SELECTED SERIES OF U.S. GEOLOGICAL SURVEY PUBLICATIONS 

Periodicals 

Earthquakes & Volcanoes (issued bimonthly). 

Preliminary Determination of Epicenters (issued monthly). 

Technical Books and Reports 

Professional Papers are mainly comprehensive scientific reports of 

wide and lasting interest and importance to professional scientists and engineers. Included are reports on the results of resource srudies and of 

topographic, hydrologic, and geologic investigations. They also include 

collections of related papers addressing different aspects of a single scientific topic. 

Bulletins contain significant data and interpretations that are of lasting scientific interest but are generally more limited in scope or 

geographic coverage than Professional Papers. They include the results 

of resource srudies and of geologic and topographic investigations; as well 

as collections of short papers related to a specific topic. 

Water-Supply Papers are comprehensive reports that present significant interpretive results of hydrologic investigations of wide interest 

to professional geologists, hydrologists, and engineers. The series covers 

investigations in all phases of hydrology, including hydrogeology, 

availability of water, quality of water, and use of water. 

Cb'culars present administrative information or important scientific 

information of wide popular interest in a format designed for distribution 

at no cost to the public. Information is usually of short-term interest. 

Water-Resources Investigations Reports are papers of an interpretive nature made available to the public outside the formal USGS publications series. Copies are reprouuced on request unlike formal USGS 

publications, and they are also available for public inspection at 

depositories indicated in USGS catalogs. 

Open-File Reports include unpublished manuscript reports, maps, 

and other material that are made available for public consultation at 

depositories. They are a nonpermanent form of publication that may be 

cited in other publications as sources of information. 

Maps 

Geologic Quadrangle Maps are multicolor geologic maps on 

topographic bases in 7 1(1.- or 15-minute quadrangle formats (scales mainly 1 :24,000 or 1 :62,500) showing bedrock, surficial, or engineering geology. Maps generally include brief texts; some maps include strucrure 

and columnar sections only. 

Geophysical Investigations Maps are on topographic or planimetric 

bases at various scales; they show results of surveys using geophysical 

techniques, such as gravity, magnetic, seismic, or radioactivity, which 

reflect subsurface strucrures that are of economic or geologic significance. 

Ma'ly maps include correlations with the geology. 

Miscellaneous Investigations Series Maps are on planimetric or 

topographic bases of regular and irregular areas at various scales; they 

present a wide variety of format and subject matter. The series also includes 7 1/2-minute quadrangle photo geologic maps on planimetric bases 

which show geology as interpreted from aerial photographs. Series also 

includes maps of Mars and the Moon. 

Coal Investigations Maps are geologic maps on topographic or 

planimetric bases at various scales showing bedrock or surficial geology, stratigraphy, and structural relations in certain coal-resource areas. 

Oil and Gas Investigations Charts show stratigraphic information 

for certain oil and gas fields and other areas having petroleum potential. 

Miscellaneous Field Studies Maps are multicolor or black-andwhite maps on topographic or planimetric bases on quadrangle or irregular areas at various scales. Pre-1971 maps show bedrock geology 

in relation to specific mining or mineral-deposit problems; post-1971 

maps are primarily black-and-white maps on various subjects such as 

environmental studies or wilderness mineral investigations. 

Hydrologic Investigations Atlases are multicolored or black-andwhite maps on topographic or planimetric bases presenting a wide range 

of geohydrologic data of both regular and irregular areas; principal scale 

is 1:24,000 and regional srudies are at 1:250,000 scale or smaller. 

Catalogs 

Permanent catalogs, as well as some others, giving comprehensive listings of U.S. Geological Survey publications are available under 

the conditions indicated below from the U.S. Geological Survey, Books 

and Open-File Reports Section, Federal Center, Box 25425, Denver, 

CO 80225. (See latest Price and Availability List) 

"Publkatlons of the Geological Survey, 1879-1961" may be purchased by mail and over the counter in paperback book form and as a 

set of microfiche. 

"Publications of the Geological Survey, 1962-1970" may be purchased by mail and over the counter in paperback book form and as a 

set of microfiche. 

"Publications of the U.S. Geological Survey, 1971- 1981" may be 

purchased by mail and over the counter in paperback book form (two 

volumes, publications listing and index) and as a set of microfiche. 

Supplements for 1982,1983, 1984, 1985,1986, and for subsequent 

years since the last permanent catalog may be purchased by mail and 

over the counter in paperback book form. 

State catalogs, "List of U.S. Geological Survey Geologic and 

Water-Supply Reports and Maps For (State)," may be purchased by mail 

and over the counter in paperback booklet form only. 

"Price and Avallablllty List of U.S. Geological Survey Publications," issued annually, is available free of charge in paperback booklet form only. 

Selected copies of a monthly catalog" New Publications of the U.S. 

Geological Survey" available free of charge by mail or may be obtained 

over the counter in paperback booklet form only. Those wishing a free 

subscription to the monthly catalog "New Publications of the U.S. 

Geological Survey" should write to the U.S. Geological Survey, 582 

National Center, Reston, VA 22092. 

Note.--Prices of Government publications listed in older catalogs, 

announcements, and publications may be incorrect. Therefore, the 

prices charged may differ from the prices in catalogs, announcements, 

and publications. 
The Paxton Group 

of Southeastern New England 

By PATRICK j. BAROSH and GEORGE E. MOORE, JR. 

The Paxton Schist -is herein elevated to 

group status. The upper part of the former 

Paxton Schist is now called the 

Southbridge Formation, and the lower part 

of the former Paxton Schist is now called 

the Dudley Formation 

U.S. GEOLOGICAL SURVEY BULLETIN 1814 
DEPARTMENT OF THE INTERIOR 

DONALD PAUL HODEL, Secretary 

U.S. GEOLOGICAL SURVEY 

Dallas L. Peck, Director 

Any use of trade names in this publication is for descriptive 

purposes only and does not imply endorsement by the U.S. 

Geological Survey 

UNITED STATES GOVERNMENT PRINTING OFFICE : 1988 

For sale by the Books and Open-File Reports Section, 

U.S. Geological Survey, Federal Center, 

Box 25425, Denver, CO 80225 

Library of Congress Cataloging in Publication Data 

Barosh, Patrick J. 

The Paxton Group of southeastern New England. 

(U.S. Geological Survey bulletin; 1814) 

Bibliography: p. 

Supt. of Docs. no.: I 19.3:1814 

1. Geology, Stratigraphic-Pre-Ordovician. 2. Geology-New England. 

3. Paxton Group. I. Moore, George E. II. Title. Ill. Series. 

QE75.B9 no. 1814 557.3 s [551.7'31'0974] 87-19569 

[QE660] 
CONTENTS 

Abstract 1 

Introduction 1 

Acknowledgments 1 

History of stratigraphic nomenclature 1 

Revised stratigraphic nomenclature 4 

Characteristic lithologies of the Paxton Group 4 

Dudley Formation 6 

Southbridge Formation 7 

Paxton Group undivided 9 

Geomorphic expression 9 

Age 9 

Correlation 10 

Original lithology and environment of deposition 10 

References 11 

Appendix: Measured stratigraphic sections of the Paxton Group 13 

FIGURES 

1. Index map of southeast New England showing location of the 7I/2-minute 

quadrangles involved with the type section of the Paxton Group and their 

regional geologic setting 2 

2. Diagram showing history of the stratigraphic nomenclature of the Paxton 

Group in the Worcester area, Massachusetts, and adjacent Connecticut 3 

3. Map of parts of the Webster and Southbridge Quadrangles, Massachusetts, 

showing location of type sections of the Dudley and Southbridge Formations 

(reference section for the Paxton Group) S 

4. Columnar section showing the Paxton Group and bordering stratigraphic 

units 6 

5. Diagram showing regional correlation of the Paxton Group 7 

TABLE 

1. Mineralogic composition of rock samples from the Southbridge Formation 8 

Contents Ill 

The Paxton Group of Southeastern New Eng,and 

By Patrick J. Barash and George E. Moore, Jr. 

Abstract 

The Paxton Schist of Perry and Emerson (1903), 

referred to as the •Paxton Quartz Schist• by Emerson (1917), 

consists of medium-gray, thin- to medium-bedded, fine- to 

coarse-grained schistose granulite, which weathers the same 

color or slightly darker with a brownish cast. It is preOrdovician and probably late Proterozoic in age. The Paxton 

is herein elevated to group status. The Paxton as revised 

excludes strata now assigned to the overlying Brimfield 

Group (Peper and others, 1975). The lower, fine-grained part 

of the Paxton is herein named the Dudley Formation, and the 

upper, interbedded, fine- to coarse-grained part is referred to 

as the Southbridge Formation (Pease, 1972). An excellent 

reference section for the Paxton is present along the northeast side of the Quinebaug River southeast of Southbridge, 

Mass. The approximate thickness of exposed mapped width 

of the Paxton is 4,700 meters (m), of which the Dudley forms 

1 ,000 m and the Southbridge 3, 700 m. 

The Paxton conformably overlies the Oakdale Formation and underlies the Brimfield Group in its type area in 

central Massachusetts. It forms a northeast-trending belt 

extending from east-central Connecticut into southern Maine 

and probably into the central Maine coast. It is correlative 

with the Hebron Formation in eastern Connecticut, the upper 

part of the Berwick Formation in southern Maine, and the Rye 

Formation on the New Hampshire coast. 

A slight coarsening of the unit toward the northwest 

suggests a source in that direction. 

INTRODUCTION 

A series of stratigraphic studies was conducted in 

northeastern Connecticut and adjacent Massachusetts 

(fig. 1) both to aid in quadrangle mapping and to gain a 

better understanding of the regional stratigraphy and 

structure. The informally named "Paxton Group" 

(Barosh, 197 6, 1977) is one of the units that has been 

studied extensively, and various stages of its investigation 

are reported on in several abstracts, open-file reports, 

and guidebook articles. This report presents a summary 

of this work and a formal definition of stratigraphic 

terms. The Paxton is herein formally revised and raised 

Manuscript approved for publication, July 22, 1987. 

to group status. The Paxton Group, as revised, includes 

the Dudley Formation, which is herein proposed for 

strata previously informally referred to as the "lower 

Paxton" by Barosh {1976) and Pease and Barosh {1981 ), 

and the Southbridge Formation of Pease {1972). 

The recognition of the Paxton Group and its divisions provides important structural control in an area of 

similar lithologies. The study of this group also has been 

instrumental in establishing the proper stratigraphic 

sequence in the region and a better understanding of its 

geologic history. The Paxton has been followed southwestward to its terminus in east-central Connecticut and 

northeastward across New Hampshire into southern 

Maine, and thus plays a key role in integrating the 

geology across this region. 

Acknowledgments 

This work was supported mainly by the U.S. Geological Survey in cooperation with the States of Connecticut and Massachusetts, and in part by the U.S. Nuclear 

Regulatory Commission. Carl K. Johnson assisted in 

measuring some stratigraphic sections. The aid of M.H. 

Pease, Jr., throughout this study is gratefully appreciated. 

HISTORY OF STRATIGRAPHIC 

NOMENCLATURE 

The Paxton Schist was first described by Perry and 

Emerson {1903) in their study of the Worcester, Mass., 

area, although it was mentioned earlier by Emerson 

{1898), who referred to it as the "Paxton Whetsto.ne 

Schist." They described the Paxton as quartzose mtca 

schist, of brownish-gray color and frequent}~ containing 

alternating lighter bands of greenish color, lymg between 

the Oakdale Quartzite on the east and the Brimfield 

Schist on the west. These three units, the Oakdale, 

Paxton, Brimfield, form a gently to moderately west 

dipping conformable sequence in the Worcester region. 

