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GEOLOGY
OF
THE MEMPHREMAGOG QUADRANGLE
AND THE SOU'I'HEASTERN PORTION
OF THE IRASBURG QUAI)RANGLE
VERMONT
CHARLES G. DOLL
VERMONT GEOLOGICAL SURVEY
CHARLES G. DOLL, State Geologist
Published by
VERMONT DEVELOPMENT COMMISSION
MONTPELIER, VERMONT
BULLETIN NO. 3 1951

TABLE OF CONTENTS
PAGE
Abstract .• 7
Introduction ....................... 8
General Statement ........... 8
Location ......................... 8
Acknowledgments .................... 10
Previous work ..................... 10
Method of investigation ................. 10
Physiography ....................... 11
Topography....................... 11
Weathering ....................... 12
Drainage ........................ 12
Glaciation ....................... 13
Sedimentary rocks ..................... 15
General statement .................... 15
Cram Hill formation ................... 16
General description .................. 16
Type locality ..................... 16
Distribution . . . . . . . . . . . . . . . . . . . . . . 16
Relative thickness .................... 17
Age......................... 17
Lithological detail ................... 17
Shaw Mountain formation ................ 18
Type locality ..................... 18
Distribution . . . . . . . . . . . . . . . . . . . . . . 18
Relative thickness ................... 18
Age......................... 19
Northfield slate ...................... 20
Type locality ..................... 20
Distribution . . . . . . . . . . . . . . . . . . . . . . 20
Age......................... 21

PAGE
Ayers Cliff formation . . . . . . . . . . . . . . . . . . . 22
General description . 22
Type locality ..................... 22
Distribution . . . . . . . . . . . . . . . . . . . . . . 22
Age ......................... 23
Barton River formation . . . . . . . . . . . . . . . . . . 25
Type locality ..................... 25
Distribution . . . . . . . . . . . . . . . . . . . . . . 25
Age ......................... 26
Slates ....................... 27
Phyllites ...................... 28
Quartites ..................... 29
Limestones ..................... 30
Schists ....................... 31
Irasburg conglomerate ................. 32
Westmore formation ................... 33
Type locality ..................... 33
Distribution . . . . . . . . . . . . . . . . . . . . . . 34
Age ......................... 34
Phyllites ...................... 35
Limestones ..................... 36
Quartzites ..................... 36
Schists ....................... 36
Irruptive rocks ...................... 37
The Bolton igneous group and associated granites ...... 38
Granite plutons ..................... 41
Sedimentary inclusions ................. 43
Age of the granites . . . . . . . . . . . . . . . . . . . 44

PAGE
Sills and dikes ...................... 45
Pegmatites ....................... 47
Quartz veins ...................... 48
Structure ......................... 49
General statement ..................... 49
Indian Point syncline . . . . . . . . . . . . . . . . . . . 50
Indian Point segment ................. 50
Brownington syncline .................. 51
North Neighborhood anticline .............. 52
Ware Brook thrust . . . . . . . . . . . . . . . . . . . . 52
En echelon reentrants . . . . . . . . . . . . . . . . . . . 55
Black River fault .................... 58
Summary of arguments for structural interpretations . 58
Minor structures . . . . . . . . . . . . . . . . . . . . . 60
Folds . . . . . . . . . . . . . . . . . . . . . . . . . 60
Faults........................ 62
Bedding ....................... 63
Bedding-cleavage relations ............... 64
Sinuosity of beds ................... 64
Plastic flow of the calcareous rocks . . . . . . . . . . . . 65
Boudinage ...................... 66
Linear element .................... 70
Metamorphism ...................... 71
Minerals ....................... 71
Chlorite ...................... 71
Biotite ....................... 72
Garnet ....................... 72
Andalusite ..................... 72
Staurolite ..................... 73
Sillimanite ..................... 73
Lime-silicate minerals ................ 73
Amphibole ..................... 74
Historical geology ..................... 74
Economic geology ..................... 77
References used ...................... 78

Illustrations
PLATE PAGE
1. Geological map and structure sections of the Irasburg-
Memphremagog area . . . . . . . . . . . . . . . In pocket
2. Weathering, glaciation ................ 82, 83
3. Photomicrographs of Barton River formation ...... 84, 85
7. Photomicrographs of Westmore formation ........ 92, 93
8. Photomicrographs of Westmore formation ....... 94, 95
9. Bolton igneous group, granites ............. 96, 97
10. Granites . . . . . . . . . . . . . . . . . . . . . . 98,99
11. Brecciated granite, folded sill, pegmatite, quartz vein . 100, 101
12. Quartz mass, folds ................. 102, 103
13. Drag-fold, shearing in limestone, marginal fault in granite,
longitudinal fault . . . . . . . . . . . . . . . . . 105 . 104,105
14. Wedge-shaped fracture in phyllite occupied by limestone,
bedding ..................... 106, 107
15. Bedding, boudinage . . . . . . . . . . . . . . . . 109 . 108,109
16. Bedding-cleavage relationships, sinuous limestone bed,
sheared flow fold .................. 110, 111
17. Folds, schist inclusion in limestone .......... 112, 113
FIGURE
1. Index map ......................9
2. Disrupted granite streamers ...............46
3. Pegmatite-granite age relationships ...........47
4. Ptygmatic folds ....................61
5. Boudinage . . . . . . . . . . . . . . . . . . . . . . . 67
6. Boudinage and faulted bed ...............69

GEOLOGY
OF
THE MEMPHREMAGOG QUADRANGLE
AND THE SOUTHEASTERN PORTION
OF THE IRASBURG QUADRANGLE
VERMONT
By
CHARLES C. I)OLL
ABSTRACT
Among six formations mapped, three are new and, therefore, described
in greater detail. They are the Ayers Cliff, Barton River, and Wcstmore
formations, and embrace the belt occupied by the Waits River formation.
More than 21,000 feet of strata ranging in age from Ordovician to
possibly I)evonian, constitute a variety of rock types exhibiting middle-and
high-grade metamorphism.
A quartz conglomerate basal to the Cram Hill formation has been
located, and the stratigraphic position of the Irasburg conglomerate is
identified with the base of the Barton River formation. The Northfield
slate continues as a distinct unit in Canada and lies below the Tomifobia
slates and limestones of Clark.
Prominent structural features of late Devonian origin are the plutons
composed of dark granite invaded by a light, coarser granite. On the
west shore of Lake Memphremagog the Devonian granites are intruded
by metabasic rocks consanguineous with those in the Owl Head Moun-tairi
region in Canada. The frequency of sills is related to the structures
in the sedimentary rocks. Milky quartz veins of large dimensions are
especially distinctive in the Barton River formation.
Northeast-trending folds and faults are related to the Acadian dis-turbance.
Northwest of the axis of the Brownington syncline and in-cluding
the tract containing the North Neighborhood anticline and

Indian Point syncline, the beds are predominantly overturned. The
symmetry of the folds has been disturbed by the piercement of intrusives.
The Ware Brook thrust, lying between the Northfield late and the
Ayers Cliff formation, continues as the Bunker thrust in Canada and is
traceable for more than 100 miles. A feature of importance associated
with this fault, is a window in the Cram Hill formation exposing Ayers
Cliff limestone. Genetically related to the Ware Brook thrust are the
en echelon reentrants representing flaws in fanlike arrangement with
respect to a major tectonic arc swinging toward the Gaspé from northern
Vermont. The Black River fault merges with a fault mapped in the
Tomifobia River valley in Canada which, projected northeastward,
coincides with the flaw in the Massawippi reentrant. Noteworthy are
the igneous masses on the southwest sides of the reentrants.
Superb examples of minor structures are impressive of their significance
in the structural development of the region. Their effects are cumulative
and are indicated by folds, faults, plastic flow, boudinage, and lineation.
INTRODUCTION
General Statement
Although small parts of the area described in this report received
early attention, much of the geology remained unknown. The area,
therefore, afforded an opportunity for detailed work which would serve
as a beginning in the correlation of Vermont rocks with those on the
other side of the International Border in Canada, thus adding to the
knowledge of the Appalachian folded belt in this region. A prime con-sideration
is the location of the area within a great tectonic are whose
geology is much better known to the southwest and northeast than it
is here at the greatest bend. The present work might serve as a nucleus
and reference for subsequent geological research in the region.
Location
The mapped area covers the Memphremagog quadrangle and a part
of the adjacent Irasburg quadrangle, in northeastern Vermont (Fig. 1).
On the Memphremagog quadrangle it touches upon the International
Boundary between longitudes 72 ° 00' and 72° 15' west, extending south
to latitude 44° 45' north. The adjoining portion on the west in the
Irasburg quadrangle, lies southeast of a northeast diagonal in the east
rectangle and includes the southeast rectangle.
8

74 73 72 71
-
I
- - - ••i
I / • GUECC 91,.-
- /
._/ I..• C
' T /
• ___
PBLIRLING TON dO /I(tB RY
I .4/ MOMTPELIER
.- —..
rMOIVT '
I R(/TI-AND R/vLRt/cr I N.H.
I :
CF//CORD
I's GTO OAEENC 2 '
— I I M14S3. I
g * __ I9 MILES
ARIAS MAPPING IN IRA$SURG -
MAPPED PROGRESS /.IEMPMQEMA GOG
FIG. 1—INDIX MA. AREA
47
46
45
44
43

AcbnowLedgments
• The writer is extremely grateful to the members of the Department
of Geology in Columbia University, who have shown an interest in this
problem. He is especially thankful to Professor Walter H. Bucher for his
stimulating and valuable guidance and to Professor Marshall Kay for
helpful suggestions. Dr. Robert K. Doten gave appreciable aid in the
early part of the study of the thin sections and, in this connection, the
writer wishes to express his thanks for the kindly advice given by Pro-fessor
S. James Shand. Professor Elbridge C. Jacobs has made available,
through the Vermont Geological Survey, financial aid for a part of one
field season; his interest in the work is appreciated. Clarence G. Bailey
and Harrison W. Cooke, Jr., assisted ably in the field for two seasons.
Appreciation is expressed to Mr. L. S. Walker for rock analyses.
Previous Worb
'F he earliest work pertaining to the geology east of the Green Moun-tains,
appears in the first and second reports of the Vermont Geological
Survey, by Adams (1845 and 1846, respectively). Thompson (1848)
describes anew the "calcareo-mica slate" of Adams. A more compre-hensive
study of the rocks was made by Hitchcock (1861), who termed
them "calciferous mica schist." Incidentally, Hitchcock (1861, p. 573)
conceived the granite to be metamorphosed stratified rock. Early studies
of the geology of the northern part of this region were made by Hall
(1871, and in Hitchcock, 1861, p. 719). Parts of the area mapped were
investigated by Richardson (1905-1906, 1907-1908, and 1911-1912) and
by Jacobs (1921-1922).
In the terrane bordering on the International Boundary in Canada,
pioneer work was done by Logan (1852 and 1863). Further studies were
completed by Ells (1894), Kerr (1923), and Clark (1934). More recently,
a geologic map accompanied by a brief description, by Ambrose (1943),
shows the rocks equivalent to the three new formations herein proposed,
undifferentiated.
Method of Iiwestigation
The greater part of six summers was spent in detailed mapping of the
Memphremagog and one-sixth of the adjacent Irasburg quadrangles,
comprising in all an area of 262 square miles. Reconnaissance studies
were made in surrounding regions, including Canada where some work
has been done.
10

