The Russell Mountain 

Formation, a New Stratigraphic 

Unit in Western Massachusetts

By NORMAN L. HATCH, JR., ROLFE S. STANLEY, and STEWART F. CLARK, JR.

CONTRIBUTIONS TO STRATIGRAPHY

GEOLOGICAL SURVEY BULLETIN 1324-B

Prepared in cooperation with

the Massachusetts Department of Public Works

A thin unit of calc-silicate rock 

and quartzite is defined and 

assigned a Middle Silurian age
UNITED STATES DEPARTMENT OF THE INTERIOR 

WALTER J. HICKEL, Secretary

GEOLOGICAL SURVEY 

William T. Pecora, Director

Library of Congress catalog-card No. 73-608173

U.S. GOVERNMENT PRINTING OFFICE 

WASHINGTON: 1970

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

Washington, D.C. 20402 - Price 10 cents (paper cover)
CONTENTS

Page

Abstract ..._.....-___.........-_._.___........._.........__........._____.._..._.._._......._.........._.._.....___. Bl

Introduction ....................................................................................................... 1

Distribution ........................................................................................_.......... 3

Lithology .............................................. ...................................._....................... 3

Type area ........................................... ___.....__.___._..__.__._._..____..__...__....__..._.._... 4

Upper and lower contacts. ..---......... .. ................................................... .. 5

Thickness ........................_................................................................................... 7

Correlation and age ................................................................................... 7

References ................................................................................................... 10

ILLUSTRATION

Page

FIGURE 1. Generalized geologic map of the Blandford and Woronoco 

guadrangles showing distribution of the Russell Mountain 

Formation and surrounding rocks. . ................ ....... .. B2

ill

CONTRIBUTIONS TO STRATIGRAPHY

THE RUSSELL MOUNTAIN

FORMATION, A NEW 

STRATIGRAPHIG UNIT IN 

WESTERN MASSACHUSETTS

By NORMAN L. HATCH, JR., ROLFE S. STANLEY, and 

STEWART F. CLARK, JR.

ABSTRACT

A thin discontinuous unit of calc-silicate granulite and quartzite has been 

mapped on the east limb of the Berkshire anticlinorium in southern Massachusetts and is here named the Russell Mountain Formation. It overlies rocks 

continuous with the Hawley Formation of Middle Ordovician age and underlies the Goshen Formation of Middle Silurian to Early Devonian age. Largely 

on the basis of a correlation with the Shaw Mountain Formation of Vermont, 

the Russell Mountain Formation is assigned a Middle Silurian age.

INTRODUCTION

Mapping of stratified Paleozoic rocks on the east limb of the 

Green Mountain-Berkshire anticlinorium from the Vermont State 

line southward across most of western Massachusetts has shown 

that in southwestern Massachusetts a thin discontinuous unit of 

calc-silicate granulite and quartzite occurs between the Goshen 

Formation of Middle Silurian to Early Devonian age and rocks of 

probable Middle Ordovician age that correlate with the Hawley 

Formation in northwestern Massachusetts. It is herein proposed 

that this calc-silicate-quartzite unit be named the Russell Mountain 

Formation after exposures on Russell Mountain in the Woronoco 

quadrangle, Massachusetts (fig. 1).

The fieldwork was done in cooperation with the Massachusetts 

Department of Public Works.

Bl
B2 CONTRIBUTIONS TO STRATIGRAPHY

Middle Ordovician and 

Goehen Formation older rocks, undivided

42*0 7'30"