The unit was described from a type area west of Worcester in the western part of the Worcester North and 

Worcester South 7¥2" quadrangles, and the name was 

taken from Paxton, a town that lies a little farther west 

History of Stratigraphic Nomenclature 
7'!' 71° 70" 

440 

I 

I 

NEW ~ HAMPSHIRE I 

~ 

0 10 20 30 40 50 MILES 

I I I I I I I I I I I I I 

0 10 20 30 40 50 60 70 KILOMETERS 

____..._......_...._ Fauh, dashed where approximately located, hachures 

on apparently downthrown side 

• Thrust fault, sawteeth on upper plate 

Figure 1. Index map of southeast New England showing 

location of the 71h-minute quadrangles involved with the type 

section of the Paxton Group and their regional geologic 

setting. 

(fig. 1 ). No type section was given. Strata in this area are 

typical of the Paxton, but are not well exposed. Emerson, 

who in 1917 referred to the unit as the "Paxton Quartz 

Schist," also shows belts of Paxton within the eastern part 

of the Brimfield. Emerson (1917, p. 62) stated that "the 

Paxton passes in pitching folds beneath the Brimfield" in 

this area. In addition, he considered the possibility that 

the Paxton and overlying Brimfield might be higher 

metamorphic grade equivalents of the Oakdale and a 

unit to the east, the Worcester Phyllite, respectively, thus 

creating a structural symmetry with matching units on 

either side of the valley near Worcester (fig. 2). Emerson 

(1917) shows the Brimfield, Paxton, and Oakdale strata 

extending southward to the Connecticut border. The 

Brimfield Schist was recognized in Connecticut, but 

strata equivalent to the Paxton and Oakdale were not 

divided and were mapped as the Hebron Gneiss by 

2 The Paxton Group of Southeastern New England 

Gregory and Robinson (1907). Gregory and Robinson 

(1907) locally separated a micaceous schist interval 

within the Hebron. 

The bedrock geology of much of this sequence in 

eastern Connecticut was mapped during the period 

1955-68, at a scale of 1:24,000, by the U.S. Geological 

Survey. 

As a result of this work, which was summarized by 

H.R. Dixon and L.W. Lundgren, Jr. (1968), the muscovitic schist interval of Gregory and Robinson (1907) was 

separated as a new formation, the Scotland Schist. Dixon 

and Lundgren hypothesized the Scotland Schist to lie 

along the center of a recumbent isoclinical syncline, the 

axis of which traced a sinuous path across eastern Connecticut. Rocks of the Hebron Formation were mapped 

structurally above and below the Scotland; those above 

were considered to be on the overturned limb of the 

syncline. The Brimfield Schist, which lies structurally 

above the Hebron, was also considered to be overturned. 

Dixon and Lundgren thus essentially reversed the order 

of the stratigraphy, placing the Scotland Schist at the top, 

the Hebron Formation in the middle, and the Brimfield 

Schist at the base. This interpretation, which has been 

followed by Rodgers (1985) on the geologic map of 

Connecticut, is incompatible with the information set 

forth in this report. 

From 1966 to 1975 a program of detailed geologic 

quadrangle mapping under the direction of M.H. Pease, 

Jr., was undertaken in the type area of the Brimfield 

Schist of Connecticut and Massachusetts. This work 

resulted in revision of the Hebron Formation and Brimfield Schist and in recognition that the stratigraphic 

section is not overturned, as interpreted by Dixon and 

Lundgren, but is in a right-side-up homoclinical sequence. It also demonstrated that the "folds" of Paxton in 

the Brimfield of Emerson (1917) are intervals of amphibolite and pyroxene-bearing biotite schist and gneiss 

within the Brimfield and not part of the Paxton. The 

Brimfield was elevated to group status and subdivided, 

from base upward, into the Bigelow Brook, Hamilton 

Reservoir, and Mount Pisgah Formations (Pease, 1972; 

Peper and Pease, 1975, 1976; Peper and others, 1975). 

The first quadrangle mapped under this program 

was the Eastford Quadrangle (Pease, 1972). The Hebron 

Formation was divided into two formations separated by 

the northeast-trending Eastford fault. The strata northwest of the fault were found to underlie and be older than 

the Brimfield; they were formally named the Southbridge 

Formation, for extensive exposures in the town of Southbridge, Mass., immediately on strike to the north of the 

Eastford Quadrangle. These strata, which have been 

mapped by G.E. Moore, Jr. (1978), are equivalent to the 

upper part of the Paxton of Emerson (1917). Pease 

recognized that the Brimfield overlying the Southbridge 

is younger and in right-side-up sequence. The Hebron 
WORCESTER AREA 

Emerson (1898, 1917) 

EASTFORD QUAD. WEBSTER QUAD. WORCESTER AREA 

Barosh (1976, 1977) 

WORCESTER AREA 

Pease (1972) Barosh (1974) This report 

"0 Ci)Q) -

Q)U) ... U.t::: Oi::E 8= ·~~ ._> 

0~ 

Cl) ~~ 

Scotland 

Schist 

Q. 

::I 

e 

(!) 

"0 

G) 

; Bigelow 

E Brook 

Q. 

::I 

e 

(!) 

"0 

G) 

; Bigelow 

E Brook 

Hebron 

·.:: 

Cl) Formation ·.:: 

Cl) Formation 

Formation 

Southbridge • Southbridge Southbridge 

Formation Q. Formation ::I Q. Formation Q. ::I 

::I 

e e 

(!) 

e 

(!) 

1n Q) :E ... (!) Bigelow "0 Brook G) 

c: 

0 

x c: 

0 

x ~ ~ ; Formation 

E Hebron IV 

Q.. 

"lower Paxton" 

IV 

Q.. Dudley 

~ IV 

::I ·.:: Formation ~ Formation IV 0 ::I Q) 0 iii c: "0 0 ~ 

x IV 

IV 0 

Cl) 

~ ~""""""""""""~ 

Oakdale Oakdale Oakdale 

Southbridge Formation Formation Formation 

Formation 

Figure 2. History of the stratigraphic nomenclature of the Paxton Group in the Worcester area, Massachusetts, and adjacent 

Connecticut. Not a correlation chart. 

Formation and Scotland Schist were restricted to the 

southeast side of the fault. For lack of evidence to the 

contrary at the time of publication of the geologic map of 

the Eastford Quadrangle, Pease accepted the stratigraphic sequence of Dixon and Lundgren (1968) for the 

strata east of the fault and placed them as younger than 

the Brimfield (fig. 2). 

A study of the Oakdale and Paxton strata in 

adjacent Massachusetts was started in the early 1970's 

when a program of geologic mapping under the direction 

of P.J. Barosh, then with the U.S. Geological Survey, was 

undertaken in the region from north of Worcester into 

the northeast corner of Connecticut. The division of the 

Hebron into Southbridge and Hebron made by Pease 

(1972) was recognized in the Webster Quadrangle as a 

stratigraphic division, even where the Eastford fault is 

absent (Barosh, 1974). The reduced Hebron of Pease 

·(1972) was found to be older than the overlying Southbridge (Barosh, 1974, 1976, 1977, 1984; Barosh and 

others, 1977). The Oakdale of Emerson (1917) was 

found to lie stratigraphically beneath Pease's Hebron and 

to extend into Connecticut, where it is stratigraphically 

the eastern part of the Hebron (Barosh, 1974) (fig. 2). 

Again, this west-dipping sequence is shown to be rightside-up, and not on the overturned limb of a recumbent 

syncline as interpreted by Dixon and Lundgren (1968). 

Because both the Paxton and Oakdale strata are 

well represented at the type areas, the names were 

retained. The Paxton Quartz Schist was informally revised as the "Paxton Group" (Barosh, 1976, 1977); the 

term "Southbridge Formation" was retained for the 

upper part of the Paxton Group, and the underlying 

strata were informally designated "lower Paxton" 

(Barosh, 1976, 1977) (fig. 2). The name "Oakdale Quartzite" was changed to "Oakdale Formation" because it is 

mostly metasiltstone, with little or no true quartzite 

(Barosh, 1974, 1977; Peck, 1975). Grew (1970) also used 

the term "Oakdale Formation," but included additional 

strata under that term. 

Subsequent geologic mapping in eastern Connecticut has shown that the Scotland Schist is a member 

within the Oakdale (Barosh and Pease, 1981; Pease and 

Barosh, 1981). Such muscovite schist lenses are characteristic of the Oakdale and are found in its type area. A 

definitive report by Pease (in press) correlates the 

Oakdale Formation and Paxton Group with strata in 

northeast Connecticut and formally redefines the 

Hebron and Scotland stratigraphic units. 

History of Stratigraphic Nomenclature 3 
REVISED STRATIGRAPHIC NOMENCLATURE 

This report formally elevates the Paxton to group 

status and introduces the name "Dudley Formation" for 

the strata of the Paxton Group that lie beneath the 

Southbridge Formation (fig. 2). The type area of the 

Southbridge Formation assigned by Pease (1972) to 

"nearly continuous exposures in the hills north of the 

Quinebaug River and east of the town of Southbridge" is 

herein expanded. The type section was designated by 

Pease (1972) to extend from Cady Brook in the Southbridge Quandrangle southeast to the quadrangle border 

and did not include the lower part of the formation. The 

type section is herein extended southeastward into the 

Webster Quadrangle along the northeast side of the 

Quinebaug River to the top of the Dudley Formation at 

a railroad bed crossing of a stream tributary to the 

Quinebaug about 1 kilometer (km) southeast of the 

highway bridge over the river in West Dudley (see 

appendix for specific location) (fig. 3). The Dudley 

Formation is named for the town of Dudley, Mass. The 

type section, which lies entirely within the town of 

Dudley, adjoins the Southbridge section at the railroad 

bed crossing and extends southeast along the northeast 

side of the Quinebaug River to a small pond southeast of 

Mill Road (see appendix for specific location) (fig. 3). 

The Dudley and Southbridge have thus far been 

separated by mapping only in southern Massachusetts 

and northeastern Connecticut. Farther north in Massachusetts and New Hampshire, these strata are mapped as 

Paxton Group undivided. 

Thin units of similar strata shown by Emerson 

(1917) as Paxton farther west, between bands of Brimfield, are shown by Peper and others (1975) to be 

stratigraphic components of the Brimfield Group and are 

excluded from the Paxton. 

CHARACTERISTIC LITHOLOGIES OF THE 

PAXTON GROUP 

The Paxton Group is a sequence of metagraywacke 

strata lying above metasiltstone strata of the Oakdale and 

below the first significant sillimanite schist unit of an 

alternating schist and gneiss sequence of the Bigelow 

Brook Formation at the base of the Brimfield Group (fig. 

4). Both contacts are conformable. 

The Paxton Group consists mostly of thin- to 

medium-bedded, fine- to coarse-grained graywacke that 

has undergone moderate to high-grade regional metamorphism. The beds have a schistose to granulose texture and are composed chiefly of quartz, feldspar, and 

biotite, which gives them a salt and pepper appearance. 

Calc-silicate-bearing beds occur at many horizons 

throughout the section and form lighter colored bands 

4 The Paxton Group of Southeastern New England 

with a greenish tint. The general composition of the 

Paxton is similar to that of the metasiltstone of the 

Oakdale Formation, but the Paxton is coarser grained 

(almost entirely in the sand size range) and lacks the 

silicic siltstone and thick muscovite schist interbeds that 

are found in the Oakdale. Pegmatite bodies are common 

in the Paxton and commonly constitute 15 percent of the 

section and locally up to 25 percent. The overlying 

Brimfield is a more heterogeneous unit containing rustyweathering schist interbedded with various types of 

gneissic rock (fig. 5). 

