Prepared in cooperation with the 

Vermont Geological Survey

Bedrock Geologic Map of the Montpelier and Barre West 

Quadrangles, Washington and Orange Counties, Vermont

By Gregory J. Walsh, Jonathan Kim, Marjorie H. Gale, and Sarah M. King

Pamphlet to accompany 

Scientific Investigations Map 3111

2010

U.S. Department of the Interior

U.S. Geological Survey
U.S. Department of the Interior

KEN SALAZAR, Secretary

U.S. Geological Survey

Marcia K. McNutt, Director

U.S. Geological Survey, Reston, Virginia: 2010

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Suggested citation:

Walsh, G.J., Kim, Jonathan, Gale, M.H., and King, S.M., 2010, Bedrock geologic map of the Montpelier and Barre 

West quadrangles, Washington and Orange Counties, Vermont: U.S. Geological Survey Scientific Investigations 

Map 3111, 1 sheet, scale 1:24,000, 36-p. text.

The text and map of this report are part A, and the database is part B. Both parts are available online at: 

http://pubs.usgs.gov/sim/3111/

ISBN 978 1 4113 2950 8
i

Contents

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

Stratigraphy ....................................................................................................................................................1

Rocks of Pre-Silurian Age ...................................................................................................................1

Moretown Formation (Cambrian and Ordovician)..................................................................2

Cram Hill Formation (Ordovician) ..............................................................................................6

Metadiabase and Greenstone Dikes (Ordovician? and Silurian?) ......................................6

Rocks of the Connecticut Valley-Gaspé Synclinorium...................................................................8

Shaw Mountain Formation (Silurian)........................................................................................9

Northfield Formation (Silurian and Devonian?) ......................................................................9

Waits River Formation (Silurian and Devonian)....................................................................10

Gile Mountain Formation (Devonian)......................................................................................12

Igneous and Metasomatic Rocks ....................................................................................................13

Granitic Dikes (Devonian).........................................................................................................13

Quartz Veins (Devonian) ...........................................................................................................13

Lamprophyre or Diabase Dikes (Cretaceous).......................................................................14

Economic Geology.......................................................................................................................................14

Structural Geology.......................................................................................................................................14

Ductile Structures...............................................................................................................................14

First-Generation Foliation—S1.................................................................................................15

Second-Generation Foliation—S2...........................................................................................15

Third-Generation Foliation—S3 (Acadian S1)........................................................................20

Moretown Formation “Pinstripe”............................................................................................20

Fourth-Generation Foliation—S4 (Acadian S2)......................................................................22

Fifth-Generation Foliation—S5.................................................................................................23

Shady Rill Fault...........................................................................................................................23

Richardson Memorial Contact-Dog River Fault Zone..........................................................24

Brittle Structures.................................................................................................................................26

Metamorphism .............................................................................................................................................29

References Cited..........................................................................................................................................32

Figures

1. Index map of quadrangle-scale bedrock geologic mapping in the area of 

the Montpelier and Barre West quadrangles, central Vermont. ..........................................2

2. Simplified regional geologic map showing the setting of the Montpelier 

and Barre West quadrangles......................................................................................................3

3. Simplified stratigraphic section for the Montpelier and Barre West quadrangles...........4

4. Photographs of coticule in the Cram Hill Formation...............................................................7

5. Photographs of a metadiabase dike at Putnamville, Vt. ........................................................8

6. Photographs of the Waits River Formation ............................................................................11

7. Rose diagram showing the strike of 11 steeply dipping Cretaceous dikes ......................14

8. Schematic diagrams illustrating the distribution and style of the 

five ductile fabrics in the map area .........................................................................................16
ii

9. Simplified geologic map showing the major structural zones in the area and 

the distribution and orientation of significant ductile deformational fabrics ...................17

10. Photographs of F3 (Acadian F1) folds in the Waits River Formation............................................18

11. Lower hemisphere equal area projections (stereonets) of poles to penetrative 

foliation and their associated lineations and maps showing D3 linear features .............19

12. Photographs of “pinstripe” fabric in the Moretown Formation..........................................21

13. Stereonet and photographs of S4 and L4 fabric .....................................................................22

14. Stereonet and photograph of S5 and L5 fabric .......................................................................23

15. Cross-sectional sketch and composite panoramic photograph of the 

roadcut across the Richardson Memorial Contact and Dog River 

fault zone at Interchange 8 on I–89 .........................................................................................25

16. Stereonets and rose diagrams of fractures in the 

Barre West and Montpelier quadrangles...............................................................................27

17. Photographs of joint types ........................................................................................................28

18. Shaded-relief map and interpretive summary diagram of fracture types and principal 

fracture trends in the area of the Montpelier and Barre West quadrangles ...................30

19. Photomicrographs and sketches of porphyroblasts in the Acadian garnet zone ...........31

Table

 1. Regional correlation of Taconian and Acadian deformational fabrics, 

central Vermont ...........................................................................................................................15

Conversion Factors

Inch/Pound to SI

Multiply By To obtain

Length

inch (in.) 2.54 centimeter (cm)

inch (in.) 25.4 millimeter (mm)

foot (ft) 0.3048 meter (m)

mile (mi) 1.609 kilometer (km)

SI to Inch/Pound

Multiply By To obtain

Length

centimeter (cm) 0.3937 inch (in.)

millimeter (mm) 0.03937 inch (in.)

meter (m) 3.281 foot (ft) 

kilometer (km) 0.6214 mile (mi)

meter (m) 1.094 yard (yd) 
Bedrock Geologic Map of the Montpelier and Barre West 

Quadrangles, Washington and Orange Counties, Vermont

By Gregory J. Walsh,1 Jonathan Kim,2 Marjorie H. Gale,2 and Sarah M. King2

Introduction

The bedrock geology of the Montpelier and Barre West 

quadrangles consists of Silurian and Devonian metasedimentary rocks of the Connecticut Valley-Gaspé synclinorium 

(CVGS) and metasedimentary, metavolcanic, and metaintrusive rocks of the Cambrian and Ordovician Moretown and 

Cram Hill Formations. Devonian granite dikes occur throughout the two quadrangles but are more abundant in the Silurian 

and Devonian rocks. The pre-Silurian rocks are separated from 

the rocks of the CVGS by the informally named “Richardson 

Memorial Contact” (RMC), historically interpreted as either 

an unconformity (Cady, 1956; Doll and others, 1961) or a fault 

(Westerman, 1987; Hatch, 1988).

Previous mapping in the area includes the earliest work 

by Richardson (1916) in the towns of Calais, East Montpelier, 

Montpelier, and Berlin. Cady (1956) mapped the 15-minute 

Montpelier quadrangle, and his work represents the first 

published geologic map on a topographic base in the capital 

region (fig. 1). Unpublished mapping by Richard Jahns from 

1937 to 1940 in the 15-minute Barre quadrangle (fig. 1) was 

subsequently described in Currier and Jahns (1941) and White 

and Jahns (1950) and used by Doll and others (1961) on the 

State geologic map. An unpublished reconnaissance map of 

the 7.5-minute Barre West quadrangle dated 1984 by Norman 

Hatch contained compilation information that was subsequently published in a regional paper on the CVGS (Connecticut Valley trough of Hatch, 1988).

Mapping in adjacent areas includes preliminary 1:24,000-

scale work in the Northfield (Westerman, 1994) and Middlesex 

quadrangles (Gale and others, 2006) (fig. 1). Murthy (1957) 

and Konig (1961) mapped the adjacent East Barre and Plainfield 15-minute quadrangles, respectively (fig. 1).

The results of this report represent mapping by G.J. Walsh, 

Jonathan Kim, and M.H. Gale from 2002 to 2005. S.M. King 

assisted Kim and Gale from 2002 to 2003. A.M. Satkoski (Indiana University) assisted Walsh, and L.R. Pascale (University 

of Vermont) and C.M. Orsi (Middlebury College) assisted Kim 

and Gale as summer interns in 2003. This study was designed 

to map the bedrock geology in the area. This map supersedes 

a preliminary map of the Montpelier quadrangle (Kim, Gale, 

and others, 2003). A companion study in the Barre West quadrangle (Walsh and Satkoski, 2005) determined the levels of 

naturally occurring radioactivity in the bedrock from surface 

measurements at outcrops during the course of 1:24,000-scale 

geologic mapping to identify which rock types were potential 

sources of radionuclides. Results of that study indicate that the 

carbonaceous phyllites in the CVGS have the highest levels of 

natural radioactivity.

Stratigraphy

The metamorphic and igneous rocks in the Montpelier 

and Barre West quadrangles range in age from Cambrian 

to Cretaceous. Cambrian and Ordovician metasedimentary, 

metavolcanic, and metaigneous rocks of the Cram Hill and 

Moretown Formations are exposed west of the Richardson 

Memorial Contact (RMC), an unconformity that separates preSilurian rocks to the west from Silurian and Devonian rocks to 

the east (fig. 2). Rocks east of the RMC occur in the Connecticut Valley-Gaspé synclinorium (CVGS) and include the 

metasedimentary Shaw Mountain, Northfield, Waits River, and 

Gile Mountain Formations (fig. 3). The metamorphic rocks are 

cut by Devonian granite dikes and quartz veins and Cretaceous 

diabase or lamprophyre dikes.

Rocks of Pre-Silurian Age

The Moretown and Cram Hill Formations occur west of 

the RMC (fig. 2). In southeastern Vermont, metasedimentary 

and metavolcanic rocks of the Moretown Formation are cut 

by calc-alkaline arc-related tonalite and trondhjemite gneisses 

that yield Cambrian and Ordovician U-Pb zircon ages of about 

496 to 462 Ma (mega-annum) (Ratcliffe and others, 1997). 

The Late Cambrian to Middle Ordovician ages obtained from 

the intrusive rocks provide a minimum age for deposition of 

the metasedimentary and metavolcanic rocks of the Moretown 

Formation, and here we assign a Cambrian and Ordovician age 

to these rocks, in accordance with the time scale of Gradstein 

and others (2004). In Springfield, Vt., the Cram Hill Formation 

1

 U.S. Geological Survey, Montpelier, VT 05601.

2

 Vermont Geological Survey, Waterbury, VT 05671.
2 Bedrock Geologic Map of the Montpelier and Barre West Quadrangles, Washington and Orange Counties, Vermont

Figure 1

43°

73° 72° 45°

44°

CANADA

NEW

HAMPSHIRE

NEW YORK

MASSACHUSETTS

VERMONT

East Barre

Montpelier Plainfield

Barre

Middlesex Montpelier

Northfield Barre West

150 30 KILOMETERS

50 10 15 MILES EXPLANATION

7.5-minute quadrangles (scale 1:24,000)

15-minute quadrangles (scale 1:62,500)

Montpelier (Cady, 1956)

Plainfield (Konig, 1961)

East Barre (Murthy, 1957)

Barre (Richard Jahns, unpublished data)

Barre West (N.L. Hatch, Jr., unpublished data)

Northfield (Westerman, 1994)

Middlesex (Gale and others, 2006)

Richardson Memorial Contact

Area of this study

Figure 1. Index map of quadrangle-scale bedrock geologic mapping in the area of the Montpelier and 

Barre West quadrangles, central Vermont. Area of this study shown in yellow.

contains felsic volcanic rocks that yield an Early Ordovician 

U-Pb zircon age of 484±4 Ma (Ratcliffe and others, 1997); 

thus we assign an Ordovician age to these rocks.

The pre-Silurian metasedimentary and metaigneous 

rocks of the Moretown and Cram Hill Formations, and their 

along-strike correlatives, extend from northern Vermont 

to southern Massachusetts and are considered part of the 

lithotectonic Rowe-Hawley belt (RHB) of Stanley and Hatch 

(1988). In most recent tectonic models, the RHB represents lithologies juxtaposed in an arc-trench environment 

(for example, Stanley and Ratcliffe, 1985; Kim and Jacobi, 

1996). In Massachusetts, where the RHB was defined, the 

Rowe, Moretown, and Hawley, respectively, represent the 

accretionary wedge, forearc, and western limit of a Taconian 

(Ordovician) arc. In central and northern Vermont, the Rowe 

is equivalent to the Ottauquechee and Stowe Formations, and 

the Cram Hill Formation is equivalent to the black slates in the 

Hawley Formation.

Moretown Formation (Cambrian and Ordovician)

Cady (1956) first assigned the metasedimentary rocks 

(granulite, quartzite, phyllite, and slate) on the eastern side 

of the Northfield Mountains in central Vermont (fig. 2) to the 

Moretown Formation. In his report, the Moretown Formation 

had a dominant quartz-albite-sericite-chlorite granulite unit 

and a carbonaceous slate and phyllite unit. Doll and others 

(1961), however, considered the Moretown as a member of 

the Missisquoi Formation. Currier and Jahns (1941), Cady 

(1956), and Doll and others (1961) suggested an Ordovician 

age on the basis of stratigraphic position of the Moretown 
Stratigraphy 3

U D

RMC

Craftsbury

Wolcott

Montpelier

Northfield

Barre

DRFZ

SRF

Connecticut Valley-Gaspé 

synclinorium

Dgm

DSu

72°45'

44°

72°30'

44°15'

44°30'

44°45'

Northfield Mountains

Wrightsville

belt

Dumpling

Hill

belt

DSu

Omw

Dg

Och

Och

Och

Omd

Pre-Silurian rocks, undivided

Axial trace of the Townshend-Brownington

syncline (Acadian F1

)

Cram Hill Formation of the Wrightsville belt (Ordovician)

Moretown Formation of the Wrightsville belt

(Ordovician and Cambrian)

Moretown Formation of the Dumpling Hill belt

(Ordovician and Cambrian)

Thrust fault—Sawteeth on upper plate

Reverse fault—U, upthrown side; D, downthrown side

Gile Mountain Formation (Devonian)

Shaw Mountain, Northfield, and Waits River 

Formations, undivided (Devonian and Silurian)

Dgm

DSu

Och

Dg Barre Granite (Devonian)

Omw

—Richardson Memorial Contact (RMC)—

EXPLANATION

Omd

0 5 10 15 KILOMETERS

0 5 10 MILES

Figure 2. Simplified regional geologic map showing 

the setting of the Montpelier and Barre West 

quadrangles (outlined). DRFZ, Dog River fault zone; 

RMC, Richardson Memorial Contact; SRF, Shady 

Rill fault.
4 Bedrock Geologic Map of the Montpelier and Barre West Quadrangles, Washington and Orange Counties, Vermont

Gile Mountain 

Waits River 

Thickly bedded limestone and phyllite (DSwt)

Thinly bedded limestone and phyllite (DSwl2

)

Phyllite (DSw2

)

Garnetiferous phyllite (DSwg)

Northfield

Cram Hill

Moretown

Thinly bedded limestone and phyllite (DSwl1

)

Thinly bedded limestone and phyllite (DSwl1

)

Shaw Mountain

Principal rock types (map unit) Formation Age

Silurian and Devonian

Phyllite and quartzite (Dgm) Devonian

Silurian and Devonian(?)