The standard topographical map, enlarged to a scale of 3 inches to the
mile, served as a base in the field work. Most points and outcrops were
located by the method of resection, excepting in wooded tracts where
locations were established by means of pace-and-compass. Contacts
between formations were traced in detail. A total of 172 thin sections
were studied.
PHYSIOGRAPHY
Topography
The area is hilly to mountainous, rising from an elevation of 682 feet
at the shore of Lake Memphremagog in the northwestern part to the
greatest elevation of 2935 feet on the summit of Goodwin Mountain in
the southeastern corner. The southeasterly increase in elevation is con-trolled
largely by the progressively more resistant lithologies of the
sedimentary formations in that direction. The lowest sedimentary
surface is underlain by the relatively weak limestones of the Ayers Cliff
formation and the highest sedimentary surface by the dominantly
siliceous Westmore formation. By and large, stream dissection has
attained a mature stage in a topography modified by continental glacia-tion.
The topography reflects the rock types and structures, as, for example,
the domical granite hills extending northwestward from Elm Hill to
Salem Hill in the central igneous body, and the hogback ridges exempli-fied
by Shattuck and Dowling hills. The former reveal the massive
structure of the more resistant igneous rocks and the latter the bedded
structure of the more resistant among the steeply-dipping metamor-phosed
sediments. Barton Mountain is a conspicuous monadnock of
granite near the southern margin of the area.
Elevated terraces in the vicinity of Lake Memphremagog record
post-glacial uplift of the region. Two well-marked planes occur at
elevations of about 700 feet and 1000 feet to the north and east of the
city of Newport. The lower terrace is well-developed on the east side of
the lake at Indian Point and Lake Park. The higher level is present on
Pine Hill, directly east of Newport City, from whence it can be followed
around the north end of the central igneous body and southeasterly to
West Charleston. It probably represents, at least in part, an elevated
delta of the Clyde River which was built into glacial Lake Memphrema-gog
and has subsequently been dissected by stream erosion. Its surface
11

contains the lakes peripheral to the central igneous body and is deeply
incised by the Clyde River downstream from Salem Pond. Levels are
manifest on the east side of the Barton River Valley south of Coventry
Station at elevations of 760 feet and 960 to 1000 feet.
Weathering
Chemical weathering has penetrated along the bedding in the dipping
limestones to depths of more than 2 feet, leaving a rusty-brown siliceous
residue. On some limestone exposures it has etched a pock-marked
surface, the elongate solution cavities delineating the bedding (P1. 2,
fig. 1). Spheroidal weathering is well-developed in the mafic granites
on the slope east of West Charleston, and has produced subangular to
rounded "cobbles" wrapped in extremely fissile shells, in a dense, hard
phyllite in the Black River escarpment (P1. 2, fig. 2).
A rather unusual display of differential weathering occurs in a pasture
approximately half a mile northwest of Brownington Village (P1. 2, fig. 3).
A resistant, steeply-dipping stratum of dense, calcareous phyllite is here
separated into segments resembling a row of tombstones, and thus,
might aptly be termed tombstone weathering. Continued weathering
has opened the pronounced vertical joints, causing individual slabs to
become more or less isolated. The weaker adjacent layers lie concealed
under a mat of grass.
Drainage
The region is situated in the Memphremagog basin, from which the
drainage moves northerly to the St. Lawrence embayment. With the
exception of occasional "cross-overs," the main streams are subsequent
throughout the greater parts of their courses. The Clyde River meanders
over thick deposits of outwash material in its upper couise, but shows
adjustment to rock structure in the vicinity of West Charleston where it
flows through a picturesque gorge. Downstream from West Charleston
it follows the contact between the central igneous body and the Barton
River formation, curving around the northern border of the former and
then descending rapidly from Clyde Pond across the regional structure
in a series of cascades to the level of Lake Memphremagog. Two other
major streams controlled by geological structure are the Barton and
Black rivers, the latter following a faultline valley in the lower part
of its course. The Willoughby River and Brown ington Branch flow on
glacial deposits throughout their lengths, the former crossing the regional
12

trends of the bedrock. Waterfalls and rapids are not uncommon on the
small tributaries that descend rapidly from the uplands. Of greater
magnitude in the narrows of the major streams, they present spots of
inviting scenery, as at Coventry on the Black River and at West Charles-ton
on the Clyde River. The gorge of the Clyde River at West Charleston
is an example of stream derangement due to glacial action (Doll, 1941-
1942).
Excepting Johns River, which drains a restricted area north of Derby
Pond, and Brownington Branch, the important streams have their
sources in lakes, the Clyde River, in addition, flowing through a chain
of lakes along its course. Seymour Lake and Echo Pond, which extend
beyond the eastern margin of the quadrangle, discharge their waters
into the Clyde River at East Charleston (Island Pond quadrangle).
Noteworthy are the locations of Clyde, Derby, Salem and Brownington
ponds in depressions with elongation on the contact between the central
igneous body and the Barton River formation, indicating structural
control. Clyde Pond is supported by a dam built for hydroelectric power.
Glaciation
The effects of continental glaciation are quite evident in the region
generally. They appear as both erosional and depositional features, the
former best displayed on outcrops at the higher elevations.
Glacial striae, often accompanied by grooves, indicate a general
south-southeasterly movement of the ice, with local variations. On a
single exposure the measured striae range from S 400 E to S 23° W, in
consequence of the local topography. In places where the striae corre-spond
in direction to the structural trend of the sediments, the direction
of ice movement was probably guided by the flange- or rail-like edges of
the steeply-dipping, resistant strata, to which the plastic bottom of the
ice could have been molded. Such controlled glacial erosion could have
modified valleys now containing subsequent streams. Chatter marks
are sometimes associated with the striae on smoothed rock surfaces. A
striking profile of large-scale roches moutonnées is exhibited by the
southeasterly succession of eminences beginning with Barton Mountain
on the northwest and including May Pond, Valley, and Wheeler* moun-tains,
and Mt. Hor,* as viewed in a southwesterly direction from the
pasture on the 2160-foot divide northeast of Westmore Village. In their
*Lyndonville quadrangle.
13

profiles of maximum asymmetry, the relatively gentle stoss and cuffed
lee slopes illustrate clearly the southeasterly direction of glacial motion.
The northeast-trending Westmore mountain range of resistant rocks
is breached transversely by glacial troughs, of which some contain lakes
as, for instance, Crystal and Willoughby lakes. These erosional features
resemble closely the geomorphic pattern on Mount Desert Island,
Maine, described by Johnson (1925, pp. 95-99).
The southeastward trend of the Willoughby trough containing Lake
Willoughby, particularly the southern half in the Lyndonville quad-rangle,
is a fine example of effective glacial scouring. The most impressive
part of the trough lies between Mt. Pisgah* on the east and Mt. H or*
on the west, where the lake reaches a depth of 210 feet,t thus making
the difference in elevation of the lake bottom and the summit of Mt.
Pisgah some 1800 feet at this point. However, the location of the greatest
sounded depth of 308 feet,t i% miles to the north, and the huge talus
piles sloping well into the lake from the commanding cliffs on both sides,
suggest that overdeepening had added, at least, several hundred feet
to the relief here before glacial and colluvial deposition. State Highway
No. 5A is located for approximately 2 miles on forested talus along the
east side of the lake. Incidentally, the highway affords a choice view
of the imposing cliffs of the U-shaped trough, where it approaches the
beach from the south at the south end of the lake. Jacobs (1919-1920,
p. 297) has interpreted the Willoughby trough as a grahen modified by
glacial erosion.
Deposits of glacial till and stratified drift are strewn over the area.
Thick boulder clay, underlain in places by intercalated sands and
laminated clays, is exposed in high banks along the Willoughby River.
In the river bank at Evansville an iron-stained sand layer between
laminated clays exhibits thin laminations, especially at the border of a
partially cemented seam separating 3 inches of coarser sand below from
13 inches of finer, somewhat clayey sand above. The sand is cross-bedded,
and above the cemented seam it is folded in addition. The de-positional
sequence indicates the existence of a glacial lake dammed up
by the ice front into which boulder clay was dumped during a temporary
advance of the ice. The deformation of the upper lake beds below the till
is apparently due to the unequal loading of the glacial till.
Glacial erratics are scattered over the whole region. They are of many
*Lyndonville quadrangle.
tVermont Lake Studies project, Vermont Geological Survey, Summer, 1948.
14

varieties and sizes, some of enormous bulk and weight overlooking the
valleys from the higher elevations (P1. 2, fig. 4). In addition to those of
local origin are erratics that have been transported for known and un-known
distances, but all showing the direction of glacial motion. Es-pecially
significant are erratics of the Bolton lavas from the Owl Head
Mountain region in Canada on the west side of Lake Memphremagog.
SEDIMENTARY ROCKS
General Statement
Within the area covered, the sedimentary rocks can be divided into
six formations comprising a variety of rock types, with a total thickness
of approximately 21,400 feet.
They have been named, from top to bottom:
SUMMARY TABLE
Silurian or
Lower Devonian
Silurian
Westmore formation
Barton River formation
Mainly phyllites; schists,
limestones and quartzites.
Slates and limestones locally
abundant; schists, quart-zites,
basal conglomerate.
TJNCONFORM ITY
Ordovician
Ayers Cliff formation Gray to blue-gray lime-stones,
arenaceous lime-stones,
minor slates.
Northfield Slates Gray to black slates, thin
sandy and calcareous beds.
UNCONFORMITY
Shaw Mountain formation Basal quartz conglomerate,
sandy and tuffaceous rocks,
thin calcareous beds.
UNCONFORMITY
Cram Hill formation Dominantly slates; basal
conglomerate, quartzites,
schists, tuffaceous rocks,
greenstones.
Three formations are discussed at greater length, because they are
herewith proposed for the first time. They range from Ordovician to
15

possibly middle Silurian or even early Devonian. Metamorphism has
not only altered their compositions to varying degrees by recrystalliza-tion,
but also has coarsened their textures in many cases. The following
descriptions of the sedimentary rocks include petrographic details.
Cram Hill Formation
GENERAL DESCRIPTION
The term Cram Hill formation was given by Currier and Jahns (1941,
p. 1493) to a series of slates, phyllites, schists and quartzites in central
Vermont. The complete breadth of outcrop of the Cram Hill formation
does not appear on the map, because its western limit has not been
mapped in this area. However, the writer has made a traverse up the
bed of Ware Brook, finding a quartz conglomerate at the South Newport
road crossing, composed of saccharoidal quartz pebbles drawn out in a
lustrous, blue-gray, schistose matrix. This conglomerate probably
marks the base of the Cram Hill formation, as it underlies rocks ex-hibiting
typical Cram Hill lithology. It is very probably equivalent to
the quartz conglomerate reported from the western edge of the town of
Irasburg by Richardson (1911-1912, p. 150). In central Vermont green-stone
intrusivcs are said to occur near the bottom of the formation
(Currier and Jahns, 1941). From Walker Pond northward the formation
is in contact with granite. The Cram Hill formation is regarded here as
the upper part of the Missisquoi schist of Richardson (19 19-1920, p. 62).
TYPE LOCALITY
The Cram Hill formation has its type locality in central Vermont
(Currier and Jahns, 1941, p. 1494).
DISTRIBUTION
The Cram Hill formation has been followed from the southwest corner
of the east rectangle (Irasburg quadrangle) northward to State Highway
No. 105 leading to Newport City. North of this point the formation is
concealed under surficial deposits and the waters of Lake Memphrema-gog.
At Walker Pond it borders on the granite which underlies Coburn
Hill to the northwest. On the southeast side of Walker Pond and again
on the lower slopes of Coburn Hill on the Newport City farm, the slates
of the Cram Hill formation are infolded with the granites. The formation
is best exposed in the highlands from West Hill southward.
16

RELATIVE THICKNESS
From the base of the Shaw Mountain conglomerate in Ware Brook
to the horizon of greenstone intrusives the formation has a thickness of
approximately 1000 feet, but from the base of its own conglomerate
to the base of the Shaw Mountain conglomerate it is 2630 feet thick.
At State Highway No. 105 directly northeast of Walker Pond the thick-ness
is between 500 and 600 feet. The intense crumpling and shearing
of these rocks preclude an accurate estimate of thickness, hence the
thicknesses indicated above are approximations.
AGE
Currier and Jahns (1941, P. 1496) placed the Cram Hill formation in
the Ordovician. The writer concurs in this view, which identifies this
formation with the fossiliferous Magog slates of Trenton age (Ruede-mann,
1919, pp. 122-124, 130) at the Castle Brook locality west of
Magog, Quebec, and considers its stratigraphic position directly below
the Shaw Mountain formation yielding fossils with Ordovician affinities.
LITHOLOGICAL DETAIL
The Cram Hill formation is composed mainly of gray to black slates
which are more or less persistent throughout its thickness. The section
in Ware Brook begins with the basal conglomerate directly below black
crinkly slates including dark greenstone sills. Although much of the
lower half of the section is under cover, the visible exposures show a
black fissile slate intercalated with quartzites, greenstone sills and
tuffaceous rocks. The basal conglomerate is underlain by chlorite- and
quartz-mica schists, quartzites and greenstones of undetermined age.
In the middle of the section gray, argillaceous slates grade downward
into black carbonaceous slates, which in turn give place to thin, gray
calcareous beds forming the 10-foot face of a waterfall. Argillaceous
slates again appear above the waterfall. The horizon of calcareous beds
is regarded by the writer as a window of the Ayers Cliff formation on the
basis of lithologic similarity and stratigraphic position and is discussed
in a later section. Stratigraphically below the argillaceous slates at the
crest of the waterfall are sericite and chlorite schists, quartzites and
greenstone intrusives. The formation is also intruded by granite sills
and dikes; granite commonly cuts the formation along its outcrop, as
on the south end of West Hill.
The upper part of the section consists of slates which are interbedded
17

with quartzites, grits, tuffaceous rocks and greenish-gray breccias, the
innumerable fractures of which are coated with brown iron stain.
Because of their occurrence within the Cram Hill formation and its
observed northward extension, the greenstones are identified with those
on the west side of Lake Memphremagog. The granite intrusions are
considered by the writer to be of the same age as the granites generally
in the region mapped; they are certainly well within the area occupied
by the major granite plutons.
Shaw Mountain Formation
GENERAL DESCRIPTION
The name Shaw Mountain was given by Currier and Jahns (1941, p.
1496) to a formation of interbedded conglomerate, tuffs, and crystalline
limestones in the Barre, Vermont, region. Because of the occurrence of
a fossiliferous horizon in central Vermont, the formation becomes an
important stratigraphic unit. However, no fossils have been discovered
in this formation in northern Vermont.
TYPE LOCALITY
The type section is in central Vermont at the base of Shaw Mountain
DISTRIBUTION
The Shaw Mountain formation is traceable from a brookbed on the
slope southwest of Kidder School, northeastward to the hill directly
south of Walker Pond, a distance of 734 miles. It has good continuity of
outcrop from about half a mile southwest of Ware Brook to the brook
on the northeast side of Cleveland Hill, otherwise its exposures are
limited and interrupted. The conglomerate member of the formation is
well exposed where it is crossed by Ware Brook and gives the formation
topographic expression because of its resistance to erosion. The fine-grained
members higher in the formation are locally and poorly exposed.
RELATIVE THICKNESS
The Shaw Mountain formation is not uniformly thick along its strike,
but varies from 0 to about 500 feet in thickness. Since the tuffs and limy
layers are extremely poorly exposed, it is impossible to get a measure
of the true thickness of the formation. However, on the upper slopes
about a quarter mile north of Ware Brook a few scattered exposures of
the tuffs permitted a complete traverse across the outcrop of the forma-
18

