Middle Cambrian

CAMBRIAN

Middle Ordovician Middle Devonian Upper Cambrian Upper Ordovician Upper Devonian

STAGESTAGE

Lower Cambrian Lower Ordovician Lower Devonian

Middle Cambrian Middle Ordovician Middle Devonian Upper Cambrian Upper Ordovician Upper Devonian Lower Cambrian Late Mesoproterozoic Neoproterozoic Middle Mesoproterozoic

Y3A

Y3B

Y3C

Z

Y1

Y2

Y3A

Y3B

Y3C

Z

Y1

Y2

Early Mesoproterozoic Lower Ordovician Lower Devonian Lower Silurian Upper Silurian

Lower Silurian Upper Silurian

ORDOVICIAN SILURIAN

Middle

Upper

Lower

Lower

Miocene

CRETACEOUS

JURASSIC

TERTIARY

DEVONIAN

CAMBRIAN PRECAMBRIAN

Late

Mesoproterozoic Neoproterozoic Middle Mesoproterozoic Early Mesoproterozoic

PRECAMBRIAN

ORDOVICIAN SILURIAN DEVONIAN

544 Ma 495 Ma 485 Ma 470 Ma 464 Ma 458 Ma 453 Ma 449 Ma 441 Ma 428 Ma 419 Ma 418 Ma 409 Ma 394 Ma 387 Ma 382 Ma 375 Ma 365 Ma 413.5 Ma

544 Ma

571 Ma571 Ma

900 Ma900 Ma

1000 Ma1000 Ma

1100 Ma1100 Ma

1200 Ma1200 Ma

1300 Ma1300 Ma

1350 Ma1350 Ma

1400 Ma1400 Ma 495 Ma 485 Ma 470 Ma 464 Ma 458 Ma 453 Ma 449 Ma 441 Ma 428 Ma 419 Ma 418 Ma 409 Ma 394 Ma 387 Ma 382 Ma 375 Ma 365 Ma 413.5 Ma

DRESBACH FRANCONIAN TREMPEALEAUAN CHAZY BLACK RIVER TRENTON EDENIAN MAYSVILLIAN RICHMONDIAN

TREMADOCIAN ARENIGIAN

CROIXIAN IBEXIAN WHITEROCKIAN MOHAWKIAN CINCINNATIAN

LLANVIRNIAN

LLANVIRNIAN

CARADOCIAN ASHGILLIAN LLANDOVERY WENLOCK LUDLOW PRÍDOLÍ LOCHKOVIAN PRAGIAN EMSIAN EIFELIAN FRAS- NIAN GIVE- TIAN

FRASNIAN GIVE- TIAN

FAMENNIAN

DRESBACH FRANCONIAN TREMPEALEAUAN CHAZY BLACK RIVER TRENTON EDENIAN RICHMONDIAN

ARENIGIAN

CROIXIAN MOHAWKIAN CINCINNATIAN

CARADOCIAN ASHGILLIAN PRAGIAN EMSIAN EIFELIAN FAMENNIAN

ˆ

MAYSVILLIAN

IBEXIAN WHITEROCKIAN

LLANDOVERY WENLOCK LUDLOW PRÍDOLÍ LOCHKOVIAN

ˆ

TREMADOCIAN

Snd

* 425 Ma

Sbd

* 419 Ma

Sbg

* 421 Ma

Scm

* 419 Ma

Ohi

* 450 Ma

Dfpg

*365 Ma *364 Ma

Dbmg

Dg *392 Ma

Dfqm

*410 Ma

Dlr *407 Ma

Dr

* 412,414 Ma

*407 Ma

Dbgn

* 365 Ma

368 Ma

Dbbg

BRONSON HILL AREA

NEW HAMPSHIRE PLUTONIC SUITE

FITCHLITTLETON

AREA

Littleton Formation

PIERMONT 

AND OTHER

ALLOCHTHONS

AMMONOOSUC VOLCANICS

OF BILLINGS (1935)

?

MOUNT EQUINOX AND

ARLINGTON AREA

unconformities

?

?

?

 unconformity ?

 unconformity

?

DORSET MOUNTAIN AREA Netop Formation Austin Glen Graywacke after Potter (1972)

Bull Formation and Nassau Formation

Whipstock Breccia

of the Walloomsac

Formation 

FORBES (largely tectonic)

HILL

CONGLOMERATE

AND 

BRECCIA

TACONIC ALLOCHTHON

(syn- and post-emplacement)

DORSET MOUNTAIN AND MOUNT EQUINOX AREA

TACONIC ALLOCHTHON (GIDDINGS BROOK,

SUNSET LAKE, AND SUDBURY SLICES) AND

ROCKS OF THE BENNINGTON AREA

?

GRANITE

DIKES

DERBY

PLUTON

BLACK

MOUNTAIN

GRANITE

WILLOUGHBY PLUTON

VICTORY

PLUTON

FRENCH

POND

GRANITE

OTHER DEVONIAN

GRANITES

AND PLUTONS

AGE UNCERTAIN

(See DMU for

unlisted symbols)

BARRE

PLUTONS

EAST BETHEL

PLUTONS

NULHEGAN

PLUTON

CHESTER

DOME

GRANITE

SAWYER

MOUNTAIN

BELT

Littleton

Formation

NORTHEASTERN

VERMONT

CENTRALEASTERN

VERMONT

SOUTHEASTERN

VERMONT

SHAW MOUNTAIN, NORTHFIELD, WAITS RIVER

AND GILE MOUNTAIN FORMATIONS

FAIRLEE QUARTZ

MONZONITE

BETHLEHEM GNEISS AND

KINSMAN QUARTZ MONZONITE

NEWPORT

INTRUSIVE

COMPLEX

BRAINTREE

INTRUSIVE

COMPLEX

HIGHLANDCROFT

PLUTONIC

SUITE

OLIVERIAN

PLUTONIC SUITE

Partridge Formation

Clough Quartzite

Partridge Formation

COMERFORD

INTRUSIVE COMPLEX

LAKE MEMPHREMAGOG INTRUSIVE SUITE

WHITE MOUNTAIN IGNEOUS SUITE

(consisting of plutons and dike swarms

of Jurassic to Early Cretaceous age)

Brandon Lignite

?

?

?

?

?

 unconformity ?

Dalton Formation

SOUTHERN GREEN

MOUNTAINS

ST. ALBANS

AREA

ADIRONDACK LOWLANDS AND

LAKE CHAMPLAIN LOWLANDS

 VERMONT VALLEY SEQUENCE AND 

MIDDLEBURY SYNCLINORIUM

Hoosac Formation

COVER ROCKS EAST

OF GREEN MOUNTAIN MASSIF

COVER ROCKS OF GREEN

MOUNTAIN ANTICLINORIUM

West Bridgewater

Formation

West Bridgewater

Formation

unconfomity

CORRELATION OF MAP UNITS

(Some lesser units listed in the Description of Map Units may not be shown here. Asterisk indicates U-Pb zircon age.)

LAURENTIAN MARGIN

ROWE – HAWLEY ZONE

Beekmantown Group

Zutc

Zsp

(serpentinite)

VOLCANIC ARC INTRUSIVE AND VOLCANIC

ROCKS OF THE NORTH RIVER IGNEOUS SUITE

OF THE ROWE–HAWLEY ZONE

JOSLIN TURN

PLUTON

INTRUSIVE

ROCKS

LAYERED FELSIC

AND MAFIC ROCKS,

IN PART VOLCANIC

BRANCH BROOK

DIKE AND SILL

COMPLEX

ROWE SCHIST

(many units fault bounded)

Cooper Hill

Member

Cram Hill Formation

lower structural level

higher structural level

Moretown Formation

Ottauquechee Formation

Underhill

Formation

Fairfield Pond Monastery Formation Formation

Tibbit Hill

Formation

Pinney Hollow

Formation

Pinnacle Formation

Tyson Formation

Plymouth

Formation

Hazens Notch and

Fayston Formations

Stowe Formation

CRAM HILL FORMATION

OF THE NEWPORT CENTER AREA

Cram Hill Formation

Tillotson Peak

Complex

STRUCTURAL COMPLEXES

Belvidere Mountain

Complex

units completely

fault bounded

ULTRAMAFIC ROCKS

(tectonically intercalated)

?

CORE ROCKS

OF THE

VERNON DOME

* 502 Ma

* 496 Ma

* 486 Ma

 * 483 Ma

* 471 Ma

* 469 Ma

CONNECTICUT VALLEY TROUGH

TRANSITIONAL MARGIN ROCKS EARLY TO LATE TACONIAN ACCRETED TERRANE

break in scale

break in scale

24 Ma

100 Ma

144 Ma

159 Ma

? ? ?

CUTTINGSVILLE STOCK

ASCUTNEY MOUNTAIN IGNEOUS COMPLEX

MONADNOCK

MOUNTAIN

PLUTON

DIKES

BARBER HILL

STOCK

INTRUSIVE ROCKS

PARAGNEISS

ADIRONDACKS IN VERMONT AND IN THE WHITEHALL, N.Y., AREA

?

?

?

?

? ?

?

CARDINAL BROOK INTRUSIVE SUITE

MOUNT HOLLY COMPLEX

Green Mountain massif

Cavendish Formation

(age problematic)

Early Mesoproterozoic or

Neoproterozoic in part

Rocks at Devils Den

(age problematic)

Chester and Athens domes

CHITTENDEN INTRUSIVE SUITE

STRATTON MOUNTAIN

IGNEOUS SUITE

GREEN MOUNTAIN MASSIF

AND EASTERN DOMES:

INTRUSIVE ROCKS

OF THE GREEN MOUNTAIN AND LINCOLN MOUNTAIN

MASSIFS AND EASTERN DOMES

Eastern flank of the Green Mountain massif

and eastern domes

?

?

SOUTH LONDONDERRY IGNEOUS SUITE

?

?

?

?

?

?

Subdivisions and symbology of the Mesoproterozoic on this map follow the time scale used by Tony Davidson 

on the 1998 geologic map of the Grenville province (Geological Survey of Canada Map 1947A, scale 

1:2,000,000). Because late orogenic activity of the Grenville orogeny is younger than 1,000 Ma we adopt 

the much more functional boundary between Neoproterozoic and Mesoproterozoic of 900 Ma following the 

usage of Davidson (1998) rather than that of Plumb (1991). Chronostratigraphic subdivisions in the Ordovician are after Fortey (2000).

*

*492 Ma

*409 Ma

1121 Ma,1119 Ma

*

Basalt at

East Hoosick

Jd

Kpd Kmd

Kab

Kag

Kas

Khf

Kahg

Kns

Kqs

Kes

Jmsy

Jmg

Jme

Kav Kfd

Kgd

Kbh

Ssm

Dgqs Dgqs

Dgq

Dgqs

Dgr

Dga

Dga

Dga

Dga

Dga

Dga

Dgq

DSw

DSws

DSn

DSwac

Scv

DSnl

DSnq

Ss

DSwb

DSwb

DSwqc

DSwgs

DSwv

DSwc

DSwq

DSwc

DSwa

Sv

Sf

Dl

(DSwb)

Dco

Dcoa

Dia

Di Dir

Di Dir

Dih

Dih

DSfr

DSfra

Dgm

Dga

DSw

Dgmr

Dgmc

DSwi

407 Ma *

Dl

Dla Dlr

Sng

Ol

* 442-444 Ma

Scd Scg

Dkq

Dm

Sf

Srr

Sr

Src

Sg

Sc

Op

Opa

Opr

Oaa

Svf

Op

Obqd

Oogt Oobg Oohg

Sc

Ombq

Omfs Omwhg

Omwhb

Omwhv

Oma

Oma

Omb

Omp

Oma

Zu

Oma

Opr

Oar Oa

Oaa

Oaa

Oaa

Oap

Oarq

Oarq

Oarq

Oat

Oam Oac

Oam

Owc

Ows

Oal

Oalp Oali Oalm

Oar Oaa

Oma

Ombq

Omq

Omfgc

Ochv

Omfv

Omp

Omfv

Ontw

Oj

Ont

Onb

Onnt

Onbs

Onr Onbm

Och

Ocha

Ocha

Ochq

Ochfg

Ochic Ochfs

Onbw

Onbwm

Ochq

Omwh

Omwhb

Ochfg

Ochic

Ochq

Ochs

Omhb

Omw

Ofh

Obvb

Owwu

Owbl

Oww

Ow

Oag

Ochv

Ochfv

Ochu

Ochu

Och

Ochsb

Ochcv Ochuc

Ochp

Ochcv

Ochfg

Ochpq

Ocha

Ochfv

Otl

Ohc

Ohl

Ogf

Oh

Oha

Oib

Ogf

Obr

Ov

Ocgu Ocp

Odp

Opi

(Ocbrp)

Osp

Ochd

Ofh

Omi

Oo Otl

Ogf

Ohc

Oh

Ofh

Ohl

Omi

Ocbe

Ocbu

Oi

Ow

Oilc

Oil

Owbl

Owl

Oml

Ocw Ocbrp

Oo

Ofcrp Ofcpi

Omm

Opaw

Oir

Owb

Owb

Ob

Obku

Ob

Ocu

Os

sp sp

d d

w w

m m

Ob

Ohg

Og

Osk

Oskl

Osks

p

pdo

pdo

psc

psc

psh

pq

pq

pc

Os

Ocu

Ofcs

Ofcw

Ofa

Ogm

Ow

ti

pt

Owl

Ogmw

Ogml

Osw sp

d

w

m

Os

Ocu

Opo

ls

hh

eb

wcu

wc

wcnb

wcbb

Osw

Omc Omc

Omq

Omfs

Omb Omq

Omgt

Omfv

Omc Oma

Ombb

Oma

Omfq

Omp

Omp

Zu

Zra

Zrfb

Zsws

Zsa

Zsgt

Zsd

Zs

o

opw

obq

ocf

oa

om

Oals

Zbq

Znq

Znab

Zbms

Zngs

Zngq

Zn

Zngs

Znw

Znw

Znq

Zngq

Zngq

Zd

Zra

Zrgs

Zra

Zra

Zra

 Zrr Zbu

Zbf

Zbc

Zbg

Zbs

Zbagn

Zrrgt Zrr

Zrs

Zrs

Zrch

Zrc

Ztm

Ztp Zjg

Zswa

Zswa

Zsa

Zsg

Zsbg

Zsa

(Zsg)

Zj

oq

oa of

Za

Zap

Ztagn

Zsa

(Zsg)

du

c

du

ca

ls

ls

d d Zbp

Zmpq

co

Zbb

(Znb)

Zzh

Zbmg

Zbk

Zbm

(Znm)

Znr

Znr

Zbv

c

du

Zphw

Zphq

Zpha

Zphw Zphb

Zpha

Zphf

Zph

Zhn

Zhnn

Zhng

Zf

Zfqz

Zfq

Zfs Zfc

Zfw

Zfa

Zth

Zun

Zunw

Zung

Zunql

Zungs

Zpu

Zpva

Zpvc

Zpvf

Zpv

Zfp

Zwb

Zpc

Zpc

Zps

Zpw

Zmt Zfd

Zmf Zmq

Zmp Zmmt

Zfco

Zfq

Zfb

Zps

Zpw Zpwd

Zpc

Ztg

Ztab

Ztbs Ztq

Ztrg

Ztc Ztq

Ztd

Ztgr

Ztc

Ztc

pd

pfq

Zhcgt

Zhs

Zhbs Zhgab

Zhq

Zhd

Zhtm

Zhab

Zhrab

Zhtm

Zhtm

Zhgt Zhs

Zhq

Zhc

Zhabc

Zhc

Zhab

Zh

Zd

Zd

Zdb

Zds

Zdfq

Zdq

Zdq

Zd

Zdc

Zdc

Zds

Zdb

Zdm Zdph

du

c

cb

ca

du

c c

Zdi

Y3Cp

Y2bt Y2ba

Y3Agd Y3Agb

Y3Aphg

Y3Cp

Y3Bp Y3Bg

Y3Ala

Y2lg Y2gg Y2ch

* 1244 Ma Y2ap

Y3Ag

Y3Ama

Y3Apg Y3Agg Y3Ama Y3Amb

* 1149 Ma

Y3Agb

Y3Ccbsa

Y3Ccbhr

Y3Cbsa *945,

955 Ma

Y3Ccbbh

* 962 Ma

Y3Ccbs

* 571 Ma

* 965 Ma

Y3Ccbsr

* 1309 Ma

Y2lgg

Y2lga

Y2pha

Y2phg

Y2bv

Y2cp

Y3Abga Y3Afg

Y1dg

* 1393 Ma

Y1bm Y1bmp

Y1rt

* 1367 Ma

Y1rta

Y1fg

Y1fga

Y1tg

Y1,2bg

Y1,2bg

Y1,2be

Y2mig Y2wg Y2q

Y2a

Y1a Y1rs

Y2lq

Y1cfs

Y1cs

Y1?cm

Y1cg

Y2hg

Y1q

Y2rs

Y2rss

Y2rgt

Y2dm

Y2

m Y2cs

Y?

mfsY?q

Y?dm

Y?

cms

Y2wxcs Y2wxg

Y2wxd

Y2wxs

Y2wxq

Y2bgt Y2myu

Y1,2be

Y2 Y hgn 2cs Y2qz Y2cs

Y2bpg

Y2bmg

Tmb

Dnqm

(Dbg)

(Dqm)

(Ddg)

(Dg)

(Debg)

(Dedg)

(Degr)

(Dwdg)

Ddbg

Dwmz

Dwwz

Dwhz

Ddrz

Dbqm

Dvbg

Dg

* 1221 Ma

* 1326 Ma

* 1321 Ma

1037 Ma

1348 Ma

1372 Ma

1370 Ma

*

* *

* 1383 Ma

* 1342 Ma

*

U.S. DEPARTMENT OF THE INTERIOR

U.S. GEOLOGICAL SURVEY

MARCIA K. McNUTT, DIRECTOR

Prepared in cooperation with the

STATE OF VERMONT, VERMONT AGENCY OF NATURAL RESOURCES,

VERMONT GEOLOGICAL SURVEY

LAURENCE R. BECKER, STATE GEOLOGIST
DESCRIPTION OF MAP UNITS

[Minerals are listed in order of increasing and approximate abundance. 

Minerals that are variably present are shown in parentheses with ±. Nos. 

1–51 refer to uranium-lead (U-Pb) zircon age samples listed in table 1 on the 

back of this sheet and shown on the geologic maps]

Brandon Lignite (lower Miocene)—Organic silt, sand and gravel and slumped 

and dismembered lignite occurring as elongate disrupted deposits in underlying 

kaolin, residual hematite, and ochre deposits near Brandon. Lignite was let down 

into kaolin perhaps by karst collapse along a concealed west-dipping normal fault 

between the Dunham Dolostone on the west and the Cheshire Quartzite on the 

east. Deposit largely concealed but known from historic underground workings for 

kaolin, hematite ochre, and lignite

White Mountain Igneous Suite (Early Cretaceous and Jurassic)

Cuttingsville stock (Early Cretaceous)—Composite stock and intrusive breccia 

dikes consisting of augite and hastingsite syenite, nepheline and sodalite syenite, 

essexite, and monzodiorite. Associated dikes of monchiquite, camptonite, bostonite, and spessartite. Average of five K-Ar ages 101 Ma; ages range between 

103±4 and 99±2 Ma (Armstrong and Stump, 1971)

Nepheline and sodalite syenite, hornblende syenite

Quartz syenite

Essexite (alkali gabbro)

Andesite breccia containing xenoliths of Mesoproterozoic gneiss and 

autoclasts of felsic alkalic and fine-grained mafic rocks

Ascutney Mountain igneous complex (Early Cretaceous)—Consists of two 

plutons, a partial ring dike, and screens of volcanic rocks. K-Ar ages of 122 to 120 

Ma (Foland and Faul, 1977)

Ascutney Mountain stock

Medium- to coarse-grained biotite-microperthite-orthoclase-albite granite

Hornblende granite occurring as small intrusive masses in Kas

Syenite-porphyrite to sericite-perthite-hornblende-biotite syenite; contains 

minor fayalite, augite, and quartz; occurs as a partial ring dike in the Little 

Ascutney stock

Trachytic to rhyolitic tuffs, and breccias containing fragments of volcanic rocks 

having trachytic flow structure and layering. Interpreted as volcanic rocks of 

the edifice

Hornfels—Dense, compact hornfels consisting of recognizable but altered 

schists of the country rock. Shown only around main Ascutney Mountain stock 

in structural continuity with rocks outside the contact aureole. Locally 

aluminous rocks of the Waits River Formation contain andalusite, sillimanite, 

cordierite, pleonaste, and corundum; calcareous pelites contain diopside, 

quartz-wollastonite, plagioclase, grossular garnet, and scapolite

Little Ascutney stock

A composite gabbro-diorite stock having two (eastern and western) intrusive 

centers defined by weakly developed igneous foliation. Gabbro is intruded by 

abundant, poorly defined areas of diorite. Includes two areas of syenite (Kas)

Gabbro and diorite—Medium- to coarse-grained augite-hornblende-biotite 

gabbro infiltrated by hornblende and biotite diorite

Paisanite dike—Fine-grained syenitic dike similar to spherulitic dikes found 

within the plutons and in the adjacent country rocks. One paisanite dike occurs 

well outside the Ascutney Mountain stocks in the saddle between the Chester 

and Athens domes

Barber Hill stock (Early Cretaceous)

A small, 0.5-km-long, northwest-trending stock consisting of a coarse-grained alkali 

syenite core, a fine-grained quartz syenite border, and associated trachyte dikes (Kfd). 

