Changes in Nomenclature of Upper Precambrian 

to Lower Paleozoic(?) Formations in the 

Natick Quadrangle, Eastern Massachusetts, 

and Their Tentative Correlations With 

Recks in Rhode Island and 

Ccnnecticut

GEOLOGICAL SURVEY BULLETIN 1395-E

Prepared in cooperation with the 

Commonwealth of Massachusetts 

Department of Public Works

Changes in Nomenclature of Upper Precambrian 

to Lower Paleozoic (?) Formations in the 

Natick Quadrangle, Eastern Massachusetts, 

and Their Tentative Correlations With 

Rocks in Rhode Island and 

Connecticut

By ARTHUR E. NELSON

CONTRIBUTIONS TO STRATIGRAPHY

GEOLOGICAL SURVEY BULLETIN 1 395 - E

Prepared in cooperation with the 

Commonwealth of Massachusetts 

Department of Public Works

Three formations are named and defined in a 

3,500-meter section of upper Precambrian to 

lower Paleozic(f) sedimentary and volcanic 

rocks in eastern Massachusetts

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1974
UNITED STATES DEPARTMENT OF THE INTERIOR 

ROGERS C. B. MORTON, Secretary

GEOLOGICAL SURVEY 

V. E. McKelvey, Director

Library of Congress catalog-card No. 74-600146

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

Washington, D.C. 20402 Price 35 cents (paper cover)

Stock Number 2401-02549
CONTENTS

Page

Abstract _________________________________-__ El 

Introduction __ __ _________ _ 1

Stratified rocks _ _ __________________ 4

Rice Gneiss _____ ______________________ 6

Westboro Quartzite _________________________ _ 7

Kendal Green Formation ________________________ 8 

Cherry Brook Formation ______________ _ 8

Claypit Hill Formation ________________________ 10 

Correlations of formations in eastern Massachusetts with rock units

in Rhode Island and Connecticut ____________________- 10 

References cited _ 14

ILLUSTRATIONS

Page 

FIGURE 1. Map of the Natick and part of the Concord quadrangles E2

2. Generalized geologic map of the Natick quadrangle ____ 4

3. Generalized sections and tentative correlations of some

rocks in Connecticut, Massachusetts, and Rhode Island- 11

TABLE

Page

TABLE 1. Stratigraphic succession and thickness of sedimentary and 

volcanic rock units presently recognized in the Natick 

quadrangle _ _.___________________ E3

m

CONTRIBUTIONS TO STRATIGRAPHY

CHANGES IN NOMENCLATURE OF UPPER 

PRECAMBRIAN TO LOWER PALEOZOIC(?)

FORMATIONS IN THE NATICK

QUADRANGLE, EASTERN MASSACHUSETTS,

AND THEIR TENTATIVE CORRELATIONS

WITH ROCKS IN RHODE ISLAND

AND CONNECTICUT

By ARTHUR E. NELSON

ABSTRACT

Approximately 3,500 meters of upper Precambrian to lower Paleozoic (?) 

metamorphosed sedimentary and volcanic rocks are exposed in the northwestern half of the Natick quadrangle. The lower part of this sequence is 

intruded by Precambrian granodiorite; the upper part is faulted out.

As a result of the detailed mapping, it is possible to name and define 

several formations in this rock sequence: a unit of upper Precambrian biotite gneiss, schist, quartzite, and amphibolite is named the Rice Gneiss; a 

unit of mafic and felsic volcanic rocks is named the Cherry Brook Formation; 

a unit of fine-grained felsic and mafic gneiss and schist is named the Claypit Hill Formation; and the previously named Kendall Green Slate is renamed the Kendal Green Formation.

The upper Precambrian to lower Paleozoic (?) rocks are tentatively correlated with formation of the Blackstone Series in Rhode Island and with 

the Plainfield, Quinebaug, and Mamacoke Formations in Connecticut.