tion, which gave a thickness of 300 feet. One mile north of Ware Brook
a thickness of 500 feet was measured. In the bed of a brook half a mile
south of Ware Brook the conglomerate is absent but the tuffs are 85
feet thick. In another brook bed southwest of Kidder School there are
about 45 feet of tuffs and no conglomerate. The formation is thickest
where the conglomerate is present and thins greatly where the con-glomerate
is missing. Because of its prominence where present, the thick-ness
of the conglomerate can be fairly accurately measured as, for
instance, where it is crossed by Ware Brook and is about 120 feet thick,
and in a brook on the south side of Cleveland Hill, where it is approxi-mately
200 feet thick.
Locally, along the strike, the formation thins visibly and even disap-pears
completely as, for example, on the northeast side of Cleveland Hill.
At a road junction half a mile north of this point it is 16 feet thick,
intricately sheared and full of cavities, some filled with a limonitic
powder and quartz grains. The variations in thickness of the Shaw
Mountain formation are due in part to original deposition, in which the
quartz conglomerate is the basal member in the thickest portions. How-ever,
brecciation, shearing, flow structure and faulting show that tectonic
forces have played an important part in altering the apparent thickness.
At the exposure southeast of Walker Pond, the formation is intensely
sheared and brecciated, and abundantly porous due to the weathering of
sulphides.
AGE
Currier and Jahns (1941, p. 1501) placed the Shaw Mountain formation
in the Ordovician, on the basis of crinoid stems found in a crystalline
limestone member.
LITHOLOGICAL DETAIL
The most conspicuous member of this formation, a quartz conglomer-ate
at its base, stands as a cliff on the north side of Ware Brook (Irasburg
quadrangle), contrasting with the lower relief to the east underlain by
the less resistant Northfield slates. Because of its prominent exposures,
the quartz conglomerate makes an excellent mapping unit, despite its
absence at intervals along the strike.
The pebbles consist of quartz through most of the thickness, but a
darker phase approximately one foot thick at the top contains pebbles
of a gray, banded slaty rock. Most pebbles are small, occasional ones
having a length of 5 to 6 inches. They are elongated as though subjected
19

to tectonic stress, possessing a schistosity which plunges steeply to the
northwest, as, for example, a foliation plunge of 700 N 50° W a mile
north of Ware Brook.
In places the conglomerate is cut by veins of milky quartz, generally
along the strike but occasionally crossing it. Thin black lenses along the
bedding are the result of the alteration of suiphides. Generally the
schistose matrix exhibits a limonite stain which penetrates between the
grains of quartz and sericite.
The quartz conglomerate is overlain by fine-grained, dark gray to
sugary white, laminated sandy and tuffaceous layers which weather
pinkish-tan to brown. These are usually poorly exposed owing to their
susceptibility to erosion. Thin calcareous zones appear to have irregular
and sparse occurrence near the top of the formation.
Northfield Slate
GENERAL DESCRIPTION
A group of slates as redefined by Currier and Jahns (1941, p. 1501)
and lying between the younger Ayers Cliff and older Shaw Mountain
formations, constitute the Northfield slate. Along its whole outcrop, it
is overturned toward the southeast and therefore appears to rest uncon-formably
on the Ayers Cliff formation. Convincing evidence, however,
proves the contact to be a thrust fault. As pointed out by Currier and
Jahns, the stratigraphic position of the Northfield slate has in the past
lacked satisfactory explanation, chiefly because this slate was incorrectly
correlated, by C. H. Richardson (1907-1908, p. 276), with slates defi-nitely
known to be within the Ayers Cliff and, very probably, the
Barton River formations.
TYPE LOCALITY
The type locality appears to be a quarry near the village of Northfield
I)I5TRIBuTI0N
Good exposures of the Northfield slate can be traced northward along
the prominent escarpment west of the Black River to the vicinity of
West Hill School. Northward they are concealed by recent deposits but
appear again southeast of Walker Pond, from whence they continue as
widely scattered low outcrops to Lake Memphremagog. Along this
traverse the formation is generally well exposed where it is crossed by
20

brooks flowing down the escarpment, especially where the escarpment is
steep. Its superior resistance to erosion when contrasted with the
neighboring Ayers Cliff formation, is readily seen in the topographic
expression of each.
RELATIVE THICKNESS
Throughout most of its outcrop the Northfleld slate varies between
850 and 900 feet in thickness. However, in the proximity of West Hill
School its thickness increases to about 1200 feet, but north of this point
the formation thins to about 860 feet as measured across the low hill
southeast of Walker Pond. Although the formation is poorly exposed
farther north, projections of outcrop data indicate that it apparently
thins noticeably to the shore of Lake Memphremagog, not as the result
of primary deposition, but of the gradual cutting out by a fault.
AGE
Since the Shaw Mountain formation is regarded as of Ordovician age,
the Northfleld slate which lies stratigraphically above it cannot be older;
because of fossil evidence in the underlying formation it is referred to the
Ordovician.
LITHOLOGICAL DETAIL
The Northfield slate is gray to black, weathering to yellow- or reddish-brown
on the cleavage surfaces. In places it contains bands of a lighter
gray sandy material which in some instances composes thin layers.
Calcareous beds occur at various horizons, becoming more abundant
toward the top of the formation. An occasional massive, black layer of
limestone is rich in pyrite grains, crushed in the course of deformation
and drawn out into glossy streaks in the direction of greatest elongation.
The slates are both smooth and highly crinkled on the bedding and
cleavage surfaces and not infrequently do they show excellent bedding
and cleavage relationships indicating the beds to be overturned to the
southeast.
A thin zone exhibiting small, white quartz pebbles was found in the
lower part of the formation where it is crossed by a brook on the north-east
side of Cleveland Hill. The pebbles which occur in a predominantly
limestone horizon are not at all abundant. This is probably equivalent
to the nodular zone described by Currier and Jahns (1941, p. 1502). The
basal conglomerate described by Currier and Jahns (1941, p. 1502) has
not been located in this area. It has been seen, however, at the base of
21

Bunker Hill in Canada, not far above the fault and about I j4 miles
southwest of Lake Massawippi. Its absence southward is probably due
to cutting out by the fault.
Ayers Cliff Formation
GENERAL DESCRIPTION
C. H. Richardson (1905-1906, p. 86, 115) applied the term Waits
River limestone to the calcareous members of a group of poorly differ-entiated
strata traversing the length of the state east of the Northfield
slate. Because a variety of other rocks are present the group became
known later as the Waits River formation (Currier and Jahns, 1941,
p. 1491). The writer has succeeded in delimiting three stratigraphic units
in this belt of rocks and has named them Ayers Cliff formation, Barton
River formation, and Westmore formation (Plate 1). Thus, because of
the new interpretation of these rocks, the altogether too comprehensive
terms Waits River formation (Currier and Jahns, 1941), and Tomifobia
formation (Clark, 1934), become inadequate. The Ayers Cliff formation
constitutes the westernmost of the newly proposed formations and
comprises a belt of impure limestones, calcareous sandstones, and minor
slates.
TYPE LOCALITY
The type section from which the formation receives its name, is in a
series of road cuts beginning half a mile west of the village of Ayers
Cliff at the south end of Lake Massawippi in Canada. Good exposures
within the area mapped may be seen at Coventry Falls in the Black
River, one-fourth mile northwest of Coventry Village, on Stony Hill 2
miles northwest of the village of Irasburg, and on the shore of Lake
Memphremagog at Lake Park. Other exposures are few and scattered.
DISTRIBUTION
The general paucity of outcrops is due to the inferior resistance of
the formation to erosion, consequently it lies generally in valleys. With
the exception of a short distance across the more resistant slates at the
nose of the Indian Point syncline at Coventry Village, the Black River
is confined to this formation. Despite the common lack of exposures, the
Ayers Cliff formation is traceable from the vicinity of Round Hill (Iras-burg
quadrangle) northward into Canada.
22

RELATIVE THICKNESS
Owing to the dearth of outcrops, the thickness of the Ayers Cliff
formation is difficult to measure, but from data available a thickness of
4500 feet is indicated.
AGE
The Ayers Cliff formation overlies the Northfield slate which has been
identified with the lower Tomifobia slates in Canada (Currier and Jahns,
1941, p. 1510). The Tomifobia slates which lie east of the Bunker thrust,
are reported to have yielded graptolites of Trenton age (Clark, 1934,
p. 12). In a later description they are called non-fossiliferous (Ambrose,
1943). Thus far no fossils have been found in the Ayers Cliff formation
in the area mapped. According to Clark (personal communication) the
graptolites were found in slates at the Tomifobia railroad station which
is far to the east of the expected stratigraphic position of the Northfield
slate in Canada. The writer's identification, based upon his own field
work and reconnaissance in Canada, shows that the Tomifobia locality
lies well within the area covered by his Ayers Cliff formation.
In the light of these facts, therefore, it appears that the correlation
of the Northfield slate with the Tomifobia formation is incorrect. The
Northfield slate in Canada composes the sole of the Bunker thrust at
Bunker Hill.
The Ayers Cliff formation is at least middle Ordovician (Trentonian)
or younger, since the Northficld slate over which it lies rests uncon-formably
upon the fossiliferous Shaw Mountain formation of middle
Ordovician age (Currier and Jahns, 1941, pp. 1500-1501).
LITHOLOGICAL DETAIL
The Ayers Cliff formation is commonly gray to blue-gray with inter-bedded
light and dark gray banded layers. The beds are generally thin,
slabby, fine- to medium-grained, and in places extremely fissile. At
Stony Hill they are thick, massive and contain considerable sand. The
lighter colored and white, marbleized varieties are normally coarser
grained than the darker, and are, in many places, friable due to the large
amount of sand present. The varying proportions of silica cause a range
from arenaceous limestones to calcareous sandstones. Some of the
friable limestones might more correctly be termed calcareous sandstones,
judging from a study of thin sections and the chemical analyses shown
in Table 1, even though the external appearance and vigorous efferves-cence
suggest limestone.
23

By and large, the formation possesses a fair degree of crystallinity due
to metamorphism. Certain horizons are especially dark and carbonace-ous,
lacking somewhat in luster. Throughout the formation are narrow
beds of dark gray slates and occasional phyllites which become more
abundant in the lower and upper parts, thus suggesting a gradational
contact and possible conformable relationship to the subjacent and
superjacent formations, both of which are composed largely of slates.
In thin section, calcite ranges from less than 15 per cent to as much as
65 per cent which, with proportionate differences in the amounts of
quartz, indicates that the formation consists of highly impure carbonate
rocks. Minerals present besides those already mentioned as composing
the major part of the rocks, are porphyroblasts of tremolite, chlorite,
muscovite, diopside and occasional titanite. The chlorites inclose zircons,
many of which are surrounded by pleochroic haloes; the chorites appear
to have replaced biotite. Diopside is developed in appreciable quantities
near igneous contacts, particularly in porcelainized zones. Suiphides in
parallel arrangement are confined largely to carbonaceous bands. Some
of the bands are rich in sericite and alternate with others abounding in
carbon. As is evidenced by the composition of these rocks, the original
sediments were probably calcareous sands and muds and impure lime-stones.
TABLE 1-Chemical analyses of limestones
A B C D H F G
Water 0.04 0.03 0.10 ..
Organic matter 0.52 0.26 0.64 0.55 0.64 0.40 0.46
Insoluble matter 76.78 39.34 65.56 33.63 62.98 38.19 32.23
Calcium carbonate 20.99 51.25 29.26 54.63 33.47 56.84 61.10
Magnesium carbonate 1.67 3.88 3.24 3.64 0.92 1.02 5.69
Iron & aluminum oxides 0.00 2.80 1.04 ..
Potassium silicate . . . . . . 1.15 trace 0.42 trace
Sodium silicate . . . . . . 5.97 trace 2.79 trace
Undetermined 0.00 2.44 0.16 0.70 1.99 0.34 5.52
A. Barton River formation. Southwest slope of Cargill Hill.
B. Barton River formation. Beside abandoned road, 1 3f miles west of Orleans.
C. Barton River formation. Road cut 3Y4 miles northwest of Barton Village.
D. Ayers Cliff formation. Shore of Lake Memphremagog, Lake Park.
H. Ayers Cliff formation. Stony Hill, 2 miles northwest of Irasburg Village.
F. Ayers Cliff formation. East shore of Lake Memphremagog at International Boundary.
G. Ayers Cliff formation. Black River Valley, 33 miles southwest of Newport City.
Analyses by L. S. Walker, Chemist in charge, Regulatory Service, Agricultural Experiment
Station. University of Vermont.
24