K-Ar biotite age of 114±2 Ma (Armstrong and Stump, 1971) and Rb/Sr whole-rock 

isochron on trachyte dikes of 125±5 Ma (McHone and Corneille, 1980)

Monadnock Mountain pluton (Middle Jurassic)

Composite stock of quartz syenite, syenite granite, and essexite. K-Ar age of 175±4 

Ma (Foland and Faul, 1977)

Quartz syenite—Greenish-gray to pink hornblende-biotite quartz syenite

Granite—Hornblende-biotite-microperthite granite, gradational into quartz syenite

Essexite—Pyroxene-biotite-hornblende andesine gabbroic rock grading into 

quartz syenite

Dikes associated with Monadnock Mountain pluton—Granite, syenite, quartz 

bostonite, camptonite, aplite, and pegmatite

Dikes of White Mountain Igneous Suite—Largely Early Cretaceous, but some may 

be Middle Jurassic (McHone, 1992)

Predominantly mafic and intermediate dikes of diabase, <1 m to 3 m thick, consisting 

of olivine-augite diabase, lamprophyre, calcite amygdaloidal mafic dikes; alkali basalt, 

monchiquite and granitic, rhyolite, trachyte and foidal felsic dikes; and spherulitic 

trachyte dikes. Only felsic dikes near intrusive centers are distinguished as Kfd; 

elsewhere, felsic dikes are not shown separately. Orientation gives strike of dikes 

measured; spot locations from literature without strikes are not shown. Distribution 

uneven owing to nonuniform reporting; however, three general areas contain dike 

swarms: (1) probable Middle Jurassic dikes of syenite diabase, and lamprophyre 

associated with Monadnock Mountain pluton; (2) Early Cretaceous swarms associated 

with Barber Hill stock near Lake Champlain and extending eastward to swarm of 

lamprophyre at western margin of Connecticut Valley trough; and (3) a southern 

Early Cretaceous swarm of foidal felsic, mafic, and lamprophyre dikes associated with 

plutons at Mount Ascutney and Cuttingsville and extending westward into the Taconic 

Range. Commonly dikes are nondeformed and chilled, but locally they are offset by 

minor faults that are either northeast-trending normal or strike-slip. Notable faulted 

dikes occur on the east side of Monadnock Mountain, 3.2 km west of Little Ascutney 

Mountain, along U.S. Route 4 southwest of Proctor, and immediately west of the 

Cuttingsville stock

New Hampshire Plutonic Suite

Devonian intrusive rocks 

(four general designators are used: Dbg, binary and biotite granite and granodiorite, undifferentiated; Dqm, quartz monzonite; Ddg, diorite and gabbro; and Dg, 

small dikes. Only Dbg and Dg are shown in the Description of Map Units)

Binary and biotite granite and granodiorite, undifferentiated—Includes small 

dikes labelled Dg

Igneous rocks of the Northeast Kingdom batholith of Ayuso and Arth 

(1992)—Plutons identified on map

Derby pluton—Light-gray, medium- to coarse-grained, massive, epidote-biotitemuscovite porphyritic granodiorite and minor tonalite (Ddbg), with a rim zone of 

granodiorite (Ddrz). Rb/Sr whole-rock isochron age of 370±17 Ma (Ayuso and 

Arth, 1992)

Echo Pond pluton—Light-gray to pink, medium- to coarse-grained, massive, 

seriate to porphyritic granodiorite and granite (Debg) and outer zone of quartz 

gabbro and quartz diorite (Dedg), and inner zone of granite (Degr)

West Charleston pluton—Dark-gray, medium- to coarse-grained, massive, 

quartz-biotite-hornblende (±pyroxene) gabbro and diorite

Nulhegan pluton—Light-gray to dark-gray, medium- to coarse-grained, massive, 

biotite-clotted, hornblende-quartz monzodiorite, minor granodiorite, and granite 

divided into a western zone (Dnwz), inner zone (Dniz), and core of quartz monzonite (Dnqm). Rb/Sr whole-rock age of 390±14 Ma (Ayuso and Arth, 1992)

Willoughby pluton—Light-gray to pink, medium- to very coarse grained, massive, 

miarolitic garnet-muscovite peraluminous leucogranite. Varies from a pegmatitic 

main zone (Dwmz) to biotitic granodioritic western zone (Dwwz), to inner 

hydrothermally altered zone (Dwhz). Rb/Sr whole-rock age of 376±9 Ma (Ayuso 

and Arth, 1992)

Averill pluton—Gray to pink, medium- to coarse-grained garnet-muscovite-biotite 

granite and pegmatite, undifferentiated

Newark pluton—Pinkish-gray to cream-colored, medium- to coarse-grained 

magnetite-microcline-perthite-biotite granite

Victory pluton—A western zone of medium- to fine-grained biotite-muscovite 

granite and minor hornblende-biotite tonalite and an eastern, more melanocratic 

zone of biotite-hornblende quartz monzonite like that in the Nulhegan pluton, as 

well as biotite granodiorite

Maidstone pluton—Almost-white to dark-gray, locally pink, medium- to coarsegrained hypidiomorphic, granular, biotite-muscovite-microcline-plagioclase 

granite; accessories include apatite, sphene, pyrite, and magnetite

Overprint pattern—Shows areas of intricately mixed country rock, hornfels, and 

abundant dikes and sills of granite. Underlying color and symbol identify country 

rock unit

Other plutons of the New Hampshire Plutonic Suite

Knox Mountain pluton—Light-gray, medium-grained, quartz-rich biotitemuscovite granite. Has distinctly more potassium feldspar and is lighter gray than 

rocks of the East Barre plutons

East Barre plutons—Gray, homogeneous, fine- to medium-grained muscovitebiotite granodiorite. U-Pb zircon Sensitive High Resolution Ion Microprobe 

(SHRIMP) age of 368±4 Ma, no. 47 (Aleinikoff and others, 2011)

East Bethel plutons—Very light-bluish-gray to white, medium-grained, muscovitebiotite quartz monzonite, locally orbicular; commercially known as “Bethel white” 

and similar to the predominantly lighter-colored granitic rocks of southern Vermont

Stiles Pond pluton—Gray, medium-grained, nonfoliated biotite-muscovite tonalite

Porphyritic, light-gray, hypabyssal biotite granite and tonalite in sill-like 

bodies—Contains phenocrysts of euhedral and embayed quartz, euhedral microcline with Carlsbad twinning (in granite), plagioclase, and euhedral biotite 

(±muscovite)

Biotite metadiorite in unit Dgq northeast of St. Johnsbury—Medium-lightbluish-gray, fine-grained, foliated and lineated

Devonian granitic rocks of southern Vermont

Black Mountain pluton of the Guilford dome—Weakly foliated, light-gray to 

whitish-gray, garnet-biotite-muscovite granite, minor pegmatite, and aplite dikes 

(Dg). Rb/Sr muscovite age of 383±7 Ma (Naylor, 1971) and a U-Pb zircon upperintercept age of 364±4 Ma, no. 48 (Aleinikoff and others, 2011)

Granite and trondhjemite dikes of Chester and Athens domes and west of 

the Connecticut Valley trough—Light-gray to white, garnet-muscovite-biotite 

granodiorite at Gassetts quarry, having a U-Pb zircon SHRIMP age of 392±6 Ma, 

no. 46 (Aleinikoff and others, 2011), from rims on Proterozoic-age cores (J.N. 

Aleinikoff, USGS, written commun., 2002); and whitish-gray muscovite-rich 

quartz monzonite and granodiorite, granite pegmatite, and aplite which occur as 

crosscutting nonfoliated dikes within the core of the domes and as folded and 

well-foliated dikes on the east and west flanks of the domes; also granite dikes and 

small stocks of very light gray to white, muscovite-rich, locally garnet-bearing, fineto medium-grained biotite-muscovite quartz monzonite and granodiorite, locally 

orbicular, that intrude cover rocks east of the Green Mountain massif from Jamaica 

to Northfield, including the Liberty Hill locality and the granodiorite stock east of 

Plymouth. The latter contains inherited zircon with rims having an imprecise 

SHRIMP age of about 380 to 390 Ma (Aleinikoff and others, 2011); a similar dike 

south of Plymouth has a U-Pb zircon SHRIMP age of 365±5 Ma, no. 49 

(Aleinikoff and others, 2011). These closely resemble undated white granodiorites 

of the Bethel area and dikes in the Chester and Athens domes; also resemble small 

dikes of granite, trondhjemite, and quartz monzonite largely west of the Connecticut Valley trough

ROCKS OF THE LAURENTIAN MARGIN

Adirondack lowlands and Lake Champlain lowlands

(west of the Orwell and Champlain thrusts)

Hathaway Formation (Upper Ordovician)—Clasts of limestone, dolostone, 

sandstone, and chert within beds of black shale and chert 

Iberville Formation (Upper Ordovician)—Dark-gray shale with thin discontinuous beds of crossbedded and graded dolomitic siltstone

Stony Point Formation (Upper Ordovician)—Dark-gray calcareous shale with 

beds of bluish-gray limestone

Cumberland Head Formation (Upper Ordovician)—Interbedded graded 

bioclastic limestone, bluish-gray calcareous shale, and laminated shale 

Glens Falls Limestone (Upper Ordovician)—Dark-bluish-gray-weathering, thinly 

bedded dark-gray to black granular limestone; locally grades upward into sootyweathering shaly limestone beds rich in fragments of the trilobite Cryptolithus

Black River Group, undivided (Upper Ordovician)—Thin-bedded to massive 

dolostone, sandy dolostone, and light-gray limestone; vertical burrows in basal 

beds; upper beds fossiliferous with black chert 

Orwell Limestone (Upper Ordovician)—Dove-gray-weathering, black to darkgray, fine-grained poorly fossiliferous limestone

Chazy Group (Upper and Middle Ordovician)

Chazy Group, undivided (Upper and Middle Ordovician)—Dark- to light-gray, 

massively bedded fossiliferous limestone and calcareous sandstone 

Valcour Formation (Upper Ordovician)—Dark- to light-gray fossiliferous limestone 

Crown Point Formation (Middle Ordovician)—Gray, massively bedded fossiliferous limestone 

Day Point Formation (Middle Ordovician)—Gray, thin-bedded to massive 

sandstone and fossiliferous limestone 

Beekmantown Group (Middle Ordovician to Upper Cambrian)

Beekmantown Group, undivided (Middle Ordovician to Upper Cambrian)—Gray 

limestones, fossiliferous limestones, and dolostones

Providence Island Dolostone (Middle and Lower Ordovician)—Light-buff-tanweathering, massive to thick-bedded, fine-grained dark-gray dolostone; has 

“beeswax-scored” surfaces; contains thin layers of fossiliferous bluish-gray 

limestone (largely equivalent to the Bridport Member of the Chipman Formation, 

north of Orwell)

Fort Cassin Formation (Middle and Lower Ordovician)—Shown locally from 

Whitehall, N.Y., to Orwell, Vt. Laterally equivalent to Providence Island Dolostone

Root Pond Quartzite Member (Middle and Lower Ordovician)—Light-gray to 

tannish-white, well-bedded and vitreous steel-gray quartzite interbedded with 

orangey-tan- and beige-weathering dolostone and thin beds of fossiliferous 

limestone. Named for occurrences near Root Pond in the Benson quadrangle, 

but herein extended to include thin lenses of quartzite that occur interbedded at 

several positions in the Fort Cassin Formation. Interbedded limestones contain 

upper Ibexian conodonts southwest of Root Pond (J.E. Repetski, USGS, written 

commun., 2004)

Sciota Limestone Member (Middle and Lower Ordovician)—Light-gray, finegrained, and dark-gray, fossiliferous, and platy bluish-gray limestone. Contains 

upper Ibexian to lower Whiterockian conodonts at the type locality near Sciota 

School House, in the Benson quadrangle (J.E. Repetski, USGS, written 

commun., 2004)

Ward Siltstone Member (Lower Ordovician)—Light-tan to gray, thinly bedded 

and crossbedded, calcareous and dolomitic siltstone and quartzite in beds similar 

to the quartzite of the Root Pond Quartzite Member (Ofcrp)

Fort Ann Formation (Lower Ordovician) (Shown only in New York 

State)—Medium- to dark-gray and mottled, medium- to thick-bedded dolomitic 

limestone and buff-weathering dolostone

Great Meadows Formation (Lower Ordovician)—Light-gray, medium-grained, 

medium- to thick-bedded dolostone, locally cherty; contains lens of light-grayweathering fossiliferous limestone (Ogml)

Winchell Creek Member—Tan-weathering, gray, well-bedded and crossbedded 

laminated quartzite and dolostone; sandy beds weather to a woody-grained 

surface texture

Whitehall Formation (Lower Ordovician and Upper Cambrian)—Predominantly 

light-gray and pinkish-gray, coarse-grained dolostone and cherty dolostone, 

containing layers of gray limestone (Ocwl)

Ticonderoga Formation (Upper Cambrian)—Light-gray, yellowish-gray- to buffweathering quartzose dolostone, pebbly dolomitic quartzite, and interbedded 

quartzite

Potsdam Sandstone (Upper Cambrian)—Light-gray, tan, and dark-gray, wellbedded pebbly quartzite, crossbedded vitreous quartzite, and local conglomerate

----------unconformity----------

Neoproterozoic and Mesoproterozoic rocks of the Adirondacks in Vermont and in the Whitehall, N.Y., area

Intrusive Rocks

Diabase dikes (Neoproterozoic)—Dark-gray to greenish-gray, very fine grained, 

ocellar basaltic to medium-grained augite-plagioclase diabasic dikes, occurring as a 

subvertical northeast-trending discontinuous zone in the center of Bald Mountain

Pegmatite dikes (Late Mesoproterozoic)—Pinkish-gray to light-gray, unfoliated, 

magnetite-biotite (±tourmaline) granite pegmatite, <1 m to 10 m thick. Crosscuts 

Ottawan foliation and locally fills narrow, northeast-trending, steeply dipping 

normal ductile shear zones

Metagabbro (Late Mesoproterozoic)—Garnet-hornblende (±olivine) gabbro and 

dioritic gneiss; similar rock mapped in the Chittenden Intrusive Suite in Vermont

Granodioritic augen gneiss and quartz monzonite gneiss (Late 

Mesoproterozoic)—Light-gray to pinkish-gray, garnet-biotite-plagioclase-microperthite augen granodioritic gneiss, locally massive but well foliated. Contains 

deformed phenocrysts (augen) aligned in old relict flow (?) foliation

Pharaoh Mountain Gneiss of Wiener and others (1984) (Late to Middle 

Mesoproterozoic)—Rusty-grayish-brown- to brown-weathering, knubbly coarsegrained magnetite-garnet-hornblende and pyroxene-bearing charnockitic gneiss 

and garnet-hornblende granite gneiss. Has large polycrystalline aggregates of 

plagioclase as much as 1.5 cm long, recrystallized from pre-Ottawan phenocrysts 

(?) of plagioclase. Contains mappable and folded screens of marble, calc-silicate 

rock (Y2

cs), mafic diopside-hypersthene gneiss, and interbedded sillimanite-garnet 

quartzite (Y2

qz). Interpreted as largely intrusive but may contain some charnockitic 

gneiss of uncertain origin

Biotite tonalite gneiss (Y2

bt) and mafic gneiss (Y2ba) (Middle

Mesoproterozoic)—Predominantly chalky-white-weathering, massive biotite 

tonalite gneiss having screens, dikes, or sills of more mafic gneiss. Passes laterally 

into white, fine-grained trondhjemitic aplite near contacts with larger screens of 

paragneiss. U-Pb zircon Thermal Ionization Mass Spectrometry (TIMS) age of 

1329±37 Ma (McLelland and Chiarenzelli, 1990) obtained from exposure 1.5 km 

west of Austin Hill on the west side of South Bay, west of Whitehall, N.Y. Contains 

lenses and screens of rusty sulfidic garnet-biotite-feldspar-quartz schist, dark-gray 

garnet-feldspar quartzite, and calc-silicate gneiss on south end of Austin Hill. Unit 

interpreted as intrusive into some paragneiss units that are here older than 

1328±32 Ma (McLelland and Chiarenzelli, 1990)

Paragneiss

Hague Gneiss of Alling (1918) (Middle Mesoproterozoic)—Yellowish-grayishgreen to rusty-sulfidic-weathering, garnet (large)-sillimanite-biotite-orthoclaseplagioclase-quartz schist or gneiss, locally containing mappable and discontinuous 

lenses, layers or pods of quartzite, marble, or calc-silicate rock. Contains a coarse 

sillimanite-feldspar gneissosity older than the regional Ottawan foliation

Quartzite (Middle Mesoproterozoic)—Light-tan to yellowish-gray, massive to 

well-layered magnetite-garnet quartzite and magnetite-biotite-garnet quartzite in 

beds as much as 10 m thick. Occurs in two layers, one within or attached to the 

Hague Gneiss and one within biotite-quartz-plagioclase gneiss (Y2

bpg) beneath the 

Hague Gneiss. The latter is rich in microcline and passes through interbedding 

into a quartzose facies of Y2

bpg

Marble and calc-silicate gneiss (Middle Mesoproterozoic)—Medium-dark-gray 

to light-gray diopside-phlogopite-scapolite-calcite marble, phlogopite-tremolite-talc 

schist, and dark-gray diopside-hornblende (actinolite)-plagioclase calc-silicate gneiss

Zdi

Y3Cp

Y3Agb

Y3Agd

Y3Aphg

Y2

bt

Y2

ba

Y2

hgn

Y2

qz

Y2

cs

Kns

Kqs

Kes

Kab

Kag

Kahg

Kas

Kav

Kpd

Kbh

Jmsy

Jme

Khf

Kgd

Oha

Oib

Osp

Ochd

Ogf

Obr

Oo

Ocgu

Ov

Dbg

Ddbg

Ddrz

Debg

Dedg

Degr

Dwdg

Dnqm

Dniz

Dnwz

Dwmz

Dwwz

Dwhz

Dabg

Dnbg

Dvbg

Dmbg

Dkbg

Dbbg

Dbqm

Dst

Dhg

Dd

Dbmg

Ocp

Odp

Obku

Ofcpi

Opi

Ofcrp

Ofcs

Ofcw

Ofa

Ogm

Ogml

Ogmw

Ow

Owl

ti

pt

Tmb

Dg

Jmg

Jd

Kmd

Kfd
Biotite-quartz-plagioclase gneiss (Middle to Early Mesoproterozoic)— 

Light-greenish-gray to pinkish-gray, well-foliated and well-layered quartz-rich 

gneiss and more mafic biotite-hornblende-pyroxene-quartz-plagioclase gneiss 

irregularly distributed within unit. Unit may be in part older than the tonalitic 

gneiss (Y2

bt)

Mafic gneiss (Middle to Early Mesoproterozoic)—Dark-gray to black, 

fine-grained, magnetite-garnet-hornblende-biotite-diopside-plagioclase gneiss, 

commonly containing beds of dark-gray vitreous magnetite-garnet quartzite, 2 to 5 

cm thick, tremolite-pyroxene gneiss, and biotite-rich, rusty-weathering garnetquartz schist and gray sulfidic sillimanite quartzite. Occurs as screens within 

tonalitic gneiss and the Pharaoh Mountain Gneiss and is interpreted as 

paragneisses older than the tonalitic gneiss (Y2

bt)

Vermont Valley sequence and Middlebury synclinorium

(above the Orwell and Champlain thrusts)

Hortonville Formation (Upper Ordovician)—Dark-gray siliceous shale and 

phyllite containing thin beds of bluish-gray argillaceous limestone and minor beds 

of gray to tan quartzite. Grades into limy shales of the Stony Point Formation. 