Silurian

Ordovician

Cambrian and Ordovician

Greenstone, schist, and conglomerate 

Phyllite (DSn)

R M C

Connecticut Valley-Gaspé synclinorium

Carbonaceous phyllite and greenstone

Wrightsville 

belt

Metadiabase dikes

Figure 3

Granofels, schist, and greenstone

Dumpling 

Hill

belt

Phyllite (DSw1

)

SRF

unconformity

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.

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Figure 3. Simplified stratigraphic section for the Montpelier and Barre West quadrangles. RMC, Richardson Memorial Contact; 

SRF, Shady Rill fault.

Formation rocks in an east-facing homoclinal sequence 

beneath the Silurian and Devonian lithologies of the CVGS. 

The Moretown Formation extends into northernmost Vermont 

where it is truncated by the Acadian Coburn Hill thrust fault 

(for example, Gale, 1980; Kim, Coish, and others, 2003) and 

into south-central Massachusetts where it is cut out along the 

Acadian Prospect Hill thrust fault (Zen, 1983; Stanley and 

Hatch, 1988).

In the northwestern half of the map, the Moretown 

Formation occurs in the Wrightsville and Dumpling Hill belts 

(fig. 2). The Wrightsville belt also contains the Cram Hill 

Formation and is bounded to the east by the RMC-Dog River 

fault zone and to the west by the Shady Rill fault. The Moretown Formation contains similar metasedimentary rock types 

in both the Dumpling Hill and Wrightsville belts, with the 

exception that mafic rocks were not observed in the Dumpling 

Hill belt. Two types of mafic rocks occur in the Wrightsville 

belt: (1) greenstone and ankeritic greenstone interpreted as 

metamorphosed extrusive volcanic or volcaniclastic rocks 

interbedded with clastic rocks and (2) metadiabase and 

greenstone intrusive dikes or sills. In the field, however, it is 

not always possible to separately map greenstone and metadiabase or to see features that would conclusively demonstrate 

extrusive versus intrusive origin. Mafic rocks with a diabase 

texture (metadiabase) are locally in contact with finer grained 

greenstones that lack plagioclase porphyroclasts and a diabase 

texture. Such contacts appear gradational, and crosscutting 

relations are not always visible, suggesting that the protoliths 

of these rocks represent (1) basaltic rocks cut by diabase 

dikes, (2) basaltic flows with textural variability, or (3) diabase 

dikes with textural variability. Regardless of the difficulties 

in interpreting possible protoliths, we show the mafic rocks in 

the Wrightsville belt three ways on our map: (1) as separate 

map units—greenstone (OЄmg) interbedded in the Moretown 
Stratigraphy 5

Formation or as younger metadiabase dikes (SOdg), (2) as 

point symbols showing locations of greenstone or metadiabase 

too small to map as separate units at 1:24,000 scale, and (3) as 

a subset of 1 and 2 showing geochemistry sample locations of 

Twelker (2004). Previous workers in this and adjacent areas 

also recognized both older greenstone layers and younger 

greenstone or metadiabase dikes in the eastern part of the 

Moretown Formation (Cady, 1956; Cua, 1989; Westerman, 

1987, 1994).

In the pre-Silurian section of the Montpelier 15-minute 

map, Cady (1956) mapped two metasedimentary units in the 

Moretown Formation: (1) Om, quartz-albite-sericite-chlorite 

granulite with “greenstone beds” in the eastern part and 

(2) Omsp, carbonaceous slate and phyllite. Both units were 

intruded by metamorphosed mafic sills and dikes (metadiabase 

and greenstone) in areas designated by a green-stippled pattern

on his map. The dominant map-scale structure shown by Cady 

(1956) in this area is an isoclinal fold defined by the carbonaceous slate and phyllite. The mafic dikes were interpreted to 

postdate this fold because he mapped them across its eastern 

limb. While we do not agree with the way Cady (1956) showed 

the folding of the carbonaceous rocks, especially because he 

did not describe multiple folding events, we do agree that the 

dikes cut a period of folding (F2) in the Moretown Formation. 

In this report, we subdivide the Moretown Formation of Cady 

(1956) into several new map units that define a more complex 

map pattern than was previously recognized.

We found that the two Moretown Formation units, defined 

by Cady (1956) as non-carbonaceous (Om) and carbonaceous 

(Omsp) end members, actually could be subdivided into units 

containing greater or lesser amounts of the end members. 

Our mapping of Cady’s carbonaceous slate and phyllite in the 

northwestern part of the 7.5-minute Montpelier quadrangle 

shows that parts of the formation are exclusively gray and 

black phyllites with interlayered quartzite (OЄmdh). Other 

parts are gray and black phyllites that contain interlayered 

green phyllite and green granofels (OЄmsr); these latter noncarbonaceous green rocks are absent from OЄmdh. In addition, 

we subdivide some areas previously mapped as homogeneous 

quartz-albite-sericite-chlorite granulite (granofels in our terminology) into two map units composed of green phyllite and 

granofels (OЄmpb and OЄm) and two units of green phyllite 

and granofels interlayered with grayish-black phyllites (OЄmsr

and OЄmw). On this map, the Dumpling Hill belt is divided 

into three units: OЄmpb, OЄmsr, and OЄmdh; the Wrightsville 

belt is divided into four units: OЄm, OЄmw, OЄmg, and OЄmq. 

Our map reflects the relative amounts of carbonaceous (gray 

to black) versus non-carbonaceous (greenish) rocks and the 

distribution of mafic rocks. Like Cady (1956), we find that 

the metadiabase dikes and greenstones are geographically 

restricted to the eastern outcrop belt of the Moretown Formation and the entire Cram Hill Formation in an area that we 

define as the Wrightsville belt.

In contrast to Cady (1956), we found that the metadiabase and greenstone dikes and interbedded greenstone layers 

are absent west of the inferred Shady Rill fault. This fault 

separates gray and black phyllites and quartzite (OЄmdh) of 

the Dumpling Hill belt to the west from interlayered gray 

and black to green phyllites and granofels (OЄmw) and green 

phyllite and granofels (OЄm) of the Wrightsville belt to the 

east. Although Cady (1956) shows that the dikes cut across a 

map-scale isoclinal fold structure, our mapping suggests that 

this early structure is truncated along the Shady Rill fault and 

that rocks previously mapped within the eastern limb of this 

structure are actually part of the Wrightsville belt. As we map 

it, the inferred Shady Rill fault separates units that contain 

mafic rocks to the east from those that do not contain mafic 

rocks to the west, but it is also a boundary that divides rocks 

that preserve the oldest composite map-scale fold structures 

(F1/ F2) in the area (Dumpling Hill belt) from those that have 

been strongly overprinted by F3 folds (Wrightsville belt) (see 

discussion below in Structural Geology section). Although 

we cannot rule out the possibility that the absence of mafic 

rocks in the Dumpling Hill belt is related to some fundamental 

change in the original depositional setting of the rocks, we 

prefer a fault model because older structures in the quartziterich Dumpling Hill belt are preferentially preserved, and the 

mapped boundary is sharp and parallel to a zone of penetrative 

foliation with consistent northwest-trending lineations.

In the Wrightsville belt, the most abundant unit of the 

Moretown Formation is OЄm, which consists of grayish-green 

to green and silver schist, phyllite, and granofels and quartzrich “pinstripe” granofels. Metadiabase and greenstone bodies 

are abundant and are locally mapped separately (see discussion above). Locally, OЄm contains layers of small-pebble 

conglomerate (OЄmq). In the central one-third of the map area 

there are two separate stratigraphic belts of OЄm, a wide belt 

west of and a narrow belt east of the Cram Hill Formation, 

whereas in the northern half of the map area, there is one belt. 

This narrow belt of the Moretown Formation, east of the Cram 

Hill, is interpreted as a repeated part of the section about an 

early fold (F1? or F2 as shown on the map) of the Cram Hill 

Formation, based largely on the symmetrical distribution of 

Cram Hill rocks mapped west of the Dog River fault zone 

and south of Interchange 8 on Interstate 89 (I–89), and on the 

lithologic similarity to rocks found farther west. This inferred 

early fold of the Moretown and Cram Hill Formations is not 

continuous, however, and depending on the latitude, either the 

Ochr unit of the Cram Hill Formation or OЄm is adjacent to the 

RMC-Dog River fault zone, and the early fold is truncated. 

Alternatively, the Moretown Formation rocks we map to the 

east of the Cram Hill Formation may be part of the Shaw 

Mountain Formation exposed above the pre-Silurian section without any fold repetition. The lack of repetition and 

symmetry in the northern part of the Montpelier quadrangle 

may support this alternate explanation. Locally OЄm displays 

characteristic magnetite octahedra, especially along I–89 and 

U.S. Route 2 between Montpelier and Middlesex. Excellent 

exposures of OЄm are located in the Green Mountain Cemetery 

in Montpelier, in the North Branch River in Putnamville, and 

on the northern side of State Route 12 in Berlin, west of the 

railroad bridge.
6 Bedrock Geologic Map of the Montpelier and Barre West Quadrangles, Washington and Orange Counties, Vermont

In the northern one-third of the map, grayish-green 

granofels and “pinstripe” granofels are interlayered with 

gray, dark-gray, green, and black phyllites that, together with 

largely unmapped but abundant mafic rocks, constitute the 

OЄmw unit of the Moretown Formation. The contact between 

OЄm and OЄmw is gradational by intercalation and, therefore, 

interpreted to be stratigraphic. The OЄmw unit is present in the 

northern part of the field area to the west of OЄm and terminates along the trace of the inferred Shady Rill fault towards 

the south. Good roadcuts of OЄmw occur on both sides of State 

Route 12 in Putnamville.

Cram Hill Formation (Ordovician)

The Cram Hill Formation occurs as discontinuous belts 

of rock east of the main belt of the Moretown Formation and 

west of the RMC; these belts extend from the northeastern 

corner to the west-central part of the map. The Cram Hill 

Formation was first described by Currier and Jahns (1941) in 

central Vermont as greenish-gray and black phyllites and slates 

interlayered with mafic metaigneous rocks on the western side 

of the RMC. Although Currier and Jahns (1941) indicated 

that the Cram Hill Formation extended 2.5 miles (mi) north of 

Montpelier, Cady (1956) and Doll and others (1961) considered these lithologies to be part of the Moretown Formation. 

On the State map (Doll and others, 1961), the “Cram Hill 

member of the Missisquoi Formation” was abruptly terminated south of Montpelier probably because Cady (1956) did 

not map this unit. On the basis of lithologic similarity, Currier 

and Jahns (1941) correlated the Cram Hill Formation with the 

fossiliferous Middle Ordovician Magog Group black slates 

of southern Québec. Recent bedrock geologic maps from 

southern Vermont (for example, Armstrong, 1994; Ratcliffe 

and Armstrong, 2001; Walsh and others, 1996a,b) and northern 

Vermont (for example, Hoar, 1981; Gale, 1980; Kim, 1997) 

demonstrate that the Cram Hill Formation extends the entire 

length of Vermont, albeit discontinuously. The black phyllite 

of the Cram Hill Formation also can be mapped continuously into the “Ohb” unit of the Hawley Formation (Hatch 

and Hartshorn, 1968; Kim and Jacobi, 1996) in northwestern 

Massachusetts.

The dominant lithology in the Cram Hill Formation 

is a gray to black carbonaceous phyllite interlayered with 

gray phyllite and quartzite (Ochr). Mafic rocks, including 

greenstone and metadiabase, are abundant in the Cram Hill 

Formation. Most mafic rocks in Ochr appear to be intrusions 

(see separate section below on metadiabase dikes). Extensive 

exposures of the Ochr unit are found on the northern side of 

I–89 just south of Interchange 8 and in Hubbard Park in Montpelier. Ochr is bounded to the east by the RMC-Dog River 

fault zone and to the west by the interlayered unit of the Cram 

Hill Formation (Ochi). Near downtown Montpelier, however, 

a coticule-bearing unit (Ochc) bounds Ochr to the west. South 

of Montpelier, a thin belt of grayish-green granofels, phyllite, 

and greenstone mapped as Moretown Formation (OЄm) occurs 

between Ochr and the Dog River fault zone in an inferred early 

fold of rocks exposed farther west. Interlayered gray and green 

phyllites, quartzite, and granofels are the main rock types of 

the Ochi unit of the Cram Hill Formation. Subordinate lithologies include quartz-pebble conglomerate, quartzite, and mafic 

metaigneous rocks (greenstones and metadiabases). Ochi is the 

transitional unit between Ochr (Cram Hill Formation) and OЄm

(Moretown Formation) in the Wrightsville belt. This transitional contact is gradational by intercalation and is presumed 

to be stratigraphic. Typical outcrops of Ochi are located on the 

eastern side of Long Meadow Hill in Calais, on the northern 

side of I–89 just southeast of Interchange 8, and in Hubbard 

Park in Montpelier.

The coticule-bearing unit of the Cram Hill Formation 

(Ochc) (fig. 4) was mapped in the central part of the map area 

in the vicinity of Montpelier. Ochc consists of gray phyllite 

and granofels with conspicuous, 2- to 5-mm-thick, pale-pink, 

disarticulated layers of coticule (fine-grained quartz-spessartine 

rock); this unit occurs in contact with massive greenstone (with 

phenocrysts of plagioclase) and metadiabase. On the basis of 

the presence of abrupt and crosscutting contacts with the surrounding metasedimentary rocks and the presence of chilled 

margins, we believe many of these mafic metaigneous rocks 

are intrusions but cannot rule out the possibility that some of 

the massive rocks are flows. Well-exposed outcrops of Ochc

are found on the southern side of U.S. Route 2, several hundred

meters east of Montpelier High School, and in Hubbard Park.

Metadiabase and Greenstone Dikes 

(Ordovician? and Silurian?)

Cady (1956) showed generalized areas on the 15-minute 

Montpelier quadrangle where he found “metamorphosed mafic 

sills and dikes” in the pre-Silurian rocks. We observed massive metadiabase and finer grained greenstone intrusions only 

in the Wrightsville belt between the Shady Rill fault and the 

Richardson Memorial Contact (RMC)-Dog River fault zone. 

Although most contacts between these intrusions and the surrounding metasedimentary rocks of the Moretown and Cram 

Hill Formations are subparallel to the dominant foliation, 

there are some locations where the contacts cut this foliation 

at an angle (fig. 5). The dominant foliation, in most cases, is 

presumed to be the Taconian (Ordovician) S2

. Because of the 

ductility contrast between the metadiabases and the surrounding metasedimentary rocks, the metadiabases, which are typically 0.3 to 3 m wide, are locally boudinaged. Individual dikes 

are not traceable along strike from outcrop to outcrop. Thicker 

metadiabase bodies frequently have chilled margins. Petrography by Cua (1989), Twelker (2004) and Twelker and others 

(2004) show these metadiabases are quartz-epidote-chloritealbite±actinolite rocks with secondary calcite that contain 

intergrown plagioclase and epidote-actinolite pseudomorphs 

after pyroxene indicating a relict diabase texture. Two of the 

best locations for observing these intrusions are (1) outcrops in 

the North Branch River in Putnamville (near the intersection 

of State Route 12 and Norton Road) and (2) at the intersection 
Stratigraphy 7

A

B

Figure 4

Figure 4. Photographs of coticule in the Cram Hill Formation. A, Thin resistant 

layers form ridges of tightly folded coticule in an outcrop in Hubbard Park in 

Montpelier. Coticule layers are deformed by F2

 and F3 folds. B, Steeply northplunging coticule rods observed in an outcrop just south of Memorial Drive in 

Montpelier. These rods are near the Richardson Memorial Contact-Dog River 

fault zone and are colinear with F3

 fold axes.

of Ledgewood Terrace and Terrace Street in 

Montpelier (street names not on base map). On 

the map we show the dikes as separate map 

units only where we observed crosscutting relations indicating an intrusive origin.