Barton River Formation
GENERAL DESCRIPTION
The Barton River formation consists of intercalated impure calcareous
rocks ranging from limy quartzites to limestones, amphibolitic layers,
slates, phyllites, quartzites and schists. They are gray to black, the
calcareous members containing thin, porcelainized bands parallel with
the bedding. Brown iron stain is a characteristic weathered coating,
particularly of the slates and phyllites.
Calcareous beds of the Ayers Cliff formation are involved with the
folds of the overlying Barton River formation and display the same
structural behavior. Thus a structurally conformable relationship
appears to exist between both formations. However, in the village of
Irasburg and southwestward the formation is underlain by a basal
conglomerate. This conglomerate was discovered by C. H. Richardson
in 1904 and named by him Irasburg conglomerate from the town of that
name. Because of its historic as well as geologic significance, this con-glomerate
is discussed in a separate section. The contact between the
Barton River and Ayers Cliff formations is largely under cover of recent
deposits, but at a few places along the strike, as on the west slopes of
Shattuck and Dowling hills and in a pasture at the south end of the
Newport airport 234 miles east-northeast of Coventry Village, they
occur in juxtaposition.
TYPE LOCALITY
The type locality of the Barton River formation is located in Newport
City in a low cut along the main highway to Derby and on the south
flank of Shattuck Hill. Here is a section exhibiting rock types typical of
the formation. South of the city of Newport in the five-mile long escarp-ment
bordering the Black River on the west, is a series of rocks composed
largely of slates which constitute the lower and basal portions of the
Barton River formation. Stratigraphically higher in the railroad cut,
immediately north of the business center in the village of Orleans, the
formation is dominantly limestone. In the bed of Stearns Brook at Tice
near the top of the formation, limestone is again the prevailing rock.
DISTRIBUTION
The formation covers the area between the Ayers Cliff and Westmore
formations, and in addition includes the youngest beds of the Indian
Point syncline. Like the Ayers Cliff formation it is continuous from the
25

southern border of the map-area northeastward into Canada, but with
outcrops more abundant. Exposures are scarce, however, along portions
of igneous contact zones where they lie concealed under a blanket of
Pleistocene and later sediments. The more resistant sections of the
formation form prominent ridges and steep slopes, a good example of
which is the cuffed escarpment on the west side of the Black River
extending from Newport City to Coventry Village. Because the forma-tion
is generally well exposed on the higher slopes of the Barton River
Valley, particularly on its west side, the name Barton River has been
adopted for it.
RELATIVE THICKNESS
The beds of the Barton River formation are prevailingly overturned.
Moreover, the examinable exposures in the entire width of outcrop
between the west slope of the Barton River Valley at Coventry Station
to the eastern boundary at Brownington Center, show inversion of the
strata. However, even in this succession of overturned beds the width of
outcrop is not the true measure of thickness of the formation, because
minor folds, flow structure and longitudinal shear give evidence of
thickening. The presence of these structures indicating intense deforma-tion
and, in addition, the discontinuity of exposures, make the determina-tion
of thickness an approximation at best. Notable additions to the
apparent thickness of the formation must be attributed to the many
sill intrusions.
Since the structural behavior of the strata here is very similar to that
in central Vermont, the writer has based his calculations of thickness
on the tried factor of 0.4 which was used by Currier and Jahns (1941,
p. 1495). Employing this average factor, the relative thickness of the
formation becomes 8800 feet.
AGE
Recognizable fossils have not yet been found in the Barton River
formation, but elongate lustrous markings on the bedding surfaces of a
thin horizon of fine-grained, medium-gray limestone in the bed of Trout
Brook in Brownington at the Coventry townline, might, from their
shapes, he suggestive of graptolites. In general, it may be assumed that
these markings represent nothing more than mineral streaks, especially
when they are found also on cleavage surfaces. The markings in the lime-stone
in Trout Brook, however, are of several distinctive shapes and are
restricted to the bedding surfaces. Furthermore, they are confined to one
26

narrow horizon, although the lithology of this horizon, where repeated
elsewhere in the formation, is barren. They bear a striking resemblance
to many of the individuals from the classic Castle Brook locality at
Magog in Canada, which are likewise mere smears but have the ad-vantage
of being associated with easily identifiable graptolithic im-pressions.
It may be that strong movements along the bedding planes
and fine recrystallization have eradicated the structural characteristics
of the original impressions and transformed them into featureless smears
with a predominantly parallel orientation. Doctor Ruedemann holds
similar markings in the rocks from the eastern part of the State to be
graptolites (1947, p. 63 and personal communication; Doll, 1943, p. 59).
E. C. Jacobs has reported "crushed graptolites" from the bed of Trout
Brook (1921-1922, p. 101).
Regardless of the interpretation of these markings, they are in such a
poor state of preservation that the age of the formation can be deter-mined
at present only by stratigraphic methods. The formation overlies
the Ayers Cliff formation unconformably, but, unlike it, is referred to
the Silurian, because the unconformity underlies a conglomerate exhib-iting
a variety of constituents along its strike that are believed to have
come from the Taconic highlands at the close of the Ordovician, thus
indicating a major break. This age assignment is also based upon the
position of the formation stratigraphically below strata yielding fossils
of Silurian age or younger. In this connection, it is significant that "slip
cleavage" is recorded in the strata of this formation but was not observed
in the beds of the underlying formation (P1. 5, figs. 1 and 2).
LITH0L0GIcAL DETAIL
The lower part of the formation consists of about 1600 feet of domi-nantly
slates and phyllites intercalated with lesser amounts of limestones
and calcareous schists. In the middle and upper parts the calcareous
rocks increase perceptibly, locally constituting the major rock type.
The top of the formation is characterized by a noticeable change to
siliceous and argillaceous rocks composed preponderantly of phyllites.
Five main rock types have been identified and include slates, phyllites,
quartzites, limestones and schists. Although these rocks are distributed
fairly uniformly throughout the formation, each is notably more abun-dant
locally. Certain beds of limestone are weathered to a depth of 2
feet and more, leaving a dark brown, crumbly, siliceous residue.
Slates—The slates are fine-grained, banded, and extremely fissile in
27

places. They are gray to black on fresh surface, but on the weathered
surface the color is characteristically a rusty brown due to iron stain.
Thin section study shows the bands to vary from those made up nearly
of pure quartz grains and carbonaceous material to those very rich in
biotite. There are a few bands of quartz and sericite. Biotite is present
both as fine scales and large masses. Fine-grained suiphides occurring as
stringers parallel to the banding, are possibly of syngenetic origin.
Sulphides also occur in large masses throughout the rock and in quartz
veins. One band carries from 30 to 40 per cent of a reddish-brown,
translucent mineral associated with the sulphides, which may possibly
he hematite. Blotches of hematite have been determined on fracture
surfaces in the slates. Large porphyroblasts of a colorless garnet and
scattered grains of detrital, greenish-brown tourmaline, are present.
Phyllites—In a number of instances it was very difficult to distinguish
between phyllites and slates, and in such cases the specimens possessing
lustrous surfaces showing a better crystallization, were included with
the phyllites. In other respects both rock types have essentially the same
features, since they differ only in the degree of metamorphism suffered.
Besides the minerals described from the thin sections of the slates, the
phyllites carry additional varieties in accordance with a higher degree
of metamorphism. As in the slates, the groundmass is composed mainly
of quartz, scricite and carbonaceous material and, in addition, often
hiotite. Porphyrohlasts of a colorless garnet show inclusions in an unusual
pattern, in which the cut of the thin section is such as to disclose the
porphyroblast with a clearly delineated hexagonal outline bounding a
six-rayed set of remarkably straight fractures corresponding to crystallo-graphic
planes (P1. 3, fig. 1) (Cohen, 1900, P1. 17, fig. 3; Renard, 1882,
p. 16, P1. I, fig. 1). These planes expose the garnet to alteration, so that
in the more advanced stage the fractures have developed into a six-rayed
set of inclusions, giving a cartwheel pattern to the porphyroblast
(P1. 3, fig. 2). Occasional garnets are edged by a thin band of sulphide.
Biotite flakes often show parallel arrangement and at an igneous
contact they compose small veins. They are sometimes lath-shaped or
irregular in outline and pale-colored when associated with chlorite.
Numerous porphyroblasts of andalusite are rimmed by biotite and are
now much altered to quartz and muscovite (P1. 4, fig. 1). Rectangular
areas of biotite, muscovite, calcite, and quartz are suggestive of com-pletely
altered andalusite crystals. Large porphyroblasts of a pale yellow -
28

green amphibole are bent and broken where they lie across the schistosity
(P1. 3, fig. 1).
A coarsening texture and noteworthy mineral development have been
observed at igneous contacts and at the borders between the sedimentary
rocks as well. Where the phyllite is banded with impure limestone there
is a generous growth of biotite and brown tourmaline. At a quartzite
contact the phvllite carries large biotites frequently in parallel orienta-tion,
muscovite flakes, quartz and masses of radiating amphiboles. Veins
parallel with the contact contain quartz, biotite, sulphide and a little
orthoclase. Along a granite contact a zone of muscovite mixed with
calcite occurs in the phyllite. Zones of carbon-rich material continue
across the contact from the phyllite into the granite.
Quartzites—The quartzites are not abundant rocks in the formation.
They are normally thin-bedded, are seldom massive thick-bedded and
are fine- to medium-grained, sometimes displaying cross laminations.
They range from medium-gray to black and are frequently streaked
with minerals zoned parallel to the bedding. None of the quartzites
are pure, consequently they bear a variety of complex metamorphic
minerals. Some of the quartzites are calcareous and might represent
highly silicified limestones. Patchy, nonuniform effervescence of the hand
specimen might be suggestive of such an origin, as might also be the
presence of lime-silicate minerals. However, since the quartzites often
are interbedded with the limestones, the carbonate substance necessary
to form the lime-containing minerals could conceivably have been
introduced by selective diffusion from the adjacent limestone during
metamorphism. A few of the calcareous quartzites contain up to 15
per cent of calcite.
Microscopic sections show small to large biotites in varying amounts
and frequently with parallel arrangement. Orthoclase and plagioclase
are present in small amounts. Both brown and green tourmaline in
irregularly-shaped masses and specks, is disseminated widely in some
slides. Sillimanite is abundant locally in igneous contact zones where it
occurs in both sheaf-like bundles and isolated crystals (P1. 4, fig. 2).
Yellow-green, pleochroic amphibole contains scattered epidote grains
which in part are replacing the host mineral. In other instances the
amphibole shows alteration to zoisite or clinozoisite and contains many
quartz grains. Nearly colorless amphiboles occur in contact zones. The
minerals tremolite, zoisite or clinozoisite, scapolite, and plagioclase, are
29

found predominantly in calcite-bearing quartzites. Suiphides are present
in masses and as stringers and are frequently in parallel orientation.
Minerals in minor amounts are titanite, rutile and chlorite.
Lirnestones—Like the quartzites, the limestones are impure and
greatly altered. Lithologically they resemble closely the limestones of
the Ayers Cliff formation, excepting that, due to their association with
other kinds of stratified rocks and granite plutons, they contain a greater
variety and larger quantity of complex minerals produced by metamor-phism.
They are light- to dark-gray, blue-gray, mottled, and white in
narrow bands affected by hydrothermal metamorphism. The texture
becomes coarser with increase in metamorphism. Calcite composes as
much as 70 per cent of the rock, more rarely constituting the only
mineral along with more or less carbonaceous matter. Quartz has about
the same ratio that calcite has in the quartzites, generally as high as 20
per cent; occasionally it reaches 60 per cent, in which case calcite makes
up about a third of the rock. Calcite veins have been noted in some of the
limestones. They follow both bedding and fractures and are ordinarily
thin. However, one coarse-textured vein in the bed of upper Johns River
measured 7 inches in thickness and was traceable for 8 feet; its strike is
N 60° W and dip vertical.
Microscopic study shows the limestones to be largely lime-silicate
rocks. Among the lime-bearing silicates are wollastonite, tremolite,
diopside, scapolite, zoisite, clinozoisite and, possibly, vesuvianite.
Tremolite sometimes appears in brush-like groups often attached to
rectangular-shaped muscovite porphyroblasts and scattered throughout
the slide. Muscovite is occasionally abundant and in a fine-grained rock
it appears as phantom crystals visible only in crossed nicols. Biotite
flakes are often elongated parallel to the banding of the rock, and
phlogopite is present as lath-shaped crystals. Fan-shaped masses of
needle-like sillimanite occur along the contact with a fine-grained rock
composed of quartz grains and much carbonaceous material. Diopside
appears to be restricted to igneous contact zones. Much of the zoisite
and clinozoisite is polysynthetically twinned and the clinozoisite is
present sometimes as interstitial material. Nearly colorless garnets
appear in some layers as large metacrysts. Porphyroblasts of a yellow-green,
pleochroic amphibole are much corroded and replaced by quartz
and calcite. Occurrences of sulphides are framed by calcite crystals.
Specks and grains of tourmaline are green-brown and brown. Other
minerals in smaller amounts are epidote, titanite, chlorite and zircon.
30

