and Tor Limestone. June 

Canyon sequence. lkes Canyon window, Toquima Range. 

9. Roberts Mountains Formation and McMonnigal Limestone. 

Mill Canyon sequence. Ikes Canyon window, Toquima Range. 

10. August Canyon sequence. Gatecliff Formation of Kay and 

Crawford (1964). lkes Canyon window, Toquima Range. 

11. Roberts Mountains Formation. Northumberland window, 

Toquima Range. 

1 2. Roberts Mountains Formation. Pablo Canyon area, Toiyabe Range. 

1 3. Roberts Mountains Formation. Clear Creek and Dobbin 

~a ic'~ft~~~~~~~.t+-----~T~o~n~o~p=ah~~~--~--B~e~lt~~~~~~~j----~ Summit area, Monitor Range. 

14. Roberts Mountains Formation. Brock Canyon area, Monitor Range. 

1 S. Roberts Mountains Formation. Bowman Creek area, Toiyabe Range. 

1 6. Roberts Mountains Formation. Point of Rocks and Straight 0 Goldfield 

360 

0

Bakersfield 

!1110"11118 08sert 

12o" 118° 

0 25 50 75 

I I I I I I 

0 40 80 120 

Pahranagat 

Range 

; 

iL 

c 

e 

ii 

c 

f 

1£. 

116" 

100MILES 

I I 

160 KILOMETRES 

114° 

Canyons area, Toiyabe Range. 

1 7. Roberts Mountains Formation. Ravenswood area, Shoshone 

Mountains. 

1 8. Roberts Mountains Formation. Callaghan window, Toiyabe Range. 

19-20. Beacon Peak Dolomite Member of Nevada Formation. Southern part of Sulphur Spring Range. 

2 1. Lone Mountain Dolomite, type section. Lone Mountain. 

2 2. Lone Mountain Dolomite. Mahogany Hills. 

2 3. Lone Mountain Dolomite. Southern part of Fish Creek Range. 

24. Beacon Peak Dolomite Member of Nevada Formation. Oxyoke 

Canyon, Mahogany Hills. 

2 S. Late Silurian rugose corals in limestone. Antelope Peak, 

Snake Mountains. 

2 6. Roberts Mountains Formation, reference section. Bootstrap 

Hill, southern part of Tuscarora Mountains. 

2 7. Roberts Mountains Formation. Maggie Creek area, southern part of Tuscarora Mountains. 

2 8. Rabbit Hill Limestone, type section; Roberts Mountains 

Formation. Copenhagen Canyon area, Monitor Range. 

29. Vaughn Gulch Limestone, type area. Northern part of Inyo 

Mountains. 

3 0. Sunday Canyon Formation. Barrel Spring area, northern lnyo Mountains. 

31. Lone Mountain Dolomite above dark-gray limestone and 

dolomite probably correlative with Roberts Mountains 

Formation. Bare Mountain area. 

FIGURE 1.-Part of Great Basin showing distribution of the Roberts Mountains Formation and correlative formations in the intermediate 

limestone belt and fossil localities of stratigraphic importance with regard to the Roberts Mountains Formation. Approximate limits 

of the Late Silurian-Early Devonian depositional facies belts are shown by heavy lines. 

stones that are mostly thin bedded and weather in a 

platy to flaggy fashion. The basal part of the formation 

is thin-bedded blue-gray limestone with black chert 

interbeds and tabular chert nodules. Above this in the 

lower part of the formation is fine-textured thinly 

laminated limestone and calcareous shale with a few 

thin interbeds of coarse limestone. In the middle and 

upper parts of the formation, there is a change to predominantly coarser slabby-weathering blocky beds, a 

few centimetres to about 1 m thick, with partings of 

shale or laminated limestone. Crinoidal debris is 

abundant in these coarser beds, some of which are 

crinoidal bioclastic lenses containing abundant corals 

and brachiopods. As noted by Winterer and Murphy 

(1960, p. 123-129), some of the thicker beds are fossilrich calcarenite locall:y revealing graded bedding. In 

places, the platy and laminated fine-grained beds contain abundant silt-size quartz granules. Coarse depositional limestone breccias or flat-cobble mud breccias 

with limestone matrix are present as lenses in the 

upper thicker bedded sequences. 

Coarse-grained light-gray dolomitic limestone and 

dolomite occur as tongues and interbeds in the upper 

part of the formation; these dolomitic rocks can be 

traced laterally into a continuous dolomite, called Lone 

Mountain Dolomite. Silicified fossils are characteristic 

throughout the formation, especially 1n dolomitic 

limestones. 

At the type area, the Roberts Mountains Formation 

is overlain by the Lone Mountain Dolomite. At some 

other places, it grades into sequences of laminated 

limestone interbedded with thicker bedded clastic 
THE ROBERTS MOUNTAINS, NEVADA 9 

limestones that have been named the McMonnigal 

Limestone (Kay, 1960, Kay and Crawford, 1964, and 

McKee and others, 1972), the Windmill Limestone 

(Johnson, 1965, Matti and others, 1975), and the Wenban Limestone of Gilluly and Masursky (1965). 

TYPE SECTION 

The type section of the Roberts Mountains Formation is on the northwest side of Roberts Creek Mountain between the south and middle forks of upper Pete 

Hanson Creek. The formation is about 2,000 feet 

(600 m) thick in the type section, where it occupies the 

stratigraphic interval between the Hanson Creek 

Formation and overlying dolomites classified here as 

the Lone Mountain Dolomite. It is here about 70 percent limestone, with a prominent cherty member at the 

base and dolomitic limestone and dolomite interbeds or 

tongues in the upper 200 m. 

The Roberts Mountains Formation consists of wellbedded laminated dark-gray to slightly bluish-gray, 

platy, flaggy, and slabby limestone, dark-gray graded 

bioclastic limestone, calcareous shale, and subordinate 

black chert in the basal part of the formation. Most of 

the chert, shale, and laminated to shaly limestones 

occur in the lower part of the formation; the beds become on the whole thicker, coarser textured, and more 

bioclastic upward, with fewer of the laminated intercalations. Fossils are abundant in many horizons above 

the cherty interval, those in the laminated or shaly 

rocks are mainly graptolites. 

In the type section, differences in lithology and 

paleontology make feasible a three-unit subdivision of 

the Roberts Mountains Formation as unit 1, 100 m; 

unit 2, 300 m; and unit 3, 200 m, in ascending stratigraphic order. 

Unit I.-Unit 1, a fine-textured cherty unit, is made 

up of a basal chert and dolomite 1-3 m thick overlain 

by fine-grained thin-bedded laminated dark-gray limestone weathering platy and flaggy with shaly partings. 

The limestones weather light gray. The laminae usually reveal an alternation of calcareous and argillaceous or silty layers; in places, millimetre-thick limy 

layers alternate with layers containing much darkcolored matter probably composed of iron oxides with 

organic substances (Winterer and Murphy, 1960, p. 

·123). The laminated strata include dark chert layers 

and nodules elongate parallel to bedding. The distinctive bluish-black chert-bearing interval of varying 

thickness less than 3 m at the bottom of the formation, 

is about 75 percent chert that contains subordinate unchertified and undolomitized limestone lenses. Upward 

the chert decreases in amount, occurring in discontinuous 1-5 em layers separated by laminated limestone. 

Fossils are scarce in the laminated limestone, but 

shaly partings yield graptolites. The basal chert, resting upon the Hanson Creek Formation, which also is 

cherty in many places, is a widely recognized unit of 

the Great Basin Silurian. In some other areas it has 

yielded large pentameroid brachiopods. 

Unit 2.-Unit 2, thickest of the three units in the 

type section of the Roberts Mountains Formation, is 

made up of platy to flaggy dark bluish-gray fine to 

fairly coarse textured impure limestones with interbeds of bioclastic limestone as much as 1 m thick. Calcareous shaly partings and thin laminated layers separate the thicker beds, many of which are highly fossiliferous (bioclastic); much of this debris is crinoidal. 

The introduction of the thicker, rather coarsely clastic 

crinoidal beds distinguishes unit 2 from unit 1. Scattered black chert lenses and nodules are present as 

high as about the middle of unit 2. In the upper part of 

the unit are a few light-gray recrystallized layers that 

are slightly dolomitic. Tabulate corals, pentameroids, 

and other brachiopods are abundant in the many bioclastic beds; the rugose corals are subordinate. 

Unit 3.-Unit 3 is gradational with unit 2 through 

an interval wherein coarser textured crinoidal layers 

containing abundant Conchidium grade upward into a 

more uniformly thicker bedded sequence of light and 

dark-gray, somewhat blocky-weathering limestones 

that include coralline beds. About 7 5 m above its base, 

unit 3 becomes prevailingly lighter gray and less well 

bedded as it passes upward into the interbedded limestone and dolomite of the upper half. The lower coralline beds contain large heads of colonial Rugosa of 

Great Basin Silurian coral zone C. Light-gray-weathering limestones in the upper middle part of unit 3 

contain abundant silicified corals of Great Basin Silurian coral zone D. Through the upper 122m, bedding is 

poorly defined, the weathering more blocky, and fossils 

become fewer as the mixed carbonate rocks pass upward into the coarser saccharoidal dolomite of the 

overlying Lone Mountain Dolomite. 

STRATIGRAPHIC RELATIONS TO UNDERLYING 

AND OVERLYING FORMATIONS 

Careful examination of the contact separating the 

basal chert of unit 1 from the underlying Hanson 

Creek Formation has disclosed equivocal evidence of 

disconformi ty or angular discordance in the type section. Fossil evidence elsewhere, as in the Tuscarora 

Mountains (Berry and Roen, 1963), also suggests that 

some of the earliest Silurian may not be represented at 

or near the contact and hence a paraconformity exists 

in this part of the section. 

The upper limit of the Roberts Mountains Formation 

in its type section is gradational with the Lone Mountain Dolomite (Lone Mountain unit 2 at Lone Moun-
10 ROBERTS MOUNTAINS FORMATION, REGIONAL STUDY 

tain as redefined by Merriam in 1973). About 500 m of 

blocky dolomite between Roberts Mountains Formation unit 3 and richly fossiliferous lower beds of the 

Devonian Nevada Formation (or the McColley Canyon 

Formation of Murphy and Gronberg, 1970) yielded no 

fossils. Future study of the Lone Mountain Dolomite at 

Roberts Creek Mountain may show that the part of it 

correlates with part of the finer textured Beacon Peak 

Dolomite Member of the Nevada Formation of the 

Eureka district. 

FACIES CHA~GES FROM LIMESTONE TO DOLOMITE 

A planimetric map of the upper Pete Hanson Creek 

area by Winterer and Murphy (1960, p. 120, fig. 2) that 

includes the type section of the Roberts Mountains 

Formation illustrates the intertonguing relation of 

unit 3 limestone to dolomitic beds of the Lone Mountain Dolomite. Dolomitic limestones of these unit-3 

tongues contain a fa una more closely related to that of 

the Roberts Mountains limestone facies than to that of 

the Lone Mountain dolomite facies as known in the 

Eureka area (Merriam, 1973a, b). It is in Roberts 

Mountains unit 3 of the type area that we find the most 

clearly defined marginal interfingering of the intermediate limestone belt to the eastern dolomite belt in 

the Great Basin province. 

STRATIGRAPHIC PALEONTOLOGY OF THE TYPE SECTION 

The reference section for two of the five proposed 

Great Basin Silurian coral zones (Merriam, 1973a) occurs in the type section of the Roberts Mountains Formation, Silurian coral zones C and D in lithologic unit 

3 of the formation. The other Great Basin Silurian 

coral zones have not been recognized in this section. 

FOSSILS OF UNITS 1 AND 2 

Poorly preserved Monograptus sp. with plain tubular 

thecae occur in unit 1 and the lowermost part of unit 2 

(W. B. N. Berry, written commun., 1964). Fossils present in these lower beds are: 

Massive favositids Small Conchidium-like 

Cladopora sp. pentameroids 

Heliolites sp. Dicoelosia sp. 

Halysites sp. Eatonia? sp. 

Orthophyllum sp. Merista? sp. 

Pycnostylid Rugosa Atrypa sp. 

Monograptus sp. 

The characteristic Lower Silurian rugose corals of 

Great Basin Silurian coral zone A which would be expected in these lower beds have not been found here; 

those absent include the genera Palaeocyclus, Dalmanophyllum, Arachnophyllum, and Cyathophylloides. 

Fossils of early Middle Silurian (Great Basin Silurian coral zone B) were expected in the middle to upper 

beds of unit 2 but have not been found here. Rugose 

coral genera present are Tryplasma, Palaeophyllum, 

Diplophyllum, and Microplasma. Tabulate coral genera in these beds are Aulopora, Cladopora, Heliolites, 

and Halysites. In the uppermost beds of unit 2, 

brachiopods are abundant, especially medium-sized 

Conchidium-like pentameroids, some of which have 

fine radial costae, others radial costae of medi urn 

strength. Of the latter, one species (pl. 12, figs. 24--26) 

resembles the Norwegian Conchidium milnsteri Kiaer 

as described and figured by St. Joseph (1938). This 

species, reported in southern Norway Silurian zone 5b, 

St. Joseph considered to be Early Silurian (Llandoverian). Other brachiopods abundant in higher beds of 

Roberts Mountains unit 2 are the small Coelospira sp. 

and Ptychopleurella sp. 

FOSSILS OF UNIT 3 

Unit 3 of the Roberts Mountains Formation includes 

two Great Basin Silurian coral zones, C and D, and is 

the reference section for both. Coral zone C lies about 

10 m above the base of unit 3 and has yielded only 

corals, of which the following Rugosa are diagnostic: 

Entelophylloides (Prohexagonaria) occidentalis 

Merriam 

Tryplasma newfarmeri Merriam 

Denayphyllum denayensis Merriam 

Coral zone D lies about 90 m above the base and contains the following diagnostic Rugosa: 

Stylopleura berthiaumi Merriam 

Tonkinaria simpsoni Merriam 

Tryplasma duncanae Merriam 

Tabulate corals, dasycladacean algae, and brachiopods 

were abundant here in a diverse biota. The following 

are among the common associated fossils of coral 

zoneD: 

Verticillopora cf. V. annulata Rezak 

Dicoelosia sp. r 

Gypidula sp. r 

Homoeospira sp. r 

Kozlowskiellina sp. f 

Atrypa sp. 

A(:f: OF THE ROBERTS MOUNTAINS FORMATION 

OF THE TYPE SECTION 

In the time-stratigraphic sense, the greater part, but 

not all, of the Silurian System as well as the lower part 

of the Devonian System, is believed to be recorded in 

the 600 m of Roberts Mountains Formation of its type 

section. Fossil evidence indicating the early part of 

Early Silurian (Llandoverian) is lacking; the rest of 

the system is present and is represented by graptolites, 
THE NORTHERN SIMPSON PARK MOUNTAINS 11 

conodonts, and shelly fossils of Silurian age. The upper 

part of the formation is Lower Devonian in age (Klapper and Murphy, 1974; Berry and Murphy, 1975). 

The basal chert of the Roberts Mountains Formation 

(bottom of unit 1 ), present in the type section and most 

other Great Basin Silurian carbonate sections of both 

limestone and dolomite, seems to be a dependable 

marker unit. That it does transgress hypothetical time 

planes from place to place has been suggested by F. G. 

Poole (written commun., 1971), and his geologic evidence is convincing. It has also been suggested that 

there may be two or more chert sequences of different 

ages at this place in the stratigraphic column of the 

Great Basin (Jonathan C. Matti, written commun., 

197 4). This possibility remains to be demonstrated. 

The Silurian age of the basal chert has been established in several widely separated localities. In the 

northern Monitor Range at Copenhagen Canyon, the 

basal chert contains fairly large pentameroid brachiopods of Silurian character. At Mill Canyon, Toquima 

Range, a coral assemblage beneath the chert contains 

Cladopora? sp., three species of Favosites, Halysites (or 

Cystihalysites ), ~~cystiphyllum" sp., and Brachyelasma 

sp., a fauna suggesting a Silurian age. Graptolites 

from the chert in the central Toquima Range were 

identified by W. B. N. Berry as Climacograptus scalaris 

and Climacograptus cf. C. med~us; these species suggest 

an Early Silurian (Early Llandovery) age. As shown by 

Berry and Roen (1963), the beds in the southern Tuscarora Mountains that are a few feet above the basal 

chert marker contain graptolites of the Monograptus 

riccartonensis Zone of early Wenlockian age. 

Roberts Mountains unit 2 and the lower part of unit 

3 up to and including Great Basin Silurian coral zone C 

are provisionally classified as Middle Silurian (Wenlock). The lower and middle beds of unit 3, including 

coral zone D, are considered to be :Date Silurian (Ludlovian); the higher Ludlovian faunas of coral zone E 

have not been found at the type section. The graptolite 

succession on which the currently accepted SilurianDevonian boundary is based indicates that the upper 

part of unit 3 is Lower Devonian. 

ROBERTS MOUNTAINS FORMATION OF THE 

NORTHERN SIMPSON PARK MOUNTAINS 

GEOLOGIC SETTING 

Silurian and Devonian strata are exposed along the 

lower north slopes of the Simpson Park Mountains 

(Horse Creek Valley quadrangle, Nevada), most of 

which are blanketed by andesite and basalt flows. In 

some parts of the foothill area, coarse gravel and 

fanglomerate obscure the Paleozoic strata. Only that 

part of the lower north slope of the range between 

Grouse Creek and Red Hill at the northeast tip is covered in this report. 

Between Grouse Creek and Red Hill, a distance of 

about 11 km, the Paleozoic rocks are exposed in two 

areas: the Coal Canyon area (fig. 2) on the west and the 

Red Hill area on the east. Between these areas is a 

wide band of volcanic rock and gravel cover. Overthrust chert and shale of the Ordovician Vinini Formation crop out extensively in the Fye Canyon area on the 

southwest; Pennsylvanian or Permian conglomerate 

and limestone is found within the area and disconformably overlies the older Paleozoic strata. 

Between Grouse Creek and Red Hill, the Paleozoic 

beds dip 20° to about 60° E.; the steeper dips are in the 

vicinity of faults. Most faults have a northerly strike; 

in some places, faulting has caused an apparent thickening of the stratigraphic section. In general, the beds 

become progressively younger eastward; the oldest exposed rocks are the uppermost beds of the Hanson 

Creek Formation on the west in a minor canyon half a 

mile east of the mouth of Grouse Creek Canyon. 

Nearly all the Silurian and Lower Devonian section is 

exposed at Pine Hill and Pyramid Hill on the west. 

COAL CANYON AREA 

Pine Hill on the west side of Coal Canyon is underlain by a nearly continuous east-dipping section of 

Roberts Mountains Formation truncated on the east by 

the Coal Canyon fault (fig. 2). On the opposite or east 

side of Coal Canyon, Pyramid Hill is largely Rabbit 

Hill Limestone of Early Devonian age under lain along 

the lower east slopes of Coal Canyon by the uppermost 

beds of the Roberts Mountains Formation. The upper 

part of the Roberts Mountains Formation here was 

named the Windmill Limestone by Johnson (1965). 

This unit of finely laminated fine-grained limestone 

and thin- to medium-bedded clastic limestones is a recognizable formation at a number of places elsewhere in 

the region. 

At places along the west slope of Coal Canyon, the 

Coal Canyon fault is marked by a north-south zone of 

shearing and brecciation about 76 m wide. Within and 

adjacent to the fault zone, the east bedding dips are 

. steep and locally reversed to the west. The fault strikes 

about N. 5o W.; although its overall dip was not determined by field observation, it is inferred to be a 

high-angle normal fault with a possible steep east dip. 

To the south, the Coal Canyon fault passes beneath 

volcanic cover. 

COAL CANYON .FAULT ZONE 

Continuous measurement of the stratigraphic section across Coal Canyon from Pine Hill through 

Pyramid Hill must take into consideration a north-
12 ROBERTS MOUNTAINS FORMATION, REGIONAL STUDY 

116°38'40" 

40°30' .--------------------------------, EXPLANATION 

COAL CANYON FAULT 

A' 

A 

Volcanic rocks 

Rabbit Hill Limestone 

}~ 

}I Robert•M~Fonnation} ~ 

Sl 

> 

~ 

Hanson Creek Formation 8 

Contact 

~ 

0 

40°2'19' 

N 

t Geology mapped by C. w. Merriam, 1970-74, 

assisted by J. W. Miller, 1969-70 ~-- 0 Fault 

0 1000 2000 3000 4000 5000FEET 

0 500 1000 1500 METRES 

A 

CONTOUR INTERVAL 200 FEET A' 

7500' 

7000' 

6500' 

6000' 

Dashed where uncertain, 

U, upthrown side; D, downthrown side 

\22 

Strike and dip of beds 

M1334 

® 

Fossil locality 

See locality register 

Approximate position of beds with 

Monograptus praehercynicus 

2 

Approximate position of beds with 

Carlinastraea and Stylopleura 

FIGURE 2.-The Coal Canyon area, northern Simpson Park Mountains, showing relations of the Roberts Mountains Formation 

in the vicinity of the Coal Canyon fault. 

south fault break of undetermined magnitude. The 

Coal Canyon fault zone follows the steep west wall of 

the canyon for a distance of 800 m. It is best shown on 

the main northeast spur of Pine Hill, where its northsouth trace is marked by a coarse calcite-impregnated 

limestone cataclastic breccia some 76 m wide. Minor 

surfaces disclosing dip and direction of displacement 

were not found at the margins of this coarse breccia. 

The general trend of the breccia mass suggests that it 

continues southward, mostly beneath talus, and passes 

beneath a volcanic inlier in upper Coal Canyon basin 

without observed displacement of the volcanic body. 

The fault appears to have had a steep dip, but the direction of inclination has not been determined. It is 

probably a high-angle normal fault, although it might 

conceivably be a thrust fault subsidiary to a fault in 

upper Coal Canyon herein named the Rocky Hills 

thrust. Mapping in the Pine Hill block reveals a 

steepening of bedding dip as the Coal Canyon fault 

zone is approached from the west. The steepened dips 

are fault drag features suggesting either downward 

movement of the east or Pyramid Hill block or westto-east displacement of strata in the west or Pine Hill 

block on a low-angle thrust fault. The stratigraphic 

sections on the two sides of the canyon, the Pine Hill 

block on the west, the Pyramid Hill block on the east, 

are dealt with separately. 

PHYSICAL STRATIGRAPHY OF THE PINE HILL SECTION 

A nearly continuous section of Roberts Mountains 

Formation is exposed in Pine Hill west of the Coal 

Canyon fault. Only the uppermost beds of this section 

have been disturbed within the Coal Canyon fault 

zone. The Roberts Mountains Formation in the Pine 

Hill block is about 450 m thick and is here considered 

as having two lithologic units. 

The lower Roberts Mountains unit of Pine Hill is 

about 330m thick; the base is black chert, 1-2m thick, 

resting with sharp contact upon thick-bedded lightgray-weathering Hanson Creek dolomite and lime-
THE NORTHERN SIMPSON PARK MOUNTAINS 13 

stone. The succeeding Roberts Mountains consists of 

laminated thin-bedded platy and flaggy-weathering 

dark-gray impure limestone with intercalations of calcareous shale or calcareous siltstone. There are a few 

bioclastic limestone interbeds 5 or 6 em thick containing brachiopods and other fossils. Graptolites are fairly 

common in the laminated limestone and shaly units. In 

the lower 30 m above the basal chert, there are a few 

thin black chert bands and chert nodules. Lamination 

is a characteristic feature of some of the thin limy beds 

as in other areas of Roberts Mountains outcrop. 

In the lower part of the lower 330-m interval, bioclastic limestone beds are few. A l-inch, slightly 

bluish-gray fine-grained limestone is crowded with 

small silicified corals and brachiopods; another thin 

bed with unsilicified fossils yielded a smooth mediumsized Pentamerus-like brachiopod. 

About 140 m above the formation base is a limonite 

brown or reddish-stained silty sandstone bed containing abundant graptolites. 

The upper 120-m unit of the Roberts Mountains 

Formation in the Pine Hill block is an alternating 

thick and thinly bedded fairly coarse-grained darkbluish-gray limestone with calcareous shaly and silty 

intercalations. The lithologic change from the lower 

unit to the upper unit is distinct, but not abrupt. Most 

of the thicker limestone beds are bioclastic and contain 

well-preserved corals and other fossils; the most abundant are massiveFavosites colonies. About 15m of this 

limestone in the upper half of the interval, which carries a varied fauna of rugose corals and brachiopods, is 

referred to as the Carlinastraea beds. Thick beds of 

depositional breccia occur in the upper part of the 

Roberts Mountains Formation on the east side of Coal 

Canyon in the Toquimaphyllum beds of the Pyramid 

Hill section. 

The upper 120-m unit of the formation in the Pine 

Hill block is terminated on the east by the Coal Canyon fault. It is possible that the total thickness of this 

unit in unfaulted sections is much greater than 120m. 

STRATIGRAPHIC PALEOl\TOLOGY AND AGE OF 

ROBERTS MOU~T AINS FORMATION AT PINE HILL 

Fossils collected through the 450 m of Roberts Mountains Formation in the Pine Hill block show the age to 

range from Early Silurian (late Llandoverian) for the 

lower beds to the Lower Devonian (Gedinnian) for the 

upper 100m or so of the formation. This range in age is 

assigned on the basis of graptolites identified by 

W. B. N. Berry (written commun., Nov. 8, 1968). The 

upper 120-m unit contains abundant corals in the more 

massive beds; Carlinastraea, which is especially abundant, is considered representative of the Great Basin 

Silurian coral zone E. 

Coiled graptolites in beds a few feet above the basal 

chert are reported as late Early Silurian (late Llandoverian). Graptolite assemblages near the top of the 

lower 330-m unit include Monograptus praehercynicus 

Jaeger. 

Some limonitic silty limestone and siltstone beds 

about 140 m stratigraphically above the base of the 

Roberts Mountains Formation contain a graptolite assemblage reported upon by W. B. N. Berry (written 

commun., Oct. 16, 1972) as: 

Lobograptus '"scanicus" 

Monograptus bohemicus? 

Monograptus colon us 

Monograptus sp. (of theM. dubius type) 

The age of this horizon is considered by Berry to be 

early Ludlovian. Such a low position for early Ludlovian, some 310m below the top of this section, suggests 

that the Wen lockian part of the formation is relatively 

thin compared with the Ludlovian. 

The upper 120-m lithologic unit of the Roberts 

Mountains Formation at Pine Hill (the type Windmill 

Limestone of Johnson, 1965) is primarily thick-bedded 

dark-bluish-gray medium- to fairly coarse grained 

bioclastic limestone with thin-bedded limestone and 

calcareous shaly intercalations. The coarse-grained 

beds are made up of clastic debris, and most are 

graded. This unit forms prominent outcrops and the 

change from the platy and laminated limestones of the 

lower division is gradual. As described by Berry and 

Mullens (written communs., 1968), the Monograptus 

praehercynicus beds must lie near the base of this 

upper unit. Corals and brachiopods, especially corals, 

are abundant in the upper unit; the most abundant 

coral is the large, massiveFavosites. A zone about 20m 

thick above the middle of this unit has yielded. the 

following fossils: 

Favosites sp. (massive) 

C ladopora sp. 

Alveolites sp. 

Syringopora sp. 

Striatopora? sp. 

Rhegmaphyllum? sp. 

Brachyelasma sp. c 

Tryplasma sp., cf. T. duncanae (fragmentary) 

Tonkinaria simpsoni Merriam 

Stylopleura sp. c, cf. S. berthiaumi Merriam 

Carlinastraea tuscaroraensis Merriam 

Gypidula sp. 

Isorthis sp. (ventral valve) 

Small dalmanellid brachiopod (dorsal valve) 

This assemblage containing Tryplasma, Tonkinaria, 

and Stylopleura suggests that of Great Basin Silurian 

coral zone D at the Roberts Mountains Formation type 

section, although its most distinctive coral, Carlina-
14 ROBERTS MOUNTAINS FORMATION, REGIONAL STUDY 

straea, was not found at the type section. The species of 

Carlinastraea found at Pine Hill occurs in the uppermost fossil bed at Bootstrap Hill in the Tuscarora 

Mountains and at locality M1446 on the pediment 

slope north of Red Hill in the Simpson Park Mountains where it is associated with Australophyllum (Toquimaphyllum) johnsoni Merriam and Stylopleura. 

Such an association, in particular with Toquimaphyllum, suggests that there is no profound 

stratigraphic separation between the Carlinastraea 

beds at Pine Hill and those of Great Basin Silurian 

coral zone E on the east side of Coal Canyon (Pyramid 

Hill block), in which Australophyllum (Toquimaphyllum) johnsoni is the most distinctive rugose coral. Little is known of the stratigraphic range of any of these 

seemingly distinctive Rugosa. 

FOSSILS COLLECTED WITHIN THE 

COAL CANYON FAULT ZONE 

Several important fossil occurrences are within disturbed rocks of the Coal Canyon fault zone, and because of this, their true stratigraphic position remains 

uncertain. Among the fossils are the compact aseptate 

pycnostylid Stylopleura? sp. c (pl. 2, figs. 1 and 2) from 

locality M1379, Australophyllum sp. c (pl. 8, figs. 3-7), 

from locality M1318 and Verticillopora annulata (pl. 

10, figs. 1-3) from locality M1411. From their positions 

in the fault zone, it appears probable that all these 

fossils came from horizons stratigraphically higher 

than the Carlinastraea beds. 

PHYSICAL STRATIGRAPHY OF THE 

PYRAMID HILL SECTION 

In Pyramid Hill, east of the Coal Canyon fault zone, 

about 400 m of east-dipping limestone and thinly 

bedded calcareous shaly and silty deposits include the 

uppermost part of the Roberts Mountains Formation 

(the Windmill Limestone of Johnson, 1965) and the 

overlying Rabbit Hill Limestone. About 150 m of the 

Roberts Mountains Formation is present here. The 

Rabbit Hill underlying most of Pyramid Hill continues 

eastward. As the depositional contact between the two 

formations is gradational, placement is arbitrary as 

understood at this time. The paleontologic change in 

corals, however, is profound with complete disappearance upward of all Rugosa of Silurian affinities and 

Rugosa classified previously as Silurian types (Merriam, 1973a). Only the small solitary variety Syringaxon is present in the Rabbit Hill Devonian of this section. 

Within the Roberts Mountains Formation along the 

steep lower east slopes of Coal Canyon are bold massive outcrops of the more thickly bedded lenticular and 

locally fossil-rich limestones. Much of this lower slope 

is covered by talus mantle that is the source of weathered fossil material collected here. Some of the float 

fossils, like many large Rugosa, however, are traceable 

to their source beds. 

The uppermost Roberts Mountains Formation of the 

Pyramid Hill is made up of fine-textured dark- to 

medium-dark-gray laminated platy to fl.aggy limestone, and thick-bedded (2 cm-2 m) coarse slightly 

bluish-gray bioclastic limestones, most of which are 

graded. Some of the more massive beds are lenticular, 

and locally they form prominent cliff exposures. The 

bioclastic beds, which are composed in considerable 

part of crinoidal debris, also contain abundant corals, 

brachiopods, and other fossils. In some places all fossils 

are silicified and weather out a limonite brown color. 