Near base contains bluish-gray, granular, smooth-weathering fossiliferous 

limestone (Ohl) and locally a polymict limestone and dolostone-clast conglomerate 

(Ohc). Unit mapped west of the Taconic allochthon, and northwest of the Sudbury 

slice

Stony Point Formation (Upper Ordovician)—Dark-gray calcareous shale and 

beds of bluish-gray limestone

Ira Formation (Upper Ordovician)—Same description as Hortonville Formation 

above. Contains basal limestone (Oil), locally referred to as the Whipple Marble 

Member, and a polymict limestone conglomerate (Oilc). Unit mapped along east 

side of the Taconic allochthon south to Bennington

Walloomsac Formation (Upper Ordovician)—Same description as the Hortonville Formation above. Contains basal limestone member (Owl) and a black 

carbonaceous highly graptoliferous phyllite (Owbl). Tectonically shredded, silty 

varieties near and on Whipstock Hill constitute the Whipstock Breccia Member of 

Potter (1972) (Oww)

Glens Falls Limestone (Upper Ordovician)—Dark-bluish-gray-weathering, thinly 

bedded, dark-gray to black granular limestones, and gray granular limestone, 

grading locally upward into sooty-weathering shaly limestones containing beds rich 

in fragments of the trilobite Cryptolithus

Chazy, Black River, and Trenton Limestones, undifferentiated (Upper and 

Middle Ordovician)—Shown locally west of the Taconic allochthon

----------unconformity----------

Orwell Limestone (Upper Ordovician)—Dove-gray-weathering, black and 

dark-gray fine-grained limestone. Distinguished from the Middlebury Limestone 

with difficulty, especially in the area west of the Sudbury slice

Middlebury Limestone (Middle Ordovician)—Buff-streaked, dark-bluish-gray, 

thinly bedded and well-foliated dolomitic limestone, shown above the Champlain 

thrust south of Middlebury

Chazy Group (Upper and Middle Ordovician)

Chazy Group, undivided (Upper and Middle Ordovician)—Dark- to light-gray, 

massive fossiliferous limestone and calcareous sandstone

Valcour Formation(Upper Ordovician)—Dark- to light-gray fossiliferous limestone

Crown Point Formation (Middle Ordovician)—Gray, massively bedded fossiliferous limestone 

Day Point Formation (Middle Ordovician)—Gray, thinly bedded to massively 

bedded sandstone and fossiliferous limestone

Chipman Formation (Middle Ordovician)

(mapped south of Wings Point)

Bridport Member—Thickly bedded, “beeswax-scored,” orangey-beige-weathering, yellowish-gray to light-bluish-gray dolostone, dark-gray fine-grained to 

aphanitic dolostone, and minor beds of bluish-gray limestone. Transitions 

eastward into the Beldens Member with addition of limestone beds. Equivalent 

to Providence Island Dolostone (Ofcpi)

Beldens Member—Light-gray to creamy-white-weathering fine-grained 

limestone, orangey-buff-weathering dolostone, and reddish-streaked (hematite) 

calcite marble

Burchards Member—Light-bluish-gray mottled dolomitic limestone

Weybridge Member—Light-gray to cream-colored fine-grained calcite marble, 

and thin dolomitic layers, locally crossbedded; may occur as lenses at several 

positions within the Beldens Member

Bascom Formation (Middle and Lower Ordovician)—Interbedded orangey-tanto buff-weathering dolostone and bluish-gray to gray mottled dolomitic limestone 

or calcite marble and calcareous sandstone. In southern Vermont east of the 

Taconic Range, rocks mapped as Bascom Formation may include unmapped 

members of the Chipman Formation

Cutting Dolostone (Lower Ordovician)—Gray, thinly bedded dolomitic 

sandstone, grading upward into dolomitic limestone or mottled dolomitic marble. 

In southern Vermont east of the Taconic Range, unit is not recognized and may 

appear as sandy zones within rocks mapped as the Shelburne Marble

Shelburne Marble (Lower Ordovician)—Predominantly light-gray- to white- and 

bluish-gray-streaked calcite marble and massive white- and green-streaked calcite 

marble. Locally contains intermediate dolostone and gray limestone beds

Clarendon Springs Formation (Upper Cambrian)—Steel-gray-weathering, 

light-gray, massive calcitic dolostone grading upward into darker, more fissile 

calcitic dolostone containing white quartz knots near top; unit locally brecciated. 

Locally contains light-bluish-gray to whitish-gray calcite marble (spl) within 

dolostone and beneath the calcitic marbles of the overlying Shelburne Marble

Danby Formation (Upper Cambrian)—Thin, light-gray beds of vitreous quartzite 

and crossbedded sandy dolostone. Unit discontinuous in southern Vermont

Winooski Dolostone (Middle Cambrian)—Well-bedded dolostone weathering 

beige, cream, and buff, with green, red, or gray phyllite, siliceous partings, and thin 

beds of blue-quartz-pebble conglomerate and quartzite

Monkton Quartzite (Middle Cambrian)—Reddish-brown, pebbly, thin- to 

thick-bedded sandstone, orangey-gray- and buff-weathering well-bedded 

dolostone, and reddish-brown-weathering dolomitic quartzite. Unit discontinuous 

in southern Vermont

Dunham Dolostone (Lower Cambrian)—Buff- and pink-mottled and massive, or 

light-gray, pinkish-gray-weathering, and massive to poorly bedded dolostone. 

Contains distinctive small pebbles and grains of well-rounded quartz; minor beds of 

dolostone-breccia and conglomerate occur near Rutland

Cheshire Quartzite (Lower Cambrian)—Light-gray- to tannish-gray-weathering, 

massive to poorly bedded vitreous quartzite, containing layers of dark-gray biotitemuscovite-quartz phyllite near top (cb); locally contains a mappable brownweathering, gray to brown argillaceous quartzite member (ca)

Dalton Formation (Lower Cambrian and Neoproterozoic)

(unit interfingers to the north with rocks of the Tyson Formation

and to the east with rocks of the Hoosac Formation)

Dalton Formation, undivided—Heterogeneous unit consisting of rusty- to 

tan-weathering flaggy feldspathic quartzite, tan-weathering quartz phyllite, and 

feldspathic quartzite

Quartzite member—Tan to whitish-gray vitreous quartzite and minor 

blue-quartz-pebble quartzite

Dark phyllite member—Dark-gray to gray, rusty-weathering, well-laminated 

tourmaline-biotite-muscovite-quartz phyllite containing thin beds of laminated 

quartzite. Resembles dark phyllite of the Moosalamoo Formation (Zmp), with 

which it is in part correlative

Feldspathic quartzite member—Light-tan to gray-weathering, massive to 

thin-bedded, flaggy, tourmaline-muscovite-feldspar quartzite and interbedded 

phyllitic quartzite

Lustrous quartz schist member—Dark-gray to silvery-gray, tourmalinemuscovite-biotite-quartz schist and feldspathic schist and quartzite. Occurs on 

eastern flank of the southern Green Mountain massif; similar in appearance to 

Zhs of the Hoosac Formation exposed to the east

Phyllite member—Rusty-tan to gray, thinly layered phyllite, tourmalinebiotite-muscovite-quartz phyllite, and quartzite mapped along western flank of 

the Green Mountain massif in the South Wallingford area

Dolostone member—Buff, sandy, massive dolostone as lens in Zdph

Conglomerate member—Commonly tan- to yellowish-tan-weathering, 

coarse- to fine-grained quartz-pebble to -cobble, quartz conglomerate and 

schistose quartz conglomerate. Locally dark-gray biotite-muscovite-bluequartz-pebble wacke to conglomerate. Occurs at or near base of unit

Lower Cambrian and Neoproterozoic cover rocks of the Lincoln 

Mountain massif and northwestern flank of the Green Mountain 

massif

Moosalamoo Formation (Lower Cambrian and Neoproterozoic)

Feldspathic quartzite and granofels member—Gray to dark-gray, biotitealbite-quartz granofels and flaser-bedded tan to gray feldspathic quartzite; the 

latter resembles similar rocks of the Dalton Formation (Zdfq), whereas the 

former resembles albitic rocks of the Hoosac Formation (Zhab)

Quartzite member—Light-tan to gray, vitreous and non-vitreous quartzite and 

feldspathic quartzite and quartz conglomerate

Gray phyllite and metawacke member—Dark-gray, sooty-weathering, 

splintery sulfidic to non-sulfidic quartz phyllite and pebbly and gritty biotite 

metawacke

Magnetite metasiltstone member—Grayish-brown- to pale-greenweathering, well-laminated, magnetite-studded chloritic metasiltstone; near 

base contains magnetite-cemented quartz-pebble conglomerate and bedded 

magnetite quartzite. Directly overlies dolostones of the Forestdale Formation

Forestdale Formation (Lower Cambrian and Neoproterozoic)

Dolostone member—Upper part of Zfd consists of orangey-tan- to brownweathering quartz-pebble dolostone and dolomitic crossbedded feldspathic 

metasandstone; lower part of Zfd largely cream- to beige-weathering massive 

dolostone; Zfco is boulder and cobble dolostone conglomerate

Quartzite member—Grayish-tan to light-gray vitreous quartzite and white 

feldspathic gritty quartzite

Phyllite and dolostone breccia member—Dark-gray to sooty-black carbonaceous phyllite, interbedded dolostone boulder conglomerate to breccia, and 

blue- and gray-mottled sulfidic dolostone

Pinnacle Formation (Cambrian and Neoproterozoic)

Pinnacle Formation, undivided—Gray, foliated muscovite-chlorite-biotitefeldspar-quartz schist, phyllite, and metagraywacke. Quartz is commonly blue, 

and local thin conglomeratic horizons are present. Feldspathic biotite phyllitic 

metawacke is interlayered with lenses of quartz, feldspar, and gneiss-pebble to 

-cobble conglomerate (Zpc)

Light-gray phyllitic conglomerate member—Feldspathic biotite phyllitic 

metawacke interlayered with lenses of quartz, feldspar, and gneiss-pebble to 

-cobble conglomerate

Metawacke member—Gray- to light-brownish-gray-weathering, massive to 

bedded muscovite-biotite-chlorite metawacke, conglomerate, and blue-quartz 

pebbly phyllite, wacke and feldspathic quartzite; heterogeneous unit consists of 

coarse- to medium-grained clastic wacke, beige-weathering dolostone, and 

quartz-rich dolostone (Zpwd)

Metawacke and phyllite member—Light-gray, medium-grained, massive 

quartz-sericite-chlorite-albite metawacke, gray to grayish-green magnetitechlorite-muscovite-quartz schist, and phyllite or pebbly phyllite, locally rich in 

magnetite

Quartzite and quartz-pebble conglomerate member—Light-gray quartzfeldspar conglomerate and quartzite

Cobble and boulder conglomerate member—Poorly sorted, matrixsupported quartz- and gneiss-cobble to boulder conglomerate, locally containing quartzite boulders as large as 3 m in diameter, in a matrix of gray-weathering 

magnetite-calcite-chlorite-muscovite-biotite-feldspar schist

Metabasalt and volcaniclastic rocks, undifferentiated—Largely carbonateepidote-albite-chlorite (±actinolite) greenstones

Amphibolitic greenstone member— Calcite-biotite-sphene-albite-actinoliteepidote-chlorite greenstone with dark-green porphyroblasts of actinolitic 

hornblende

Calcareous greenstone member—Rusty-weathering and pitted, dark-green 

greenstone with laminae and splotches of calcareous material; locally interbedded with calcareous metagraywacke

Feldspathic greenstone member—Olive-drab-weathering, dark-green, 

fine-grained greenstone with remnant plagioclase feldspar phenocrysts up to 

1.5 cm in diameter

Tibbit Hill Formation (Cambrian and Neoproterozoic)—Largely metabasalt and 

minor metasedimentary rocks consisting of massive, fine-grained, dark-green 

metabasalt flows, pillow basalt, vesicular basalt composed of albite, epidote, 

chlorite (±actinolite); and interbedded phyllitic grits, feldspathic quartzite, chloritic 

metawacke, and basaltic tuffaceous metasedimentary rocks, all similar to rocks of 

the Pinnacle Formation. Volcanics are alkalic to transitional metabasalts

Cambrian to Middle Ordovician rocks of the St. Albans area

Morses Line Slate (Ordovician)—Medium-gray to black calcareous slate

Highgate Formation (Lower Ordovician)—Banded limestone and calcareous 

slate with local lenses of conglomerate composed of limestone, sandstone, and 

dolostone clasts in a sandy limestone matrix 

Gorge Formation (Lower Ordovician and Cambrian)—Dolomite, and dolomite 

breccia composed of angular clasts of dolostone, sandstone, and chert in a buff to 

gray quartzose dolostone

Sweetsburg Formation (Lower Ordovician and Cambrian?)—Black to gray, 

graphitic, quartzose phyllite and schist, with tan-weathering layers and pods of gray 

dolostone and black quartzite

Skeels Corners Slate (Lower Ordovician and Cambrian)—Laminated black 

slate with thin orange dolostone beds; includes massive dolostones mapped as 

Saxe Brook Formation by others in the Highgate area

 

Limestone matrix conglomerate member—Limestone and sandstone clasts 

in a limestone matrix, interbedded with sandstone

Sandy matrix conglomerate member—Limestone and sandstone clasts in a 

quartz sand matrix

Parker Slate (Cambrian)—Black arenaceous slate with dolomite horizons; 

interbedded dolostone and sandstone breccia in a dolostone matrix; and massive 

dolostone with thin sandstone beds

Dolostone member—Massive beds of white to buff dolostone

Sandstone member—Thin- to thick-bedded calcareous coarse-grained sandstone

Conglomerate member—Conglomerate with dolostone and sandstone clasts 

in a shaly matrix

Calcareous sandy conglomerate member—Conglomerate with dolostone 

and sandstone clasts in a calcareous sandy matrix

Sandy dolostone member—Sandy dolostone containing limestone clasts, 

interfingered with sandy dolostone containing dolostone clasts

Dark conglomerate member—Conglomerate consisting of round clasts of 

orange dolostone in a black arenaceous matrix

Ordovician, Cambrian, and Neoproterozoic cover rocks

north of the Lincoln Mountain massif

West Bridgewater Formation (Middle Ordovician)

Black to dark-gray, sulfidic to nonsulfidic, carbonaceous, fine-grained, well-foliated 

biotite-muscovite-quartz phyllite; contains pods and thin beds of medium-dark-gray 

and gray-and-white-mottled dolostone, thin beds of ankeritic quartzite, and, in 

upper part, rhythmically layered gray quartzite, limestone breccia and laminated 

silicic phyllite. Dolostone contains Middle Ordovician conodonts (Ibexian to 

mid-Whiterockian at West Bridgewater and Whiterockian at Buels Gore and West 

Bolton (Ratcliffe and others, 1999; Thompson and others, 2002)

Dark-gray and green phyllite member—Interbedded dark-gray and grayishgreen chlorite-muscovite-quartz-knotted albitic phyllite, containing pods of 

bluish-gray dolostone. (Correlation with West Bridgewater Formation 

uncertain.) Mapped only in the area west of Granville

----------unconformity----------

Fairfield Pond Formation (Cambrian and Neoproterozoic)—Light-gray to 

light-green, quartz-sericite-chlorite (±magnetite±biotite) phyllite and foliated quartzite

White Brook Formation (Cambrian and Neoproterozoic)—Buff to creamcolored massive dolomite and dolomitic sandstone, containing prominent zone of 

massive and specular hematite near top at Sheldon

Underhill Formation (Cambrian and Neoproterozoic)—Silvery-green quartzmuscovite-chlorite schist and phyllite, commonly with albite and magnetite; locally 

contains dolomite. Local lenses of white to pale-gray quartzite, quartz-albite 

granofels, quartz-granule chlorite (±biotite) metawacke (Zunw), and garnet schist 

(Zungs)

Greenstone and amphibolite member—Thinly bedded carbonate-albiteepidote greenstone and massive magnetite-albite-amphibole-biotite-epidote 

amphibolite; light- to dark-green, fine- to medium-grained epidote-chlorite 

albite-amphibole schist; dark-green, coarse-grained, weakly foliated epidotebiotite-albite-amphibole amphibolite

Quartz-laminated schist member—Light-gray to tan and rusty-weathering, 

fine-grained, well-foliated mylonitic albite-chlorite-muscovite-quartz (±dolomite)-laminated schist

Hazens Notch Formation (Cambrian and Neoproterozoic)

Hazens Notch Formation, undivided—Schist, gneiss, and quartzite; 

dark-rusty-brown graphitic biotite-muscovite-chlorite-quartz (±garnet) schist and 

gneiss; black albite porphyroblasts, large euhedral pyrite, and beds of dark-gray 

foliated quartzite are common. Unit includes rusty-weathering schist without 

graphite and rocks identical to Fayston Formation

Greenstone and amphibolite member—Dark-green, pitted-weathering, 

foliated mafic schist to massive greenstone containing varying amounts of 

chlorite, albite, carbonate, epidote, amphibole, and sphene; and amphibolite 

containing varying amounts of hornblende, actinolite, albite, chlorite, epidote, 

biotite, magnetite, and sphene

Schist member—Rusty-weathering, non-graphitic, sulfidic chlorite-muscovitequartz schist 

Fayston Formation (Lower Cambrian and Neoproterozoic)

Albite schist member—Silvery-green to grayish-green, medium-grained 

albite-chlorite-muscovite-quartz (±garnet±magnetite) schist with white albite 

porphyroblasts; resembles albitic schists of the Tyson Formation (Ztab) and 

green albitic granofels of the Hoosac Formation (Zhgab). Locally contains 

unmapped light-gray, thin quartzites; salt-and-pepper-colored, medium- to 

coarse-grained pyrite-magnetite-biotite-albite-quartz schist and gneiss; and 

silvery-dark-gray to rusty-weathering, medium-grained chlorite-tourmalinealbite-muscovite-quartz schist. The Fayston south of Mount Abraham is intercalated with rocks of the Tyson Formation and with the schists of the Pinney 

Hollow Formation

Greenstone member—Dark-green, pitted-weathering, foliated carbonatealbite-chlorite (±magnetite±epidote) greenstone or amphibolite

Foliated metawacke member—Salt-and-pepper-colored, medium- to coarsegrained quartz-albite-biotite gneiss

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Zdb

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Zds

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Zfb

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Zps

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Zpva

Zpvc

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Zdc

BEDROCK GEOLOGIC MAP OF VERMO

By

Nicholas M. Ratcliffe,1 Rolfe S. Stanley,2* Marjorie H. Gale,3 Peter J. Thompson,3 and Gregory J. W

With contributions by

Norman L. Hatch, Jr.,1* Douglas W. Rankin,1 Barry L. Doolan,2 Jonathan Kim,3 Charlotte J. Mehrtens,2 John N. Aleiniko

1U.S. Geological Survey, 2University of Vermont, 3Vermont Geological Survey, 4Wesleyan University, *Deceased.