Schists—These rocks comprise quartz-mica schist, andalusite schist,
hornhlende-garnet schist, biotite-garnet schist and phyllite schist. The
predominant minerals are quartz and mica, and the shades of gray to
dominantly black are due to various concentrations of carbonaceous
material in the rock. The schists are prevailingly fine-grained and lustrous
due to disseminated micas. They are not confined to any particular part
of the formation, but are found widely distributed. On the whole they
are strongly banded and foliated.
The quartz-mica schist contains either biotite or sericite as the maxi-mum
mica. Both micas are frequently elongated parallel to the banding
in the rock and also occur as large irregular and well-defined porphyro-blasts.
In some schists the biotite shows partial resorption and in others
it is strongly twinned. In one schist possessing strikingly developed
herringbone structure (due to incipient fracture cleavage) in the fine
laminae, large porphyroblasts of biotite are bent and broken to conform
with this structure (P1. 5, fig. 1). Veins of secondary biotite also occur.
Porphyroblasts of tremolite appear as fragments and phantom crystals.
Large porphyroblasts of yellow-green, pleochroic amphibole contain
much quartz. A few calcite grains show elongation with the schistosity.
Olive-colored and brown tourmaline in single grains and irregularly-shaped
masses, is fairly common. Sulphide occurs in the form of blebs
and stringers parallel to the banding and as specks in augen of quartz.
Rods of sulphide are surrounded by babes of secondary biotite (P1. 5,
fig. 2). Rectangular porphyroblasts of chlorite are in random orientation,
often cutting across the structure and also associated with partially
altered biotite.
Large interlacing porphyroblasts of andalusite resembling diabasic
texture make up an appreciable part of a few andalusite schists. Occa-sionally
the andalusite is pleochroic in a rose-colored variety (P1. 6,
fig. I). Much of it is considerably altered to quartz and muscovite; some
of it contains clinozoisite. The space between the andalusite porphyro-blasts
is occupied largely by biotite, brown tourmaline, quartz and
carbonaceous material. One thin section contains only pseudomorphs
of the pleochroic andalusite porphyroblasts composed of a mixture of
muscovite, biotite and quartz grains. Another slide shows abundant
large porphyroblasts of the variety chiastolite containing geometrically
arranged carbonaceous inclusions (P1. 6, fig. 2). They are also consider-ably
altered to quartz and muscovite. Staurolite showing inclusions, is
present as porphyroblasts.
31

The hornblende-garnet schist has large .porphyroblasts of a pale-colored
garnet and green-yellow amphibole uniformly distributed in a
groundmass of quartz and carbonaceous material. In the biotite-garnet
schist the frayed biotite porphyroblasts become invisible when their
cleavage directions do not coincide with the vibration direction of the
lower nicol, but the cleavage lines alone are clearly discernible. The
garnets are noticeably fractured and somewhat shattered, and partially
rimmed with suiphides. The foliated structure of the phyllite schist is
strongly emphasized by bands much richer in mica than others. The
rock is cut by quartz veins containing chlorite, biotite, and sulphides.
IRASBURG CONGLOMERATE
The type locality of the Irasburg conglomerate is in the bed of Lords
Creek and on the adjacent slope to the south, where Richardson (1905-
1906, p. 82) first described it. Richardson (idem, p. 83) placed it at the
base of the Ordovician while Currier and Jahns (1941, p. 1509) consider
it to be an intraformational conglomerate in the Ordovician series.
The writer regards the Irasburg conglomerate as basal to the Barton
River formation, chiefly on the basis of its stratigraphic position. It has
been traced along the boundary between the Barton River and Ayers
Cliff formations from the bed of the Black River in Irasburg Village
southwesterly to the steep slope half a mile directly east of the village
of Albany. Richardson (1917-1918, p.106) has reported this conglomer-ate
as far south as Northfield, but from his description of the locality
it is evident that he was dealing with the conglomerate basal to the
Northfield slate (Currier and Jahns, 1941, p. 1502). Furthermore, among
the five phases into which Richardson (1927-1928, p.108) divided the
Irasbtirg conglomerate on the basis of matrix composition, only the Iras-burg
and possibly the Albany phases belong to this conglomerate. The
stratigraphic position of the "Northfield phase" is cited above and the
"Coventry phase" is very probably the Shaw Mountain conglomerate.
The Irasburg conglomerate has not been studied in detail, but field
observations have brought to light some interesting facts regarding it.
The limestone matrix, which strongly resembles the limestones in the
underlying Ayers Cliff formation, is constant in composition, but the
constituents vary considerably in variety, size and amount along the
strike. The greatest variety of particles is exposed at the type locality
and range in size from dominantly pebbles to sparsely distributed
boulders. Indeed, in places along the strike only single cobbles betray
32

the presence of the conglomerate. The largest boulder recorded measures
9 feet long by 3 feet wide and, like the other elongated constituents, was
oriented with the long dimension parallel to the axes of minor folds on
the bedding planes of the matrix. Some of the boulders are bent with the
folds. The constituents are well rounded to sub-angular and, according
to Richardson (1927-1928, PP. 108-109), consist of granite, andesite,
diorite, diabase, serpentine, chlorite- and sericite schists, sericitic marble
and micaceous quartzite. To this list the writer would add dark, crystal-line
limestone, black mudstone and phyllite. The amygdaloidal structure
of some of the aphanitic constituents might be suggestive of volcanics.
A conglomerate with so large an assortment of constituentscan hardly
he intraformational, as classified by Currier and Jahns (1941, p. 1509).
Field relations show definitely that the Irasburg conglomerate is a basal
conglomerate and constitutes the earliest deposits of the Barton River
formation. Northward from Irasburg Village, the conglomerate is prob-ably
concealed under the widespread loose deposits.
Westmore Formation
GENERAL DESCRIPTION
The Westmore formation derives its name from the village of West-more
on Lake Willoughby in the southeastern corner of the Memphrema-gog
quadrangle. The rocks are largely phyllites and schists, with smaller
amounts of limestones and quartzites, all interbedded. Phyllites of
whetstone quality have been quarried at several places in the formation,
but the largest opening is located I Y4 miles due north of Lake Willoughby
in southeastern Brownington. The light-colored rocks are proportionately
greater in amount than in the formations to the west and the suiphides
appear to be greatly reduced in comparison. Field observation and
petrographical study seem to indicate that the sulphides are much more
common in the darker, more carbonaceous rocks, hence their wider
dissemination in the underlying formations,
TYPE LOCALITY
A good section is exposed in the whetstone quarry cited above. The
quarry is about 150 feet long and has been opened approximately along
the strike of the layers. The rock is massive and well bedded. Other
exposures affording additional sections, are located directly north and
south of the village of Morgan, in a pasture half a mile west-southwest
33

of Echo Pond, and in cuts along the state highway leading from West
Charleston to Island Pond.
DiSTRIBUTION
The formation has its greatest width of outcrop in the southeastern
portion of the map and narrows north of the reentrant at Pensioner Pond
south of West Charleston, continuing northward along the eastern
margin of the map into Canada. Much of the formation is obscured by
glacial and recent deposits, as for example, north of the Barton Moun-tain-
May Pond Mountain pluton. Outcrops are more abundant at the
higher elevations.
RELATIVE THICKNESS
Although the breadth of outcrop of the Westmore formation exceeds
that of the Barton River formation along the line of section, its thickness
is less because of a wide terrane of gentle dips in the southeast portion
of the map-area. Much of the formation is cut by igneous intrusions in
the same manner as the Barton River formation. Measured from the
axis of the Brownington syncline eastward, the thickness is estimated
to be 4300 feet.
AGE
In a paper published not long ago (1943), the writer described a few
specimens believed by him to represent fossils. They were found in a
mottled limestone stratum in the bed of Stony Brook just above the
farmhouse and at a point under the "S" in the town word "WEST -
MORE" on the map. The fossils have been identified as cystoid and
crinoid calyces whose structural features indicate genera belonging to the
Middle Silurian or possibly the Lower Devonian.
However, since there is some disagreement among authorities con-cerning
the true nature of the specimens, the age of the formation is at
present based on its stratigraphic position above the Barton River
formation which makes it the youngest formation in the area mapped.
Some 50 miles to the south in the Strafford quadrangle, the Barton
River formation appears to have its counterpart in the Memphremagog
formation (Doll, 1943-1944). The latter is overlain to the east by the
Gile Mountain formation of Devonian age, which resembles broadly the
lithology of the Westmore formation. The corresponding lithologies
and stratigraphic positions of these respective formations are indicative
of similar age relationships. The Westmore is therefore considerably
34

younger than Middle Ordovician and, in the writer's opinion, more likely
Silurian or conceivably Lower Devonian.
LITHOLOGICAL DETAIL
The rocks have been metamorphosed to crystalline types. The most
abundant of them are phyllites which are interbedded with smaller
amounts of schists, limestones, and quartzites. These dominantly
siliceous rocks are the southeasternmost in a series becoming progres-sively
more siliceous in this direction. Single beds range in thickness
from less than an inch to uncommonly 4 or 5 feet. Bedding is generally
well defined, but where the phyllites are successively thick in section
and dip at low angles, the bedding is determined with difficulty because
interbeds of a different lithology are rare. In general the brown weathered
surfaces of the Barton River formation are not so conspicuous in this
formation.
Ph.ylliles—These rocks are on the whole comparatively of lighter
color and more arenaceous than the same rocks in the Barton River
formation. They are light- to medium-gray and fine- to medium-grained.
Cleavage is absent or very poorly developed in the sandy phyllites,
except perhaps where it coincides with the bedding, as in the whetstone
types in which the perfect planes of parting, considered to be bedding
planes, fairly glisten with mica. Some of the beds are finely laminated.
Varying mixtures of fine-grained quartz and mica are the most
essential minerals present. In the different specimens examined, sericite
and biotite exceed one another in amounts, but in some, quartz is present
far in excess of either mica, practically conforming in composition to a
quartzite. The uniform, fine grain and shining luster distinguish them as
phyllites. In some the biotite crystals are lath-shaped and linearly
arranged with the long axis parallel to the banding in the rock, while in
others the biotite appears as porphyroblasts in part altered to chlorite.
Muscovite and sericite occur as small disseminations and the former as
fairly large crystals in random orientation and often corroded.
Tourmalines, both dark-brown and olive-colored, are well represented
as patches and as isolated crystals, sometimes elongated parallel to the
banding. Minerals in smaller amounts are zircon, chlorite, garnet, calcite
up to 10 per cent, magnetite, sulphides, possibly talc, hornblende, and
titanite. One section is cut by quartz veins and in another a vein is
composed of quartz, calcite, and sericite or talc. Carbonaceous matter
and sulphides occur in small amounts.
35

A microscopic study of a specimen of whetstone quality from the type
locality, shows abundant sericite, most of which is oriented parallel
to the structure of the rock, associated with quartz. Accessory minerals
present are feldspar, irregular brown tourmaline grains, lath-shaped
biotite, apatite and a little chlorite.
Limestones—The limestones are fine- to medium-grained, rarely
coarse-grained, and range from light-gray, sometimes mottled, to black.
They are sometimes schistose or phyllitic, and in all cases react vigorously
to acid. Calcite is present from about 20 per cent to considerable amounts.
In contrast to the phyllites, the limestones contain more carbonaceous
matter. Like the limestones in the formations already described, they
are considerably altered by metamorphism, resulting in the production
of such new minerals as diopside at igneous contacts, clinozoisite or
vesuvianite, orthoclase and microcline, titanite, epidote, and amphibole.
In one slide large porphyroblasts of amphibole are considerably corroded
and broken, and in part altered to chlorite and epidote. Clinozoisite is
occasionally interstitial to the other minerals. Numerous corroded
crystals of an olive-green biotite and rather large, irregular patches of
dark-brown tourmalines, are present in one section.
Q uartzites—Some of the quartzites are banded, with such minerals as
rectangular biotites and needles of tourmaline parallel to the banding.
A few calcareous quartzites contain about 10 per cent of calcite grains.
The micas are represented by small to moderate amounts of biotite,
chlorite, and muscovite with intergrown quartz. In some rocks rutile
needles are numerous, and there are minor quantities of apatite, zircon,
a clay mineral, magnetite, kaolinized orthoclase, garnets and titanite
partially altered to leucoxene. One specimen shows large porphyroblasts
of a colorless garnet containing about 50 per cent of quartz in a poikilitic
texture. These suites of minerals produced by metamorphism show that
the quartzites were originally impure. An occasional bed shows cross-bedding.
Schists—The schists are fine- to medium-grained and generally
exhibit a well-developed schistosity. They are light-gray to black, often
displaying a high luster due to the micas present. The kinds of schists
are quartz-mica, garnet-mica, amphibole, garnet-staurolite and staur-olite,
all containing quartz and mica as the chief minerals. The schistose
structure is largely due to the parallel orientation of the micas, and often
to the porphyroblasts as well.
36