The thicker bedded limestones above the middle of the 

unit include numerous lenticular bodies of coarsetextured depositional limestone breccia in which some 

clasts are more than a foot in greatest diameter and 

range in shape from subangular to rounded. In some of 

the beds the corals present are surrounded by a 

coarse-grained and fine-grained limestone matrix; 

some beds are graded and of uniform thickness. Above 

the interval of thicker bedded coral-rich limestone and 

depositional breccia, the Roberts Mountains Formation becomes thinner bedded in about its uppermost 23 

m, approaching the transition interval into overlying 

Rabbit Hill Limestone. In general, the lower part of the 

Rabbit Hill is much like the platy thin-bedded Roberts 

Mountains beds, but coarser textured bioclastic beds of 

the Rabbit Hill lack the bluish cast of such fossil-rich 

limestone beds in the Roberts Mountains. Tentaculites 

is common in the lower part of the Rabbit Hill Limestone. The characteristic Leptocoelia of the Rabbit Hill 

Limestone becomes abundant in Leptocoelia beds about 

100 m stratigraphically above the base of the Rabbit 

Hill as mapped. The dark-gray platy limestones and 

calcareous shale and silty beds of the Rabbit Hill commonly weather very light gray. 

In the upper part of the Roberts Mountains Formation of the Pyramid Hill section, the coral-rich more 

massive beds with depositional limestone breccia are 

referred to as the ~~upper coral zone with Toquimaphyllum." On the west side of Coal Canyon in the Pine Hill 

block, the coral-rich beds are distinguished as the 

'~lower coral zone with Carlinastraea." The upper coral 

zone with Toquimaphyllum is the primary reference 

section for Great Basin Silurian coral zone E of Merriam (1973a). These rocks are Lower Devonian in age 

based on graptolites. 

All Pyramid Hill fossils dealt with in this report 

came from a stratigraphic interval of about 50 m in the 

middle and upper parts of the Roberts Mountains Formation on the east side of Coal Canyon. This interval 
TUSCARORA MOUNTAINS 15 

includes the thicker bedded coral-rich limestone and 

allogenic depositional limestone breccia. Some of the 

fossil material came directly from the bold outcrops in 

place, but much of it was collected on the talus below 

the bold exposures. The common fossils of this 50 m 

interval are: 

Stromatoporoids 

Favosites sp. (massive) 

Cladopora sp. 

Alveolites sp. 

Stylopleura nevadensis Merriam 

Stylopleura berthiaumi Merriam 

Mucophyllum oliveri Merriam 

Kodonophyllum mulleri Merriam 

Rhizophyllum cf. R. enorme (Oliver) 

Chonophyllum simpsoni Merriam 

Kyphophyllum sp. c 

A ustralophyllum (Toquimaphyllum) johnsoni 

Merriam 

Orthostrophia sp. 

Schellwienella? sp. 

Barrandella? sp. 

Sicorhyncha? sp. 

Rhynchospirina sp. 

Plectatrypa? sp. 

Atrypa sp. 

Meristella sp. 

Kozlowskiellina sp. f 

Verticillopora cf. V. annulata Rezak 

The rugose coral assemblages in the coral-rich limestone interval of the Pyramid Hill exposures are of 

Silurian character as compared with assemblages of 

the Gotland, Sweden, Silurian standard and with those 

of Silurian strata of the Klamath Mountains, Calif., 

and Australia. 

M ucophyllum oliveri, the most distinctive fossil in 

this fauna, bears a fairly close resemblance to 

M ucophyllum of the Silurian Gazelle Formation of the 

Klamath Mountains, Calif., and to Silurian Mucophyllum crateroides (Etheridge) of Australia. Similar corals from Gotland, Sweden, have previously been referred to Schlotheimophyllum or erroneously to 

Chonophyllum. Kodonophyllum is represented in the 

Gotland section, as is the slipper coral Rhizophyllum, 

which does, however, pass upward into the Early Devonian of eastern Europe. Kyphophyllum is a Silurian 

genus in Gotland but may range into earliest Devonian 

in the Klamath Mountains. Toquimaphyllum, proposed by Merriam (1973a) as a subgenus of the longranging Australophyllum in Silurian and Devonian 

rocks, is itself known in the Great Basin in later Silurian beds. The little-known pycnostylid Rugosa, which 

include Pycnostylus and Stylopleura, are characteristic 

of the Silurian System. 

A float specimen from Coal Canyon assigned to the 

genus Salairophyllum, first reported from the Ural 

Mountains of the U.S.S.R., was probably derived from 

the higher Roberts Mountains limestone. In southeastern Alaska, Salairophyllum occurs in the Late Silurian 

limestones (Merriam, 1972) associated with Conchidium alaskensis, an index fossil of the Ludlovian 

Stage in Alaska. 

Verticillopora, the large dasycladacean alga, is 

mostly confined to Silurian rocks of the Great Basin. In 

the Vaughn Gulch Limestone of the In yo Mountains, it 

crosses the line into earliest Devonian at the base of 

the uppermost Vaughn Gulch limestone unit. 

PROBL£~1 OF THE SILURIAN-DEVONIA~ BOCJ\'DARY 

AT PYRAMID HILL 

A systematic study has been made (Merriam, 1973a) 

of the rugose corals from thick-bedded Roberts Mountains limestone of the upper coral zone with Toquimaphyllu.m, the reference section of Great Basin 

Silurian coral zone E as defined by Merriam (1973a). 

This coral zone contains distinctive genera and subgenera represented in the Silurian of Gotland, Sweden, 

in the Klamath Mountains Silurian of northern 

California (Merriam, 1972), and in the Silurian of Australia. None of these genera range into the overlying 

Rabbit Hill Limestone. 

It is significant that no fossils have been collected 

through a stratigraphic interval of about 100 m from 

the top of the uppermost Roberts Mountains thickbedded coralline limestone to the lowest fossils of the 

Rabbit Hill Limestone. The contact between the two 

formations as mapped is arbitrary, and from the coral 

evidence, with reference to Gotland, Sweden, the 

Silurian-Devonian boundary is discretionary and assumed to lie somewhere within the 100m interval. 

The rugose coral evidence bearing upon the 

Silurian-Devonian boundary clearly does not agree 

with that derived from study of the graptolites and 

from conodont research. The base of the Monograptus 

uniformis Zone, which is accepted as defining the base 

of the Devonian, places the boundary about 250 m 

lower in the section in the Pine Hill block on the west 

side of Coal Canyon. To clearly resolve this type of 

boundary problem will require the cooperative effort of 

specialists dealing with all the fossil groups represented in these rocks, emphasizing graptolites, conodonts, brachiopods, and rugose corals. 

ROBERTS MOUNTAINS FORMATION, 

TUSCARORA MOUNTAINS 

As a host rock of gold, the Roberts Mountains Formation has been traced widely in the Tuscarora Moun-
16 ROBERTS MOUNTAINS FORMATION, REGIONAL STUDY 

tains and nearby areas of Elko and northern Eureka 

Counties, Nev. Structural complexity is everywhere 

characteristic of the formation, where, as part of the 

autochthonous group of rocks, it is overridden by graptolitic shales, argillites, and cherts of the Vinini Formation (Roberts and others, 1958). Complete stratigraphic sections of the Roberts Mountains Formation 

are rare here, but the basal chert is exposed 4 miles 

(6.4 km) southwest of the Big Six Mine (Berry and 

Roen, 1963) and at the gorge on Maggie Creek 8 miles 

(12.8 km) northwest of Carlin. Rocks of the unnamed 

Devonian limestone unit of Mullens (Evans and Mullens, 1976; T. E. Mullens, unpub. data, 1975) are above 

the Roberts Mountains Formation at Bootstrap Mine 

and at Maggie Creek. The section at the Carlin mine, 

though much faulted, seems to be nearly complete. 

An excellent partial section occurs at the Bootstrap 

mine on Boulder Creek 22 miles (35.2 km) northnortheast of Dunphy, a short distance north of the 

Eureka-Elko County line. Although the basal chert is 

not exposed here, about 4 70 m of strata with several 

coral-bearing fossil zones has been measured by T. E. 

Mullens (unpub. data, 1975) at this locality. Evans and 

Mullens (1976) divide this section of rocks into two 

units, the lower 180 m called Roberts Mountains Formation and the upper 27 5 m termed unnamed Devonian limestone. We favor including the lower part of 

the unnamed Devonian limestone unit in the Roberts 

Mountains Formation because it is similar to the upper 

part of that formation at many places in central N evada, in particular, the reference section at Coal Canyon in the Simpson Park Mountains. The upper part of 

the unnamed Devonian limestone unit of Evans and 

Mullens (1976) looks like the Rabbit Hill Limestone 

and is probably correlative with that formation. An 

alternative nomenclature, in line with other studies of 

the Silurian and Lower Devonian in central Nevada, 

would term the lower part of the unnamed unit of 

Evans and Mullens (the top of our Roberts Mountains 

Formation) the Windmill Limestone (Johnson, 1965) 

and the upper part the Rabbit Hill Limestone. The 

lumping of rocks into a general unnamed unit obscures 

basic lithologic similarities and correlations and is a 

step backward in our understanding of the paleotectonics of the region. Collections of unusually wellpreserved silicified fossils made in this vicinity by R. J. 

Roberts during reconnaissance mapping of northern 

Eureka County convincingly demonstrated the Silurian age of some of the limestones. Fossil collections 

along the Mullens section traversed by Mullens and 

Merriam make possible a significant correlation with 

the Coal Canyon reference section and indirectly with 

the Roberts Mountains Formation type section. 

PHYSICAL STRATIGRAPHY OF 

THE BOOTSTRAP HILL SECTION 

Measurement of the Roberts Mountains Formation 

at Bootstrap Hill by T. E. Mullens (unpub. data, 1975) 

shows two major lithologic divisions totaling about 4 70 

m. This section does not include the base of the formation, which presumably is the black chert unit. The 

lower division, 180m of which is exposed, is made up of 

platy splitting laminated limestone with thicker interbeds of bioclastic and pelletal limestone. Of these 

strata, the fine-textured laminated limestones predominate. The upper 275 m unit consists of thicker 

bedded coarser bioclastic and pelletal limestone with a 

few intercalcalations of laminated limestone, especially the lower 50 m. Corals and brachiopods are 

abundant in some beds of the upper unit. The bioclastic 

and pelletal beds commonly exhibit graded bedding; 

many of these beds include breccia fragments and 

scour surfaces at the base. 

The Bootstrap Hill section is possibly truncated at 

the top by a thrust fault (T. E. Mullens, written commun., 1972). The coral-bearing bed, that of Carlinastraea tuscaroraensis, lies about 400 m stratigraphically 

above the bottom of the section. 

STRATIGRAPHIC PALEONTOLOGY OF THE 

BOOTSTRAP HILL SECTION 

Three faunal zones are recognizable at Bootstrap 

Hill on the basis of corals and brachiopods. These 

range in ascending age from possible Great Basin Silurian coral zone A to coral zoneD or E. The uppermost 

beds have yielded no coral fauna, but conodonts are 

varieties found in the Rabbit Hill Limestone. 

Lowest coral-brachiopod zone.-Two fossil collections were made by R. J. Roberts, one from the southwest base of Bootstrap Hill (M1120) and the other from 

the west base of the next hill to the south (M1412). 

Both collections were taken from talus masking the 

lowest exposed strata. 

The collection from locality M1412 is diverse and 

distinctive; it includes, among other fossils, the following forms: 

Cyathophylloides sp. f 

Cladopora sp. 

Alveolitid tabulate coral 

Conchidium sp. b 

Fardenia sp. b 

Ptychopleurella sp. 

Coelospira sp. b 

Kozlowskiellina sp. b 

Merista sp. 

The fossils from locality M1120 at the southwest base 

of Bootstrap Hill are Cyathoph_ylloides sp. f, 

Brachyelasma sp. b, Heliolites sp., and Favosites sp. 
TUSCARORA MOUNTAINS 17 

The fossils at both localities are silicified and associated with chertified sedimentary material that is 

characteristic of lower beds of the formation near the 

basal chert marker. The marker bed presumably is 

lower in the section but is not exposed. The primitive 

colonial rugose coral Cyathophylloides in each of these 

assemblages resembles C. fergusoni of the Great Basin 

Silurian coral zone A described in collections from the 

Toquima Range. 

Middle coral-brachiopod zone.-A 60-m stratigraphic interval starting 180 m from the base of the 

section and at the bottom of the more massive bioclastic sequence contains fossil assemblages that include 

the following forms.: 

Cladopora sp. 

Coenites sp. 

Favosites (massive) 

Stylopleura sp. b 

Calostylis? sp. 

Kodonophyllum sp. b 

Kyphophyllum sp. b 

Resserella sp. 

Leptaena sp. 

Salopina? sp. 

Gypidula sp. 

Coelospira sp. 

Trematospira? sp. 

Atrypa sp. 

H owellella sp. 

Glassia or Cryptatrypa sp. 

Upper fossil zone with Carlinastraea.-Collections 

from what is here called the Carlinastraea bed, 70 m 

stratigraphically below the top of the Bootstrap Hill 

section, were made by R. J. Roberts in 1958 and were 

supplemented by additional collections by Mullens and 

Merriam in 1969. The complex rugose coral Carlinastraea occurs in very large colonies 1 m or more in 

diameter, as it does at Coal Canyon in the Simpson 

Park Mountains. Fossils found in the Carlinastraea 

bed at Bootstrap Hill are: 

Cladopora sp. 

Alveolites sp. 

Favosites (massive) 

Rhegmaphyllum sp. 

Syringaxon? sp. 

Tryplasma sp. cf. T. duncanae Merriam 

Kyphophyllum? sp., cf. K. sp. b 

Carlinastraea tuscaroraensis n. gen., n. sp. 

Salopina? sp. (dorsal valve) 

Large dalmanellid brachiopod (ventral valve) 

Abundant crinoidal debris 

AGE OF THE ROBERTS MOUNTAINS FORMATION 

AT BOOTSTRAP HILL 

Coral and brachiopod evidence points to a Silurian 

age for part of the Bootstrap Hill section with an age 

range from Early Silurian (Great Basin Silurian coral 

zone A) for the lower beds containing Cyathophylloides 

to Late Silurian (Great Basin Silurian coral zone D or 

E) for the higher beds containing Carlinastraea. Like 

the the type and reference sections of the Roberts 

Mountains Formation, the upper part is Lower Devonian. This age, as elsewhere, is based on the graptolite 

standard which in central Nevada places the 

Silurian-Devonian boundary at a lower stratigraphic 

position than the corals would suggest. 

Except for Coelospira sp. b, the brachiopod assemblage from the lowest faunal zone shows little similarity to known assemblages from other areas; the 

brachiopods of Great Basin Silurian coral zone A are in 

general poorly known. 

The faunas of the middle coral-brachiopod zone generally fall in line with a Silurian age, in particular the 

Rugosa Stylopleura, Calostylis?, Kodonophyllum, and 

Kyphophyllum. Several of the brachiopods range upward into the Devonian; those provisionally assigned 

to Salopina?, Coelospira, and Glassia or Cryptatrypa 

are possibly more in harmony with a Silurian age. 

The remarkable colonial rugose coral Carlinastraea, 

though resembling Devonian forms conventionally assigned to Spongophyllum, is generically quite distinct. 

Carlinastraea tuscaroraensis, which is specifically 

identical to that from Bootstrap Hill, occurs in the 

Simpson Park Mountains at Coal Canyon in beds with 

a coral fauna quite similar to that of Silurian coral 

zone D in the Roberts Mountains type section. Carlinastraea of a similar kind occurs in association with 

Australophyllum (Toquimaphyllum) johnsoni and 

Stylopleura cf. S. nevadensis in beds assigned to Great 

Basin Silurian coral zone E at locality M1446 in the 

northern foothills of the Simpson Park Mountains. 

Carlinastraea at Bootstrap Hill is therefore suggestive 

of either Great Basin Silurian coral zone D or E. 

Studies of graptolites from the lower 180 m of the 

Mullens section (unpub. data, T. E. Mullens, 1975) (by 

W. B. N. Berry) give evidence for a higher position in 

the Silurian System than do the corals. Monograptus 

in beds from about 45 m above the base to about 90 m 

include: 

Monograptus sp. (plain thecae) 

Monograptus sp. (appears to have thecae with 

spines similar to those in M. chimaera) 

Monograptus sp. (of theM. dubius type?) 

Monograptus sp. (thecae appear to be similar to 

those of M. uncinatus) 
18 ROBERTS MOUNTAINS FORMATION, REGIONAL STUDY 

Berry's conclusion (written commun., Nov. 8, 1968) is 

that these graptolites are possibly of Ludlovian Late 

Silurian age. Other graptolites from horizons about 

175 m and 185 m above the base of the section are: 

Monograptus angustidens Pribyl 

Monograptus uniformis Pribyl 

Their age is given as Earliest Devonian (Monograptus 

uniform is Zone). 

ROBERTS MOUNTAINS FORMATION OF 

THE NORTHERN MONITOR RANGE 

At Copenhagen Canyon near Rabbit Hill in the 

northern Monitor Range, the Roberts Mountains Formation is represented by thin-bedded laminated 

graptolite-bearing silty limestone and thin- to 

medium-bedded clastic limestones. It is overlain by 

Rabbit Hill Limestone. These Silurian and Lower Devonian strata were studied by Merriam and Anderson 

(1942, p. 1687) and later described in more detail after 

reconnaissance geologic mapping and stratigraphic 

measurement by Merriam (1963). A recent study by 

Matti, Murphy, and Finney (1975) focuses on the stratigraphy and environment of deposition of the Silurian 

and Lower Devonian rocks of this area and revises the 

reconnaissance map. 

The most complete and measurable sequence of 

Roberts Mountains Formation in Copenhagen Canyon 

underlies an unnamed hill whose summit is about 1.6 

km north-northeast of the top of Rabbit Hill in the 

SWlft sec. 36, T. 16 N., R. 49 E. The formation to the top 

of the unnamed hill measured about 180m (Merriam, 

1963, p. 38); beds of several hundred metres more are 

present west of the hill but poorly exposed. A thickness 

of 480 m was measured by Matti, Murphy, and Finney 

(1975) on this traverse. The section is made up of platy 

to shaly weathering argillaceous limestone and calcareous shale grading upward into thin- to mediumbedded clastic limestones with fine-grained laminated 

limestone interbeds. On fresh surfaces these argillaceous beds are dark gray and fine textured; on weathering they become light gray or buff colored. Bioclastic 

and graded beds occur as sporadic interbeds in the 

middle part of the section and as the main lithologic 

type in the upper part; they are about 12 em thick and 

are composed largely of fine sandy material with 

crinoidal debris. The platy silty limestones contain an 

abundance of graptolites best seen on weathered surfaces. No thick coarse bioclastic limestone lenses containing a diverse colonial coral fauna were found in 

this section, but brachiopods, which were collected 

from high in the section, are reported by Johnson, 

Boucot, and Murphy (1967). 

The lower 30-40 m of the Roberts Mountains Formation at the unnamed hill is a very cherty limestone 

that is assumed to be correlative with, or to include, 

the basal Roberts Mountains chert marker of other 

Great Basin sections. It is, however, classified as the 

top of the underlying Hanson Creek Formation by 

Matti, Murphy, and Finney (1975). This conspicuously 

banded member consists of interbedded dark-gray or 

slightly bluish-gray fine-grained limestone and darkgray chert that weathers limonite brown. Uneven 

lenses and pinch-and-swell beds of chert, 2-12 em 

thick, make up one-third to one-half of this cherty unit. 

Above the cherty member, for at least 140 m to the 

top of the hill, are thin-bedded fine-grained argillaceous limestones that are dark gray on fresh breaks 

but weather light gray with buff- and brownish-colored 

patches. A few dark-gray chert nodules occur at places 

in this interval. 

PHYSICAL STRATIGRAPHY 

The contact at the bottom of the lowest chert bed 

reveals no convincing physical evidence of erosion and 

disconformity with the underlying Hanson Creek 

Formation, of Late Ordovician and Early Silurian age. 

Of possible significance regarding the system boundary is a persistent calcareous sandstone bed that lies 

about 12m stratigraphically below the chert. This fine 

sandstone contains abundant chert granules. According to F. G. Poole (oral commun., 1968), a sand of this 

kind occurs widely in the central Great Basin in about 

the same stratigraphic position. This bed provides a 

useful datum with reference to base of the Silurian 

System; it is especially valuable in sections lacking the 

chert marker. 

The apparent thinning of the Roberts Mountains 

Formation at Copenhagen Canyon from the relative 

thick sections to the north is part of the gradual thinning of the unit to the west and south. In the Toquima 

Range to the west, two thrust plates containing rocks 

that were originally deposited farther west (presumably in the vicinity of the Toiyabe Range) contain complete sections of Roberts Mountains Formation that 

are 106m thick and less than 3m thick, respectively. 

Similarly, in the northern lnyo Mountains, Calif., a 

northward change of the Vaughn Gulch Limestone to 

graptolite-bearing shaly deposits was accompanied by 

a thinning of strata representing the Vaughn Gulch 

interval (Ross, 1966, p. 32). 

STRATIGRAPHIC PALEONTOLOGY AND AGE 

OF THE ROBERTS MOUNTAINS FORMATION 

AT COPENHAGEN CANYON 

Studies of graptolites and conodonts provide most of 

the paleontologic evidence of age of this formation in 

the Monitor Range; they indicate the age of the forma-
DOBBIN SUMMIT, MONITOR RANGE 19 

tion as Silurian and Lower Devonian. Generically undetermined pentameroid brachiopods about 3 em long 

observed in the field near the top of the cherty unit 

suggest that this unit is best assigned to the Silurian 

System, in agreement with the graptolites and conodonts. The sporadic crinoidallimestone beds may eventually yield other shell megafossils of diagnostic age 

significance. 

Graptolites identified by Ruedemann (Merriam and 

Anderson, 1942, p. 1687) came from surface rubble a 

few feet above the chert. These were identified as 

Monograptus acus Lapworth and Monograptus pandus 

Lapworth, suggesting to Ruedemann the approximate 

age of the lower and middle Gala beds of England, or of 

the Clinton Group (Middle Silurian) and younger Silurian beds in New York State. 

Several graptolite collections made by Mullens and 

Merriam from higher in the section and identified by 

Berry include the following forms: 

(float near top of basal chert, 33m above base of formation) 

Cyrtograptus sp. 

Monograptus priodon (Bronn) 

Age: In the span of late Llandovery to early Wenlock. 

(float 33--84 m above base of formation) 

Cyrtograptus sp. 

Monograptus flemingii (Salter) 

Age: Probably Wenlock. 

(100 m above base of formation) 

Monograptus dubius (Suess) 

Monograptus uncinatus Tullberg 

Gothograptus spinosus Wood 

Age: Early Ludlow; Monograptus nilssoni-M. 

scanicus Zone. 

(approximately 106 m above base of formation) 

Monograptus sp. cf. M. nudus type? 

Monograptus sp. cf. M. jaculum type? 

Age: In the span of middle Llandovery to Ludlow. 

(90--150 m above base of formation) 

Monograptus flemingii (Salter)? 

Monograptus sp. (of theM. dubius type) 

Age: Probably late Wenlock. 

Graptolites reported by Matti, Murphy and Finney 

(1975) include Monograptus spiralis and Retiolites 

geinitzianus angustidens 1m above the top of the chert 

(33 m above the base of the formation as used here) 

these forms are late Llandoverian. Collections from 

high in the formation (in the Windmill Limestone as 

mapped by Matti and others, 1975) include Monograptus birchensis, M. praehercynicus, and M. hercynicus; 

those species indicate an Early Devonian age. 

ROBERTS MOUNTAINS FORMATION AT 

BROCK CANYON, MONITOR RANGE 

At Brock Canyon on the west side of the range, the 

Roberts Mountains Formation is exposed as parts of 

two separate thrust plates. One plate contains all the 

Middle and Upper Ordovician formations (Antelope 

Valley Limestone, Copenhagen Formation, Eureka 

Quartzite, and Hanson Creek Formation) recognized to 

the east around Antelope Valley as well as the Roberts 

Mountains Formation; the second plate contains 

Roberts Mountains Formation directly on the Antelope 

Valley Limestone. The Roberts Mountains Formation 

in both plates is finely laminated thin-bedded graptolitic silty limestone, but the basal chert is present in 

only one of the two sequences-the plate containing 

the complete series of Ordovician formations. The formation is at least 180 m thick, but the total thickness 

of the formation in either plate is unknown as it is the 

youngest unit in the respective sequences. 

ROBERTS MOUNTAINS FORMATION AT 

DOBBIN SUMMIT, MONITOR RANGE 

In the middle part of the Monitor Range at Dobbin 

Summit and Clear Creek, the Roberts Mountains Formation has been mapped by F. J. Kleinhampl 

(Kleinhampl and Ziony, 1967). In that area the formation is under lain by the Hanson Creek Formation and 

overlain by Rabbit Hill Limestone. This occurrence of 

the Roberts Mountains is of special significance as it is 

partly dolomitic, suggesting proximity to the border 

zone between the eastern dolomite belt and the intermediate limestone belt as at Roberts Creek Mountain 

and at Bare Mountain near Beatty, Nev. Rocks from 

the August Canyon thrust sequence in the Toquima 

Range that are in part correlative with the Roberts 

Mountains Formation are also dolomitic. The basal 

chert member was not found. Kleinhampl states: 

The Roberts Mountains Formation consists of two main units. The 

lower contains alternating pale brown-weathering slope-forming 

platy limestone and thinner but conspicuous medium-dark-gr~y 

ledgy limestone and dolomite containing abundant macerated foss1ls 

(crinoid columnals and corals). This unit closely resembles the Masket Shale of Kay and Crawford (1964, p. 439) in the Ikes Canyon area 

of the Toquima Range. An overlying gray massive cliffy dolomite 

and limestone unit is commonly present in the Monitor Range and is 

tentatively considered to be the upper part of the Roberts Mountains. 

It could be correlative with part of the Lone Mountain Dolomite. 

Because of the questionable age and name assignment and thinness 

of units, the Late Ordovician through Silurian strata are shown as 

undifferentiated dolomite on the northern Nye County geologic map. 

In the Dobbin Summit area, the Roberts Mountains is no more than 

about 60-120 m thick and consists mainly of the lower unit. In contrast, near Clear Creek, the lower member is 90 m thick and the 

upper gray massive dolomite member is 100m thick (Greene, 1953, 

p. 27 ). Here the top is faulted out according to Greene. 

The Rabbit Hill Limestone overlies the Roberts Mountains Formation in the Dobbin Summit area. The Rabbit Hill consists of very 
20 ROBERTS MOUNTAINS FORMATION, REGIONAL STUDY 

fossiliferous somewhat platy slope-forming limestone that is poorly 

exposed and weathers to chips and plates of pale yellowish- and pale 

reddish-gray and yellowish-brown colors. The formation may form 

an incomplete section as little as less than 100 to about 245m thick 

and truncated at its top by a low-angle fault. The fault zone is 

marked by a discontinuous very dark gray chert. 

ROBERTS MOUNTAINS FORMATION 

AT BARE MOUNTAIN 

Of special interest are those localities where the 

Great Basin Silurian gives evidence of a position near 

a lateral transition from dolomite of the eastern dolomite belt to limestone of the intermediate limestone 

belt, such as Bare Mountain near Beatty, Nev., and the 

Roberts Mountains type section of central Nevada. 

At Chuckwalla Canyon, near Bare Mountain, 

Cornwall and Kleinhampl (1960) mapped 300 m of 

Silurian rock as two formations. The upper unit, being 

entirely dolomite about 114 m thick, was assigned to 

the Lone Mountain Dolomite; the lower unit, about 

190m thick, was referred to the Roberts Mountains 

Formation; this lower unit is made up of alternating 

members of dark-gray limestone, dolomitic limestone, 

and dolomite; one-third to one-half of this sequence is 

dolomite. A Silurian age assignment is reasonable, for 

at Bare Mountain these beds occupy a stratigraphic 

interval between the Late Ordovician Ely Springs 

Dolomite and superjacent dolomite assigned to the Devonian. 

The Bare Mountain sequence can be compared with 

the Lone Mountain Dolomite at its type section. As 

presently interpreted by Merriam (1973b), the type 

Lone Mountain includes a lower dark-gray dolomite 

called Lone Mountain Dolomite unit 1 and an upper 

light-gray dolomite termed Lone Mountain unit 2. 

Lone Mountain unit 1 is lithologically comparable in 

many respects to the Roberts Mountains Formation of 

Cornwall and Kleinhampl at Bare Mountain but differs by containing no limestone. 

No fossils of stratigraphic significance were identified by Merriam (1973b) during the course of his work 

in the Lone Mountain Dolomite of the type section. The 

middle part of Lone Mountain unit 1 contains partly 

silicified brachiopods and corals, locally in abundance. 

None of the fossils prepared by acid etching were generically determinable; they include small pentameraids, small rhynchonellid brachiopods, and tabulate 

corals. Lone Mountain unit 2, the upper light-gray 

unit, has yielded a poorly preserved cerioid rugose 

coral and in dark-gray lenses of this upper division, 

colonial forms probably of the genus Entelophyllum. 

There are unconfirmed reports that larger pentamerids 

were collected from an unknown part of the Lone 

Mountain in its type section. In the Mahogany Hills 

and Fish Creek Range, Eureka County, Nev., identifiable fossils are present in Lone Mountain unit 2 (Merriam, 1973b). At Bare Mountain, the upper formation, 

or Lone Mountain Dolomite of Cornwall and Kleinhampl, has yielded no fossils. The underlying dark unit 

(Roberts Mountains Formation) contains abundant 

silicified fossils in its middle part, in both the limestone and the dolomite interbeds. 

Correlation of the Bare Mountain strata with those 

of central Nevada is based somewhat more on general 

lithologic resemblance and stratigraphic sequence 

than on fossil evidence. The silicified fossil assemblages from the middle part of the lower dark-gray 

unit (Roberts Mountains Formation of Cornwall and 

Kleinhampl ), which come mainly from dolomite interbeds, are not closely related to known faunas of the 

type Roberts Mountains Formation. Most abundant 

are pentameroid brachiopods which include a large, 

smooth Pentamerus-like genus, Conchidium of 

medium to large size, and Virgiana? sp. A similar 

Pentamerus-like genus occurs in the lower part of the 

Roberts Mountains Formation at Coal Canyon, Simpson Park Mountains, Nev. In the type section, Roberts 

Mountains pentameroids, especially Conchidium, are 

present in great abundance near the top of unit 2, that 

is, near the middle of the formation. The corals at Bare 

Mountain are Heliolites sp., large Streptelasma-like 

solitary forms, large solitary Rhabdocyclus sp. B, and 

Stylopleura sp. resembling S. berthiaumi of the Great 

Basin Silurian coral zone D. Near the base of the Bare 

Mountain section, the colonial Palaeophyllum sp. b occurs (Merriam, 1973a). 

It is significant that a very cherty dolomite member 

lies at the base of the Roberts Mountains Formation at 

Bare Mountain. This member occupies the position of 

the basal chert marker of many Great Basin sections of 

the Roberts Mountains Formation. 