2011

Cartography by Linda M. Masonic1
Carbonaceous albite schist member—Gray to medium-dark-gray, 

rusty-weathering, carbonaceous albite-chlorite-quartz-muscovite schist, containing porphyroblasts of black albite. Unit resembles gray albitic granofels and 

schist of the Hoosac Formation (Zhab)

Quartzite member—White quartzite and tan to light-gray, medium-grained 

muscovite quartzite locally rich in magnetite. Resembles quartzite of the Tyson 

Formation (Ztq)

Schist member—Silvery-green to rusty-tan, fine-grained chlorite-quartzsericite (±garnet±chloritoid±allanite) schist and phyllite. Resembles green 

phyllites of the Pinney Hollow Formation (Zph) and Mount Abraham Formation (Za) and chloritic phyllite (Ztg) of the Tyson Formation

Pinney Hollow Formation (Cambrian and Neoproterozoic)

Phyllite member—Light-greenish-gray to lustrous pale-green chloritemuscovite-quartz (±chloritoid±garnet±magnetite) phyllite. Chloritoid-rich rocks 

(Zphc) appear gritty owing to distributed porphyroblasts of chloritoid. Unit is 

locally albitic and contains minor beds of quartzite

Feldspathic quartz schist member—Light-gray to grayish-green, laminated, 

gritty feldspathic chlorite-muscovite-plagioclase-quartz schist

Metawacke member—Silvery-gray, “pinstriped,” coarse- to medium-grained, 

blue-quartz-pebble chlorite-biotite-plagioclase-quartz metawacke; locally 

conglomeratic and rich in epidote

Black phyllite member—Dark-gray to black, sulfidic biotite-plagioclase-quartz 

schist, commonly interbedded with or adjacent to amphibolite and greenstone 

member (Zpha); locally is a silvery-gray sulfidic biotite phyllite

Amphibolite and greenstone member—Dark-green to black plagioclasebiotite-hornblende (±quartz) amphibolite, epidote amphibolite, and ankeriticchlorite-magnetite-plagioclase (albite) greenstone. Shows all gradations from 

massive but well-foliated metabasalt to well-bedded basaltic volcaniclastic rock 

and volcanic metawacke

Metafelsite member—White to pale-green, laminated to massive epidotecalcite-muscovite-quartz-albite metarhyolitic gneiss or schist; is a volcanic or 

volcaniclastic rock. U-Pb zircon age of 571±5 Ma, no. 21 (Walsh and 

Aleinikoff, 1999). Contains purplish-gray feldspathic quartzite

Monastery Formation (Cambrian and Neoproterozoic)—Heterogeneous unit 

consisting of coarse-grained, gray- to rusty-brown-weathering garnet-biotitemuscovite-quartz schist, beds of gritty feldspathic quartzite (Zmtg), gray albitic 

biotite-quartz granofels, well-bedded light-gray to steel-gray biotite, minor epidotemagnetite-actinolite-chlorite feldspathic wacke, and, near base, grayish-green 

laminated chlorite-muscovite-albite granofels and phyllite. Unit mapped in 

Hancock and Ripton in part as lateral equivalent of the Tyson Formation to the 

south and the Underhill Formation to the north

Eastern flank of the Green Mountain massif and eastern domes

Plymouth Formation (Cambrian)

Dolostone member—Light-gray- to beige-weathering massive dolostone and 

bluish-gray-weathering mottled dolostone breccia and conglomerate, passing 

upward into more thinly bedded bluish-gray and buff dolostone breccia; 

dark-gray phyllitic dolostone and limestone in upper part. Correlative in part 

with boulder and conglomerate beds of the Dunham Dolostone near Rutland 

and with similar beds in the upper part of the Forestdale Formation

Feldspathic quartzite member—Thinly laminated but massive-appearing, 

gray- and brownish-gray- to tan-weathering flaggy biotite-muscovite feldspathic 

quartzite and phyllitic quartzite. Resembles feldspathic quartzite of the Dalton 

Formation (Zdfq) and similar quartzite of the Moosalamoo Formation (Zmf) 

above the Forestdale Formation

Tyson Formation (Lower Cambrian and Neoproterozoic)

(shown on the eastern and western flanks of the Green Mountain massif)

Tyson Formation, undivided—Phyllite and metawacke. Shown east of Rutland 

Albitic magnetite granofels member—Gray and greenish-gray, magnetitechlorite-(biotite)-muscovite-albite-quartz granofels and schist. Similar to gray or 

green albitic granofels of the Hoosac Formation (Zhab and Zhgab)

Ludlow Mountain aplitic gneiss (Middle Mesoproterozoic)—Light-gray to 

white, very fine grained microcline-plagioclase-quartz (±magnetite) aplitic gneiss; 

contains sparing amounts of biotite, and secondary muscovite. Unit interpreted to 

be border facies of Y2

lgg. Y2ap is similar aplitic gneiss, but is not in contact with 

either Y2

lgg or Y2phg. Exposed on Ludlow Mountain

Proctor Hill granodiorite gneiss (Middle Mesoproterozoic)—Gray to pinkishgray, gneissoid magnetite-biotite-microcline-perthite granodiorite, and locally 

microcline megacrystic gneissic granite, well-foliated and highly variable in composition, having aplitic and hornblende-rich reaction zones (Y2

pha) where in contact 

with calc-silicate rocks. Crosscuts all paragneiss units; is a thoroughly gneissic 

rock. Correlated with the Ludlow Mountain granodiorite gneiss

Cole Pond tonalite gneiss (Middle Mesoproterozoic)—Gray to medium-darkgray, biotite-rich metatonalite gneiss, having irregular screens, and xenoliths of 

more mafic hornblende-biotite tonalite or diorite gneiss. U-Pb zircon SHRIMP age 

of 1,321±9 Ma, no. 7 (Ratcliffe and others, 1991; Aleinikoff and others, 2011)

Bondville metadacite and trondhjemite gneiss (Middle Mesoproterozoic)— 

Light-gray to whitish-gray, fine-grained biotite trondhjemitic gneiss, locally containing abundant magnetite. U-Pb zircon SHRIMP age of 1,342 Ma, no. 6B (Ratcliffe 

and others, 1991; Aleinikoff and others, 2011)

Rawsonville trondhjemite gneiss (Early Mesoproterozoic)—Chalky-white to 

light-gray-weathering, medium- to coarse-grained biotite metatrondhjemite and 

aplite (Y1

rta). Dated sample with U-Pb zircon SHRIMP age of 1,367±16 Ma, no. 

3 (Ratcliffe and others, 1991; Aleinikoff and others, 2011) from crest of Bromley 

Mountain; U-Pb zircon age of 1,348±3 Ma, no. 6 (Ratcliffe and others, 1991)

Tonalite gneiss (Early Mesoproterozoic)—Medium-gray- to light-grayweathering, biotite (±hornblende) tonalite gneiss exposed on Torment Hill in 

Weston; probably correlative with the Baileys Mills tonalitic gneiss or the Felchville 

trondhjemite facies (Y1

fg) of the Chester dome, but undated

Hornblende diorite gneiss (Early Mesoproterozoic)—Coarse-grained 

hornblende-plagioclase (±quartz) dioritic gneiss and gabbroic gneiss mapped in the 

Londonderry area, where it is interpreted as metagabbro and has a U-Pb zircon 

SHRIMP age of 1,393±9 Ma, no. 1 (Aleinikoff and others, 2011)

Baileys Mills tonalitic gneiss (Early Mesoproterozoic)—Light-gray to whitishgray-weathering, medium-grained biotite-quartz-plagioclase gneiss flecked with 

coarse biotite. Contains numerous lenses of fine-grained amphibolite similar to 

amphibolites associated with calc-silicate rocks of the type Mount Holly Complex 

in Mount Holly, rather than coarser grained dioritic gneiss associated with the Cole 

Pond and Rawsonville gneisses. U-Pb zircon SHRIMP age of 1,383±13 Ma, no. 2 

(Ratcliffe and others, 1991; Aleinikoff and others, 2011)

Plagioclase-phenocrystic tonalite gneiss—Coarse-grained facies of the Baileys 

Mills tonalitic gneiss exposed on the northeast flank of the Chester dome

Felchville Gneiss (Early Mesoproterozoic)

Felchville aplitic facies—Light-gray to whitish-gray, fine-grained, magnetite 

trondhjemitic gneiss and aplitic trondhjemite, intricately intrusive into layered 

paragneisses of the Chester dome; contains xenoliths of more mafic gneiss. 

U-Pb zircon SHRIMP age of 1,372±11 Ma, no. 4 (Aleinikoff and others, 

2011). Similar fine-grained magnetite aplitic gneisses exposed in the Green 

Mountain massif are associated with tonalitic gneisses on Torment Hill, Weston

Felchville trondhjemite facies—Light-gray to whitish-gray-weathering, 

magnetite-biotite-microcline-quartz-plagioclase metatrondhjemite to granodioritic gneiss; intrudes paragneiss units of the Chester dome. U-Pb zircon 

SHRIMP age of 1,370±11 Ma, no. 5 (Aleinikoff and others, 2011)

Mount Holly Complex paragneiss (Middle to Early Mesoproterozoic)

(includes possible felsic metavolcanic rocks and volcaniclastic rocks; relative age 

uncertain; abundant interfingering of units and stratigraphic duplication likely)

Problematic rocks at Devils Den in Weston and Danby areas 

(Mesoproterozoic?)—Near Devils Den and Moses Pond includes albitic biotitemuscovite schist, chloritoid-chlorite-muscovite (±garnet) schist, dolomite marble 

and minor quartzite which resemble rocks of the Tyson Formation, and retrograde 

varieties of the paragneisses of the Mount Holly Complex. Because these rocks 

are structurally compatible with Grenvillian or older folds in the Mount Holly 

Complex and are transitional into rocks of the Mount Holly Complex, a Mesoproterozoic age is favored. Nevertheless the resemblance to rocks of the Tyson 

Formation is striking

Sandy phyllite, granofels, and cherty phyllite (Upper Ordovician)—Gray and 

grayish-green rocks associated with Whipstock breccia on Whipstock Hill but of 

uncertain correlation

Graptoliferous slate (Upper Ordovician)—Black slate of Climacograptus 

bicornis Biozone on and west of Whipstock Hill, otherwise typical of slates of the 

Walloomsac Formation shown as Ow

Rocks of the Giddings Brook, Sunset Lake, and Bird Mountain slices

Pawlet Formation (Upper Ordovician)—Light-gray, tan-weathering, 

mica-speckled, massive to thin-bedded quartz-plagioclase wacke interbedded with 

dark-gray carbonaceous slate. Contains distinctive autoclastic chips of gray slate, 

fragments of dacitic to andesitic volcanics, and subangular clasts of dark-gray 

quartz and oligoclase. Interbedded black slates contain graptolites of the C. 

bicornis Biozone (see Webby and others, 2004, fig. 2.1) (lower to middle 

Mohawkian). Interpreted as uncomformable on rocks as old as the Hatch Hill 

Formation and possibly the West Castleton Formation of the allochthon. Unit is 

indistinguishable from beds in the Austin Glen Graywacke (after Potter, 1972) 

(Oag) interpreted as synorogenic autochthonous rocks

Mount Merino Formation (Upper Ordovician)—Light-gray, powdery-weathering, and red, green, and dark-gray, thinly bedded siliceous argillite and mudstone 

distinguished from the Indian River Slate by abundance of cherty siliceous layers

Indian River Slate (Upper Ordovician)—Deep-maroon and bluish-greenweathering, well-bedded and variegated slate; contains minor centimeter-thick, 

white-weathering, red and bluish-black cherty layers characteristic of the Mount 

Merino Formation. Contains graptolites of the C. bicornis Biozone (Berry, 1961)

Poultney Formation (Middle and Lower Ordovician)—Dull-white and whitishgray-weathering, and pale-green and gray, thinly bedded to laminated slate and 

phyllite. Has distinctive beds, 1 cm to several centimeters thick, of siliceous argillite 

and metasiltstone and locally abundant thin beds of micritic black limestone near 

the base, interbedded with dark slate. Contains graptolites ranging from Ibexian to 

Whiterockian (Berry, 1961)

West Castleton and Hatch Hill(?) Formations, undifferentiated 

(Cambrian)—Black slate and gray phyllite exposed on Woodlawn and Tinmouth 

Mountains in Pawlet and Tinmouth Townships, after usage of Shumaker and 

Thompson (1967)

Hatch Hill Formation (Upper Cambrian)—Dark-gray to black, sooty- to 

rusty-weathering, splintery-fractured pyritic slate and phyllite and interbedded 

bluish-gray dolomitic quartzite

West Castleton Formation (Middle and Lower Cambrian)—Dark-gray to black, 

fine-grained slate and phyllite, interbedded with thinly laminated bluish-black 

fine-grained limestone, limestone conglomerate, and boudins (ls) of whitishgray-weathering, bluish-gray quartzite. Unit is interbedded near the base with 

green phyllite and sooty-punky-weathering calcitic quartz wacke and limestone of 

the Browns Pond Formation, which is shown separately where mapped

Eagle Bridge Quartzite (Lower Cambrian)—Dull-gray, pitted, and bluish-gray 

dolomitic quartz wacke and quartzite distinguished by small pebbles and grains of 

dark-blue to black quartz, dacitic rock fragments, and abundant plagioclase. Beds 

resembling the Eagle Bridge Quartzite may occur at several stratigraphic positions 

within the black slate and gray phyllite of the West Castleton and Hatch Hill(?) 

Formations, undifferentiated (wcu), and near the base of the Poultney Formation, and probably are not all correlative

Carbonate (Cambrian and Neoproterozoic?)—Pods, lenses, or zones of thinly 

bedded limestone (ls), dolostone (d), and limestone conglomerate in the Mettawee 

slate facies in the Bull Formation, West Castleton Formation, and Hatch Hill 

Formation. These rocks locally contain Lower Cambrian fossils, but may range in 

age from Neoproterozoic to Late Cambrian. Includes named units shown locally 

as the North Brittain Conglomerate member of the West Castleton Formation 

(wcnb), the Bebe Limestone Member of the West Castleton Formation (wcbb), 

and the Castleton Conglomerate (of Shumaker and Thompson, 1967) (co)

Browns Pond Formation of Rowley and others (1979) (Lower 

Cambrian)—Gray to black slate, punky-weathering calcitic wacke and mudstone, 

and thin limestone breccia in part equivalent to the West Castleton Formation. 

Shown only in the Granville, N.Y., area. Locally purple and green slate above 

black slate of the Browns Pond is interpreted as a lens of the Mettawee slate facies 

in the Bull Formation

Belvidere Mountain Structural Complex (Cambrian and Neoproterozoic) 

Ultramafic rocks—Brown to white-weathering, green, massive, moderately to 

fully serpentinized dunite and peridotite and schistose serpentinite; 

rusty-weathering, medium-grained talc-carbonate rock and quartz-carbonate 

(magnesite) rock

Coarse-grained amphibolite—Dark-gray, coarse-grained amphibolite and 

layered amphibolite composed of barroisite, epidote, garnet, actinolite, albite, 

chlorite, sphene, sericite, biotite, and calcite

Fine-grained amphibolite—Bluish-gray, fine- to medium-grained albite-hornblende-epidote-actinolite (±garnet) amphibolite and quartz-bearing amphibolite

Mafic schist—Green, fine-grained schist composed of chlorite, actinolite, albite, 

and epidote with biotite, calcite, sericite, quartz, sphene, pyrite, and magnetite; 

includes homogeneous schistose greenstone, albitic greenstone, and massive 

banded greenstone

Spangly schist—Silvery-blue, medium-grained tectonic mélange composed of 

muscovite schist with minor amounts of chlorite, epidote, albite, and tourmaline; 

contains fragments and discontinuous lenses of greenstone, coarse-grained 

amphibolite, and talc phyllite

Albite gneiss—White, light-gray- and green-banded, fine- to medium-grained, 

well-layered epidote-white mica-quartz-albite (±garnet±magnetite) gneiss; contains 

plagioclase and polycrystalline quartz porphyroblasts. The 0.5- to 2-cm-thick layers 

are defined by variations in the amount of quartz, albite, white mica, and chlorite. 

Gneiss is similar to gneiss at the base of the Tillotson Peak Structural Complex

Ultramafic rocks (Cambrian and Neoproterozoic)

(occur as tectonic slivers and olistoliths in blocks within the Hazens Notch, 

Ottauquechee, Stowe, Rowe, and Moretown Formations; fault symbol locally omitted)

Meta-ultramafic rocks, undifferentiated—Brown to white-weathering, green, 

massive, moderately to fully serpentinized dunite and peridotite and schistose 

serpentinite; rusty-weathering, medium-grained talc-carbonate rock and quartzcarbonate (magnesite) rock

Talc-carbonate schist—Cream-colored to light-bluish-gray, brown-weathering, 

talc-carbonate schist and talc-cabonate-rich rocks

Serpentinite—Brown-weathering, dark-green serpentinite

Volcanic-arc intrusive and volcanic rocks of the North River Igneous 

Suite of the Rowe-Hawley zone

North River Igneous Suite (Ordovician and Late Cambrian) (502±4 Ma to 

471.4±3.7 Ma)—Collection of metatonalite, metatrondhjemite, and metabasalt 

occurring as intrusive dikes, sills, and small stocks, and possibly meta-andesite and 

metadacitic tuffs. Correlative with extrusive dacitic metavolcanic and meta-andesitic 

rocks of the Moretown and Cram Hill Formations. Coextensive in part with igneous 

rocks of the Hawley Formation of Massachusetts

West Halifax Trondhjemite—Cream-colored, light-gray- to whitish-gray-weathering,coarse-grainedchlorite-biotite-muscovite-quartz-plagioclase(±garnet ±hornblende)

metatrondhjemite and metatonalite; southern lens near Massachusetts State line is 

coextensive with trondhjemite in the Hawley Formation 

Branch Brook dike and sill complex

Whitneyville facies—Light-green to medium-green, massive, epidoteilmenite-sphene-chlorite-hornblende-plagioclase amphibolite, marked by coarse 

hornblende and abundant phenocrysts of plagioclase

Williamsville facies—Dark-gray to black, poorly layered, porphyritic and 

nonporphyritic ilmenite-epidote-chlorite-plagioclase-hornblende amphibolite

South Pond facies—Light- to dark-gray and steel-blue to apple-green, finegrained hornblende-chlorite-plagioclase amphibolite, locally containing significant calcite and pyrite and interlayered felsic layers of metatrondhjemite or 

metadacite. Similar in part to the mixed gneiss facies (Onbm)

Barnard Gneiss proper (of Richardson, 1924)—Predominantly light-gray to 

whitish-weathering, massive to gneissic hornblende-biotite tonalite and biotitemuscovite-quartz-plagioclase trondhjemite; includes rare hornblendite, metadiabase, and metapyroxenite as small stocks, inclusions, and dikes. U-Pb zircon 

SHRIMP age of 496±8 Ma north of Proctorsville, no. 23 (Aleinikoff and others, 

Compton Formation (Lower Devonian)

Metasandstone member—Light-gray to tan, micaceous, locally calcareous 

metasandstone and slate or metamudstone in beds a few centimeters to tens of 

centimeters thick. Graded bedding common. Interpreted to be correlative with 

the Gile Mountain Formation

Amphibolite member—Garnetiferous hornblende schist and minor 

hornblende amphibolite

Ironbound Mountain Formation (Lower Devonian)—Medium-dark-gray to 

grayish-black lustrous slate, phyllite, and schist containing sparse to moderately 

abundant 1-mm to- 5-cm-thick beds of light-gray, fine-grained metasandstone and 

metasiltstone, commonly pyritiferous and calcareous. Some graded beds. Gradational contact with Dco above and Dir below. Interpreted to be correlative with the 

Meetinghouse Slate Member of the Gile Mountain Formation 

Halls Stream Grit Member (of Myers, 1964)—Lenticular masses of coarsegrained quartzose volcaniclastic grit and cobble metaconglomerate commonly 

with abundant dark-gray metapelitic matrix (diamictite) interlayered with 

metasandstone, metapelite, and porphyritic metarhyolite. Grit contains subangular clasts of plagioclase and potassic feldspar as large as 2.5 cm across and 

larger clasts of dark-gray slate. Conglomerate contains rounded clasts of metarhyolite, fine-grained granitoid, and rare marble, and angular clasts of dark-gray 

slate

Amphibolite member—Hornblende amphibolite and hornblende-plagioclasequartz granofels; interpreted as metabasalt and mafic volcaniclastic rock

Rhythmically graded member—Light- to medium-gray, fine-grained 

micaceous metasandstones that grade upward into subordinate dark-gray slate 

or phyllite; some rocks are calcareous. Graded sets range in thickness from a 

few centimeters to about a meter; typically they are 10 to 30 cm thick. Contact 

with Di gradational

Frontenac Formation (Devonian and Silurian)—Thick-bedded, ankeritic, 

micaceous, and feldspathic metasandstones interlayered with subordinate 

dark-gray metapelite. Metasandstone beds commonly are rusty weathering and up 

to 4 m thick; calc-silicate lenses locally present

Amphibolite member—Garnetiferous hornblende schist and minor 

hornblende amphibolite

Waits River Formation (Lower Devonian and Upper Silurian)

Muscovite porphyroblastic carbonaceous schist member—Dark-gray to 

coaly-black, fine-grained plagioclase-muscovite-quartz schist and metawacke, 

shown southeast of Springfield; in part correlative with staurolite-grade rocks 

mapped as Littleton Formation (Dl) flanking the Vernon dome (shown as 

DSwb/Dl)

Slate and phyllite member—Predominantly dark- to light-gray, lustrous, 

carbonaceous chlorite-biotite-muscovite-quartz slate, phyllite, or schist; contains 

thin beds of quartzite and only sparse layers of punky-weathering limestone. 