Although the isotopic age of the metadiabase dikes has not been determined, most dikes 

are pre-Acadian (Devonian) because their contacts with the host metasedimentary rocks are 

clearly folded by the first deformational event 

(S3) to affect Silurian and Devonian rocks, and 

the dikes are absent in the CVGS, above the 

Silurian unconformity. The dikes may be correlative in age with similar mafic dikes found 

in the Comerford Intrusive Suite on the eastern 

side of the CVGS (Rankin and others, 2007). 

Gabbrodioritic rocks in the Comerford Intrusive 

Suite are dated at 419±1 Ma (Rankin and others, 2007). Biotite-hornblende monzodiorite of 

the Braintree pluton in central Vermont has the 

same age (419.26±0.39 Ma, Black and others, 

2004) and appears to have the same relative 

age of the dikes in the Montpelier area but differs petrographically and chemically from the 

greenstones and mafic dikes in the Moretown 

Formation (Ratcliffe and Aleinikoff, 2000; 

Ratcliffe, 2006).

Trace and rare-earth element geochemistry of these intrusions indicate a backarc basin 

tectonic setting that was subject to varying 

amounts of suprasubduction zone metasomatism (Cua, 1989; Twelker, 2004; Twelker 

and others, 2004). On a regional scale, these 

metadiabases are possibly correlative with those 

in the Mount Norris Intrusive Suite of northern 

Vermont (Kim, Coish, and others, 2003), the 

Charlemont Mafic Intrusive Suite of northwestern Massachusetts (Kim and Jacobi, 1996), or 

mafic dikes in the Comerford Intrusive Suite in 

northeastern Vermont and northwestern New 

Hampshire (Rankin and others, 2007). Within 

the Rowe-Hawley lithotectonic belt of New 

England, many metadiabase dikes that are 

geochemically and petrographically similar to 

those in the Montpelier and Barre West quadrangles have been reported in northern Vermont 

(Stanley and others, 1984; Kim, Coish, and 

others, 2003), central Vermont (Cua, 1989; 

Martin, 1994), southern Vermont (Armstrong, 

1994; Walsh and Ratcliffe, 1994a,b; Ratcliffe, 

1997; Ratcliffe and Armstrong, 1999, 2001), 

and northwestern Massachusetts (Kim and 

Jacobi, 1996).
8 Bedrock Geologic Map of the Montpelier and Barre West Quadrangles, Washington and Orange Counties, Vermont

Figure 5

A B

Dike

Dike

S3

S4

S2

S2

Contact

Contact

Figure 5. Photographs of a metadiabase dike at Putnamville, Vt. A, Dark-gray-weathering metadiabase dike (SOdg) on the right side 

of the photograph shows a crosscutting intrusive contact with “pinstripe” granofels of the Moretown Formation (OЄm) on the left. The 

dike is approximately 3 m thick. Truncated planar layering in the Moretown Formation is parallel to S2

. B, Close-up photograph of the 

contact between the metadiabase dike and the granofels of the Moretown Formation. The dike cuts the dominant S2

 foliation at an 

angle, but the contact is deformed by F3

 folds and crosscut by an S4 crenulation. 

Rocks of the Connecticut Valley-Gaspé 

Synclinorium

The age of the metasedimentary rocks in the Connecticut 

Valley-Gaspé Synclinorium (CVGS), also called the Connecticut Valley trough (Hatch, 1988, 1991), is based on limited 

fossil and isotopic evidence. The stratigraphic sequence, from 

oldest to youngest, includes the Silurian Shaw Mountain, the 

Silurian and Devonian Northfield Formation, the Silurian 

and Devonian Waits River Formation, and the Devonian Gile 

Mountain Formation (fig. 3). Information on fossil localities 

from the CVGS is discussed by Hueber and others (1990).

Silurian (Llandoverian) fossils in the Shaw Mountain Formation, at the base of the CVGS, provide a lower age limit for 

the CVGS sequence (Boucot and Thompson, 1963; Boucot and 

Drapeau, 1968; Doll, 1984). Early Devonian (Emsian) plant 

fossils from the Compton Formation in Québec, the northern 

correlative of the Gile Mountain Formation, provide age control for the upper part of the CVGS (Hueber and others, 1990).

The age of the Waits River Formation is less well constrained and is assigned an age range of Silurian to Devonian. 

Aleinikoff and Karabinos (1990) and Hueber and others 

(1990) reported a conventional U-Pb zircon age of 423±4 Ma 

from a felsic rock from the Waits River Formation in Springfield, Vt. The sample is from a 50-cm-thick, light-gray, finegrained epidote-chlorite-albite-quartz granofels layer within 

a coarser grained sequence of phenocrystic feldspathic schist 

and granofels. Aleinikoff and Karabinos (1990) interpreted 

the layer as a dike but left open the possibility that it was a 

volcanic layer. Walsh and others (1996a) and Armstrong and 

others (1997) interpreted the layer as a bed because of the lack 

of unequivocal crosscutting relations and the presence of many 

similar, yet thinner, layers within a felsic volcaniclastic map 

unit. The Silurian date either provides the age for the deposition of the felsic unit at that locality, and therefore the age of 

the Waits River there, or a minimum age.

Cady (1950) reported the occurrence of cup corals from 

several localities within the Waits River Formation in the 

15-minute Montpelier quadrangle and suggested a Middle 

Ordovician age for these fossils. Cady (1956) changed the age 

of the Waits River from Ordovician to Silurian on the basis 

of regional correlations with fossiliferous rocks reported by 

Boucot and others (1953) in southern Vermont and Massachusetts. Only Cady’s (1950, p. 492) locality no. 7 could be 
Stratigraphy 9

confirmed during our mapping, and the location is shown on 

the map. In our opinion, this locality contains what appear to 

be fossil fragments in a pebbly horizon at the base of a graded 

bed of phyllite, despite the fact that Hatch (1988, p. 1056) and 

Hueber and others (1990, p. 363) reported that, on the basis of 

a study of slides and slabs by William A. Oliver, Jr., “None of 

the specimens at hand appear to be corals and none have any 

markings or structure that suggest an organic origin, although 

this is a possible origin of the objects.” This locality has yet to 

be re-examined by a paleontologist. Initial reports of Ordovician graptolites from Berlin Corners by Bothner and Berry 

(1985) and Bothner and Finney (1986) were re-evaluated by 

Hueber and others (1990) and reported to be plant fragments 

and not graptolites. Hueber and others (1990) also collected 

crinoid and echinoderm fragments from the Berlin Corners 

exposure, but the fragments did not provide specific age constraints. Plant fossil fragments without specific age constraints 

also were reported at the Catholic cemetery and Sabin’s quarry 

localities in Montpelier (Hueber and others, 1990). The upper 

age limit of the Waits River Formation is probably Early 

Devonian because it is conformably overlain by the Early 

Devonian Gile Mountain Formation.

Shaw Mountain Formation (Silurian)

The Shaw Mountain Formation consists of a number of 

discontinuous lenses of metasedimentary quartz-rich rock, 

quartz-pebble conglomerate, and ankeritic greenstone and 

green schist located along the RMC in the northern part of the 

Montpelier quadrangle. The most conspicuous lithology in 

the Shaw Mountain Formation is a rusty-weathering, locally 

sulfidic quartz-pebble conglomerate. Although the clasts 

are dominantly composed of vein quartz, foliated clasts of 

rocks that resemble those found in the Moretown Formation 

are locally present. The conglomerate (Ss) in the Montpelier 

quadrangle occurs as lenses within a heterogenous unit (Ssg) 

consisting largely of ankeritic greenstone and calcarous green 

schist; in the absence of the quartz-pebble conglomerate, it is 

difficult to separate these lithologies from rocks in the underlying Moretown or Cram Hill Formations. 

The Shaw Mountain Formation was first defined by 

Currier and Jahns (1941) in central Vermont as an east-facing 

succession of massively bedded quartz-pebble conglomerate, platy soda rhyolite tuff, and crinoidal limestone. In the 

15-minute Montpelier quadrangle, Cady (1956) also recognized the quartz-pebble conglomerate and limestone and 

included a calcite-chlorite-albite schist unit above the Moretown Formation and beneath the quartz-pebble conglomerate 

unit. In the Montpelier 7.5-minute quadrangle we observe that 

the calcareous schist (Ssg) in the Shaw Mountain Formation 

is not just beneath the quartz-pebble conglomerate but above 

it as well, and that the conglomerate occurs as discontinuous lenses within our ankeritic greenstone and green schist 

unit (Ssg). Other exposures of calcareous greenstone occur 

within the Moretown or Cram Hill Formations. We also note 

that the “crystalline limestone” reported by Cady (1956), 

“a little northwest of a sharp bend in Long Meadow Brook,” 

is simply a punky-weathering ankeritic chlorite-muscovitealbite-quartz granofels with abundant post-tectonic carbonate 

 porphyroblasts. In southern Vermont, similar units containing ankeritic greenstone and calcareous quartzite have been 

mapped as either unnamed rocks (unit DScv of Ratcliffe, 

2000b) or as part of the Northfield Formation (unit DSng of 

Ratcliffe and Armstrong, 2001). In northern Vermont, Konig 

and Dennis (1964) describe the Shaw Mountain Formation as 

dominantly crystalline limestone, calcareous metaquartzite, 

and phyllite but with subordinate amounts of greenstone and 

calcareous quartz-pebble conglomerate. 

Konig and Dennis (1964) reported that bryozoans, 

brachiopods, corals, and echinoderm debris were found in 

the crystalline limestone of the Shaw Mountain Formation in 

the 15-minute Hardwick quadrangle and that the analysis of 

the fossil age ranges suggested a Silurian to Early Devonian 

age. Other work on the Shaw Mountain Formation fossils (for 

example, Boucot and Thompson, 1963; Doll, 1984; Westerman, 1987) indicates a Middle Silurian age.

Numerous Late Silurian along-strike correlatives to 

the Shaw Mountain Formation are well exposed in southern 

Québec, where the Acadian deformation is less intense than 

in Vermont, and stratigraphic relations are clearer. Lavoie and 

Asselin (2004) group these Silurian units of southern Québec 

into autochthonous and allochthonous categories depending on whether the units are found in the pre-Silurian (Dunnage or Internal Humber) or CVGS tectonic provinces. The 

autochthonous units, which are directly correlative with the 

Shaw Mountain Formation in Vermont, comprise the St. Luc, 

Cranbourne, and Lac Aylmer Formations and the Glenbrooke 

Group. These units grade upward from basal quartz-pebble 

conglomerate that unconformably overlies pre-Silurian terranes of the Dunnage and Internal Humber zones to sandstone 

and siltstone and finally to fossiliferous limestone (Lavoie and 

Asselin, 2004). The Late Silurian (Pridolian) ages of these 

units are based on fossils primarily found in the limestone. 

Although all autochthonous units clearly exhibit unconformable bases, some (for example, Lac Aylmer Formation) may 

also be cut on one side by a Devonian fault.

Northfield Formation (Silurian and Devonian?)

The Northfield Formation consists of dark-gray phyllite 

(DSn) that contains thin layers (≤20 cm) of micaceous quartzite 

and rare matrix-supported conglomerate (DSnc). The Northfield Formation occurs at the base of the CVGS and crops 

out continuously, although with variable thickness, through 

both quadrangles. Currier and Jahns (1941) and Cady (1956) 

mapped these rocks as the Northfield slate, and Doll and others (1961) established the name Northfield Formation.

Thin impure limestone beds are very rare but increase in 

abundance at the eastern contact with the Waits River Formation (DSwl1

), confirming reports by other workers (Currier and Jahns, 1941; Doll, 1951; Cady, 1956; Hatch, 1988). 

Hatch (1988) reported that graded bedding in the Northfield 
10 Bedrock Geologic Map of the Montpelier and Barre West Quadrangles, Washington and Orange Counties, Vermont

Formation indicated that it was stratigraphically above the 

Waits River Formation. Due to the lack of definitive topping 

criteria in the Northfield Formation in the map area, we cannot 

confirm or refute Hatch’s findings. The phyllite is well exposed 

in roadcuts east of Interchange 8 on I–89 and in outcrops in 

the Dog River located east of State Route 12 and the railroad 

tracks approximately 2.4 km south of the Montpelier-Barre 

West quadrangle boundary. In the northern part of the study 

area, the Northfield Formation is in sharp contact with the 

Shaw Mountain, Cram Hill, and Moretown Formations to the 

west and is in gradational contact with the Waits River Formation to the east. South of Horn of the Moon Pond, we map the 

sharp, western contact of the Northfield Formation as a fault.

The conglomerate near the base of the Northfield Formation (DSnc) was seen at one place along the Dog River in the 

Barre West quadrangle. This matrix-supported conglomerate 

occurs within the Northfield Formation, not at the contact 

between the Northfield and Cram Hill Formations. Although 

poorly exposed, the rock was described and seen elsewhere 

by Currier and Jahns (1941). In fact, the outcrop on the Dog 

River was photographed and appears as figure 1 in Currier 

and Jahns (1941, p. 1494). The outcrop is overgrown now, but 

tectonically elongated clasts are still visible in the phyllitic or 

slaty matrix. Currier and Jahns (1941) report that the clasts 

consist of rocks found in the Cram Hill and Shaw Mountain 

Formations. Along the Dog River, the conglomerate occurs 

as an approximately 2- to 3-m-thick layer within the phyllitic matrix. A second exposure in the Barre West quadrangle 

described by Currier and Jahns (1941, p. 1502) could not be 

confirmed by our mapping. 

Waits River Formation (Silurian and Devonian)

The Waits River Formation consists dominantly of 

interbedded phyllite and impure limestone or marble (DSwt, 

DSwl1, and DSwl2), with minor amounts of phyllite (DSw), 

garnetiferous phyllite (DSwg), and quartzite (DSwq). The Waits 

River Formation occupies the majority of the Barre West 

quadrangle and the eastern half of the Montpelier quadrangle. 

The most distinctive aspect of the Waits River Formation is 

the presence of metamorphosed impure limestone or marble. 

Historically, workers have used both the terms “marble” and 

“limestone.” White and Jahns (1950, p. 187) noted that the 

term “limestone” was “long-established local usage.” Cady 

(1956, footnote 1) provides a possible explanation as follows: 

“Though the crystalline limestones are strictly marbles, the 

geologists who have studied these rocks have long referred 

to them as limestone rather than marble, probably because of 

their poor commercial qualities compared to the marbles of 

western Vermont.”

Doll and others (1961) also used the term “limestone” 

on the State map, and we continue the traditional usage here. 

The limestone is typically bluish gray and weathers to a punky 

brown, earthy crust. The limestone is considered siliceous and 

impure because it typically contains 60 to 80 percent calcite, 

20 to 40 percent quartz, and less than 5 percent muscovite 

and (or) biotite. The protolith of this rock was probably sandy 

limestone, according to the classification of Williams and others (1954) and Compton (1962).