INTRODUCTION

This report presents changes in stratigraphic nomenclature of 

a succession of upper Precambrian to lower Paleozoic (?) rocks in 

the Natick quadrangle, Massachusetts. Three stratigraphic units 

are formally named, one previously named unit is renamed, and 

possible correlations with rocks in Rhode Island and Connecticut 

are given. Stratigraphic studies undertaken in the Natick quadEl
E2 CONTRIBUTIONS TO STRATIGRAPHY

rangle (fig. 1) are part of a larger program of geologic mapping 

in Massachusetts by the U.S. Geological Survey, in cooperation

42°22'30"

2 KILOMETERS

FIGURE 1. Map of the Natick and part of the Concord quadrangles, X 

indicates type locality.
NATICK QUADRANGLE E3

with the Department of Public Works of the Commonwealth of 

Massachusetts.

The geologic section in the Natick quadrangle consists of sedimentary and volcanic rocks of Preeambrian to Carboniferous age 

(table 1). Figure 2 is a generalized geologic map. The prominent 

northeast-trending Basin fault separates Silurian to Carboniferous 

rocks of the Boston basin on the southeast from older rocks on 

the northwest. The older rocks are distinctly different in lithology 

and have been regionally metamorphosed to the almandine amphibolite fades. A batholith, stocks, and dikes of granodioritic 

to gabbroic composition have intruded parts of the section northwest of the Basin fault. This report discusses the nomenclature 

and stratigraphy of the upper Preeambrian to lower Paleozoic (?) 

rocks.

Much of the quadrangle is covered by a veneer of glacial deposits 

(Nelson, 1974) that conceals contacts between formations. Therefore, thicknesses of or contact relations between stratigraphic 

units are not precisely known. However, the interpretations preTABLE 1. Stratigraphic succession and thickness of sedimentary and volcanic 

rock units presently recognized in the Natick quadrangle

Estimated 

thicknena 

(metera)

Upper Silurian to Carboniferous:

Cambridge Slate ________________________ 370 

Brighton Melaphyre ____________________ 1,070

Roxbury Conglomerate ____________ ._ 1,130

Mattapan Volcanic Complex:

Laharic member __________________ 33&

Andesitic volcanic member _________________ 850

Siliceous pyroclastic member ______________ 760

BREAK IN SEQUENCE

Preeambrian Z to lower Paleozoic (?):

Amphibolite ___________________________ 460

BREAK IN SEQUENCE

Claypit Hill Formation 1 ____________________ 460-610

UNCONFORMITY

Cherry Brook Formation 1 :

Amphibolite _________________________ 610 

Felsic tuff __________________________ 290 

Preeambrian Z(?):

Kendal Green Formation 8 ___________________ 216

Preeambrian Z:

Westboro Quartzite _______________________ 980 

Rice Gneiss 1 __________________________ 760

Total thickness in quadrangle _____ 8,440

1 New name. 

a Renamed.
E4 CONTRIBUTIONS TO STRATIGRAPHY

42° IS'

2 MILES

2 KILOMETERS

FIGURE 2. Generalized geologic map of the Natick quadrangle.

sented here appear to be in general agreement with those established elsewhere in eastern Massachusetts (Norman Cuppels, oral 

commun., 1968), in Connecticut (Goldsmith, 1966), and in Rhode 

Island (Quinn, 1971).

STRATIFIED ROCKS

A series of nonfossiliferous formations that apparently are a 

conformable sequence is present in the northern and western
V

NATICK QUADRANGLE 

CORRELATION OF MAP UNITS

E5

Break in sequence 

Unconformity

ti&z^mm. * *P ^Pzp cJ

<PzpCc

pu

CARBONIFEROUS TO 

UPPER SILURIAN

LOWER PALEO2OIC(?) 

TO PREC AM BRIAN Z

PRECAMBRIAN Z

DESCRIPTION OF MAP UNITS

UNDIVIDED ROCKS OF THE BOSTON BASIN

e

 CLAYPIT HILL FORMATION

AMPHIBOLITE

 CHERRY BROOK FORMATION 

UNDIVIDED

AMPHIBOLITE

FELSIC TUFF

 KENDAL GREEN FORMATION

WESTBORO QUARTZITE

 RICE GNEISS

UNDIVIDED PLUTONIC ROCKS, MOSTLY 

DEDHAM GRANODIORITE

PzpCca

_^ 7 

PzpGct <

pu

 New or revised stratigraphic name

 Contact Approximately located

 Fault - U, upthrown side; D, downthrown side

Folds 

Anticline

Syncline

FIGURE 2. Continued.

part of the quadrangle. All or parts of these rock units are also 

exposed in quadrangles to the north, northeast, and west. In order
E6

of decreasing age, these rocks are the Rice Gneiss, Westboro 

Quartzite, Kendal Green Formation, and Cherry Brook Formation. 