* 1, I

JS2J2*T_A NEW HAMPSHIRE 

MASSACHUSETTS

UNDIVIDED 

ROCKS

 Report area 

CONNECTICUT

LOCATION AND GEOLOGIC SETTING 

OF REPORT AREA

EXPLANATION

ORDOVICIAN AND CAMBRIAN

DEVONIAN AND SILURIAN PRECAMBRIAN

FIGURE 1. Generalized geologic map of the Blandford and Woronoco quadrangles showing distribution of the Russell Mountain Formation and surrounding rocks. Width of outcrop of Russell Mountain Formation locally 

exaggerated.
RUSSELL MOUNTAIN FORMATION IN WESTERN MASSACHUSETTS B3

DISTRIBUTION

The present known distribution of the Russell Mountain Formation is shown in figure 1. The formation is exposed in the center of 

the racetrack at the fairground in the village of Blandford in the 

Blandford quadrangle. In the Woronoco quadrangle, it is well 

exposed on the Massachusetts Turnpike, in the north-south series 

of outcrops on Russell Mountain between the Massachusetts Turnpike and the Little River, in a group of outcrops about 1,000 feet 

south of Little River on the northeast end of Westfield Mountain, 

and on Ball Mountain.

LITHOLOGY

In the Blandford and Woronoco quadrangles, the Russell Mountain Formation consists of calc-silicate granulite, carbonate-calcsilicate rock, and quartzite. These rock types are interbedded in 

proportions that vary from one exposure to another. Calc-silicate 

granulites constitute all the exposed rock at some localities where 

they form beds a few inches to a few feet thick. Carbonate-calcsilicate rock, in beds a few feet or more thick, is the only rock at a 

few exposures and forms beds 6 inches to a foot thick intercalated 

with calc-silicate granulites at other exposures. Quartzite is the 

only exposed lithology at the Blandford fairgound. At other localities it generally forms no more than 50 percent of the exposed rock 

and is in beds a few inches to a foot thick intercalated with calcsilicate granulites.

The calc-silicate rocks are medium grained, generally massive, 

locally compositionally banded, and greenish gray and consist predominantly of variable proportions of quartz, feldspar, garnet, zoisite, tremolite, diopside, and carbonate minerals. The sizes of most 

mineral grains are within the range of 1 to 3 mm (millimeters), 

but some minerals such as tremolite form blades or aggregates as 

much as 15 cm (centimeters) long. In the roadcut on the north 

side of the Massachusetts Turnpike, alternating light and dark 

beds are distinctive. Carbonate minerals may constitute as much 

as 40 percent of some beds and less than 5 percent of others. Where 

carbonate minerals were originally abundant, outcrop surfaces 

commonly have a porous brown-weathered crust. Two good exposures of this carbonate-calc-silicate rock in the Woronoco quadrangle are on the northeast end of Westfield Mountain, 2,500 feet S. 

72° W. of the intersection of Northwest Road and Western Avenue, 

and on Ball Mountain, 3,600 feet S. 2° W. of the airway beacon. The 

rock consists primarily of quartz and carbonate minerals and 

minor amounts of zoisite, diopside, tremolite, plagioclase, and
B4 CONTRIBUTIONS TO STRATIGRAPHY

other calc-silicate minerals. In general, where carbonate is minor 

or absent, the rock is harder than carbonate-rich rocks and does 

not have the porous brown-weathered crust.

The quartzites in the Russell Mountain Formation are white, 

very light gray, or light brown where fresh and commonly weather 

slightly rusty. They generally form irregularly distributed beds 1 

to 10 in. thick within the calc-silicate granulites. Individual quartz 

grains are generally colorless and 1 to 4 mm in diameter. Boundaries between grains are generally distinct in hand specimen, and 

weathered surfaces commonly show a marked flattening of grains 

parallel both to bedding and, where present, to mica foliation. 

Grains of clear quartz 3 to 5 mm in diameter or larger strongly 

suggest that some beds are metaconglomerate. Muscovite in plates 

2 or 3 mm across is the most common accessory mineral and locally 

may form conspicuous partings that constitute as much as 10 percent of the rock. At some localities quartzite constitutes as much 

as 50 percent of the exposed rock; at others no quartzite was observed. Typical quartzites interbedded with calc-silicate rocks can 

be seen 250 ft N. 30° W. of the point where the Westfield corporate 

boundary crosses General Knox Road, at the south end of Russell 

Mountain, Woronoco quadrangle (800 ft north of where the formation crosses the Little River, fig. 1.). The quartzite exposed at the 

racetrack in the fairgound at Blandford village is 10 to 30 feet 

thick and contains abundant muscovite. The rock consists essentially of grains of glassy quartz and white muscovite 2 to 3 mm in 

diameter. Quartz pebbles as much as 2 cm in diameter are scattered throughout the quartzite. Small pits between quartz grains 

suggest the former presence in some beds of a few percent of 

carbonate minerals.