The interbedded phyllite and limestone units (DSwt, 

DSwl1, and DSwl2) are the three main map units in the Waits 

River Formation (fig. 6). These map units are separated on the 

basis of bed-thickness of interbedded limestone. To the west, 

limestone beds generally are 0.2 to 3.0 m thick and locally 

as much as 5.0 m thick in the thinly bedded unit. Phyllite 

beds in DSwl1

 and DSwl2 are generally less than 1 m thick, but 

their thickness is often difficult to determine because bedding 

planes are transposed, folded, and difficult to see. Bedding in 

the phyllite in all three units is locally defined by layer-parallel 

oxidized pyrite concentrations. The pelitic rocks are phyllitic 

in the biotite zone, schistose in the garnet zone, and locally 

calcareous. To the east, limestone beds generally are 1.0 to 

5.0 m thick and locally as much as 9.0 m thick in the thickly 

bedded unit DSwt. Phyllite beds in DSwt are generally less than 

1 m thick and locally are as much as 3 m thick. Like DSwl1

 and 

DSwl2, the thickness of the phyllite beds is often difficult to 

determine because bedding planes are transposed, folded, and 

difficult to see. In a detailed survey over a 58-m-thick section 

of DSwl1

 at Interchange 7 on I–89 in the Barre West quadrangle 

(Walsh and Satkoski, 2005), phyllite beds range from 0.15 

to 3.3 m thick and average 0.9 m thick. Limestone beds at 

Interchange 7 range from 0.3 to 8.6 m thick and average 1.8 m 

thick. At Interchange 7, a single limestone bed measured 8.6 m 

thick, and it is shown on the map as DSwt. The next thickest limestone bed measured 4.7 m thick. The Interchange 7 

locality is one of only a few places in the DSwl1 unit where a 

limestone bed greater than 5 m thick was seen, and in these 

places we map the units as DSwt. The thickly bedded unit 

(DSwt) is well exposed at Interchange 6 on I–89, at quarries 

north and south of State Route 63 just east of Interchange 6, 

along State Route 63 near the junction with Miller Road, at the 

falls on the Stevens Branch in South Barre, and below the dam 

on the Winooski River in Barre at an elevation of 600 feet. 

The thinly bedded unit (DSwl1

) is well exposed in roadcuts on 

I–89, 0.5 km south of the bridge over State Route 12, at Interchange 7, and at the overpass, 0.5 km west of Berlin Corners. 

Unit DSwl2 is well exposed in Cold Spring Brook.

Graded bedding in the Waits River Formation was rarely 

seen, but the majority of observed topping criteria suggest 

that the Waits River is steeply overturned toward the eastsoutheast. Graded beds in the limestone are less common than 

those in the phyllite and consist of 2- to 4-cm-thick horizons 

of coarse- to very coarse sand-size grains or rare pebbles of 

quartz, rock and (or) fossil fragments. Graded beds in the 

phyllite contain relatively coarse-grained bases dominated by 

quartz and feldspar and rare conglomeratic horizons with very 

coarse sand-size grains or rare pebbles of quartz, and very rare 

rock or fossil fragments. On the map, locations where graded 

beds were observed are shown with a special strike and dip 

symbol. Four fossil localities within the Waits River Formation are shown with an open diamond and are summarized 

as follows:
Stratigraphy 11

B

A

Limestone

Slate

Figure 6

Figure 6. Photographs of the Waits River Formation. A, Thinly bedded unit (DSwl1) 

shows interlayered brown-weathering impure limestone and more resistant 

gray slate on the east side of Irish Hill, about 2 km west of Interchange 6 on I–89. 

B, Thickly bedded unit (DSwt) shows unweathered limestone and slate and phyllite 

at Interchange 6 on I–89, at the start of the northbound offramp.

U.S. National 

Museum locality 

number

Location

UTM

Northing

(NAD 27)

UTM

Easting

(NAD 27)

Reference

14293 Sabin quarry 4902748 694760 Hueber and others (1990).

14294 Catholic Cemetery 4903754 694473 Hueber and others (1990).

14300 Roadcut near Berlin Corners 4898005 693031 Hueber and others (1990).

Locality no. 7 4908010 698274 Cady (1950).
12 Bedrock Geologic Map of the Montpelier and Barre West Quadrangles, Washington and Orange Counties, Vermont

The dominantly pelitic units (DSw, DSw1, and DSw2) occur 

throughout the Waits River Formation. They consist largely of 

dark-gray slate, phyllite, or schist without appreciable interbedded limestone. Very thin (<20 cm) limestone horizons may 

be present in the DSw units, but they are rare. Generally two 

large pelitic units were mapped in the area. The first (DSw1) 

occurs in the western (lower) part of the Waits River Formation within the DSwl1

 unit along the crest of Paine Mountain 

to Irish Hill, and the second (DSw2) occurs between the thinly 

and thickly bedded limestone units (DSwl1 and DSwt, respectively). In the central part of the Barre West quadrangle, the 

eastern (upper) DSw2 unit is repeated by folding. On our map 

we show the axial traces of F3 folds (Acadian F1) where we 

interpret the map distribution to reflect such folding. In places 

where we do not show axial traces, we interpret the map units 

as facies changes within the Waits River Formation. Small 

units mapped simply as DSw are interpreted as limestone-poor 

facies. Good exposures of the pelitic map unit are located 

on West Hill in Barre and at a roadcut along State Route 63, 

approximately 1.2 km east of Interchange 6 on I–89.

The garnetiferous phyllite (DSwg) occurs as a single map 

unit within the thinly bedded Waits River Formation. The 

garnetiferous phyllite is a distinctive nonsulfidic rock that 

contains abundant millimeter-scale garnet porphyroblasts. 

To the south on the eastern slopes of Paine Mountain, DSwg

is thicker than to the north and can be mapped by the occurrence of several closely spaced across-strike outcrops in a 

zone several hundred meters wide. North of Berlin Corners, 

DSwg is generally restricted to only one or two outcrops in 

a zone approximately 150 m wide. In the Montpelier quadrangle, the zone narrows to less than or equal to 100 m wide 

at the Montpelier-East Montpelier town line, before we map 

it discontinuously to the north. A typical exposure of the 

garnetiferous phyllite is located in Berlin under the powerlines 

along Berlin Street (name not on map), approximately 300 m 

northwest of the Armory in the Barre West quadrangle. The 

garnetiferous phyllite does not contain interbedded limestone. 

The DSwg unit marks the westernmost occurrence of almandine garnet in the area and coincides with the mapped Acadian 

garnet isograd. The mapped garnet isograd is a function of 

bulk composition as DSwg is probably more aluminous than 

adjacent nongarnetiferous phyllite. Immediately east of the 

DSwg unit, in the garnet zone, nongarnetiferous dark-gray 

phyllite occurs in the Waits River Formation, providing evidence for minor differences in bulk composition. Within the 

garnet zone, garnetiferous phyllite or schist occurs sporadically in other places, and almandine garnet becomes more 

abundant towards the east, but the relatively greater abundance 

of garnet in the eastern part of the Waits River Formation 

makes it difficult to separate map units solely on the presence of garnet porphyroblasts. On the map in the garnet zone, 

we show locations where conspicuous garnet porphyroblasts 

were seen at outcrops in the eastern part of the Waits River 

Formation, east of the DSwg unit. West of the isograd and west 

of the RMC, the dominant assemblage in the pelitic rocks is 

quartz-chlorite-muscovite±biotite.

Quartzite of the Waits River Formation (DSwq) is a minor 

unit and is shown in three places in the Barre West quadrangle. 

At two places (Stations 1266 and 1321 in the database), the 

map unit shows the location of single 0.5- to 2.0-m-thick 

quartzite beds, and the third location (Station 1271) shows 

thinner interbedded quartzite, phyllite, and limestone layers, generally less than 30 cm thick. The quartzites at these 

three locations consist mostly of quartz (75–90 percent) with 

variable amounts of calcite, plagioclase, muscovite, and trace 

pyrite and graphite. Depending upon which of these secondary 

minerals is the second most abundant, the rocks can either be 

called calcareous, feldspathic, or micaceous quartzite. Protoliths for these rocks probably ranged from arenite to calcareous sandstone to wacke according to the classification of 

Williams and others (1954) and Compton (1962).

Contacts between the thinly and thickly bedded Waits 

River units (DSwl1, DSwl2, and DSwt) are mapped on the basis 

of limestone beds greater than or equal to 5 m thick. Contacts 

between the phyllite unit and the limestone-bearing units are 

gradational. Contacts between the garnetiferous phyllite and 

adjacent units, although not completely exposed, are sharp 

and occur within a distance of approximately 1 m. Contacts 

for individual quartzite layers are typically sharp except where 

graded bedding was observed.

Most workers in central Vermont have named these 

rocks the Waits River Formation (Currier and Jahns, 1941; 

White and Jahns, 1950; Konig, 1961; Ern, 1963). In the East 

Barre 15-minute quadrangle, however, Murthy (1957) called 

these rocks the Barton River Formation and suggested that 

they were older and stratigraphically beneath the Gile Mountain Formation and Waits River Formation. Doll and others 

(1961) used the name Barton River member of the Waits River 

Formation for the belt of rocks west of the Gile Mountain 

Formation and suggested in their correlation of map units that 

it was laterally correlative with the Waits River rocks east of 

the Gile Mountain Formation. In fact, the State map (Doll and 

others, 1961) uses the same pink color for Waits River Formation and Barton River member of the Waits River but uses 

different map unit designators, “Dw” and “Dwb,” respectively. 

Our findings combined with regional fossil evidence (Hueber and others, 1990; Lavoie and Asselin, 2004) suggest that 

the Waits River Formation in the Montpelier and Barre West 

quadrangles is stratigraphically beneath the Gile Mountain 

Formation, in agreement with most workers. Thus Murthy’s 

stratigraphic assessment appears invalid. Our mapping also 

agrees with more recent stratigraphic work in the Connecticut 

Valley rocks, placing the Waits River Formation below the 

Gile Mountain Formation in the Townshend-Brownington 

syncline (Fisher and Karabinos, 1980; Hatch, 1988). 

Gile Mountain Formation (Devonian)

The Gile Mountain Formation consists largely of interbedded phyllite and quartzite (Dgm), with minor amounts of 

calcareous phyllite (Dgmcp) and impure limestone (Dgml). 

The Gile Mountain Formation occurs only in the southeastern 
Stratigraphy 13

corner of the Barre West quadrangle. Bedding in the interbedded phyllite and quartzite unit (Dgm) generally ranges from 

10 to 30 cm thick. Graded bedding is locally preserved and 

generally indicates that the beds are steeply overturned to the 

southeast. The interbedded sequence of phyllite and quartzite 

probably represents a sequence of turbidites. The phyllite and 

quartzite unit is well exposed in Cold Spring Brook above 

the 1,100-foot elevation. At several locations along McGlynn 

Road (name not shown on map), dark-brown-weathering, gray 

calcareous phyllite layers, 30 to 40 cm thick, occur within 

the phyllite and quartzite unit and are mapped separately as 

Dgmcp. Similar calcareous phyllite layers occur throughout 

the Waits River Formation but are not mapped separately. 

At one location near McGlynn Road, a single ~50-cm-thick 

layer of impure siliceous limestone occurs in the phyllite and 

quartzite unit, and it is mapped separately as Dgml. This location marks the only observed occurrence of limestone within 

the Gile Mountain Formation in the map area. Similar limestones occur throughout the Waits River Formation but are not 

mapped separately.

The contact between the Gile Mountain Formation and 

underlying Waits River Formation, although not entirely 

exposed, is generally gradational over a distance of tens of 

meters. The number of limestone layers in the Waits River 

Formation decreases towards the contact with the Gile Mountain Formation, while the number of thin 10- to 20-cm-thick 

quartzite, micaceous quartzite, and feldspathic quartzite layers 

increases towards the contact with the Gile Mountain. The 

upper, or easternmost, part of the Waits River Formation contains thinly interbedded phyllite and limestone (DSwl2

) below 

the contact with the Gile Mountain Formation. This part of the 

Waits River Formation contains thinner and fewer limestone 

beds than the underlying thickly bedded phyllite and limestone 

unit (DSwt), suggesting a progressive decrease in limestone 

upsection towards the Gile Mountain Formation.

Doll and others (1961) and Konig (1961) mapped these 

rocks as Gile Mountain Formation, but Murthy (1957) called 

these rocks the Westmore Formation and suggested that 

they might be correlative with his Gile Mountain Formation exposed in the southeastern corner of the East Barre 

15-minute quadrangle. The Gile Mountain Formation, as we 

map it, generally supports Hatch’s (1988, p. 1045) assignment 

to the rhythmically bedded “RQM” unit in the core of the 

Townshend-Brownington syncline, the western limb of which 

is exposed in our study area.

Igneous and Metasomatic Rocks

Granitic Dikes (Devonian)

Granitic dikes in the area range in composition from 

trondhjemite to granodiorite to muscovite-biotite granite. The 

dikes are part of the Devonian New Hampshire Plutonic Suite. 

Although not dated in the map area, similar correlative rocks 

occur throughout Vermont. A U-Pb zircon age determined by 

sensitive high resolution ion microprobe (SHRIMP) for the 

nearby Barre Granite (Murthy, 1957) is 368±4 Ma (Ratcliffe 

and others, 2001). Ratcliffe and others (2001) report a similar 

U-Pb zircon age of 366±4 Ma for the Black Mountain Granite 

in southern Vermont. Structurally, the dikes cut the bedding in 

the Silurian-Devonian rocks and generally intruded subparallel to the dominant foliation (S3

 or Acadian S1; see discussion 

below) in these rocks. Locally the dikes contain the S3 foliation, especially in thin bodies or along the margins of larger 

dikes, suggesting that some might predate or be synchronous 

with foliation development. Other dikes without a foliation 

postdate the S3 foliation but may have experienced subsequent 

flattening along their margins during continued regional deformation. The generally massive texture of the dikes makes it 

difficult to assess whether they predate or postdate the weakly 

developed S4 (Acadian S2) cleavage in this area. Under the 

microscope, however, the granite in the core of the dike at 

Crosstown Road contains no foliation or even preferred fracture orientation, suggesting that it either postdates both S3

 and 

S4 or wasinsulated from the deformation due to the massive 

texture of the rock. The structural relations combined with the 

regional zircon ages and similar regional 40Ar/39Ar metamorphic ages (Laird and others, 1984, 1993; Spear and Harrison, 

1989) clearly suggest that the granites are related to Acadian 

deformation and metamorphism.

Although some of the larger granite bodies in the 

northeastern part of the Montpelier quadrangle have elliptical shapes and crosscut the dominant foliation, most are thin 

elongate bodies that are parallel to the S3 (Acadian S1) foliation. Quarries are found in many of the largest granite bodies near the town of Adamant. Because most granite bodies 

intruded parallel to the dominant foliation, they are considered 

sills sensu lato. When viewed in three dimensions, however, 

some granite bodies parallel the dominant foliation in one part 

of an outcrop but crosscut the same foliation in other parts of 

the outcrop.