Various metamorphic terms ranging from schist to 

gneiss have been used to designate the metamorphosed 

graywacke that is most characteristic of the Paxton 

Group strata, but most of the conventional terms do not 

appear to adequately distinguish the diagnostic rock type 

of the Paxton Group from strata above and below. Very 

little of the rock is actually schist, although weathering 

locally causes a flaking and splitting of the rock along 

bedding planes that mimics schistosity. Gneiss is even 

less common, although thin bedding and sedimentary 

lamination in these strata locally appear to be accentuated by metamorphic processes to produce a gneissoid 

appearance. Grains within individual beds are generally 

equigranular, and the scattered mica flakes that produce 

a salt and pepper appearance are not generally parallel to 

bedding except near boundaries with shaly partings. The 

term "schistose granulite" is considered most suitable for 

the metagraywacke that makes up most of this group and 

is used in the following descriptions. 

The schistose granulite is medium to dark gray and 

weathers the same color or slightly darker with a brownish cast. It is an equigranular rock with a granular to 

slightly schistose texture. It is composed of 30 to 50 

percent quartz, 25 to 50 percent plagioclase, and 10 to 20 

percent biotite (table 1, samples 1-5). Medium- to darkgreen grains of diopside and actinolite-hornblende, generally less than 1 millimeter ( mm) in length, are minor 

constituents (table 1, samples 2, 3). They occur most 

commonly in the middle and upper parts of the Southbridge. The biotite, as seen in thin section, tends to be 

brownish red in rock containing iron-rich amphibole and 

pyroxene and olive brown elsewhere. It is the biotite that 

imparts a brownish cast to the weathered rock. Layers 

having a high biotite content are dark gray where fresh 

and relatively coarse grained. The plagioclase is mostly 

intermediate plagioclase but is very calcic where associated with other calc-silicate-bearing minerals. Locally, 

chlorite and muscovite are present (table 1, samples 1, 2, 

5). The more schistose strata contain garnet, generally 

amounting to less than 1 percent and less than 1 to 2 mm 

in grain size (table 1, samples 1, 4, 5). Locally, bands of 

garnetiferous gneiss and schist have been mapped separately. Within the typical gray granulite are light-gray, 

discontinuous interlayers, no more than a few millime-
Base from U.S. Geological Survey, 1:24,000 

Southbridge. 1967. photorevised 1979. 1 

and Webster, 1969 1000 

SCALE 1 40 000 0 l MILE 

2000 3000 4000 7000 FEET 

CO NTOUR INTERVAL 10 FEET 

NATIONAL GEODETIC VERTICAL DATUM OF 1929 

~ C>,£> 

QUADRANGLE LOCATION 

Figure 3. Map of parts of the Webster and Southbridge Quadrangles, Massachusetts, showing location of type sections of 

the Dudley and Southbridge Formations (reference section for the Paxton Group) (geologic data from Barosh, 1974, and 

Moore, 1978). Numbers show locations of described partial sections in appendix. The described parts of the section are shown 

by solid lines, with numbers keyed to descriptions in the appendix, and the rest by dotted lines that pass through areas of 

generally greater exposure. 

Characteristic Lithologies of the Paxton Group 5 
~ 

0 

"0 0 c Q)O. .... 0 

·- ::1 Ill·.;; 

-o E .... ~ co o E 'i: (!) - .... Q) 0 Ill 

a. 

::1 

0 

.... 

(!) 

c 

0 

)( 

co 

a.. 

C)U.. 

C:O 

c 

0 

·~ 

co 

E 

~E 

Q)8 

_g,..... 

·-M 

.... 

..0 

~ 

-::1 

0 

(/) 

c 

0 

·~ 

co 

E E 

00 

u..o 

>0 

~..-

"0 

::1 

Q 

c Q) 0 n;·~ 

-oco 

~e co .... Oo u.. 

BIGELOW BROOK FORMATION-Browngray biotite-sillimanite-garnet gneiss and 

schist, rusty weathering in part, interbedded with some calc-silicate- and sulfidegraphite-bearing units. Thin to thick bedded. 

SOUTHBRIDGE FORMATION-Medium- to 

dark-gray, interbedded fine- to coarsegrained schistose granulite and some thin 

beds, lenses, and nodules of lightgreenish-gray, calc-silicate-bearing granulite. Well to moderately bedded in thin to 

medium beds. Rare beds of mediumgray, medium-grained granulite and, near 

the top, beds and lenses of rusty-weathering sillimanite schist, dark-gray 

hornblende granulite, and very dark gray 

amphibolite. 1(}-25 percent pegmatite. 

DUDLEY FORMATION-Medium- to darkgray, fine-grained schistose granulite and 

some interlayered thin beds, lenses, and 

nodules of light-greenish-gray, calc-silicate-bearing granulite. Well bedded in 

thin to medium beds. Very few interbeds 

of other lithologies. 1(}-20 percent pegmatite. 

OAKDALE FORMATION-Medium- to darkgreenish-gray metasiltstone. Well bedded 

in thin beds that are commonly laminated. Laminae of calc-silicate minerals 

and calcite in places. Silicic in part and 

contains scattered lenses of silvery muscovite schist. 

Figure 4. Columnar section showing the Paxton Group and 

bordering stratigraphic units. 

ters thick, composed of fine-grained quartz, plagioclase, 

and a few percent biotite; these interlayers amount to 

about 10 percent of the granulite. 

Calc-silicate-bearing beds are ubiquitious in the 

Paxton, but they range from rare to abundant in any part 

of the section. The calc-silicate minerals, generally diopside, actinolite-hornblende, garnet, and sphene, occur as 

laminae, narrow diffuse layers, lenses, or nodules within 

thin beds (table 1, samples 6-10). Minor amounts of 

calcite may also be present. The calc-silicate-bearing 

beds are denser and lighter colored than the schistose 

granulite. As the amount of calc-silicate minerals 

increases, the content of biotite generally decreases and 

the color changes to greenish gray, bluish gray, or gray 

green; the rock ultimately becomes a tough, granular, 

quartz-feldspar-calc-silicate granulite with as much as 30 

percent calc-silicate minerals (table 1, samples 6-10). 

The calc-silicate rock weathers with a very distinctive 

rough, granular, pitted surface. Calc-silicate minerals 

6 The Paxton Group of Southeastern New England 

also occur locally along small fractures in which the 

minerals are usually fine to medium grained or even 

coarse grained in places. 

Local intervals within the Paxton contain thin beds 

of medium-gray schistose granulite, 1 to 10 centimeters 

(em) (0.4 to 4 inches (in)) thick, interlayered with calcsilicate-bearing beds, 0.5 to 1 em (0.2 to 0.4 in) thick. 

These sequences generally are evenly layered, presenting 

a distinctive pinstriped appearance. Such sequences are 

prominent in many areas of the Paxton. 

The Paxton is generally well bedded in thin to 

medium beds. Contacts commonly are moderately gradational, but some are sharp and well marked. Strata in 

new road cuts and other recent exposures may appear 

thick bedded or massive, but weathering brings out the 

thinner bedding. Many beds, especially thin beds, are also 

laminated, and cross-lamination occurs locally. Thin beds 

may also show a slight grading that is most easily seen on 

a weathered profile. Schistose partings commonly are 

seen to grade from the coarser bed below. 

Lithologies other than schistose granulite and calcsilicate-bearing granulite are present in the Paxton as 

lenses and thin beds mostly in the upper part. Lenses of 

light-gray, medium-grained, quartz-plagioclase granulite 

as much as 4 m thick occur in several places. Beds of 

amphibolite and sillimanite schist are also present. Also, 

mineralization related to the pegmatites has changed the 

composition of many beds. The pegmatite consists of 

quartz, microcline, and plagioclase with minor biotite, 

muscovite, lavender-pink garnet, graphite, and other 

accessories, and locally the schistose granulite may grade 

into a rock of similar composition. The composition 

varies according to amount of contained country rock 

(table 1, samples 13-17). The amount of microcline and 

muscovite generally increases, whereas the amount of 

plagioclase and biotite decreases, with increasing admixtures of the pegmatitic material. In addition, finer 

grained granitic material mineralogically related to the 

pegmatite occurs as veinlets a few millimeters thick, as 

trains of separate crystals, and, in places, as increased 

quartz content and minor amounts of microcline within , 

schistose granulite. 

DUDLEY FORMATION 

The Dudley Formation appears to be transitional 

between finer grained metasiltstone of the Oakdale Formation and coarser grained, more thickly layered strata 

of the overlying Southbridge Formation. The Dudley 

consists of schistose granulite and calc-silicate-bearing 

beds typical of the Paxton. The schistose granulite is fine 

grained, generally thin bedded, and laminated in part. 

The formation is well to moderately well bedded. An 

equigranular, fine-grained texture predominates, except 
CONNECTICUT MASSACHUSETTS NEW HAMPSHIRE MAINE 

Southbridge Formation 

Hebron Formation Paxton Group Berwick Formation 

Vassalboro Formation 

Dudley Formation 

Oakdale Formation 

~covites~ 

Gove Member of the 

Bc=tio~ G~ic Formation 

Berwick Formation 

Fault-or-intrusive contact 

Figure 5. Regional correlation of the Paxton Group (modified from Barosh and Pease, 1981). 

for biotite-rich schistose partings where the biotite commonly is slightly coarser grained and some calc-silicatebearing granulite. Quartz and feldspar grains show no 

evidence of coarsening, even by contact metamorphism 

within or adjacent to intrusive bodies. 

Both the upper and lower contacts of this formation appear to be comformable. The contact with the 

underlying Oakdale Formation is gradational over a 

stratigraphic interval of a few meters or tens of meters; it 

is readily delineated across eastern Connecticut and 

central Massachusetts. The contact with the overlying 

Southbridge Formation is less clearly defined, but it too 

appears to be gradational. The contact is placed where 

medium- to coarse-grained beds of the Southbridge first 

are commonly interlayered with the more uniformly fine 

grained Dudley. The position of this contact seldom can 

be delineated more closely than a stratigraphic interval of 

30-50 m (98--164 feet (ft)). 

The Dudley is poorly exposed in the lower part of 

its type section and moderately well exposed along a 

railroad grade in the upper part (see appendix for 

details). Strata typical of the formation are also well 

exposed south of the Quinebaug River in scattered 

outcrops 300 to 600 m (985 to 1,970 ft) on either side of 

Converse Road in the northeast corner of Woodstock, 

Conn. The upper and lower contacts are faulted in the 

type section. The maximum apparent exposed stratigraphic thickness is approximately 1,000 m (3,280 ft). 

SOUTHBRIDGE FORMATION 

The Southbridge Formation is distinguished from 

the Dudley by its mor:e varied lithology, but is still a 

generally uniform unit. Like the Dudley, it is composed 

mostly of schistose granulite, but unlike the Dudley, 

these strata alternate from thin to thick bedded and from 

fine to coarse grained. Calc-silicate-bearing beds are 

more common than in the Dudley, being most abundant 

in the middle and upper parts. 

The uppermost part of the Southbridge contains 

local interlayers of sillimanite schist, sulfidic schist, and 

amphibolite which are typical of the overlying Bigelow 

Brook Formation. Some typical rock types are as follows: 

rusty-weathering schistose granulite with appreciable 

amounts of sillimanite and lavender-pink garnet; sulfidic 

schists and schistose granulite composed of quartz, feldspar, muscovite, and graphite with or without garnet and 

sillimanite, that weather orange-brown and yellow; darkgray, medium- to fine-grained, well-foliated schistose 

granulite made up of hornblende, biotite, feldspar, and 

quartz, some with garnet (table 1, samples 11, 12); 

coarser grained, darker gray schistose granulite composed of hornblende, feldspar, and quartz; and dark-gray, 

more massive, coarse-grained amphibolite. 