TYPE AREA

The type area for the Russell Mountain Formation is on Russell 

Mountain, where, in a series of outcrops, calc-silicate granulites 

and quartzites are interbedded. The most accessible exposure is 

near General Knox Road, as mentioned above, at the south end of 

Russell Mountain. There typical quartzites and calc-silicate granulites are interbedded on a scale of 6 in. to a few feet in a ratio of 

about one part quartzite to two parts calc-silicate granulite. Bounding outcrops of pre-Silurian medium-grained muscovite-quartzbiotite-garnet schist and gray cyclically bedded quartz-muscovitebiotite-garnet-staurolite-kyanite schist and quartzose schist of the 

Goshen Formation (Hatch, 1967, p. 12-15) are about 70 feet apart; 

exposures of Russell Mountain rocks are only about 50 feet across
RUSSELL MOUNTAIN FORMATION IN WESTERN MASSACHUSETTS B5

strike. Other less accessible exposures of the formation in the type 

area form a narrow band of outcrops north to the top of Russell 

Mountain and contain the same lithologies in approximately the 

same proportions and in about the same exposed width as at the 

south end of the mountain.

UPPER AND LOWER CONTACTS

Both the top and the bottom of the Russell Mountain Formation 

are readily defined on the basis of the presence of calc-silicate 

granulite, carbonate-calc-silicate rock, and quartzite in the Russell 

Mountain Formation and the absence of these rocks, except as 

noted, in the underlying and overlying formations.

The Russell Mountain Formation is overlain by gray, somewhat 

rusty-weathered carbonaceous cyclically bedded schists of the 

Goshen Formation (Hatch, 1967). The contact is sharp and is 

readily drawn where both units are exposed; no interbedding of 

the lithologies characteristic of the two formations was observed. 

Attitudes of bedding and schistosity in adjacent exposures of Russell Mountain and Goshen rocks are generally parallel within the 

limits of observation, and no evidence of unconformity of this contact has been seen. Although minor calc-silicate rocks are present 

in the Goshen, they have not been recognized in the basal few hundred feet of the formation and where present typically occur only 

as thin lenses and isolated beds, 6 inches to 2 feet thick, that are 

mineralogically zoned with respect to the surrounding aluminous 

schists. This zoning, which presumably results from reaction between contiguous calcareous and aluminous beds during regional 

metamorphism, commonly consists of outer darker hornblende-rich 

zones around an inner lighter zone rich in quartz and feldspar with 

diopside, zoisite, and garnet. Quartzites in the upper part of the 

Goshen (Hatch, 1967, p. 14) are distinctly different from the 

coarser grained muscovite-rich Russell Mountain quartzites. They 

are finer grained and grittier, generally contain garnet and more 

biotite than muscovite, and form beds a few feet to tens of feet 

thick.

Underlying the Russell Mountain Formation is a sequence of 

fine- to medium-grained silvery-gray to gray-brown schists and 

gneisses that intertongue with the Hawley Formation (Hatch, 

1967) to the north (Hatch and Stanley, 1970). This contact is also 

sharp and readily recognized where exposed; it involves no interbedding of characteristic lithologies, and attitudes of bedding and 

schistosity in adjacent exposures of the two formations are generally parallel within the limits of observation. The underlying
B6 CONTRIBUTIONS TO STRATIGRAPHY