Quartz Veins (Devonian)

Quartz veins crop out in the two quadrangles, and the 

locations of larger veins are indicated either as map units 

(Dq) where they are large enough to map or with symbols. A 

strike and dip symbol represents the average orientation of 

the generally tabular bodies, and point symbols show locations where orientations could not be determined. The veins 

are folded in places and generally predate the regional S4

(Acadian S2) cleavage. Late tabular quartz veins postdate all 

the deformation and have either a late-metamorphic origin or 

a post-metamorphic igneous or a metasomatic origin. Anderson (1987) studied similar veins in north-central Vermont and 

concluded that most of the veins have a metamorphic origin 

and that some veins (especially those in northeastern Vermont) have a metasomatic origin related to New Hampshire 

series plutons. The veins are assigned a Devonian age. Small, 

unmapped, highly folded and disarticulated quartz veins in 

the Moretown and Cram Hill Formations may be related to 

Taconian (Ordovician) metamorphism.
14 Bedrock Geologic Map of the Montpelier and Barre West Quadrangles, Washington and Orange Counties, Vermont

Lamprophyre or Diabase Dikes (Cretaceous)

Lamprophyre or diabase dikes occur as tabular steeply 

dipping, outcrop-scale dikes throughout the two quadrangles, 

and their locations and orientations are shown by strike and 

dip symbols. Eleven dikes dip greater than or equal to 74° and 

have a preferred east-west strike (fig. 7), generally parallel to 

the major joint trends (see Brittle Structures section).

n = 11

Figure 7

N

Figure 7. Rose diagram showing the strike 

of 11 steeply dipping Cretaceous dikes. Data 

are plotted using Structural Data Integrated 

System Analyser (DAISY 4.01) software 

by Salvini (2004). North is marked by “N,” 

and the number of data points is indicated 

by “n.” 

The dikes are assigned a Cretaceous age on the basis of the 

122.2±2 Ma age of the intrusive complex at Ascutney Mountain (Foland and others, 1985) and on a regional summary by 

McHone (1984) for similar dikes throughout New England 

and Québec.

Economic Geology

A number of quarries, both active and abandoned, exist 

in the Montpelier and Barre West quadrangles. Most granite 

quarries in the area are inactive. A number of granite quarries 

in the Adamant area were active in the late 1800s to 1900s 

(Dale, 1909, 1923; Cady, 1956). In Adamant, the Lake Shore 

granite quarry opened in 1902 (Dale, 1909) and was abandoned prior to 1915 (Dale, 1923). The Patch granite quarry 

was opened around 1893 (Dale, 1909) and was active at least 

until the 1950s when Konig (1961) mapped the 15-minute 

Plainfield quadrangle. Abandoned granite quarries in Berlin 

south of Crosstown Road were operated in the 1870s (Collier, 

1872). The Berlin quarries, which have no formal name in 

the literature, were owned by C.M. Ayers and opened sometime after 1858 according to records of the Berlin Historical 

Society (Richard Turner, written commun., 2006). Unpublished documents on file at the Vermont Geological Survey 

indicate that the quarry also went by the name of “S. Fruchter 

quarry.” The Berlin granite quarries were abandoned by the 

time of Richardson’s mapping in 1914 to 1915 and probably 

sometime before then as Dale (1909) did not include them in 

his study. Abandoned slate quarries are found throughout the 

Waits River Formation in the two quadrangles. In downtown 

Montpelier, the Langdon quarry and Sabin quarry were abandoned prior to Richardson’s (1916) study. Richardson (1916) 

mentions two abandoned quarries in the Montpelier quadrangle, which were not visited in our study: the Cutler quarry and 

an unnamed quarry on the road from Montpelier to Adamant. 

Other small, unnamed, abandoned quarries or prospects occur 

in quartzite of the Cram Hill Formation and in quartz veins.

Currently, there are three active slate and crushed stone 

quarries in the Waits River Formation. Black Rock Coal, Inc., 

received a permit in 2002 for a new quarry in Calais southwest 

of Bliss Pond for slate and granite extraction. Brousseau, Inc., 

operates a quarry in Berlin just southeast of Interchange 6 on 

I–89, and Lague, Inc., operates a quarry in Berlin along State 

Route 62, just uphill of the junction with U.S. Route 302. The 

locations of all identified quarries and prospects are shown 

on the map and are included in the GIS database section of 

this report.

Structural Geology

Ductile Structures

Five generations of ductile deformation and associated 

structures are recognized in the area. The five generations 

are designated D1

 through D5, and their associated fabrics are 

summarized in table 1. The oldest two periods of deformation 

(D1

 and D2 ) are interpreted to be the result of the Ordovician 

Taconian orogeny and the youngest three periods of deformation (D3

–D5) the result of the Devonian Acadian orogeny 

because D1

 and D2 occur only in the pre-Silurian rocks, and D3

is the oldest fabric in the CVGS.

The distribution of deformational fabrics is not uniform 

across the map area (fig. 8C). For discussion, the area is 

divided into three structural zones: Zone I is the Dumpling 

Hill belt of the Moretown Formation, Zone II is the Wrightsville belt of the Moretown and Cram Hill Formations, and 

Zone III is the CVGS (figs. 2, 8, and 9). The zones divide 

the map area into three structural domains, which reflect the 

dominance of Taconian structures (Zone I), an overlap domain 

(Zone II), and Acadian structures (Zone III), respectively.

Schematic diagrams in figure 8 show the evolution 

and distribution of the five deformational fabrics across the 

map area. The area is complexly deformed, and, because the 

three oldest deformational events (D1

–D3) produced variably 

penetrative coplanar fabrics and associated tight to isoclinal 

folding, it is often difficult to determine the absolute ages 
Structural Geology 15

Table 1. Regional correlation of Taconian and Acadian deformational fabrics, central Vermont.

[NA, not applicable]

This study Offield and 

Relative Walsh Kim and others 

timing of and Ratcliffe Walsh Gale (1993); Deformation Foliation Paleozoic Falta (2000a,b) (1998) (2004) Woodland 

intrusive (2001) (1977) rocks

D Weak dome-stage cleavage S (Acadian S ) NA S F and F S F 5 5 3 5 4 5 3 3

D Northeast-striking/northwest-dipping and S (Acadian S ) S S Acadian F S F 4 4 2 3 4 2 2 2 Granite 

dikes lesser northwest-striking/northeast-dipping 

 cleavage and folds

D Dominant schistosity with tight-isoclinal S (Acadian S ) S S F or S F 3 3 1 2 3 3 1 1

 folding in Devonian and Silurian rocks Acadian F1

Cleavage to fault-related fabric along Metadiabase 

and greenstone 

dikes

Dog River fault zone

D Dominant schistosity and “pinstripe” in Taconian S 2 2 S S F NA NA 1 2 2

 Moretown Formation, to relict foliation 

where overprinted by Acadian S1 

D Relict layer-parallel foliation in Moretown Composite 1 S F Taconian(?) NA NA 1 1

and Cram Hill Formations Taconian S /S1 0

of fabrics in the field. In such instances, our map shows the 

dominant planar fabric with an undetermined relative age of 

“Sn” in the pre-Silurian rocks because the dominant foliation 

is not the same absolute age across the map area. The orientation of planar features is reported in right-hand rule here and 

in the accompanying GIS database.

First-Generation Foliation—S1

The oldest foliation in the area is a relict layer-parallel 

tectonic schistosity (S1

) observed primarily in Zones I and II. 

It is best preserved in Zone I, especially on the western side of 

Dumpling Hill. The relict fabric is characterized by a lepidoblastic texture of aligned micas that is subparallel to compositional layering in these rocks. The compositional layering 

appears to be bedding. Definitive folds associated with this 

oldest relict fabric were not seen at the outcrop but appear to 

be responsible in part for the map pattern seen in the Dumpling Hill belt (fig. 9). There, the green and dark-gray carbonaceous phyllite unit (OЄmsr) is interpreted to define a refolded 

fold pattern whose axial surface (F1

) generally trends northwest-southeast and is deformed by upright second-generation 

folds (F2) (fig. 9). Definitive F1 fold axes and mineral lineations were not positively identified in the field, so this earliest 

phase of deformation is largely based on interpretation of the 

map pattern. This relict period of deformation (D1

) is attributed to the Taconian orogeny. 

Bed-parallel foliation defined by aligned quartz and 

mica is present in the Silurian and Devonian rocks, especially as thin laminations in the impure siliceous limestone 

or marble (fig. 10D). This fabric is not tectonic but rather 

diagenetic (Passchier and Trouw, 2005), as there are no axial 

planar folds associated with these laminations and they are 

deformed by the first period of folding recognized in these 

rocks (D3

). These laminations are, therefore, considered 

primary (S0

) with enhancement due to subsequent growth of 

metamorphic minerals.

Second-Generation Foliation—S2

The second-generation foliation (S2) is generally the 

dominant planar fabric in the pre-Silurian rocks of Zones I 

and II. In Zone I, bedding (S0) and S1 are folded by steeply 

west-dipping, steeply plunging asymmetric isoclinal folds 

(F2

) with associated axial planar schistosity (S2). Secondgeneration (F2

) fold axes are parallel to downdip mineral 

“aggregate lineations” (Piazolo and Passchier, 2002; Passchier 

and Trouw, 2005), such as quartz rods (L2

). These downdip F2

 and L2 lineations show a mean trend of 350°, 72° in 

Zone I and 359°, 65° in Zone II (fig. 11A,B). The phyllitic 

units contain a well-developed closely spaced schistosity, and 

the granofelsic rocks locally contain compositionally segregated bands of alternating micaceous and quartzofeldspathic 

material that give the rocks a “pinstripe” appearance. This 

“pinstripe” texture is typical of the Moretown Formation, 

and, because it is observed to postdate bedding, it is a tectonic 

fabric produced by metamorphic differentiation and is not 

bedding. Bedding is typically transposed by the S2

 foliation, 

especially along the limbs of F2

 folds, but is locally preserved 

in F2

 hinges and in massive quartzites. Zone II is bound by 

the Shady Rill fault (west) and the RMC (east) or Dog River 

fault zone (fig. 9). The dominant foliation in Zone II is the S2

, 

or, locally the S3

 foliation, and relict S1 is locally preserved 

in F2

 or F3 fold hinges. Locally, in Zone II, S2 is overprinted 

by S3

 especially towards the Dog River fault zone, where the 

dominant fabric is controlled by S3

 (fig. 8).
16 Bedrock Geologic Map of the Montpelier and Barre West Quadrangles, Washington and Orange Counties, Vermont

Zone II

(Wrightsville belt)

Zone I

(Dumpling Hill belt)

Zone III

(Connecticut ValleyGaspé synclinorium)

D1 D2 D3

A

B

S0

S1

S2

S3

S4

S5

SRF RMC-DRFZ F1

F1

Distribution

Mostly Zone III, less common 

in Zone II, and rare in Zone I

Zones I–III

Zones I and II

Zones I and II

Zones I–III 

Fabric

West East

C

Zone III 

EXPLANATION

[For A and B]

F5 fold axis

F2 fold axis

F1

 fold axis—

Orientation

unknown

North-trending,

steeply plunging

F1 and F2

F4 F5

F3

Zone I Zones I and II

Eastern part of Zone II 

and most of Zone III

Less common More common

Northwest striking

and northeast dipping

Northeast striking 

and northwest dipping

Eastern part of Zone II and all of Zone III

axial 

surface

North-plunging F3

 fold axis

Variable plunges

S3

 foliation

Eastern part of Zone II and all of Zone III

Figure 8. Schematic diagrams 

illustrating the distribution and style 

of the five ductile fabrics in the 

map area. A, Schematic downplunge view of penetrative D1

 to D3

foliations and folds. These three 

periods of deformation produced 

tight to isoclinal folds. D4

 and D5

produced nonpenetrative open 

folds and (or) crenulation cleavages 

and are not shown in this diagram. 

B, Schematic cross section 

showing the distribution of fabrics. 

Bedding (S0

) is present in all zones 

but it is not the same age. In Zones I 

and II, bedding is difficult to see in 

most outcrops because it is parallel 

to and transposed by subsequent 

deformation. “F1

” shows the 

location of relict fold hinges. 

C, Schematic block diagrams 

showing the general style of folding 

(F1

–F5) and the distribution of the 

folds across the map area.
Structural Geology 17

U

D

Pre-Silurian rocks, undivided

0 1 2 3 MILES

0 4321 5 KILOMETERS

Wrightsville

Dumpling Hill

Montpelier

Barre

Dog River fault zone

Shady Rill fault

DSu

72°37’30” 72°30'

44°15'

44°22'30”

Och

Thrust fault of Taconian age, parallel to S2—Sawteeth on upper plate

Och

?

Richardson Memorial Contact

U

D

Omw Omd

Shaw Mountain, Northfield, and Waits River Formations, undivided

(Devonian and Silurian)

DSu

Och

Omw

—Richardson Memorial Contact (RMC)—

Cram Hill Formation of the Wrightsville belt (Ordovician)

Moretown Formation of the Wrightsville belt (Ordovician and Cambrian)

Moretown Formation of the Dumpling Hill belt (Ordovician and Cambrian)

Reverse fault of Acadian age, parallel to S3

 (Acadian S1)—U, upthrown side; 

D, downthrown side

Omd

Zone I

Zone II

Zone III

EXPLANATION

Trace of S2 showing dip of axial surface and trend of fold axis

S1

 in pre-Silurian rocks

Trace of S3

 showing dip of axial surface and trend of fold axis—Acadian S1

in Silurian and Devonian rocks

S0 in pre-Silurian rocks 

Figure 9

Strike and dip of S4 cleavage—Acadian S2 in Silurian and Devonian rocks 

U

D

Pre-Silurian rocks, undivided

0 1 2 3 MILES

0 4321 5 KILOMETERS

Wrightsville

Dumpling Hill

Montpelier

Barre

Dog River fault zone

Shady Rill fault

DSu

72°37’30” 72°30'

44°15'

44°22'30”

Och

Thrust fault of Taconian age, parallel to S2—Sawteeth on upper plate

Och

?