Unconformably overlying the Cherry Brook is the Claypit Hill 

Formation.

RICE GNEISS

The oldest rocks exposed in the quadrangle are a sequence of 

intercalated variably textured and layered biotite gneiss, schist, 

and quartzite. These rocks are here named the Rice Gneiss after 

Rice Road, along which much of the formation is exposed (figs. 

1, 2). The type locality is the exposure just northeast of the intersection of Massachusetts Rte. 30 and Rice Road in the northwestern part of the Natick quadrangle. Other exposures of the 

formation are in the Weston town forest about 0.4 mile (0.64 km) 

west of Regis College and along the west side of the north-trending ridge that is half a mile east of Rice Road.

The formation reaches a maximum thickness of 760 m and is 

mostly thin bedded, although beds and layers range from 0.5 cm 

to 1 m in thickness. The rocks are foliated and, where observed, 

the foliation is parallel to the lithologic layering. The formation 

generally strikes north and is folded about north-trending fold 

axes. It is apparently conformably overlain to the west by the 

Westboro Quartzite, and the lower part of the gneiss unit is intruded by the Dedham Granodiorite.

Most of the Rice Gneiss is a medium- to dark-gray, fine- to 

medium-grained, equigranular to inequigranular plagioclasequartz-biotite gneiss that is interlayered with equigranular to inequigranular and irregularly layered biotite-plagioclase-quartz 

gneiss and schist, quartz-biotite-microcline-muscovite schist, and 

some thin beds of quartzite and f eldspathic quartzite. Locally, the 

Rice Gneiss is garnetiferous, is intruded by small granitic and 

pegmatitic veins, and, in places, contains irregular pods and veinlets of silexite. Except for the quartzites, which undoubtedly were 

originally accumulations of almost pure quartz (beach) sand, 

most of the formation resulted from metamorphism of tuffaceous 

materials that were variably mixed with quartz sand.

The Rice Gneiss is not known to correlate with any other rock 

unit in Massachusetts, and as fossils have not been found in it, 

its age is not known for certain. However, the formation is believed to be late Precambrian (Precambrian Z) in age because 

it is intruded by the Dedham Granodiorite from which Zartman 

(written commun., 1971) obtained a zircon isotopic age of 630±20 

m.y. from a sample collected in the Natick quadrangle. Fairbairn,
NATICK QUADRANGLE E7

Moorbath, Ramo, Pinson, and Hurley (1965) also consider the 

Dedham Granodiorite exposed at nearby Dedham to be of Late 

Precambrian age.

WESTBORO QUARTZITE

Westboro Quartzite was originally named by Perry and Emerson (1903, p. 155) for exposures consisting mostly of quartzite 

in Westboro, Mass. In the Natick quadrangle, the Westboro is 

predominantly quartzite and feldspathic quartzite variably interlayered with mica-quartz schist and some amphibolite. The formation is exposed in several fault blocks across the northern part of 

the quadrangle and in a large area in the southwestern part (fig. 

2); in addition, many small inclusions of these rocks are present 

in the younger Dedham Granodiorite.

The Westboro has a maximum thickness of about 980 m in the 

Natick quadrangle. It strikes north in the west-central part of 

the quadrangle where it is principally exposed and, like the underlying Rice Gneiss, is folded around north-trending axes. Although 

contacts with older and younger rocks were not observed, the 

Westboro appears to be conformably overlain by the Kendal 

Green Formation in the northeastern part of the quadrangle and 

in the adjoining Concord quadrangle.

Three distinct units make up the Westboro in the Natick quadrangle, but because contacts are concealed by glacial deposits the 

units could not be mapped. The lower unit is a light-gray massively bedded almost pure quartzite with minor interbedded biotite 

gneiss. The massive character of the rock at some exposures makes 

it difficult to recognize bedding, but locally beds are in excess of 

5 m thick.

Ah assemblage of dark- to medium-gray fine-grained biotite 

and hornblende gneisses and schists, relatively pure quartzite, 

feldspathic quartzite, and amphibolite make up the middle unit 

of the Westboro. These rocks are interlayered in all proportions, 

and the beds vary widely in thickness, but, with the exception of 

a 5.5-m bed, most beds are between 3 cm and 1.5 m thick.. Biotite 

gneiss and schist are the predominant rock types in the lower 

part of this unit; amphibolite is the least common type.