The surface trace of the contact with the overlying 

Bigelow Brook Formation is a fault along much of its 

extent, but in places the stratigraphic contact appears to 

be gradational and conformable. Peper and others (1975, 

Southbridge Formation 7 
CD 

~ CD 

"tt 

:s 

~ 

G) 

0 

c 

"0 

0 

-

w 

c 

:; 

CD • ; 

.. 

:s 

z 

CD 

~ 

111 

:s 

CQ 

ii 

:s 

Q. 

Table 1. Mineralogic composition of rock samples from the Southbridge Formation 

~n percent. Samfle numbers keyed to description of rock types in text and stratigraphic section localities described in appendix; empty cells mean mineral not present; tr, trace. 

etrology by G .. Moore, Jr.] 

Schistose granulite 

Rock type ................... Typical Muscovite- Calc-silicate-bearing Horn61ende- Pegmatitic-bearing rock bearing rich 

Samele no ................... 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 

Quartz ..................... 47.5 43.9 46.9 33.3 31.5 48.5 40.0 45.3 30.5 18.9 50.6 17.2 34.2 39.1 29.0 26.9 32.0 

Plagioclase .................. 27.2 31.8 30.2 48.1 26.9 24.9 31.8 29.5 29.0 40.2 22.1 33.9 37.8 25.7 19.8 26.5 27.2 

(% anorthite content) ......... (51) (50) (50) (45) (37) (35) (40) (48) (48) (86) (69) (54) (67?) (48) (22) (37) 

Microcline . . . . . . . . . . . . . . . . . . tr 0.2 3.4 7.7 36.6 38.8 28.8 

Biotite ..................... 18.7 18.5 18.8 15.6 19.9 10.8 17.3 13.6 20.2 16.0 26.4 tr 22.8 10.2 1.6 6.2 

Chlorite .................... 1.9 4.1 tr tr 15.9 tr 3.1 

Muscovite ................... 2.1 tr 15.3 3.3 3.5 2.5 5.1 

Tremolite-actinolite . . . . . . . . . . . . 0.2 13.9 tr 5.5 

Hornblende ................. 3.4 3.0 2.2 2.7 9.5 19.8 

Diopside ................... 5.9 6.8 17.6 31.4 

Garnet ..................... 0.7 tr 1.6 4.1 0.1 

Graphite ................... tr tr 1.9 1.2 tr 0.1 tr 0.9 tr 

Apatite .................... tr tr tr tr tr tr tr tr tr tr 1.4 tr tr tr tr 

Zircon ..................... tr tr tr tr tr tr tr tr tr tr 0.1 tr tr tr tr tr 

Allanite .................... tr tr tr tr tr tr tr tr tr 

Magnetite-hematite ............. tr tr tr tr tr tr tr 

Epidote-zoisite . . . . . . . . . . . . . . . tr tr tr 

Rutile ..................... tr tr tr tr 

Sphene .................... tr tr tr tr tr tr tr tr tr 

Pyrite-hematite . . . . . . . . . . . . . . . tr tr tr tr tr 0.3 2.3 

Tourmaline. . . . . . . . . . . . . . . . . . tr 

Calcite ..................... tr 4.3 

Trace amount . . . . . . . . . . . . . . . . 1.9 1.5 0.7 1.4 0.4 0.7 2.0 2.4 2.7 2.4 1.8 0 0.9 1.4 0.9 0.6 0.6 
p. 6) noted an increase in the thickness and number of 

sillimanite schist and gneiss beds over an interval of a few 

tens of meters at the contact in the Worcester area. At a 

gradational contact near Moodus, Conn., a few widely 

spaced 1-m (3-ft) interbeds of sillimanite schist occur in 

the upper Southbridge; these increase in number over 

about 30m (98ft) to form half the strata at the base of 

the Bigelow Brook Formation. The contact is placed 

where sillimanite schist and sulfidic schist first appear to 

dominate the section. 

Pease (1972) divided the Southbridge Formation in 

the Eastford Quadrangle into a lower and an upper 

member. Much of the lower member is less well layered 

and is more uniform than the upper member and is 

characterized by the presence of potassium feldspar 

megacrysts. This rock type probably represents partially 

metasomatized strata perhaps derived from massive infusion of pegmatitic feldspar rather than a stratigraphic 

unit as interpreted by Pease; it has not been mapped 

outside the Eastford Quadrangle. Felsic rock, similar in 

composition to pegmatite, also is common in the middle 

part of the formation, where it makes up the bulk of some 

outcrops. The rock, which is finer grained than pegmatite, is very light gray to white, medium grained, granular, 

composed of quartz, plagioclase, 2 to 3 percent biotite, 

and as much as 5 percent microcline. The microcline is 

white and occurs in ovoid grains with granulated borders 

about 5 mm across by 10 mm long. 

The maximum apparent stratigraphic thickness of 

the Southbridge Formation is about 3,700 m (12,140 ft) 

in the type section. The measured thickness of the type 

section in the Southbridge Quadrangle is 1,893 m ( 6,211 

ft) (appendix), and the estimated thickness of the extended type section in the Webster Quadrangle is 1,800 m 

(5,906 ft). Pease (1972) estimated a thickness of 4,200 m 

(13,780 ft) in the Eastford Quadrangle, but this includes 

1,550 m (5,085 ft) for the questionable lower member 

that may possibly be thickened by an infusion of pegmatitic material. 

PAXTON GROUP UNDIVIDED 

Strata of the Paxton Group have been traced in 

several northeast-trending fault blocks from east-central 

Connecticut into Maine. It has been divided into the 

Southbridge and Dudley Formations thus far only in 

central Massachusetts and northeastern Connecticut; 

outside of this area it is undivided. Detailed field mapping should lead to the extension of these formations 

over a much wider area. Subtle but accumulative changes 

in facies across broad areas of poor exposure, however, 

will probably preclude its division everywhere. The more 

distant undivided Paxton is still composed of its characteristic lithologies and remains a valid and very useful 

stratigraphic unit. 

The Paxton becomes generally finer grained southeastward across New Hampshire and adjacent Massachusetts and contains interbeds of metasiltstone in its 

southeastern part, but it still is clearly distinguishable 

from the more homogeneous metasiltstone of the Oakdale, which also becomes finer grained to the southeast. 

A distinctive "pinstripe" lithology consisting of thinly 

interbedded schistose granulite and calc-silicate-bearing 

granulite is a characteristic lithology of the Paxton Group 

in New Hampshire and Maine. The Rye Formation 

(Novotny, 1969) of the New Hampshire coast consists 

largely of this "pinstripe" lithology and is correlated with 

the Paxton (Barash, 1984). Farther southeast in another 

fault block, granite forming the Isle of Shoals contains 

pendants of schistose granulite that are correlated with 

the Paxton. These contain a few thin, interlayered units of 

thin-bedded, laminated amphibolite. 

The total stratigraphic thickness of the Paxton 

Group cannot be determined too closely as it is cut by 

faults of indeterminate displacement, but an approximate 

thickness can be given. The maximum exposed stratigraphic thickness along the type section in the Southbridge and 

Webster Quadrangles is approximately 4,700 m (15,421 

ft). Farther north in Massachusetts and New Hampshire 

the section is incomplete owing to faulting and therefore 

appears somewhat thinner. 

GEOMORPHIC EXPRESSION 

The Paxton Group in the type area is intermediate 

in resistance to weathering. It lies between the valleyforming Oakdale to the east and the ridge-forming 

Brimfield to the west. The Dudley Formation is less well 

exposed than the overlying Southbridge, which forms 

intermediate slopes against the upland of the Brimfield 

west of Worcester. This relative degree of weathering of 

the Paxton is the same farther north, where the Paxton 

and Oakdale strata form the coastal lowlands of New 

Hampshire and southern Maine. 

The rock types within the Paxton vary greatly in 

their resistance to erosion. Pegmatite appears to be the 

most resistant rock in much of the area and commonly 

makes up more than 50 percent of the total outcrop in 

the upper part of the group. Many outcrops consist of a 

meter or two of pegmatite with several centimeters of 

country rock exposed at top and bottom; the schistose 

granulite is next in order of resistance, and calc-silicatebearing granulite is least resistant. The relative thickness 

of these rock types as exposed in the field and in the 

measured sections is thus probably not a true measure of 

their abundance in the Paxton. 

AGE 

No fossils have been found in the Paxton Group or 

in any stratigraphic unit associated with the Paxton. 

Age 9 
Radiometric dates of related igneous rocks intrusive into 

the Paxton and related stratigraphic units do provide 

possible minimum ages. An approximate age of 395 m.y. 

(Zartman and Naylor, 1984) has been assigned to the 

Canterbury Gneiss, which intrudes the Oakdale. An 

approximate age of 440 m.y. (R.E. Zartman, pers. 

commun., 1980) has been assigned to the Hedgehog Hill 

sill (Peper and Pease, 1975), which intrudes the Hamilton Reservoir Formation of the Brimfield Group, which 

overlies the Paxton at a much higher stratigraphic level 

(Peper and others, 1975). Thus the Paxton is at least as 

old as pre-Late Ordovician. Detrital zircons collected 

from the Oakdale Formation in east-central Massachusetts give a late Middle Proterozoic age of 1,188 m.y. 

(Aleinikoff and others, 1979). This date may represent a 

maximum possible age for the Oakdale. 

In New Hampshire, the Paxton and Brimfield 

Groups are intruded by the Massabesic Gneiss Complex, 

a migmatitic pegmatitic granite (Barosh and others, 

1977, p. 45-48). Semidigested Paxton strata along its 

southeast side, in particular, imparts a "gneissoid" texture to the Massabesic. Zircon dated as 600 to 650 m.y. 

old from the migmatitic Massabesic (Besancon and 

others, 1977; Lyons and others, 1982) appears to be from 

the Paxton and may also indicate a maximum age for the 

Paxton. The Paxton Group is thus pre-Late Ordovician 

and provisionally is considered Late Proterozoic in age. 

In addition, the conformity of early thrust faults affecting 

the Paxton with Late Proterozoic syntectonic structures 

to the east of the Lake Char fault (fig.1) suggests that the 

structures developed at the same time and, if so, would 

indicate a Proterozoic age for the Paxton. 

CORRELATION 

The Oakdale-Paxton-Brimfield sequence has now 

been followed into southern Maine, and the Paxton 

Group has been correlated with units to the north, both 

along strike and in separate structural blocks between the 

Fitchburg pluton and the Clinton-Newbury fault zone 

(Barosh and others, 1977; Barosh and Pease, 1981; 

Barosh, 1984) (fig. 1). 

In New Hampshire, strata of the Paxton Group are 

repeated in two separate fault blocks and also correlate 

with the Rye Formation on the coast (Barosh, 1984, fig. 

9), and pendants of strata on the Isle of Shoals appear to 

be part of a fourth block. The Paxton Group along with 

part of the Oakdale Formation can be traced into the 

Berwick Formation in southern Maine (Barosh and 

others, 1977; Barosh and Pease, 1981) (fig. 5). The Gove 

Member of the Berwick Formation and the Gonic Formation in Maine represent the Scotland Schist Member 

of the Oakdale Formation (Barosh and Pease, 1981; 

Pease, in press). 