ROBERTS MOUNTAINS FORMATION OF 

THE NORTHERN TOQUIMA RANGE 

Good exposures of the Roberts Mountains Formation 

are found north of Petes Canyon, in the area between 

Ikes and Mill Canyons, and in the area around East 

and West Northumberland Canyons in the northern 

part of the Toquima Range. The formation in these 

localities occurs in different tectonic plates that have 

presumably been thrust from sites of deposition west of 

the Toquimas. A simplified geologic map, figure 3, 

outlines these structural relations. A total of five 

sequences of lower and middle Paleozoic rocks are 

present in the thrust slices; when unraveled palinspastically, they represent rocks from a large region in 

central Nevada. 
Cenozoic, Mesozoic, and upper Paleozoic rocks 

....1...... 

Fault 

Bar and ball on down thrown side 

THE NORTHERN TOQUIMA RANGE 

Petes Canyon window 

EXPLANATION 

Upper plate of Roberts Mountains thrust 

Western and transitional 

--

facies of lower 

and middle Paleozoic rocks 

----········· Thrust fault 

Sawteeth on upper plate, dotted where concealed 

21 

Lower plate of Roberts Mountains thrust 

~11111111111~ Eastern and some transitional facies of lower 

and middle Paleozoic rocks 

Contact 

FIGURE 3.-The northern Toquima Range showing Paleozoic sequences that contain Silurian rock in separate thrust sheets. Based on 

geologic mapping by E. H. McKee in 196~ 70. 
22 ROBERTS MOUNTAINS FORMATION, REGIONAL STUDY 

PETES CANYON WINDOW 

The Roberts Mountains Formation in the vicinity of 

Petes Canyon (fig. 1, loc. 7; fig. 3) is exposed in the 

Petes Canyon window in the Roberts Mountains thrust 

(McKee and Ross, 1969). An incomplete section of the 

formation is present here as the uppermost unit in the 

autochthon. A number of partial sections including the 

basal black chert unit are found; the thickest of these, 

in the central part of sec. 10, T. 16 N., R. 46 E., southeast corner of Lander County, contains more than 100 

m of strata. The thickness of the order of 300 m estimated by McKee and Ross (1969) should probably be 

revised to about 200-250 m. 

The basal contact with rocks mapped -as the Hanson 

Creek Formation seems conformable, though obscured 

by small faults or alluvium in most places. No angular 

discordance was found between the Roberts Mountains 

and Hanson Creek, but fossil evidence suggests a 

hiatus between these formations. 

The Roberts Mountains above the basal black chert 

is mostly thin-bedded platy-splitting graptolitebearing argillaceous limestone. A few medium-bedded 

limestones contain a rich coral fauna, but the stratigraphic relation of these beds is not known because of 

structural complications. Graptolites, which provide 

the evidence for the age of lower parts of the formation, 

include monograptids ranging from upper Lower Silurian (Llandovery) into the upper part of the Middle 

Silurian (Wenlock and possibly lower Ludlow). The 

coral-bearing limestone beds contain forms typical of 

the Rabbit Hill Limestone of Early Devonian age. 

IKES CANYON WINDOW 

JUNE CANYOl'\ SEQUENCE 

In the area between Ikes and Mill Canyons, carbonate strata of lower and middle Paleozoic age are exposed in a window in the Roberts Mountains thrust 

called the Ikes Canyon window (fig. 1, loc. 8; fig. 3). The 

Roberts Mountains Formation (or its correlatives) occurs in three somewhat different sequences of rocks 

that have been thrust together and are now exposed in 

this window. The upper thrust plate, named the June 

Canyon sequence by Kay and Crawford (1964), contains a metre or so of thin-bedded, platy-splitting graptolitic limestone between massive beds of Ordovician 

limestone and the Tor Limestone of Late Silurian and 

Early Devonian age. The upper contact with the Tor is 

conformable; the lower contact with Ordovician limestone appears conformable but may be a fault. In all 

places but one (approximately 1,500 m west of Ikes 

cabin site), the massive limestone units (Ordovician 

limestone and Tor) are in fault contact, the relatively 

incompetent Roberts Mountains limestone having 

been sheared out between them. 

The total thickness of Roberts Mountains Formation, here made up entirely of the thin-bedded graptolitic limestone, is about 3m. Fragments of the graptolite 

Monograptus aff. M. praehercynicus indicate that the 

few feet of strata that make up the formation in this 

thrust plate correlate with the upper part of the formation elsewhere in central Nevada and are of Lower Devonian age. Corals from the bottom part of the Tor 

above the graptolite horizon are typical of the Great 

Basin Silurian coral zone E (McKee and others, 1972), 

which is included in the Lower Devonian because of 

the underlying Monograptus praehercynicus. 

MILL CANYON SEQCENCE 

The middle thrust plate, named the Mill Canyon sequence by Kay and Crawford (1964) (fig. 1, loc. 9; fig. 3), 

contains a complete section of the Roberts Mountains 

Formation with both graptolites and corals. These 

strata are well exposed on the ridges above the lower 

reaches of Ikes Canyon. 

The formation here is about 110m thick and consists 

mostly of thin-bedded platy argillaceous limestone 

with increasing amounts of medium (5--30 em) graded 

beds of clastic limestone toward the top. There is no 

chert at its base, and it rests with no obvious disconformity on massive limestone that contains Upper Ordovician fossils. The lowest fossils (graptolites) in the 

Roberts Mountains of the Mill Canyon sequence occur 

within a foot of its base and are Middle Silurian forms 

(McKee, 1975). The fossil evidence indicates a hiatus 

representing a time period of considerable duration at 

the base of the formation. The upper contact with the 

McMonnigal Limestone, gradational across an interval 

of about 25 m, was arbitrarily drawn where mediumbedded gray clastic limestone typical of the McMonnigal becomes the dominant lithology. 

Graptolites that occur throughout the formation include late Middle Silurian (late Wenlock) forms at the 

base, Upper Silurian Ludlow) types somewhat higher, 

and Monograptus praehercynicus, which is Lower Devonian, in the upper part of the formation and in the 

bottom of the McMonnigal Limestone. 

The Roberts Mountains--McMonnigal sequence has 

yielded coral faunas in normal order representing 

three, A, D, and E, of the five Great Basin Silurian 

coral zones. Coral zone A is represented by 

Arachnophyllum kayi with which Cyathophylloides 

fergusoni and N eomphyma crawfordi are associated. 

Above this horizon, coral zone D contains Stylopleura 

nevadensis, Tonkinaria sp., and large Verticillopora 

annulata. Coral zones A and D are in the Roberts 

Mountains Formation; coral zone E lies in the McMonnigal Limestone and includes A ustralophyllum 
THE TOIYABE RANGE 23 

(Toquimaphyllum) johnsoni and a species of Kyphophyllum. 

AUGUST CANYON SEQUENCE 

Rocks in the lowest thrust plate in the Ikes Canyon 

window (fig. 1, loc. 10, fig. 3) were named the August 

Canyon sequence by Kay and Crawford (1964). It was 

assumed by these geologists that this sequence of 

strata is in situ, but it is possible that these rocks, along 

with the overlying two plates (Mill Canyon and June 

Canyon sequences), have moved from another region. 

As its base has not been found, there is no structural 

evidence bearing on the problem; stratigraphic considerations such as regional facies patterns shed little 

light on the site of deposition of the rocks. These strata 

contrast so markedly with the strata of equivalent age 

in the overlying thrust plates that new formational 

names proposed by Kay (1960) and Kay and Crawford 

(1964) seem appropriate. Rocks correlative with the 

Roberts Mountains Formation include all or most of 

the Gatecliff Formation of Kay (1960), the Bastille 

Limestone Member of the Masket Shale of Kay and 

Crawford (1964), and probably the lower part of the 

upper member of the Masket Shale of Kay and Crawford (1964). The name Masket Shale was used by these 

workers (1964) for strata in the Mill Canyon and June 

Canyon sequences; in this report and in others (McKee 

and others 1972; McKee, 1976), those strata are called 

the Roberts Mountains Formation. 

The Gatecliff Formation of Kay and Crawford is 

comprised of three distinctive units, all dolomitic. It 

overlies with no apparent discordance dark-colored 

limestone containing a distinctive fauna considered to 

be Upper Ordovician (McKee, 1976). This Upper Ordovician limestone was named the Caesar Canyon 

Limestone by Kay and Crawford (1964). Corals indicative of the Silurian have been collected from the basal 

unit of the Gatecliff (McKee, 1976), which is a lightgray lithographic dolomite. The middle unit of the 

Gatecliff is dolomite distinctive by the presence of 

rounded quartz sand grains; no fossils have been found 

in this rock. The upper unit of the Gatecliff is dolomite 

and chert similar to the basal chert unit of the Roberts 

Mountains Formation in most of central Nevada. No 

fossils have been collected from this chert in the August Canyon sequence, but a few miles south, s similar 

chert unit in what is called the Prospect sequence by 

Kay and Crawford (1964) has yielded graptolites that 

indicate an Early Silurian age. The Bastille Limestone 

Member of the Masket Shale of Kay and Crawford is 

mostly unfossiliferous gray dolomite with mediumbedded bioclastic limestones at the top. These limestones contain a rich coral fauna equated with the 

Great Basin Silurian coral zone E. Part or possibly 

most of Silurian time is represented by the underlying 

dolomite or at the basal contact with the underlying 

Caesar Canyon Limestone of Kay and Crawford. The 

upper part of the Masket Shale of Kay and Crawford is 

thin-bedded laminated silty limestone, part of which 

may correlate with the upper part of the Roberts 

Mountains Formation and with the Rabbit Hill Limestone. It is of Lower Devonian age on the basis of a 

variety of Lower Devonian conodont forms (McKee, 

1976). 

NORTHUMBERLAND WINDOW 

About 8 km south of the Ikes Canyon window, eastern to transitional facies (mostly carbonate) rocks are 

exposed in the Northumberland window in the Roberts 

Mountains thrust (fig. 1, loc. 11; fig. 3). The rocks in 

this window constitute the Prospect and Striped Hill 

sequences of Kay and Crawford (1964), presumed to 

have been thrust from the southwest to their present 

location in the north-central part of the Toquima 

Range (Kay and Crawford, 1964, fig. 8). 

Both the Prospect and Striped Hill sequences contain Roberts Mountains Formation (called Masket 

Shale and Gatecliff Formation by Kay and Crawford, 

1964) as their uppermost unit. The formation is typically thin-bedded platy-splitting argillaceous tanweathering limestone similar to rocks mapped as 

Roberts Mountains Formation in most other places in 

central Nevada. Black cherty limestone occurs at the 

base of the formation. Monograptids from the chert 

zone at Water Canyon north of East Northumberland 

Canyon are indicative of the Lower Silurian (lower 

Llandovery). An Early and Middle Silurian age is assigned to the overlying platy unit of the Striped Hill 

sequence by Kay and Crawford (1964, fig. 5). 

ROBERTS MOUNTAINS FORMATION 

IN THE TOIYABE RANGE 

The Roberts Mountains Formation crops out in 

widely separated localities along most of the extent of 

the Toiyabe Range. Many of these occurrences mark 

the westernmost exposures of the formation at a given 

latitude; these outcrops lie approximately along long 

117°15'. It is assumed that these outcrops have not 

been tectonically transported (thrust) from the west as 

have many thrust plates in the Toquima Range. 

Localities where partial or complete sections of Roberts 

Mountains Formation are exposed include: Callaghan 

window (fig. 1, loc. 18), about 24 km northeast of Austin; Dry Creek area (fig. 1, loc. 6), 11 km south-southwest of Austin; Point of Rocks and Straight Canyon 

area (fig. 1, loc. 16), about 27 km southwest of 

Austin; and Pablo Canyon (fig. 1, loc. 12), about 16 km 

west of Round Mountain. The formation crops out at a 
24 ROBERTS MOUNTAINS FORMATION, REGIONAL STUDY 

few other localities in the Toiyabe Range where it has 

not been studied in detail. 

CALLAGHAN WINDOW 

Lower Paleozoic carbonate strata are exposed in the 

Callaghan window (fig. 1, loc. 18) in the Roberts Mountains thrust about 24 km north of Austin (Stewart and 

Palmer, 1967; Stewart and McKee, 1968). The Roberts 

Mountains Formation is the top unit in the autochthonous sequence and occurs in scattered outcrops in 

the southern and northwestern parts of the window. 

Since it is the top unit, its thickness is not known. 

About 60 m can be measured in partial sections, but 

the formation is probably three to four times thicker in 

this part of the Toiyabe Range. The more than 1,000 m 

reported by T. E. Mullens (unpub. data, 1975) seems 

excessive on the basis of other measured sections in the 

region. The Roberts Mountains Formation lies on different rock units at localities only a few miles apart. In 

the Boone Creek area in the northern part of the window, it lies on Antelope Valley Limestone. There is no 

obvious angular discordance between these formations, but a hiatus spanning the Upper Ordovician and 

possibly part of the Lower Silurian must be represented at the contact. In the southern part of the window, it rests on rocks originally considered to be equivalent to the Hanson Creek Formation (Stewart and 

Palmer, 1967) but now considered likelier to be correlative with the Copenhagen Formation (Stewart and 

McKee, 1975). About 40 m of strata lithologically different from the underlying Antelope Valley Limestone 

and overlying Roberts Mountains separates these formations. At all places in the Callaghan window, the 

Roberts Mountains consists of a basal black chert 

about 10m thick overlain by light-gray platy-splitting 

silty limestone that contains monograptids. No coralline limestone has been found in the incomplete sections of the formation in this area. 

DRY CREEK AREA 

On the west side of the Toiyabe Range about 11 km 

southwest of Austin, in the Dry Creek area, the 

Roberts Mountains Formation (fig. 1, loc. 6) is the uppermost unit of a section that includes Ordovician, 

Cambrian, and Precambrian strata below. About 

120m of tan- or gray-weathering platy argillaceous 

limestone makes up the formation in this area. There 

is no basal chert unit, and the formation lies with apparent conformity on medium-bedded Antelope Valley 

Limestone. A few fragments of Monograptus have been 

found in these platy rocks, and a collection of poorly 

preserved corals comes from a thicker bed of limestone 

near the top of the section. The corals, which include 

Favosites and Zelophyllum sp., suggest a Silurian age, 

probably in the upper part of the system. In overall 

aspect, this section resembles the Mill Canyon sequence of the Toquima Range, a sequence of strata in a 

thrust plate assumed to have originated in the general 

area of the Dry Creek section. 

POINT OF ROCKS AND STRAIGHT CANYON 

A faulted sequence of lower Paleozoic strata is exposed in the western and central part of the Toiyabe 

range in an area that includes Straight Canyon and an 

area of about 10 km2 south of Reeds Canyon, including Point of Rocks Canyon about 27 km south of Austin 

(fig. 1, loc. 16). Here the rocks dip generally to the 

north, forming a homoclinal sequence. This seemingly 

simple structure is complicated by at least one thrust 

parallel to the strike of bedding and other faults that 

cut out, or repeat, parts of the section. Stratigraphic 

thicknesses are estimates based on a number of traverses across the section. The best exposure of the lower 

part of the Roberts Mountains Formation and underlying units is in Straight Canyon (sec. 18, T. 16 N., R. 

43 E.) about 1.6 km west of the Kingston ranger station. Here about 3 m of dark chert and limestone that 

make up the basal part of the Roberts Mountains lies 

on a composite unit about 15 m thick of cherty limestone and dark shale containing cryptolithoid trilobites. These rocks are probably best correlated with 

units in the Toquima Range named Hanson Creek 

Formation (in Fetes Canyon window) or Caesar Canyon Limestone in the August Canyon sequence of the 

Ikes Canyon window. There is no angular discordance 

between the unit and the Roberts Mountains chert, but 

they are probably separated by a hiatus as elsewhere 

in central Nevada. Above the chert is about 100 m or 

more of gray-weathering platy argillaceous limestone 

typical of the graptolite facies. A few monograptids 

were found a short distance above the basal chert in 

Straight Canyon and higher in the section on the west 

side of Point of Rocks Canyon. The section from Point 

of Rocks Canyon to the north side of the adjacent unnamed canyon to the north (unsurveyed sec. 36, T. 

17 N., R. 42 E.) reveals about 300 m of thin-bedded 

Roberts Mountains Formation. This thickness, however, is subject to speculation and is probably excessive, for at least half the section is poorly exposed on 

the dip slope, and numerous faults mapped at other 

places in the region are probably present here. Scattered graptolites collected in these rocks indicate that 

they are forms considered to range from late Early 

Silurian (late Llandovery) to Devonian in age (Stewart 

and McKee, 1976). Further evidence for unresolved 

structural complications is that the succession of graptolite zones does not correspond to a simple traverse 
LIMESTONES OF THE NORTHERN INYO MOUNTAINS 25 

across the section. It is suggested here that the actual 

thickness of the formation in this part of the Toiyabe 

Range is of the order of150 m. Thin- to medium-bedded 

bioclastic limestones become more numerous toward 

the top of the formation. Graptolites in this transition 

zone are of the Monograptus hercynicus group. Higher 

in the section, a massive limestone (about 4 m thick) 

contains the corals Billingsastraea? sp. T, a new 

species, and a new species of a Hexagonaria-like genus. 

PABLO CANYON AREA 

A faulted slice of Roberts Mountains Formation occurs in Pablo Canyon in the Toiyabe Range about 16 

km west of the town ofRound Mountain (fig. 1, loc. 12). 

The top of the formation here is everywhere faulted, 

and it is faulted at the base in most places. In the few 

places where the basal chert unit is exposed, it lies on 

3-6 m of shaly and cherty rock that contains Ordovician graptolites. Most of the formation is gray- to tanweathering thin-bedded platy-splitting silty limestone 

typical of the graptolitic facies seen elsewhere in central Nevada. The locality in Pablo Canyon is the westernmost occurrence of recognizable Roberts Mountains 

Formation at this latitude. 

ROBERTS MOUNTAINS FORMATION IN THE 

SHOSHONE MOUNTAINS 

A partial section of Roberts Mountains Formation 

crops out in the Shoshone Mountains in the Ravenswood area about 24 km northwest of Austin (fig. 1, loc. 

17); the westernmost outcrops of the formation at this 

latitude are almost directly north of the Point of Rocks 

and Pablo Canyons sections along long 117°15'W. 

The formation here, as at the other places at this general latitude, is mostly graptolite-bearing thin-bedded 

platy-splitting silty limestone. About 250m ofrocks of 

this lithologic type occurs above a thin black chertbearing unit that in turn lies on either Middle Ordovician Antelope Valley Limestone or shale, chert, and 

limestone of an unnamed unit tentatively correlated 

with the Copenhagen Formation (Stewart and McKee, 

1976). 

SILURIAN AND LOWER DEVONIAN 

LIMESTONES OF THE NORTHERN 

INYO MOUNTAINS, CALIF. 

MAZOURKA CANYON 

VAUGHN GULCH LIMESTONE 

Within the intermediate limestone belt, the southernmost Silurian and Lower Devonian rocks of the 

Great Basin crop out at Mazourka Canyon, northern 

Inyo Mountains, Calif. (fig. 1, loc. 29). No exposures of 

these limestones have been found between the Inyo 

Mountains and the Toquima or Toiyabe Ranges, a distance of about 200 km. Named the Vaughn Gulch 

Limestone by Ross (1963, p. B81), these beds were for 

many years after their first geologic examination in 

1912 believed to be entirely Devonian (Kirk, 1918; 

Stauffer, 1930). Geologic mapping of the Cerro Gordo 

mining district by the U.S. Geological Survey in 1946 

stimulated renewed interest in these limestones when 

it was suspected that the Silurian and Lower Devonian 

Hidden Valley Dolomite (McAllister, 1952) of the 

southern Inyo and Panamint Mountains changes 

northward and westward to limestone as represented 

at Mazourka Canyon. Systematic collecting and study 

of the Vaughn Gulch and Hidden Valley Rugosa and 

dasycladacean algae began in 194 7 with the Cerro 

Gordo work, during which the Vaughn Gulch section 

was measured and mapped. A study of these rocks by 

Waite (1953) pointed to the Silurian age of most of the 

formation and demonstrated northward facies changes 

into more argillaceous graptolite-bearing beds in the 

Mazourka Canyon area. Detailed geologic mapping of 

the Independence quadrangle by Ross (1963, 1965, 

1966) further clarified the stratigraphic and structural 

relations, and work by Stevens and Ridley (197 4) 

brought forth additional field evidence of northwestward change to graptolitic facies within the Vaughn 

Gulch. Correlation of the Vaughn Gulch with the 

Roberts Mountains Formation was made possible by 

comparative studies of its rugose corals and dasycladacean algae in the 60's. Stratigraphic details and fossil 

zonation as here presented came mainly from Merriam's field investigation during the years 1946--48 

when most of the fossil collecting was done by the U.S. 

Geological Survey. 

PHYSICAL STRATIGRAPHY 

The Vaughn Gulch Limestone, in its type section, 

the ridge northwest of Vaughn Gulch near the mouth 

of Mazourka Canyon 4 km northeast of Kearsarge 

(Ross, 1963, 1966), is an unbroken sequence about 

460 m thick resting conformably upon the Late Ordovician Ely Springs Dolomite and overlain unconformably by Mississippian conglomerate and quartzite 

of the Perdido Formation (McAllister, 1952, p. 22). The 

formation consists of well-bedded medium- to dark-gray 

impure carbonaceous limestone, argillaceous limestone, and calcareous siltstone including many fossilrich beds. Some of the more argillaceous and silty 

interbeds weather in subdued fashion, becoming light 

gray, stained pink, or orange in places. Black chert 

zones are stratigraphically significant, occurring at the 

base and top of the formation; elsewhere minor chert is 

present as scattered nodules or thin lenses. Platy and 

fiaggy exposures predominate, with limestone ranging 
26 ROBERTS MOUNTAINS FORMATION, REGIONAL STUDY 

from 2.5 to 15 em separated by calcareous shaly or 

siltstone partings. Thicker limestone beds, some exceeding 1 m, are fairly common; many of them are 

coarsely bioclastic. These thicker beds weather out 

prominently and are most numerous in the middle part 

of the formation. 

As noted by Ross (1966, p. 31), readily mappable 

lithologic subdivisions were not found within the 

Vaughn Gulch Limestone of the type section. Its faunal 

distribution, however, is conveniently subdivided into 

a lower part 107 m thick, a middle part 220 m thick, 

and an upper part 140m thick. 

Lower division of the Vaughn Gulch Limestone.-

This part of the formation, about 107 m thick, consists 

largely of platy to flaggy partly laminated dark-gray to 

bluish-gray argillaceous limestone weathering light 

gray in places. It is more uniformly bedded with fewer 

bioclastic and fossil beds than higher parts of this formation. A persistent dark-gray chert member at the 

bottom, about 5 m thick, corresponds to that occurring 

near the base of the Silurian System elsewhere in the 

Great Basin. Weak partial dolomitization and nodular 

chert decrease upward to the lowest fossil bed of Great 

Basin Silurian coral zone A, which lies 40 m above the 

basal cherty beds. The few fossil beds in this division 

contain abundant Heliolites and favositids; more distinctive zone indicators like Dalmanophyllum are uncommon. 

Middle division of the Vaughn Gulch Limestone.-

The 220 m of limestone constituting the middle part of 

the Vaughn Gulch Limestone includes prominent 

medium- to dark-gray richly fossiliferous coralline and 

bioclastic beds in its upper half, of which the uppermost 100 m falls within Great Basin Silurian coral 

zone E. The dark-gray bioclastic beds range from 25 em 

to more than 1 m and are commonly sculptured into 

prominent ribs separated by subdued intervals of 

thin-bedded silty or argillaceous limestone weathering 

a lighter gray. Much of the bioclastic material of these 

thick fossil beds is crinoidal debris. Some of the fossils 

that weather in relief are complete and partially 

silicified and impregnated with limonite. Below the 

middle of this 220 m division, the limestones are, in 

general, thin bedded and show fewer bioclastic members. No fossil accumulations with true biohermal relief were found. Chert is a minor constituent. Some 

100m of beds in the middle of this 220-m division contain an abundance of the large dasycladacean alga 

Verticillopora annulata. Though long ranging, these 

calcareous algae appear to be most numerous in the 

Great Basin Silurian coral zone D. 

Upper division of the Vaughn Gulch Limestone .-A 

140-m upper interval of the Vaughn Gulch Limestone 

includes those beds between the top of Great Basin 

Silurian coral zone E and the Mississippian disconformity. Bioclastic beds within the topmost 25m contain 

an abundance of poorly preserved fossils. Contorted 

layers of dark-gray chert in the upper 10 m are associated with massive dark-bluish-gray crinoidallimestone with silicified partly macerated limonite-stained 

brachiopods, favositids, and both solitary and colonial 

large rugose corals. Below the upper beds, the limestone is partly laminated and platy down to the lower 

strata adjoining coral zone E where thicker bioclastic 

and coralline beds become more numerous. Graptolite 

and conodont evidence reported by Stevens and Ridley 

(1974) indicate that the upper part of the formation is 

Lower Devonian and probably as young as Middle Devonian. 

STRATIGRAPHIC PALEONTOLOGY 

Large collections of fossils made by Stauffer (1930) 

from limestone in what is now the type section of the 

Vaughn Gulch Limestone are the basis for his comparison and correlation with the Kennett Formation of 

northern California and assignment at that time of the 

limestone to the Devonian System. The fossils were 

meticulously zoned by Stauffer within a 500-m measured section comprising 14 numbered stratal units. In 

general, these units can be alined fairly well with 

those of the present measurement. As the Silurian and 

Devonian Rugosa of western North America were unknown at the time of Stauffer's work, the listed identifications of these forms in the Vaughn Gulch have 

little definitive significance by present standards. 

Nonetheless, the bed-by-bed tabulations by Stauffer 

clearly reflect the overall coralline nature of much of 

the formation and reveal the diversity of these coral 

assemblages. The lists show a relative abundance of 

tabulate corals including massive Favosites, the slender digitate Cladopora, and the less commonHeliolites. 

Stromatoporoids are listed throughout but do not appear to have been especially important as limestone 

builders here. The spherical sponge H india is reported 

in several beds. Brachiopod and trilobite identifications are largely of questionable value, no doubt partly 

because the preservation is poor, and these fossil 

groups are comparatively scarce in the coral-rich beds. 

The abundant dasycladacean alga Verticillopora was 

at that time unrecognized in these deposits. 

The biostratigraphy ofthe Vaughn Gulch Limestone 

as here presented is dependent upon study of the 

rugose corals and dasycladacean algae. Great Basin 

Silurian rugose coral zonation of Merriam (1973a), 

treated elsewhere herein, is based upon combined 

range and distribution data for these fossils in the 

Roberts Mountains Formation, the Hidden Valley 

Dolomite, and the Vaughn Gulch Limestone. The 
LIMESTONES OF THE NORTHERN INYO MOUNTAINS 27 

dasycladacean alga V erticillopora, which ranges upwards from Great Basin Silurian coral zone B to E and 

above this horizon, is abundant and probably peaks in 

coral zone D. Of the five Great Basin Silurian coral 

zones A through E, only zones A and E have been identified with certainty in the Vaughn Gulch Limestone. 

The Vaughn Gulch Limestone, judged by comparable thicknesses and fauna, occupies most or all of the 

stratigraphic interval of the Hidden Valley Dolomite 

to the south and east. Great Basin Silurian coral zones 

A and B are typified by distinctive rugose coral assemblages in the Hidden Valley, whereas zones C, D, 

and E have their reference occurrences in the Roberts 

Mountains Formation. 

Coral zone A .-Great Basin Silurian coral zone A is 

represented in the lower 107 m unit of the Vaughn 

Gulch by beds containing the columellate solitary 

rugose coral Dalmanophyllum sp. A, about 40 m above 

the top of the basal chert marker units; also occurring 

with the genus is a small tryplasmid, a pycnostylid 

coral, favositids, Heliolites, and Camerotoechia. Other 

zone A indicators like Palaeocyclus, Arachnophyllum, 

and Cyathophylloides have not been found in the 

Vaughn Gulch Limestone. 

Verticillopora beds.-Strata in the middle part of the 

220-m middle unit of the Vaughn Gulch contain an 

abundance of the large Verticillopora annulata. This 

algal genus ranges in decreasing numbers on up 

through the overlying Great Basin Silurian coral zone 

E into the lowermost beds of the upper 140-m unit of 

the Vaughn Gulch, above which it has not been found. 

Although the rugose coral fauna of Great Basin Silurian coral zone D has not been found in the Vaughn 

Gulch, it is not improbable that the beds in which Verticillopora annulata is most abundant occupy that 

interval in which Silurian Verticillopora appears to 

have peaked. 

Coral zone E.-Great Basin Silurian coral zone E 

occupies the uppermost 100-m interval of the middle 

unit of the Vaughn Gulch Limestone. These upper beds 

include units 12, 13, and 14 of Stauffer (1930, p. 86-

89). The large and diverse coral fauna contains an 

abundance of tabulates including Favosites, Cladopora, Syringopora, and Heliolites, together with the 

distinctive Silurian rugose corals Australophyllum 

(Toquimaphyllum) sp. similar to A. johnsoni, Kyphophyllum sp., and Chonophyllum-like species. Rhizophyllum sp. D Oliver is represented by float material, 

doubtless from coral zone E, and probably by ~~calceola 

sandalina Lamarck" of the Stauffer list from his unit 

12. Verticillopora ranges upward into coral zone E. 

With this assemblage is the brachiopod Plectatrypa sp. 

Crinoidal debris is abundant; the stromatoporoids, 

though present, appear to be subordinate. 

Stauffer's rather lengthy faunal lists from the interval of coral zone E include brachiopods, among them 

Camarotoechia, Atrypa, Gypidula, Athyris, Trematospira, Schizophoria, and Eatonia. 

Fossils of the upper Vaughn Gulch Limestone.-

Except for the lowermost 8 m, the upper part of the 

Vaughn Gulch Limestone has yielded few well-preserved fossils. The lowermost beds contain the highest 

known Verticillopora, Australophyllum sp. v, and 

Cladopora and other favositids. Near the top of the 

formation at locality M1090 are poorly preserved 

rugose and tabulate corals, large Atrypa, and indeterminate spiriferoid brachiopods. Among the Rugosa are 

a large possible member of the Halliidae that resembles Aulacophyllum and a colonial genus that has features of Acinophyllum or Diplophyllum. Other fossils 

present are cystiphylloids, digitate and massive favositids, and stromatoporoids. Australophyllum sp. v resembles A. landerensis of the central Nevada Rabbit 

Hill Limestone of Early Devonian age. The diverse and 

highly distinctive Rabbit Hill fauna has not been found 

in this unit where it would be expected. 

AGE 

The age of the Vaughn Gulch Limestone, based on 

its coral fauna, ranges from Early Silurian (Llandoverian) to possible Early Devonian. Dalmanophyllum sp. 

A in the lower unit is an indicator of Great Basin Silurian coral zone A. Beds with abundant Verticillopora 

annulata in the middle of the middle lithologic unit of 

the Vaughn Gulch probably bracket Great Basin Silurian coral zone D although the rugose coral fauna of 

zoneD was not found in these strata, and it is probable 

that Verticillopora reached its greatest development in 

coral zone D. Great Basin Silurian coral zone E, at the 

top of the middle unit, when compared with the Gotland, Sweden, standard, is Late Silurian (late 

Ludlovian). 