The upper unit is a light-gray thick- to massively bedded quartzite in which bedding is difficult to observe. A few thin intercalations of biotite gneiss are found near its base.

The Westboro probably formed from the accumulation of varying amounts of volcanic materials (tuff) and quartz (beach) 

sand in a depositional basin. At times, little if any volcanic debris
y E8 CONTRIBUTIONS TO STRATIGRAPHY

was deposited, and relatively thick deposits of quartz sand were 

laid down, which eventually resulted in the thick units of quartzite. At other times, volcanic detritus was mixed with the quartz 

sand, which resulted in feldspathic quartzite, gneiss, and schist. 

The amphibolites were originally mafic tuffs or basaltic lava 

flows.

The Westboro is nonfossiliferous. Like the Rice Gneiss, it has 

been intruded by Precambrian Dedham Granodiorite and is presumed to be of late Precambrian (Precambrian Z) age.

KENBAL GREEN FORMATION

The name Kendal Green Formation is herein changed from the 

original usage of Hobbs (1899, p. 110), who called the same rocks 

the Kendall Green Slate. The Kendal Green is not a slate; it is 

primarily a very fine grained, light-tan, thinly laminated, felsic 

tuff that is interlayered with dark-greenish-gray fine-grained 

thinly laminated tuff and some discontinuous layers of quartzite. 

In addition, the spelling is changed to conform to that of the geographic name, Kendal Green. The Kendal Green has an estimated 

maximum thickness of 215 m in the Natick quadrangle. The age 

of the Kendal Green, although uncertain, is probably late Pre= 

cambrian (Precambrian Z).

The relationship between the Westboro Quartzite and Kendal 

Green is critical to the stratigraphy of eastern Massachusetts. 

Farther to the northeast, Kenneth Bell (written commun., 1973) 

indicates that mafic volcanic rocks similar to the upper part of 

the Cherry Brook Formation rest conformably on the Westboro 

Quartzite and, furthermore, that rocks resembling the siliceous 

tuff of the Kendal Green overlie the mafic volcanics. In the Natick 

quadrangle, however, the Kendal Green appears to overlie the 

Westboro; unfortunately, exposures between the two formations 

are too sparse to resolve the problem satisfactorily. One can assume that either a fault or an unconformity separates the two 

formations. In the Natick quadrangle area, however, field relations 

do not support evidence for a fault, as neither gouge nor breccia 

zones have been observed and neither formation is truncated. 

Furthermore, bedding within the two formations is essentially 

parallel. Therefore, it is believed the Kendal Green rests conformably on the Westboro and that a pulse of felsic volcanism 

produced, in the Natick area, the siliceous tuff prior to the deposition of the mafic volcanic rocks.

CHEERY BROOK FORMATION

Overlying the Kendal Green Formation is a thick assemblage of
NATICK QUADRANGLE E9

mostly amphibolite with some felsic volcanic rocks at the base. 

This assemblage is here named the Cherry Brook Formation, 

after Cherry Brook along which a large part of the formation is 

present. The type locality is approximately 1 mile (1.6 km) north 

of the Natick quadrangle in the adjoining Concord quadrangle, 

where several exposures are located southeast of the Merriam 

Street crossing of Cherry Brook. Other exposures are present 

along Merriam Street, on some small hills east of Merriam Street, 

and north of the railroad in the Natick quadrangle. Felsic volcanic rocks are present about 0.6 mile (0.96 km) east of Merriam 

Street along the railroad in the Natick quadrangle.

The Cherry Brook Formation is as much as 900 m thick in the 

Natick quadrangle and more than 1,200 m thick in the adjoining 

Concord quadrangle (Nelson, unpub. data). The rocks are folded, 

but the axes trend northeast rather than north as in the Rice 

Gneiss and Westboro. Bedding is typically obscure and variable, 

ranging from several centimeters to 1 m or more thick. These 

rocks have been metamorphosed to amphibolite fades and, where 

determined, the schistosity is parallel to bedding.