rocks have been temporarily and informally designated units 4 and 

5 by Stanley (1967). They contain no quartzites having a grain 

size coarser than about 0.5 mm and no calcareous quartzites or 

carbonate-calc-silicate rocks. They do locally contain beds of 

plagioclase-hornblende amphibolite of presumed igneous origin that 

are mineralogically and texturally distinct from the calc-silicate 

granulites of the Russell Mountain Formation. Pods a few inches 

thick and 6 to 10 inches long of medium-grained massive carbonatefree calc-silicate rock are present in a few places but are readily 

distinguished from the calc-silicate granulites of the Russell Mountain Formation by their pod shape and by the medium-grained gray 

or gray-brown muscovite-quartz-biotite-garnet schists with which 

they are associated. Thus, the change across this contact is from 

metagraywackes and metashales and minor metavolcanic material 

to metamorphosed sandy dolomites and quartz sandstones.

The Hawley Formation underlies the Goshen Formation in the 

northern part of the Blandford quadrangle and the quadrangles on 

strike to the north (Hatch and others, 1970). No rocks like those of 

the Russell Mountain Formation have been recognized along this 

contact. The Hawley contains quartzites, but they are much finer 

grained than the Russell Mountain quartzites, are generally gray, 

black, or pink and commonly are finely laminated in shades of 

gray and pink. Many of them may be metacherts. Rocks associated 

with the Hawley quartzites are generally gray, rusty-weathered 

carbonaceous schist and plagioclase-hornblende amphibolite of 

presumed igneous origin. Although rare scattered pods a few 

inches across of calc-silicate rock have been seen in the Hawley 

Formation, they are generally associated with the carbonaceous 

schist rather than with the quartzites. Thus, the Hawley and Russell Mountain quartzites are lithologically distinctly different. 

The calc-silicate rocks of the two formations are also readily distinguished both by their pod shape in the Hawley, as contrasted 

with their bedded character in the Russell Mountain, and by the 

rocks with which they are associated. For this reason the rocks of 

the Russell Mountain Formation could not reasonably be considered Hawley Formation or correlative therewith.

Although attitudes of bedding and schistosity in adjacent exposures of Russell Mountain and underlying rocks are generally parallel within the limits of observation, an unconformity is inferred 

at the base of the Russell Mountain. If the correlations and age 

assignments of the Hawley and Goshen Formations are correct 

(Hatch, 1967), the contact between these two units represents a 

hiatus between Middle Ordovician and at least Middle Silurian and
RUSSELL MOUNTAIN FORMATION IN WESTERN MASSACHUSETTS B7

is the Taconic unconformity. The Russell Mountain Formation 

crops out along this unconformity in southern Massachusetts. Although the evidence is not conclusive, detailed mapping of thin 

stratigraphic units in the rocks below the Russell Mountain Formation in the vicinity of Russell Mountain suggests some truncation 

of these units by the Russell Mountain. This relationship, the evidence from correlations presented below, and the change in depositional environment from a relatively deep-water assemblage of 

graywacke, shale, volcanic rocks, and chert to a shallower water 

carbonate-quartzite assemblage all point to the Taconic unconformity being at the base of the Russell Mountain.

THICKNESS

At the northeast end of Westfield Mountain, 110 feet of nearly 

vertical beds of the Russell Mountain Formation is exposed. At the 

south end of Russell Mountain near General Knox Road, the Russell Mountain Formation is no more than 70 feet thick. Other exposures indicate minimum thicknesses of 10 to 100 feet. Beds in the 

Russell Mountain Formation on Ball Mountain commonly have 

gentle dips, and in places a few tens of feet of beds appear to underlie areas a few hundred feet across. The structure in this area 

is complex, however, and stratigraphic thicknesses in excess of 

110 feet may be present locally.

The formation is known to be absent at a number of well-exposed localities along the contact between the pre-Silurian rocks 

and the Goshen Formation in the area of figure 1. North of the 

Blandford racetrack the formation is missing in Massachusetts. 

Thus, on the basis of the mapping in the area of figure 1, the thickness of the Russell Mountain Formation is 0 to 110 feet.