10 The Paxton Group of Southeastern New England 

The undivided Paxton continues farther northeastward into Maine as the Vassalboro Formation, and 

apparently as the Bucksport Formation as well. The 

Berwick continues north-northeast past the latitude of 

Portland, Maine, as the Vassalboro Formation. Near 

Lewiston, Maine, the Vassalboro contains thin belts of 

rusty schist mapped as Waterville Formation by Osberg 

and others (1985). These correlate with schist lenses at 

the top of the Paxton; however, the Watetville farther 

north near its type area is a different and apparently 

much younger stratigraphic unit. The Bucksport Formation lies in a different fault block to the southeast along 

the central Maine coast (Osberg and others, 1985) and is 

composed mainly of strata characteristic of the Paxton. It 

is tentatively correlated with the Paxton on the basis that 

it is of similar lithology and order of thickness and is 

adjacent to strata resembling the Brimfield in the Casco 

Bay Group. Part of the Bucksport north of Penobscot 

Bay is composed of metasiltstone, and there it may 

contain strata equivalent to the Oakdale as well. 

The present indicated extent of the Paxton Group 

is about 450 km (280 miles (mi)) from near Moodus, 

Conn., to the north side of Penobscot Bay on the central 

Maine coast. It is thus one of the more widespread 

stratigraphic units in New England. 

ORIGINAL UTHOLOGY AND ENVIRONMENT 

OF DEPOSITION 

The composition, texture, and sedimentary structures of the Paxton Group indicate that it consists of a 

very thick, rather monotonous pile of metamorphosed 

graywacke with very thin shaly layers and many limy 

intetvals that probably vary from zones with calcite 

cement to calcareous graywacke and mudstone; a few 

beds and lenses of cleaner, more quartzose sandstone are 

interlayered in places, and rare thicker shale beds occur 

near the top. Calcareous concretions or disrupted calcareous beds are present in some intetvals. The graywacke 

was probably derived from sediments containing a large 

component of pyroclastic and other volcanic debris. 

Intetvals with calcareous cement and mud provided the 

material for the calc-silicate minerals, and a few very limy 

beds and lenses or, less likely, basaltic tuff later formed 

amphibolites. Lenses and beds of shale, containing 

aluminous-rich clay, interbedded near the top of the unit 

are represented by sillimanite schist intervals in the 

section. 

The very thin to medium beds, which are commonly graded, suggest that the sands were deposited on a 

marine slope at some intermediate distance offshore. 

Turbidity currents were common, as inferred by graded 

sand beds and, more commonly, by thin mud cappings 

from slowly settling finer grained material. The general 
increase upward in grain size, thickness of bedding, and 

greater lithologic heterogeneity suggests that deposition 

took place progressively closer to shore and source with 

time. These changes within the Paxton appear to be a 

subtle reflection of the same general changing environment with time, as indicated by the change from the 

uniform silt of the Oakdale to the more heterogeneous 

deposits in the Brimfield Group. A progressive decrease 

in grain size and apparent increase in lime content to the 

southeast across different structural blocks of the Paxton 

in New Hampshire indicates the source lay to the northwest. 

REFERENCES 

Aleinik.off, J.N., Zartman, R.E., and Lyons, J.B., 1979, U-THPB geochronology of the Massabesic Gneiss and the 

granite near Milford, south-central New Hampshire: New 

evidence for Avalonion basement and Taconic and Alleghenian disturbances in eastern New England: Contribution to Mineralogy and Petrology 71, p. 1-11. 

Barosh, P.J., 1974, Preliminary bedrock geologic map of the 

Webster Quadrangle, Massachusetts-Connecticut: U.S. 

Geological Survey Open-File Report 74-192, 2 p., scale 

1:24,000. 

---1976, Stratigraphy of the Webster-Worcester region, 

Massachusetts, in Cameron, Barry, ed., Geology of southeastern New England (New England Intercollegiate Geologic Conference, 68th annual meeting guide book): Princeton, N.J., Science Press, p. 352-365. 

---1977, Preliminary map showing bedrock geology superposed on aeromagnetic base map of the Worcester region, 

Massachusetts, Connecticut, and Rhode Island: U.S. Geological Survey Open-File Report 77-131, 46 p., scale 

1:125,000. 

---1984, Regional geology and tectonic history of southeastern New England, in Hanson, L.S., ed., Geology of the 

coastal lowlands from Boston, MA to Kennebunk, ME 

(New England Intercollegiate Geologic Conference, 76th 

annual meeting guide book): Salem, Mass., Salem State 

College, p. 1-35. 

Barosh, P.J., Fahey, R.J., and Pease, M.H., Jr., 1977, Preliminary compilation of the bedrock geology of the land area of 

the Boston 2° sheet, Massachusetts, Connecticut, Rhode 

Island and New Hampshire: U.S. Geological Survey OpenFile Report 77-285, 142 p., scale 1:125,000. 

Barosh, P.J., and Pease, M.H., Jr., 1981, Correlation of the 

Oakdale and Paxton Formations with their equivalents 

from eastern Connecticut to southern Maine [abs.]: Geological Society of America, Abstracts with Programs, v. 13, 

p. 122. 

Besancon, J.R., Gaudette, H.E., and Nylor, R.S., 1977, Age of 

the Massabesic Gneiss, southeastern New Hampshire: 

Geological Society of America, Abstracts with Programs, 

v. 9, no. 2. 

Dixon, H.R., and Lundgren, Lawrence, Jr., 1968, Structure of 

eastern Connecticut, in Zen, E-an, White, W.S., and 

Hadley, J.B., eds., Studies of Appalachian geology, p. 

219-230. 

Emerson, B.K., 1898, Geology of old Hampshire County, 

Mass., comprising Franklin, Hampshire, and Hampden 

Counties: U.S. Geological Survey Monograph 29, 790 p. 

--1917, Geology of Massachusetts and Rhode Island: U.S. 

Geological Survey Bulletin 597, 289 p., map scale 

1:250,000. 

Gregory, H.E., and Robinson, H.H., 1907, Preliminary geologic 

map of Connecticut: Connecticut Geological and Natural 

History Survey Bulletin 7, 39 p. 

Grew, E.S., 1970, Geology of the Pennsylvanian and prePennsylvanian rocks of the Worcester area, Massachusetts: 

Ph.D. thesis, Harvard University, 263 p. 

Lyons, J.B., Boudette, E.L., and Aleinikoff, J.N., 1982, The 

Avalon and Gander zones in central eastern New England, 

in St.-Julien, Pierre, and Belund, Jacques, Jr., eds., Major 

structural zones and faults of the northern Appalachians: 

Geological Society of Canada Special Paper 24, p. 43-66. 

Moore, G.E., Jr., 1978, Preliminary bedrock, surficial, and 

structural data maps of the Southbridge Quadrangle, 

Massachsuetts and Connecticut: U.S. Geological Survey 

Open-File Map 78-220, 16 p., scale 1:24,000. 

Novotny, R.F., 1969, The geology of the seacoast region, New 

Hampshire: New Hampshire Department of Resources 

and Economic Development (Concord) 4/p. geologic map, 

scale 1:62,500 (Dover and Exeter 15' quadrangles). 

Osberg, P.H., Hussey, A.M., II, and Boone, G.M., eds., 1985, 

Bedrock geologic map of Maine: Maine Geological Survey, scale 1:500,000. 

Pease, M.H., Jr., 1972, Geology of the Eastford Quadrangle, 

Windham and Tolland Counties, Connecticut: U.S. Geological Survey Geologic Quadrangle Map GQ-1023, 3 p., 

scale 1:24,000. 

---in press, Correlation of the Oakdale Formation and 

Paxton Group of central Massachusetts with strata in 

northeastern Connecticut: U.S. Geological Survey Bulletin. 

Pease, M .. H., Jr., and Barosh, P .J., 1981, Distribution and 

structural significance of the Oakdale Formation in northeastern Connecticut, in Boothroyd, J.S., and Hermes, 

O.D., eds., Geological field studies in Rhode Island and 

adjacent areas (New England Intercollegiate Geologic 

Conference, 73d annual meeting guide book): Kingston, 

University of Rhode Island, p. 17-34. 

Peck, J.H., 1975, Preliminary bedrock geologic map of the 

Clinton Quadrangle, Worcester County, Massachusetts: 

U.S. Geological Survey Open-File Report 75-658, 30 p., 

scale 1:24,000. 

Peper, J.D., and Pease, M.H., Jr., 1975, Geology of the Westford Quadrangle, Connecticut: U.S. Geological Survey 

Geologic Quadrangle Map GQ-1214. 

---1976, Summary of stratigraphy in the Brimfield area, 

Connecticut and Massachusetts, in Page, L.R., ed., Contributions to the stratigraphy of New England: Geological 

Society of America Memoir 148, p. 253-270. 

References 11 
Peper, J.D., Pease, M.H., Jr., and Seiders, V.M., 1975, Stratigraphic and structural relationships of the Brimfield 

Group in northeast-central Connecticut and adjacent Massachusetts: U.S. Geological Survey Bulletin 1389, 31 p. 

Perry, J.H., and Emerson, B.K., 1903, The geology of Worcester, Massachusetts: Worcester, Mass., Worcester 

Natural History Society, 166 p. 

12 The Paxton Group of Southeastern New England 

Rodgers, John, compiler, 1985, Bedrock geological map of 

Connecticut: Connecticut Geological and Natural History 

Survey, scale 1:225,000. 

Zartman, R.E., and Naylor, R.S., 1984, Structural implications 

of some radiometric ages of igneous rocks in southeastern 

New England: Geological Society of America Bulletin, v. 

95,no.5,p. 522-539. 
APPENDIX: MEASURED STRATIGRAPHIC 

SECTIONS OF THE PAXTON GROUP 

Stratigraphic Description of the Upper Part of 

the Type Section of the Southbridge 

Formation 

The type section of the Southbridge Formation is in 

the Southbridge and Webster Quadrangles, Mass., along 

the northeast side of the Quinebaug River. The section 

extends from the base where an unused railroad bed 

crosses a side stream 1,036 m (3,400 ft) southeast of the 

bridge over the river at West Dudley (380,700 ft north; 

471,675 ft east, Massachusetts Coordinate Grid System), 

and thence northwestward along an old railroad cut to 

the edge of the Southbridge Quadrangle (387 ,500 ft 

north; 464,075 ft east, Mass. Coord.). There it is offset 

northward to a point 350 ft north of the Dudley Hill Road 

at the border of the two quadrangles (389,080 ft north; 

466,520 ft east, Mass. Coord.), and thence northwesterly 

along the steep slopes on the north side of the Quinebaug 

River and around the buildings of the American Optical 

Company to an unnamed brook just east of the Charlton 

Street School. At that point it is offset north along the 

brook to the school, and thence northwesterly to a point 

on Cady Brook at the end of Fairlawn Avenue (395,715 

ft north; 459,740 ft east, Mass. Coord.), where the top is 

against the Black Pond fault. The description below is of 

the upper half of the Southbridge. This is the only part of 

the Paxton Group for which there is detailed petrographic work. However, the rock types sampled occur throughout the section and the mineralogic compositions are 

considered representative of the entire Paxton. 

In the measured part of the type section of the 

Southbridge about 60 percent is covered, 10 percent is 

pegmatite, 2 percent is calc-silicate-bearing granulite, 

and 28 percent is gray, schistose granulite and schist. The 

metasedimentary rock exposed in this part of the section 

is about 93 percent gray, schistose granulite and schist 

and about 7 percent calc-silicate-bearing granulite. 

Numbers refer to localities of partial sections measured (fig. 3). 

Locality 7 

Exposure measured by means of a Jacob's staff and clinometer, 

starting at a point on the east edge of the Southbridge Quadrangle 110 

m (350 ft) north of the Dudley Hill Road, thence upsection northwesterly along the steep slopes on the north side of the Quinebaug 

River and around the buildings of the American Optical Company to 

an unnamed brook just east of the Charlton Street School, thence 

offset north along the brook to the school, and thence northwesterly to 

a point on Cady Brook at the end of Fairlawn Avenue. Description is 

given from top toward base. 