In the Natick quadrangle, the lower part of the formation is a 

light- to pinkish-gray, fine- to medium-grained, massive felsic 

crystal tuff with a few thin beds of dark medium-grained biotitequartz-f eld spar schist; this part is as much as 290 m thick.

Amphibolite and intercalated biotite schist and quartzite constitute the upper part of the Cherry Brook. The predominant rock 

type is amphibolite; it is equigranular to inequigranular, fine 

to coarse grained, thin to thick layered, and locally striped with 

thin alternating discontinuous felsic and mafic bands. In places, 

the rocks are massive and typically amygdaloidal. Some exposures 

show a vague suggestion of pillow structures.

In the Natick quadrangle, the Cherry Brook Formation is a 

thick sequence of metamorphosed volcanic tuffs and flows. Felsic 

tuffs formed the lower part of the formation; later, vast accumulations of basaltic to andesitic tuffs and flows were deposited to 

form the upper part of the formation.

The age of the Cherry Brook is uncertain. Previously, these 

rocks were considered to be part of the Marlboro Formation of 

Precambrian (?) age (Emerson, 1917, p. 25). However, detailed 

mapping in the Natick (Nelson, 1974) and Framingham (Nelson, 

unpub. data) quadrangles shows that these rocks do not correlate 

with the Marlboro Formation exposed at the type locality in Marlboro, Mass. The Cherry Brook overlies the Kendal Green Forma-
E10 CONTRIBUTIONS TO STRATIGRAPHY

tion and is believed to be late Precambrian to early Paleozoic (?) 

in age.

CLAYPIT HILL FORMATION

Unconformably overlying the Cherry Brook Formation is an 

assemblage of hornblende- and biotiite-bearing gneisses interleaved with felsic gneiss and amphibolite. These rocks are here 

named the Claypit Hill Formation for exposures near Claypit 

Hill Road. The type locality includes exposures along the railroad between 0.1 and 0.4 mile (0.16-0.64 km) east of Claypit 

Hill Road. Other exposures of this .rock can be seen along an unnamed road, about 0.25 mile (0.4 km) north of the quadrangle, 

that runs east from Draper Road in the Concord quadrangle.

A thick cover of glacial deposits (Nelson, 1974) conceals most 

of the formation, and data on its thickness and structure are 

sparse. Nevertheless, it is estimated to be between 460 and 610 

m thick. The upper part is truncated 'by a fault in the Natick 

quadrangle. Where observed, the bedding is parallel to schistosity 

and ranges from about 8 cm to 0.5 m in thickness.

Most of the Claypit Hill is a dark-greenish-gray, fine-grained 

hornblende-plagioclase-quartz-epidote gneiss. It is interlayered 

with medium-gray fine- to medium-grained almost equigranular 

biotitejplagioclase-quartz-m.uscovite gneiss that locally contains 

garnet and rarely sillimanite; medium- to dark-gray fine-grained 

hornblendeHbiotite-plagioclase-quartz gneiss; medium- to dark-gray 

equigranular biotite-plagioclase-quartz-microcline gneiss; and 

minor thin beds of dark-gray fine- to medium-grained amphibolite. 

In places, epidote, chlorite, and sericite are abundant. It is possible that other less resistant rock types are concealed by surficial 

deposits, but none have been observed to date.

The age of the Claypit Hill is uncertain, however, as the formation apparently unconformably overlies the Cherry Brook, which 

is believed to be of late Precambrian to early Paleozoic (?) age; 

the Claypit Hill is tentatively assigned a late Precambrian to 

early Paleozoic (?) age.

CORRELATIONS OF FORMATIONS IN EASTERN

MASSACHUSETTS WITH ROCK UNITS IN RHODE

ISLAND AND CONNECTICUT

Upper Precamibrian to lower Paleozoic (?) rocks in the Natick 

quadrangle are believed to correlate with some formations in 

Rhode Island and Connecticut that occupy the same relative stratigraphic position and have similar thicknesses and litftologic 

characteristics (fig. 3). The stratigraphic sections that are be-
§dl

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C3- 

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Formation nfield Pla 

1 '1 

39:

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Q Formation Quinebaug 

33

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SERIES BLACKSTONE

XOIXVN 113
E12 CONTRIBUTIONS TO STRATIGRAPHY

lieved to correlate with one another are: in eastern Massachusetts, 

a section about 3,465 m thick that includes the Rice Gneiss, Westboro Quartzite, and Kendal Green, Cherry Brook, and Claypit 