Shown south of the Pomfret dome where rocks typical of the Gile Mountain 

Formation are absent, and near Randolph

Volcanic and volcaniclastic rocks—Mapped with Standing Pond Amphibolite 

Member of Memphremagog Formation (of Doll, [1945]) and Putney Volcanics 

(of Trask, 1980). Shown only diagrammatically in Correlation of Map Units; 

not shown on the map. In the Correlation, units DSwf, DSwgs, DSwa, and 

DSwv are locally shown as Sv; on the map they are shown individually

Felsic volcanic member—Light-gray to grayish-green, chlorite-biotitemuscovite-plagioclase-quartz schist and fragmental quartz-plagioclase granofels 

or metatuff. In Springfield, contains a dated metafelsite layer interpreted as a 

dike cutting the Standing Pond Volcanics, that yielded a U-Pb zircon TIMS age 

of 423±4 Ma, no. 32 (Aleinikoff and Karabinos, 1990; Hueber and others, 

1990)

Garbenschiefer member—Rusty-brown to silvery-gray, coarse-grained, garnet 

(large)-muscovite-biotite-hornblende schist and hornblende-fascicule schist

Mafic member—Massive, coarse-grained hornblende-plagioclase gneiss and 

granofels; finely foliated hornblende-plagioclase amphibolite; actinoliteepidote-chlorite greenstone

Volcaniclastic rock member—Silvery-grayish-green to light-gray, muscovitebiotite (chlorite)-plagioclase-quartz schist and granofels

Coarsely porphyritic, greenish-gray, light-bluish-gray, or medium-bluish-gray 

metarhyolite tuff, lapilli tuff, and tuff breccia. Quartz and plagioclase phenocrysts commonly as large as 5 mm

Metamorphosed aphyric rhyolite tuff

Medium-light-bluish-gray, medium-bluish-gray, medium-dark-gray, to mediumdark-greenish-gray metasiltstone and phyllite, and medium-gray feldspathic 

metawacke. Purple tinge common; coticule and magnetite locally abundant

Siliceous and argillaceous dolomite and calcareous pelite

Dark-gray to grayish-black, rusty-weathering sulfidic slate and phyllite interlayered with felsic tuffs and minor sandy rocks; locally forms the base of the 

Ammonoosuc Volcanics

Washburn Brook Formation (Upper and Middle Ordovician)

Metamorphosed gray siltstone, quartzite, volcanogenic chert, and ironstone, all 

typically containing coticule and magnetite

Metamorphosed sedimentary breccia interlayered with dark-gray slate and 

micaceous siltstone. Clasts include light-colored, fine-grained metasandstone 

and metasiltstone of the Albee Formation, dark-gray or greenish-gray slate, and 

coticule-bearing metasiltstone and chert as well as sparse quartz pebbles. 

Matrix consists of fine-grained metasandstone, metasiltstone, or dark-gray or 

greenish-gray slate

Albee Formation (Ordovician and Cambrian)—Light-gray to greenish-gray, 

white-weathering, fine-grained feldspathic metasandstone and metasiltstone, and 

light-gray to greenish-gray to dark-gray phyllite. Lesser amounts of quartzite. Rare 

calc-silicate nodules. Generally sharply bedded, but graded beds as well as slump 

structures are locally obvious. Tourmaline is a sporadic accessory mineral. May be 

sulfidic (either pyrite or pyrrhotite) and rusty weathering. “Pinstriping” is common. 

U-Pb zircon SHRIMP age of 492.5±7.8 Ma from a porphyritic tonalite sill about 2 

km east of West Bath, N.H. (D.W. Rankin, USGS, unpub. data, 2011)

Dark-gray slate and phyllite member—Commonly sulfidic and rusty weathering. Indistinguishable from the Scarritt Member, but crops out in small areas

Iron-formation member—Ironstone, magnetite-rich rock and coticule

Magnetite-rich areas—Shown as an overprint

Scarritt Member—Dark-gray slate interlayered with thin beds of light-gray, 

fine-grained micaceous and feldspathic metasandstone (typically ribby weathering). Abruptly graded beds <1 cm to 30 cm thick are locally common as is 

channeling and, in places, soft-sediment deformation. Commonly sulfidic and 

rusty weathering

Y2lga

Y2

phg

Y2

pha

Y1

rta

Y2

cp

Y2

bv

Y1

rt

Y1

tg

Y1

bm

Y1

bmp

Y1

fga

Y1

fg

Y1

dg

?

Oat

Oarq

Oap

Owc

Ows

Opaw

Oag

Omm

Oir

Opo

Owwu

Owbl

wcu

hh

eb

wcnb

wcbb

co

Zbp

wc

ls

ls

d

Oal

Oalm

Oalp

Oali

Oals

Dco

Dcoa

Di

Dih

Dia

Dir

DSfr

DSfra

Sv

DSwf

DSwgs

DSwa

DSwv

DSwb

DSwb/Dl

DSws

Oac

Oam

Zfc

Zfqz

Zfs

Zmt

Zmtg

pd

pfq

Ztab

Zt

Zbu

Zbc

Zbf

Zbg

Zbs

Zbagn

Zu

Zutc

Zsp

Onbw

Onbwm

Onbs

Ontw

Onb

Zph

Zphc

Zphq

Zphw

Zphb

Zpha

Zphf

SCIENTIFIC INVESTIGATIONS MAP 3184

BEDROCK GEOLOGIC MAP OF VERMONT

SHEET 3 OF 3 (FRONT)
Chlorite-muscovite phyllite and schist member—Pale-greenish-gray to yellowish-greenish-gray, chlorite-muscovite-quartz phyllite and schist; locally 

contains beds of pebbly metawacke and magnetite phyllite. Similar to but finer 

grained than the metawacke and phyllite member of the Pinnacle Formation 

(Zps)

Quartz phyllite member—Rusty-weathering, gray to grayish-green, chloritemuscovite-quartz phyllite and minor beds of pebbly-quartz metawacke

Quartz-pebble phyllite and wacke member—Gray to grayish-green, biotitechlorite-quartz-pebble phyllite; albitic metawacke is similar to metawacke 

member of the Pinnacle Formation but more thinly bedded and contains less 

metawacke. Albitic biotite-(chlorite)-quartz granofels and wacke locally present

Quartzite member—Gray to very light gray, vitreous and nonvitreous, massive 

to thin-bedded quartzite, magnetite and biotite quartzite, and feldspathic quartzite, locally interbedded with dolostone. Similar to quartzite in the Forestdale 

Formation (Zfq)

Dolostone member—Largely massive, gray-, beige-, and pinkish-grayweathering dolostone, beds of pebbly quartz dolostone, and pink- to orangetan-weathering dolostone as lenses in phyllite. Contains beds of bluish-gray 

and whitish-gray vitreous quartzite. Similar to dolostone of the Forestdale 

Formation (Zfd)

Albite schist member—Dark-gray to black, locally carbonaceous, 

rusty-brown-weathering biotite-rich quartz schist and dark biotite-albite schist

Conglomerate member—Massive to well-bedded chlorite-biotite 

(±albite)-quartz-pebble, -cobble, and -boulder conglomerate, feldspathic 

conglomeratic metawacke, and locally a dolomite-cemented feldspathic quartzpebble conglomerate. Occurs at base and in lower part of the Tyson Formation

Hoosac Formation (Lower Cambrian and Neoproterozoic)

Hoosac Formation, undivided—Heterogeneous unit consisting mainly of 

dark-gray to medium-light-gray-weathering, white-plagioclase-studded schist, gray 

slabby quartz-rich muscovite (±garnet) schist, and layers of dark-gray biotitic quartzite and metawacke

Garnet schist member—Lustrous, green, ilmenite-chlorite-chloritoid-garnetmuscovite-quartz (±paragonite) schist; resembles Pinney Hollow Formation but 

lacks amphibolite. Aluminous schists at Devils Den and aluminous rocks of the 

Cavendish Formation may be correlative

Biotite phyllite member—Coal-black, lustrous, rusty- to non-rustyweathering, biotite-muscovite-plagioclase-quartz schist and phyllite, containing 

lenses of white laminated quartzite as beds and discoidal boudins

Turkey Mountain Metabasalt Member—Dark-green to black, hornblendeplagioclase (±garnet±epidote) amphibolite and grayish-green epidoteplagioclase ankeritic greenstone; grades into epidote-quartz-plagioclase 

volcaniclastic wacke. Occurs as lenses at multiple stratigraphic levels. Lower 

layers are transitional and alkalic metabasalts; higher units are typical midocean 

ridge basalt (MORB)-type metabasalts

Dolomite marble member—Light-gray-, cream- or pinkish-gray-weathering, 

medium- to fine-grained phlogopite-quartz-dolomite marble. Occurs as thin 

beds in gray albitic granofels member (Zhab); locally contains beds of vitreous 

to bluish-gray laminated quartzite

Albite schist and granofels member—Rusty-weathering, medium- to 

dark-gray, black albite-biotite-quartz schist and granofels, marked by large 

spangles of muscovite and weathered-out pits of dolomite or ankerite

Quartzite member—Light-gray-, yellowish-gray- to dark-dull-gray-weathering, 

biotite or muscovite quartzite, feldspathic quartzite, and pebbly muscovitic quartzite, commonly occuring as basal member or as layers in schist member (Zhs)

Schist member—Lustrous, dark-gray to silvery-gray tourmaline-muscovitebiotite-quartz schist and steel-gray muscovitic quartzite

Garnet biotite schist member—Medium-dark-gray to lustrous silvery-gray 

garnet-biotite-muscovite-plagioclase-quartz schist and feldspathic garnet schist; 

associated with Zhs member which it laterally replaces

Chlorite albite schist and granofels member—Pale-green to light-greenishgray, chlorite-magnetite-white-albite-spotted-quartz granofels and schist

Albite-quartz granofels member—Light-gray- to whitish-gray-weathering, 

massive to thickly bedded medium-grained biotite-white albite-quartz granofels; 

locally is a medium-gray, finer grained, more biotite-rich albitic quartz schist of 

gneissic aspect

Albite granofels and gneiss-boulder conglomerate member—Light-gray, 

massive, coarse-grained biotite-white albite-quartz granofels like Zhab but 

containing boulders of pegmatite and of granitic gneiss, and disarticulated beds 

of albitic granofels as pseudoconglomerate

Conglomerate and quartzite member—Light-grayish-tan-weathering, 

biotite-muscovite-quartz conglomerate and pebbly muscovite quartzite, and 

dark-medium-gray blue-quartz biotite quartzite and schist

----------unconformity----------

Neoproterozoic and Mesoproterozoic rocks of the Green Mountain

and Lincoln Mountain massifs and eastern domes

Cardinal Brook Intrusive Suite (Neoproterozoic)

(965±4 Ma to 945±7 Ma)

Mafic dikes—Medium- to coarse-grained, foliated, actinolite-chlorite-calciteepidote retrograded metadiabasic dikes; commonly have relict diabasic texture

Stamford Granite—Light-gray to medium-gray, very coarse grained biotiteplagioclase-microcline rapakivi granite; contains large megacrysts of microcline 

perthite having rims of plagioclase that contain inclusions of biotite and garnet. 

Unit includes lesser irregular dikes and segregations of hornblende-biotite ferrodiorite and ferromonzonite. A fine-grained facies consisting of white-weathering, 

muscovite-biotite-microcline-plagioclase aplitic granite (Y3Ccbsa) locally forms a 

border facies or thin internal dikes. U-Pb zircon upper-intercept age of 962±1 Ma, 

no. 20 (revised from Karabinos and Aleinikoff, 1990)

Somerset Reservoir Granite—Light-pinkish-gray-weathering, biotite-microclineperthite or porphyritic rapakivi granite and pegmatitic granite; where deformed is 

a mylonitic augen gneiss. White to pinkish-gray, medium-grained plagioclasemicrocline-perthite aplitic to pegmatitic granite (Y3Cbsa) forms dikes in country 

rocks and irregular border facies. U-Pb zircon upper-intercept age of 965±4 Ma, 

no. 19 (Karabinos and Aleinikoff, 1990)

Harriman Reservoir Granite—Light-gray to pinkish-gray, biotite-plagioclasemicrocline megacrystic granite and augen gneiss; rapakivi texture locally 

preserved. Unit occurs in the Rayponda and Sadawga domes

Bull Hill Gneiss of Richardson (1931)—Light-pinkish-gray to gray, very coarse 

grained to medium-grained and mylonitic biotite-plagioclase-quartz-microcline 

augen gneiss; locally has large ovoidal relict microcline with rapakivi rims and 

intrusive breccia containing xenoliths of gneissic units of the Mount Holly 

Complex. Restricted to the Chester and Athens domes, occurring in the core as 

well as in fault slivers along the eastern and western margins, and tectonically 

intercalated with rocks of the Mount Holly Complex and the Hoosac Formation. 

U-Pb zircon upper-intercept ages of 945±7 Ma, no. 17, and 955±5 Ma, no. 18 

(Karabinos and Aleinikoff, 1990) 

Mount Holly Complex intrusive rocks (Mesoproterozoic)

Pegmatite (Mesoproterozoic)—Light-gray to pinkish-gray, biotite-muscovite 

(±garnet±tourmaline±magnetite) granite pegmatite as crosscutting pods and larger 

bodies. Albitic garnet-muscovite pegmatite common in metapelitic rocks of the 

Mount Holly Complex, and especially prominent in the northern and east-central 

parts of the Green Mountain massif. Assignment of individual pegmatites to Y3C is 

highly interpretive based on crosscutting of gneissosity and weakly deformed 

character

Albitic biotite granite and pegmatite at Baker Brook (Mesoproterozoic)—

Pinkish-gray garnet-biotite-albite pegmatite and granitic augen gneiss, distinguished by abundant rose-colored zircon; U-Pb zircon SHRIMP age of 1,037±6 Ma, no. 

16 (Aleinikoff and others, 2011). Undated light-gray biotite granite gneiss (Y3Bg)

containing abundant rose-colored zircon also is confined to the Pine Hill slice

Muscovite-chlorite-garnet schist—Light-silvery-green to grayish-green, 

lustrous muscovite-chlorite-quartz (±garnet±chloritoid±ilmenite) schist and 

biotite-albite-muscovite-quartz schist. Unit is highly variable both in texture and 

in composition (from ultrafine-grained phyllonitic schist to medium-grained 

muscovite-garnet schist). Albitic varieties tend to contain more biotite and less 

muscovite. Rock is highly retrograded and contains abundant chlorite derived 

from the breakdown of garnet that contained large anhedral quartz and grains of 

coarse muscovite and biotite. Robust grains of rutile are abundant. Chloritoid 

commonly occurs in the fine-grained sericitic matrix but locally is found within 

large subhedral garnets. The contact with adjacent Y?mfs is gradational and 

determined by a higher abundance of biotite (commonly chloritized) and albite in 

Y?mfs near Y?cms. The contact with Y2rs of the Mount Holly Complex is 

gradational

Biotite-muscovite-plagioclase-quartz schist—A highly heterogeneous unit, 

distinguished from Y?

cms by its generally rusty-weathering, nonlustrous appearance and by the abundance of large albite crystals, conspicuous large plates of 

muscovite and biotite, and abundant clinozoisite. Locally contains fresh garnet 

as inclusions in albite, or abundant totally retrograded chlorite-sericite clots after 

original highly poikiloblastic garnet. Near the contacts with Y1fga, abundant sills 

of granitic gneiss, plagioclase-tourmaline veins and highly albitic, very coarse 

grained schist occur. Unit is interbedded near its base with either garnetmuscovite-quartz-plagioclase quartzite (Y2

q) or a fine-grained, black hornblendegarnet amphibolite (Y2

a) or calc-silicate rock (Y2cs), all of the Mount Holly 

Complex and containing pegmatite (Y3Cp)

Dolomite marble—Beige to pinkish-gray-weathering, pyrite-bearing, mediumand fine-grained phlogopite-chlorite-dolomite marble exposed in cliffs east of the 

road at Devils Den. Grades into chlorite-biotite (±actinolite)-carbonate schist at 

structural base and has sharp contact with structurally overlying quartzite (Y?

q)

Quartzite—Light-gray to pinkish-gray, magnetite-muscovite-plagioclase quartzite at Devils Den. Grades into structurally overlying biotite-muscovite feldspathic 

schist and garnet-bearing feldspathic gneiss that contains pegmatite

Cavendish Formation (Early Mesoproterozoic)

The term “Cavendish Formation” is restricted to two belts of rocks within the 

Chester dome; the larger belt occurs at Cavendish and on Hawks Mountain, and a 

less extensive belt, containing similar rocks, occurs near Star Hill. An Early 

Mesoproterozoic age is here favored for the Cavendish Formation on the basis of 

(1) the presence of deformed pegmatite (Y3Cp) and areas of Felchville Gneiss (Y1fg

and Y1

fga) within the Cavendish and (2) the marked resemblance of members of the 

Cavendish to aluminous and feldspathic schists, calc-silicate rocks, and quartzites 

within the Mount Holly Complex. Similarities to rocks of the Hoosac Formation are 

also striking and cannot be altogether dismissed; however, the Hoosac Formation 

lacks pegmatite and contains distinctive and well-bedded albitic granofels, mafic 

volcanics, and coarse pebble-to-cobble conglomerate, all absent from the Cavendish. Zircons from a quartzite lens in dolomite marble at locality 4 have Pb-Pb ages 

between 1,290 and 934 Ma and suggest some of the marble of the Cavendish may 

be younger than the Felchville Gneiss (Karabinos and others, 1999). Retrograded 

muscovite-rich, chlorite-spotted, chloritoid-bearing quartz phyllites and garnet 

granofels and other rocks of the Wilcox Formation (Y2

wxs) closely resemble those 

of the Cavendish Formation, as do chloritic-muscovitic retrograded Y2

rs members 

of the Mount Holly Complex in the Green Mountain massif. Dolomite marble, 

talc-tremolite rock, diopside quartzite, calc-silicate gneiss, and lustrous chloritespotted, chlorite-muscovite-rich retrograded garnet gneiss and schist in the Mount 

Holly Complex contain abundant pegmatite (Y3Cp) on Blue Ridge Mountain in 

Chittenden and are identical but lower-grade correlatives of the Cavendish Formation. The coarse garnet-staurolite- and kyanite-bearing Gassetts Schist Member is 

interpreted to be an Acadian remetamorphosed product of the retrograde 

aluminous rocks now seen throughout the Mount Holly Complex of the Green 

Mountain massif and in the Pine Hill area

Gassetts Schist Member—Lustrous, yellowish-grayish-green, ilmenitestaurolite (±kyanite)-garnet (large)-plagioclase-biotite-muscovite-quartz schist 

and warty-textured, dark-gray, biotite-rich garnet (large)-plagioclase-quartz 

schist. Passes locally into greenish, chlorite-spotted, magnetite-garnet (small)- 

plagioclase granofels in which large chlorite clots appear to replace earlier large 

garnet crystals. Unit closely resembles retrograded chlorite-spotted, biotitegarnet-plagioclase-quartz granofels and garnet-quartz-feldspar schist or gneiss 

of the Wilcox Formation of the Mount Holly Complex (Y2

wsx)

Feldspathic schist and granofels member—Light-gray to medium-dark-gray, 

rusty-weathering,white-plagioclase-spotted biotite-quartz-plagioclase granofels, 

massive grayish-green chlorite-spotted, magnetite-studded, biotite-plagioclasequartz granofels and gneiss, and porphyroclastic plagioclase-augen-biotite 

mylonite gneiss. Unit less well-bedded than granofels of the Hoosac Formation 

and lacks amphibolites common in the Hoosac flanking the Chester and 

Athens domes

Marble and calc-silicate member—Highly variable unit. Includes white, 

coarse-grained calcite marble; beige to gray, medium- to coarse-grained 

phlogopite-tremolite-dolomite-quartz-(±talc) marble; greenish actinolitedolomite-calcite marble; phlogopite-diopside-scapolite-calcite-dolomite marble; 

coarse-grained dark-green diopside (±hornblende±zoisite)-calc-silicate rocks; 

white talc-tremolite (±dolomite)-calc-silicate schist; and minor quartzite, 

diopside quartzite, and schistose bluish-gray marble. Contains pods, stringers, 

and larger masses of granite pegmatite and interlayered aplitic gneiss. Marble 

and calc-silicate rocks are identical to units (Y2cs) within the biotite-quartzplagioclase paragneiss member (Y1,2bg) of the Mount Holly Complex of the 

Green Mountain massif and eastern domes

Altered rocks adjacent to the Chittenden Intrusive Suite

Albite-magnetite-studded gneiss (Late Mesoproterozoic)—Gray or greenishgray, albite- and magnetite-studded granulose biotite-quartz-plagioclase gneiss, 

containing chloritized biotite and garnet. Occurs as altered varieties of Y1,2bg near 

1,150-Ma intrusive augen gneisses of the Chittenden Intrusive Suite (Y3Ama); in 

the Lincoln Mountain massif a dark-gray biotite-microcline-chlorite-spotted gneiss 

contains magnetite grains as much as 1 cm in diameter

Aluminous schists and gneisses of the Washington Gneiss and Wilcox 

Formation and related rocks 

Retrograde gneiss (Mesoproterozoic)—Mylonitic chlorite-biotite-microclinequartz gneiss, occurring as a sliver in the Shelburne Marble, South Wallingford

Washington Gneiss (Middle Mesoproterozoic)—Dark-rusty-grayish-brownweathering, graphitic garnet-plagioclase-biotite-quartz (±sillimanite) schist; 

rusty-weathering blue-quartz-ribbed quartz schist; and garnet quartzite and 

rusty-weathering layers of sulfidic calc-silicate rock. Exposed in southernmost part 

of Green Mountain massif. Distinctive quartz ribbing decreases northward where 

more aluminous, less quartzofeldspathic rocks are mapped as Y2

rs

Quartz schist and gneiss (Middle Mesoproterozoic)—Dark-tan- to rusty-tanweathering, garnet-muscovite-biotite-quartz-plagioclase gneiss and rusty schist, 

locally containing abundant chloritized garnet; lustrous yellowish-grayish-green 

phyllonitic retrograde varieties contain chloritoid-chlorite and relict garnet (red dot 

overprint). Unit locally includes steel-gray-weathering, garnet (small)-quartz-biotite 

gneiss and quartzite (Y2

bgt)

Carbonaceous sulfidic schist (Middle Mesoproterozoic)—Dark-gray, 

rusty-weathering carbonaceous to graphitic schist associated with quartzite and 

calc-silicate rock near Killington

Wilcox Formation (Middle Mesoproterozoic)—Lustrous to rusty-weathering 

biotite-muscovite (±chloritoid) schist and retrograde coarse-garnet schist; probably 

is the retrograde equivalent of charnockitic garnet-rich feldspathic quartz gneisses 

of the eastern Adirondacks. Locally contains mappable quartzite, garnet quartzite, 

calc-silicate gneiss, and marbles, mapped separately 

Quartzite member—Tan, yellowish-gray-weathering garnet-muscovite quartzite and feldspathic retrograde-garnet quartz gneiss

Garnetiferous quartzite and quartz schist member—Lustrous muscovitechlorite-chloritoid or muscovite-chlorite-biotite-clinozoisite retrograde schistose 

quartzite and large-garnet schist. Resembles a retrograde variety of the Hague 

Gneiss (of Alling, 1918) (Y2

hgn) near Whitehall, N.Y.