Richardson Memorial Contact

U

D

Omw Omd

Shaw Mountain, Northfield, and Waits River Formations, undivided

(Devonian and Silurian)

DSu

Och

Omw

—Richardson Memorial Contact (RMC)—

Cram Hill Formation of the Wrightsville belt (Ordovician)

Moretown Formation of the Wrightsville belt (Ordovician and Cambrian)

Moretown Formation of the Dumpling Hill belt (Ordovician and Cambrian)

Reverse fault of Acadian age, parallel to S3

 (Acadian S1)—U, upthrown side; 

D, downthrown side

Omd

Zone I

Zone II

Zone III

EXPLANATION

Trace of S2 showing dip of axial surface and trend of fold axis

S1 in pre-Silurian rocks

Trace of S3

 showing dip of axial surface and trend of fold axis—Acadian S1

in Silurian and Devonian rocks

S0 in pre-Silurian rocks 

Figure 9

Strike and dip of S4 cleavage—Acadian S2 in Silurian and Devonian rocks 

Figure 9. Simplified geologic map 

showing the major structural zones 

in the area and the distribution and 

orientation of significant ductile 

deformational fabrics. In addition to 

the structural differences between 

the three zones, the Moretown 

Formation in the Dumpling Hill belt 

(Zone I) lacks interlayered greenstone 

and the Ordovician(?) and Silurian(?) 

metadiabase and greenstone dikes 

found in the Wrightsville belt (Zone II).
18 Bedrock Geologic Map of the Montpelier and Barre West Quadrangles, Washington and Orange Counties, Vermont

A B

C D

E F

S0

S3

Limestone

Slate

Figure 10

1 cm

L3

S3

Area of B

S4

 slip surface

S4

BW–1061A

Figure 10. Photographs of F3 (Acadian F1) folds in the Waits River Formation. In all photographs, the white dotted line is 

bedding (S0) and the red solid line is S3. A, Oblique view looking east at large, tight F3 folds along I–89, 1 km southeast of 

Interchange 8. Bedding is defined by concentrations of rusty-weathering sulfide (pyrite) horizons and alternating layers 

of slate and limestone. White rectangle shows area of photograph B. B, Down-plunge view looking northeast showing F3

folds of bedding, steep S3 cleavage, and north-plunging L3 cleavage-bedding intersection lineation. C, Cross-sectional view 

showing tight F3 folds of weakly visible bedding in slate and phyllite along State Route 63, 1 km east of I–89, Interchange 6. 

View is to the north, west is to the left. D, Isoclinally folded bedding laminations typical of folds in impure siliceous limestone 

or marble. E, Folded bedding laminations in limestone (top) are generally invisible in the slate at the outcrop but can be seen 

in thin section (inset; white rectangle shows location of sample). Here, the contact between limestone and slate also exhibits 

slip. Cross-sectional view from roadcut on State Route 63, 0.5 km east of I–89, Interchange 6. View is to the north, west is 

to the left. F, Isoclinal F3 folds in thinly interbedded calcareous metapelite and limestone (gray and white, top) and massive 

siliceous limestone or marble (dark gray and brown, bottom). View is to the south, west is to the right. Cross-sectional view 

from roadcut on State Route 62, 1 km northwest of junction with U.S. Route 302.
Structural Geology 19

74

51

48

51

55

52 50

82

51

51 44

68 44

44

46 24

51 44

52 39 39 57 65

63

40 50

19

49

72

46

59

57

58 39

48 49

41 55

45

25

64

59 35

43

59 44 22 31

31

37

32

43

27 44 26 35

26

5

41

5 27

27

31

39

48 30

37

36

33

21

28

30

30 45

22

33

31

40

32 54

44 11 52

41

26

52

76

39

4145 38 42

18

21 48 22

33

6

2

9

14

15

6

9

8

32 19

40 24

20 12

22

24 33

23

35

28

21 42

41

13

29

64 41 37

14

38

24 18

11

21

32

44

1

36 11

34

44

33

49

50

59

50

15

55

48

48

46

15

56 30

8

45

63 43

63

58

16

45

65

50 52

35

40

50

48

45 58

55

54

45

43 34

24

30

58

18 18

34 32 42

30

26

39

20 36 61 66

71

61 47

55

68

70 55

51

48

58 45 56 61

61

62

59

62

66

24

59

58

45

7

34

42

60

69

66

67

45

42

71

12

54

54

42

35

9

16

0

0 21 3 KILOMETERS

1 2 MILES

Zone I

Zone II

Zone III

DRFZ–RMC

SRF

N N

C D

N N

A B

DRFZ–RMC

SRF

ZONE I

ZONE II

ZONE III

27

31

Bearing and plunge of D3 linear features

L3

 crenulation, intersection lineation, mineral aggregate

lineation, or stretched-pebble lineation

F3

 fold axis Summary of D3

linear trends

E

F

Figure 11

EXPLANATION

Zone I

Pole to S2

 (n = 191)

L2

 lineation (n = 42)

Mean L2

 attitude: 350°, 72°

EXPLANATION

Zone II

Pole to S2

 (n = 655)

L2

 lineation (n = 115)

Mean L2

 attitude: 359°, 65°

EXPLANATION

Zones I and II

Pole to S3

 (n = 83)

L3 lineation (n = 49)

Mean L3

 attitude: 19°, 36°

EXPLANATION

Zone III

Pole to S3

 (n = 1207)

L3

 lineation (n = 215)

Mean L3

 attitude: 357°, 46°

EXPLANATION

Figure 11. Lower hemisphere equal area projections (stereonets) of poles to penetrative foliation and their associated lineations 

(A–D) and maps showing D3 linear features (E,F ). A and B, Poles to foliation (S2) and lineations (L2) in Zone 1 (A) and Zone II (B). 

C and D, Poles to foliation (S3

) and lineations (L3) in Zones I and II (C) and Zone III (D). Note the similarity in foliation orientation 

between S2

 and S3. Also note, however, that L2 lineations plunge more steeply to the north than do L3 lineations. Thus the D3

deformation is generally coplanar but not coaxial. Data are plotted using Structural Data Integrated System Analyser (DAISY 4.01) 

software by Salvini (2004). North is marked by “N,” and the number of data points is indicated by “n.” DRFZ, Dog River fault zone; 

RMC, Richardson Memorial Contact; SRF, Shady Rill fault.
20 Bedrock Geologic Map of the Montpelier and Barre West Quadrangles, Washington and Orange Counties, Vermont

Third-Generation Foliation—S3 (Acadian S1)

The third-generation foliation (S3) is variably penetrative 

across the area and varies from a spaced cleavage in Zone I to 

a penetrative schistosity or cleavage in Zones II and III. The 

S3 foliation is most penetrative in the vicinity of the Dog River 

fault zone (see discussion below). The S3 foliation is the oldest 

and dominant deformational fabric in the CVGS and strikes 

northeast and dips steeply northwest (fig. 11C,D).

The S3 foliation also is referred to as “Acadian S1” 

because it is the first deformation in the CVGS. The S3 foliation is associated with tight to isoclinal folds (F3 ) of older S1

and S2 foliations in Zones I and II and large map-scale tight 

to isoclinal folds (F3, or Acadian F1) of bedding (S0) in the 

CVGS. Lineations associated with S3 include crenulations 

and intersection lineations in Zones I and II. These western L3

lineations are parallel to F3 fold axes. The most common L3

lineation in Zone III is a cleavage-bedding intersection. Mineral aggregate lineations and stretched-pebble lineations occur 

near the Dog River fault zone, and here they show a northnorthwest trend that is oblique to the overall north-northeast 

trend of intersection, crenulation, and fold axis lineations in 

other parts of the map area (fig. 11E,F ). F3 fold axes in the 

Dog River fault zone are subparallel to the aggregate lineations and stretched-pebble lineations.

Large map-scale F3 folds in the pre-Silurian rocks are not 

apparent due to the difficulty in mapping marker horizons in 

these rocks. Third-generation (F3) fold axes vary from gently 

to moderately north plunging in Zones I and II (fig. 11E,F ). 

In Zone III, the fold axes also plunge moderately to gently 

to the north, but gentle plunges to the south occur especially 

in the central and southern part of the Barre West quadrangle 

(fig. 11E,F; see map). Because outcrop-scale F3 fold hinges 

and L3 cleavage-bedding intersection lineations in the central 

part of the Barre West quadrangle plunge gently both to the 

north and south, our map and cross sections A–A′ and B–B′

show doubly plunging F3 anticlines and synclines. In the 

northern two-thirds of the map (in Zone III), F3 folds and L3

lineations consistently plunge to the north.

Large outcrop-scale F3 (Acadian F1) folds were observed 

at almost all large roadcuts in the CVGS (fig. 10). Smallscale F3

 folds are preferentially preserved in the limestones 

of the CVGS where bed-parallel laminations, defined by 

aligned muscovite, quartz, and calcite, show isoclinal folds 

(fig. 10D–F). Such folds are difficult to see at outcrop scale in 

the pelitic rocks of the CVGS but were seen locally in thin section (fig. 10E). Bain (1931) and Ern (1963) called these “flow” 

or “flowage” folds. Unlike bedding in the pre-Silurian rocks 

of Zones I and II, bedding in the CVGS (Zone III) is well preserved and readily visible at most large exposures, especially 

in the Waits River Formation. In the CVGS, the S3 foliation is 

parallel to bedding in some outcrops, but in many outcrops it 

dips more gently to the west than the bedding. Despite the tight 

to isoclinal nature of the F3 folds, the relation where bedding is 

steeper than cleavage and both dip steeply to the west is consistent with the generally overturned nature of the bedding on the

western limb of the Townshend-Brownington syncline (fig. 2).

Moretown Formation “Pinstripe”

Hatch and Hartshorn (1968) first described a dominant 

lithology in the Moretown Formation in northwestern Massachusetts as “pinstripe” granulite. Hatch and Stanley (1988) 

characterized this “pinstriping” as 1- to 3-mm-thick quartzplagioclase layers separated by thin partings of mica. Earlier, 

Cady (1945) recognized and described this fabric in central 

Vermont, and this “pinstripe” fabric is characteristic of a major 

map unit in the Moretown Formation. The “pinstriping” we 

observed, both mesoscopically and microscopically during this 

study, is a tectonic fabric characterized by alternating quartzfeldspar (QF) and mica (M) domains (fig. 12D). We observed 

three generations of “pinstripe” tectonic fabric in the Moretown Formation; the first two are presumed to be Taconian, 

whereas the third is Acadian. The first generation is the oldest 

metamorphic tectonic fabric in the field area (S1) and consists 

of alternating quartz-feldspar and chlorite-muscovite layers 

that are associated with a mapped folding event that, enigmatically, was not seen at outcrop scale. The S1

 fabric is folded by 

steeply plunging isoclinal F2 folds that have an axial planar 

“pinstripe” fabric (S2) (fig. 12A,B). Locally, especially near 

the Dog River fault zone, F3 folds are severely tightened to the 

point that a third generation of “pinstriping” develops axial 

planar to the F3 folds where the foliation shears out the limbs. 
Structural Geology 21

A B

C

D

M

QF

2 mm

Figure 12. Photographs of “pinstripe” fabric in the 

Moretown Formation. A, Large-amplitude isoclinal 

F2

 fold along U.S. Route 2 in the easternmost part 

of the adjacent Middlesex quadrangle, 0.52 km 

west of the border with the Montpelier quadrangle. 

These isoclinal folds deform a previously developed 

S1

 “pinstripe” foliation. B, Close-up of nose of F2

fold shown in photograph A. Earlier S1

 “pinstripe” 

foliation is isoclinally folded and a second 

“pinstripe” foliation developed axial planar to the 

F2

 folds. In the absence of such fold closures, it is 

often difficult to distinguish S1

 from S2. C, “Pinstripe” 

parallel to a composite S1

–S2 foliation deformed by 

upright F3

 folds. D, Photomicrograph of “pinstripe” 

showing alternating quartz-feldspar (QF) and mica 

(M) domains. Figure 12
22 Bedrock Geologic Map of the Montpelier and Barre West Quadrangles, Washington and Orange Counties, Vermont

Fourth-Generation Foliation—S4 (Acadian S2)

The fourth-generation foliation (S4) is a spaced cleavage with associated crenulation lineations (L4

) and open folds 

(F4

). S4 is widespread in Zone III but decreases towards the 

west, where it is sporadically identified in Zone II and rarely 

identified in Zone I. The S4

 foliation is the second-generation 

fabric in the CVGS; thus it is also referred to as “Acadian 

S2.” The S4

 foliation is associated with outcrop-scale open 

folds (F4

) of older foliations that mostly strike northeast and 

dip moderately northwest but also strike northwest and dip 

northeast consistent with a kink, or box-fold, geometry seen 

at some outcrops (fig. 13). Fourth-generation fold axes (F4

) 

and crenulation lineations (L4

) are gently to moderately north 

plunging (fig. 13A). In the southeastern part of the Barre West 

quadrangle, the S4

 fabric strikes northwest and dips moderately northeast, and there it deforms the S3

 foliation and map 

unit contacts into a map-scale kink fold. At most outcrops in 

Zone III, the L4

 crenulation fabric is readily visible in the finer 

grained metapelitic rocks of the CVGS, but it is poorly developed or absent in the massive impure limestones. Aligned 

biotite flakes are locally found parallel to the L4

 lineation, 

especially in the Gile Mountain Formation (fig. 13D), as are 

pressure shadows around garnet (see section on Metamorphism). Regionally, S4

 is the foliation that forms the “cleavage 

arch” of White and Jahns (1950).

N

A

B

D

L3

L4

C

S3

S4

Figure 13

Zones I–III

Pole to S4

 (n = 219)

L4

 lineation (n = 276)

Mean L4

 attitude: 359°, 31°

EXPLANATION

Figure 13. Stereonet and photographs of S4 and L4 fabric. A, Stereonet of poles to S4 and L4 lineations, mostly from Zone III. 

Note the concentration of poles to S4

 shows preferred northwestern and northeastern strikes with northeastern and 

northwestern dips, respectively. Data are plotted using Structural Data Integrated System Analyser (DAISY 4.01) software 

by Salvini (2004). North is marked by “N,” and the number of data points is indicated by “n.” B, Photograph showing crosssectional view of conjugate box-type F4

 folds in impure limestone of the Waits River Formation; view is to the north, west is 

to the left. C, Photograph showing cross-sectional view of typical northeast-striking and northwest-dipping S4

 cleavage and 

steeply dipping S3

 cleavage in the Waits River Formation; view is to the north, west is to the left. D, Photograph of crosssectional view onto the plane of S3

 showing L3 and L4 lineations; view is to the west, south is to the left. The L3 lineation 

shows the intersection of bedding and S3

 foliation in the Gile Mountain Formation. The light-colored horizon on top is 

psammitic, and the gray horizon is pelitic. The L4

 lineation is defined by crenulations and aligned biotite flakes. 
Structural Geology 23

Fifth-Generation Foliation—S5

The fifth-generation foliation (S5) is weakly developed 

cleavage or kink bands with associated crenulation lineations 

(L5) and rarely developed outcrop-scale folds. S5 occurs sporadically in Zone III and rarely occurs in the western zones. 

The S5 foliation is the third-generation fabric in the CVGS; 

thus it is also referred to as “Acadian S3.” The S5 cleavage is 

recognized in areas where a clear L4 crenulation lineation was 

overprinted by the S5 cleavage or an L5 crenulation lineation (fig. 14) or in places where F4

 axial surfaces are broadly 

warped into upright folds. In many places, only the L5 crenulation lineation was visible at the outcrop, and it was difficult 

to clearly identify the orientation of the plane of S5. The S5/L5

fabric is only readily visible in the finer grained metapelitic 

rocks of the CVGS, and it is not developed in the massive 

impure limestones. Limited structural data show variable 

orientations for S5 and gently plunging northeast-southwest L5

lineations (fig. 14). Regionally, S5 is the dome-stage foliation 

(Woodland, 1977; Fisher and Karabinos, 1980; Offield and 

others, 1993; Walsh, 1998; Ratcliffe, 2000a,b).