CORRELATION AND AGE

No fossils have been found in the Russell Mountain Formation, 

nor have any been found in any of the pre-Triassic rocks on the 

east limb of the Berkshire anticlinorium in Massachusetts or 

Connecticut. The Russell Mountain Formation is younger than 

units 4 and 5 of Stanley (1967), which are correlated with the 

Hawley Formation by Hatch and Stanley (1970) on the basis of 

intertonguing facies relationships. The age of the Hawley, based 

on correlations with Vermont, is considered by Hatch (1967, p. 12) 

to be Middle Ordovician.

The Russell Mountain Formation is overlain by the Goshen Formation which "may ... include rocks that range in age from Middle 

Silurian to [Early] Devonian" (Hatch, 1967, p. 15). The Russell
B8 CONTRIBUTIONS TO STRATIGRAPHY

Mountain thus cannot be older than Middle Ordovician or younger 

than Middle Silurian.

Although no rocks in the stratigraphic position of the Russell 

Mountain Formation have been seen in Massachusetts north of 

Blandford village, similar rocks do crop out in this stratigraphic 

position as a discontinuous series of lenses throughout much of 

eastern Vermont, where they are called the Shaw Mountain Formation (Doll and others, 1961). The Shaw Mountain Formation, 

as originally described by Currier and Jahns (1941, p. 1496-1501). 

contains a variety of rocks including quartz conglomerate and 

quartzite, soda rhyolite tuff, and crinoidal limestone. In the Plainfield quadrangle, Vermont, Konig (1961, p. 30) states that "most 

of the [Shaw Mountain] section is composed of thin-bedded calcareous quartzite which locally grades into fine-grained metamorphosed quartz conglomerate." In describing this calcareous 

quartzite, he says (p. 30), "On a fresh exposure this rock is light 

gray, but upon weathering develops a light-tan to dark-brown cellular rind which may be as much as one to two inches thick." This 

description applies equally well to the porous brown-weathered carbonate-calc-silicate rock of the present area described on page 3. 

Although Currier and Jahns (1941, p. 1497) describe stretched 

pebbles in the Shaw Mountain conglomerate with long axes as 

much as 11 inches long, Konig (1961, p. 31) describes the conglomerate in the Plainfield quadrangle as having pebbles with "diameters ranging from 4 to 25 millimeters." Konig's pebbles are thus 

comparable in size to the pebbles observed in the Russell Mountain 

rocks. The two principal lithologies of the Plainfield, Vt., area, 

calcareous quartzite and quartz conglomerate, are thus very similar to two of the principal lithologies of the present area.

Greenstones, soda rhyolite tuff, crystalline limestone, and cummingtonite schist have been reported by Currier and Jahns (1941, 

p. 1496-1501), Konig (1961, p. 31), and Doll, Cady, Thompson, 

and Billings (1961) as local minor lithologies in the Shaw Mountain Formation. None of these rock types have been recognized in 

the Russell Mountain Formation, but their limited areal extent in 

Vermont and small size of the area of Russell Mountain rocks 

studied to date should rule out the use of this fact as an argument 

against correlating the Shaw Mountain and Russell Mountain 

Formations.

Boucot (1968) has assigned to the Shaw Mountain a Wenlock 

age apparently based on the following evidence. As reported by 

Boucot and Thompson (1963, p. 1318), the Shaw Mountain contains Howellella near Albany, Vt. The type of Howellella found
RUSSELL MOUNTAIN FORMATION IN WESTERN MASSACHUSETTS B9

has a known stratigraphic range of Cs (late Llandovery) to early 

Gedinnian (Manlius-Coeymans). Furthermore, according to Berry 

and Boucot (1970), the stratigraphic position of the Shaw Mountain just above the Taconic unconformity and the absence of Early 