Fault contact with the Bigelow Brook Formation at Black Pond fault along Cady 

Brook 

Covered ................................. . 

Schistose granulite, fine- to mediumgrained, greenish-gray, contains quartz, 

feldspar, chlorite, graphite, and pyrite 

(table 1, sample 2); partly silicified, slickensided surfaces, irregular pods of quartz 

Co~ered . (along Fairlawn Avenue) (offset 

1nsect1on) ............................. . 

Pegmatite, foliated, contains subhedral feldspar crystals to 15 em (6 in) in diameter. 

Schistose granulite, fine- to mediumgrained, light-gray, granulated, rustyweathering, containing quartz, feldspar, 

and biotite, chloritized, pegmatitic pods 

to 60 em (2ft) thick .................. . 

Covered ................................. . 

Schistose granulite, fine- to mediumgrained, light-gray to blue-gray, granular, 

quartz, feldspar, 5 to 10 percent biotite. 

Part of granulite is bleached, chloritized, 

and greenish gray. Some has layers of 

fine-grained quartz and feldspar 2 to 5 

mm (0.08 to 0.20 in) thick. Foliated 

pegmatite 1 m (3 ft) thick ............. . 

Covered (across a north-south side street) . 

Schistose granulite, like next exposure above 

(table 1, sample 1); 2m (6ft) of pegmatite ................................... . 

Covered (across street) ................... . 

Schistose granulite, fine- to mediumgrained, medium-gray to light-blue-gray; 

rusty-weathering, very quartzose beds 

with ± 1 percent pyrite (table 1, sample 

13). Pegmatite pods to 15 em (6 in) thick 

(in schoolyard) ....................... . 

Covered intervals, three, alternating with 

three outcrops of fine-grained, mediumgray, slightly schistose quartz-feldsparbiotite granulite containing discontinuous layers 2 to 10 mm (0.1 to 0.4 in) 

thick of vitreous quartz and quartzfeldspar and 10 percent greenish-gray 

calc-silicate granulite in beds to 5 em (2 

in) thick; 42.7 m (140 ft) covered, 7.6 m 

(25 ft) granulite (offset from brook just 

east of Charlton Street school) ........ . 

Covered interval, 1.5 m (5 ft) of foliated 

pegmatite near middle ................ . 

Granulite, fine- to medium-grained, light- to 

medium-gray, 10 percent calc-silicate 

granulite and 40 percent pegmatite ..... Covered intervals, five, alternating with five 

outcrops of foliated pegmatite, and layers 

of fine- to medium-grained, light-gray, 

schistose granulite as much as 1.5 m (5 ft) 

thick; 35m (115ft) covered, 13.7 m (45 

ft) pegmatite, 3.1 m (10 ft) of schistose 

granulite (offset 152m (500ft) south) .. 

Schistose granulite, two layers, fine- to 

coarse-grained, medium-gray, containing 

quartz, feldspar, and biotite with discontinuous layers of coarse-grained vitreous 

Thickness 

Meters Feet 

21.6 71 

116.0 380 

6.1 20 

10.7 35 

9.1 30 

3.0 10 

6.1 20 

13.7 45 

18.3 60 

1.5 5 

50.3 165 

25.9 85 

4.6 15 

51.8 170 

Appendix: Measured Stratigraphic Sections of the Paxton Group 13 
quartz and quartz and feldspar 2-6 mm 

(0.2 in) thick; 15 percent nodules and 

thin beds of gray-green quartz-feldspardiopside calc-silicate granulite; and 25 

percent pods of foliated pegmatite, alternating with two covered inteiVals, 6.7 m 

(22ft) of schistose granulite, 1.5 m (5 ft) 

of calc-silicate-bearing granulite, 2.4 m (8 

ft) of pegmatite, 13.7 m ( 45 ft) covered. 

(This unit and following three are along 

road.) ................................ . 

Schistose granulite, 20.7 m (68 ft); calcsilicate, 4.9 m (16 ft); pegmatite, 7.9 m 

(26 ft); all like that of unit above ...... . Covered ................................. . 

· Schistose granulite, two bands, fine- to 

coarse-grained, light- to medium-gray, 

granular to slightly schistose, containing 

quartz, feldspar, biotite, and calc-silicate 

minerals; discontinuous layers of quartz 1 

to 5 mm (0.04 to 0.2 in) thick, thin beds 

of gray-green quartz-feldspar-diopside 

granulite, and pods of foliated pegmatite 

to 1 m (3 ft) thick, and 13.7-m (45-ft) 

covered inteiVal near top of unit (across 

parking lot road); 20.7 m (68 ft) of 

schistose granulite, 4.6 m (15ft) of calcsilicate granulite, 3.6 m (12ft) of pegmatite ................................... . 

Covered inteiVal with 1.2 m (4 ft) of 

schistose granulite and 1.2 m (4 ft) of 

pegmatite near bottom of unit ........ . 

Pegmatite, foliated in pods to 3.6 m (12 ft) 

thick; bands and septae of gray, schistose 

granulite as much as 1.5 m (5 ft) thick; 3 

m (10 ft) of schistose granulite; 18.3 m 

(60 ft) of pegmatite ................... . 

Schistose granulite, fine- to coarse-grained, 

medium-gray, containing quartz, feldspar, and biotite with 10 percent beds 

and nodules of gray-green quartz-feldspardiopside, calc-silicate granulite, 10 percent pegmatite, and 25 percent covered. 

Schistose granulite, like inteiVal above, with 

3.4 m (11 ft) of calc-silicate-bearing granulite, 7 m (23ft) of pegmatite in pods to 

1.2 m ( 4 ft) thick; one pegmatite is foliated to very highly sheared (table 1, sample 16). (Unit extends to crest of the 

178-m (570-ft) knob northeast of American Optical Company.) ............... . 

Covered inteiVals alternating with many thin 

bands of gray, schistose granulite and 

pegmatite and minor calc-silicatebearing granulite; 7.3 m (24 ft) of 

schistose granulite, 8.8 m (29 ft) of pegmatite, 0.6 m (2 ft) of calc-silicatebearing granulite ...................... . Covered ................................. . 

Calc-silicate-bearing granulite, fine- to 

coarse-grained, light-greenish-gray, containing quartz, feldspar, diopside, and 

many light-gray quartz-feldspar folia 1.5 

to 10 mm (0.1 to 0.4 in) thick (table 1, 

Thickness 

Meters Feet 

24.4 80 

33.5 110 

36.6 120 

42.7 140 

16.8 55 

21.3 70 

36.6 120 

47.2 155 

71.6 235 

21.3 70 

14 The Paxton Group of Southeastern New England 

sample 10). Unit highly folded and has 

axial plane cleavage ................... . 

Covered inteiVals alternating with thin 

bands of gray, schistose granulite and 

pegmatite; schistose granulite, fine to 

coarse grained, medium gray, containing 

quartz, feldspar, and biotite; 3.7 m (12ft) 

of gray, schistose granulite, 2.4 m (8ft) of 

pegmatite ............................ . 

Schistose granulite, gray like that in unit 

above; 0.6 m (2 ft) of pegmatite, and 0.6 

m (2ft) of calc-silicate-bearing granulite 

Covered inteiVals alternating with many thin 

bands of gray, schistose granulite and 

pegmatite; 8.5 m (28ft) of tray, schistose 

granulite, 2.4 m (8ft) of pegmatite. (Unit 

lies across brook at American Optical 

Company settling pond.) (offset to south 

to end of cliff) ........................ . 

Schistose granulite, fine- to mediumgrained, blue-gray, evenly bedded, containing quartz, feldspar, and biotite; 

some beds contain many 1- to 2-mm-

(0.04- to 0.1-in-) thick, light-gray layers 

of quartz-feldspar, some mediumgrained, schistose beds contain graphite; 

granitic veinlets from 2 mm (0.1 in) veinlets to 1.5 m (5 ft) pods of pegmatite; 4 m 

(13 ft) of calc-silicate-bearing granulite . 

Schistose granulite, fine- to mediumgrained, light-gray, granular, fine- to 

coarse-grained, light- to medium-gray, 

slightly schistose, containing quartz, feldspar, and biotite, with and without diopside; some beds weather rusty and contain very little biotite; folia of quartz and 

of quartz-feldspar, 1 to 10 mm (0.04 to 

0.4 in) thick, form 5 percent of the rock; 

lenses as much as 10 by 75 em ( 4 by 30 in) 

are 90 percent quartz and 10 percent 

feldspar and contain clots of quartzfeldspar, hornblende, and diopside as 

much as 7.5 by 12.5 em (3 by 5 in); 2.4 m 

(8 ft) of pegmatite in pods to 1 m (3 ft) 

thick; 1.8 m (6ft) of calc-silicate-bearing 

granulite ............................. . 

Schistose granulite, like unit above, 5.6 m 

(18 ft); pegmatite, 1.5 m (5 ft); calcsilicate-bearing granulite, 0.6 m (2 ft); 

covered inteiVals of 3 m (10 ft) at base 

and 1.5 m (5 ft) at top. (Unit lies over 

gully.) ................................ . 

Schistose granulite, some beds with only 

biotite; biotite chloritized in some beds, 

and some beds are graphitic (table 1, 

sample 8); some light-gray bands 1 to 6 

mm (0.04 to 0.2 in) thick are crosscutting, 

pegmatitic quartz and feldspar; calcsilicate-bearing nodules of quartz, feldspar, diopside, and sphene to 10 by 40 em 

(4 by 16 in) and beds to 10 em (4 in) 

thick; nodules of vitreous quartz to 10 by 

38 em ( 4 by 15 in) may be concretions or 

vein quartz, 3 m (10 ft) of pegmatite in 

Thickness 

Meters Feet 

4.6 15 

35 115 

13.7 45 

122.2 401 

53.3 175 

35 115 

12.2 40 
Thickness 

Meters Feet 

pods to 1.2 m (4 ft), 3 m (10 ft) of 

calc-silicate-bearing granulite. (offset 

from cliff along river at pipeline crossins) 29 

Covered intervals alternating with many thm 

bands of pegmatite, gray, schistose granulite, and calc-silicate-bearing granulite; 

7.6 m (25ft) of gray, schistose granulite, 

0.6 m (2 ft) of calc-silicate granulite, 2.4 

m (8 ft) of pegmatite . . . . . . . . . . . . . . . . . . 32 

Pegmatite, foliated, in many pods 0.6 to 2.1 

m (2 to 7 ft) thick; some gray, slightly 

schistose granulite as septae or at base of 

pegmatites; and covered intervals; 16.8 m 

(55 ft) of pegmatite, 2.1 m (7 ft) of 

schistose granulite, 14.6 m (48 ft) covered................................... 33.5 

Covered interval, 1.2 m (4 ft) of pegmatite 

near top . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16.5 

Schistose granulite, fine- to coarse-grained, 

medium-gray and gray granulite consisting of quartz, feldspar, and biotite and 

interlayered thin beds of gray-green 

quartz-feldspar-diopside calc-silicatebearing granulite; pegmatite pods to 3.7 

m (12 ft) thick; 4.6 m (15 ft) near middle 

and 3 m (10ft) at top are covered; 5.5 m 

(18 ft) of pegmatite, 1.2 m (4 ft) of 

calc-silicate-bearing granulite, 7.6 m (25 

ft) covered, 19.5 m (64 ft) of schistose 

granulite . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33.8 

Schistose granulite, gray granulite; some 

greenish, chloritized, and calc-silicatebearing in thin beds and nodules to 10 by 

30 em (4 by 12 in); pods of pegmatite to 

2.4 m (8 ft) thick: 3 m (10 ft) pegmatite, 

mostly in upper part; 1.5 m (5 ft) calcsilicate-bearing granulite . . . . . . . . . . . . . . . 29 