In the absence of conclusive evidence from the coral 

faunas, the upper lithologic unit of the Vaughn Gulch 

is viewed as Late Silurian or Early Devonian. Australophyllum sp. v at its base resembles, but is not 

conspecific with, A. landerensis from the Lower Devonian Limestone Rabbit Hill. Near the top is a large 

Aulacophyllum-like coral, possibly of Early Devonian 

age; the cystiphylloids and the Acinophyllum-like 

coral might also be Devonian. 

Graptolite and conodont evidence and correlation 

with the Sunday Canyon Formation noted by Stevens 

and Ridley (197 4, p. 28) suggests that the formation 

extends upward to the Middle Devonian. 

Comparable thicknesses of the Vaughn Gulch Limestone and the more easterly Hidden Valley Dolomite, 

as well as stratigraphic relations with bracketing 
28 ROBERTS MOUNTAINS FORMATION, REGIONAL STUDY 

units strongly suggest that both occupy about the same 

stratigraphic interval. Because of facies differences, 

only Great Basin Silurian coral zone A has been recognized. As shown by McAllister (1952), the Hidden Valley is largely of Silurian age and includes the reference 

occurrences of Great Basin Silurian coral zones A and 

B. The uppermost beds of this dolomite are of Early 

Devonian age in the Siegenian-Emsian range. It is 

probable that the highest Vaughn Gulch strata may be 

correlative with the fossil-bearing part of the Hidden 

Valley Dolomite. This correlation is made by Stevens 

and Ridley (1974, fig. 2). 

SUNDAY CANYON FORl\fATION 

The Silurian and Lower Devonian limestones of the 

intermediate limestone belt change facies to shale laterally within a relatively short distance in the Mazourka Canyon area of the northern Inyo Range, Calif. 

Detailed geologic mapping of the Vaughn Gulch Limestone northward for 19 km toward Badger Flat by Ross 

(1966) shows a progressive thinning of the formation 

and the change to calcareous shale, siltstone, and argillaceous limestone. Tongues of Vaughn Gulch bioclastic limestone reappear north of the type section, 

but within 8 km, near Barrel Spring, the general 

character of the deposits has become such as to justify 

the use of another name, Sunday Canyon Formation, 

for rocks correlative with the Vaughn Gulch Lime-. 

stone. The more shaly facies continues northward 

another 10 km to Badger Flat and becomes progressively thinner. How much of the thinning is due to 

depositional processes such as initial deepening with 

less sedimentation of open marine waters toward the 

north and how much to erosional thinning at the unconformity with the overlying Mississippian is not 

known. The calcareous shales yield mainly graptolites, 

but occasional small Vaughn Gulch-type bioclastic 

lenses as far north as Al Rose Canyon contain rugose 

corals. In general, however, the proportion of carbonate material decreases toward the north (Ross, 1966, 

p. 32). 

AGE 

The age of the Sunday Canyon Formation has been 

determined mainly by means of abundant monograptids, nearly all collected near the base of the formation. 

Among the species present are (identified by W. B. N. 

Berry and R. J. Ross, Jr.): 

Monograptus cf. M. dubius (Suess) 

Monograptus dub ius (Suess) 

Monograptus sp. (theM. tumescens type) 

Monograptus sp. (slender rhabdosomes, plain 

thecae) 

Monograptus sp. (theM. vulgaris type) 

Monograptus cf. M. scanius Tullberg 

These forms suggest an age range in the Silurian from 

Wenlock to Ludlow. A locality 45 m above the base of 

the formation (USGS-D179-SD) yielded Monograptus 

cf. M. uniformis Pribyl, which is considered to be Early 

Devonian. 

The problem of dating the Sunday Canyon is the 

same as that relating to the Roberts Mountains Formation in that the standard time scale based on graptolites is different than that based on corals and other 

benthonic organisms and usually suggests relatively 

younger ages for particular horizons. In the Mazourka 

Canyon exposures, it is not unlikely that most of the 

graptolitic deposits are relatively low in the Silurian 

column. 

The rugose coral A ustralophyllum stevens i Merriam, 

from the upper 12 m of the Sunday Canyon, is of possible Early Devonian age. 

Stevens and Ridley (197 4), on the basis of graptolites 

and conodonts, indicate that the formation extends to 

the Middle Devonian. 

THE SILURIAN-DEVONIAN BOUNDARY 

IN CENTRAL NEVADA 

We do not attempt here to delve into the philosophical aspects of stratigraphy with respect to time boundaries, lithofacies, biofacies, and systemic definitions. 

Placement of the Silurian-Devonian boundary within 

the carbonate sequence of the central Great Basin is a 

problem when attempts are made to compare rugose 

coral zonation based on similarities with the Gotland, 

Sweden, sequence with graptolite zonation which is 

the accepted guide for time boundaries in this part of 

the geologic column. Any study of the Roberts Mountains Formation should, however, point out the conflict, where and how it arises, and what the current 

geologic thinking is on this matter. This problem is a 

classic one in stratigraphy involving lateral change of 

facies, time-transgressive rock units, and definition of 

time boundaries by faunas from different reference 

sections at different places in the world. Specifically, 

the Silurian-Devonian boundary is a troublesome 

boundary that has been the subject of much discussion 

and a number of international symposia beginning in 

1958 and continuing to this time. The SilurianDevonian Boundary Committee of the International 

Stratigraphic Commission has established a generally 

accepted boundary which proves to be viable in the 

Great Basin and in most parts of the world. This 

boundary is based on graptolites. 

Placement of the boundary in many sections of lower 

Paleozoic rock in central Nevada is difficult because geologic structure is extremely complex and easily interpreted sequences of strata are rare. We point for examples to the section at Coal Canyon in the Simpson Park 
STRATIGRAPHIC AND AGE VALUES OF RUGOSE CORALS 29 

Mountains (see p. 11), which appears superficially to 

be simple but contains at least one fault with uncertain 

offset in a critical part of the section. Detailed mapping 

is almost always a necessity before attempting stratigraphic studies in this region, and frequently even 

with careful mapping and repeated visits to the field, 

the relation of rock units remains clouded. When the 

geologic difficulties are added to the subtleties of 

faunal interpretation in a narrow belt of rocks deposited at the transition between shallow and deeper 

water, one realizes why placement of the SilurianDevonian boundary has been disputed in this part of 

the world. Part of the problem rests on what fossils are 

available and what forms are used to define the 

boundary-what yardstick we are measuring with. 

When only one form is present, for example corals or 

graptolites, the section can be matched with similar 

standards elsewhere in the world. But, where more 

than one form is present, as in central Nevada, and the 

rocks have been correlated on the basis of lithology, the 

faunal yardsticks do not agree. Several basic explanations can account for this difference: various forms 

have different time ranges at different places in the 

world, or the standard sections such as that at Gotland, 

Sweden, or the Din ant Basin, Belgi urn, do not contain 

rocks wholly correlative. In central Nevada, the graptolite Monograptus praehercynicus is used by Berry 

(1970) to indicate the base of the Monograptus uniform is Zone. This zone is considered by most members of 

the Silurian-Devonian Boundary Committee of the International Stratigraphic Commission to be the lowest 

Devonian zone, and hence is accepted here as basal 

Devonian although no agreement exists on precisely 

what graptolite species or subspecies should be used to 

denote the base of the zone. Monograptus praehercynicus is found in the Roberts Mountains Formation 

at a number of places, and in a few places it occurs in a 

stratigraphic interval that also contains the coralline 

fauna diagnostic of the Great Basin Silurian coral zone 

E as defined by Merriam (1973a). In the central 

Nevada limestone belt represented by the Roberts 

Mountains Formation, the Silurian-Devonian boundary based on graptolites and on conodonts is a hundred 

metres or more lower in the same sequence of strata 

than the boundary based on rugose corals and calcareous algae. 

AN APPRAISAL OF STRATIGRAPHIC 

ANDAGEVALUESOFRUGOSECORALSAND 

ASSOCIATED FOSSILS, WITH DESCRIPTION 

OF PREVIOUSLY UNKNOWN KEY RUGOSA 

.Most of the Cordilleran Rugosa listed and referred to 

in this report as related to the age and correlation of 

Great Basin Silurian rocks of the intermediate limestone belt are described in papers by Merriam (1972; 

1973a) and a paper by Oliver, Merriam, and Churkin, 

(1975). 

With continued geologic mapping, new Silurian 

rugose corals have since been discovered in the central 

Great Basin, and other Rugosa previously unknown in 

certain assemblages have been found in association at 

new localities. The stratigraphic ranges of some genera 

and species have been extended by further collecting 

and stratigraphic investigation. 

Recent researches upon little-known taxonomic 

groups of Rugosa have resulted in a greatly improved 

understanding of their internal structure, their value 

as indicators of the Silurian and Devonian Systems, 

and their geologic ranges. The two principal groups of 

corals are those lacking dissepiments ( nondissepimented corals) and those having dissipiments (dissepimented corals). The nondissepimented Rugosa 

with which we are concerned are the Family Kodonophyllidae, the Family Pycnostylidae, and the Family 

Tryplasmatidae. The dissepimented Rugosa of special 

interest here are the Family Spongophyllidae, including the new colonial genus Carlinastraea. Others of 

interest are assigned to the Family Endophyllidae, like 

the subgenus Australophyllum (Toquimaphyllum) and 

other forms of A ustralophyllum. Among the Family 

Kyphophy llidae, there are new and undescribed 

species of Kyphophyllum. 

The dasycladacean algal group including Verticillopora is discussed briefly; insofar as known, this large 

and complex alga commonly associated with Silurian 

Rugosa ranges upward only into the lower part of the 

Devonian System. 

RUGOSE CORALS OF SPECIAL STRATIGRAPHIC VALUE 

SILURIAN NONDISSEPIMENTED RUGOSA 

Family KODONOPHYLLIDAE 

The Family Kodonophyllidae, which so far as known 

is confined to the Silurian of the Great Basin, comprises solitary and colonial nondissepimented Rugosa 

having long lamellar septa, a very wide stereo zone, 

and flat tabulae or distally arched tabellae that may 

combine with septal tips t0 form an axial structure and 

calicular boss. 

Two subfamilies of Kodonophyllidae are recognized: 

Kodonophy llinae and Mycophy llinae. These subfamilies and their taxonomy have been discussed in 

some detail by Merriam (1973a). 

The genus Kodonophyllum Wedekind is present in 

the Late Silurian (Great Basin Silurian coral zone E) 

on the east side of the Coal Canyon fault, where it is 

represented by the large Kodonophyllum mulleri Merriam (pl. 4, figs. 5, 6). Kodonophyllum sp. b (pl. 5, 
30 ROBERTS MOUNTAINS FORMATION, REGIONAL STUDY 

figs. 22--24), described below, occurs in the middle 

coral-brachiopod zone at Bootstrap Hill, Tuscarora 

Mountains. 

Subfamily KODONOPHYLLINAE Merriam 

Members of the subfamily Kodonophyllinae Merriam are very thick walled fasciculate colonial and 

platelike solitary Rugosa having the characteristics of 

the family Kodonophyllidae. The tabulae and tabellae 

arch distally, combining with septal ends to form an 

axial structure and a calicular boss. 

Kodonophyllum mulleri Merriam (1973a), of the 

upper part of the Roberts Mountains Formation, is a 

medium to large solitary coral with deep calice and 

large calicular boss (pl. 4, figs. 5, 6). The major septal 

count is about 48; septa, somewhat thickened throughout, are excessively thickened in the wide peripheral 

stereozone and in the axial structure, where they 

are obscured by merging with stereoplasm and septal 

terminations. 

Kodonophyllum mulleri Merriam occurs in the 

northern Simpson Park Mountains in the upper part of 

the Roberts Mountains Formation; locality M1107, 

Great Basin Silurian coral zone E. 

Kodonophyllum sp. b 

Plate 5, figures 22-24 

Figured material.-USNM 166481. Roberts Mountains Formation; Bootstrap Hill, Tuscarora Mountains, 

Nev., locality M1314. 

Diagnosis.-Slender, subcylindrical Kodonophyllum 

with axial arching of wide tabulae, moderate to low for 

the genus. 

Transverse thin sections .-Thick major septa 

number about 24, most of which extend to the axial 

structure. Minor septa buried in stereozone, which is 

one-fourth of corallite diameter. Septal grooves are 

broad and shallow. No discrete epitheca. 

Longitudinal thin sections.-Tabulae are rather 

closely spaced, very uneven; many are complete, periaxially depressed, and rise nonuniformly toward axis. 

Axial rise is moderate to low for this genus. Trabeculae 

in wide stereozone is steeply inclined outward. 

Comparison with related forms .-Kodonophyllum 

mulleri of the Roberts Mountains Formation is a 

larger, more robust species with more numerous septa 

than Kodonophyllum sp. b. It also has a more pronounced axial rise of tabulae. K. truncatum (Linnaeus) 

of the Gotland Silurian, a colonial form having 

ceratoid corallites, has a somewhat wider stereozone 

than the subcylindrical K. sp. b; otherwise features in 

detailed thin-section resemble those of the Nevada 

species. 

Occurrence.-Roberts Mountains Formation; southern Tuscarora Mountains, Nev. Bootstrap Hill, locality 

M1314. In middle coral-brachiopod zone near bottom of 

upper 275 m lithologic division. 

The range of Kodonophyllum in the classic Gotland 

Silurian column is Wenlockian to Ludlovian; occurrences in Great Britain are reported as Wenlockian. In 

the Great Basin, the occurrence in coral zone E is late 

Ludlovian, in the Tuscarora Mountains at Bootstrap 

Hill in the middle coral-brachiopod zone, perhaps as 

old as high Wenlock, but more likely Ludlovian. 

Certain early Middle Devonian (Great Basin Devonian coral zone D) occurrences of Kodonophyllum-like 

corals of the Nevada Formation (Grays Canyon Limestone Member of the Eureka area) have the very wide 

peripheral stereozone of Kodonophyllum; the longitudinal features are unknown. These forms are probably 

aberrant developments from the Siphonophrentis 

(Breviphrentis) group that is characteristic of Great 

Basin Devonian coral zone D (Merriam, 1973c). 

Subfamily MYCOPHYLLINAE Hill 

Genus Mucophyllum Etheridge 

Members of the subfamily Mycophyllinae, characterized by large discoid to turbinate corallites with a 

broad calicular platform and a fiat-bottomed central 

pit, are especially characteristic of the Silurian. Septa 

are numerous and thick and in contact laterally forming a wide, thick stereozone. Tabulae are complete and 

straight to undulant. Longitudinal sections show the 

fine incremental layering of a very thick stereoone 

transected by nearly vertical trabecular pillars. 

Schlotheimophyllum of the Gotland Silurian has a 

similar growth habit but differs by having a more complex axial structure, more like that of Kodonophyllum. 

Mucophyllum is known from Australia and from the 

Klamath Mountains, Calif. All occurrences are in Silurian deposits of late Wenlockian to Ludlovian age. 

Mucophyllum oliveri (pl. 4, figs. 1-4) has nearhorizontal and undulant tabulae that are thickened 

where merging with the longer septa. M. oliveri comes 

from the east block of the Coal Canyon fault at Coal 

Canyon, northern Simpson Park Mountains, in the 

upper part of the Roberts Mountains Formation; locality 1108; Great Basin Silurian coral zone E. 

Family STREPTELASMATIDAE Nicholson 

Genus Brachyelasma Lang, Smith, and Thomas 

Simple, solitary, nondissepimented Rugosa with 

partly complete tabulae ranges from Late Ordovician 

into the Silurian of the Great Basin. The tabulae bend 

downward as they approach the wall. Major septa do 

not reach the axis, though they commonly extend more 

than half that distance. Some species have a fossula. 

Brachyelasma resembles the Devonian Breviphrentis, which has a wider stereozone and undergoes re-
FAMILY PYCNOSTYLIDAE STUMM 31 

peated rejuvenescence to form long segmented coralla 

not found in Brachyelasma. 

Two species of Brachyelasma occur in the Roberts 

Mountains Formation. Brachyelasma sp. c (pl. 5, figs. 

25, 26) comes from locality M1383 in the lower coral 

beds of the west fault block at Coal Canyon, Simpson 

Park Mountains; Brachyelasma sp. b (pl. 12, figs. 

29--33) is from locality M1120 at Bootstrap Hill, Tuscarora Mountains, in the lower coral-brachiopod zone 

with Cyathophylloides. 

Family STAURIIDAE Edwards and Haime 

Genus Cyathophylloides Dybowski 

Cyathophylloides, a primitive colonial nondissepimented rugose coral, is related to Favistella (or 

Favistina Flower) and to the phaceloid Palaeophyllum. 

These corals are common in the Upper Ordovician, but 

Cyathophylloides and Palaeophyllum range upward 

into the Lower Silurian. 

Cyathophylloides forms massive cerioid colonies 

with narrow corallites having 12-14 smooth, simple 

lamellar major septa that meet axially where they may 

be twisted but do not form a discrete axial structure. 

Tabulae are complete; minor septa are short to fairly 

long. Cyathophylloides is represented in the Roberts 

Mountains Formation by C. fergusoni Merriam of 

Great Basin Silurian coral zone A in the Mill Canyon 

sequence at Ikes Canyon, Toquima Range. A similar 

species C. sp. f (pl. 12, figs. 27, 28) comes from the 

lowermost coral-brachiopod zone at Bootstrap Hill 

(locs. M1120, M1412). 

Family TRYPLASMATIDAE Etheridge 

The family Tryplasmatidae, characterized by 

spinose or acanthine septa, is especially common in 

rocks of the Silurian System. Tryplasmids have been 

reported in strata of the Devonian (Hill, 1956, p. F312; 

Oliver, 1960, p. 15) and are known in Late Ordovician 

rocks of Sweden. Reviews of the classification have 

been published by Hill (1936) and by Merriam (1973a). 

They are readily distinguished from the other nondissepimented Rugosa that have wide complete tabulae 

by their acanthine septa, and they do not have the wide 

stereozone of the Kodonophyllidae or the multiple 

interior calice offsets of the pycnostylids. The 

Stauriidae-like Palaeophyllum of the Late Ordovician 

and Silurian has medi urn to long lamellar septa. 

The general characteristics of the tryplasmids are 

well shown by the undescribed Gotland species Tryplasma sp. g of the Hemse Group (Ludlovian) (pl. 3, 

figs. 16-19), T. newfarmeri Merriam (pl. 3, figs. 10-15) 

of Great Basin Silurian coral zone C, and T. duncanae 

Merriam (pl. 3, figs. 8, 9) of Great Basin Silurian coral 

zone D. 

Family PYCNOSTYLIDAE Stumm 

Pycnostylid rugose corals are among the most abundant and distinctive nondissepimented genera in certain facies of the Silurian System. It is possible these 

corals have Devonian descendants like Cyathopaedium 

and Fletcherina. None are known in rocks of Late 

Ordovician age. 

The pycnostylids are colonial fasciculate Rugosa 

having subcylindrical corallites. The septa are very 

short and vertically continuous, or lacking. The stereozone is narrow. Most tabulae are complete and unarched medially. There are no dissepiments. Reproduction is by multiple offsets peripherally from the calice 

interior. 

The Silurian genera are Pycnostylus Whiteaves, 

Stylopleura Merriam, and Fletcheria Edwards and 

Haime. Cerioid colonial genera like Maikottia Lavrusevitch and similar large undescribed genera from 

the Roberts Mountains Formation are provisionally 

assigned to this family. 

The taxonomy of the Pycnostylidae has been treated 

in some detail by Merriam (1973a). 

Genus Pycnostylus Whiteaves 

With the type species Pycnostylus guelphensis Whiteaves of the Guelph Dolomite, Guelph, Ontario, (pl. 1, 

figs. 16-19), Pycnostylus is characterized by only four 

internal calice offsets or peripheral offsets. Pycnostylus 

elegans Whiteaves probably has a greater number of 

offsets (pl. 1, fig. 20). Pycnostylus is not known to possess the lateral connecting elements of Stylopleura. 

Several poorly known Asiatic and Australian corals 

referred to by Hill (1940) as ((ampleximorphs" are 

doubtfully related to Pycnostylus. These corals are reported to have amplexoid lamellar septa. Several 

little-known Silurian corals of similar character have 

been classified as Pycnostylus by Hill (1940) as 

Amplexus by Grabau (1930) and by Shimizu, Ozaki, 

and Obata (1934), and asAmplexoides by Wang (1947). 

Pycnostylus Whiteaves is probably not a junior synonym of Fletcheria Edwards and Haime as interpreted 

by several workers. Fletcheria tubifera Edwards and 

Haime from Gotland has no septa but it does have a 

distinctive wall structure, and some of the tabulae (or 

large tabellae) are distally convex (pl. 3, figs. 1-7). 

Forms assigned by Norford (1962, pl. 15) to Fletcheria 

are probably best placed in Pycnostylus. A similar Pycnostylus, Pycnostylus sp. 1 (pl. 2, fig. 10), occurs in the 

Lone Mountain Dolomite but has not been found in the 

Roberts Mountains Formation. 

Genus Stylopleura Merriam 

The genus Stylopleura with type species S. berthiaumi Merriam (1973a), which was first found in the 

upper part of the Roberts Mountains Formation unit 3, 
32 ROBERTS MOUNTAINS FORMATION, REGIONAL STUDY 

is a phaceloid to cerioid coral. It differs from Pycnostylus by having a large number of subequal peripheral 

offsets of internal calice offsets and long tubularconnecting elements between corallites. Open bushy 

forms have trumpet-shaped flaring calices. 

Of the described species of Stylopleura, Stylopleura 

berthiaumi of Great Basin Silurian coral zones D and E 

(pl. 1, figs. 1-9; pl. 2, figs. 8, 9) has a more open 

phaceloid construction with flaring calices than the 

other species. S. nevadensis of Great Basin Silurian 

coral zone E (pl. 2, figs. 3-6) tends to be of more 

crowded phaceloid to subcerioid compact construction 

with fewer lateral elements. Also found is Stylopleura 

cf. S. nevadensis, n. gen., n. sp. (pl. 2, fig. 7.) 

Stylopleura sp. b 

Plate 1, figures 10-12 

Stylopleura sp. b, known from isolated fragmentary 

corallites at Bootstrap Hill, Tuscarora Mountains, resembles S. berthiaumi, but the specimens in the collection do not include those with reproductive calices. The 

long tubular connecting processes are well shown. 

Stylopleura sp. b occurs at localities M1314 and 

M1315 in the middle coral-brachiopod zone of the 

Roberts Mountains Formation at Bootstrap Hill, where 

it is associated with Kodonophyllum sp. b, Kyphophyllum sp. b, and Calostylis? sp. 

Stylopleura sp. c, cf. S. berthiaumi Merriam 

Plate 1, figures 13-15 

Stylopleura sp. c, cf. S. berthiaumi is a fairly compact 

phaceloid Stylopleura from the lower coral zone of the 

west block of the Coal Canyon fault at Coal Canyon, 

northern Simpson Park Mountains. It has the multiple 

calice offsets but none of the lateral connecting elements of S. berthiaumi. This form occurs here in the 

same beds with Carlinastraea tuscaroraensis and Tonkinaria simpsoni Merriam and is accordingly regarded 

as an occupant of the approximate interval of Great 

Basin Silurian coral zone D. 

COMPACT CERIOID PYCNOSTYLIDAE OF SILURIAN 

LIMESTONE FACIES 

Unusually large phaceloid to cerioid Rugosa lacking 

multiple peripheral offsets and resembling Stylopleura 

nevadensis Merriam are known from Late Silurian 

limestones of the Cordilleran belt. Being compact or 

appressed, these specimens do not show lateral connecting elements. Some, like Stylopleura? sp. T (Merriam, 1973a), have very wide corallites, a very thick 

wall, and closely spaced tabulae; others, like the large 

aseptate pycnostylid Stylopleura? sp. c from Coal Canyon in the Simpson Park Mountains, have a very thin 

wall without septa. The septate forms have short longitudinally continuous septa. 

Corals provisionally assigned to this informal group 

are Maikottia sp., cf. M. turkestanica Lavrusevich of 

the Porcupine River, Alaska (Merriam, 1973a), Stylopleura? sp. T of the Ikes Canyon area, Toquima 

Range, Nev., and the compact thin-walled aseptate 

pycnostylid species Stylopleura? sp. c from Coal Canyon, Simpson Park Mountains, here described. 

Stylopleura? sp. c 

Plate 2, figures 1, 2 

Stylopleura? sp. c is a large compact species. Corallites are as much as 24 mm wide and have a very thin 

straight wall. Septa are absent. Tabulae are closely 

spaced, uneven, and have a pronounced sag axially. 

Most tabulae are entire, but some near the periphery 

are short and terminate against a complete tabula. The 

similarity of this form to the Australian Silurian 

Yassia Jones in longitudinal section is deceiving, as it 

lacks the dissepiments of Y assia in the strict sense. 

Occurrence.-A single incomplete corallum from 

Coal Canyon, Simpson Park ~viountains, Nev., locality 

M1379, in sheared Roberts Mountains limestone at the 

west edge of the Coal Canyon fault zone. 

DISSEPIMENTED RUGOSA OF THE GREAT BASIN 

SILURIAN LIMESTONE FACIES 

Rugose corals with dissepiments, uncommon in the 

Cordilleran Late Ordovician, had become abundant by 

mid-Silurian time with the appearance of the lykophyllids, Entelophylloides, Petrozium, and other genera. Several Late Silurian colonial dissepimented 

groups disappeared by the end of the Silurian or the 

earliest Devonian, and new ones appeared in early 

Middle Devonian time. Families of special importance 

in the Late Silurian of the Great Basin intermediate 

limestone belt are the Spongophyllidae and the Endophy llidae. 

Family SPONGOPHYLLIDAE Dybowski 

Genus Carlinastraea, n. gen. 

Type species .-Carlinastraea tuscaroraensis n. gen., 

n. sp., here designated; Late Silurian, upper beds of the 

Roberts Mountains Formation, Nev. 

Diagnosis.-Cerioid spongophyllid having slender, 

fairly thick walled corallites, a strong marginarium of 

large to very large, steeply inclined lonsdaleioid dissepiments, and a nonuniform pattern of partially 

aborted septa in the tabularium of some corallites. 

Remarks.-Direct comparison of Carlinastraea with 

the most nearly related genus, Spongophyllum Edwards and Haime, is not possible as the Edwards and 

Haime (1853) type material of S. sedgwicki (the type 

species) has been lost and only the original published 

illustrations (pl. 6, figs. 1-4) remain as a basis for 
FAMILY SPONGOPHYLLIDAE DYBOWSKI 33 

reappraisal. These illustrations (Edwards and Haime, 

1853, pl. 56, figs. 2, 2a-2e) with little doubt figure two 

different corals: (1) group 1 (pl. 56, figs. 2d, e), a thinwalled genus having many small peripheral 

lonsdaleioid dissepiments, (2) group 2 (pl. 56, figs. 2, 

2a-2c), a genus having narrower, moderately thickwalled corallites, lacking or nearly lacking conspicuous lonsdaleioid dissepiments. It is not likely that the 

two forms fall within the range of variation of a single 

genus and species; so far this possibility is unknown. 

The usually accepted characterization of Spongophyllum is that of lonsdaleioid group 1, and it is with this 

group that Carlinastraea is compared. Comparison of 

Spongophyllum sedgwicki to Lonsdaleia by Edwards 

and Haime (1851, p. 425; 1853, p. 242) is further evidence that the original diagnosis is that of a cerioid 

rugose coral with well-developed lonsdaleioid dissepiments. 

It is unfortunate that Jones (1929, p. 89) selected as 

the ((neotype" of Spongophyllum sedgwicki a float 

specimen in ((a dark coloured pebble" from ((South 

Devonshire." Although not figured by Jones in 1929, 

thin sections of this ((neotype" were illustrated by 

black and white drawings by Birenheide (1962, p. 

6S-7 4, pl. 9, fig. 8, pl. 10, fig. 10). The Birenheide 

figures show a coral without conspicuous lonsdaleioid 

dissepiments, agreeing reasonably well with nonlonsdaleioid group 2 of the Edwards and Haime type 

illustrations. 

Comparing Carlinastraea with group 1 lonsdaleioid 

Spongophyllum of Edwards and Haime, the new genus 

Carlinastraea differs by having a much thicker wall 

with strong wall crests and all corallites have much 

larger lonsdaleioid dissepiments. The septa of Carlinastraea, being less continuous radially than those of 

Spongophyllum sedgwicki, are marked peripherally by 

septal crests. Aborting of septa, a feature of Carlinastraea, is unknown in S. sedgwicki. Mature corallites 

without lonsdaleioid dissepiments, as in group 2 of the 

Edwards and HaimeS. sedgwicki, were not observed. 

Carlinastraea tuscaroraensis n. gen., n. sp., occurs in 

the upper part of the Roberts Mountains Formation. As 

recorded by Edwards and Haime, the Spongophyllum 

types came from Devonian strata of Torquay, Devonshire, England. The Jones-selected neotype, being a 

float cobble, fails to confirm this occurrence. Recent 

studies of southern England Devonian Rugosa by 

Taylor (1950), Middleton (1959), and Webby (1964) 

make no reference to Spongophyllum. Two species of 

Spongophyllum (sp. A and sp. B) have been reported 

from the McCann Hill Chert of Alaska by Oliver (in 

Oliver and others, 1975); he considered it to be Early(?) 

to Late Devonian (Emsian? to Frasnian). Elsewhere in 

the Cordilleran belt of western North America, there 

are no records of strongly lonsdaleioid cerioid Devonian corals that closely resemble group 1 of S. 

sedgwicki or the new genus Carlinastraea. 

Species from the Ural Mountains, USSR, assigned to 

Spongophyllum by Shurygina (1968) are herein assigned to the new genus Carlinastraea. Shurygina 

(1968, p. 121-135, pl. 59, figs. 1-3) reported these questionable species as Lower Devonian. The coral fauna 

that is included with Spongophyllum [Carlinastraea] 

by Shurygina in these Ural beds is more suggestive of 

the forms in the Late Silurian of Gotland. Among the 

genera from the Urals so listed are Spongophylloides, 

Tryplasma, Neomphyma, and Rhizophyllum. Also included is Salairophyllum, which in southeastern 

Alaska occurs with the large Late Silurian Conchidium alaskense and, at Coal Canyon, Simpson Park 

Mountains, Nev., occurs as float, doubtless from high 

beds of the Roberts Mountains Formation. 

Carlinastraea tuscaroraensis n. gen., n. sp. 

Plate 6, figures 5-7; plate 7, figures 1-4 

Type and figured specimens .-Holotype USNM 

166482, upper beds of the Roberts Mountains Formation, locality M1313, Bootstrap Hill, Nev. Figured 

specimens USNM 166483, locality M1384, Coal Canyon, Nev.; USNM 166484, locality M1409, Cortez, Nev. 

Diagnosis .-Large massive Carlinastraea. The 

coralla have several hundreds of very narrow corallites 

whose septa are marked peripherally by strong wall 

crests; septa are mostly thin, nonuniform, and irregularly wavy; the largest lonsdaleioid dissepiments subtend one-fifth of a corallite circumference. 