Calc-silicate gneiss and marble member—Dark-green, massive, diopsidehornblende rock, lenses of bluish-gray to gray, medium- to coarse-grained 

calcite marble and calcite-diopside marble and dolomitic talc-phlogopitetremolite schist

Dolomite marble member—Beige-weathering to whitish-gray, fine-grained 

dolomite marble

Okemo Quartzite (Middle Mesoproterozoic)—Light-tan to whitish-gray, massive 

vitreous quartzite in beds several meters thick, interlayered with rusty-grayishbrown garnet-muscovitic quartzite and aluminous sericite-muscovite-tourmaline 

retrograde phyllite. Occurs as a thick unit on Ludlow Mountain, in Okemo State 

FUPb f dl f135932 M126162 M

Bull Formation (Lower Cambrian and Neoproterozoic)

Mud Pond Quartzite Member (Lower Cambrian)—Buff- to gray-weathering 

vitreous quartzite as much as 6 m thick, containing deeply weathered ovoidal 

areas of carbonate-cemented quartzite 

Bomoseen Graywacke Member (Neoproterozoic)—Pale-reddish-brown to 

light-gray-weathering, medium- and fine-grained, massive to thickly bedded, 

olive-green to gray micaceous quartz-feldspar graywacke and siltstone, locally 

containing coarse detrital muscovite, biotite, and autoclastic slate chips. 

Resembles finer grained parts of the Rensselaer Graywacke Member of the 

Nassau Formation (of Potter, 1972), and the Bird Mountain Grit (of Dale, 

1900). Unit interfingers with and grades laterally into the Mettawee slate 

facies. In the Mt. Anthony area is shown as Znb (Bomoseen Member of the 

Nassau Formation of Potter, 1972)

Mettawee slate facies (Neoproterozoic)—Predominantly greenish-gray to 

pale-lustrous-green chlorite-muscovite-quartz phyllite; and green and purple, 

bedded and mottled phyllite. Locally contains boudins and thin beds of 

limestone and pods of pinkish-gray to cream-white dolostone, and minor 

quartzite. Unit interfingers with the West Castleton Formation above and 

laterally grades into the Bomoseen Graywacke Member. Also shown as Znm

(Mettawee Member of the Nassau Formation of Potter, 1972)

Zion Hill Quartzite Member (Lower Cambrian and Neoproterozoic)— 

Light-greenish-gray to whitish-gray-weathering, massive vitreous quartzite; 

locally contains quartz-pebble conglomerate and wacke near the base. Unit 

commonly 5 to 10 m thick but is as much as 65 m thick; occurs as many lenticular quartzites within the Mettawee slate facies in the Bull Formation, not 

restricted to one horizon

Bird Mountain Grit of Dale (1900) (Lower Cambrian and Neoproterozoic)— 

Dark-gray to greenish-gray and whitish-gray, massive chlorite-quartz wacke, 

pebble conglomerate, and purplish-gray hematitic lithic wacke. Unit is rich in 

fragmental plagioclase, phosphatic nodules, fragments of gray quartzite, and 

purple and green slate chips. Interpreted as a coarse-grained variant of part of the 

Zion Hill Quartzite Member, well exposed in and around Bird Mountain. Unit 

resembles in stratigraphic position and lithology the Rensselaer Graywacke 

Member of the Nassau Formation (of Potter, 1972) in the Bennington area (Znr)

Biddie Knob Formation (Lower Cambrian and Neoproterozoic)—Predominantly green, purple and purplish-red, chloritic hematitic slate and phyllite, massive 

to thinly bedded. Has rare thin beds of white vitreous quartzite and contains 

abundant chloritoid. Underlies the Bird Mountain Grit (of Dale, 1900) and grades 

into the green slate of the Mettawee slate facies in the Bull Formation, probably in 

part correlative with the green phyllite member of the Netop Formation (Zngs) of 

the Dorset Mountain slice

Rensselaer Graywacke Member of the Nassau Formation of Potter (1972) 

(Lower Cambrian and Neoproterozoic)—Includes basaltic volcanics (Zbv)

Rocks of the Dorset Mountain slice

(includes Dorset Mountain proper and Mount Equinox, southward to West 

Mountain near Bennington)

Carbonaceous phyllite and siltstone (Lower Cambrian and 

Neoproterozoic)—Medium- to dark-gray carbonaceous phyllite, gray slate, and 

metasiltstone, locally containing light-gray, medium- to thick-bedded quartzite and 

dolomitic quartzite (Zbq). Unit resembles rocks of the Netop Formation but lacks 

the distinctive lenses and pods of bluish-gray dolostone of the Netop on Dorset 

Mountain, although lenses of whitish quartzite are present

Netop Formation (Cambrian and Neoproterozoic)—Predominantly light- to 

medium-gray and grayish-green phyllite and metasiltstone. Includes the following 

mappable informal members: greenish-gray laminated albite-metasiltstone 

(Znab), and dark-gray phyllite containing bluish-gray dolostone and 

tan-weathering to locally mappable gray-weathering dolomitic quartzite (Znq). 

The Netop Formation may be in part equivalent in age and facies to parts of the 

West Castleton and Hatch Hill Formations, but may extend lower and into the 

Neoproterozoic

Chlorite phyllite member—Light-green to gray, lustrous, 

chlorite±chloritoid-muscovite-quartz phyllite and greenish-gray metasiltstone. 

Locally contains beds of grayish-green vitreous quartzite and quartz-pebble 

conglomerate, and thin beds of chloritic wacke, all shown as Zngq (unit is in 

part equivalent to rocks of the Mettawee slate facies and Zion Hill Quartzite 

Member of the Bull Formation)

Wacke member—Bluish-gray, fine-grained metawacke and metasiltstone, 

perhaps equivalent to the Bomoseen Graywacke Member of the Bull Formation

ROCKS OF THE ROWE-HAWLEY ZONE

Ordovician, Cambrian, and Neoproterozoic allochthonous cover sequence 

east of the Green Mountains—Rift and drift stage metasedimentary and 

metavolcanic rocks and tectonic inclusions of ultramafic rocks described

in west-to-east tectonic stacking sequence

Ottauquechee Formation (Cambrian)

Carbonaceous phyllite member—Predominantly dark-gray to black, 

carbonaceous to highly graphitic, fine-grained sulfidic biotite-muscovite-quartz 

phyllite having silicic laminae. Includes black quartzites not mapped separately

Coarse-muscovite schist member—Silvery-green albite-chlorite-quartzmuscovite (±garnet) schist characterized by coarse muscovite porphyroblasts

Black quartzite member—Dark-bluish-gray to black, fine-grained vitreous 

quartzite. Beds are as thick as 30 m or are thin and interbedded with black 

phyllite

Feldspathic schist and granofels member—Gray and grayish-green, biotitechlorite-muscovite-albite-quartz schist or phyllite and granofels; contains 

coticule, locally richly garnetiferous

Carbonaceous albite schist member—Tan- to dark-gray-weathering, 

carbonaceous, medium- to coarse-grained chlorite-plagioclase-muscovitequartz schist and interbedded tan, gray, and bluish-gray quartzite

Schist and quartzite member—Light-gray to tan, rusty-weathering, laminated 

sandy muscovite-plagioclase-quartz schist and tan quartzite

Amphibolite and greenstone member—Dark-green plagioclase-hornblende 

(±quartz) amphibolite and rusty-pale-green, punky-weathering ankeriticchloritic greenstone

Carbonate-bearing quartzite member—Heterogeneous unit consisting of ankeritic greenstone, ankeritic or dolomitic muscovite quartzite, bluish-gray calcareous quartzite, and pods of brecciated dolostone. Exposed at Plymouth Five Corners

Metawacke member—Tan to gray phyllitic metawacke composed of rounded 

to angular grains of quartz, blue quartz, albite, and traces of detrital rock 

fragments in a fine-grained matrix of quartz, sericite, and chlorite. Feldspathic 

metawacke is common; quartz grains range in size from 0.5 mm to 0.5 cm. 

Conglomerate and breccia occur locally at The Knob (northwest of Lake Eden) 

and just north of the Lowell-Westfield town line

Stowe Formation (Cambrian and Neoproterozoic?)

Schist and phyllite member—Predominantly fine-grained, lustrous, 

well-foliated, silvery-green, grayish-green, and bright-green, quartz-ribbed and 

-knotted, magnetite-chlorite (biotite)-albite (plagioclase)-sericite (muscovite)-

quartz phyllite and schist. Locally richly garnetiferous and biotite-flecked schist 

(Zsgt) at higher grades; areas rich in metadiabase dikes shown by overprint 

and symbol (Zsd)

Sericite schist member—Quartz-sericite phyllite and schist

Carbonaceous phyllite member—Interlayered grayish-green and 

rusty-weathering black quartzose phyllite, similar to dark carbonaceous phyllites 

of the Ottauquechee Formation (o)

Large-garnet schist member—Silvery-green to grayish-green, garnet (large)- 

plagioclase-biotite (chlorite)-quartz-muscovite schist. Comparable to garnet 

schist member of the Rowe Schist in southern Vermont and around the 

Chester and Athens domes (Zrgs)

Amphibolite and greenstone member—Dark-green hornblende-rich biotiteplagioclase (±garnet) amphibolite, epidote-hornblende-plagioclase-quartz 

amphibolite, and light-grayish-green, rusty-weathering, carbonate-pitted 

SHRIMP age of 496±8 Ma north of Proctorsville, no. 23 (Aleinikoff and others, 

2011); U-Pb zircon age of 471.4±3.7 Ma south of Bethel, no. 26 (Karabinos and 

others, 1998) 

Tonalite gneiss—Medium-grayish-green, medium-grained hornblende-biotite 

tonalite gneiss, with minor amphibolite. U-Pb zircon TIMS age of 486±3 Ma, no. 

24 (Aleinikoff and others, 2011), from 4 km northwest of Brockways Mills, near 

Bartonsville

Mixed felsic and mafic rocks—Heterogeneous composite intrusive well-layered 

unit consisting of biotite and hornblende metatrondhjemite, garnet-hornblendeplagioclase amphibolite, and metadiabase dikes; locally called Ruger Hill facies 

(Onr) in the Spring Hill syncline (Ratcliffe and Armstrong, 2001). Layering 

thickness ranges from 5 cm to 1 m. Unit may be in part metavolcanic as well as 

intrusive. Resembles well-layered undated felsic and mafic volcanics intercalated 

with metasediments of the Cram Hill Formation (Ochv)

Metatrondhjemite and metatonalite—Light-gray to whitish-gray, coarse-grained 

muscovite-biotite-quartz-plagioclase metatrondhjemite on the east flank of the 

Chester dome; similar to Onb, Onnt, and Ontw

Newfane tonalite—Light-gray to cream-weathering, massive to gneissic, 

hornblende-biotite and muscovite-biotite metatrondhjemite and metatonalite. 

Forms a thick, sill-like intrusive extending northward from South Newfane, where 

it intrudes metavolcanics (Ochv) of the Cram Hill Formation. U-Pb zircon SHRIMP 

age of 502±4 Ma, no. 22 (Aleinikoff and others, 2011) 

Metasedimentary host rocks of the North River Igneous Suite

Cram Hill Formation (Middle? and Early Ordovician)

(western part of the Cram Hill Formation is in part correlative with

Whetstone Hill Member of the Moretown Formation)

Cram Hill Formation, undivided—Predominantly dark-gray to grayish-green 

quartz-chlorite-(biotite)-muscovite phyllite; contains 1- to 2-cm-thick beds of 

dark-gray metasiltstone and quartzite, and thicker beds of dark-bluish-gray vitreous 

quartzite, grayish-green to light-yellowish-green sericite phyllite (felsic tuffs) and 

cobble to boulder conglomerate, and greenstone. Mapped north of the Braintree 

Intrusive Complex and near Brattleboro

Granofels member—Dark-medium-gray biotite-plagioclase-quartz granofels 

and grayish-green chlorite-plagioclase-quartz granofels; contains thin layers of 

ankerite-epidote greenstone, ankerite-spotted feldspathic granofels, and 

coticule. Locally hornblende rich at higher metamorphic grade

Feldspathic schist and granofels member—Medium-dark-gray to dark-gray, 

rusty-weathering garnet-biotite-muscovite-quartz-plagioclase schist and 

granofels; has coarse spangles of muscovite and locally is kyanite rich. Mapped 

in core of Spring Hill syncline

Ironstone, quartzite, and coticule member—Dark-gray- to sooty-blackweathering siliceous ironstone, magnetite quartzite, garnet quartzite, 

rusty-weathering amphibolite, coticule, and pods of orangey-gray to pinkishgray-weathering dolostone

Felsic and intermediate metavolcanic member—Occurs at different 

stratigraphic levels. Includes dark-gray and white layered metadacite and 

meta-andesite, gray- to tan-weathering blue-quartz phenocrystic metadacitic 

agglomerate, and grayish-green fragmental metadacitic and meta-andesite 

breccia. Similar to the volcanic agglomerate (Omwhv) within the Whetstone 

Hill Member of the Moretown Formation. A similar felsic layer interlayered 

within the Cram Hill Formation has a U-Pb zircon SHRIMP age of 483±3 Ma, 

no. 25 (Aleinikoff and others, 2011) 

Felsic volcanic member—Light-gray to whitish-gray, fine-grained sericitequartz-phenocrystic phyllitic metatuff and whitish pyritiferous soda-rhyolite 

metatuff. Abundant screens and layers occur within mafic rocks of the North 

River Igneous Suite and at scattered localities north of the Braintree intrusive 

complex and in the Coburn Hill area

Amphibolite and greenstone member—Light-greenish-gray, feldspathic 

chlorite-actinolite greenstone and bedded andesitic to basaltic tuff and 

amphibolite, associated with ironstone, coticule, and minor pods of dolostone

Quartzite and quartz-pebble conglomerate member—Tan- to 

gray-weathering, quartz-pebble and -cobble conglomerate, feldspathic quartzite 

and associated slabby, rusty-weathering amphibolite and coticule

Gray quartz schist member—Rusty-grayish-brown-weathering, locally 

splintery-fractured, dark-gray to steel-gray biotite-quartz-feldspathic schist and 

quartzite and interbedded carbonaceous, small-garnet papery muscovite 

phyllite and schist similar to Ochs

Carbonaceous schist member—Light-grayish-brown- to tan-weathering, 

medium-dark-gray, fine-grained garnet (small)-biotite-muscovite phyllite and 

schist. Similar to phyllite facies (Omwh) in the Whetstone Hill Member of the 

Moretown Formation

Cram Hill Formation of the Newport Center area

(in part correlative with the St. Daniel Group of Québec)

Phyllite-chip conglomerate and slate conglomerate member—Dark-gray, 

carbonaceous garnet-pyrite-sericite-chlorite-quartz phyllite with clasts of 

siltstone, phyllite, quartzite, and dark-gray slate breccia interbedded with 

Coburn Hill Metabasalt Member (Ochcv). Unit correlative with the St. Daniel 

Group of Québec

Coburn Hill Metabasalt Member—Light-green, fine- to medium-grained, 

massive carbonate-biotite-quartz-sphene-chlorite-actinolite-epidote greenstone 

with deformed pillows; interfingers with the Umbrella Hill Conglomerate 

Member (Ochuc) and with phyllite-chip conglomerate (Ochsb)

Phyllite member—Gray to silvery-green, sericite-chlorite-quartz phyllite with 

thin beds of rusty-weathering, pearly-white, fine-grained granofels. Interlayered with Ochuc and Ochsb at the contacts. Mapped locally in the Albany area

Umbrella Hill Conglomerate Member—Quartz-pebble and phyllitic-fragment 

conglomerate, and tan to gray phyllite. Occurs as lenses, locally unconformable with the underlying Stowe Formation at Umbrella Hill; occurs at different 

stratigraphic levels in the Cram Hill Formation north of Albany. Interbedded 

with Coburn Hill Metabasalt Member (Ochcv) and phyllite-chip conglomerate 

and slate conglomerate member (Ochsb) north of Albany

Phyllite and quartzite member—Light-gray to tan, rusty-weathering, finegrained quartz-sericite-chlorite-albite phyllite, quartzite, and flinty sulfidic 

granofels; thin layers of felsite, conglomerate, and breccia occur in the vicinity of 

Coburn Hill. Paper schist fabric occurs locally on the west side of Coburn Hill

Moretown Formation (Lower Ordovician to Cambrian?)

Granofels and phyllite member—Light-gray to tan, fine-grained albitechlorite-sericite-quartz phyllitic quartzite interlayered with light-greenish-gray 

quartzofeldspathic granofels and dark-gray phyllite. Contains numerous 

boudinaged, massive to foliated, dark-green metamorphosed mafic dikes and 

sills 

Interbedded quartzite and phyllite member—Light-gray laminated quartzite 

and vitreous quartzite interbedded with gray phyllite and schist 

Harlow Bridge quartzite member—Buff-weathering, tan to green, 

fine-grained massive to thinly bedded quartzite intercalated with green phyllite 

and schist 

Quartz schist member—Bluish-black, rusty-weathering, fine-grained albitesericite-chlorite-quartz schist with pyrite

“Pinstriped” granofels member—Light-gray to pale-green, whitish-grayweathering, chlorite-biotite-plagioclase-quartz granofels and tectonically 

“pinstriped” granofels and feldspathic biotite quartzite

Carbonaceous and sulfidic schist member—Rusty-weathering, dark-gray 

biotite-muscovite-quartz (±garnet) schist, carbonaceous schist, and gray, 

splintery-fractured, biotitic sulfidic quartz schist. Contains layers of 

rusty-weathering amphibolite, coticule, and vitreous quartzite (Ombq). A prominent zone that extends from the north end of the Chester dome and near 

Proctorsville southward to near Townshend contains abundant ultramafic rocks 

(Zu)

Quartzite member—Dark-gray to steel-bluish-gray vitreous quartzite in beds as 

much as 10 m thick but commonly less than 1 m thick. Resembles quartzites 

of the Ottauquechee Formation (obq)

Feldspathic quartzite member—Light-grayish-brown- to tan-weathering 

biotite-muscovite feldspathic quartzite and muscovitic quartz schist

Crow Hill Member of Hall (1959)—Gray quartzite and feldspathic quartzite, 

in part volcaniclastic and locally interbedded with amphibolite

Quartzite and feldspathic quartzite member—Light-gray to tan, thinly 

bedded quartzite in beds 2 to 10 cm thick, exposed north of the Chester dome 

and south of Springfield; contains detrital zircon having Grenvillian provenance

Quartz-cobble and schistose metaconglomerate member—Light-gray 

muscovite-quartz schist and quartz conglomerate and dark-gray carbonaceous, 

polymict schistose quartz conglomerate, associated with DSwb, DSwb/Dl, 

DSws, and DSwv southeast of Springfield

Ayers Cliff Member—Gray- to bluish-gray, fine- to medium-grained, thinly 

bedded calcareous metasandstone, quartzose metalimestone, and fissile, 

laminated calcareous metasandstone and phyllite

Irasburg Conglomerate (member)—Gray- to bluish-gray polymict limestone 

metaconglomerate containing pebbles to cobbles of limestone, pelite, granite, 

and intermediate to felsic volcanic rocks; also locally occurs in the Northfield 

Formation

Calcareous granofels member—Carbonaceous phyllite containing meterthick beds of calcareous granofels. Unit occurs only in Massachusetts

Carbonaceous phyllite and limestone member—Dark-gray to silvery-gray, 

lustrous, carbonaceous muscovite-biotite-quartz (±garnet) phyllite containing 

abundant beds of punky-brown-weathering, dark-bluish-gray micaceous quartzrich limestone in beds ranging from 10 cm to 10 m thick

Northfield Formation (Lower Devonian and Upper Silurian)—Dark-gray to 

silvery-gray, lustrous, fine-grained carbonaceous quartz-muscovite phyllite and 

silicic phyllite, and garnet-rich biotite-muscovite-quartz schist; contains millimeterto centimeter-thick beds of gray quartzite and metasiltstone, and thicker beds of 

quartz-feldspar grit or quartzite near base. Contains only minor beds of quartzose 

limestone (DSnl); transition zone into Waits River Formation west of the Guilford 

dome consists of as much as 5 percent beds of punky limestone

Quartzite, grit, and conglomerate member—Dark-gray quartz-pebble 

metawacke and gray quartzite and conglomerate at base of the Northfield 

Formation, south of Springfield

Shaw Mountain Formation (Upper to Lower Silurian)—White to yellowish-gray 

quartz-pebble conglomerate and conglomeratic quartzite, having clasts of milkywhite quartz as much as 2.5 cm in diameter in a white to tan quartzite matrix, in 

beds 0.5 to 1 m thick; and yellowish-gray to light-gray phyllitic quartzite, quartzpebble to -granule phyllite, and steel-gray to tan vitreous quartzite in beds as much 

as 5 m thick

Basal volcaniclastic and metasedimentary member—Heterogeneous, thin 

(<10 m thick) unit of interbedded quartzite, amphibolite, felsic granofels, and 

phyllite, occurring at the base of the Waits River Formation on the north end of 

the Chester dome. Interpreted as recycled volcaniclastic rocks derived from the 

underlying volcanic and intrusive rocks in the Cram Hill Formation

INTRUSIVE ROCKS (SILURIAN)

Lake Memphremagog Intrusive Suite (Late Silurian)

(425±3 Ma to 418.5±2 Ma)

Newport Intrusive Complex

Granodiorite—Tan to light-bluish-gray, brown-weathering, medium- to coarsegrained, equigranular to porphyritic foliated granodiorite composed of quartz, 

plagioclase, perthite, microcline, biotite, and sericite

Diorite and trondhjemite—Metamorphosed diorite, trondhjemite, and diabase, 

consisting of massive to foliated, light-gray to grayish-green, chalky-weathering 

diorite with xenoliths of green phyllite and trondhjemite; and massive, 

tan-weathering, medium- to coarse-grained trondhjemite with xenoliths of diabase. 