Covered intervals, five, alternating with four 

bands of medium-gray, schistose granulite, fine- to coarse-grained, contains 

quartz, feldspar, biotite, and locally disseminated diopside (table 1, sample 9), 

and coarse, foliated pegmatite; 5.8 m (19 

ft) of gray, schistose granulite, 3.4 m (11 

ft) of pegmatite.. . . . . . . . . . . . . . . . . . . . . . . 105.1 

Pegmatite, white, feldspar crystals up to 10 

em ( 4 in) across; beds and numerous 

septae to 20 em (8 in) thick; gray, 

schistose granulite and calc-silicatebearing granulite; 12m (40ft) of pegmatite, 10.7 m (35 ft) of gray, schistose 

granulite, 1.4 m (5 ft) calc-silicatebearing granulite. . . . . . . . . . . . . . . . . . . . . . . 24.4 

Covered. (across Dresser Hill Road and 

brook) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 198.1 

Schistose granulite, medium- to coarsegrained, medium- to light-gray, granular 

to slightly schistose; feldspar crystals, 

mostly 5 to 10 mm (0.2 to 0.4 in) long, 

form as much as 10 percent of the rock; 

abundant stringers of vitreous quartz 1 to 

3 mm (0.04 to 0.1 in) thick and as much 

as 45 em (18 in) long, and similar stringers of pegmatitic quartz-feldspar granulite commonly 2 to 5 mm (0.1 to 0.2 in) 

95 

105 

110 

54 

111 

95 

345 

80 

650 

thick; foliated pegmatite in pods as much 

as 1.4 m (5 ft) thick, and covered intervals; 7.9 m (26 ft) of pegmatite, 19.2 m 

(63ft) of covered interval, 17.1 m (56ft) 

of schistose granulite .................. . 

Covered interval; 4.6 m (15ft) of pegmatite, 

septae of gray, schistose granulite near 

middle; 4.3 m (14ft) of pegmatite, 0.3 m 

(1 ft) of gray, schistose granulite ....... . Schtstose granulite; light-gray folia of pegmatitic quartz-feldspar, 2 to 10 mm (0.1 

to 0.4 in) thick, form 5 percent of the 

schistose granulite; 2 percent calcsilicate-bearing granulite in thin beds and 

pods, contains hornblende adjacent to 

some pegmatites; pegmatite in pods as 

much as 1m (3ft) thick, in part strongly 

foliated, medium grained, and with 

ungranulated feldspar crystals to 1.7 em 

(0.67 in) across, and in part foliated, 

coarse grained, and with ungranulated 

feldspar crystals to 15 em (6 in) across; 

4.3 m (14ft) of pegmatite, 0.6 m (2ft) of 

calc-silicate granulite .................. . Covered intervals, three, alternating with 

two bands of foliated pegmatite and gray, 

schistose granulite; 1.8 m (6ft) of granulite, 7.3 m (24ft) of pegmatite ........ . Schistose granulite, fine- to mediumgrained, light-gray, granular, some biotitepoor and quartzose, some containing 

about 1 percent lavender-pink garnet to 2 

mm (0.1 in) in diameter, garnet concentrated along certain bedding planes; 2.1 

m (7ft) of pegmatite ................. . Covered ............... · .................. . 

Schistose granulite, light-gray to mediumblue-gray, containing quartz-feldspar and 

10 percent biotite; stringers of vitreous 

quartz 2 to 4 mm (0.1 to 0.2 in) thick and 

pegmatitic quartz-feldspar 2 to 5 mm (0.1 

to 0.2 in) thick; concretions of calcsilicate-bearing rock to 15 by 60 em ( 6 by 

24 in) and beds to 10 em (4 in) thick; 

pods of foliated pegmatite to 0.6 m (2 ft) 

thick. Feldspar crystals to 10 mm (0.4 in) 

make up 5 percent of gray, schistose 

granulite; a few small garnets around 

some of these crystals; 4.2 m (14 ft) of 

calc-silicate-bearing granulite, 2.1 m (7 

ft) of l?egmatite ....................... . Covered mterval, with 2.4 m (8 ft) of gray, 

schistose granulite in upper half, like that 

in unit above, but more biotite and with 

about 3 percent hornblende and a trace 

of garnet (table 1, sample 3), and with a 

pod of foliated pegmatite 2.1 m (7 ft) 

thick ................................. . 

Schistose granulite, medium- to coarsegrained, medium- to light-gray, granular 

to slightly schistose; feldspar crystals to 

10 mm (0.4 in) form 5 percent of the 

schistose granulite; pegmatite pods to 0.6 

m (2 ft) thick make up 5 percent of the 

rock .................................. . 

Thickness 

Meters Feet 

44.2 

18.3 

22.9 

45.7 

40 

4.6 

42.7 

32 

15.2 

145 

60 

75 

150 

131 

15 

140 

105 

50 

Appendix: Measured Stratigraphic Sections of the Paxton Group 15 
Schistose granulite, similar to unit above, 

but mostly granular; 10 percent pegmatite in pods to 3.7 m (12 ft) thick, tourmaline in lower, well-foliated part of one 

pegmatite and feldspar crystals to 10 em 

(4 in) in top part; 3m (10ft) of pegmatite; top 3 m (10 ft) covered .......... .. Covered ................................. . Schistose granulite, medium- to coarsegrained, medium- to light-gray, granular 

to slightly schistose feldspar crystals to 8 

mm (0.3 in) and 5.2 m (17ft) of pegmatite; 4.9 m (16 ft) covered ............ .. Covered intervals, with two thin bands of 

pegmatite near middle, 1.2 m (4 ft) of 

pegmatite ............................ . Schistose granulite, fine- to coarse-grained, 

medium- to light-gray, somewhat schistose; quartz-feldspar-biotite-trace graphite schistose granulite; and fine, lightgray granular quartz-feldspar-biotite 

schistose granulite; interbeds up to 1.3 

em (0.5 in) thick of light-gray, quartzose 

granulite, layers of pegmatitic quartzfeldspar 3 to 8 mm (0.1 to 0.3 in) thick 

form 5 percent of the rock; pods of 

pegmatite up to 45 em (18 in) thick in top 

part contain quartz, feldspar, biotite, 

trace muscovite, 1 percent garnet up to 2 

mm (0.1 in) in diameter, and feldspar 

crystals up to 6.5 em (2.5 in) long; 2.4 m 

(8 ft) of pegmatite at top of unit ...... . Covered ................................. . Edge of quadrangle, 110 m (350 ft) north of 

Dudley Hill Road 

Total ............................... . 

Thickness 

Meters Feet 

35 115 

12.2 40 

15.2 50 

15.2 50 

32 105 

45.7 150 

1,893 6,211 

The lower part of the Southbridge Formation is 

exposed along the northeast side of the Quinebaug River 

in the Webster Quadrangle. This section extends from 

the west edge of the quadrangle to the faulted base of the 

formation southeast of West Dudley where a stream 

crosses the Penn-Central railroad 1,036 m (3,400 ft) 

southeast of the bridge on the West Dudley road. The 

part from the west edge of the quadrangle to 300 m (984 

ft) west of Blackmere cemetery is very well exposed along 

the Grand Trunk railroad bed that borders the northeast 

side of the river. The rest is moderately exposed in 

scattered outcrops on the slope and hill crest above the 

river. The lithology is generally uniform and the same as 

the described upper part, except that the part southeast 

of Durfee Road is finer grained and transitional into the 

top of the Dudley Formation. The thickness of the lower 

part of the section is estimated at approximately 1,800 m 

(5,904 ft), but the effects due to displacement by faults 

crossed are unknown. 

16 The Paxton Group of Southeastern New England 

Stratigraphic Description of Parts of the Type 

Section of the Dudley Formation 

The type section of the Dudley Formation is in the 

Webster Quadrangle, Dudley, Mass., along the northeast 

side of the Quinebaug River from a pond over a covered 

branch of the Eastford fault approximately 305 m (1,000 

ft) southeast of Mill Road (375,000 ft north; 476,650 ft 

east, Mass. Coord.) along scattered outcrops across the 

south end of a hill to an old railroad cut on the northeast 

side of the Quinebaug River, thence northwest along the 

railroad bed to a covered fault contact with the Southbridge Formation at a side stream 1,036 m (3,400 ft) 

southeast of the bridge over the Quinebaug River at 

West Dudley Road (380,700 ft north; 471,675 ft east, 

Mass. Coord.). Exposures occur in cuts along the PennCentral (PC) railroad tracks, the adjacent, nevercompleted Grand Trunk (GT) railroad bed, and local 

roads and in scattered natural outcrops. Given below are 

descriptions from several representative measured exposures along the type section. Locations are given in 

relation to the intersection of the Penn-Central railroad 

and Mill Road. Descriptions are given from top toward 

base. 

Locality 6 

Exposure in cut along GT railroad about 1,875 m (6,150 ft) N. 36° W. 

of intersection, near section used for road to gravel pit. 

Schistose granulite, fine-grained, mediumgray to brownish-gray, weathers darker, 

composed of biotite, quartz, and feldspar, thin-bedded and commonly lamina .. 

ted, generally well-bedded. Lower 2.3 m 

(7.5 ft) contains small quartz lenses and 

Thickness 

Meters Feet 

is less well bedded. Top covered . . . . . . . 4.0 13.1 

Schistose granulite and granulite, interbedded: Fine-grained, medium-gray to 

brownish-gray, schistose granulite, composed of biotite, quartz, and feldspar; 

fine-to medium-grained, light-to mediumgray and greenish-gray granulite, composed of quartz, feldspar, minor biotite, 

and calc-silicate minerals. Unit weathers 

slightly darker; thin bedded and commonly laminated; secondary quartz stringers abundant locally. Conformable with 

unit above. Base covered............... 7.5 24.6 

Total..................................... 11.5 37.7 

Locality 5 

Exposure in cut along GT railroad about 1,768 m (5,800 ft) N. 34° W. 

of intersection used for road. 

Schistose granulite and granulite, interbedded: Fine-grained, medium-gray to 

Thickness 

Meters Feet 
brownish-gray, schistose granulite that 

weathers slightly darker, composed of 

biotite, quartz, and feldspar; fine- to 

medium-grained, light- to medium-gray 

and greenish-gray granulite that weathers 

slightly darker, composed of quartz, feldspar, minor biotite, and calc-silicate 

minerals. Unit contains thin beds of granulite locally 1 em (0.4 in) apart; well 

bedded. Contacts slightly gradational to 

sharp. Covered above ................. . Schistose granulite and granulite, interbedded. Similar to unit below but with relatively more schistose granulite; thin bedded with laminations common. 

Conformable and gradational above .... Granulite and schistose granulite, interbedded: Schistose granulite as in unit below; 

fine-to medium-grained, light-to mediumgray granulite that weathers slightly 

darker, composed of quartz, feldspar, 

minor biotite, and some calc-silicate 

minerals; granulite in thin beds less than 

25 em (9.8 in) thick interbedded with thin 

beds and seams of schistose granulite. 

Conformable and gradational above .... Schistose granulite, fine-grained, mediumgray to brownish-gray, weathers slightly 

darker, composed of biotite, quartz, and 

feldspar, thin-bedded, moderately well 

bedded; few interbeds of light-gray granulite. Conformable and gradational 

above. Base covered .................. . 

Total .................................... . 

Locality 4 

Thickness 

Meters Feet 

5.0 16.4 

6.0 19.7 

4.1 13.5 

4.2 13.5 

19.3 63.3 

Two natural outcrops in woods northwest of GT railroad bed 1,585-

1,676 m (5,200-5,500 ft) N. 29° W. of intersection. 