Hill Formations; in northeast Rhode Island, the Blackstone Series, 

which is about 3,300 m thick (Quinn, 1953, p. 266) and which includes the Mussey Brook Schist, Quinnville Quartzite (formerly 

Westboro Quartzite), Sneech Pond Schist, and Hunting Hill Greenstone (Quinn and others, 1948, p. 10-13; Quinn, 1971, p. 12-13) ,° 

in southern Connecticut, the Plainfield and Mamacoke Formations 

that are about 3,360 m thick (Goldsmith, 1966, p. J3-J7); in 

northern Connecticut, the Plainfield and Quinebaug Formations 

(Dixon, 1968) of unknown thickness.

The Rice Gneiss is believed to correlate with the Mussey Brook 

Schist of Rhode Island (Quinn and others, 1948) and with part 

of the lower part of the Plainfield Formation of Connecticut 

(Goldsmith, 1966, p. J7). In Rhode Island the Mussey Brook 

Schist, made up of rocks (mica schist, quartz-feldspar gneiss, 

quartzite, and some minor lenses of marble) somewhat similar 

to the Rice Gneiss, is estimated to be about 985 m thick (Quinn 

and others, 1948, geologic map). The Mussey Brook underlies the 

Quinnville Quartzite, formerly called the Westboro Quartzite 

(Quinn, 1971, p. 8). In Connecticut, the lower part of the Plainfield Formation is made up of a thick sequence of white quartzite that grades downward into a thick section of micaceous schist, 

gneiss, and feldspathic quartzite (Goldsmith, 1966, p. J7). The 

description of these underlying rocks suggests they are similar 

to the Rice Gneiss; in addition, they occupy the same relative 

stratigraphic position.

The Westboro Quartzite in eastern Massachusetts probably 

correlates with the Quinnville Quartzite in Rhode Island and with 

most of the Plainfield Formation in Connecticut (Goldsmith, 1966, 

p. J6-J7; Dixon, 1968). As previously mentioned, the Westboro 

Quartzite is informally divided into lower, middle, and upper parts 

in the Natick quadrangle. In Rhode Island, the Quinnville Quartzite consists of quartzite beds above and below the Albion Schist 

Member (Quinn and others, 1948, p. 12), which is principally a 

fine-grained quartz-mica schist. The lower and upper parts of the 

Westboro Quartzite in eastern Massachusetts most probably correlate with the quartzite beds below and above the Albion Schist 

Member of the Quinnville Quartzite in Rhode Island; the middle 

part of the Westboro in Massachusetts probably correlates with 

the Albion Schist Member in Rhode Island.

As much as 980 m of the Westboro Quartzite is present in the
NATICK QUADRANGLE E13

Natick quadrangle, and Quinn, Ray, and Seymour (1948, p. 11) 

report the Westboro ranges from about 330 to 980 m thick in the 

Pawtucket quadrangle, Rhode Island.

Correlation of the Westboro Quartzite with the Quinnville is 

substantiated by Emerson and Perry (1907, p. 10-11), who early 

in the century traced rocks (Westboro Quartzite) at Westboro, 

Mass., southward to Rhode Island, where they form part of the 

Blackstone Series.

In southern Connecticut, the Plainfield Formation can be divided into three parts (Goldsmith, 1966, p. J6-J7) : the lower part 

consists of quartzite beds that grade downward into micaceous 

gneiss and schist; the middle part is made up of biotite-quartzfeldspar gneiss, calcsilicate gneiss, amphibolite, schist, and some 

thin beds of quartzite; the upper part is principally quartzite with 

some minor intercalations of mica gneiss and schist. All three 

parts of the Plainfield, with the exception of those gneisses and 

schists below the thick sequence of quartzite in the lower part, 

most probably correlate with the corresponding parts of the 

Westboro Quartzite in Massachusetts. In addition, Lundgren 

(1966, p.- 33) reports that the Plainfield Formation in southern 

Connecticut can be traced eastward to Rhode Island where equivalent rocks are mapped as part of the Blackstone Series (Westboro Quartzite of Lundgren, 1966).