Shady Rill Fault

Two significant ductile faults occur in the map area: the 

Shady Rill fault and the Dog River fault zone. The Shady Rill 

fault (SRF) is mapped as an overturned conjectural thrust fault 

that separates the Dumpling Hill belt from the Wrightsville 

belt. The presence of the SRF is inferred by four lines of evidence: (1) The northwest-trending early folds and fabric (D1

) 

and quartzite-rich unit (OЄmdh) found in the Dumpling Hill 

belt could not be mapped to the east across the SRF; (2) mafic 

rocks found in the Wrightsville belt are absent in the Dumpling Hill belt; (3) the interlayered green and dark-gray phyllite 

unit of the Moretown Formation (OЄmw) terminates to the 

south as if truncated; and (4) the mapped contact is parallel 

to a zone of penetrative foliation with consistent northwesttrending lineations. Although similar metasedimentary rocks 

occur on both sides of the SRF, they differ in the absence of 

mafic rocks and the greater abundance of quartzites to the 

west. The absence of mafic rocks in the Dumpling Hill belt 

does not alone provide evidence for the fault, but may suggest 

that the two zones of the Moretown Formation (OЄmdh and 

OЄm) were not originally continuous during both deposition 

of the volcanic and volcaniclastic rocks and intrusion of the 

dikes. More significantly, the mapped trace of the SRF is 

parallel to the dominant foliation in the rocks and appears to 

be related to the S2 (Taconian) foliation. The metadiabase and 

greenstone dikes found in the Wrightsville belt postdate the S2

foliation and predate the S3 foliation, and, if the absence of the 

dikes to the west is related to transport, then the SRF might 

have experienced some movement during D3 time. The dominant fabric is penetrative near the SRF; however, it is not as 

readily apparent as the D3 deformation in the Dog River fault 

zone. We hypothesize that the SRF was initially a Taconian, D2

or earlier, east-dipping thrust fault that juxtaposed the Wrightsville belt over the Dumpling Hill belt. We cannot rule out the 

possibility that juxtaposition, or possible reactivation of the 

SRF, occurred during Acadian D3 deformation. The contact 

was subsequently rotated through the vertical to its current 

westward dip during later Acadian deformation.

Figure 14

N

A B

L3

L4

L5

Zones I–III

Pole to S5

 (n = 6)

L5 lineation (n = 20)

EXPLANATION

Figure 14. Stereonet and photograph of S5 and L5 fabric. A, Stereonet of poles to S5 and L5 lineations. Data are plotted 

using Structural Data Integrated System Analyser (DAISY 4.01) software by Salvini (2004). North is marked by “N,” and 

the number of data points is indicated by “n.” B, Photograph of cross-sectional view onto the plane of S3 showing three 

lineations (L3, L4, and L5) in the Waits River Formation; view is to the west, south is to the left. The L3 lineation shows the 

intersection of bedding and S3 foliation, and L4 and L5 are crenulations. 
24 Bedrock Geologic Map of the Montpelier and Barre West Quadrangles, Washington and Orange Counties, Vermont

Richardson Memorial Contact-Dog River 

Fault Zone

In central Vermont, the Richardson Memorial Contact 

(RMC) is a boundary of controversial origin (tectonic versus 

stratigraphic) that separates pre-Silurian rocks to the west 

(Cram Hill and Moretown Formations) from Silurian and 

Devonian rocks to the east (Shaw Mountain, Northfield, and 

Waits River Formations). Richardson (1919) thought that the 

quartz-pebble conglomerates of the Shaw Mountain Formation 

sat unconformably on the Moretown and Cram Hill Formations, 

and later work supported this interpretation (Currier and Jahns, 

1941; White and Jahns, 1950; Doll and others, 1961). On the 

basis of mapping along the RMC in the Northfield-Montpelier 

area, Westerman (1987) suggested that the RMC corresponds to 

the “Dog River fault zone” along which pre-Silurian and Silurian rocks were juxtaposed. In central and southern Vermont, 

the RMC has been mapped as an unconformity, with only localized offset along syntectonic Acadian faults (Currier and Jahns, 

1941; White and Jahns, 1950; Armstrong, 1994; Martin, 1994; 

Walsh and others, 1994; Walsh and Ratcliffe, 1994a,b; Walsh 

and others, 1996a,b; Ratcliffe, 1996, 2000a,b; Ratcliffe and 

Armstrong, 1999, 2001). In Massachusetts, Hatch and Stanley 

(1988) interpreted the RMC equivalent as a décollement called 

the “surface of Acadian structural disharmony” (SASD). This 

interpretation was based primarily on the disparity in size and 

amplitude of first-generation Acadian isoclinal folds found in 

Silurian rocks (large high-amplitude) versus those found in the 

underlying pre-Silurian rocks (small low-amplitude). In addition, the SASD was rarely deformed by any of these isoclinal 

folds. Cross sections by Hatch and Hartshorn (1968) and Hatch 

and Stanley (1988) portray the isoclinally folded Silurian and 

Devonian rocks as a crumpled rug above a décollement at 

the top of the pre-Silurian section. Kim (1996) noted a thin 

(~5 cm), highly fissile, papery schist zone in the garnet schist 

of the Devonian Goshen Formation and lithologic truncations 

along the SASD in northwestern Massachusetts.

On this map, the best exposure of the RMC and Dog 

River fault zone occurs at a roadcut at Interchange 8 on I–89 

(fig. 15). The RMC is located near the southeastern end of 

the cut (fig. 15). The RMC separates light-green muscovitequartz-calcite-chlorite-plagioclase granofels with minor 

greenstone, which we map as Moretown Formation, from 

dark-gray carbonaceous phyllite of the Northfield Formation. 

The contact between the two formations is sharp and parallel 

to the S3 foliation (fig. 15C). The roadcut shows a strongly 

developed penetrative S3 fabric as the dominant foliation in 

all the rocks. Across the outcrop, however, the S3 fabric shows 

varying degrees of transposition of bedding and older fabrics. 

A zone of high strain and intense transposition associated 

with S3 extends from about 10 m east of the RMC to approximately 80 m west of the RMC, and this is the Dog River fault 

zone as we map it (fig. 15). In the Northfield and Waits River 

Formations more than 10 m east of the RMC, bedding is 

deformed into isoclinal F3 folds, but it is not transposed. As the 

RMC is approached from the east, bedding is progressively 

transposed in the Northfield Formation. From the western 

edge of the Northfield Formation to a point approximately 

80 m west of the RMC, bedding and at least one, perhaps two, 

older schistosities in the Cram Hill and Moretown Formations are transposed, and quartzite layers are preserved only 

as tectonic slivers. Thus, the RMC at this roadcut is a faulted 

surface within an approximately 90-m-wide fault zone, and the 

original unconformable relation is not preserved here. In the 

vicinity of the Dog River fault zone, L3 lineations consisting of 

quartz rods, stretched pebbles, and F3 fold axes are subparallel, indicating high strain and showing moderate plunges to 

the northwest (fig. 11). Away from the Dog River fault zone, 

the L3 lineations and F3 fold axes show greater variability and 

locally much shallower plunges to the north-northwest and 

south (fig. 11). 

Kinematic analysis of three oriented thin sections from 

the Interchange 8 roadcut shows west-side-up reverse relative motion. Type II S-C mylonitic fabrics (Lister and Snoke, 

1984) in all three samples show S-surfaces that correspond to 

the S3 fabric and microscopic C-surfaces that were not recognized in the field. Two samples (BW–1308A and BW–1308B, 

fig. 15) collected from a muscovite-carbonate-plagioclasechlorite-quartz granofels at the RMC and a muscovite-quartzcalcite-chlorite-plagioclase granofels 2 m west of the RMC, 

display Type II S-C fabrics, mica fish, and slightly asymmetric 

porphyroclasts with consistent west-side-up relative motion. 

The asymmetric fabrics are overprinted by late, post-tectonic 

carbonate and lesser muscovite porphyroblasts. The third 

sample, a micaceous quartzite from a tectonic sliver about 

8 m west of the RMC, shows similar microstructures with 

the same relative displacement but also contains many symmetrical fabrics indicative of flattening. Combined with the 

consistent northwest-trending lineations, the overall sense of 

displacement in the Dog River fault zone is reverse, left-lateral 

transpression, in agreement with the findings of Westerman 

(1987). Because the RMC currently dips steeply to the west, 

these kinematics either support west-side-up reverse motion 

or initial east-side-down normal motion along an east-dipping 

normal fault followed by rotation of the fault plane through 

the vertical by subsequent D4 or D5 deformation. 

Although the RMC is a pronounced tectonic boundary in 

most parts of the study area, it does not continuously follow 

the same lithologic contacts from north to south. We define 

the RMC in the study area sensu stricto as the base (western 

side) of the Shaw Mountain Formation where present or the 

contact between the Moretown or Cram Hill Formation and 

the Northfield Formation where the Shaw Mountain Formation is absent. Using this boundary as a reference, we found 

places where this surface does not exhibit strong tectonic 

overprinting like that found at Interchange 8. For example, 

at an outcrop of Shaw Mountain Formation cited by Cady 

(1956) on the eastern flank of Hersey Hill in the town of 

Calais, a metamorphosed coarse quartz-pebble conglomerate 

with isolated metamorphic rock fragments shows virtually no 

downdip stretching or flattening of pebbles that would indicate 

high-strain in a fault zone. We have seen the intensely sheared 
Structural Geology

25

DSn

DSwl1

OЄmg 

and

 OЄm

Ochi Ochr

Ochi Ochi

Ochq

Ochq

Ochq

Ochq

Ochq

Ochi

Richardson

Memorial

Contact

Zone of shearing parallel to S3 (Acadian S1)

(Dog River fault zone)

NW SE

Approximately 80 meters wide

Waits River Formation (Devonian and Silurian)—

Interbedded gray phyllite and limestone

Northfield Formation (Devonian and Silurian)—

Dark-gray phyllite

Dark-gray to black phyllite

DSwl1

DSn

—Richardson Memorial Contact—

Cram Hill Formation (Ordovician)

Interlayered gray, silvery-gray, and gray-green phyllite

with thin quartzite

Ochi

Ochq Quartzite

Moretown Formation (Ordovician and Cambrian)—Light-green granofels and greenstone 

Ochr

OЄmg

and

OЄm

Area of C

EXPLANATION

AB

C

S3

S4

RMC

BW–1308A

OЄ

BW–1308B

mg and OЄm

DSn

S4

S0 ) , Cross-sectional sketch (A B and A Figure 15.

and composite panoramic photograph (B) of the roadcut across the Richardson Memorial Contact (RMC) and Dog River fault zone at Interchange 8 on I–89. C, Photograph showing the RMC in detail 

 foliations. and S4 and the orientation of the S3

See text for discussion.
26 Bedrock Geologic Map of the Montpelier and Barre West Quadrangles, Washington and Orange Counties, Vermont

quartz-pebble conglomerates of the Shaw Mountain Formation that mark the Dog River fault zone south of Montpelier 

(Westerman, 1987), and the level of strain observed on Hersey 

Hill is not comparable. Although the exact position of the 

fault zone is not known at Hersey Hill, the lack of tectonic 

overprint in the conglomerate suggests that the fault zone was 

either deflected to the east into the Silurian and Devonian 

rocks or that it has ended. On our map we terminate the Dog 

River fault zone just north of Horn of the Moon Pond in East 

Montpelier because we were unable to clearly map the strong 

tectonic overprint any farther north. Admittedly identifying 

fault zone fabrics in the relatively monotonous CVGS rocks is 

difficult. We think it is reasonable to assume that the relatively 

undeformed metaconglomerates of the Shaw Mountain Formation were unconformably deposited on the underlying Cram 

Hill Formation. Thus, the RMC as an unconformity and the 

Dog River fault zone are not always coincident. Currier and 

Jahns (1941) mapped the RMC in Northfield and found that 

the unconformity was both folded and faulted. This observation was also reported by White and Jahns (1950) and later 

confirmed by N.M. Ratcliffe (written commun., 2008).

The RMC in central Vermont is either an unconformity 

or an Acadian fault zone, and, in some places, it is both. In 

order to understand the tectonic history of this contact, it is 

critical to examine the geologic context of correlative Silurian 

lithologies from southern Québec where the deformation and 

metamorphic overprint of the Acadian orogeny are much less 

severe. In southern Québec, the contact between the Silurian 

units and the underlying pre-Silurian lithologies of the Dunnage and Internal Humber tectonic zones is predominantly a 

Late Silurian unconformity marked by basal quartz-pebble 

conglomerate (Lavoie and Asselin, 2004). The majority of 

these Late Silurian units grades upward from basal quartzpebble conglomerate to sandstone and siltstone to fossiliferous 

limestone (Lavoie and Asselin, 2004) making them nearly 

identical to the members of the Shaw Mountain Formation 

(for example, Currier and Jahns, 1941; Cady, 1956; Konig and 

Dennis, 1964). One of the most striking aspects of the configuration of the authochthonous Late Silurian units in southern 

Québec is that the St. Luc, Cranbourne, and Lac Aylmer 

Formations and Glenbrooke Group occur as outliers unconformably overlying pre-Silurian rocks west of the Devonian 

La Guadeloupe fault. This fault separates pre-Silurian rocks to 

the west from Silurian and Devonian metasedimentary rocks 

of the CVGS to the east (Cousineau and Tremblay, 1993; 

Tremblay and others, 2000; Lavoie and Asselin, 2004) and is 

a possible along-strike correlative to the Dog River fault zone 

because it occurs at the same stratigraphic boundary, the RMC. 

Whereas the basal contacts of the St. Luc and Cranbourne 

Formations and the Glenbrooke Group with the underlying 

pre-Silurian rocks are unconformable, the Lac Aylmer Formation contacts have a dual nature. The northwestern side of the 

Lac Aylmer Formation unconformably overlies Dunnage Zone 

lithologies; however, the southeastern side is coincident with 

the La Guadeloupe fault (for example, Cousineau and Tremblay, 1993; Tremblay and others, 2000). The Dog River fault 

zone and the La Guadeloupe fault both show a northwestsoutheast transport direction, but, unlike the Dog River fault 

zone, the La Guadeloupe fault dips to the southeast and shows 

high-angle east-over-west, northwest-directed relative motion 

(Tremblay and others, 1989; Tremblay and St.-Julien, 1990; 

Labbé and St.-Julien, 1989). Although the Acadian motion 

along the La Guadeloupe fault is reverse northwest directed, 

earlier motion along this fault may have been normal (Tremblay and Castonguay, 2002). According to Alain Tremblay 

(Université du Québec à Montréal, oral commun., 2006), the 

fault zone in the lower plate west of the La Guadaloupe fault is 

much wider because strain was preferentially partitioned into 

the Ascot Complex rocks. We see a similar relation in central 

Vermont where the fault zone is wider in the pre-Silurian rocks 

but the higher strain is recorded in the upper plate.