Devonian strata along strike in Vermont or Quebec older than 

Siegen (Becraft-Oriskany) suggest that the Shaw Mountain is of 

Silurian age. In addition, the Peasley Pond Conglomerate, which is 

siir.ilar to the conglomerate in the Shaw Mountain, in the adjacent 

Mernphremagog area of southern Quebec underlies strata of early 

Ludlow age. This reasoning suggests that the Shaw Mountain cannot be older than late Llandovery (Cs) nor younger than earliest 

Ludlow and presumably is the basis for Boucot's (1968, p. 84) 

assignment of the Shaw Mountain to a Wenlock age. On the basis 

of the similarity of the principal lithologies of the two formations 

and their similar stratigraphic position, the Russell Mountain Formation is believed to be the lateral equivalent of the Shaw Mountain Formation of Vermont. On the basis of this correlation, the 

Russell Mountain is assigned a Wenlock age, which is approximately equal to the middle part of the Middle Silurian of the American standard section. (For comparison of the European and 

American sections, see Pavlides and others, 1968, fig. 5-2, p. 66.) 

Rocks present to the south in Connecticut are lithologically similar to, and may be stratigraphically correlative with, the rocks of 

the Russell Mountain Formation. Further study of these possible 

correlations is in progress.

REFERENCES

Berry, W. B. N., and Boucot, A. J., 1970, Silurian of North America: Geol.

Soc. America Spec. Paper 102. (In press.) 

Boucot, A. J., 1968, Silurian and Devonian of the northern Appalachians, in

Zen, E-an, White, W. S., Hadley, J. B., and Thompson, J. B., Jr., eds.,

Studies of Appalachian geology northern and maritime: New York,

Interscience Publishers, p. 83-94. 

Boucot, A. J., and Thompson, J. B., Jr., 1963, Metamorphosed Silurian brachiopods from New Hampshire: Geol. Soc. America Bull., v. 74, no. 11, p.

1313-1334. 

Curlier, L. W., and Jahns, R. H., 1941, Ordovician stratigraphy of central

Vermont: Geol. Soc. America Bull., v. 52, no. 9, p. 1487-1512. 

Doll, C. G., Cady, W. M., Thompson, J. B., Jr., and Billings, M. P., 1961,

Centennial geologic map of Vermont: Montpelier, Vt., Vermont Geol.

Survey, scale 1:250,000. 

Hatch, N. L., Jr., 1967, Redefinition of the Hawley and Goshen Schists in

western Massachusetts: U.S. Geol. Survey Bull. 1254-D, 16 p. 

Hatch, N. L., Jr., Norton, S. A., and Clark, R. G., Jr., 1970, Geologic map of

the Chester quadrangle, Massachusetts: U.S. Geol. Survey Geol. Quad.

Map GQ-858. (In press.)
BIO CONTRIBUTIONS TO STRATIGRAPHY

Hatch, N. LM Jr., and Stanley, R. S., 1970, Stratigraphic continuity and facies 

changes in formations of early Paleozoic age in western Massachusetts 

and tentative correlations with Connecticut [abs.]: Geol. Soc. America 

Abstracts with Programs, v. 2, no. 1, p. 23-24.

Konig, R. H., 1961, Geology of the Plainfield quadrangle, Vermont: Vermont 

Geol. Survey Bull. 16, 86 p.

Pavlides, Louis, Boucot, A. J., and Skidmore, W. B., 1968, Stratigraphic evidence for the Taconic orogeny in the northern Appalachians, in Zen, 

E-an, White, W. S., Hadley, J. B., and Thompson, J. B., Jr., eds., Studies 

of Appalachian geology northern and maritime: New York, Interscience 

Publishers, p. 61-82.

Stanley, R. S., 1967, Geometry and age relations of some minor folds and 

their relation to the Woronoco nappe, Blandford and Woronoco quadrangles, Massachusetts, in New England Intercollegiate Geol. Conf., 59th 

Ann. Mtg., Oct. 13-15, 1967, Guidebook for field trips in the Connecticut 

Valley of Massachusetts: Amherst, Mass., p. 48-60.

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