Schistose granulite, fine-grained, mediumgray to brownish-gray, weathers slightly 

darker, wavy, irregular, thin beds less 

than 30 em (11.8 in) thick, minor calcsilicate-bearing granulite, minor small 

pegmatitic pods. Top covered ......... . Schistose granulite, fine-grained, mediumgray to brownish-gray, weathers slightly 

darker, composed of biotite quartz and 

feldspar, thin-bedded; contains thin pegmatitic quartz-feldspar stringers and 

lenses less than 30 em (11.8 in) thick. 

Conformable with unit above. Base covThickness 

Meters Feet 

5.1 16.7 

ered ................................... -=3=.3- 10.8 

Total . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.4 27.5 

Locality 3 

Exposure along GT railroad bed 1,021 m (3,350 ft) N. 2?D W. of 

intersection. This is northeast of and above the next-described exposure (locality 2) and may have slight overlap at southeast end. 

Measured section starts at southeast end of cut where narrow dirt road 

extends northward from railroad bed. Section is disturbed at southeast 

end by a few northwest-dipping thrust faults with related adjacent 

small folds and contorted beds. Movement on thrust faults is west over 

east. 

Granulite and schistose granulite: Fine- to 

medium-grained, light- to medium-gray 

and greenish -gray, calc-silicate-bearing 

granulite composed of quartz, feldspar, 

minor biotite, and calc-silicate minerals, 

interbedded with fine-grained, mediumto dark-gray and brownish-gray, schistose 

granulite composed of biotite, quartz, 

and feldspar. Unit weathers slightly 

darker, generally thin bedded and laminated in part, may be in few medium 

beds. Contacts sharply gradational to 

Thickness 

Meters Feet 

gradational. To.P covered............... 21.8 69.9 

Granulite and schistose granulite, interbedded: Fine- to medium-grained, light- to 

medium-gray granulite that weathers 

slightly darker, composed of quartz, feldspar, minor biotite, and calc-silicate 

minerals; fine-grained, medium-gray to 

brownish-gray, schistose granulite that 

weathers slightly darker, composed of 

biotite, quartz, and feldspar. Unit contains thin to medium beds up to 50 em 

(19.7 in) that are commonly laminated; 

well-bedded with slightly gradational to 

sharp contacts. Conformable with unit 

above . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 23.0 

Granulite and schistose granulite, interbedded, similar to second unit below, but 

beds slightly thicker near base; gradual 

increase in percentage of schistose granulite toward top, where it forms about 

two-thirds of unit; well bedded but locally 

wavy owing to tectonic movement. Conformable with unit above............... 14 45.9 

Granulite, fine-grained, light- to mediumgray, weathers slightly darker, composed 

of quartz, feldspar, minor biotite, and 

calc-silicate minerals; three beds, 20 to 

85 em (7.9 to 33.5 in) thick, separated by 

thin beds of fine-grained, medium-gray 

to brownish-gray, schistose granulite that 

weathers slightly darker; well bedded, 

but with slight pinch and swell variations 

in thickness. Sharp to slightly gradational 

contacts. Conformable with unit above. . 1.4 4.6 

Granulite and schistose granulite, interbedded, similar to unit below except beds are 

slightly thicker; some calc-silicatebearing granulite in small pods in addition to beds. Contains some thin, irregular pegmatite lenses. Conformable 

contact with unit above . . . . . . . . . . . . . . . . 3 9.8 

Appendix: Measured Stratigraphic Sections of the Paxton Group 17 
some thin, irregular pegmatite lenses. 

Conformable contact with unit above ... 

Granulite and schistose granulite, interbedded, similar to unit below; bedding contorted. A granitic dike, striking northsouth and dipping 35° W. that separates 

unit from one above probably intruded 

along a thrust fault ................... . 

Granulite and schistose granulite: Fine- to 

medium-grained, light- to medium-gray 

and greenish-gray, calc-silicate-bearing 

granulite that weathers slightly darker 

and is composed of quartz, feldspar, 

minor biotite, and calc-silicate minerals 

inter-bedded with fine-grained, medium: 

to dark-gray and brownish-gray, schistose 

granulite that weathers slightly darker 

and is composed of biotite, quartz, and 

feldspar. Unit is thin bedded, 1-10 em 

(0.4-3.9 in), and laminated in part; well 

bedded where not contorted and 

sheared. Small, irregular, crosscutting 

granitic body, possible following a thrust 

fault, separates this unit from that above. 

Schistose granulite and granulite: Finegrained, medium-gray and brownish-gray 

to dark-gray, schistose granulite that 

weathers slightly darker and is composed 

of biotite, quartz, and feldspar, interbedded with fine-grained, light- to mediumgray, calc-silicate-bearing granulite that 

weathers slightly darker and contains less 

biotite than does the schistose granulite. 

Unit is thin bedded, 1-8 em (0.4-3.1 in), 

and commonly is laminated; well bedded, 

but wavy to contorted. Northwestdipping thrust fault forms contact with 

unit above ............................ . 

Schistose granulite, fine-grained, mediumgray to brownish-gray, weathers slightly 

darker, composed of biotite, quartz, and 

feldspar; thin bedded and laminated at 

top, but most of unit has shear foliation 

approximately parallel to bedding; contains few small quartz stringers; pegmatite at exposed base. Two foliated, finegrained granitic dikes (15 em and 20 em 

(5.9 and 7.9 in)) at exposed top of unit to 

northwest, parallel to small thrust fault, 

striking N. 20° E. and dipping 300 NW., 

that forms contact with unit above. Base 

Thickness 

Meters Feet 

3 9.8 

2 6.6 

6 19.7 

2.2 7.2 

covered . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.5 _g 

Total .................................... About 61.5 196.8 

18 The Paxton Group of Southeastern New England 

Locality 2 

Exposure along PC railroad 1,037 m (3,400 ft) N. 300 W. of 

intersection. 

Schistose granulite, fine-grained, mediumgray to brownish-gray and dark-gray, 

weathers slightly darker, composed of 

biotite, quartz, and feldspar; thin bedded, 

range 1-50 em (0.4-19.7 in), mainly 

3-15 em (1.2-5.9 in), and commonly 

laminated; few interbeds, less than 5 em 

(2 in) thick, of fine- to medium-grained, 

slightly less granulite with only minor 

biotite and containing some calc-silicate 

minerals; generally well bedded, but contains slightly wavy beds that have lineations owing to tectonic movement. Contains minor amount of small quartzfeldspar veinlets and pods ............. . 

Locality 1 

Thickness 

Meters Feet 

11 36.1 

Exposure in a cut along the GT railroad 305 m {980 ft) due north of 

the Intersection of the PC railroad and Mill Road. 

Schistose granulite interbedded with calcsilicate-bearing granulite: Fine-grained, 

medium-gray, brownish-gray, and minor 

dark-gray, schistose granulite that weathers slightly darker, composed of biotite, 

quartz, and feldspar; biotite imparts a 

slightly schistose texture, especially at the 

top of beds; beds may be slightly graded. 

Smaller amount of fine- to mediumgrained, light-to medium-gray to greenishgray granulite that weathers slightly 

darker and is composed of quartz, feldspar, minor biotite, and calc-silicate 

minerals. Generally thin bedded (1-20 

em (0.4-7.9 in)), a few beds appear to 

reach 1 m (3.28 ft) in thickness, but are 

probably multiple beds. Contacts generally slightly gradational to sharp. Usually 

well bedded, but beds may be slightly 

undulating to locally contorted and variable in thickness owing to tectonic movement. Contains small pods and stringers 

of quartz and feldspar in places. Section 

is uniform, with some variation in bed 

thickness and amount and thickness of 

calc-silicate-bearing granulite interbeds. 

Base and top covered ................. . 

Thickness 

Meters Feet 

46 151 


AVAILABILITY OF BOOKS AND MAPS OF THE U.S. GEOLOGICAL SURVEY 

Instructions on ordering publications of the U.S. Geological Survey, along with prices of the last offerings, are given in the current-year issues of the monthly catalog "New Publications of the U.S. Geological Survey." Prices of available U.S. Geological Survey publications released prior to the current year are listed in the most recent annual "Price and Availability LisL" Publications 

that are listed in various U.S. Geological Survey catalogs (see back inside cover) but not listed in the most recent annual "Price and 

Availability List" are no longer available. 

Prices of reports released to the open files are given in the listing "U.S. Geological Survey Open-File Reports," updated monthly, which is for sale in microfiche from the U.S. Geological Survey, Books and Open-File Reports Section, Federal Center, Box 

25425, Denvez, CO 80225. Reports released through the NTIS may be obtained by writing to the National Technical Infoonation 

Service, U.S. Department of Commerce, Springfield, VA 22161; please include NTIS report number with inquiry. 

Ordez U.S. Geological Survey publications by mall or over the counter from the offices given below. 

BY MAIL 

Books 

Professional Papen, Bulletins, Water-Supply Papers. Teclmiques 

of Water-Resources Investigations, Circulars, publications of general interest (such as leaflets, pamphlets, booklets), single copies of Earthquakes 

& Volcanoes, Preliminary Determination of Epicenters, and some miscellaneous reports, including some of the foregoing series that have gone 

out of print at the Superintendent of Documents, are obtainable by mail 

from 

U.S. Geological Suney, Books and Open-File Reports 

Federal Center, Box 25415 

Denver, CO 80215 

Subscriptions to periodicals (Earthquakes & Volcanoes and 

Preliminary Detennination of Epicenters) can be obtained ONLY from 

the 

Superintendent of Documents 

Government Prlntlq omce 

Washtnpon, D.C. 20402 

(Check or money order must be payable to Superintendent of Documents.) 

Maps 

For maps, address mail orders to 

U.S. Geological Suney, Map Distribution 

Federal Center, Box 15286 

Denver, CO 80215 

Residents of Alaska may order maps from 

Alaska Distribution Section, U.S. Geological Suney, 

New Federal Building - Box 1l 

101 Twelfth Ave., Fairbanks, AK 99701 

OVER THE COUNTER 

Books 

Boob of the U.S. Geological Survey are available over the 

counter at the following Geological Survey Public Inquiries otJicea, Ill 

of which are authorized agents of the Superintendent of Documents: 

• WASHINGTON, D.C.--Main Interior Bldg., 2600 corridor, 

Ulth and C Sts., NW. 

• DENVER, Colorado--Federal Bldg., Rm. 169, 1961 Stout St. 

• LOS ANGELES, California-Federal Bldg., Rm. 7638, 300 N. 

Los Angeles St. 

• MENLO PARK, California--Bldg. 3 (Stop 533), Rm. 3128, 

345 Middlefield Rd. 

• RESTON, Vlrglnia--503 National Center, Rm. 1C402, 12201 

SWllise Valley Dr. 

• SALT LAKE CITY, Utah-Federal Bldg., Rm. 8105, 125 

South State St. 

• SAN FRANCISCO, California--Customhouse, Rm. 504, 555 

Battery St. 

• SPOKANE, WISbJncton-U.S. Courthouse, Rm. 678, West 

920 Riverside Ave .. 

• ANCHORAGE, Alaska-Rm. 101, 4230 University Dr. 

• ANCHORAGE, Alaska-Federal Bldg, Rm. E-146, 701 C St. 

Maps 

Maps may be purchased over the counter at the U.S. Geological Survey offices where boob are sold (all addresses in above list) and 

at the following Geological Survey offices: 

• ROLLA, Mlssourl--1400 Independence Rd. 

• DENVER, Colorado--Map Distribution, Bldg. 810, Federal 

Center 

• FAIRBANKS, Alaska-New Federal Bldg., 101 Twelfth Ave.