The Kendal Green Formation, which apparently overlies the 

Westboro in eastern Massachusetts, may represent a f acies change 

from Sneech Pond Schist in Rhode Island, but its counterpart in 

southern Connecticut is not known. The Kendal Green is predominantly a very fine grained thinly laminated ash-fall tuff that 

includes light-tan to gray felsic tuff and intercalated thinly laminated dark-greenish-gray tuff. The Sneech Pond Schist is principally a fine-grained quartz-mica schist of either green or gray 

color. Although these two formations contain different lithologies, 

they may be time equivalents.

The Cherry Brook Formation overlies the Kendal Green Formation in the Natick quadrangle; it is an assemblage of mafic to intermediate volcanic flows and volcaniclastic deposits that are intercalated with some minor schists and gneisses. This volcanic sequence together with the overlying gneisses and amphibolites of 

the Claypit Hill Formation probably correlates with a somewhat 

similar volcanic sequence in Rhode Island called the Hunting Hill 

Greenstone. The Hunting Hill, which is the upper part of the 

Blackstone Series, contains several types of metamorphosed
E14 CONTRIBUTIONS TO STRATIGRAPHY -

basaltic rocks that have been altered to greenstone, some of 

which are massive and some schistose.

Parts of the Mamacoke in southern Connecticut (Goldsmith, 

1966, p. J5 and J6) and the Quinebaug Formation in northern 

Connecticut (Dixon, 1968) are believed to be time equivalents of 

the Cherry Brook and Claypit Hill Formation in eastern Massachusetts. The M*amacoke, which overlies the Plainfield in southern Connecticut, contains a variety of rocks ranging from amphibolite to dark equigranular biotite-plagioclase gneiss and gray 

biotite-quartz-feldspar gneiss. Its stratigraphic position is tEe 

same as the combined Cherry Brook and Claypit Hill, but the 

overall lithologic types do not closely resemble the Massachusetts 

rocks although they may represent fades changes.

The Quinebaug Formation in northern Connecticut occupies 

the same stratigraphic position as the Cherry Brook and Claypit 

Hill Formations and, in addition, consists of a similar heterogeneous assemblage of volcanic rocks (Dixon, 1968).

Because the ages of some formations are in doubt, the correlations presented above are necessarily tentative. In eastern Massachusetts some of the rocks undoubtedly are Precambrian in age, 

and others may be as young as Ordovician. In Rhode Island, although the age of the rocks is somewhat uncertain, the Blackstone 

Series is considered to be Precambrian(?) in age (Quinn and 

others. 1948, p. 9: Quinn, 1971, p. 11). Direct evidence for the 

age of the Plainfield Formation^f Connecticut is lacking; it is 

considered to be of Cambrian and Ordovician age (Goldsmith and 

Dixon, 1968^. F-01 or Cambrian (?) age (Harwood and Goldsmith, 1971); in southern Connecticut Lundgren (1966, p. 33) 

correlated the Plainfield with a part of the Blackstone Series of 

Precambrian (?) age.

REFERENCES CITED

Dixon, H. R., 1968, Bedrock geologic map of the Danielson quadrangle, 

Windham County, Connecticut: U.S. Geol. Survey Geol. Quad. Map 

GQ-696.

Emerson, B. K., 1917, Geology of Massachusetts and Rhode Island: U.S. 

Geol. Survey Bull. 597, 289 p.

Emerson, B. K., and Perry, J. H., 1907, The green schists and associated 

granites and porphyries of Rhode Island: U.S. Geol. Survey Bull. 311, 

74 p.

Fairbairn, H. W., Moorbath, S., Ramo, A. 0., Pinson, W. H., Jr., and Hurley, P. M., 1965, Rb-Sr age of granitic rocks of southeastern Massachusetts and the age of the Lower Cambrian at Hoppin Hill, in Variations in isotopic abundances of strontium, calcium, argon and related

ir
NATICK QUADRANGLE E15

subjects: U.S. Atomic Energy Comm., 13th Ann. Prog. Rept. for 1965, 

Massachusetts Inst. Technology, Department of Geology and Geophysics, 

NYO-3943, Contract At (30-1)-1381, p. 3-10.

Goldsmith, Richard, 1966, Stratigraphic names in the New London area, 

Connecticut, in Contributions to stratigraphy, 1965: U.S. Geol. Survey 

Bull. 1224-J, p. J1-J9.

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