Numerous crosscutting quartz-feldspar veinlets show in relief on the weathering 

surface. Unit intrudes Cram Hill Formation. U-Pb zircon SHRIMP age of 425±3 

Ma, no. 39 (Aleinikoff and others, 2011) 

Braintree Intrusive Complex

Biotite-bearing metagranodiorite, metagranite, and meta-aplite of the Mount 

Nevis pluton—Yellowish-gray to light-gray, medium- to coarse-grained magnetitebiotite-mesoperthite granodiorite and granite having a U-Pb zircon SHRIMP age of 

421±7 Ma, no. 38 (Aleinikoff and others, 2011). Has mutually intrusive contacts 

with associated metadiorites. Unmapped dike of Sbg in the layered, mixed felsic 

and mafic rocks (Onbm) of the North River Igneous Suite at Bridgewater has a 

U-Pb zircon age of 418±1 Ma, no. 37 (Aleinikoff and Karabinos, 1990)

Metadiorite to metamonzodiorite—Medium-gray-weathering, porphyritic dikes 

and sills of fine- to medium-grained hornblende-biotite diorite and quartz diorite, 

and coarse-grained quartz monzodiorite. Has a U-Pb zircon TIMs age of 419±0.39 

Ma, no. 36 (Black and others, 2004). Narrow zone of garnet-biotite-plagioclasecordierite hornfels in the Moretown Formation postdates dominant foliation 

(Taconian) in host rocks

Comerford Intrusive Complex

(a sheeted dike to pegmatitic diorite complex)

Abundant, foliated to weakly foliated, metatholeiitic mafic dikes; some sheeted. 

Shown as overprint

Foliated to nonfoliated, fine-grained to pegmatitic metagabbro, metadiorite, and 

metatonalite; aplitic metatonalite; and metadiabase. U-Pb zircon ages of pegmatitic metadiorite from three bodies (Comerford quarry, Leighton Hill, and Peaked 

Mountain) are, respectively, 419.8±2.6 Ma, no. 33; 419.3±1.3 Ma, no. 34; and 

418.5±2.0 Ma, no. 35 (Rankin and others, 2007)

Nonfoliated to foliated pegmatitic metatonalite to metagabbro

Piermont and other allochthons

Rangeley Formation (Lower Silurian)—Interlayered, commonly 

rusty-weathering quartz-feldspar micaceous granofels and dark-gray mica schist 

containing porphyroblasts of garnet, staurolite, and kyanite. Calc-silicate lenses 

common in the granofels; granule and pebble metaconglomerate locally are 

present. Separate mappable units of quartz conglomerate (Src) and rusty sulfidic 

schist (Srr) occur in Fall Mountain nappe near Bellows Falls

Greenvale Cove Formation (Lower Silurian)—Thin-bedded muscovite-biotitegarnet-staurolite-kyanite schist and micaceous quartz-feldspar granofels; some 

calc-silicate lenses and layers

BRONSON HILL ARCH INTRUSIVE ROCKS

French Pond Granite (Late Devonian)—Pink to gray, nonfoliated, porphyritic to 

coarse-grained biotite granite; phenocrysts of potassium feldspar are as large as 2 

by 3 cm. U-Pb zircon age of 364±5 Ma, no. 50 (Moench and Aleinikoff, 2003)

Bethlehem Gneiss (Early Devonian)—Medium- to coarse-grained, equigranular 

to porphyritic, muscovite-biotite-microcline-plagioclase metaquartz monzonite; 

contains garnet, sillimanite-andalusite and cordierite; intrudes rocks of the Rangeley Formation in New Hampshire. U-Pb zircon age of 407±5 Ma, no. 43 (Kohn 

and others, 1992) at Bellows Falls

Kinsman Quartz Monzonite of Billings (1955) (Early Devonian)—Medium- to 

coarse-grained, potassium-feldspar-megacrystic, biotite granodiorite gneiss of the 

Ashuelot pluton. U-Pb zircon age of 403±2 Ma (R.D. Tucker, USGS, written 

commun., 2008)

Fairlee Quartz Monzonite (Early Devonian)—Greenish-gray, pink-tinged, 

weakly foliated, coarse-grained to porphyritic biotite granite of the Fairlee pluton. 

U-Pb zircon age of 410±5 Ma, no. 42 (Moench and Aleinikoff, 2003)

Moulton Diorite (Early Devonian)—Dark-gray, medium-grained metadiorite 

composed mainly of secondary minerals such as saussuritized plagioclase, amphibole, epidote, chlorite, and calcite 

Dikes and sills of porphyritic and nonporphyritic metarhyolite of Hunt Mountain intrusive into the Albee Formation (Early Devonian)—Some contain 

xenoliths of dikes of the Comerford Intrusive Complex (Scd). U-Pb zircon ages of 

414±4 Ma, no. 40, and 412±2 Ma, no. 41 (Lyons and others, 1997; Moench and 

others1995)

Zd

Y3Abga

Y2

wg

Y2

wxs

Y2

rss

Y2

wxq

Y2

wxg

Y2

wxcs

Y2

wxd

Y2

lq

Y2rs

Y2bgt

Y3Ccbs

Y3Ccbsa

Y3Ccbsr

Y3Ccbhr

Y3Ccbbh

Y?

c m s

Y?

m f s

Y3Cbsa

Y?

d m

Y?

q

Dfpg

Dbgn

Dkq

Dfqm

Scd

Scm

Scg

Sr

Srr

Src

Sg

Yur

Zmpq

Zbb

(Znb)

Zbm

(Znm)

Zzh

Zbmg

Znr

Zbk

Znq

Zn

Znab

Zngs

Zngq

Znw

DSwc

DSwq

DSwqc

DSwac

DSwi

DSwt

DSw

DSn

DSnl

DSnq

Ss

Scv

Dm

Dr

Y1

c g

Y1

c fs

Y1?c m

Y1

c s

Ztg

Ztrg

Ztgr

Ztq

Ztd

Ztbs

Zhcgt

Zhbs

Zhtm

Zhd

Zhrab

Zhq

Zhs

Zhgt

Zhgab

Zhab

Zhabc

Zh

o

om

obq

of

ocf

oq

oa

Zs

Zsd

Zsbg

Zsgp

Zsgt

Zsa

Zsg

Ochu

Ochfg

Ochfs

Ochic

Ochv

Ochfv

Ocha

Ochq

Och

Ochs

Ochsb

Ochcv

Ochp

Ochuc

Ochpq

Omw

Omq

Omhb

Ombb

Omp

Omb

Ombq

Omfq

Onbm

Onr

Onnt

Ontd

Ont

Sng

Snd

Sbg

Sbd

Zbv

Zbms

Zbq

Y3Cp

Y3Bp

Y3Bg

opw

ocq

Ztc

Zhc

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map, scale 1:62,500. (Also available at http://www.anr.state.vt.us/dec/geo/ 

bulletins.htm.)
Granulose albitic gneiss (Mesoproterozoic?)—Massive to poorly layered, highly 

lineated, light-tannish-gray to grayish-green, medium-grained, granulose, epidotemagnetite-biotite (chlorite)-muscovite-albite-quartz gneiss, veined with magnetite; 

spots of ankerite and clots of chlorite after original amphibole, pyroxene, or garnet 

are common. Highly altered rock is perhaps metasomatic and related to 1,170- to 

1,120-Ma period of granitic intrusions. Unit shows all gradations from pinkish-gray 

biotite-quartz-plagioclase gneiss having centimeter-thick veins of garnet-bearing 

albitic micropegmatite, to nonlayered albitic granulose white gneiss. Occurs in 

central Green Mountain massif from Plymouth to Shrewsbury, on Robinson Hill, 

and along the eastern margin of the Green Mountain massif east of Rutland

Chittenden Intrusive Suite (Late Mesoproterozoic)

(1,149±8 Ma to 1,119±3 Ma)

Hornblende gabbro-diorite (Mesoproterozoic)—Biotite-hornblende (±pyroxene) gabbro and diorite at Robinson Hill in Shrewsbury; exhibits fine-grained chill 

contact that crosscuts paragneiss units. Unit also in Lincoln Mountain massif and 

at Brandon Gap; similar rock mapped in the Adirondacks

Microcline-augen granite and monzogranite gneiss—Gray to whitish-gray, 

coarse-grained biotite-microcline megacrystic granite and monzogranitic gneiss; 

passes locally into more equigranular granitic gneiss (Y3Ag) and locally into 

extensive areas of biotite pegmatoid granitic gneiss (Y3Apg), locally muscovitebearing. Enclaves of metasedimentary units in these granites and associated 

gneisses are locally albitized and enriched in magnetite; enclaves of highly 

aluminous altered rocks now contain restites of chloritoid and abundant sericite. 

U-Pb zircon ages of 1,119±3.3 Ma (no. 15) and 1,121±1.4 Ma (no. 14) 

determined on samples near Sherburne Center and on Telegraph Hill east of 

Chittenden Reservoir by Karabinos and Aleinikoff (1990)

Microcline-magnetite augen gneiss at Brandon Gap—Pinkish-gray to mediumdark-gray, biotite-magnetite-microcline-plagioclase augen gneiss. U-Pb zircon 

SHRIMP age of 1,149±8 Ma, no. 13 (Aleinikoff and others, 2011). Unit is associated with minor exposures of metadiorite to tonalitic gneisses; crosscuts a gneissosity in country rocks and may extend northward along eastern limb of Lincoln 

Mountain massif as unit Y3Ama

Granitic gneiss of Chittenden Intrusive Suite (?)—Light-gray, coarse-grained, 

biotite-microcline megacrystic to even-grained granite gneiss closely associated 

with 1,149- to 1,120-Ma augen gneisses, in the northern part of the Green Mountain massif. Not distinguishable with certainty from older granitoids of the Stratton 

Mountain Intrusive Suite of the central and southern Green Mountains

Microcline augen gneiss of Lincoln Mountain massif—Light- to medium-gray, 

medium-grained, biotite-quartz-plagioclase-microcline gneiss; contains microcline 

augen as much as 4 cm in length

Stratton Mountain Intrusive Suite (Middle Mesoproterozoic)

(1,244±8 Ma to 1,221±4 Ma)

Biotite-granitic gneiss—A heterogeneous unit consisting of granitic and granodioritic and aplite biotitic microcline-rich gneisses, highly gneissic and locally 

migmatitic, occurring in the southern part of the Green Mountain massif. U-Pb 

zircon TIMS age of 1,221±4 Ma, no. 12 (Ratcliffe and others, 1991; Aleinikoff 

and others, 2011) obtained from Londonderry. Unit intrudes rocks of South 

Londonderry Igneous Suite

Aplitic gneiss—Light-gray to white, fine-grained aplitic granite gneiss as border of 

Y2gg or as thin dikes or sills in paragneiss units

College Hill Granite Gneiss—Light-gray to medium-dark-gray, porphyritic 

biotite-microcline-perthite granodioritic gneiss and pegmatite. Strongly deformed, 

lineated, and saturated with less deformed later pegmatite; grades outward into a 

migmatitic border exhibiting decreasing concentration of microcline megacrysts. 

Forms a single large intrusive mass on College Hill in Jamaica and west of Stratton 

Mountain; truncates structure in older gneisses. U-Pb zircon TIMS age of 1,244±8 

Ma, no. 11 (Ratcliffe and others, 1991; Aleinikoff and others, 2011)

Granitic gneiss of Lincoln Mountain massif (MiddleMesoproterozoic)—Heterogeneous unit consisting of medium-grained biotite-microcline-plagioclase gneiss 

and pinkish-gray, medium- to coarse-grained microcline-perthite granitic gneiss. 

Interpreted as intrusive granitic rock older than Y3 rocks of Chittenden Intrusive 

Suite

Migmatitic and mylonitic rocks of uncertain origin

Migmatitic gneiss (Middle Mesoproterozoic)—Light-gray and pinkish-gray to 

yellowish-gray, massive, medium-grained plagioclase granitic gneiss, and migmatite-veined biotite-plagioclase gneiss. Occurs prominently in Jamaica, in Andover 

in the Chester dome, and in Weston where it appears to form an integral part of 

Y1,2bg, but also locally appears to be intrusive. A mixed rock of uncertain origin. 

U-Pb zircon SHRIMP age of 1,326±4 Ma, no. 8 (Aleinikoff and others, 2011), 

suggests affinity with metamorphic and igneous events associated with the Middle 

Mesoproterozoic Ludlow Mountain and Proctor Hill granodiorite gneisses of the 

South Londonderry Igneous Suite. Age of migmatization is younger than 1,326 Ma

Mylonitic gneiss (age uncertain)—Highly schistose, biotite-muscovite (±chlorite) 

feldspathic mylonite and mylonitic gneiss mapped near Brandon Gap; in the Pine 

Hill slice near South Wallingford is mapped as Yur

South Londonderry Igneous Suite (Middle and Early Mesoproterozoic)

(1,393±9 Ma to 1,309±6 Ma)

Ludlow Mountain granodiorite gneiss (Middle Mesoproterozoic)—Light-gray, 

medium- to fine-grained garnet-biotite-microcline-perthite granodiorite, 

magnetite-studded white aplite, and kyanite-tourmaline pegmatite. Contains 

0.5-cm clots of muscovite possibly after beryl. Intrudes quartzite, lustrous schists

(Y1rs), and calc-silicate rocks on Ludlow Mountain. U-Pb zircon SHRIMP age of 

1,309±6 Ma, no. 9 (Aleinikoff and others, 2011)

Forest. U-Pb ages of detrital zircons range from 1,359±32 Ma to 1,261±62 Ma, 

no. 10 (Aleinikoff and others, 2011), and suggest derivation from trondhjemitic 

gneiss of the South Londonderry Igneous Suite

Quartzite, undifferentiated (Middle to Early Mesoproterozoic)—Tan to 

rusty-brown or gray, thinly layered garnet-biotite quartzite and schistose quartzite 

associated with aluminous schists and calc-silicate rocks or interbedded within 

biotite-quartz-plagioclase paragneiss. Unit probably occurs at various stratigraphic 

levels; may be Early Mesoproterozoic in part (Y1q)

Dolomite marble (Middle Mesoproterozoic)—Light-gray to yellowish-gray, 

coarse-grained dolomite-phlogopite-scapolite marble; pyritiferous varieties 

weather salmon pink to beige. Unit occurs on West Mountain in Chittenden, in 

Sherburne Center, Weston, and in the Pine Hill slice; is commonly associated with 

tremolite-talc marble and tremolite-talc schist

Calcite marble (Middle Mesoproterozoic)—Light-bluish-gray and white, coarseand medium-grained calcite-diopside marble and calcite-diopside-talc marble in 

beds or pods less than 5 m thick, interbedded with or passing laterally into other 

calc-silicate rock

Calc-silicate rock (Middle Mesoproterozoic)—Heterogeneous unit consists of 

dark-green hornblende-diopside rock or pale-green diopside rock; hornblendecalcite-diopside knotted rock; and rusty-weathering, beige scapolite-quartzplagioclase gneiss, tremolite-phlogopite schist, and diopside quartzite

Amphibolite (Middle Mesoproterozoic)—Dark-grayish-green, fine-grained 

quartz-hornblende-plagioclase amphibolite, locally garnetiferous, and mediumgrained hornblende-plagioclase amphibolite. Occurs with belts of calc-silicate 

rocks and as lenses within biotite-quartz-plagioclase paragneiss. Unit probably 

includes both meta-igneous and metasedimentary rocks intercalated throughout 

the Early and Middle Mesoproterozoic-age rocks of the Mount Holly Complex

Hornblende-plagioclase gneiss (Middle Mesoproterozoic)—Medium- to 

coarse-grained hornblende dioritic-appearing gneiss

Garnet-biotite gneiss (Middle Mesoproterozoic)—Dark-gray- to rusty-grayishbrown-weathering, sulfidic muscovite-biotite-magnetite gneiss or schist marked by 

abundant small garnets, biotite, and fine laminae of quartz and plagioclase. 

Contains thin belts of amphibolite and calc-silicate gneiss

Biotite-quartz-plagioclase gneiss (Middle and Early Mesoproterozoic)—A 

widespread, heterogeneous unit of well-layered, predominantly biotite-quartzplagioclase gneisses containing variable amounts of magnetite, hornblende, and 

garnet, and little potash feldspar. Plagioclase-rich layers contain epidote-crowded 

plagioclase and isolated igneous quartz grains and probably are metadacitic 

volcanics and volcaniclastic rocks. Unit varies from very dark gray biotitic gneiss to 

light-gray more plagioclase- and quartz-rich gneiss, contains quartz-rich layers, 

minor amphibolites, rusty-weathering garnetiferous quartzites, and calc-silicates 

and marbles which locally are mappable. Association suggests an accumulation of 

volcaniclastic and clastic sediments. Areas of Y1,2bg associated with 1,400- to 

1,350-Ma intrusive rocks range down into the Early Mesoproterozoic, whereas the 

upper parts may be Middle Mesoproterozoic. Rocks mapped as Y1,2bg may not all 

be correlative

Biotite-epidote-quartz gneiss and epidotic quartzite (Middle and Early 

Mesoproterozoic)—Light-pale-yellowish-green to gray quartzite gneiss containing 

abundant epidote and locally magnetite, and frosted round grains of quartz associated with diopside-bearing quartzite 

Quartz schist (Early Mesoproterozoic)—Rusty-weathering sulfidic schist and 

minor amphibolite older than part of the South Londonderry Igneous Suite

THE TACONIC ALLOCHTHON

Five structural slices of the Taconic allochthon in Vermont (Zen, 1961, 1972; 

Potter, 1972) contain rocks ranging in age from Neoproterozoic to Ordovician. The 

lowermost slices, the Sunset Lake, Giddings Brook, and North Petersburg slices, 

contain the complete stratigraphic range whereas the higher and more easterly Bird 

Mountain and Dorset Mountain slices are inferred to contain largely Cambrian and 

Neoproterozoic rocks and to exhibit different facies from those of the lower slices. 

The structural boundaries among the slices are commonly late post-emplacement 

imbricate thrust faults, thus complicating both the inferred stacking sequence and 

the identification of primary emplacement relations. For example, the boundary 

and distinction between the Bird Mountain and Giddings Brook slices is particularly 

uncertain and is not shown on this map; there may be no distinction. Although the 

structural stacking sequence and boundaries are indefinite, the names are useful for 

describing geographic areas and stratigraphic distinctions and are retained here for 

descriptive purposes (see Zen, 1961, 1964, 1967).