Transverse thin sections.-Wall is stereoplasmically 

thickened, has about 26 prominent, mostly obtuse wall 

crests uniformly spaced. Major septa are thin, smooth, 

unevenly wavy, nonuniform, and number 12-14-the 

longest reach the axis; septal crests are developed, peripherally in some corallites. Lonsdaleioid dissepiments 

number 6 to about 10 in a peripheral cycle and vary 

greatly in size; the largest subtend one-fifth of the 

corallite circumference. Minor septa, weakly developed, show as wall crests and sporadic outer septal 

crests. 

Longitudinal thin sections.-Tabularium is less than 

one-fourth to more than one-third of corallite width; 

delicate tabulae are only in part complete, sag irregularly proximally, and for the greater part are rather 

closely spaced. Lonsdaleioid dissepiments, predominantly large with very steep axial inclination, are arranged in one to three columns on each side. 

Fine structure .-Stereoplasmic wall is without discrete trabeculae and shows very fine calcitic fibers 

transversely oriented; faint lamellar texture in some 

places is developed toward inner wall surface. 
34 ROBERTS MOUNTAINS FORMATION, REGIONAL STUDY 

Comparison with related forms .-Carlinastraea 

giganteum (Shurygina) of the Ural Mountains, USSR 

(Shurygina, 1968, p. 135, pl. 59, figs. 1, 2), differs from 

the new species by having less developed wall crests, 

straighter septa, and less steeply inclined lonsdaleioid 

dissepiments. Carlinastraea originalis (Zhmaev), also 

of the Urals (Shurygina, 1968, p. 134, pl. 59, figs. 3a-b), 

has less developed wall crests and more aborted septa 

than C. tuscaroraensis. 

Occurrence.-Upper part of the Roberts Mountains 

Formation, northern Simpson Park Mountains, Nev.: 

locality M1384, Coal Canyon, west side in beds with a 

fauna believed to represent Great Basin Silurian coral 

zone D. Tuscarora Mountains, Nev., locality M1313, 

Bootstrap Hill. Carlinastraea cf. C. tuscaroraensis, 

Cortez Mountains, Nev., locality M1409, pl. 8, figs. 1, 2. 

Family ENDOPHYLLIDAE Torley 

Genus Ketophyllum Wedekind 

The solitary genus Ketophyllum is common in the 

Silurian of Gotland, Sweden, and in eastern Europe. 

Only fragments of Ketophyllum sp. t (pl. 10, figs. 18, 

19) have been collected by McKee in the Toquima 

Range, Nev. Some species of Ketophyllum are virtually 

indistinguishable from the Devonian Tabulophyllum 

except for the presence of a weak fossula in some forms 

of Ketophyllum (Wedekind, 1927); this structure is 

usually not visible in Tabulophyllum. Both have a very 

wide tabularium and closely spaced straight to somewhat undulant tabulae, many of which are complete. 

Both genera have a peripheral band of large lonsdaleioid dissepiments, and the thin septa break up peripherally as septal crests. 

Ketophyllum sp. t occurs in the Toquima Range at 

locality M1393 in the Mill Canyon sequence on the 

south side of Ikes Canyon a mile northwest of the 

canyon mouth. 

Genus Australophyllum Stumm 

Large colonial heads of Australophyllum are common in Great Basin Silurian coral zone E, where it is 

represented by the subgenus A ustralophyllum (Toquimaphyllum). Other forms of Australophyllum 

sensu stricto occur in the same uppermost beds of the 

Silurian limestone facies and, though sparsely represented, range upward into the Lower Devonian Rabbit 

Hill Limestone. Some Middle Devonian species that 

were referred to A ustralophyllum in the past have but 

few sporadic lonsdaleioid dissepiments and are 

perhaps best assigned to other genera. The 

lonsdaleioid subgenus Toquimaphyllum has a 

worldwide geographic distribution. A similar form occurs to which the generic name Klamathastraea has 

been given (Merriam, 1972) in Late Silurian beds of 

the Gazelle Formation, Klamath Mountains, Calif. 

Klamathastraea differs from Toquimaphyllum by having a much wider tabularium, tabulae with a marginal 

depression, and a pronounced tendency to abort septa 

in mature growth stages. 

Australophyllum (Australophyllum) sp. c 

Plate 8, figures 3-7 

Diagnosis.-Large Australophyllum with corallites 

of greatly varying width; lonsdaleioid dissepiments are 

in restricted peripheral patches only; tabulae closely 

spaced, in places crowded; septa are minutely wavy 

with spines and bumps in the periaxial band. 

Transverse thin sections .-Corallites, highly variable in size, range in diameter from 9 to 28 mm at the 

same distal corallum surface. Septal count is about 62 

in large corallites. Major septa reach the axis and are 

twisted near it; minor septa range from one-half to 

three-fourths length of major septa. Septa, locally 

thickened in dissepimentarium, may be slightly thickened in tabularium, wherein they become minutely 

wavy and ornamented laterally with spines and nodes. 

Narrower corallites show stereoplasmic wall thickening. Some larger lonsdaleioid patches quite irregular. 

Longitudinal thin sections.-Tabularium width is 

one-fourth to one-third of corallite diameter. Dissepiments are medium to large in as many as nine columns 

on each side of wider corallites. Outer dissepiments are 

much less steeply inclined than inner ones. Tabulae 

are mostly close spaced or crowded; many are complete 

with a wavy proximal sag. Inner septal extensions 

have numerous lateral spines and bumps. 

Comparison with other forms.-Australophyllum 

(Toquimaphyllum) johnsoni Merriam of Great Basin 

Silurian coral zone E has a much more continuous and 

uniform marginarium of lonsdaleioid dissepiments 

that are less steeply inclined; its tabularium is narrower than that of A ustralophyllum sp. c. A ustralophyllum landerensis Merriam has fewer septa, a more 

fully developed pattern of lonsdaleioid dissepiments, 

and fewer lateral spines and bumps on axial extensions 

of septa. Australophyllum sp. v of Late Silurian and 

Early Devonian beds in the Vaughn Gulch Limestone 

has a similarly restricted pattern of lonsdaleioid dissepiments but it differs by having narrower, thicker 

walled corallites and fewer septa; the septa are unthickened and lack the abundant lateral spines and 

nodes of A ustralophyllum sp. c. A similar coral from 

locality M1445 near the Big Six mine, Tuscarora 

Mountains, has the spiny septal extensions of A ustralophyllum sp. c but has very few small lonsdaleioid 

dissepiments and a thicker wall. The Tuscarora Mountains coral also differs by having localized crossbar 

carinae. 
FAMILY ENDOPHYLLIDAE TORLEY 35 

Occurrence.-Coal Canyon, Simpson Park Mountains; locality M1318 in Coal Canyon fault zone on 

west side of canyon. Although this coral head was not 

collected in place and the locality is in deformed strata 

within the fault zone, its field location suggests that it 

may have come from beds stratigraphically above the 

lower Carlinastraea coral beds of the west fault block. 

Australophyllum (Australophyllum) sp. v 

Plate 8, figures 8-11 

Diagnosis.-Australophyllum has predominantly 

narrow, fairly thick-walled corallites and a restricted 

pattern of lonsdaleioid dissepiments; septa are mostly 

thin with very few nodes and spines in periaxial band. 

Transverse thin sections .-Septal count is about 42 

in average corallites. Some major septa reach axis; 

minor septa, mostly less than half the length of the 

major septa, commonly appear only as septal crests 

peripherally. Septa are slightly wavy. Lonsdaleioid 

dissepiments are medium and small and are restricted 

or absent in some corallites. 

Longitudinal thin sections.-Tabularium is onethird to less than one-fourth of corallite diameter; 

tabulae are partly complete, closely spaced, and sagging. Dissepiments are steeply inclined, 4--7 columns 

on each side. Periaxial extensions of septa are nearly 

devoid of nodes and spines. Thickened wall shows no 

discrete trabecular structure. 

Comparison to related forms.-Australophyllum sp. 

v is most closely related to A. landerensis Merriam 

from Lower Devonian beds of the northern Toquima 

Range, Nev. The Devonian form differs by having 

somewhat thickened and more wavy septa in the 

tabularium; the periaxial extensions of septa show 

more lateral nodes and bumps than in A. sp. v. Australophyllum sp. c has scattered, much wider corallites with a septal count of 62, and its periaxial septal 

extensions show abundant lateral spines and nodes. 

Occurrence and age .-Mazourka Canyon, northern 

In yo Mountains, Calif.; upper middle and upper beds of 

the Vaughn Gulch Limestone. Locality M1093, bottom 

of the upper unit of the Vaughn Gulch Limestone of 

Late Silurian and Early Devonian(?) age. Locality 

M1410 about 50 feet stratigraphically below M1093. 

Subgenus Toquimaphyllum Merriam 

(subgenus of Australophyllum Stumm) 

Toquimaphyllum, a cerioid compact subgenus of 

Australophyllum, has a wide continuous marginarium 

of predominantly large lonsdaleioid dissepiments; the 

peripheral dissepiments are nearly fiat or dip axially 

at low angles. The tabularium is narrow to moderately 

wide; the tabulae are closely spaced, sagging, and are 

without a marginal depression. The septa are thin, 

smooth, fairly straight, and discontinuous peripherally 

as septal crests. Some mature corallites have much 

shortened or obsolete septa. 

A ustralophyllum (Toquimaphyllum) differs from 

Australophyllum sensu stricto by the greater development of large lonsdaleioid dissepiments forming a continuous marginarium, by the presence of septal crests 

peripherally, and by its tendency to lose septa in some 

mature corallites. The septa of Toquimaphyllum lack 

the carinae reported by Stumm (1949, p. 34) in Australophyllum sensu stricto. Endophyllum differs by 

having a much wider tabularium; the tabulae being 

nearly fiat to slightly arched medially with a peripheral sag. The type species of Endophyllum shows a tendency to lose the outer wall, thus becoming partially 

aphroid. As known, Endophyllum does not, like Toquimaphyllum, have a tendency to shorten and lose 

septa. 

Australophyllum (Toquimaphyllum) johnsoni Merriam (pl. 6, figs. ~10) is the most abundant and distinctive rugose coral of Great Basin Silurian coral zone 

E (Late Silurian). The relations of this subgenus and 

its worldwide distribution are discussed in some detail 

by Merriam (1972a). 

The type species Australophyllum (Toquimaphyllum) johnsoni Merriam comes from the Roberts Mountains Formation of the Mill Canyon sequence of the 

Ikes Canyon area, Toquima Range, Nev. Much of the 

study material was collected from the upper beds of 

the Roberts Mountains Formation at Coal Canyon, 

Simpson Park Mountains. 

Australophyllum (Toquimaphyllum) johnsoni Merriam 

Plate 6, figures 8-10 

Collections from several localities in Silurian limestones between the northern Simpson Park Mountains 

and the northern In yo Mountains of California contain 

many complete and fragmentary colonies of this 

species. A ustralophyllum (Toquimaphyllum) johnsoni 

has been found only in strata of Great Basin Silurian 

coral zone E. A detailed description of this species and 

a review of its taxonomy have recently been published 

by Merriam (1973a) 

This species is characterized by wide corallites, the 

major septa normally reach the axis and break up 

peripherally as septal crests. Most mature corallites 

have a narrow tabularium and a correspondingly wide 

dissepimentarium in which the outer dissepiments are 

nearly flat. Partially aseptate corallites show only 

abbreviated tips of major septa. 

Occurrence.-Upper beds of the Roberts Mountains 

Formation in the Mill Canyon sequence at Ikes Canyon, Toquima Range; locality M1114 (type locality). 

Upper beds of the Roberts Mountains Formation in 

east block of Coal Canyon fault zone, Coal Canyon, 

northern Simpson Park Mountains; several localities 
36 ROBERTS MOUNTAINS FORMATION, REGIONAL STUDY 

including M1106 and M1108. Foothill exposures 2.4 

km north of Red Hill, SEV!NE¥1 sec. 5, T. 25 N., R. 50 

E., Simpson Park Mountains; locality M1446. Upper 

part of middle unit of Vaughn Gulch Limestone (these 

specimens differ slightly from typical A. johnsoni), 

Mazourka Canyon, northern Inyo Mountains; locality 

M1115. Australophyllum, possibly A. johnsoni, occurs 

in the Antelope Peak section 19 km north of wells, 

Elko County, Nev. 

Family CHONOPHYLLIDAE Holmes 

Genus Chonophyllum Edwards and Haime 

Chonophyllum shares some characteristics of 

Ketophyllum and other members of the Endophyllidae, 

but it is solitary and usually has a narrower tabularium than most endophyllids. The lonsdaleioid pattern 

of Chonophyllum is much more irregular or less uniform and localized in peripheral patches. 

Chonophyllum simpsoni Merriam (pl. 7, figs. 5, 6; 

pl. 9, figs. 9, 10) from the uppermost part of the Roberts 

Mountains Formation is a large trochoid to ceratoid 

species with major septa reaching the axis and a narrow tabularium. Its tabulae are closely spaced, undulant, and mostly incomplete with marginal tabellae. 

Inner dissepiments are commonly anguloconcentric in 

transverse section. 

Chonophyllum simpsoni Merriam occurs at locality 

M1108 in the east block of the Coal Canyon fault, Coal 

Canyon, Simpson Park Mountains, Nev., the upper 

part of the Roberts Mountains Formation. 

Family KYPHOPHYLLIDAE Wedekind 

This large and somewhat heterogeneous provisional 

group of Silurian Rugosa as revised by Merriam 

(1973a) contains about eight gene;ra as follows: 

Kyphophyllum Wedekind 

Strombodes Schweigger 

Petrozium Smith 

Entelophyllum Wedekind 

Entelophylloides Rukhin (as a subgenus) 

Entelophylloides (Prohexagonaria) Merriam 

Neomphyma Soshkina 

?Tonkinaria Merriam. 

Of these genera, Kyphophyllum and Tonkinaria are of 

greatest importance to the stratigraphy of the intermediate limestone facies. 

Genus Kyphophyllum Wedekind 

Kyphophyllum builds large bushy phaceloid colonies; its subcylindrical corallites have a narrow 

stereozone and medium-narrow closely spaced tabulae. 

Restricted segments of the marginarium are occupied 

by large, irregular lonsdaleioid dissepiments. In the 

Roberts Mountains Formation and Vaughn Gulch 

Limestone, this genus is represented by K. nevadensis 

Merriam, K. sp. b, K. sp. c, K. sp. t, and other undescribed species. In the Great Basin, Kyphophyllum occurs in Great Basin Silurian coral zone E (Late Silurian). 

Kyphophyllum nevadensis Merriam 

Plate 9, figures 1-3 

Kyphophyllum nevadensis has medium-wide to narrow corallites of variable diameter with a small 

number of major septa (about 22) and sporadic groups 

of relatively large lonsdaleioid dissepiments. 

Occurrence.-Ikes Canyon (Mill Canyon sequence), 

Toquima Range, Nev. Great Basin Silurian coral zone 

E. Locality M1114, northwest side of Copper Mountain 

in lower part of the McMonnigal Limestone. 

Kyphophyllum sp. b 

Plate 5, figures 15--21 

Kyphophyllum sp. b has very narrow corallites for 

the genus, a few wavy major septa (about 20), very few 

lonsdaleioid dissepiments, and lateral offsets that are 

attached at former calice rims. The dissepiments are 

all steeply inclined or vertical. Longitudinal exterior 

ribbing is strongly developed. 

Occurrence.-Tuscarora Mountains, Nev. Locality 

M1314, middle part of the Roberts Mountains Formation. 

Kyphophyllum sp. c 

Plate 9, figures 4-8 

Kyphophyllum sp. c has large corallites for the 

genus and a large number (about 60) of long, smooth, 

somewhat wavy septa, many of which are greatly 

lengthened minor septa. Longitudinal sections of K. 

sp. c are similar to those of K. nevadensis with a few 

large localized lonsdaleioid dissepiments. Some corallites are joined by lateral processes not observed inK. 

nevadensis. 

Occurrence.-Coal Canyon, Simpson Park Mountains, Nev. Locality M1380, upper part of the Roberts 

Mountains Formation. 

Kyphophyllum sp. t 

Plate 10, figures 14-17 

Kyphophyllum sp. t has narrow corallites of greatly 

varying diameter. The larger corallites have about 20 

long, somewhat wavy major septa and very short 

minor septa. All dissepiments are steeply inclined. The 

stereozone is relatively wide for this genus. 

Occurrence.-Toquima Range, Nev. Late Silurian 

and Devonian Tor Limestone of the June Canyon sequence; locality M1397. 

Genus Tonkinaria Merriam 

Tonkinaria, a solitary or loosely phaceloid genus, 

commonly has a flaring trumpet-shaped calice, ceratoid to turbinate corallites, and a narrow tabularium. 

The wall is a narrow stereozone, the septa are thin, and 
FOSSILS ASSOCIATED WITH RUGOSE CORALS 37 

major septa reach or are slightly withdrawn from the 

axis. Dissepiments are mostly large, elongate, and 

steeply inclined. Multiplication is by peripheral calice 

offsets, of which there may be several on a single flaring calice rim. 

Occurrence.-Tonkinaria simpsoni Merriam, the 

type species, comes from locality M1100 (pl. 5, figs. 

1-9) in Roberts Mountains Formation unit 3 and Great 

Basin Silurian coral zone D of the reference section; 

locality M1103 in the Mill Canyon sequence at Ikes 

Canyon, Toquima Range, Nev., in Great Basin Silurian coral zoneD; and locality M1383 (pl. 5, figs. 10-14) 

on the west side of Coal Canyon, Simpson Park Mountains, where it occurs in the west block of the Coal 

Canyon fault together with Carlinastraea tuscaroraensis and Stylopleura. 

Family CALOSTYLIDAE Roemer 

Genus Calostylis Lindstrom 

Fragmentary and rather poorly preserved solitary 

rugose corals from Bootstrap Hill, Tuscarora Mountains, are referred provisionally to Calostylis. This 

Silurian genus occupies a peculiar relation to all other 

Rugosa (Smith, 1930, p. 294) by possessing perforate 

septa and a spongy axial structure. 

Calostylis? sp. (pl. 7, figs. 7, 8) occurs at locality 

M1314, Bootstrap Hill, Tuscarora Mountains, Nev., in 

the middle part of the Roberts Mountains Formation. 

Family LYKOPHYLLIDAE Wedekind 

Solitary lykophyllid Rugosa have not been found to 

be among the more abundant corals of the Great Basin 

Silurian limestone. They may have been overlooked in 

collecting in limestone, however, as they are fairly 

numerous in the Hidden Valley Dolomite. This family 

is well represented in the Silurian of Gotland and 

elsewhere in Europe where the genera include Phaulactis, Cyathactis, Pycnactis, and Ryderophyllum. 

The Lykophyllidae are medium and large solitary 

Rugosa with many columns of small to medium, rather 

steeply inclined dissepiments and a fairly wide tabularium made up of closely spaced, uneven, mostly incomplete tabulae and flat tabellae. Greatly thickened 

septa of early growth stages persist ontogenetically to 

at least early adult growth. A fossula is not generally 

present in mature transverse sections. 

In the Great Basin Silurian, the Lykophyllidae are 

represented by abundant Ryderophyllum in Great 

Basin Silurian coral zone B of the Hidden Valley 

Dolomite (Merriam, 1973a) but are unknown in higher 

horizons of the dolomite facies and have not been identified from limestone facies of the better known sections. A lykophyllid resembling Ryderophyllum from 

an undetermined stratigraphic horizon in the Tuscarora Mountains is figured here (pl. 12, figs. 34-36). 

FOSSILS ASSOCIATED WITH RUGOSE CORALS 

IN GREAT BASIN SILURIAN LIMESTONES 

Tabulate corals, crinoids, brachiopods, and dasycladacean algae are common members as well as a Hercynella-like mollusk (pl. 10, fig. 20) of Great Basin 

Silurian coral communities. In general, the most 

abundant fossil remains of the limestone coralline 

facies are favositids, including entire massive heads of 

Favosites (pl. 10, figs. 9-13) and digitate forms (pl. 10, 

fig. 8). With these branching corals are the more slender ramose genera Cladopora (pl. 10, figs. 5--7) and 

Coenites. Halysites is rather uncommon and seems to 

be absent from the higher Silurian beds. Crinoids are 

represented by large volumes of crinoidal debris filling 

interstices and making crinoidal limestone, but no articulated or partial crinoid crowns were collected. 

Limestone beds that contain silicified fossils yield 

abundant well-preserved brachiopods during extraction of the coral material by the acid technique. Among 

such occurrences are the Great Basin Silurian zone D 

coralline beds in unit 3 of the Roberts Mountains Formation type section, the upper coral-rich beds of Great 

Basin Silurian coral zone E at Coal Canyon, Simpson 

Park Mountains, and the lower beds of this formation 

at Bootstrap Hill, Tuscarora Mountains, Nev. 

A few of the more distinctive brachiopods occurring 

with Silurian corals are illustrated herein. The following brachiopods occur in unit 3 of the type section 

Roberts Mountains Formation: 

Dicoelosia sp. r (pl. 11, figs. 1~22) 

Gypidula sp. r (pl. 11, figs. 25, 26) 

Homoeospira sp. r (pl. 11, figs. 15--17) 

Kozlowskiellina sp. f (pl. 11, figs. 9-12) 

Silicified brachiopods from Great Basin Silurian 

coral zone E on the east side of Coal Canyon are: 

Kozlowskiellina sp. f (pl. 11, figs. 13, 14) 

Plectatrypa? sp. c (pl. 11, figs. 23, 24) 

From the Roberts Mountains Formation of the 

Bootstrap Hill area, Tuscarora Mountains, unusually 

well preserved silicified brachiopods were collected by 

R. J. Roberts from a large talus slab at the base of the 

slope where the lowest beds of the formation are partly 

exposed. Other rocks in the same collection contained 

Cyathophylloides sp. f, an indicator of coral zone A. 

The following associated brachiopods are figured in 

this report: 

Conchidium sp. b (pl. 12, figs. 1~22) 

Fardenia sp. b (pl. 12, figs. ~15) 

Coelospira sp. b (pl. 12, figs. 1-7) 

Kozlowskiellina sp. b (pl. 12, figs. 16, 17, 23) 

Kozlowskiellina sp. f, which occurs in both Great 

Basin Silurian coral zones D and E, bears a rather 

close resemblance to Plicocyrtina sinuplicata Havlicek 

as figured by Lenz (1972, pl. 1, figs. 1-20). According to 
38 ROBERTS MOUNTAINS FORMATION, REGIONAL STUDY 

Lenz, the Canadian species is of Early Devonian (late 

Siegenian) age. 

In the type section of the Roberts Mountains Formation, the brachiopod Conchidium is most abundant and 

diverse near the top of lithologic unit 2 and below 

Great Basin Silurian coral zone C. These pentameroid 

brachiopod faunas have not been studied in detail. The 

form resembling Conchidium miinsteri Kiaer is illustrated (pl. 12, figs. 24-26). 

DASYCLADACEAN ALGAE AS INDICATORS 

OF THE SILURIAN 

The family Dasycladaceae of green calcareous algae 

has a very long geologic range, through the Paleozoic 

to the present day. One of its subgroups, the Verticilloporaea (Rezak, 1959), throve in Great Basin Silurian 

seas, occupying environments favorable for the corals. 

In the Great Basin province, the family is well represented by the genus Verticillopora Rezak (pl. 10, figs. 

1-4; pl. 11, figs. 1-8), some of whose individuals attained a relatively large size for the family. Verticillopora is a fairly reliable Great Basin Silurian indicator, as its remains have not yet been recognized in 

Ordovician strata and it is rarely found in rocks of 

early Devonian age. Its usefulness as a Silurian fossil 

was not recognized until recently; the cylindrical and 

conical thalli were generally ignored; collectors regarded them as fragmentary sponges or crinoid columnar segments, both of which they resemble in gross 

surficial features. Moreover, the dasycladaceans not 

uncommonly occur in crinoidallimestone. 

The classification of living and fossil dasycladacean 

algae has been reviewed by Pia (1926, p. 105). In 1959, 

Rezak described Great Basin Silurian algal forms collected by U.S. Geological Survey mapping parties. 

Most of these specimens were assigned to the new 

genus Verticillopora Rezak. This genus is usually preserved by silicification. Its thallus commonly has the 

externally jointed appearance of a large crinoid stem 

with numerous rather uniformly perforated columnar 

segments. Internally the structure differs markedly 

from that of a crinoid column by having a wide, commonly five-sided or polygonal central chamber that 

housed the stipe (Rezak, 1959, p. 119), surrounded by 

cycles of small radiating tubes or canals that contained 

the lateral rays. Externally each segment reveals the 

small-ray canal pores (pl. 11, figs. 3, 6). Some individuals (pl. 10, figs. 1-3) have long, stout, tubular rootlike 

processes. 

Verticillopora ranges upward from Great Basin Silurian coral zone B through coral zone E and into the 

Early Devonian. Unlike some rugose coral genera, 

V erticillopora is present in both limestone and dolomite facies of the Great Basin Silurian. This algal 

group seems to have attained its peak of development 

in limestone facies of Great Basin Silurian coral zone 

D. In the Vaughn Gulch Limestone of the lnyo Mountains, for example, the middle part of the formation 

below Great Basin Silurian coral zone E is heavily 

populated by Verticillopora annulata Rezak. The Verticillopora beds have yielded much of the best study 

material of this interesting calcareous algal family. 

CONODONTS OF THE ROBERTS MOUNTAINS FORMATION 

By jOHN W. HUDDLE 

Conodonts are abundant in much of the Roberts 

Mountains Formation. The presence of these microfossils where no megafossils occur makes their use especially important for stratigraphic studies and geologic 

mapping. Many conodont identifications were made for 

geologists mapping in the Carlin gold mine vicinity 

and other areas of the central Great Basin where the 

Silurian and Devonian strata are intensely deformed 

and would otherwise remain undated paleontologically. In order to correlate the isolated conodont occurrences with more continuous sections of the Roberts 

Mountains Formation, during this investigation conodont-bearing material was collected from beds yielding 

distinctive rugose corals and other megafossils of age 

significance. Conodont control sections have been 

measured in areas that have been mapped geologically 

in the Toquima, Monitor, and Simpson Park Ranges. 

Much more bed-by-bed conodont collecting remains to 

be done in these more continuous Silurian and Devonian control sections. An important conodont study of 

the type section of the Roberts Mountains Formation 

and nearby locations in the Roberts Mountains is that 

of Klapper and Murphy (1974); this study serves as a 

reference for comparison of other collected stratigraphic intervals in the central Great Basin. 

A chart (table 2) of Roberts Mountains Formation 

conodont assemblages collected from the Toquima 

Range and localities between the Toquima Range and 

the Tuscarora Mountains lists conodont stratigraphic 

ranges. In addition, conodonts from the overlying Rabbit Hill Limestone are included. 

The largest assemblages of conodonts listed here 

come from the upper part of the Roberts Mountains Formation at Coal Canyon, Simpson Park Mountains, on 

both the west and east sides of the Coal Canyon fault, 

and in the August Canyon sequence at Gatecliff in the 

Toquima Range. Here the name Bastille Limestone 

Member of the Masket shale of Kay and Crawford 

(1964) is used for strata correlative with part of the 

Roberts Mountains Formation. 

Conodont form taxa are used in this report. Some 

multielement taxa are recognized, but until the mul-
LOCALITY REGISTER OF MAJOR FOSSIL LOCALITIES 39 

tielement taxonomy is generally used, the form taxa 

will serve for stratigraphic studies. 

Comments on some of the collections of specific stratigraphic interest are: Locality KV-70--19 (8827-SD) 

(table 2, No. 6), from the Carlinastraea beds, Coal Canyon in the Simpson Park Mountains. 

The presence of Spathognathodus remscheidensis indicates that 

this collection is Early Devonian according to conodont zonation. 

The faunal list gives form taxa because it is simpler to use for 

stratigraphic purposes until the multielement taxonomy is more 

completely established. Spathognathodus inclinatus and several 

of the bar-type conodonts listed above (table 2) are part of a multielement taxon called 'Apparat-H' by Walliser (1964), Hindeodella excavata by Jeppsson (1969), and Ozarkodina inclinata 

by Walliser (1972). 

Locality KV-70--24 (8829-SD) (table 2, No. 7), Carlinastraea beds, Coal Canyon, Simpson Park Mountains. 

Spathognathodus remscheidensis indicates an Early Devonian 

age for this collection and Rotundacodina elegans has been 

reported only from Early Devonian rocks. The new species of 

Spathognathodus is similar to S. remscheidensis but has aborted 

and small denticles anterior to the basal cavity. 

Two conodont assemblages from the upper part of 

the Roberts Mountains Formation on the east side of 

the Coal Canyon fault in the Pyramid Hill block (table 

2, Nos. 8 and 9) are from the interval of Great Basin 

Silurian coral zone E (collection 8216-SD, table 2, 

No. 8, made by T. E. Mullens): 

The list includes only form taxa, and several of the bar elements 

belonged to multielement species. The age of the fauna is Early 

Devonian according to the known conodont ranges. This age is 

indicated by Spathognathodus remscheidensis, Spathognathodus 

transitans, and the form of Spathognathodus inclinatus, which is 

the one common in Lower Devonian rocks. The Icriodus is only a 

small fragment and is not specifically identifiable, but it also 

suggests a Devonian age. The Scolopodus devonicus is known only 

from Devonian collections. Many of the other conodonts range 

from Silurian to Devonian. Although there are few Late Silurian 

faunas described now (1973), all the evidence available indicates a 

Devonian age for this collection. 

Collection 8828-SD (table 2, No. 9): 

The two species of Rotundacodina were described by Carls and 

Gandl (1969) from the Lower Devonian of northeastern Spain. 

These species and Spathognathodus remscheidensis indicate an 

Early Devonian age for this collection. The new species of 

Spathognathodus, S. sp., differs from S. remscheidensis by having 

aborted anterior denticles instead of tall anterior denticles as inS. 

remscheidensis. Spathognathodus sp. occurs with Spathognathodus boucoti Klapper, an Early Devonian species, in a collection made by T. E. Mullens near Carlin, Nev. (USGS loc. 8447-

SD). This occurrence supports my opinion that S. n. sp. cf. 

Spathognathodus remscheidensis is an Early Devonian species. 

Klapper reports (oral commun., March 1971) the occurrence of 

what is probably the same species with aborted anterior denticles 

in the Gedinnian Windmill Limestone of Johnson and Murphy 

(1969) at a stratigraphic horizon of 1,617 feet (493 m) in the west 

Coal Canyon section in the Simpson Park Mountains and on Pete 

Hanson Creek in the Roberts Mountains. It is unfortunate that 

species of Icriodus are not present in these collections of Silurian 

Coral Zone E to confirm the Early Devonian age of the Zone in 

terms of conodont chronology. Klapper and Murphy (1974), reported I. woschmidti from Birch Creek in the Roberts Mountains 

in the upper part of Roberts Mountains Formation. 

Bed-by-bed collecting will be required to firmly establish conodont zonal distribution in these western 

Silurian and Devonian strata. Lowermost Devonian on 

the conodont scale conforms closely to that of the graptolite scale, placing the base of the Devonian System 

below or within Great Basin Silurian coral zone E. Although only a few conodonts have been identified from 

the Rabbit Hill Limestone, most of these are distinctive Early Devonian forms not recognized in the 

Roberts Mountains Formation. 