The quartz-mica schists frequently contain muscovite plates and
crystals, in addition to sericite flakes and augen of biotite. The augen
are arranged with their long axes parallel to the schistosity and are
composed of separate crystals of biotite and in a few cases small amounts
of muscovite (P1. 7, fig. 1). In some the rock is crowded with biotite
crystals in random orientation.
Considerable carbonaceous matter darkens the garnet-mica schist.
The garnets are large, colorless porphyroblasts containing numerous
inclusions. Also present are some large, much-corroded, yellow-green
amphibole porphyroblasts (P1. 7, fig. 2). In addition are many random
oriented biotite crystals, some of them wholly or partially altered to
chlorite. The amphibole schists carry large, yellow-green amphiboles
more or less corroded or replaced. In one specimen the amphibole is
considerably replaced by a mixture of quartz, calcite, epidote and
clinozoisite.
In the staurolite schists the staurolite is often shattered and replaced
by quartz, and occasionally appears as remnants where it is strongly
corroded. It occurs in euhedral prisms and as cross sections, oriented
and unoriented with regard to the schistosity (P1. 8, fig. 1). It frequently
contains carbon impurities and in some porphyroblasts the carbon along
with the sulphide inclusions show a linear parallelism corresponding in
direction to that of the groundmass, regardless of the orientation of the
porphyroblasts. Garnets and sulphides are found surrounded by bleached
zones of quartz, muscovite and biotite (P1. 8, fig. 2). Quartz and carbon
appear in some garnets possessing a pinkish tinge. Tourmaline is com-mon
to all schists, as are also quantities of titanite, rutile and zircon.
IRRUPTIVE ROCKS
General Statement
The largest intrusions are plutons of granite which forced their way
into the strata by pushing them aside. These granites have also invaded
an earlier dark, hornblendic granite. With the exception of the north-eastern
portion of the area, granite sills and dikes fairly abound. They
are especially numerous in the southwestern and eastern portions of the
area. Pegmatites and aplites are common in the granites, occasionally
extending into the sediments. Among the multitudinous quartz veins,
the huge veins of milky quartz which follow the general regional strike,
deserve mention. The resistant granite masses support the dominant
elevations and the sediments occupy the lowlands generally.
37

In the northwest corner of the Memphremagog quadrangle, metabasie
rocks have been studied in detail and indicate a relationship to rocks of
similar composition in the Owl Head Mountain region to the north in
Canada. The igneous rocks are younger than the sediments and are
believed by the writer to have been intruded sometime during the
Acadian orogeny.
The Bolton Igneous Group and Associated Granites
An area of intrusive metabasic rocks borders the west side of Lake
Memphremagog north of Holbrook Bay. These rocks are associated with
granites, the granites becoming much more predominant south of Hol-brook
Bay. The rock types indicate that the area is largely in a transition
zone between basic rocks to the north in Canada, and granites to the
south. They consist of fine- to medium-grained metadiorites and related
rocks, and more or less contaminated granites, some of the latter in
places exhibiting porphyritic textures in which the feldspars are as much
as 12 mm. long.
Northward in Canada these rocks merge with the metagabhros and
metabasalts of Clark and Fairbairn (1936), called by them the Bolton
igneous group. The map by Clark and Fairbairn (idem, p. 15) indicates a
southward extension of the Bolton igneous group across the International
Boundary and that by Ambrose (1943) shows its continuation south-easterly
along the lakeshore in the direction of the area of metadiorites.
In addition, a petrographic sequence from the metagahhros in Canada
through the metadiorites to the granites on the south, is suggestive of
the consanguinity of these rocks. Because of these field relationships,
the writer has adopted the term Boltori igneous group for this strip of
basic rocks.
The diorites and related rocks are gray to dark green. Thin section
study of the diorites shows pale green to greenish-yellow amphiholes of
varying intensities of pleochroism, plagioclase, and biotite as predom-inant
minerals. The amphiboles are somewhat shattered and chioritized.
Some sections contain smaller amounts of orthoclase in addition to
plagioclase. The plagioclase grains display the customary twinning, are
anhedral to subhedral, and are often greatly altered and saussuritized.
In some cases zoisite and tremolite are prominent among the alteration
products. The hiotites are commonly altered to chlorite, especially in the
highly chloritic, schistose rocks and they range from pale green to
greenish-brown. A great deal of secondary carbonate is present in some
38

of the rocks and large masses of twinned calcite as well, the latter often
occurring as amygdules. Suiphides are present in varying quantities,
having considerable representation in both the acid and basic rocks and
ranging from dust particles, distributed largely at mineral boundaries
and along cleavages, to rather large individuals. Minerals in minor
amounts generally are quartz, muscovite, leucoxene, titanite, apatite,
zircon, and epidote. Epidote occurs also as thin veins.
The granitcs have been altered to varying degrees by the invading
basic rocks, as is shown by their compositions. They are light- to dark-gray,
sometimes having a greenish cast. In texture they are fine to coarse,
and commonly porphyritic. Besides the essential minerals of granites
which are of themselves present in varying amounts, are plagioclase,
carbonate, greenish-brown biotite, muscovite, chlorite, apatite, titanite,
epidote, and suiphides. Some of the rocks contain considerable secondary
carbonate, probably as an alteration product of the plagioclase. The
feldspars show much alteration to secondary products and are somewhat
shattered as well. The potash feldspars are often kaolinized, and quartz
contains numerous inclusions. Considered as a group these rocks repre-sent
hybrid types for the most part, as might be expected in an igneous
contact area. Purer granites are found directly south of this area.
The structural relationships and textural differences show definitely
that the basic rocks are intrusive into the granites. That the basic rocks
are younger than the granites, is revealed conclusively by dikes of the
former penetrating the granites and containing granite xenoliths (P1. 9,
fig. 1). These dikes attain widths of more than 16 feet, and are known to
extend outward from the main mass of basic rock and to strike in the
general direction of the Owl Head Mountain region to the north in
Canada. Schistose drag at the borders of some of them is oriented so as
to confirm the suggested direction of intrusion. The dikes display contact
effects such as chill zones and amygdaloidal bands 5 inches wide in
places. The amygdules, filled with calcite and light-colored feldspathic
material, appear to be due to the escape of gases at the time of intrusion
of the dike. Associated with the feldspathic amygdules in places are
extremely thin to thread-like veinlets of the same material. Some of the
veinlets ramify, but none of them extend to the granite contact. Since
they are associated with the feldspar amygdules and have the same
composition, it is concluded that they originated at the same time and
in the same manner as the amygdules.
The contacts between the basic and acidic rocks are well defined, due
39

to strong textural and erosional contrasts. The granite wall rock is coarse
to porphyritic, with feldspars half an inch long and smaller quartz insets.
At the contact with the basic rock it stands out in sharp relief and has a
decided greenish color because of exomorphic effects.
The granites are locally brecciated and contain fragments which are
both angular and subangular. The fragments range in size from a few
inches to huge inclusions. Good examples of the brecciated granite may
be seen in a pasture bordering the Lake road on the east and half a mile
due south of Maxfield Light. Here two enormous granite inclusions
measure 60 feet by 10 feet and 45 feet by 20 feet, respectively. One in-clusion
contains an apophysis of the basic rock matrix. Granite xenoliths
are also well displayed in the exposure on the lakeshore at Maxfield
Light.
In places the basic rocks are traversed by ridges of resistant material
which follow fracture systems. The ridges are from a fraction of an inch
to 4 inches high, and are composed of basic material with injected
siliceous seams running lengthwise of the ridge. In following the fracture
systems they enclose triangular, rectangular and rhombic polygons of
various dimensions, thus giving the surface of the outcrop a reticular
pattern (P1. 9, fig. 2). In general the major directions of the ridges are
north-south and east-west, with minor variations. Those trending north-south
show east-west displacements of an inch to as much as 4 inches.
No displacements were seen in the north-south direction. The intricate
fracturing of the basic rocks and the siliceous injections along these
fractures, appear to be late effects in the intrusion of the basic magma.
From the foregoing paragraphs it can be seen that the Bolton igneous
group is younger than the granites. Nowhere have these rocks been ob-served
in contact with sediments younger than the Cram Hill. However,
the granites contain infolded slates in places and farther to the south the
Lowell Mountain pluton has intruded the Cram Hill, Shaw Mountain,
Northfield, and Ayers Cliff formations, sending dikes out into the lower
members of the Ayers Cliff formation. Because the Shaw Mountain
formation is at least Ordovician in age (Currier and Jahns, 1941, p.
1500), the granites must be younger. According to Clark (1934, p. 13)
the Stanstead granite, which is the age equivalent of the granites in this
area, is Devonian. The writer concurs in this view and, since the Bolton
igneous group is intrusive into these granites, he is forced to the con-elusion
that the Bolton igneous group is at least Devonian in age. Cooke
(1948, p. 17) has reached the same conclusion with regard to the age of
40

the Bolton lavas, which Clark (1936) believes to be the extrusive equiva-lents
of the basic intrusives.
Structural features already described in both the Bolton igneous
group and the granites, suggest that the former was intruded during a
period of orogeny. Petrographical studies show further evidence of the
activity of distortional forces in bent, shattered, and intensely folded
mineral grains. Supported by the age relations already determined, the
induced structures are probably indicative of the Acadian orogeny.
Granite Plutons
The granites constitute several varieties and are distributed widely
in the area. They occur as large bodies covering considerable portions
of the central and southern rectangles. Smaller exposures occur near and
at the eastern and northern margins of the map. Some of these are con-tinuous
with larger bodies on the adjacent quadrangles. The domical
elevations, such as Salem, Hopkinson, Sugar, and Elm hills in the central
igneous body, and Barton Mountain in the southern part of the quad-rangle,
are surface expressions of the granites.
By and large the granites are medium- to coarse-grained, granitoid
rocks and light to dark gray depending upon the amount of biotite and
hornblende present. Dark hornblende granite occurs in two places at the
border of the arcuate body extending northward from West Charleston.
Granites containing abundant biotite are locally prominent, especially
in the masses in the eastern part of the map-area. In places the granites
are porphyritic, containing feldspar phenocrysts as large as 1 centimeter.
A medium-grained, light gray, equi-granular, binary granite is quarried
at the Willey Granite Quarry northwest of Derby Center. A micro-scropic
study of this granite reveals as major minerals orthoclase,
microcline, quartz, muscovite, and biotite. A few grains of titanite and
apatite, and some zircon needles occur as accessory minerals. The quartz
contains numerous inclusions. Some of the feldspars are kaolinized and
there is a small amount of chlorite, probably as an alteration of the
biotite.
The mineralogic composition of a specimen from Sugar Hill consists of
orthoclase, microcline, oligoclase, quartz, and hiotite. The biotites are
large and contain apatite and zircon inclusions, the latter surrounded
by pleochroic haloes and frequently elongated with the cleavage in the
biotite. Much of the biotite "frames" many of the feldspars producing
41

a pattern resembling mortar structure. An occasional plagioclase is
zoned. Minerals in lesser amounts are muscovite, garnet, tourmaline,
titanite, and some carbonate. The muscovite is associated with quartz.
A few grains of quartz possess myrmekitic intergrowths. Some of the
biotites show alteration to chlorite and many of the feldspars are partially
kaolinized. In a hand specimen the lighter feldspars stand out promi-nently
against the darker background of quartz and biotite, thus giving
the rock a slightly porphyritic effect.
A specimen of granite from the south shore of Echo Pond is ver
similar in general appearance to the Willey Quarry granite, except tli
the quartz grains are much more conspicuous. In thin section it sho -
orthoclase, microcline, oligoclase, quartz, and biotite, with smaller
amounts of muscovite, apatite, zircon, tourmaline, and sulphide. The
hiotite encloses both apatite and zircon, and is occasionally associated
with suiphide, which appears to be replacing it. Some of the plagioclase
exhibits zonal structure. There is a little quartz with graphic inter-growths.
Kaolin is present as a coating on some of the feldspars.
About a mile southeast of the village of West Charleston, at a road
junction, is an exposure of a dark, coarse-grained, mafic granite com-posed
of quartz, microcline, a little sodic plagioclase (oligoclase), biotite,
pale yellow and light green, pleochroic hornhlende, a few zircon crystals,
and a little magnetite. The biotite is partially altered to hornblende and
contains streaks of magnetite often following the cleavage of the biotite.
Magnetite streaks also follow the cleavage directions of the replacing
hornblende. The hornblende attains a length of 1 centimeter.
Orbicular granite occurs on the Hitchins farm on the northeast slope
of Prospect Hill in Brownington Village. This locality was mentioned
by E. C. Jacobs (192 1-1922, pp. 107-108) and very probably is the local-ity
referred to by S. R. Hall (1871, pp. 74-75). The nodules are spheroidal
with average dimensions of about 2.5 cm. x 1.5 cm. They are composed
largely of black, lustrous, crinkly biotite which envelopes grains of
feldspar and quartz. The granite is light gray, medium-grained, and
contains as prominent minerals quartz, orthoclase, sodic feldspars,
muscovite, and biotite. The micas tend to surround the feldspar and
quartz grains in a manner similar to that described above in the specimen
from Sugar Hill. This mineral arrangement is suggestive of the early
stages in the development of the nodular forms in the continued thicketi-ing
or growth of the hiotite around one, or several, of the feldspar and
quartz particles. Areas of corrugated biotite studded with feldspar and
42