Forbes Hill conglomerate and breccia in the Ira and Hortonville Formations 

(Upper Ordovician)—Black slate containing angular to irregular chips of greenishgray to yellowish-gray slate, quartz wacke, and limestone; interpreted by Zen 

(1961) as sedimentary wildflysch

Vesicular basalt breccia at East Hoosick (Upper Ordovician)—In the Walloomsac

Formation; perhaps intrusive

Whipstock Breccia in the Walloomsac Formation (Upper Ordovician)—Largely 

a tectonic breccia formed in situ; contains abundant pseudo-pebbles

Wildflysch-like conglomerates within the Hortonville, Ira, and Walloomsac Formations occur as local areas of black slate rich in inclusions of quartzite, greenish-gray 

slate, wacke, and punky-weathering bluish-gray limestone, interpreted as sedimentary breccias, deposited in front of the advancing Taconic allochthon (Upper 

Ordovician) (Zen, 1961; Potter, 1972; Fisher, 1985). Exposed near the western 

and northern margin of the allochthon and in the Bennington area at the type 

Whipstock. Here and at many localities the Forbes Hill and Whipstock breccias are 

tectonic breccias formed in situ by disruption of thin to thick beds, laminae, and 

carbonate-quartz-sulfide veins rather than clastic sedimentary rocks. The cleavage 

and related folding commonly is a late strain-slip cleavage characterized by a strong 

down-plunge lineation parallel to reclined hingelines of minor folds of foliation and 

compositional layering. Units are retained although interpretation as sedimentary 

wildflysch deposits is in part questionable

amphibolite, and lightgrayishgreen, rustyweathering, carbonatepitted 

ankerite-magnetite-albite-epidote (plagioclase) feldspathic greenstone and 

interbedded feldspathic quartzite (Zsg). Locally a mafic basaltic metawacke 

and interbedded amphibolite

Kyanite schist member—Silvery-blue, medium- to coarse-grained chloritemuscovite-quartz schist (±garnet±kyanite±chloritoid); contains characteristic 

spangly muscovite and elongated knots of quartz and layers of pinkish coticule, 

exposed in the Worcester Mountains

Amphibolite member—Dark-green to black, massive, medium- to coarsegrained, layered albite-epidote-hornblende amphibolite; possibly is a

meta-intrusive. Exposed in the Worcester Mountains

Jay Peak Formation (Cambrian and Neoproterozoic)

Schist member—Light-grayish-green, fine-grained, chlorite-muscovite-quartz 

phyllite or schist and quartzite; white quartzofeldspathic layers alternate with 

green chloritic phyllitic layers; locally albitic

Greenstone member—Green, carbonate-albite-epidote-chlorite greenstone

Mount Abraham Formation (Cambrian and Neoproterozoic)—Lustrous, silverygreen to bluish-gray, fine- to medium-grained, white mica-chloritoid-quartz-chlorite 

schist and phyllite, locally with minor garnet and magnetite porphyroblasts (Zap). 

Distinctive chlorite streaks and 1-cm rusty needles of altered kyanite are common

Rowe Schist (Cambrian and Neoproterozoic?)

Mapped in southern Vermont where the uppermost part is continuous with 

amphibolites, schists, and feldspathic schists of the Rowe Schist of Massachusetts. 

These upper units are continuous with rocks of the Stowe Formation to the north. 

Units in the middle and lowermost structural positions (above the Hoosac Formation) are in a similar structural position as rocks of the Ottauquechee and Pinney 

Hollow Formations, although structural continuity and correlations with the 

Ottauquechee and Pinney Hollow Formations are uncertain owing to extensive 

structural duplication by thrust faulting and folding

Amphibolite and greenstone member—Predominantly very dark green to 

black, finely foliated biotite-plagioclase amphibolite to dark-green to lightgreenish-gray, chlorite-plagioclase-ankerite greenstone and interlayered gray 

biotitic feldspathic volcaniclastic rock and feldspathic quartzite. Amphibolites 

have transitional basalt to MORB compositions; greenstones have MORB 

compositions

Chlorite phyllite member—Pale-green to dark-green, lustrous, magnetitechlorite-muscovite-quartz phyllite and schist, highly tectonically laminated near 

larger ultramafic bodies (Zu). Unit typical of lustrous chloritic schists of the 

Stowe Formation farther north

Garnet schist member—Mainly yellowish-green, lustrous, biotite-chloritemuscovite-plagioclase-quartz-garnet schist, distinguished by large garnets and 

coarse cross-biotite. Typical of rocks within the Stowe Formation elsewhere

Biotite-plagioclase schist and gneiss member—Gray and light-gray-weathering, medium- to coarse-grained biotite-plagioclase-sericite-quartz schist and 

gneiss, commonly flecked with large cross-biotite. Locally contains coarse garnet

Cooper Hill Member—Dark-gray or green, dull-gray- and rusty-weathering, 

slabby, well-foliated, quartz-rich muscovite-biotite-plagioclase-quartz schist, 

garnet schist, and splintery chlorite-chloritoid-muscovite-plagioclase 

(±garnet)-quartz schist, with minor feldspathic biotite gneiss. Unit noncarbonaceous and atypical of the Ottauquechee Formation except for minor layers of 

carbonaceous schist (Zrc)

Graphitic schist and quartzite member—Dark-gray- to sooty-grayweathering, sulfidic, graphitic biotite-muscovite-plagioclase-quartz schist, 

containing thin beds of dark-bluish-gray vitreous quartzite. Restricted to minor 

occurrence in Zrch, along the base of the major amphibolite above Zrch, 

and within amphibolite at a structurally high position within the Rowe Schist 

near the Massachusetts State line. Closely resembles rocks typical of the 

Ottauquechee Formation but at a different structural or stratigraphic level

Chlorite schist member—Rusty-gray- to yellowish-brown-weathering, lustrous, 

non-carbonaceous, well-foliated chlorite-quartz-muscovite (±plagioclase) schist

Garnet-biotite feldspathic schist member—Dark-grayish-brown-weathering, 

coarse-grained garnet-biotite-plagioclase-quartz schist

EARLY TO LATE TACONIAN ACCRETED TERRANE OF THE 

ROWE-HAWLEY ZONE

Eastern allochthonous sequence, oceanic and accretionary realm,

ultramafic inclusions, volcanic-arc intrusives, and volcanic rocks

Tillotson Peak Structural Complex (Cambrian)—Mafic schist and amphibolite 

unit. Dark-bluish-gray, fine- to medium-grained, massive to foliated blueschist 

composed of amphibole (glaucophane, barroisite, and actinolite), epidote, garnet, 

chlorite with minor magnetite, pyrite, and apatite. Quartz and garnet coticule occur 

locally. Eclogite occurs locally, delimited by green, medium-grained layers and pods 

of garnet, omphacite, glaucophane, epidote, quartz, albite, and white mica 

Pelitic schist—Silvery-gray, medium-grained schist composed of white mica, 

quartz, chlorite (±garnet±albite±glaucophane±chloritoid); local centimeter-thick 

lenses of coticule

Albite gneiss—White, light-gray- and green-banded, medium-grained, 

well-layered epidote-white mica-quartz-albite (±garnet±magnetite) gneiss with 

plagioclase and polycrystalline quartz porphyroblasts. Green, chloritic layers 2 to 

10 cm thick also contain chlorite pseudomorphs after garnet. Gneiss is similar to 

gneiss at the base of the Belvidere Mountain Structural Complex

pqq

Granofels and coticule member—Grayish-green, chlorite-biotite-plagioclasequartz granofels and schist containing abundant fine layers of pinkish-gray 

small-garnet quartzite and coticule

Chlorite schist member—Pale-greenish-gray, lustrous and nonlustrous 

chlorite-muscovite feldspathic schist and schistose granofels. Local richly 

garnetiferous variant (Omgt)

Garnet schist member—Greenish-gray feldspathic garnet schist; grades into 

Omfs

Hornblende fascicule schist and granofels member—Light-gray to grayishgreen chlorite-muscovite-biotite-plagioclase-quartz schist, conspicuous sprays 

of hornblende, and biotite-hornblende-plagioclase granofels

Carbonaceous schist member—Dark-gray, fine-grained carbonaceous biotite-muscovite-quartz (±garnet) phyllite and schist. Occurs west of Montpelier

Amphibolite and greenstone member—Includes light-pale-green chloritic 

ankeritic greenstone; black, fine-grained hornblende-plagioclase 

(±garnet±epidote) amphibolite; and hornblende-spotted “dioritic” amphibolite 

(Omd)

Mariposite-bearing metarodingite member—Bright-green and white, fineto medium-grained, variably foliated calcite-quartz-albite-mariposite-actinolitetremolite-epidote-zoisite granofels to gneiss. Associated with greenstone and 

ultramafic rocks in Roxbury

Felsic metavolcanic member—Gray, purplish-gray, and light-gray dacitic to 

andesitic metavolcanic and metavolcaniclastic rocks, similar to Omwhv

Whetstone Hill Member of the Moretown Formation

Phyllite facies—Predominantly medium-dark-gray to lustrous-tan, fine-grained 

garnet-biotite-muscovite phyllite and carbonaceous phyllite; contains layers of 

dark-gray quartzite, coticule, and ironstone, locally mapped separately

Black sulfidic carbonaceous schist facies—Dark-gray, sooty- and 

rusty-weathering, sulfidic biotite-muscovite-plagioclase-quartz schist and 

granofels; is a lateral variant of Omwh. Contains layers of rusty-weathering 

amphibolite and dark-gray quartzite

Coticule and quartzite facies—Dark-gray to light-gray, vitreous magnetite 

quartzite, and coticule

Metavolcanic facies—Pale-tannish-gray- to purplish-gray-weathering, phyllitic 

metadacitic volcanic breccia, agglomerate, and grayish-green fragmental 

meta-andesitic breccia; may occur at several levels

Metasiltstone facies—Pale-greenish-gray, finely laminated, magnetitechlorite-biotite feldspathic metasiltstone and pale-greenish-yellow-weathering 

muscovite-chlorite-quartz phyllite

CONNECTICUT VALLEY TROUGH

Gile Mountain Formation (Lower Devonian) 

Gile Mountain Formation, undivided—Shown in cross section only

Quartzite and metapelite member—Gray to light-gray, fine-grained 

micaceous quartzite a few centimeters to tens of centimeters thick, interbedded 

with dark-gray graphitic slate, phyllite, or schist

Meetinghouse Slate Member—Dark-gray slate and phyllite containing sparse 

to moderately abundant beds of light-gray, fine-grained metasandstone and 

metasiltstone, 1 mm to 1 cm thick

Felsic metavolcanic member—Very light gray, fine-grained porphyritic 

metafelsite schist or granofels near Maidstone Lake. Groundmass recrystallized 

to an aggregate of quartz, microcline, plagioclase, biotite, muscovite, and 

apatite; grain size about 0.05 mm. Relict phenocrysts of embayed quartz, 

microcline (some in granophyric intergrowths with quartz), and saussuritized 

plagioclase. U-Pb zircon age of 407.0±3.3 Ma, no. 45 (Rankin and Tucker, 

2009)

Grit—Lenticular masses of metamorphosed quartzose volcaniclastic grit and 

conglomerate, commonly having abundant dark-gray pelitic matrix interlayered 

with sandstone, pelite, and porphyritic rhyolite (Dgmr). Conglomerate contains 

rounded clasts of rhyolite, fine-grained granitoid, and angular clasts of 

dark-gray slate. Correlative with Halls Stream Grit Member of the Ironbound 

Mountain Formation (of Myers, 1964) to the north

Quartz-pebble metaconglomerate member—Thin lens of metadiamictite 

with abundant dark-gray, pyritic, and calcareous metapelite matrix at the base 

of the Meetinghouse Slate Member (Dgm), south of Bradford

Rhythmically graded member—Light- to medium-gray, fine-grained 

micaceous quartzite to dark-gray muscovite-quartz-biotite carbonaceous phyllite 

or schist in beds 10 to 25 cm thick; and dark-gray micaceous phyllite or schist 

containing beds of micaceous quartzite; locally thickly bedded. Detrital volcanic 

zircons yield a U-Pb age of 409±5 Ma, no. 51 (McWilliams and others, 2010)

Thick-bedded micaceous feldspathic quartzite member—Brown to gray, 

noncarbonaceous quartz-mica schist and feldspathic quartzite in beds 50 cm to 

5 m thick; gradational to Dgqs through interbedding of phyllite beds and 

decrease in thickness of quartzite beds

Amphibolite member—Hornblende amphibolite and hornblende-plagioclasequartz granofels; interpreted as metabasaltic and volcaniclastic rocks

others, 1995)

Biotite-quartz diorite gneiss of Vernon dome (Late Ordovician)—Light-gray, 

well-foliated subporphyritic biotite (±hornblende)-quartz diorite and trondhjemite 

gneiss; forms sills in overlying Ammonoosuc Volcanics

Highlandcroft Plutonic Suite (Early Silurian to Middle Ordovician)

Epizonal to mesozonal, foliated and metamorphosed (greenschist facies)

plutons exposed northwest of the Ammonoosuc fault. Compositions

range from granite to diorite to lesser amounts of gabbro

Lost Nation granite—Foliated biotite and (or) hornblende granite; locally diorite 

and lesser amounts of gabbro. Where present, potassium feldspar is microcline. 

Contact aureole is in the Albee Formation. U-Pb zircon ages of 442±4 Ma, no. 

30 (Moench and Aleinikoff, 2003), and 444.1±2.1 Ma, no. 29 (Rankin and 

Tucker, 2009); and U-Pb sphene age of 443±3 Ma, no. 31 (Moench and 

Aleinikoff, 2003)

Highlandcroft Granodiorite of Billings (1935, 1937)—Medium-greenish-gray to 

dark-greenish-gray, medium-grained, foliated metamorphosed granite, granodiorite, and tonalite containing quartz, microcline, saussuritized plagioclase, 

hornblende, biotite (chlorite alteration), and secondary calcite and sericite. 

Nonconformably overlain by the Clough Quartzite and Fitch Formation. U-Pb 

zircon age of 450±5 Ma, no. 28 (Lyons and others, 1986)

Joslin Turn Tonalite—Greenish-gray to light-brownish-gray, medium-grained, 

weakly foliated metamorphosed tonalite. Primary minerals include quartz, plagioclase, biotite, magnetite, pyrite, and apatite; secondary minerals include chlorite, 

epidote, sericite, and calcite. Granophyric intergrowths of quartz and plagioclase. 

U-Pb zircon age of 469±1.5 Ma, no. 27 (Moench and Aleinikoff, 2003)

Oliverian Plutonic Suite (Late Ordovician)

Hornblende metagabbro—Dark-green, coarse-grained, well-foliated hornblende-andesine metagabbro

Biotite granite—Pink, medium-grained muscovite-biotite-microcline-perthite 

granite and gneissic granite, and aplite of the Lebanon dome

Granodioritic to quartz dioritic gneissic border phase of Oobg, perhaps in part 

metasomatic

Stratified rocks of the Bronson Hill arch and Sawyer Mountain belt

Littleton Formation (Lower Devonian)—Medium-dark- to dark-gray slate 

interlayered with light-gray, fine-grained micaceous quartzite; in southeastern 

Vermont near the Vernon dome Dl is equated with DSwb and may be older than 

in the Bradford area

Metarhyolite—White-weathering, medium- to dark-gray, foliated and 

laminated, aphanitic to very fine grained granofels to schist or metatuff, welded 

tuff, and lithic tuff commonly with a few percent millimeter-size quartz and 

microcline phenocrysts. U-Pb zircon age of 407.5±3.9 Ma, no. 44 (Rankin 

and Tucker, 2000)

Metamorphosed mafic volcanic rocks 

Fitch Formation (Lower Devonian and Upper Silurian)—Metamorphosed 

limestone, calcareous sandstone, siltstone, and pelite. Some limestone conglomerate and polymict conglomerate with calcareous matrix. Locally equivalent to 

Madrid and Smalls Falls Formations in Chesterfield, N.H., area

Sawyer Mountain Formation (Devonian and Silurian)—Greenish-gray to 

dark-gray, pyritic, locally calcareous phyllite and light-gray, locally pyritic and 

calcareous, fine- to medium-grained, feldspar-rich metasandstone; some beds 

punky weathering. Graded grit and conglomerate beds (having cobble-size clasts of 

quartz and felsite) toward base. Interpreted as transitional between Connecticut 

Valley and Bronson Hill sequences and correlative with Frontenac Formation

Felsic metavolcanic rocks—Includes volcanic debris flow, laminated tuff, and 

strongly foliated felsite

Clough Quartzite (Lower Silurian)—Quartzite and quartz-cobble metaconglomerate; on Skitchewaug Mountain, upper quartzite (Scq) and lower conglomerate and 

granofels (Scc) are mapped. Locally contains quartz-cobble conglomerate with 

abundant dark-gray phyllite matrix that resembles phyllite of the Littleton Formation

Partridge Formation (Upper Ordovician)—Dark-gray to grayish-black, 

rusty-weathering sulfidic slate and phyllite interlayered with felsic volcanic rocks 

and tuffs, and amphibolite (Opa)

Metarhyolite—Greenish-gray, light-bluish-gray, or medium-bluish-gray metarhyolite tuff, lapilli tuff, tuff breccia, and lava. Generally porphyritic with 5 to 20 

percent plagioclase and, in some places, quartz phenocrysts and minor 

amphibolite

Ammonoosuc Volcanics of Billings (1935) (Upper and Middle Ordovician)

Ammonoosuc Volcanics, undivided—A heterogeneous unit of interlayered 

and interfingering metamorphosed volcanic, volcaniclastic, and sedimentary 

rocks. Compositions range from basalt to sodic rhyolite. Fragmental rocks 

dominate (tuff to tuff breccia), but include sparse mafic pillow lava and felsic 

lava. Sedimentary protoliths include dark-gray sulfidic shale, ironstone, 

siltstone, graywacke, volcanic conglomerate, and rare limestone

Greenish-gray, light-bluish-gray, or medium-bluish-gray metarhyolite tuff, lapilli 

tuff, tuff breccia, and lava. Generally porphyritic with 5 to 20 percent plagioclase and, in some places, quartz phenocrysts. Generally strongly foliated with 

waxy sheen on foliation surfaces 

Dark-greenish-gray to medium-bluish-gray metamorphosed andesitic and 

basaltic tuff, crystal tuff, and tuff breccia; minor pillow lava. Commonly 

contains plagioclase and (or) altered mafic phenocrysts

Y1rs

Y2

q

Y1

q

Y2

dm

Y1,2be

Dgm

Dgmr

Dgmg

Y3Ama

Y3Ag

Y3Apg

Y3Amb

Y3Ama

Y3Agg

Y3Ala

Y2

lg

Y2

gg

Y2

ch

Y2

ap

Y2

mig

Y2

myu

Y2

lgg

Dgmc

Obqd

Ofh

Oww

Obvb

Ol

Oj

Dgqs

Dgmu

Dgq

Dl

Dlr

Dla

Sf

Ssm

Svf

Sc

Scq

Scc

Op

Opa

Ohi

Oohg

Oobg

Oogt

Opr

Oa

Oaa

Zsws

Zswa

Zj

Zjg

Za

Zap

Zra

Zrs

Zrgs

Zrfb

Zrch

Zrc

Zrr

Zrrgt

Ztm

Ztp

Omfgc

Omfs

Omgt

Omhfs

Omc

Oma

Omd

Omr

Omfv

Omwh

Omwhb

Omwhq

Omwhv

Omwhg

Dgr

Y3Agb

Y3Afg

Y2

m

Y2

cs

Y2

a

Y2

hg

Y2

rgt

Y1,2bg

Y1

a

Ztagn

Dga

Oar

ONT

Walsh1

off,1 and J. Gregory McHone4

This map is available for sale by U.S. Geological Survey, Information 

Services, Box 25286, Denver Federal Center, Denver, CO 80225

For product and ordering information:

World Wide Web: http://www.usgs.gov; Telephone 1-888-ASK-USGS

Any use of trade, product, or firm names in this publication is for descriptive 

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

Suggested citation:

Ratcliffe, N.M., Stanley, R.S., Gale, M.H., Thompson, P.J., and Walsh, G.J., 

2011, Bedrock geologic map of Vermont: U.S. Geological Survey Scientific 

Investigations Map 3184, 3 sheets, scale 1:100,000.

GIS database compiled by Gregory J. Walsh and Marjorie H. Gale

Digital cartography by Linda M. Masonic

Edited by James R. Estabrook

The Vermont Geological Survey would like to thank former State Geologists 

Charles Ratte for initiating State support and Diane Conrad for continued work 

on this map.

 ́

Printed on recycled paper 

)

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