LOCALITY REGISTER OF MAJOR FOSSIL 

LOCALITIES IN THE ROBERTS MOUNTAINS 

FORMATION AND CORRELATIVE STRATA 

Roberts Mountains, Nev. 

MllOO.-Roberts Creek Mountain quadrangle, Nevada. Northwest 

side of Roberts Creek Mountain on measured section 550 m N. 79° 

W. of summit 9219 at altitude 8,680 feet. Upper part of Roberts 

Mountains Formation, unit 3. 

M1102 .-Roberts Creek Mountain quadrangle, Nevada. Northwest 

side of Roberts Creek Mountain. Lower beds of Roberts Mountains 

Formation unit 3 with Prohexagonaria. In measured reference 

section. 

Northern Simpson Park Mountains, Nev. 

M1032.-Horse Creek Valley quadrangle, Nevada. East side of Coal 

Canyon in NW% sec. 21, T. 25 N., R. 49 E. Rabbit Hill Limestone. 

Collected by R. J. Roberts, 1954. 

M1075.-Horse Creek Valley quadrangle, Nevada. Near mouth of 

Coal Canyon, east side along top of ridge of summit 6909. Rabbit 

Hill Limestone, Lower Devonian. 

M1076.-Horse Creek Valley quadrangle, Nevada. Near mouth of 

Coal Canyon, east side. Mostly float below top of ridge of summit 

6909 and downslope to west. Rabbit Hill Limestone, Lower Devonian. 

M1105.-Horse Creek Valley quadrangle, Nevada. Coal Canyon; 

float at canyon bottom 0.6 km south of mouth of Coal Canyon. 

Material probably from upper part of the section or upper coralrich limestone breccia below Rabbit Hill Limestone. 

M1105a.-Horse Creek Valley quadrangle, Nevada. Coal Canyon; 

float at canyon bottom 0.6 km south of mouth of Coal Canyon. 

Material probably from upper part of the section or upper coralrich limestone breccia below Rabbit Hill Limestone. 

M1106.-Horse Creek Valley quadrangle, Nevada. Coal Canyon 

near mouth in SE% sec. 17, T. 25 N., R. 49 E.; east side of canyon at 

altitude about 6,300 feet. Coral-rich limestone depositional breccia 

in upper part of the Roberts Mountains Formation and below Rabbit Hill Limestone. 

M1107.-Horse Creek Valley quadrangle, Nevada. About 0.6 km 

south of mouth of Coal Canyon on east side of canyon and about 

60 m above canyon bottom. Coral-rich limestone and depositional 

limestone breccia. Roberts Mountains Formation. 

M1108.-Horse Creek Valley quadrangle, Nevada. Coal Canyon, 

near mouth. Float collections below coral-bearing depositional 

breccia on east side of canyon below locality M1107. Roberts 

Mountains Formation. 

MlllO.-Horse Creek Valley quadrangle, Nevada. Coal Canyon, 

near mouth. Coral-rich breccia limestone near top of Roberts 

Mountains section on east side of canyon. Collection made by A. J. 

Boucot, 1964. 

M1310.-Horse Creek Valley quadrangle, Nevada. SE% sec. 17, T. 

25 N., R. 49 E. West side of summit 6909 (Pyramid Hill) near top. 
40 ROBERTS MOUNTAINS FORMATION, REGIONAL STUDY 

TABLE 2.-0ccurrence chart of conodont species collected from Silurian and Lower Devonian formations in central Nevada 

[Conodont species listed are form taxa. Identification by .J. W. Huddle. Multielement apparatus reconstructions in the sense of Jeppson ( 19691 and Klapper and Philip (19711 have not 

been attempted] 

flcodina sp ---------------------------------------------- Belodella devonica (Stauffer)------------------------------

Belodella resima (Philip) -------------------------------- Belodella sp __ _ _ __ ____ ______ ________ _ _ __ __ _ _ _ _ ____ _ _ __ __ x 

Eantiognathus lipperti Bischoff____________________________ x Hibbardella sp ____ __ _____ _ ____ __ __ ______ _ _ __ __ _ _ _ ___ __ _ _ x 

X 

9 

X 

X X X 

10 11 12 13 14 15 

X X 

X 

X 

Hindeodella sp ------------------------------------------ x x X X X X X X X 

Icriodus latericrescens Branson and Mehl (subspecies not determined) -------------------------------------------- Icriodus latericrescens huddlei Klapper and Ziegler _______ _ Icriodus latericrescens subspecies B Klapper1 ______________ b. 

Icriodus latericrescens aff. I. latericrescens subspecies B Klapper____________________________________________________ x 

Icriodus sp ---------------------------------------------- Ligonodina sp ------------------------------------------ Lonchodina walliseri Ziegler------------------------------ Lonchodina sp _________________________________________ _ 

Neoprioniodus excavatus (Branson and Mehl) _____________ _ Neoprioniodus multiformis? Walliser _____________________ _ 

Oneotodus? beckmanni Bischoff--------------------------- x 

X 

X 

X 

X 

X 

X X 

X 

X 

X 

X X 

X 

X 

X X 

X X X 

Ozarkodina denckmanni Ziegler -------------------------- x X X X X 

Ozarkodina gaertneri Walliser ---------------------------- Ozarkodina media Walliser ------------------------------ Ozarkodina aff. 0. media Walliser _______________________ _ Ozarkodina typica Branson and MehL ____________________ _ 

Ozarkodina ziegleri Walliser ------------------------------ Ozarkodina aff. 0. ziegleri Walliser _____________________ _ 

Ozarkodina sp ------------------------------------------ x Paltodus aff. P. migratus Rexroad _______________________ _ 

X 

X 

X 

X X X 

X 

X 

X 

X 

Paltodus sp ___________________________________________ _ X X 

X X 

X 

Panderodus sp _________________________________________ _ X X 

Pelekysgnathus furnishi Klapper-------------------------- sp _______________________________________ _ 

Plectospathodus extensus Rhodes _________________________ _ X 

Plectospathodus aff. P. alternatus Walliser _______________ _ Plectospathodus sp ____ _____ _ ________ ______ __ ______ _ _ __ __ x X 

Po?ygr:at~us foveolatus Philip and Jackson _______________ _ 

Prwnwdma sp ------------------------------------------ x X 

X X 

X 

X 

X 

X 

X ~ 

X X 

X 

X 

X 

X 

X 

Rotundacodina elegans Carls and Gandl _________________ _ X X 

Rotundacodina noguerensis Carls and Gandl _____________ _ X 

Scolopodus devonicus Bischoff and Sannemann ____________ x X 

Spathognathodus inclinatus inclinatus Rhodes ____________ x X X X X 

Spathognathodus primus (Branson and Mehl)l ___________ _ 

Spathognathodus eosteinhornensis Walliser1 _____________ _ 

Spathognathodus remscheidensis Ziegler1 _________________ _ X X 

Spathognathodus n. sp., cf. S. steinhornensis remscheidensis x 

X b, b, 

X X X 

X Ziegler _______________________________________________ _ 

Spathognathodus transitans Bischoff and Sanneman1 _____ _ X 

Spathognathodus cf. S. transitans Bischoff ________________ x 

~~t!!:::~:?:~::u~~~P:::::::::::::::::::::::::::::::::::::: Trichonodella blanda (Stauffer) --------------------------

Trichonodella blanda? (Stauffer)--------------------------

X 

X 

X X X 

X 

X 

Trichonodella inconstans Walliser ________________________ x X 

Trichonodella sp _______________________________________ _ 

Geographic locality: 

1. 9165-SD _________ Toquima Range, Mill Canyon in 

August Canyon structural se~ 

quence. 2. 9166-SD _________ _ _____________ do _______________ _ 

3. 8214-SD _________ Monitor Range, Copenhagen 

Canyon. 4. 8304-SD _________ _ _____________ do _______________ _ 5. 9167-SD _________ _ _____________ do _______________ _ 

6. 8827-SD _________ Northern Simpson Park Mountains, 

Coal Canyon. 

X X X 

Formation: 

Bastille Limestone Member of Masket Shale of Kay and Crawford 

(1964). 

Upper member of Masket Shale of 

Kay and Crawford (1964). 

Roberts Mountains Formation ___ _ 

______________ do _______________ _ 

Rabbit Hill Limestone ___________ _ 

Thick-bedded upper part of Roberts 

Mountains Formation (mapped 

as Windmill Limestone by John- son (1965) and Johnson and Murphy (1969). 

Approximate stratigraphic position 

of fossil collection: 

31 m above top of chert member of 

Gatecliff Fm. of Kay (1960). 

91 m above top of chert member of 

Gatecliff Fm. of Kay (1960). 

119 m above base of formation. 

187 m above base of formation. 

Upper 31 m of formation at type 

section. 

Carlinastraea beds; unmeasured locality about 460 m above base of 

formation of west side of Coal 

Canyon. 2 
LOCALITY REGISTER OF MAJOR FOSSIL LOCALITIES 41 

TABLE 2.-0ccurrence chart of conodont species collected from Silurian and Lower Devonian formations in central Nevada-Continued 

Geographic locality: Formation: 

Approximate stratigraphic position 

of fossil collection: 

7. 8829-SD ________ _ --------------do _______________ _ _ _____________ do _______________ _ Carlinastraea beds; unmeasured locality near 8827-SD. 

8. 8216-SD ________ _ --------------do---------------- _ _____________ do---------------- Unmeasured locality; east side Coal 

Canyon about 520 m above base 

of formation. 2 

9. 8828-SD ________ _ --------------do _______________ _ _ _____________ do---------------- Unmeasured locality; east side Coal 

Canyon about 550 m above base 

of formation. 2 

10. 9168-SD ________ _ --------------do _______________ _ Rabbit Hill Limestone ___________ _ Unmeasured locality; east side Coal 

Canyon about 70 m above base of 

formation. 2 

11. 8228-SD ________ _ Tuscarora Mountains, Bootstrap Roberts Mountains Formation ___ _ Lower 15 m of exposed section. 

Hill. 

12. 8219-SD ________ _ -------------- do _______________ _ _ _____________ do _______________ _ 37 m above base of exposed section. 

119 m above base of exposed section. 

244 m above base of exposed section. 

13. 8219A-SD ______ _ --------------do _______________ _ _ _____________ do _______________ _ 

14. 8215-SD ________ _ --------------do _______________ _ Roberts Mountains Formation ___ _ 

(thick-bedded facies). 

15. 8826-SD _________ Carlin area, Maggie Creek _______ _ Rabbit Hill Limestone ___________ _ Unmeasured locality east side of 

Maggie Creek. 

'Some occurrences of this taxon are anomalous with respect to its stratigraphic range as previously reported from central Nevada (Klapper, 1968; Klapper and others, 1971: Klapper and Murphy, 19751, the Canadian Yukon CKlapper, 1969; Fahr~Eus 1971 ), and Europe CZiegler, 19711, and relative to monograptlds of the Monograptus uniformu; and Monograptus 

hercynicus groups. In order to accommodate this discrepancy, the anomalous stratigraphic occurrence of the taxon is shown as a Ll.. 2The cited stratigraphic footage above base of the formation is estimated. 

Upper 60 m of Rabbit Hill Limestone on this slope platy limestone 

with abundant trilobites. 

M1317.-Horse Creek Valley quadrangle, Nevada. West side of Coal 

Canyon in sec. 20, T. 25 N., R. 49 E. near middle of north boundary, altitude about 6,600 feet. About 503 m stratigraphically above 

base of the Roberts Mountains Formation. Colonial rugose corals 

in ·place. 

M1318.-Horse Creek Valley quadrangle, Nevada. West side of Coal 

Canyon, about 152m west of canyon bottom at altitude 6,400 feet. 

Float material oflargeAustralophyllum, probably from Coal Canyon fault zone in the Roberts Mountains Formation. 

M1331.-Horse Creek Valley quadrangle, Nevada. Coal Canyon. 

SW%,SW% sec. 16, T. 25 N., R. 49 E.; east side of summit 6909 

(Pyramid Hill), altitude 6,840 feet just east of section line, 150 m 

southeast of flag station 6909. Rabbit Hill Limestone. 

M1332.-Horse Creek Valley quadrangle, Nevada. Coal Canyon 

area, top of Pyramid Hill (summit 6909), northwest of M1331, at 

flag station. Rabbit Hill Limestone. 

M1333.-Horse Creek Valley quadrangle, Nevada. Coal Canyon 

area. West side of Coal Canyon, NE% sec. 20 near section line, 

305 m northwest of hill 6400 at altitude 6,560 feet. About same 

zone as M1317. Dark-gray well-bedded limestone with abundant 

Favosites and other corals including a pycnostylid. Brachiopods 

present. Roberts Mountains Formation. 

M1334.-Horse Creek Valley quadrangle, Nevada. Coal Canyon 

area. SE% sec. 17, T. 25 N., R. 49 E. on west side of Coal Canyon 

460 m northwest ofhill6400 at altitude 6,560 feet and 200m north 

of M1333, Roberts Mountains Formation. Dark-gray limestone 

with corals and brachiopods. 

M1379.-Horse Creek Valley quadrangle, Nevada. West side of Coal 

Canyon near its mouth, SE% sec. 17, T. 25 N., R. 49 E.; 460 m N. 

78° W. of summit of hill 6909, altitude 6,400 feet. East-dipping 

limestone of Roberts Mountains Formation, fault sliver in Coal 

Canyon shear zone. On crest of northeast-extending spur. 

M1380.-Horse Creek Valley quadrangle, Nevada. Coal Canyon, 

850 m south of canyon mouth; NE% sec. 20, T. 25 N., R. 49 E.; 

2,200 feet S. 33° W. of summit of hill 6909 on east side near top 

small knoll in canyon, altitude 6,400 feet. Upper beds of Roberts 

Mountains Formation, Great Basin Silurian coral zone E. 

M 1381 .-Horse Creek Valley quadrangle, Nevada. Coal Canyon east 

side, 760 m south of canyon mouth, 520 m S. 40° W. of summit of 

hill 6909, altitude 6,320 feet. Upper beds of Roberts Mountains 

Formation. 

M1383.-Horse Creek Valley quadrangle, Nevada. Coal Canyon, 

west side sec. 17 near middle of south edge, T. 25 N., R. 49 E. At 

crest northeast spur 670 m S. 79° W. of summit of hill 6909, altitude 6,580 feet. Roberts Mountains Formation. 

M1384.-Horse Creek Valley quadrangle, Nevada. Coal Canyon 

west side, NE% sec. 20, T. 25 N., R. 49 E.; 760 m S. 53° W. of 

summit 6909, altitude 6,520 feet. Roberts Mountains Formation. 

Carlinastrae a tuscaroraensis locality. 

M1411.-Horse Creek Valley quadrangle, Nevada. West side of Coal 

Canyon 0.8 km south of canyon mouth at altitude 6,360 feet on 

northwest side of small limestone knob, altitude 6,400 feet. 

Roberts Mountains Formation with Verticillopora. 

M1446.-Horse Creek Valley quadrangle, Nevada. Foothills on 

north side of Simpson Park Mountains; 2.4 km north ofRed Hill in 

SE%NE% sec. 5, T. 25 N., R. 50 E. Low pediment exposures of 

Roberts Mountains Formation. 

M1448.-Horse Creek Valley quadrangle, Nevada. East side of Pine 

Hill, 150m south ofmiddle ofnorth edge of sec. 20, T. 25 N., R. 49 

E., near north-south midline of section; altitude 6,500 feet. Roberts 

Mountains Formation. In coral beds with Carlinastraea. 

M1449.-Horse Creek Valley quadrangle, Nevada. Top of main 

northeast spur of Pine Hill, 213 m north of south boundary of sec. 

17, T. 25 N., R. 49 E., at north-south midline of section. Roberts 

Mountains Formation. In coral beds with Carlinastraea. 

M1450.-Horse Creek Valley quadrangle, Nevada. Coal Canyon, 

east side about 335 m south of canyon mouth at altitude 6,300 feet. 

Coral collection mostly float material. Great Basin Silurian coral 

zone E. Roberts Mountains Formation. 

M1451.-Horse Creek Valley quadrangle, Nevada. Coal Canyon, 

east side about 100m south of canyon mouth at altitude 6,280 feet. 

Coral collections mostly loose float material. Great Basin Silurian 

coral zone E. Roberts Mountains Formation. 

M1452.-Horse Creek Valley quadrangle, Nevada. Coal Canyon, 

west side about 460 m south of canyon mouth, altitude 6,300 feet. 

Within the Coal Canyon fault zone. Roberts Mountains Formation. 

M1453.-Horse Creek Valley quadrangle, Nevada. Coal Canyon in 

NE% sec. 20, T. 25 N., R. 49 E., on top of small knoll 0.8 km south 

of canyon mouth, altitude 6,400 feet. Great Basin Silurian coral 

zone E. Roberts Mountains Formation. 
42 ROBERTS MOUNTAINS FORMATION, REGIONAL STUDY 

M1454.-Horse Creek Valley quadrangle, Nevada. Coal Canyon 

about 975 m south of canyon mouth, altitude 6,400 feet on top of 

spur on which the Middle Devonian Woodpecker Limestone 

Member of the Nevada Formation is apparently overridden by an 

upper plate comprising parts of the Roberts Mountains Formation 

and overlying Rabbit Hill Limestone. 

M1455.-Horse Creek Valley quadrangle, Nevada. Coal Canyon 

about 975 m south of canyon mouth, altitude 6,400 feet, on top of 

spur about 60 m east of M1454. Mixed Devonian assemblage apparently from both the Middle Devonian Woodpecker Limestone 

Member of the Nevada Formation and the Lower Devonian Rabbit 

Hill Limestone tectonically involved in the thrust. 

M1456.-Horse Creek Valley quadrangle, Nevada. South middle 

part of sec. 17, T. 25 N., R. 49 E., at crest of main northeast spur, 

altitude 6,600 feet. In thick-bedded limestone with rugose corals. 

Roberts Mountains Formation. 

Cortez Mountains, Nev. 

M1409.-Cortez quadrangle, Nevada. West base of Cortez Mountains about 1.6 km southeast of the town of Cortez. NE% sec. 17, T. 

26 N., R. 48 E., 2.6 km N. 76° E. of BM 5748, altitude 6,400 feet. 

Roberts Mountains Formation. Carlinastraea; probable float 

material. 

Sulphur Spring Range, Nev. 

MJ148.-Garden Valley quadrangle, Nevada. Southern part of Sulphur Spring Range. East side of range in northeast corner sec. 35, 

T. 23 N., R. 52 E. Lone Mountain Dolomite with corals 0.8 km 

north-northwest ofBM 5867 on east-west spur, altitude 6,100 feet. 

Southern Tuscarora Mountains, Nev. 

MJJ20.-Tuscarora Mountains near north end of Eureka County, 

Nev.; "Round Mountain," bottom of hill at southwest end. Collected by R. J. Roberts, June 1958. Roberts Mountains Formation 

limestone. 

M1313.-Bootstrap mine area, Nevada. Bootstrap Hill section. 

Roberts Mountains Formation about 400 m stratigraphically 

above base of section on top of knob. Carlinastraea bed. 

M1314.-Bootstrap mine area. Bootstrap Hill stratigraphic section 

200-250 m stratigraphically above base. Roberts Mountains Formation. 

MJ3J5.-Bootstrap mine area. Bootstrap Hill stratigraphic section 

about 230 m stratigraphically above base. Roberts Mountains 

Formation. 

MJ4J2.-Tuscarora Mountains, Nev. Advance quadrangle sheet 

USGS Tuscarora 3SW (7-7-68); Elko County, Nev., near north 

edge of Eureka County. Bootstrap Hill area southwest ofBootstrap 

Hill. Just north of Eureka County-Elko County line at bottom of 

ridge about 300m east of Dunphy-Tuscarora road and about 1,830 

m S. 17o W. oftop of Bootstrap Hill. Probably a large float boulder; 

contains silicified brachiopods in abundance. 

MJ4J3.-Tuscarora Mountains, Nev. Northeast Eureka County. 

Northeast of the Lynn window of R. J. Roberts. Collected by R. J. 

Roberts, 1958. Corals. Possibly in Jack's Creek drainage northeast 

of Big Six mine. Roberts Mountains Formation. 

Toquima Range, Nev. 

M1103 .-Dianas Punch Bowl quadrangle, Nevada. Ikes Canyon. 

About 1.6 km up canyon from mouth on north side and about 

100m in altitude above creek bottom, altitude 7,900 feet. Southeast of Ikes cabin. Roberts Mountains Formation or Masket Shale 

of Kay and Crawford (1964). Coral-rich limestone with Verticillopora. 

M1JJ4.-Dianas Punch Bowl quadrangle, Nevada. Ikes Canyon 

area; 200 m northwest of summit 8474 (Copper Mountain), altitude 8,300 feet. In McMonnigal Limestone. Coral fauna with 

Toquimaphyllum. Great Basin Silurian coral zone E. 

MJ147.-Northeast corner of Wildcat Peak quadrangle. SW%SW% 

sec. 16, T. 16 N., R. 46 E., on top of divide west of Henry Meyer 

Canyon, altitude 6,960 feet. Roberts Mountains Formation in beds 

with a fauna similar to that in the Rabbit Hill Limestone surrounded by graptolitic beds of Silurian age. 

M1393 .-Dianas Punch Bowl quadrangle, Nevada. South side oflkes 

Canyon, a little less than 1. 7 km northwest of canyon mouth. 

McMonnigal Limestone. 

M1394.-Southeast corner of Wildcat Peak quadrangle. On north 

side of Mill Canyon 1,525 m west of east border of quadrangle on 

top of spur, altitude 8,560 feet and 730 m north of south boundary 

of quadrangle. Bastille Limestone Member of Masket Shale of Kay 

and Crawford (1964). 

M1395.-Southeast corner of Wildcat Peak quadrangle. On north 

side of Mill canyon, altitude 8,000 feet and 2,400 m west of east 

border of quadrangle. Bastille Limestone Member of Masket Shale 

of Kay and Crawford (1964). 

M1396.-Southeast corner of Wildcat Peak quadrangle, 1,220 m 

west of east border of quadrangle and 1,130 m north of south 

boundary of quadrangle; altitude 8,500 feet. Bastille Limestone 

Member of Masket Shale of Kay and Crawford (1964). 

MJ397.-Wildcat Peak quadrangle, Nevada. South side of Stoneberger Basin, 2.4 km southeast of top of Whiterock Mountain at 

altitude 9,100 feet, just east of letter "n" in word "Basin" of 

"Stoneberger Basin" (Wildcat Peak quadrangle). Tor Limestone. 

Northern lnyo Mountains, Calif. 

MJ090.-Independence quadrangle, California. East of Kearsarge at 

mouth of Mazourka Canyon. In NE14 sec. 8, T. 13 S., R. 36 E. 

Within 6 m of top Vaughn Gulch Limestone. Poorly preserved 

fossils of probable Early Devonian age. 

MJ09J.-Independence quadrangle, California. At mouth of 

Mazourka Canyon. Near east line of sec. 8, T. 13 S., R. 36 E. at 

middle of NE%, 366m north of Vaughn Gulch creek bottom, altitude 4,840 feet. About 46 m stratigraphically above chert unit at 

base of Vaughn Gulch Limestone. 

MJ092.-Independence quadrangle, California. Same measured section as M1091, west of east section line of sec. 8 in NE%, altitude 

4,880 feet. Middle part of Vaughn Gulch Limestone about 305 m 

stratigraphically above the Eureka Quartzite equivalent. 

M1093 .-Independence quadrangle, California. East of Kearsarge at 

mouth ofMazourka Canyon. In NE14 sec. 8, T. 13 S., R. 36 E. Base 

of upper unit of Vaughn Gulch Limestone about 412 m stratigraphically above Eureka Quartzite equivalent and 137 m below 

top of Vaughn Gulch Limestone. 

MJ115.-Independence quadrangle, California. East ofKearsarge at 

mouth of Mazourka Canyon. Measured section of Vaughn Gulch 

Limestone about 34m stratigraphically below horizon of M1093. 

Rugose coral bed. 

M 1116 .-Independence quadrangle, California. At mouth of 

Mazourka Canyon in measured section in which are localities 

M1092 and M1093. Coral bed about 9-15 m stratigraphically 

below M1093, near top middle unit of Vaughn Gulch Limestone. 

MJJ28.-Independence quadrangle, California. East ofKearsarge at 

mouth of Mazourka Canyon. In measured section about 52 m 

stratigraphically below M1093 in higher middle part of the 

Vaughn Gulch Limestone. Beds with Verticillopora. 

MJ385.-Independence quadrangle, California. Sec. 8, T. 13 S., 

R. 36 E. Vaughn Gulch Limestone, Silurian. Probably same zone 

as locality M1128. Verticillopora. Collected by Craig D. 

Ross, 1961. 

MJ4JO.-Independence quadrangle, California. Mazourka Canyon 

east of Kearsarge in measured section. At top of middle unit of 

Vaughn Gulch Limestone and about 15 m stratigraphically below 

locality M1093. 

Gotland, Sweden 

M1382.-Gotland, Sweden. Hemse Group. Stop 40 of Internat. Geol. 

Cong. guidebook, 1960. Boardman collection, Sept. 10, 1960. 
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Page 

A 

Acinophyllum 27 

Acknowledgments 

Acodina sp _ 

----------------------2 

Acrospirifer kobehana fauna ___ _ 

acus. Monograptus ___ _ 

AI Rose Canyon _____________ _ 

Alaska. southeastern __ _ 

40 

3 

19 

28 

15 

alaskense, Conchidium __________________________ 33 

alaskensis. Conchidium _________________ 15 

Algae, calcareous ____________________ 2, 4, 5, 26,29 

dasycladacean 4, 5. 10. 15, 25, 26, 27. 29 

alternatus, Plectospathodus ----- 40 

Ah•eolites sp ____ _ ----13,15.17 

Amplexoides ________________ _ ---- 31 

Amplexus __ 31 

angustidens, Monograptus 

Retiolltes geillltzianus _ 

annulata, Vertzczllopora 

----------------------- 18 

Antelope Peak 

Antelope Valley 

Antelope Valley Limestone_ 

Antilles. Netherlands ______ _ 

Arachnophyllum 

kayi 

Athyris 

19 

5, 10, 14, 15, 22, 

26, 27; pls.10. 11 

7 

-------- 19 

19, 24, 25 

Atrypa ____________________________ -

10, 27 

5, 22 

27 

------- 27 

sp 5, 10, 15, 17 

August Canyon sequence _______ 23. 24 

August Canyon thrust sequence 19,40 

Aulacophyllum _ 27 

Aulopora _______________________________________ 10 

Australia______ 4, 15,30 

Australophyllum 

landerenszs _______ _ 

steuensi 

15, 29, 34 

27, 34. 35 

-------- 28 

!Australophylluml sp. c ________________ 34; pl. 8 

sp. v ______________________________ 35; pl. 8 

!Toquimaphylluml_ 29, 34, 35 

johnsoni 

sp --------

sp. c __ 

sp. v 

5, 14, 15, 17, 22, 23, 

27, 34, 35; pl. 6 

27 

14, 34, 35 

---------- 27, 34, 35 

IAustralophyllum I sp. c, Australophyllum ____ 34; pl. 8 

sp. v, Australophyllum_____ _ _______ 35; pl. 8 

B 

Badger Flat ------- 28 

Bare Mountain _______________________ 7, 19 

Roberts Mountains Formation ________________ 20 

Barrandella sp _________________ 5, 15 

Barrel Spring 28 

Bastille Limestone Member 23, 40 

Bathurst, R. G. C., cited __ 

Beacon Peak Dolomite Member. 

Nevada Formation __ 

beckmannt, Oneotodus 

3, 10 

40 

Belodella det•onica -------------------------- 40 

resima _ 40 

sp ________________________________________ 40 

Berry, W. B. N., cited_ 2, 11, 13, 19, 28 

berthiaumi, Stylopleura _ 5, 10, 13, 15, 20, 

31, 32; pis. 1, 2 

INDEX 

[Italic page numbers indicate major references] 

Page 

Big Six Mine ___________ ____________ 16. 34 

Bighorn Dolomite, Ordovician ___________________ _ 

Billingsastraea sp. T 25 

Bioherms, scarcity _____________________________ 4 

Birch Creek _______________ _ 

birchensis, Monograptus __ 

7 

19 

bohemicus, Monograptus _________________ 13 

Boone Creek area _________________________ 24 

Bootstrap Hill, Tuscarora Mountains 2. 14, 16, 

30, 31, 32, 33, 34. 41 

Bootstrap Hill section, age ______________________ 17 

lowest coral-brachiopod zone 

mi-ddle coral-brachiopod zone 

physical stratigraphy _ 

stratigraphic paleontology 

16 

17 

16 

16 

upper fossil zone with Carlinastraea __________ 17 

Bootstrap mine area __ ____________ 2, 7, 16 

Boucot, A. J .. cited _____________________________ _ 

Boulder. Creek 16 

Brachiopods __ 4, 5, 8, 10, 14, 15, 16, 17.-18, 20, 26, 27 

dalmanellid_ 13. 17 

pentameroid ______________ 9, 10, 11, 13, 19,20 

rhynchonellid ------------------------------ 20 

silicified ___ ________________ 13 

spiriferoid 

Brachyelasma 

sp. b _ 

sp. c __ 

sp --------------------------

Breccias, depositionaL 

Breviphrentis _________ _ 

IBret•iphrentisl, Siphonophrentis ___ _ 

27 

------------ 30 

16, 31; pl. 12 

13, 31; pl. 5 

5, 11 

5, 13, 14, 15 

------------- 30 

30 

c 

Caesar Canyon Limestone ________________ _ 23.24 

Calcarenite 8 

Calceola sandalina 

Callaghan window 

Calostylis 

--------------- 27 

23,24 

------------ 17 

sp _____ _ _____________________ 17, 32; pl. 7 

Camerotoechia --------------------------- 27 

Carlin, Nev ----------------------------- 3, 41 

Carlin gold ores. Nev _ 2 

Carlin Mine ________________________________ 7, 16 

Carlinastraea _____________________ 13, 14, 17,29,32 

beds 13, 14, 17, 35. 40, 41 

giganteum --------------------------------- 34 

originalis __ _ 

tuscaroraensis 

34 

5, 13. 16. 17, 32, 33: pis. 6. 7. 8 

sp -

[Carlinastraea], Spongophyllum 

Cerro Gordo mining district 

Chert granules _____________________ _ 

nodules 

pl. 8 

33 

4, 25 

18 

26 

chimaera, Monograptus _________________________ 17 

Chonophyllum 15, 27 

simpsoni_ 

Chuckwalla Canyon 

5, 15; pis. 7, 9 

20 

Cladopora 10, 26. 27; pl. 1 

sp. v _______________ _______________ pl. 10 

sp____ 5, 10, 11.13,15,16, 17 

Clear Creek ------------------------------------ 19 

Climacograptus medius ____________________ _ 

scalaris 

11 

11 

Page 

Clinton Group, New York State __________________ 19 

Coal Canyon, fault zone _______________ 11, 12,13. 35 

fault zone, fossils_____ _ _____ 14 

Simpson Park Mountains 2, 5, 11, 13, 

14, 15, 16, 17' 20, 28. 