quartz grains occupy the more basic portions of the granite. Orbicular
granites have been reported from other localities (B. Hitchcock, 1861,
pp. 563-563; Adams and Barlow, 1910, pp. 127-139). The latter dis-cusses
the origin of the orbicules. The literature on orbicular granite
can not be gone into here (see citations given).
SEDIMENTARY INCLUSIONS
Remnants of the sedimentary rocks are numerous as inclusions in the
igneous bodies. Their structures in most cases do not conform to those
of the region, but in the central granite mass a large majority of recorded
measurements show that the structural orientation of the inclusions is
conformable with the long axis of the mass as well as with the structure
of the sediments along the southwest and northeast contacts. Although
the tectonics of the granites have not yet been studied in detail, it is
believed that this structural conformity might possibly be correlated
with the flow direction in the granite.
With few exceptions, the bedding of the inclusions has gentle to
moderate dips. In places, small areas of sediments lie in shallow synclinal
contacts with the granite; in these the bedding is, generally, also synclinal
(P1. 9, fig. 3). Some of these sedimentary remnants, still retaining a
structural conformity with the regional rocks, might conceivably be
preserved portions of the original roof of the igneous body.
The inclusions possess distinct outlines and are lens-shaped and tabular
generally, the shapes being determined largely by the bedded structure
(P1. 9, fig. 4). On the west slope of Sugar Hill near the Brownington-
Derby Center road, interbedded limestone and phyllite at several levels,
dip beneath the granite cliff at relatively low angles (P1. 10, fig. 1).
The inclusions show well the effects, both structurally and mineral-ogically,
of the intrusions on the sedimentary rocks. The limestones
frequently possess a conspicuous flow structure, while the more resistant
beds yielded by breaking, bending, and faulting. Shallow folds, some of
them overturned, are not uncommon. At the actual contact contami-nated,
highly micaceous granite or "granitized" sediments exhibit
pronounced flow structure, filling in the spaces between ruptured
sedimentary layers (P1. 10, fig. 2). Occasional smaller inclusions are
hollow shells in which the less resistant interior has been weathered out,
the dense, hard shells attesting to the efficacy of the intrusive (P1. 10,
fig. 3). Saucer-like depressions bordered by hard, prominent rims,
ordinarily half an inch thick, compose the surface of many of them.
43

Granite sills in lit-par-lit fashion occur in patches of the sedimentary
rocks having steep dips. Like the sedimentary beds beside them, they
thicken and thin and are drawn apart along the strike, producing a
boudinage-like structure. Disjointed beds, often displaced across the
strike and tilted at varying steep angles, are prominent features in the
foliated groundmass of the contaminated granite. Besides disclosing the
former extent of the sedimentary rocks the inclusions, by their structures
and to a certain extent orientations, may ultimately shed light on the
manner in which the granite came into being.
The forceful intrusive nature of the magma is also shown by the struc-tures
in the wall rock bordering the central igneous mass, which they
parallel. Furthermore, the inward dips of the country rock around the
perimeter of this body, suggest a funnel-shaped intrusive. In a limited
number of places at the edge of the intrusion, foliation was discernible,
but over its areal extent in general the rock appears massive. Additional
evidence of the pervasiveness of the intruding magma is again shown
by the central igneous mass whose expansive force has deflected the
regional northeast strike of the country rock, resulting in bulges in the
sediments toward the northwest and southeast (Plate 1).
The sediments flanking the intrusives in the southern and southeastern
sections of the map-area, dip radially outward. While the main part of
the plutonic body southwest of Orleans is concordant, its eastward
extension appears discordant, as revealed by its structural relationship
to the bordering sediments. With this possible exception, these bodies
are conformable and laccolithic in behavior. The narrow, concordant
body longitudinal between West Charleston and Cargill Hill, has the
structural attributes of a sill, or possibly a phacolith.
AGE OF THE GRANITE5
An earlier dark, biotite and, in places, hornblende granite, has been
invaded by a light gray, coarser granite. Apophyses of the younger
granite traverse the dark granite in various directions and inclusions
of the earlier occur in the later granite (P1. 10, fig. 4). On the west slope
of the 1600-foot hill southeast of West Charleston, an intrusive breccia
contains rounded and angular fragments of the dark phase (P1. 11, fig. 1).
Both granites intrude the sedimentary rocks, and are therefore
younger than the latter. The youngest sediments constitute the West-more
formation, which is considered by the writer to be Middle Silurian
or possibly Lower Devonian in age (Doll, 1943). On the basis of the above
44

relations a late Devonian age is favored for the granites. Such an age
assignment is in accordance with the determinations made by earlier
investigators.
Sills and Dikes
Sills are much more widespread than dikes. They are parallel to the
bedding and foliation of the sedimentary rocks, but in an occasional
vertical or horizontal section they have been observed to cut the struc-tures
with a slight obliquity. They are common in all of the formations,
but especially abundant in the Barton River formation. Great con-centrations
of them, such as occur in the southwestern part of the
quadrangle west of the Barton River Valley, might be indicative of
their close proximity to the underlying granite mass. Locally, sills
follow in rapid succession across the strike and, in a few instances, a
sill continued as thinning ramifications interfingering with the sediments.
The great preponderance of sills over dikes throughout the area might
be explained structurally. The strata are relatively thin and steeply
dipping, both conditions being highly favorable to the formation of sills.
Individual transverse fractures, which might accommodate dikes, are
rarely continuous, due largely to the inhomogeneity and high inclination
of the beds. In contrast, the steep bedding planes and accompanying
cleavage have considerable continuity in depth and longitudinally as
well, thus affording readily accessible openings. Barrell (1902, p. 294)
calls attention to inclined strata as avenues of escape in a discussion of
infiltration of strata. This same structural weakness is here extended to
include invasion of strata. Excepting for the property of homogeneity,
the situation is analogous to the up-ended layers in ice-packs.
The sills range in thickness from 8 inches to 33 feet and are frequently
traceable for considerable distances along the strike. One sill 16 feet
thick was traced for more than 1800 feet along the strike, and another
14 feet thick, for 1000 feet.
Prominent joints across the strikes of both sills and dikes are common.
Many of them contain quartz veins, while others served as surfaces of
faulting along which successive segments were given en echelon arrange-ments.
In a few cases the segments were drawn apart and rotated (Fig.
2). An occasional dike is bordered by a fault contact along which the
sediments exhibit drag and displacements of a few inches to several feet.
Sediments at sill contacts are often strongly contorted and the sills
infolded with the sediments (P1. 11, fig. 2).
45

Neither the sills nor the dikes were studied petrographically, but
those observed in the field were essentially granitic in composition,
ranging from fine to coarse in texture, sometimes porphyritic. Some of
them become apli ic a1on Ibeir exiensions. The contact zoneS in some
Figure 2. At Cobb Brook on oust side of Pine lull road. Three stages in disruption
of granite streamers in slates of the Barton River formation. Disruption of one
streamer has advanced to the boudinage stage. The sketch covers a width of 8 feet.
are chilled, in others pegmatitic. Conspicuous minerals are feldspars,
quartz, muscovite, biotite, and black tourmaline. The tourmaline occurs
in small dendriform patterns. In a few sills the prominent minerals are
parallel to the adjacent sedimentary structures. Likewise in places in the
sediments a copious development of coarse muscovites shows a linear
46

parallelism with the contact. Slate inclusions are infrequent in the sills
and dikes.
Only one basic dike was encountered in the field cutting the sediments.
It crosses the road about half a mile north of the "T" in the township
word "WESTMORE." It is 3Y2 feet thick and strikes N 52° W.
The sills and dikes are presumably comagmatic with the granite
plutons, and since they also cut the sediments they are considered
younger than the latter. Structural evidence indicates that some of the
sills were affected by the orogeny which folded the regional rocks, thus
tending to show that they are older than the orogeny. The writer, how-ever,
believes that the sills were emplaced at intervals during the late
Devonian.
Pegmautes
Pegmatites are associated with the granite as dikes and irregular
masses. They occur also in the sediments as dikes and sills, but are much
more numerous within and nearest the igneous bodies. The pegmatitic
areas are gradational into the granite and occasionally send off apophyses.
They represent segregation centers of residual magmatic liquids. The
pegmatites contain as prominent minerals quartz, potash feldspars
(cleavelandite in some), muscovite, black tourmaline and garnet. In
some dikes the tourmaline and garnet are concentrated at the granite
contact, the tourmaline attaining a length of one inch. The feldspars
reach lengths of 6 inches and the muscovites one and one-half inches.
Generally there are no visible contact effects at the borders of the sedi-xx
1/
Figure 3. Southeast slope of Barton Mountain on north side of Barton-Lake
Willoughby highway, 1 3 miles west of elevation 1404. Three generations of peg-matite
veins in granite. The sketch covers a width of 5 feet.
47

mentary rocks, but some of the limestones exhibit blanched contacts
an inch or more wide.
In the granite the pegmatites were injected along tension joints,
certain sets of which show displacements of small magnitudes, usually
measurable in inches (P1. 11, fig. 3). These displacements probably
indicate expansion of the igneous mass while the magma was still actively
rising. Three generations of pegmatites have been noted in the granites,
an exposure of which may be seen beside the road between Barton Village
and Lake Willoughby on the southeast side of Barton Mountain (Fig.
3). The later pegmatites appear to he coarser grained than the earlier,
and preceding the pegmatite injections are narrow intrusions of granite
(P1. 11, fig. 3). Some pegmatite dikes continue as aplites along the strike.
The pegmatites are considered to be genetically related to the granites
and are therefore presumably of practically the same age as the granites.
Quartz Veins
Countless numbers of quartz veins traverse all of the rocks in the area.
There are several generations of them. They follow the bedding, frac-tures,
cleavage, and schistosity, and in many instances exhibit 'book
structure" in the fissile rocks. Many of the veins are drag-folded along
with the sedimentary rocks, while others cut across the folds. Cross-cutting
veins may be restricted to a single stratum or they may traverse
a series of strata. Not infrequently are veins faulted on a small scale,
usually in a succession of step faults. Quartz also occurs as veins between
the walls of small faults, often showing slickensided surfaces.
Outstanding are the thick milky quartz veins of considerable extent
along the bedding of the sedimentary rocks. In some cases they attain
thicknesses of more than 10 feet, and can be traced along the strike for
distances exceeding 150 feet. One vein located on a hillside just off the
main highway to Lake Willoughby, and half a mile northeast of the
East Brownington School, has a visible width of 40 feet. Another vein
about 10 feet thick is exposed for 145 feet along the strike and 14 feet
down the dip, in a field on the west side of the Barton River Valley a
mile and a half south of Coventry Station (P1. 11, fig. 4). These veins
occur in the siliceous and calcareous sediments alike, and are most
abundant in the Barton River formation.
Veins occurring in the buff gray limestone are in places very irregular
in outline and are frequently broken into lens-like segments. The hackly
borders and discontinuity of the veins along the strike are probably due
48

to the dynamic effect during plastic flow of the limestone; plastic flow is
a conspicuous feature of the limestones. The quartz veins in the siliceous
sediments generally possess well-defined sharp and smooth borders.
Many of the quartz veins are not pure, but carry such minerals as
calcite, mica, or less commonly feldspar. These minerals usually show
good crystallization and fair size. Occasionally iron suiphides are present.
Hackly-fringed quartz veins in the limestones sometimes contain
muscovite scales and frequently irregular clusters of ironstained calcite.
More rarely do quartz veins contain feldspar, in which case they ap-proach
pegmatite in composition and may even grade into the latter.
Not only are the quartz veins folded conformably with the sediments,
but they also show ptygmatic folding. Good examples of ptygmatic
folds occur in the limestones possessing flow structure (Fig. 4). As thin
slate bands in the same exposure also exhibit ptygmatic folds (P1. 17,
fig. 1), it is the writer's opinion that the quartz veins were injected prior
to the movements producing this type of fold. Ptygmatic folding occurs
in rocks that have undergone plastic flowage during regional deformation
and igneous intrusion. Thick lenticular masses of quartz occasionally
occur as bulges around which the strata bend and thin (P1. 12, fig. 1).
Several of the quartz veins carry inclusions of slate or limestone.
The observations cited above show that the great majority of the
quartz veins and masses are definitely related to the processes which
folded the sedimentary rocks, and some may have antedated the orogeny.
Quartz veins also cut the pegmatites, thus revealing late injections.
Quartz in all of its forms may be considered then to represent several
ages.
STRUCTURE
General Statement
The rocks of the Memphremagog area are strongly folded and faulted,
and the whole further complicated by the injection of igneous masses. A
striking feature is the excessive amount of overturn to the southeast
throughout the whole stratigraphic section northwest of the axial region
of the Brownington synclinc, the degree of overturn increasing toward
the southeast. The dominant structural elements from northwest to
southeast are: the Ware Brook thrust and associated Stony Hill and
Lake Memphremagog reentrants, the Indian Point syncline, the Black
River fault, the North Neighborhood anticline, and the Brownington
syncline.
49