Brittle Structures

The planar brittle structures, or fractures, identified in 

this study are separated on the basis of whether or not they are 

related to an older fabric in the metamorphic rocks. Fractures 

that are parallel and related to older sedimentary or metamorphic fabrics due to structural inheritance occur along bedding, 

axial surfaces of folds, cleavage, compositional layering, 

schistosity, and veins. Fractures that cross the sedimentary or 

metamorphic fabric of the rocks include brittle faults, joints, 

and joint sets. The orientation of joints measured in this study 

includes those with trace lengths greater than 20 cm (Barton 

and others, 1993). Joints were measured subjectively using 

methods described in Spencer and Kozak (1976) and Walsh 

and Clark (2000), and the dataset includes the most conspicuous joints observed in a given outcrop. Fracture data (fig. 16) 

are plotted on stereonets (lower hemisphere equal area projections) and rose diagrams (azimuth-frequency) using the Structural Data Integrated System Analyser (DAISY 4.01) software 

by Salvini (2004). Rose diagrams generated with the DAISY 

software use a Gaussian curve-fitting routine for determining 

peaks in directional data (Salvini and others, 1999) that was 

first described by Wise and others (1985). The rose diagrams 

include strike data for steeply dipping fractures (dips ≥60°, 

after Mabee and others, 1994).

Five minor outcrop-scale faults were observed in the area 

and are shown by strike and dip symbols on the map. Faults 

were identified by slickensided surfaces. Many other fractures 

are identified in the accompanying database and are not plotted on the map with individual strike and dip symbols. Joints 

and joint sets measured in this study include fractures with no 

displacement that are not clearly associated with parting along 

a preexisting structure in the rock, such as foliation, axial 

surfaces, cleavage, and so forth. Spacing of joint sets ranges 

from approximately 10 cm to 1 m with an average of 35 cm. 

Most joints are unmineralized, but a few contain trace patches 

of sulfide minerals, quartz, calcite, dolomite, or gypsum.

In the pre-Silurian rocks west of the RMC, the steeply 

dipping joints are dominated by throughgoing fractures that 
Structural Geology 27

All 

n = 2622

West of RMC

n = 558

East of RMC

n = 2064

All

n = 1906

West of RMC

n = 492

East of RMC

n = 1414

All (dip ≥60o)

n = 1706

West of RMC (dip ≥60o)

n = 271

East of RMC (dip ≥60o)

n = 1066

East of RMC (dip ≥60o)

n = 1435

All (dip ≥60o

)

n = 1273

West of RMC (dip ≥60o)

n = 207

Fractures Joints

Figure 16

foliation

foliation

foliation

foliation

foliation foliation

334o

, 36o

N N

N N N N

N N

N N N N

Figure 16. Stereonets (top) and rose diagrams (bottom) of fractures in the Barre West and Montpelier quadrangles. Stereonets 

show poles to all fractures and joints, contoured at 1 percent intervals. Rose diagrams only show strike of steeply dipping (dip ≥60°) 

fractures and joints. Data in the left column labeled “Fractures” include partings along bedding, axial surfaces of folds, cleavage, 

compositional layering, schistosity, veins, brittle faults, joints, and joint sets. Major trends labeled “foliation” include partings along 

axial surfaces of folds, cleavage, compositional layering, and schistosity. Data in the right column labeled “Joints” is a subset of the 

data on the left and include only brittle faults, joints, and joint sets. The number of data points in each diagram is indicated by “n.” 

RMC, Richardson Memorial Contact.
28 Bedrock Geologic Map of the Montpelier and Barre West Quadrangles, Washington and Orange Counties, Vermont

cross entire outcrops with trace lengths on the 

order of meters and tend to cross the foliation 

at a high angle (fig. 17B); these joints are called 

“crossing” fractures (Barton and others, 1993). 

In the Silurian and Devonian rocks east of the 

RMC, crossing fractures are less abundant than 

to the west, and many of the fractures abut the 

bedding (fig. 17A), or abut the foliation; these 

joints are called “abutting” fractures (Barton 

and others, 1993). The difference in relative 

abundance of crossing and abutting fractures is 

probably a function of rock homogeneity. West 

of the RMC, the rocks are macroscopically 

more homogeneous and contain less distinct 

layering and thus less contrast in mechanical properties. East of the RMC, the rocks are 

dominated by the mechanically heterogeneous 

Waits River Formation with its well-foliated 

interbedded slate and phyllite horizons alternating with more massive impure limestone beds.

Fracture data for the area (fig. 16) show 

that fractures are dominated by three trends: 

(1) steeply west-dipping, north-northeaststriking parting along the foliation, (2) steeply 

dipping, west-northwest-striking joints, and 

(3) gently to moderately northeast-dipping 

and northwest-striking sheeting joints. For the 

analysis, the data were separated into locations east and west of the RMC according to 

the distribution of crossing and abutting joints 

and into fractures and joints for the purpose of 

illustrating the strong fracture trends found in 

the rocks due to parting along the metamorphic 

foliation. Despite the recognized difference 

in the distribution of crossing and abutting 

joints across the RMC, the overall fracture and 

joint trends are similar across this boundary 

(fig. 16). The principal difference in fracture 

trends across the RMC is the abundance of 

moderately northeast-dipping and northweststriking joints in the rocks of the Moretown 

and Cram Hill Formations. This trend is similar 

to the strike and dip of the S4 cleavage (compare with fig. 13A), and it is possible that the 

joints measured in this orientation west of the 

RMC may represent a structural weakness in 

the rocks that was not distinctly recognized in 

the field as the S4 cleavage.

A

B

Limestone

Limestone

Schist

Figure 17

Figure 17. Photographs of joint types. A, Abutting joints in the Waits River 

Formation. Joints present in the schist terminate at the contact with the 

limestone on State Route 63 in Barre (station BW–1137). B, Northwest-striking 

and northeast-dipping joints (white arrows) and north-northwest-striking, 

steeply dipping crossing joints (yellow arrows) in the Moretown Formation at 

Interchange 8 on I–89 (station 62402–2). Fractures parallel to the foliation are 

apparent in both photographs.
Metamorphism 29

A summary diagram for steeply dipping fractures in the 

area (fig. 18) shows the Montpelier and Barre West quadrangles on a shaded relief map of central Vermont. Fracture 

analysis shows that the principal fracture trends are dominated 

by foliation-parallel parting both east and west of the RMC, 

and this north-northeast topographic grain is clearly visible 

on the shaded relief map. West of the RMC, kilometer-scale 

west-northwest-trending drainage patterns and valleys are 

probably associated with the principal trends of crossing joints 

measured in our study. East of the RMC, however, the westnorthwest trends are not as prominent, and we speculate that 

the more subdued topographic expression is the result of the 

abutting nature of the joints. Thus the distinct layering in the 

Silurian and Devonian rocks, and especially the well-layered 

Waits River Formation, inhibits the formation of kilometerscale crossing joints and joint sets.

Metamorphism

The rocks in the Montpelier and Barre West quadrangles 

were metamorphosed to greenschist facies conditions. Rocks 

in the CVGS experienced peak metamorphic conditions in 

the garnet zone, and the pre-Silurian rocks experienced peak 

metamorphic conditions in the biotite zone. Laird and others 

(1984) presented petrologic data that showed that both Ordovician (Taconian) and Devonian (Acadian) metamorphic events 

were preserved in the pre-Silurian rocks west of the RMC, 

whereas only Devonian metamorphism affected the Silurian 

and Devonian rocks east of this discontinuity. With the exception of the Belvidere Mountain, Tillotson, and Worcester mafic 

complexes (for example, Laird and others, 1984, 1993, 2007; 

Gale, 1986; Kim and others, 2001), the pre-Silurian lithotectonic belts of northern Vermont underwent biotite-garnet-grade 

Taconian metamorphism followed by muscovite-chloritegrade Acadian retrogression. Devonian metamorphism in the 

CVGS is mostly biotite to garnet grade but locally reached 

sillimanite grade (Doll and others, 1961; Laird and others, 

1993). On the basis of 40Ar/39Ar ages, the Taconian metamorphism in central and northern Vermont occurred around 471 

to 460 Ma (excluding the Belvidere Mountain Complex), and 

the Acadian metamorphism occurred around 397 to 350 Ma 

(Sutter and others, 1985; Spear and Harrison, 1989; Laird and 

others, 1993).

Laird and others (1984, 1993, 2007) used the geochemical composition of amphiboles (Na M4 and Tschermakite 

substitutions) in mafic rocks from central and northern Vermont to delineate high (~12–14 kilobars (kb)), medium-high 

(~9–11 kb), medium (~5–7 kb), and low (~3–4 kb) pressure 

facies series. The vast majority of the mafic rocks analyzed 

were from the pre-Silurian section. It is important to note that 

all amphiboles (actinolite) analyzed from metadiabases of the 

Wrightsville belt in the Montpelier and Barre West quadrangles fell in the low pressure facies series. Amphiboles from 

mafic rocks in the central part of the CVGS south of the field 

area also plot in the low-pressure facies series. Amphiboles 

analyzed by Laird and others (1984, 1993) from lithotectonic 

belts to the west of the Moretown Formation in north-central 

Vermont fit in the medium- and medium-high-pressure 

facies series.

The greenschist facies metamorphism that affected 

rocks of the Montpelier and Barre West quadrangles during 

the Taconian and Acadian orogenies were directly associated 

with discrete deformational events. Five deformational events 

affected the pre-Silurian section (D1–D5), whereas three deformational events affected the Silurian and Devonian section 

(D3–D5).

The greenschist facies rocks of the pre-Silurian Wrightsville and Dumpling Hill belts are dominantly chloritemuscovite grade with biotite present locally. Although no 

almandine garnet was found in either the Wrightsville or 

Dumpling Hill belts in the map area (spessartine is probable 

in coticules), Gale and others (2006) found isolated garnetbearing layers in parts of the Moretown Formation to the 

west. The first two deformation events (D1 and D2) in the 

pre-Silurian section produced isoclinal folds with penetrative axial planar foliations defined by alternating domains 

of quartz-feldspar (QF) and chlorite-muscovite±biotite (M). 

These two deformational events and the associated greenschist 

facies metamorphism are assumed to be Ordovician or, at 

least, pre-Devonian.

The third deformational event (D3) to affect the preSilurian rocks was the first event in the Silurian and Devonian 

rocks east of the RMC and is Devonian in age. The locally 

penetrative axial planar S3 foliation is composed both of 

reoriented S1/S2 micas and newly formed micas. S3 is more 

penetrative in the vicinity of the Dog River fault zone and is 

the dominant fabric in Silurian and Devonian rocks. 

In the Montpelier and Barre West quadrangles, the 

Acadian garnet isograd divides the CVGS into two northnortheast-trending belts. The garnet isograd is mapped on the 

distribution of the garnetiferous phyllite in the Waits River 

Formation (DSwg); west of this limit the rocks experienced 

subgarnet grade metamorphism during the Acadian (east of 

the RMC) or during both the Acadian and Taconian orogenies 

(west of the RMC). In the garnet zone, inclusion patterns in 

garnet and biotite porphyroblasts indicate that both minerals grew after the development of the S3

 foliation but prior 

to or during the early stages of S4 cleavage development 

(fig. 19A,B). Microscopic study shows that the S4 foliation 

wraps around garnet porphyroblasts in most samples, indicating that cleavage development or modification continued 

after porphyroblast growth. One sample shows deformed S3

inclusion trails in garnet indicating that porphyroblast growth 

began after the onset of D4 deformation (fig. 19A). During D4, 

quartz pressure shadows formed around biotite and garnet, and 

the pressure shadows are aligned with the L4 crenulation lineation. These findings indicate that peak metamorphic conditions 

occurred after D3 but prior to the completion of D4 deformation. Subsequent to D4

, some garnet porphyroblasts exhibit 

static retrogression to chlorite (fig. 19C,D). In these places, 
30 Bedrock Geologic Map of the Montpelier and Barre West Quadrangles, Washington and Orange Counties, Vermont Barre Montpelier

RMC

Winooski River

5 KILOMETERS

00

5 MILES

5 KILOMETERS

00

5 MILES

Montpelier

RMC

Winooski River

Barre

Crossing joints and parting along foliation

Abutting joints and parting along foliation

Foliation

Crossing 

joints Abutting

joints

Figure 18

A

B

) of fracture types and principal fracture trends in the area of the Montpelier and Barre West quadrangles. 

.vcgi.org) hillshade dataset generated from the USGS National Elevation Dataset (NED). 

) and interpretive summary diagram (

B Shaded-relief map (

A

ermont Center for Geographic Information (http://www

Figure 18.Shaded-relief map from the VRMC, Richardson Memorial Contact.
Metamorphism 31

Figure 19

S

3

gt + qz

bt

bt

bt bt

bt

bt

bt

qz

qz

qz

ms+qz+ch

ms+qz+ch

bt bt

S

4

S

3

S

4

qz

qz qz’

bt

qz

qz’

S ms+qz+ch

3

gt

ch+qz

crack

S

4

ms+qz+ch

ch+qz+ms

ch

ch

ch

qz

qz

S

3

S

4

ABCD

0.5 mm

BW–1226

BW–1072

BW–1100

BW–1152

0.5 mm

1.0 mm

1.0 mm

001

cleavage

Figure 19. Photomicrographs 

(left) and sketches (right) of 

porphyroblasts in the Acadian 

garnet zone. A, Garnet (gt) 

and biotite (bt) are post-S

3

and syn-S

4

. Garnet contains 

deformed S

3

 inclusion trails, 

and biotite contains quartz 

(qz) pressure shadows. 

Sample BW–1100, plane light, 

2.5X. B, Biotite is post-S

3

and syn-S

4

. Biotite overgrew 

quartz pressure shadows 

(qz') indicating incremental 

growth during D

4

. Sample 

BW–1072, plane light, 6.3X. C, Euhedral chlorite (ch) 

pseudomorph indicting static 

replacement of garnet. Note 

how S

4

 is deflected around 

the pseudomorph indicating 

cleavage developed after 

garnet. Sample BW–1152, 

plane light, 2.5X. D, Similar to 

C, but garnet is completely 

replaced and basal 001 

cleavage in chlorite is aligned 

with relict crystal faces of 

garnet indicating chlorite 

growth took place after D

4

. 

Sample BW–1226, polarized 

light, 6.3X. ms, muscovite.
32 Bedrock Geologic Map of the Montpelier and Barre West Quadrangles, Washington and Orange Counties, Vermont

chlorite formed euhedral, undeformed pseudomorphs after 

garnet and, locally, some chlorite grew in sheets with the basal 

001 cleavage subparallel to the shape of the original garnet 

crystal faces (fig. 19C,D). Because the chlorite in the garnet 

pseudomorphs is undeformed, this period of retrogression 

occurred after D4 and may have occurred after D5, although no 

fabrics associated with D5 were observed microscopically.

Regionally, other workers have reported similar results to 

our findings, with the exception that peak Acadian metamorphism in eastern Vermont, toward the core of the Acadian high, 

locally outlasted what we consider D4 deformation. In the area 

of Acadian doming in the Strafford-Willoughby arch in eastern 

Vermont, Menard and Spear (1994) found that staurolite and 

kyanite grew after D4 at temperatures of approximately 550 to 

600 °C. In the Royalton area, Woodland (1977) found that biotite growth postdated D3

 but predated D4 and D5, garnet growth 

predated D5 and in part predated D4, and staurolite and kyanite 

predated D5. In the Hartland area, Walsh (1998) reported that 

garnet porphyroblasts grew syn-D4 to post-D4. In the Chester dome, Ratcliffe (2000a, p. 17) reports that peak Acadian 

metamorphic assemblages grew syn-tectonically with respect 

to his “. . .northeast- and northwest-trending cleavages,” which 

probably correspond to either our D4 or D5 structures.

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