29. 30, 31, 32. 33, 35, 40, 41 

Coal Canyon area __________________ 11, 15, 40.41 

Coal Canyon basin _ 12 

Coal Canyon fault_ ______________ 29, 30,32 

Coelospira _________ ---------------------------- 17 

sp. b __________________ 16, 17; pl. 12 

sp ___ _________ _____________ 10, 17 

Coenites sp _______________________ 17 

colonus, Monograptus _________ _ 

Conchidlllm ________________ _ 

alaskense 

alaskenszs 

13 

9, 20 

33 

15 

miinsteri ____________ 10; pl. 12 

sp. b 16; pl. 12 

sp ______________ _ _____________ pl. 12 

Conodonts ________ 2, 4, 11, 15, 16. 18. 19, 26, 28,29 

Copenhagen Canyon________________ 3, 7. 11, 18,40 

Roberts Mountains Formation, age ___________ 18 

stratigraphic paleontology _______________ 18 

Copenhagen Formation ____ 19, 24, 25 

Coral zone E. age ____________________ 4 

Coral zones. reference section ____________________ 10 

Corals_________ 2, 4, 5, 8, 14, 16, 20. 22,24 

dissepimented _____________________________ 29 

nondisspimented ___ _ __________________ 29 

pycnostylid _______________________ 27 

rugose_ 1, 2, 5, 9. 10, 13. 14, 15, 20, 26, 27, 29 

age value _____________________________ 29 

cerioid _ 32 

colonial 2, 9, 17. 20. 26, 29, 32 

key ___________________________________ 29 

lykophyllid 32; pl. 12 

special stratigraphic value ______________ 29 

stratigraphic value ______________________ 29 

zonation____________ 28 

silicified ____________________________________ 13 

streptelasmids 5 

tabulate_____________________ 9. 10, 20,27 

alveolitid ------------------------------ 16 

Cordilleran belt ______________ 32,33 

Cordilleran geosynclinal seaway _______ 1 

Cortez gold or.es, Nev ___________________ ________ 2 

Cortez Mountains 

Cortez quadrangle 

3, 7, 34 

3.4 

crateroides, Mucophyllum ______________________ 15 

Crawford, J.P., cited ______________________ _ 

crau{ordi, Neomphyma 

Cress, Leland, cited_ 

Crinoids_ 

5, 22 

2 

4, 8, 14. 17, 26,27 

Cryptatrypa ____ _ --------------------- 17 

sp ------------------

Cyathopaedium _ 

---------------- 17 

31 

Cyathophylloides __________________ _ --10,17,27,31 

ferguson~ __________________ ------

sp. f ___________ _ 

5, 17. 22,31 

16. 31; pl. 12 

Cyrtograptus sp ____________________ 19 

Cystihalysites_ _ __ ______ __ ______ 11 

ICystihalysitesl magnitubus, Halysites 5 

Cystiphyllum sp -------------------------------- 11 

Cystiphylloids __________________________ 27 

47 
48 

Page 

D 

Dalmanella sp __ ---------------- 5 

Dalmanophyllum _________ ______ __ 10, 26 

sp. A __________________ 5. 27 

Daly, R. A., cited___ ________________ ___________ 6 

denayensis, Denayphyllum _______________ _ 5, 10 

Denayphyllum denayensis 5, 10 

denckmanni. Ozarkodina 

Devonian System _ 

deuonica, Belodella 

det•onicus, Scolopodus 

Dicoelosia sp. r _ 

sp-

----------------- 40 

10 

------------ 40 

-------- 40 

5, 10: pl. 11 

5, 10 

Dinant Basin, Belgium, standard ________________ 29 

Diplophyllum ______________________________ 10,27 

Dobbin Summit, Monitor Range__________________ 7 

Monitor Range, 

Roberts Mountains Formation 

Dolomite _ 

-- 19 

1, 3, 8, 9 

6 

6 

diagenetic origin ___ _ 

eastern belt 

facies ______ _ 

origin _ _ ______________ _ 

3,10 

6 

Great Basin, Silurian ____________________ _ 

Guelph, Ontario ________________ 31 

hydrothermal type ___________ __________ 6 

lithographic _ ___________ ________________ 23 

marine, origin 6 

penecontemporaneous___ _ __________ _ 

problem ___ _ _____________________ _ 

reefs_ 

regional_ 

regional problem __ _ 

saccharoidal ____ _ 

4 

6,7 

6 

Dolomite belts, Great Basin, distribution 6 

Dolomitization 7. 26 

metasomatic 

regional __ 

Dry Canyon, Toiyabe Range _ 

Dry Creek area 

dubius, Monograptus ____ _ 

duncanae, Tryplasma 

E 

Eantiognathus lipperti 

East Northumberland Canyon 

Eastern dolomite belt ____ _ 

---------- 23,24 

13. 17, 19, 28 

5, 10, 13, 17,31: pl. 3 

----------- 40 

---------- 20, 23 

1, 7, 10, 19, 20 

Eatonia ------------ 27 

sp 

elegans, Pycnostylus 

Rotundacodina __ _ 

Elko County _ 

Ely Springs Dolomite __ _ 

Endophyllidae _ 

Endophyllum _ 

enorme, Rhizophyllum __ _ 

Entelophylloides 

IProhexagonaria I occidentalis 

Entelophyllum 

---------- 10 

---------- 31: pl. 1 

------- 40 

3, 7, 16 

20.25 

29, 32,34 

35 

5, 15 

32 

5. 10 

-------- 20 

eosteinhornensis, Spathognathodus_ 

Eureka County 

40 

3, 16, 20 

10, 30 

19 

Eureka district __ _ 

Eureka Quartzite 

Evans, J. G., cited 

Evans and Mullens, unnamed Devonian 

limestone unit _ 

excauatus, Neoprioniodus __ 

extensus, Plectospathodus 

Fairbridge, R. W., cited 

Fardenia sp. b _ 

Fault, thrust 

Favistella __ _ 

Fat•istina_ 

Fal'Osites 

sp. c _ 

sp. d 

sp ---

Favositids 

F 

16 

----------- 40 

40 

6 

16; pl. 12 

16 

31 

31 

11, 13, 17, 24, 26, 27 

pl. 10 

------ pl. 10 

13, 15, 16 

10, 26, 27 

INDEX 

fergusoni, Cyathophylloides __ 

Fish Creek Range _________ _ 

Page 

5. 17, 22, 31 

20 

flemingii. Monograptus 19 

Fletcheria ___ ---------------· __________________ 31 

tubifera ______________________________ 31: pl. 3 

Fletcherina ___ ________________________ 31 

Fossils ___________________ 9 

Coal Canyon fault zone _ 14 

Mullens section ----------------------------- 16 

Pyramid Hill _______________________________ 14 

silicified __ 

unit 1 

------------ 8, 14, 16, 17, 20 

10 

unit 2 ___ ---------------------------------- 10 

unit 3 10 

foueolatus, Polygnathus _________________________ 40 

furnishi. Pelehysgnathus 40 

Fye Canyon area _______________________________ 11 

G 

gaertneri, Ozarhodina ___________________ 40 

Gala beds, England______________________ 19 

Gatecliff Formation __ 

Gazelle Formation 

geinitzianus angustidens, Retiolites 

23,40 

15, 34 

19 

giganteum, Carlinastraea 34 

Glassia ________________________ 17 

sp ----------- ---------------------------- 17 

Gold __ _ 3 

Gothograptus spinosus ____________________ 19 

Gotland, Sweden _________ 34 

corals 2, 30 

reefs ______ 4. 5 

rugosa___ _______________________ 4, 15 

standard ___ 27, 29 

Graptolite facies ____________________________ 24,25 

Graptolite standard, age _____ _ ______________ 17 

Graptolite zonation_________________ 28 

Graptolites ________________ 1, 4, 9, 10. 11, 13, 14, 15. 

17' 18, 19, 22, 23, 24, 25. 26, 28, 29 

Great Basin 4, 28 

Grays Canyon Limestone Member, 

Nevada Formation 

Graywacke belt, Pacific belt_ 

Great Basin. brachiopods 

30 

4 

chert sequences __ 

conodonts 

------------------- 11 

4 

coral zonation, Silurian _______ _ 

Silurian, reference section ___ _ 

4, 26 

10, 14 

deposi tiona! facies belts __________ _ 1 

dolomite belts, distribution __________________ 6 

eastern dolomite belt 

graptolites 

1, 7, 10, 19, 20 

4, 28 

intermediate limestone belt___ 1, 7. 10, 19, 

20, 25, 28, 29, 32 

limestone facies ___________________________ 4 

Silurian ________ _ __ 32 

Lower Devonian, paleontologic zoning 4 

reference sections ______________ 4 

Rugosa, dissepimented _____________________ 32 

Silurian, coral zone A __ 

coral zone B ___________ _ 

4, 10, 16, 17, 

22, 26, 27, 28, 31 

4, 10, 27, 28 

coral zone C 4. 9, 10, 11, 31 

coral zoneD _________ 4, 9, 10, 11, 13, 16, 17, 

20, 22, 26, 27, 30, 31, 32, 34 

coral zone E ________ 4, 11, 13, 14, 15, 16, 17, 

22, 23, 26, 27, 29, 32, 34, 35 

limestones_ 

distribution 

------------------ 4 

6 

paleontologic zoning 4 

Great Britain __ _______________________ 30 

Great Lakes, reefs ______ _______________________ 4 

Grouse Creek 11 

Grouse Creek Canyon ______________ _ ----------- 11 

Guelph Dolomite, Guelph, Ontario 31 

guelphensis, Pycnostylus ___________________ 31; pl. 1 

Gypidula _ _______________ _____________ __ 27 

sp. r _ 

sp 

---------------- 5, 10: pl. 11 

-------------------- 13,17 

Gypsum __ _ 

Page 

H 

Halliidae _______________________________ _ ------ 27 

Halysites ___________________________________ 10, 11 

(Cystihalysitesi magnitubus __________________ 5 

sp ---------------------------------------- 5, 10 

Hanson Creek dolomite _________________________ 12 

Hanson Creek Formation__ 3, 9, 11, 18, 19, 22, 24 

Hanson Creek limestone__________ 12, 13 

Heliolites ___ 10, 26, 27 

sp _____________________________ 5, 10, 16,20 

Hemse Group 

Hercynella 

hercynicus, Monograptus 

31 

pl. 10 

19, 25 

Hexagonaria 25 

Hibbardella sp ---------------------------------- 40 

Hidden Valley Dolomite ____________ 4, 25, 26, 27,28 

Hindeodella sp ---------------------------------- 40 

Hindia 26 

Homoeospira sp. r _______________ 5, 10: pl. 11 

Horse Creek Valley quadrangle_ 3, 4, 11 

Howellella sp____________________ 17 

Hsu, K. J., cited __ ___________________ 6 

huddlei, Icriodus latericrescens 40 

Humboldt River Valley ______ _ 

Icriodus latericrescens __ ________________________ 40 

latericrescens huddlei ________________________ 40 

subsp. B ------------------------------- 40 

sp _________________________ 40 

Ikes Canyon ______ _ 

Ikes Canyon window _ 

20, 22, 32, 34, 35 

-------------- 22, 23. 24 

August Canyon sequence ________________ 23, 24 

June Canyon sequence ______________________ 22 

Mill Canyon sequence _____ 22, 23, 24, 31, 34, 35 

inclinatus inclinatus, Spathognathodus_ 40 

inconstans, Trichonodella _ _ __________ _ 40 

Independence quadrangle _____________________ _ 25 

Independence Range 

Intermediate limestone be It _____ _ 1, 7. 10, 19, 20, 

25, 28, 29, 32 

International Stratigraphic Commission 28, 29 

Introduction _______________ ____________ 1 

Investigation, history---------------------------- 3 

purpose ______ __ ______ ____ ________ __ __ _ _ __ __ 2 

&0~ 2 

Inyo Mountains, Calif_____ 1, 2, 4, 7. 15, 18, 28,35 

limestones---------------------------------- 25 

Inyo Range_ _________________ 7 

Isorthis sp _ ------------------------- 13 

J 

jaculum, Monograptus _____ 19 

Johnson, J. G., cited ____________________________ 2 

johnsoni, Australophyllum (Toquimaphyllumi __ 5, 14, 

15, 17, 22, 23,27, 34,35: pl. 6 

June Canyon sequence ______________________ 22, 23 

Kay, Marshall, cited 

hayi, Arachnophyllum 

K 

3 

5, 22 

Kennett Formation------------------------------ 26 

Ketophyl/um ___________ 34 

sp. t _____________ 34: pl. 10 

Klamath Mountains, Calif ___ 15, 30, 34 

Klamathastraea ________________________________ 34 

Kleinhampl, F. J., quoted ________________________ 19 

Kodonophyllidae ____________________________ 29, 31 

Kodonophyllinae _____ _ _________________ 29,30 

Kodonophyllum ______________ 15, 17, 29,30 

mu/leri ________________ 5, 15, 29,30: pl. 4 

truncatum _________________________________ 30 

sp. b_ ________________________ 29, 30, 32: pl. 5 

Kozlowshiellina sp. b ___________ 16, 17: pl. 12 

sp. f ___________ 5, 10, 15: pl. 11 

Kyphophyllidae _____________________ 29 

Kyphophyllum __________________ 15, 17, 23,29 

nevadensis _ _ _______________________ 5: pl. 9 

sp. b _____________________________ 17.32: pl. 5 

sp. c ___________ _ _____ 5, 15: pl. 9 
Ky phophyllu m -Continued 

sp. t ___________ _ 

sp 

L 

Laketown Dolomite_ 

Page 

pl. 10 

17, 27 

Lander County---------------------------------- 22 

landerensis, Australophyllum ______________ 27, 34,35 

laterierescens, Icriodus _____________ _ 

huddlei. Icriodus _______ _ 

40 

40 

subsp. B,Icriodus___ _ _______________ 40 

Leptaena sp ________________________ 17 

Leptocoelia ______ ___ _____ __ ______ __ ____ __ ____ ____ 14 

beds ___ ----------------------------- 14 

Ligonodina sp __________________ 40 

Limestone, argillaceous __ 24, 26 

bioclastic ______________ 13, 14, 16, 23, 25, 26,28 

breccia 12, 14, 15 

cherty ______________________________________ 24 

crinoidal __________ 19, 26 

dolomitic _______ ____________________ 8, 10 

facies, Silurian _ ----------- 32 

graptolitic __________ _ -------------- 22,25 

intermediate, Silurian ______________________ 6 

Inyo Mountains, Calif_ _______________________ 25 

marine, reefs________________________________ 4 

Ordovician---------------------------------- 22 

Roberts Mountains _________________________ 22 

Limestones, lnyo Mountains, Calif __________ 25 

Lower Devonian ____________________________ 25 

Silurian ------------------------ 25 

geographic distribution _________________ _ 

lipperti, Eantiognathus _________________ 40 

Lobograptus scanicus _______ 13 

Lonchodina wa1liseri ______________________ 40 

sp --------------------------------- 40 

3, 9, 10 

3 

Lone Mountain _______________________ _ 

saccharoidal dolomites __________ _ 

Lone Mountain Dolomite __ 3, 6, 8, 9, 19, 20, 31 

dolomite facies ________________ 10 

lateral equivalence__________________________ 3 

Roberts Creek Mountain ___________ 3, 10 

saccharoidal ________________ 9 

type section ---- 3, 20 

unit 1 20 

unit 2 ______ 9, 20 

Lone Mountain reeL___ 6 

Lonsdaleia ___ _ __________________________ 33 

Ludlovian faunas __ _ 

Ludlovian Stage, Alaska 

Lykophyllids __________________ _ 

M 

mcal/isteri, Palaeocyclus porpita _ 

11 

15 

32; pl. 12 

Petrozium _________________________________ _ 

McCann Hill Chert, Alaska__ _________________ 33 

McColley Canyon Formation ______________ 10 

McKee, E. H., cited_____ ____________ 2 

McMonnigal Limestone _______________________ 9, 22 

Maggie Creek, Tuscarora Mountains_ 2, 7, 16, 41 

magnitubus. Halysites !Cystihalysites) ____________ 5 

Mahogany Hills -------------------------------- 20 

Maikottia 31 

turkestanica -------------------------------- 32 

spMasket Shale __ _ 

32 

---- 3, 19, 23 

Bastille Limestone Member ______________ 23,40 

Masursky, Harold, cited_ 

Matti, Jonathan C., cited ________________________ 2 

Mazourka Canyon ____________________ 2. 4,25, 28,35 

Mazourka Canyon area _ 28 

media, Ozarkodina ------------------------------ 40 

medius, Climacograptus ________ ____________ __ 11 

Merista sp _____________________ 10, 16 

Meristella sp ---------------------------------- 5, 15 

Microplasma ------------------------------ 10 

migratus, Paltodus _ ---------------------------- 40 

Mill Canyon, Toquima Range __________ 11, 20, 22, 40 

Mill Canyon sequence __________ 22, 23, 24, 31, 34,35 

Miller, J. W., cited _ ______________ __________ 2 

INDEX 

Page 

Monitor Range _________________________ 3, 7, 11, 40 

physical stratigraphy____________ 18 

Roberts Mountains Formation _______________ 18 

Dobbin Summit _____________ 19 

Monograptids 

Monograptus 

22. 23. 24, 28 

17, 24 

acus _____ _____________ _________________ 19 

angustidens ___________________ 18 

birchensis 

bohemicus __ 

chimaera _________ _ 

19 

13 

------------ 17 

co/onus ------------------------------------- 13 

dubius_____________ 13, 17, 19,28 

flemingii __________________ _ _________ 19 

hercynicus __ 

jacu/um ____________________ _ 

19, 25 

19 

19 

19 

19 

nilssoni-Monograptus scanicus Zone 

nudus _________ _ 

pandus 

praehercynicus ____________________ 13. 19, 22, 29 

priodon __________ 19 

riccartonensis Zone __________________________ 11 

scanius __________ 28 

spiralis -------------------- 19 

tumescens 28 

uncinatus ------------------------------- 17, 19 

uniformis ---------------------------- 4, 18,28 

wziformis Zone 2. 15, 18, 29 

uulgaris ------------ ----- 28 

sp --- ------------------ 10, 13, 17, 19, 28 

Mount Callaghan, Toiyabe Range _ __________ 7 

Mount Lewis area ______________________ 3 

Mucophyllum ____ _ __________________ 15,30 

crateroides ______________ _ 

olh•eri 

Mudflats _____________ _ 

Mullens, T. E., cited 

Mullens section _________ _ 

------------------ 15 

5, 15, 30; pl. 4 

7 

------ 2, 16, 17 

16, 17 

mullen·, Kodonophyllum __________ 5, 15, 29, 30; pl. 4 

mu/tiformis, Neoprioniodus 40 

miinsteri, Conchidium ____________________ 10; pl. 12 

Murray, R. C., cited____ ________________ 6 

Mycophyllinae ______________ 29, 30 

N 

Neophyma ____ ______ __ ___ ___ __ ____ __ ______ __ _ __ 33 

crawfordi ____________________ ------ __ ---- 5, 22 

Neoprioniodus excapatus _______________ 40 

mu/tiformis -------------------- 40 

Nevada Formation _______________ _ 

Beacon Peak Dolomite Member ___ _ 

3, 10, 30 

3, 10 

Grays Canyon Limestone Member_ _ _____ 30 

nemdensis, Kyphophyllum _________________ 5; pl. 9 

Stylopleura 5, 15, 17, 22, 32; pl. 2 

newfarmeri, Tryplasma ___________ 5, 10, 31; pl. 3 

Niagaran Series, reefs _____________________ __ 4, 5 

noguerensis, Rotundacodina _____________________ 40 

Northumberland area, Toquima Range 7 

Northumberland window ________________________ 23 

Prospect sequence ________________________ 23 

Striped Hill sequence ________________________ 23 

nudus, Monograptus 19 

0 

occidentalis, Entelophylloides (Prohexagonaria I __ 5, 10 

olh•eri, Mucophyllum __ __________ 5, 15, 30; pl. 4 

Oneotodus beckmanni _ 40 

originalis, Carlinastraea ____________________ 34 

Orthophyl/um sp _______________________________ 10 

Orthostrophia sp ---------------------------- 5, 15 

Ozarkodina denckmanni 40 

gaertneri ____________________________________ 40 

media _____________________________________ 40 

typica 

ziegleri __________ _ 

sp ---------------

p 

40 

40 

40 

Pablo Canyon, Toiyabe Range____________________ 7 

Pablo Canyon area _ _____________ 23,25 

Pacific Border graywacke belt 

Pacific border province 

Palaeocyc/us ---------------

porpzta mcallisteri __ 

Palaeophyllum ______________ _ 

sp. b _______________ _ 

Paleontologic zoning, Great Basin 

Paleozoic rocks 

Paltodus migratus 

sp ------------

49 

Page 

1, 6 

1 

10, 27 

------------ 5 

10, 31 

------------ 20 

4 

-------------- 11 

40 

---------------- 40 

Panamint Mountains_ ____________ 25 

Panderodus sp ________________________________ 40 

pandus, Monograptus _____ ---------··------ 19 

Pelekysgnathus furnishi _ ---------------- 40 

sp --- ------------------ 40 

Pentamerus __________________________________ 20 

Perdido Formation ________________ _ 25 

Persian Gulf ________________ _ ------------------ 7 

Pete Hanson Creek __________ _ 9 

Pete Hanson Creek area ---------------- 10 

Fetes Canyon ________________ 20 

Petes Canyon window _______________________ 22, 24 

Petrozium __ _ 32 

mcallisteri 

Pine Hill ____ _ --------------- -------------- 11, 12 

age ------------ ------- 13 

stratigraphic paleontology ___________________ 13 

Pine Hill section, physical stratigraphy ____ 12, 14, 15 

Plectatrypa sp. c _______________ pl. 11 

sp __________________ 5, 15,27 

Plectospathodus alternatus _____________ 40 

extensus 

sp ----------

Point of Rocks area 

Polygnathus {ot•eolatus 

Porcupine River, Alaska _____ _ 

porpita mcallisteri, Palaeocyclus 

praehercynicus, Monograptus 

Pray, L. C., cited _____ _ 

40 

------------ 40 

23, 24, 25 

40 

-------- 32 

13, 19, 22, 29 

6 

primus, Spathognathodus_ ____________ 40 

priodon, Monograptus _________________ 19 

Prioniodina sp ___ ____________________ 40 

(Prohexagonaria I occidentalis, Entelophylloides __ 5, 10 

Prospect sequence, chert unit __________ 23 

Ptychopleurella sp ____________________ 10, 16 

Pycnactis sp. K _ _________________ ______________ 5 

Pycnostylid _________________________ 10, 14. 15, 31 

Pycnostylidae_______ ____________________ 29.31 

cerioid ____________________ _ ------ 32 

Pycnostylus _ _ ____________________________ 15,31 

elegans _________ __________________ 31; pl. 1 

guelphensis ______ ___________________ 31; pl. 1 

sp. 1 _____________________________ 31; pl. 2 

Pyramid Hill _____ ___________________ 11, 12, 14 

Silurian-Devonian Boundary ________________ 15 

Pyramid Hill section __________________ 13, 14 

physical stratigraphy _______________________ 14 

R 

Rabbit HilL _________ _ 18 

Rabbit Hill Limestone 11, 14, 15, 16, 18, 19, 22, 

23, 27, 34, 40, 41 

Ravenswood area, Shoshone Range _ 

Red Hill __________ -------------------------

Reeds Canyon, Toiyabe Range __________ _ 

7, 25 

11,14 

7, 24 

Reef, Lone Mountain ___________________________ _ 

Reefs, building ________________________________ _ 

core rock_____________ _ ______________ _ 

dolomite______________________ 4 

Gotland, Sweden____________ 4, 5 

Great Lakes 4 

marginal beds ------------------------------ 5 

marine limestone _____________________ 4 

Niagaran Series ___________ 4, 5 

patch ____________________________ 5 

Roberts Mountains Formation, scarcity ________ 4 

scarcity ___________________ ____________ 4 

remscheidensis, Spathognathodus ________________ 40 

Spathognathodus steinhornensis 40 

resima, Belodella ____ __________________________ 40 
50 

Resserella sp 

Page 

17 

19 

20 

Retiolites geinitzianus angustidens _ 

R habdocyclus sp. B 

sp. d 

Rhegmaphyllum sp. h_ 

sp -

Rhizophyllum __ 

enorme 

sp. D 

R hynchospirina sp _ 

Roberts Creek Mountain __ _ 

Roberts Mountains, Nev 

rugosa_ 

Silurian limestones __ 

Roberts Mountains Formation, age 

August Canyon sequence 

Bare Mountain 

black chert unit ___ _ 

Bootstrap Hill section, age 

physical stratigraphy _ 

13, 17 

15, 33 

5, 15 

5, 27 

5, 15 

3, 7, 9, 10, 19 

---- 7, 14 

---- 4 

3 

1, 2, 11, 20 

--- 23, 24 

-- 20 

-- 22, 23, 24, 25 

stratigraphic paleontology ___ _ 

---- 17 

16 

-- 16, 32 

19 

23,24 

18, 19, 20 

--------- 20 

11' 14, 15, 35 

11 

---- 4, 16, 20 

2 

3, 18 

18 

18 

3 

Brock Canyon, Monitor Range __ 

Callaghan window ___ _ 

chert marker 

cherty dolomite member 

Coal Canyon area _ 

Coal Canyon fault zone __ _ 

Coal Canyon section __ _ 

conodonts 

Copenhagen Canyon _______ _ 

age 

stratigraphic paleontology 

Cortez Mountains ____ _ 

Dobbin Summit, Monitor Range 

dolomite facies 

origin 

dolomite problem 

Dry Creek area _______ _ 

facies changes _______ _ 

geologic mapping __ 

geologic setting 

gold __ _ 

graptolite faunas __ 

Great Basin _________ _ 

Ikes Canyon window __ _ 

June Canyon sequence 

lateral equivalence ___ _ 

19 

---- 3,10 

23,24 

------ 10 

--- 2 

11 

3 

---- 3 

1, 4 

---- 22, 23, 24 

------ 22. 23 

3 

limestone _____ _ ----------- 1, 5, 14 

limestone facies 

lithology ____ _ 

--------------- 10 

5, 8, 9, 12, 13, 16, 

18, 19, 20, 23, 24 

lower coral zone with Carlinastraea __________ 14 

Mill Canyon sequence ______ 22, 23, 24, 31, 34, 35 

Monitor Range ____________________________ 18 

physical stratigraphy________ _ _____ 18 

Pablo Canyon area ______________________ 23,25 

Petes Canyon window ___________________ 22, 24 

Pine Hill, age ______________________________ 13 

stratigraphic paleontology _______________ 13 

Pine Hill section______ _ _____ 12, 14, 15 

Point of Rocks area __ 23, 24, 25 

Prospect sequence ___ 23 

Pyramid Hill, Silurian-Devonian 

Boundary, problem _ 15 

Pyramid Hill section ____________ 13, 14 

physical stratigraphy __ _ __________ 14 

redefinition _____ __________ 2 

reefs, scarcity _____________________________ 4 

reference section_____________ 4, 16, 17 

Roberts Creek Mountain _ ______________ 3, 5, 7 

Roberts Mountains, Nev ______________________ 7 

Shoshone Mountains ________ 25 

Shoshone Range __________ _________________ 3 

Silurian limestones__________________________ 4 

Simpson Park Mountains _ ______________ 3, 11 

Straight Canyon area ____________________ 23,24 

stratigraphy____________________ 2, 9, 10, 12, 13 

stratigraphic paleontology___ _ ___________ 10 

stratigraphic relations _____ 9 

Striped Hill sequence_______ 23 

INDEX 

Page 

thickness ____ 9, 12, 13, 14, 16, 18, 19, 20, 22, 25 

Toiyabe Range ________________ __ 23, 25 

Toquima Range_____________________ 3,20, 24 

Tuscarora Mountains _ ---------------- -- 15 

type area ________________ _ ----- 7, 8, 10 

type section 3, 9, 10, 16, 17, 20 

age ___ _____________________________ 10 

unit 1 __ _______________________ 9, 11 

unit 2 _ ________ 9, 10, 11, 20 

unit 3 _ ____________________ 9, 10, 11, 31 

upper coral zone with Toquimaphyl/um ______ 14 

Roberts Mountains thrust_ ________________ 22 

August Canyon sequence 

Ikes Canyon window 

----------- 23 

-------------- 22, 23 

June Canyon sequence _________________ 22, 23 

Mill Canyon sequence _________________ 22, 23 

Northumberland window __ _ ______ 23 

Petes Canyon window__________ _ _________ 22 

Roberts, R. J., cited ____________ _______ 2, 16 

Rocky Hills thrust _____________ 12 

Ross, D. C., cited_____ _ ______________ _ 

Ross. R. J., Jr., cited ___ _ ------------------ 28 

Rotundacodina elegans -- 40 

noguerensis ______________ ---------- 40 

Round Mountain _____ _______________ 25 

Rugosa______ 2, 4, 5, 10, 13, 14, 15, 17, 25, 26, 27,29 

age value ___________________ 29 

assemblages 

Australia 

----------- ---------------- 15, 27 

--------------- 4, 15 

cerioid _____ _ ------------ ----------------- 32 

colonial 2, 9, 17, 20, 26, 29, 32 

dissepimented _____ _ --------------- ----- 32 

eastern Europe ___ _ ---------- 4 

England ___ _ --------------- 4 

Gotland, Sweden _ 

key 

----------- ------- 4, 15 

---------- 29 

Klamath Mountains, Calif _____________ 15 

lykophyllid ____________ 32: pl. 12 

nondissepimented, Silurian ---------- 29 

pycnostylid _____________ 10, 14, 15 

Silurian ____ ________________ 4, 15 

Silurian, stratigraphic distribution_______ ____ 4 

special stratigraphic value _________ 29 

stratigraphic value _____ _ 

zonation _ 

Ryderophyllum ubehebensis _ 

s Salairophyllum __ 

sp -

Salopina ________ _ 

sp -------

sandalina, Ca/ceola ___________ _ 

scalaris, Climacograptus 

scanicus, Lobograptus _ 

scanius, Monograptus _______ _ 

Schellwienella sp __ 

Schizophoria __ 

Schlotheimophyllum 

Schneider, J., cited _________ _ 

Schuchert, Charles. cited 

Sco/opodus devonicus __ _ 

sedgwicki, Spongophy/lum __ 

Shales, graptolitic __________________ _ 

Shale-graywacke facies 

----- 29 

28 

-------- 5 

------- 15, 33 

5 

17 

17 

27 

11 

13 

28 

5, 15 

---- 27 

15, 30 

6 

-------- 6 

-------- 40 

32, 33: pl. 6 

16 

Shoshone Mountains, Nev _________ ______________ 2 

Shoshone Range _____________________ _ 

Sicorhyncha sp _____________ _ ------- 5, 15 

Silurian-Devonian boundary _________ 1, 2, 11, 15, 17 

central Nevada__ 28 

problem _________ 15 

Pyramid Hill __ --------- 15 

Silurian-Devonian Boundary Committee ______ 28, 29 

Silurian limestone, Great Basin, distribution______ 6 

Silurian limestones, geographic distribution _____ _ 

Silurian System ___ 4, 10, 15, 19, 26, 31 

Silurian zone 5b, Norway ________________________ 10 

Simpson Park Mountains _________ 2, 3, 7, 14, 16, 17, 

32, 35, 40 

simpsoni, Chonophyllum _____________ 5, 15; pis. 7, 9 

Page 

simpsoni, Chonophy/lum-Continued 

Tonkinaria __ _ _____________ 5, 10, 13, 32; pl. 5 

Siphonophrentis !Breviphrentis) ------------ _____ 30 

Skeats, E. W., cited___ ___________ ______________ 6 

Spathognathodus eosteinhornensis ____ ________ 40 

inclinatus inclinatus ____ 40 

primus _________ ___________________________ 40 

remscheidensis _________ 40 

steinhornensis remscheidensis _______________ 40 

transitans ___ _ 

sp --

spinosus, Gothograptus _____________ _ 

40 

40 

19 

spiralis, Monograptus ____________ _______________ 19 

Sponge__ ____________ __________________ 26 

Spongophyllidae ________________________ 29, 32 

Spongophylloides _______________________ ------- 33 

Spongophyllum _____________________ 17, 32,33 

sedgwicki __ __________________ 32, 33; pl. 6 

[Carlinastraea] __________ ---------------- 33 

sp. A _______________ _ _______ 33 

sp. B _____________________________________ 33 

Stauriidae ________ _ __________________________ 31 

Steidtmann, Edward, cited __________ ________ 6 

steinhornensis remscheidensis, Spathognathodus __ 40 

Stevens, C. H., cited _____________ ______________ 2 

stevensi, Australophyllum ________________ ------- 28 

Stewart, J. H., cited _________ ------------

Straight Canyon area _______________________ 23,24 

Strepte/asma ______________ ----------- ------- 20 

Streptelasmatidae _______ ------------------- 30 

Striatopora sp _ _ ___________ _ ------------ 13 

Striped Hill sequence ______ _ ------- 23 

Stromatoporoids ______ 4, 5, 15, 26, 27 

Stylopleura _____ _ ____ 13, 14, 15, 17,31 

berthiaumi ______ 5, 10, 13, 15, 20, 31, 32; pis, 1, 2 

nevadensis _______________ 5, 15, 17, 22, 32; pl. 2 

sp. b ___________________ 17, 32; pl. 1 

sp. c ______________________ 13, 14, 32; pis. 1, 2 

sp. T ______________________________________ 32 

sp --- -------------- 20 

Sunday Canyon Formation _____ 2, 27,28 

age _____________________________________ 28 

Swales Mountain ___________ 7 

Synprioniodina sp _________ _ 

Syringaxon 

sp- -----------

Syringopora _____ _ 

sp 

Tabulophyllum _______ _ 

Tentaculites 

Thrust fault 

Thrust plates 

Toiyabe Range 

Tonkinaria ____________ _ 

T 

40 

------------ 14 

17 

27 

13 

------------ 34 

----------- 14 

------------ 16 

18, 19, 22, 23, 24 

2, 18, 23, 25 

------------ 13 

simpsoni 

sp ---

----------- 5, 10, 13, 32; pl. 5 

-------- 22 

Toquima Range_____ 2, 3, 7, 11, 17, 18, 19, 

23, 24, 25, 34, 35, 40 

Ikes Canyon area _______________________ 32, 35 

Mill Canyon sequence ______ 22, 23, 24, 31, 34, 35 

Roberts Mountains Formation _________ 3, 20, 24 

Toquimaphyllum __ _ ______ 14, 15, 34, 35 

beds __ __ __ _ _ __ __ _ _ _ _ _ _ __ _ _ _ _ __ _ _ _ _ __ __ _ _ _ _ _ _ 13 

(Toquimaphyllum!, Australophyllum ______ 29, 34, 35 

johnsoni, Australophyllum __________ 5, 14, 15, 17, 

22, 23,27, 34, 35; pl. 6 

sp., Australophyllum _ ___________ 27 

Tor Limestone _ ------------------------------ 22 

Torquay, Devonshire, England ____________________ 33 

transitans, Spathognathodus ______ _______________ 40 

Trematospira ____ ------------------------------- 27 

sp _________________________________________ 17 

Trichonodella blanda ___________________________ 40 

inconstans __________________________________ 40 

sp _____________ 40 

Trilobite ________________________________________ 26 

cryptolithoid ___ ---------------------------- 24 

truncatum, Kodonophyllum ______________________ 30 
Page 

Tryp/asma ---------------------------- 10, 13, 33 

duncanae ________________ 5, 10, 13, 17, 31; pl. 3 

newfarmeri 5, 10, 31; pl. 3 

sp. g _ ___________________ 31; pl. 3 

sp ____________________ 13,17 

Tryplasmatidae _ _ _ _ 29, 31 

Tryplasmid _ _ ___________ 27, 31 

tubifera. F/etcheria ________________ 31; pl. 3 

tumescens, Monograptus ______ ___________________ 28 

turkestanica, Maikottia __________________________ 32 

Tuscarora Mountains, Nev __ _ 

tuscaroraensis, Car/inastraea 

typica, Ozarkodina 

u 

2, 3, 7, 9, 11, 

15, 16. 30, 34, 41 

5, 13, 16, 17, 

32, 33; pis. 6. 7, 8 

40 

ubehebensis, Ryderophy/lum _ ____________ 5 

Ulrich, E. 0., cited _____________________________ _ 

uncinatus, Monograptus ____________ _ 

uniformis, Monograptus ____ _ 

Ural Mountains, U.S.S.R _ 

17, 19 

4, 18, 28 

15, 33, 34 

INDEX 

Page 

v VanTuyl, F. M .. cited ____________ ___________ 6 

Vaughn Gulch ______________________ 25 

Vaughn Gulch Limestone __ 1, 15, 18, 25, 34, 35 

age _______________________________________ 27 

black chert zones_ _______________ __ 25 

chert member 

coral zone A 

coral zone E _ 

-------- 26 

------------ 27 

------ 27 

lower division _______________ _ ___ 26 

middle division ____________________________ 26 

physical stratigraphy__ _ __________ 25 

stratigraphic paleontology ___________________ 26 

thickness _______________ _____________ 26 

type section_ 

upper, fossils _______________ _ 

25,26 

-- 27 

upper division __ _ __________________ 26 

Verticil/opora beds _________________________ 27 

Vaughn Gulch limestone unit ____________ 15 

Verticz/lopora 

ranges _ 

annulata 

4, 15, 26, 27, 29 

-------- 4 

5, 10, 14, 15, 22, 26, 27; pis. 10, 11 

Fertici//opora-Continued 

sp ------- ---------------

Vinini Formation __________ _ 

Virgiana sp 

uulgaris, Monograptus _ 

w 

Wall Canyon, Toiyabe Range 

51 

Page 

5; pl. 10 

11, 16 

20 

28 

wallisen, Lonchodina ________________________ 40 

Water Canyon ----------------------------- ____ 23 

Wenban Limestone------------------------------ 9 

West Northumberland Canyon ___ 20 

Western graywacke belL _______________________ _ 

Willow Creek ________________________ _ 

Windmill Limestone 9, 11, 13, 14, 16, 19, 40 

Y, Z 

Yassia _______________________ _ 

Zelophyllum sp _______________________ _ 

ziegleri, Ozarkodina ______ _ 

----- 32 

24 

40 

PLATES 1-12 

[Contact photographs of the plates in this report are available, at cost, from the U.S. Geological Survey Photographic Library, 

Federal Center, Denver, Colorado 80225] 
FIGURES 

PLATE 1 

1-9. Stylopleura berthiaumi Merriam 

1-6. Great Basin Silurian coral zone D. Roberts Mountains Formation, unit 3. Locality 

MllOO, Roberts Creek Mountain, Nev. 

1. View of broken calice interior showing three offsets. Para type, USNM 159384a. x 2. 

2. Lateral view of two corallites from a large colony (paratype USNM 165359) showing 

connecting elements. x 1. 

3. Calice view showing multiple calice budding. Para type USNM 159383. x 2. 

4. Partial lateral view of holotype. USNM 159382. x 1 Y2. 

5. Partial lateral view of paratype showing lateral element attached to Cladopora 

branch. USNM 159384. x 1. 

6. Longitudinal thin section. USNM 165358a. x 2. 

7-9. Great Basin Silurian coral zone E. Roberts Mountains Formation. Locality M1106, 

Coal Canyon, Simpson Park Mountains, Nev. USNM 159385. x 1. 

7. Lateral view. 

8. Calice view. 

9. Partial interior view showing calice offsets. 

10-12. Stylopleura sp. b 

10-11. Silurian Roberts Mountains Formation. Locality M1314, Bootstrap Hill, Tuscarora 

Mountains, Nev. 

10. Lateral view of broken corallite. x 1%. 

11. Lateral view of piece of corallite showing base of hollow lateral element. x2. 

12. Longitudinal thin section. x2. Silurian. Roberts Mountains Formation. Locality 

M1315, Bootstrap Hill, Tuscarora Mountains, Nev. 

13--15. Stylopleura sp. c, cf. S. berthiaumi 

Great Basin Silurian coral zone D. Roberts Mountains Formation. Locality M1317, Coal 

Canyon, Simpson Park Mountains, Nev. x2. 

13. Longitudinal thin section. 

14, 15. Transverse thin sections. 

16, 17. Pycnostylus guelphensis Whiteaves? 

Longitudinal and transverse sections. x2. Unenlarged copies of plate X, figures 4, 4a in 

Lambe (1901 ). Silurian, Guelph Dolomite; Ontario, Canada. 

18, 19. Pycnostylus guelphensis Whiteaves. 

Unenlarged copies of two ofWhiteaves' type illustrations (Whiteaves, 1884, pl. 1, figs. 1a, b). 

Silurian, Guelph Dolomite; Ontario, Canada. x 1. 

18. Transverse section of corallum. 

19. Lateral view of broken corallite with two remaining offsets; note lack of exterior 

longitudinal ribbing. 

20. Pycnostylus elegans Whiteaves. 

Anterior end of a mature corallite with several offsets. Note external ribbing. x 1. Unenlarged copy of one of Whiteaves' (1884) type illustrations. 

Silurian, Guelph Dolomite; Ontario, Canada. 
GEOLOGICAL SURVEY PROFESSIONAL PAPER 973 PLATE 1 

9 

7 8 

20 

17 

3 

5 

10 

16 

11 12 

18 

13 14 15 19 

STYLOPLEURA AND PYCNOSTYLUS 
FIGURES 

PLATE 2 

1, 2. Stylopleura? sp. c 

Transverse and longitudinal thin sections. x2. Silurian, Roberts Mountains Formation. 

Locality M1379, Coal Canyon, Simpson Park Mountains, Nev. 

3-6. Stylopleura neuadensis Merriam 

Great Basin Silurian coral zone E. Roberts Mountains Formation. Coal Canyon, Simpson 

Park Mountains, Nev. 

3, 4. Longitudinal and transverse thin sections of same colony. Paratype, USNM 

159431a. x 2. Locality M1380. 

5. Upper surface of holotype, USNM 159431. x '12 . Locality M1107. 

6. Longitudinal thin section of holotype showing a lateral connecting element. USNM 

159431. x2. Locality M1107. 

7. Stylopleura cf. S. neuadensis n. gen., n. sp. 

Longitudinal thin section. x2. Great Basin Silurian coral zone E. Roberts Mountains Formation. Locality M1381 , Coal Canyon, Simpson Park Mountains, Nev. 

8, 9. Sty lopleura berthiaumi Merriam 

Great Basin Silurian coral zone D. Locality M1103, Ikes Canyon, Toquima Range, Nev. 

8. Lateral view of flaring calice. x 1. 

9. Lateral view of same individual showing connecting element. x 1. 

10. Pycnostylus sp. 1 

Longitudinal thin section. x3. Silurian, Lone Mountain Dolomite. Locality M1148, southern Sulphur Spring Mountains, Nev.; 4.8 km south of Romano Ranch. 
GEOLOGICAL SURVEY PROFESSIONAL PAPER 973 PLATE 2 

3 

4 

7 

6 

2 

9 

10 

STYLOPLEURA ANDPYCNOSTYLUS 
FIGURES 

PLATE 3 

1-7. Fletcheria tubifera Edwards and Haime. 

1. Lateral view of cora!lum. Copy of original type figure of Edwards and Haime (1851, pl. 

16, fig. 5). Silurian, Gotland, Sweden. x 1 Yz . 

2-7. Silurian, Slite Group (Wenlockian); Slite, Liinnaberget, Gotland, Sweden. 

2. Lateral view of corallum showing corallite surface ornamentation. x2. 

3. Transverse thin section. x 2. 

4, 5. Longitudinal thin sections. x2. 

6, 7. Transverse sections showing multiple calice offsets and wall structure. Note absence of septa. x6. 

8, 9. Tryplasma duncanae Merriam 

Great Basin Silurian coral zone D. Roberts Mountains, Formation, unit 3. Locality MllOO, 

Roberts Creek Mountain, Roberts Mountains, Nev. 

8. Lateral view of holotype , USNM 159374. x2. 

9. Oblique cal ice view of para type, USNM 159375. x5. 

10-15. Tryplasma newfarmeri Merriam 

Great Basin Silurian coral zone C. Roberts Mountains Formation, unit 3. Locality M1102, 

Roberts Creek Mountain, Nev. 

10, 11. Longitudinal thin sections of holotype, USNM 159377. x3. 

12, 13. Longitudinal thin sections of holotype, USNM 159377. x8. 

14, 15. Transverse thin sections ofholotype, USNM 159377. x8. 

16-19. Tryplasma sp. g 

These figures are a ll of the same corallum. Silurian, Hemse Group (Ludlovian); locality 

M1382, Gotland, Sweden. 

16. Transverse thin section. x2. 

17. Transverse thin section. x4. Enlargement of part of figure 16. 

18, 19. Longitudinal thin sections. x2. 
GEOLOGICAL SURVEY PROFESSIONAL PAPER 973 PLATE 3 

2 

9 

7 

15 

18 

8 

16 

13 12 10 

FLETCHER/A AND TR YPLASMA 
FIGURES 

PLATE 4 

1-4. Mucophyllum oliueri Merriam 

Great Basin Silurian coral zone E. Locality Mll08, Coal Canyon, Simpson Park Mountains, Nev. 

1. Longitudinal section of para type , USNM 159391. Photographed in water. x 1. 

2. Transverse section of holotype, USNM 159390. Smoothed surface photographed in 

water. x 1. 

3. Longitudinal thin section of holotype, USNM 159390. x4. 

4. Part of transverse thin section of holotype, USNM 159390, showing pattern of 

trabeculae. x 2. 

5, 6. Kodonophyllum mulleri Merriam 

Transverse and longitudinal thin sections of holotype, USNM 159386. x4. Great Basin 

Silurian coral zone E. Locality Mll07, Coal Canyon, Simpson Park Mountains, Nev. 
GEOLOGICAL SURVEY PROFESSIONAL PAPER 973 PLATE 4 

MUCOPHYLLUM AND KODONOPHYLLUM 
FIGURES 

PLATE 5 

1-14. Tonkinaria simpsoni Merriam 

1- 9. Great Basin Silurian coral zone D. Roberts Mountains Formation, unit 3. Locality 

M1100, Roberts Creek Mountain, Roberts Mountains, Nev. 

1, 2. Lateral (x1V2) and calice (X2) views ofparatype, USNM 159402. 

3, 4. Transverse (X4) and longitudinal (x3V2) thin sections ofparatype, USNM 159404. 

5. Transverse thin section. USNM 159405. x2. 

6. Calice view. x 2. 

7. Longitudinal thin section of same individual. x3. 

8, 9. Lateral exterior and calice views of holotype, USNM 159403. x 1 V2 . 

10--14. Great Basin Silurian coral zone D. Roberts Mountains Formation. Locality M1383; 

Coal Canyon, Simpson Park Mountains, Nev. 

10. Oblique lateral view of corallum showing bases of three offsets at cal ice rim. x2. 

11-13. Calice rim of three coralla showing offsets. x2. 

14. Calice view. x2. 

15--21. Kyphophyllum sp. b 

Silurian, Roberts Mountains Formation. Locality M1314; Bootstrap Hill, Tuscarora Mountains, Nev. 

15. Lateral view of coral lite showing a single offset. x 2. 

16. Lateral view of partial corallum x2. 

17. Lateral view ofcalice interior. x2. 

18, 19. Transverse and longitudinal thin sections of corallite. x 3. 

20, 21. Transverse and longitudinal thin sections of corallite. x3. 

22--24. Kodonophyllum sp. b. 

Transverse and longitudinal thin sections of three corallites. x 3. Silurian, Roberts Mountains Formation. Locality M1314, Bootstrap Hill, Tuscarora Mountains, Nev. 

25, 26. Brachyelasma sp. c. 

Transverse and longitudinal thin sections of same individual. x 1 V2. Great Basin Silurian 

coral zone D. Roberts Mountains. Formation. Locality M1383; Coal Canyon, Simpson 

Park Mountains, Nev. 
GEOLOGICAL SURVEY 

4 

10 

23 

22 

24 

• 

. . 

. 

5 

PROFESSIONAL PAPER 973 PLATE 5 

11 

18 

7 

9 

21 

25 

16 17 

TONKINARIA, KYPHOPHYLLUM, KODONOPHYLLUM, AND BRACHYELASMA 
FIGURES 

PLATE 6 

1-4. Spongophyllum sedgwicki Edwards and Haime. 

Copies of original figures of the type material of Edwards and Haime (1850--54, pl. 56, figs. 

2a, c, d, e). Torquay, England; according to Edwards and Haime from the Devonian strata. 

1. Transverse section enlarged (Edwards and Haime, fig. 2d, x 1 'h). 

2. Longitudinal section enlarged (Edwards and Haime, fig. 2e, x 1 'h). This section is 

conceivably from same corallum as figure 1. 

3, 4. Transverse sections enlarged (Edwards and Haime, figs. 2c and 2a, x 1 Y2). These 

figures probably do not represent the same species and are possibly not congeneric 

with corals illustrated by figures 1 and 2 of this plate. 

5--7. Carlinastraea tuscaroraensis n. gen., n. sp. 

5. Transverse thin section. x3. Great Basin Silurian coral zone D. Roberts Mountains 

Formation. Locality M1384, Coal Canyon, Simpson Park Mountains, Nev. 

6, 7. Transverse and longitudinal thin sections of holotype, USNM 166482. x21/2. Roberts 

Mountains Formation. Locality M1313 , Bootstrap Hill. 

8--10. Australophyllum (Toquimaphyllum)johnsoni Merriam 

Transverse and longitudinal thin sections of holotype, USNM 150420. x2. Great Basin 

Silurian coral zone E. Locality M1114, Ikes Canyon, Toquima Range, Nev. 
GEOLOGICAL SURVEY PROFESSIONAL PAPER 973 PLATE 6 

3 

6 

2 

5 7 

4 9 

10 8 

SPONGOPHYLL UM, CARLINASTRAEA, AND A USTRALOPHYLL UM 
FIGURES 

PLATE 7 

1-4. Carlinastraea tuscaroraensis n. gen., n. sp. 

1-3. Transverse and longitudinal thin sections of holotype, USNM 166482. x6. Roberts 

Mountains Formation. Locality M1313, Bootstrap Hill, Tuscarora Mountains, Nev. 

4. Longitudinal thin section. x 6. Great Basin Silurian coral zone D. Roberts Mountains 

Formation. Locality M1384, Coal Canyon, Simpson Park Mountains, Nev. 

5, 6. Chonophyllum simpsoni Merriam 

Transverse a nd longitudinal thin sections of holotype, USNM 159408. x 1 Vz. Great Basin 

Silurian coral zone E. Roberts Mountains Formation. Locality Mll08, Coal Canyon, 

Simpson Park Mountains, Nev. 

7, 8. Calostylis? sp. 

Transverse thin sections. x 3. Roberts Mountains Formation. Locality M1314, Bootstrap 

Hill, Tuscarora Mountains, Nev. 
GEOLOGICAL SURVEY PROFESSIONAL PAPER 973 PLATE 7 

2 

3 

4 

7 

8 

CARLINASTRAEA, CHONOPHYLLUM, AND CALOSTYLIS? 
FIGURES 

PLATE 8 

1, 2. Carlinastraea sp., cf. C. tuscaroraensis, n. gen., n. sp. 

Transverse and longitudinal thin sections of same cor all urn. X 2. Roberts Mountains Formation. Locality Ml409, Cortez Mountains, Eureka County, Nev. 

3-7. Australophyllum (Australophyllum ) sp. c 

Locality Ml318, west side of Coal Canyon in fault zone, Northern Simpson Park Mountains, Nev. All the thin sections are from same corallum. 

3-5. Transverse thin sections. x 2. 

6, 7. Longitudinal thin sections. x 2. 

8-11. Australophyllum (Australophy llum ) sp. v 

Vaughn Gulch Limestone. Mazourka Canyon, northern Inyo Mountains, Calif. 

8, 9. Transverse and longitudinal thin sections of same corallum. x 2. Locality Ml410. 

10, 11. Transverse and longitudinal thin sections of another corallum. x2. Locality 

Ml093. 
GEOLOGICAL SURVEY PROFESSIONAL PAPER 973 PLATE 8 

3 

4 

2 

5 

8 6 

10 

9 11 7 

CARLINASTRAEA AND AUSTRALOPHYLLUM 
FIGURES 

PLATE 9 

1-3. Kyphophyllum neuadensis Merriam 

Great Basin Silurian coral zone E. Locality M1114, lkes Canyon, Toquima Range, Nev. 

Holotype, USNM 159425. 

1. Transverse thin section. x4. 

2. Transverse thin section. x2. 

3. Longitudinal thin section. x2. 

4-8. Kyphophyllum sp. c 

Transverse and longitudinal thin sections. Great Basin Silurian coral zone E. Locality 

M1380, Coal Canyon, Simpson Park Mountains, Nev. 

4, 6, 8. Transverse thin sections. x 2. 

5, 7. Longitudinal thin sections. x2. 

9, 10. Chonophyllum simpsoni Merriam 

Transverse and longitudinal thin sections of paratype, USNM 159409. x2. Great Basin 

Silurian coral zone E. Roberts Mountains Formation. Locality M1108, Coal Canyon, 

Simpson Park Mountains, Nev. 
GEOLOGICAL SURVEY PROFESSIONAL PAPER 973 PLATE 9 

6 

5 

7 

2 

9 

KYPHOPHYLLUM AND CHONOPHYLLUM 
FIGURES 

PLATE 10 

1- 3. Verticillopora annulata Rezak. 

Roberts Mountains Formation. Locality M1411, west side of Coal Canyon, northern 

Simpson Park Mountains, Nev. All figures are of the same individual. 

1. Latex impression of exterior. x 1. 

2. Chert filling of internal cavity. x 1. 

3. Latex impression of interior. x 1. 

4. Verticillopora sp., cf. V. annulata Rezak. 

End view showing central cavity and small radial canals to exterior. x Y2. Roberts Mountains Formation, upper part. Great Basin Silurian coral zone E. Locality Mll06, east side 

of Coal Canyon near mouth, northern Simpson Park Mountains, Nev. 

5-7. Cladopora sp. v. 

Lateral views of pieces of branching colonies. x 2. 

8. Digitate favositid. 

Lateral view of piece of branching colony. x l'h . Vaughn Gulch Limestone, basal beds of 

upper unit. Locality M1093, Mazourka Canyon, northern Inyo Mountains, Calif. 

9-11. Favosites sp. c. 

Transverse and two longitudinal thin sections. x 2. Roberts Mountains Formation. Locality 

M1411, west side of Coal Canyon, northern Simpson Park Mountains, Nev. 

12, 13. Favosites sp. d. 

Transverse and longitudinal thin sections of form with very narrow corallites. x2. Roberts 

Mountains Formation, upper part. Great Basin Silurian coral zone E. Locality Mll06, 

east side of Coal Canyon near mouth, northern Simpson Park Mountains, Nev. 

14-17. Kyphophyllum sp. t. 

Lower part of Tor Limestone. Locality M1397 , Toquima Range, Nev. All fi gures are of the 

same corallum. 

14. Transverse thin section. x2. 

15-17. Longitudinal thin sections. x2. 

18, 19. Ketophyllum sp. t. 

Transverse and longitudinal thin sections of same corallum. x2. McMonnigal Limestone. 

Locality M1393, Toquima Range, Nev. 

20. Hercynella -like mollusk. 

Lateral view. x 1 Y2. Near locality Mll06, Coal Canyon, east side near mouth. Northern 

Simpson Park Mountains, Nev. 
GEOLOGICAL SURVEY PROFESSIONAL PAPER 973 PLATE 10 

14 

15 

17 

13 

9 

10 11 12 

VERTICILLOPORA, CLADOPORA, FA VOSITES, KYPHOPHYLLUM, KETOPHYLLUM, AND HERCYNELLA 
FIGURES 

PLATE 11 

1-6. Verticillopora annulata Rezak . 

1- 4. Great Basin Silurian coral zones D-E. Upper middle part of Vaughn Gulch Limestone. 

Locality Mll28, Mazourka Canyon, lnyo Mountains, Calif. 

1. Transverse view. x 1 Yz . 

2, 3. Transverse a nd lateral views of same individual. x 11/z. 

4. Lateral view. x 1 'h. 

5. Lateral view. x 1. Great Basin Silurian coral zones D-E. Locality M1385, Mazourka 

Canyon, Inyo Mountains, Calif. 

6. Transverse view. x 11/z. Great Basin Silurian coral zone D. Locality Mll03, Ikes Canyon, 

Toquima Range, Nev. Roberts Mountains Formation. 

7, 8. Verticillopora cf. V. annulata Rezak. 

Great Basin Silurian coral zone D. Roberts Mountains Formation, unit 3 near top. Locality 

MllOO, Roberts Creek Mountain, Nev. 

7. Weathered specimen showing wall of internal cavity. x 3. 

8. Weathered interior showing radial canals. x 2Vz . 

9- 14. Kozlowskiellina sp. f 

9--12. Great Basin Silurian coral zone D. Roberts Mountains Formation, unit 3 near top. 

Locality MllOO, Roberts Creek Mountain, Nev. 

9, 10. Exterior and interior of same ventral valve. x2. 

11 , 12. Interior and exterior of same dorsal valve. x3. 

13, 14. Exterior and interior of same ventral valve. x 2. Great Basin silurian coral zone E. 

Upper part of Roberts Mountains Formation. Locality Mll06, Coal Canyon, Simpson 

Park Mountains, Nev. 

15-17. Homoeospira sp. r 

Dorsal, ventral, and anterior views of same individual. x 2. Great Basin Silurian coral zone 

D. Roberts Mountains Formation, unit 3 near top. Locality MllOO, Roberts Creek Mountain, Nev. 

18, 21, 22. Dicoelosia sp. r 

Great Basin Silurian coral zone D. Roberts Mountains Formation, unit 3 near top. Locality 

MllOO, Roberts Creek Mountain, Nev. 

18. Interior of dorsal valve. x4. 

21 , 22. Dorsal and ventral exterior views of same individual. x4. 

19, 20. Dicoelosia sp. r. 

Interior and exterior views of same ventral valve. x2Vz . Great Basin Silurian coral zone D. 

Roberts Mountains Formation, unit 3 near top. Locality MllOO, Roberts Creek Mountain, 

Nev. 

23, 24. Plectatrypa? sp. c 

Dorsal and ventral exterior of same individual. x2. Great Basin Silurian coral zone E. 

Locality Mll06, Coal Canyon, Simpson Park Mountains, Nev. 

25, 25. Gypidula sp. r. 

Dorsal and ventral interior of same individua ls. x 2. Great Basin Silurian coral zone D. 

Roberts Mountains Formation, unit 3 near top. Loca lity MllOO, Roberts Creek Mountain, 

Nev. 
GEOLOGICAL SURVEY PROFESSIONAL PAPER 973 PLATE 11 

2 

6 

5 

3 

19 

7 

11 4 

9 

25 

26 

VERTICJLLOPORA, KOZLOWSKIELLINA, HOMEOSPIRA, DICOELOSIA, PLECTATRYPA?, AND GYPIDULA 
FIGURES 

PLATE 12 

1-7. Coelospira sp. b 

Roberts Mountains Formation. Locality M1412, Bootstrap Hill, southern Tuscarora Mountains. 

1. Exterior view of ventral valve. x4. 

2, 3. Dorsal valve and ventral valve exterior views of same shell. x4. 

4. Exterior view of dorsal valve. x 4. 

5. Interior view of dorsal valve. x4. 

6. Interior view of ventral valve. x4. 

7. Interior view of dorsal valve. x4. 

8--15. Fardenia sp. b 

Roberts Mountains Formation. Locality M1412, Bootstrap Hill, southern Tuscarora Mountains. 

8. Interior view of ventral valve. x2. 

9, 10. Exterior and interior views of same dorsal valve. x2. 

11, 12. Exterior and interior views of same dorsal valve. x 2. 

13, 14. Exterior and interior views of same dorsal valve. x2. 

15. Interior view of ventral valve. x 2. 

16, 17, 23. Kozlowskiellina sp. b 

Roberts Mountains Formation. Locality M1412, Bootstrap Hill, southern Tuscarora Mountains. 

16, 17. Exterior and interior views of same ventral valve. x2. 

23. Exterior view of dorsal valve. x 2. 

18--22. Conchidium sp. b. 

Roberts Mountains Formation. Locality M1412, Bootstrap Hill area, southern Tuscarora Mountains, Nev. 

18, 19. Exterior and interior views of same ventral valve. x 1. 

20. Exterior view of ventral valve . . x2. 

21, 22. Exterior and interior views of same dorsal valve. x2. 

24-26. Conchidium sp., cf. C. munsteri Kiaer. 

Type section of Roberts Mountains Formation on Pete Hanson Creek. Upper beds of unit 2. Roberts Creek Mountain, Nev. 

24, 25 . Exterior ventral and lateral views of same ventral valve. x 1. 

26. Lateral view of same shell as in figures 24 and 25 split longitudinally to show medium septum and 

spondylium. x 1 V2. 

27, 28. Cyathophylloides sp. f. 

Transverse and longitudinal thin sections. x4. Locality M1412, Bootstrap Hill area, southern Tuscarora Mountains, 

Nev. 

29--33. Brachyelasma sp. b. 

Locality M1120, Bootstrap Hill southwest side, southern Tuscarora Mountains, Nev. 

29, 30. Transverse and longitudinal thin sections of same corallum. x 2. 

31-32. Transverse thin sections of same corallite. x 2. 

33. Longitudinal thin section of corallite in figures 31 and 32. x 2. 

34-36. Lykophyllid rugose coral. 

Locality M1413, northeast of Lynn window of R. J. Roberts, Tuscarora Mountains, northeast Eureka County. 

34, 35. Transverse and longitudinal thin sections of same corallum. x 2. 

36. Transverse thin section. x 2. 
GEOLOGICAL SURVEY PROFESSIONAL PAPER 973 PLATE 12 

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3 

29 

30 

11 

4 9 10 

13 5 

8 

14 

15 

18 19 

6 7 

20 

27 

24 

21 

25 

28 26 

31 32 

33 35 36 

COELOSPIRA, FARDENJA, KOZLOWSKIELLJNA, CONCHIDIUM, CYATHOPHYLLOIDES, 

BRACHYELASMA, AND LYCOPHYLLID 

12 

17 

16 

23 

22