The rocks show an abundance of minor structures which reveal the
great intensity of the orogeny. With the exception of the northwest-trending
reentrants, the prevailing direction of the folds and faults is
northeast-southwest. The structure-building movements were generated
during late Devonian time and, thus, were practically synchronous with
the Acadian orogeny.
Indian Point Syncline
The Indian Point syncline is located in the extreme western part of the
area. It extends northeastward from the vicinity of Lowell Mountain
through the village of Coventry and the city of Newport into Canada, a
distance of 16 miles. Between Lindsay Beach and a point l,4 miles
southwest of Beebe Plain, the fold is concealed by a heavy cover of drift.
The syncline is delineated best where the lower Barton River formation
occupies its core, while south of Coventry Village the scarcity of ex-posures
in the underlying Ayers Cliff formation has greatly obscured the
structure. The axial plane of the fold strikes northeastward and dips
moderately to the northwest.
The synclinal axis is convex toward the northwest, which appears to
he due to the expansive effects of the central igneous mass not far to
the southeast. That the fold is greatly overturned to the southeast, the
Indian Point segment excepted, is indicated by the extreme easterly
position of its axis which is located in the escarpment of lower Barton
River slates along the Black River immediately south of Newport City.
The position of the axis indicates an asymmetrical fold whose east liml)
is either considerably thinned or cut out in part by a fault. An appreci-able
width of the west limb is concealed by the Ware Brook thrust.
Parallelism of the bedding and axial planes of the minor folds, shows
the syncline to he a tight fold. The minor folds plunge from 13° to 450
NE, indicating a northeasterly plunge of the major syncline. Bedding
and cleavage relationships are difficult to determine generally in the
slates of the Black River escarpment, as the former is more often absent.
Occasional beds of different lithologies make possible determinations of
these relationships, and where they have been observed they show a
succession of overturned beds with tops to the east. Vertical transverse
fractures, indicating elongation, are common as prominent smooth faces.
INDIAN POINT SEGMENT
An abrupt reversal of dips on Indian Point suggests a sharp twist or a
transverse break in the Indian Point syncline where it crosses Lake
50

Memphremagog. The intensity of the minor structures and cleavage-bedding
relations indicate a strong westward overturn approaching
recumbency in which the east limb has been largely stripped by erosion.
No lateral displacement is apparent, and so it is believed that the con-trary
dips originated when the structures were rotated by the deep-seated
effects of the central igneous intrusion on the southeast. The line
separating these two areas of opposite dips runs south-southeasterly
through Newport City and South Bay, and appears to be the southeast-erly
extension of the major shear zone in the Lake Memphremagog
reentrant. Between Indian Point and the 1080-foot hill southwest of
Beebe Plain the fold is concealed by drift cover, but from this hill it
can be followed into Canada.
Browuington Syncline
The Brownington syncline is a broad, fiat, practically recumbent fold
with a strong overturn to the southeast. It covers approximately the
eastern three-fifths of the map-area, bordering the North Neighborhood
anticline on the west and extending eastward into the Island Pond quad-rangle.
Its axial plane strikes northeast and is strongly overturned to the
southeast, thus dipping gently to the northwest. The fold is character-ized
by a steep, inverted northwest limb in contrast to a southeast limb
with gentle inclination. Exposures typical of the west limb structural
relations are amply displayed at Coventry Station (P1. 16, fig. 1). On a
traverse southeasterly from Coventry Station the beds of the Barton
River and Westmore formations show pronounced overturn to the south-east
and on the long northwesterly slope of Goodwin Mountain they are
gently inclined and in normal sequence. Beds on the east limb are ex-posed
on the open slopes directly east of the East Brownington School
and in the abandoned scythestone quarry three-fourths of a mile to the
southeast and indicated on the map.
The dips of the beds become progressively less toward the southeast,
which appears to indicate that the brunt of the regional movements
building the structures was borne by the rocks in the western portion
of the area where they are broken by faults. The plunges of the minor
folds in the Barton River and Westmore formations indicate a general
plunge of 30° NE for the major fold. Locally the plunges are variable
both in direction and amount due to tectonic effects, an occasional one
on the steep northwest limb plunging as high as 80° NE. The axis of the
fold lies in the proximity of East Brownington School. From here it
51

trends northeasterly around the bulge of the plutons on the northwest
and continues beyond the eastern border of the Memphremagog quad-rangle
where its position is somewhat obscured in an area of igneous
rocks.
The fold is further complicated by overturn of beds to the northwest
on the section of the west limb between Pine Hill and Johns River. The
dips are noticeably steep, most of them being not far from vertical. The
anomalous structures in this sector are probably the result of rotation
from original northwest dips during emplacement of the central igneous
pluton whose northwest side they flank. Movement along the Lake
Memphremagog reentrant could also have had a part in reversing the
attitudes of these structures. The fold is punctured by several large-sized
igneous bodies which have distorted its symmetry and complicated the
structures.
North Neighborhood Anticline
The presence of this fold is inferred largely from its narrowing outcrop
belt northeastward between the Indian Point syncline on the northwest
and the Brownington syncline on the southeast. The North Neighbor-hood
anticline is indicated by bedding-cleavage relations in the adjacent
Barton River formation at Coventry Station (P1. 16, fig. 1). It plunges
to the northeast, with its axial plane steeply inclined to the northwest.
With one exception, the extremely small number of exposures are
located well out on the flanks and, although possessing dips not far
from the vertical, they show an overturn to the southeast. The exception
is a single outcrop of Ayers Cliff limestone at the North Neighborhood
School, which, on the basis of its location and structural attitude, is
suggestive of its position in the axial region of the fold. Its much gentler
dip in comparison to those on the flanks, tends to support this opinion
and, in addition, might be indicative of the fold's plunge. The northwest
limb of the fold is cut out by the Black River fault.
Ware Brook Thrust
This fault is the southward continuation of the Bunker thrust in
Canada and comprises the boundary between the Northfield slate on the
west and the Ayers Cliff formation on the east. Its strike is northeast,
with relative movement from the northwest. It follows the base of an
east-facing escarpment which gradually loses its topographic expression
northward and disappears under the waters of Lake Memphremagog
(Plate 1).
52

In the Ware Brook section the fault plane has a low southeasterly
dip and is exposed by erosion in a window at an elevation of about 975
feet. Here the minimum amount of horizontal displacement is 4000 feet,
which increases greatly northward. The thrust cuts across the limbs of
folds and, therefore, is believed to have developed after the folded
structures.
Throughout its length the fault is not easily recognized because of the
apparent gradation between the formations bordering it and, in addition,
its general concealment beneath a heavy spread of drift. Indeed, were
it not for evidence elsewhere than along its trace, this fault might have
remained unnoticed. In central Vermont the Northfield-Ayers Cliff
(Waits River) contact is said to be conformable (Currier and Jahns,
1941, p. 1492).
The existence of the Ware Brook thrust is shown by the following
criteria:
(1) The outcrop breadth of the Ayers Cliff formation in Canada is as
much as twice that in the area mapped. This difference probably is not
a primary phenomenon but tectonic. That the Ayers Cliff formation
possesses the same degree of structural disturbance everywhere it is
exposed negates any possible interpretation that the formation in the
area mapped was excessively thinned in comparison to its outcrop in
Canada. Furthermore, it has been observed that the Ayers Cliff forma-tion
diminishes noticeably in breadth of outcrop southward where it
passes successively the northwest-extending reentrants (discussed
separately). Additional evidence suggesting a structural explanation
for the apparent variations in outcrop width, is a window of Ayers Cliff
limestone well within the Cram Hill formation.
(2) About half way in the section at a waterfall in the bed of Ware
Brook, a window of thin-bedded Ayers Cliff limestones is "framed" by
black, carbonaceous slates. This same horizon has been located in an
exposure of slates just off the east side of State Highway No. 105, north-northeast
of Walker Pond. In Canada it is found to the east of the thrust
in a road cut in the Ayers Cliff formation near the upper end of Fitch
Bay and, again, in the prominent limestone cliffs at the southeast end of
Lake Massawippi.
This horizon is readily detectable, once it is recognized, because of
uniformity in thickness, striking lithologic similarity in the known ex-posures
and its stratigraphic position relative to the fault. In the Ware
Brook and Fitch Bay exposures the resemblances are even more marked
53

by small lenses of calcite common to both and identical. A detailed study
of a lens from the Ware Brook locality has revealed strongly twinned,
dark calcite with minor amounts of quartz grains and, in addition,
greatly strained and recrystallized organic structures. The fossil affinities
were determined by comparisons with a series of thin sections showing
several stages in the defacement of brachiopod fragments by metamor-phism.
This sequence, of which the Ware Brook specimens show the
most advanced stage, is a part of a slide collection in the Department of
Geology at Columbia University.
(3) In the northwest corner of the Memphremagog quadrangle the
greenstones adjoin the Ayers Cliff formation while along its entire length
south of Lake Memphremagog and into the Irashurg quadrangle, the
Northfield slate is close to the fault. Reconnaissance studies in the
vicinity of Craftsbury Village (Hardwick quadrangle) appear to indicate
that the Ayers Cliff formation is cut out by the southward extension of
the Ware Brook thrust. It has also been observed that southwest of the
village of Irasburg the Barton River formation rapidly converges upon
the Ware Brook thrust. The Irasburg conglomerate, which is considered
by the writer to be basal to the Barton River formation, is exposed on
the steep slope on the east side of the Black River Valley directly opposite
the village of Albany (Hardwick quadrangle) and less than three-fourths
of a mile from the thrust. This discontinuity of formations along its
strike points to the existence of the fault.
(4) On the summit and northeast side of Round Hill, 1 Y2 miles south-west
of the village of Irasburg, is an area of slates closely resembling the
Northfield slate. These slates are underlain by limestones of the Ayers
Cliff formation. This patch of presumably Northfield slate, which is
surrounded by the younger limestones of the Ayers Cliff formation, is
interpreted by the writer as a klippe.
(5) In the light of the preceding criteria, the escarpment which rises
above the trace of the fault and gains prominence southward, is con-sidered
as additional evidence for the fault.
The Ware Brook thrust can not be older than Devonian, since it
traverses rocks of lower Devonian age in the Dudswell region in Canada.
It is younger than the folding, which is considered to be late Devonian,
as it cuts across the folds. It involves the basic intrusives of the Bolton
igneous group, of late Devonian age, at Holbrook Bay and northward
on Lake Memphremagog. The writer, therefore, believes the Ware Brook
thrust to be of late Devonian age, originating during the late Devonian
orogeny but after the folding. It is interesting to note that the so-called
54

Devonian granites which are east of the fault in Canada, transect it
south of the International Boundary. Likewise, the ultra basics, which
occur to the west in the village of Lowell, gradually approach the fault
northeastward and come quite close to it in Canada.
"En Echelon" Reentrants
A cursory inspection of the Hardwick, Irasburg, Memphremagog
(U. S.), Memphremagog (Canada), Sherbrooke, Dudswell and Disraeli
quadrangles discloses en echelon reentrants along the line of the Ware
Brook-Bunker thrust. They trend northwesterly, becoming more north-erly
to the northeast. From southwest to northeast in the following
summary they are:
Linear extent Distance between
of reef/rants reentrants
Reentrant approx. miles approx. miles
Craftsbury (Hardwick quad.) 2
13
Stony Hill (Irasburg quad.)
13
Lake Memphremagog (Memphremagog
quads., U. S. and Canada) 3i/
16
Lake Massawippi (Memphremagog
quad., Canada) 3Y2
30
Dudswell (Dudswell quad., Canada)
20
Lake Aylmer (Disraeli quad., Canada)
The tabulation above shows that the lengths of the reentrants increase
northeastward and the distances between them as well. These facts are
significant since they suggest crustal displacements of progressively
greater magnitudes in a northeastward direction. These structures are
in the section of greatest curvature of a major tectonic arc which swings
from a northerly course in Vermont to a northeasterly direction in
Canada. Apparently it is the same are recognized by Keith (1923a, pp.
313-314) and described by him as one of "four great westward salients"
in the Appalachian system. This arc, here called the Vermont-Quebec
arc, is probably structurally related to the Massachusetts arc in south-eastern
New England, described by Billings (1929, pp. 131-132). In
contrast, the Massachusetts are has a decidedly sharper bend, which
appears to be due to its position well within the main structure and
nearer the source of the compression.
55

It is generally agreed that the deforming forces producing the Ap-palachian
structures were exerted from the southeast, as indicated
mainly by folds overturned to the northwest and overthrusts with
easterly dipping fault planes. However, in the area mapped the folds are
overturned to the southeast, which presents a structural anomaly in-sofar
as the long-accepted conception of Appalachian structural origins
is concerned. Inasmuch as the sediments here are associated with large-scale
intrusions their structural irregularities are probably explainable
by local aberrations in the regional deformation. The Vermont-Quebec
are lies with a westward convexity between the pre-Cambrian Adiron-dack
dome on the southwest and the Canadian shield on the north. From
an examination of Keith's map (1923a, facing p. 309) it appears that the
pre-Cambrian areas acted as buttresses at both ends of the arc while the
Paleozoic rocks were being subjected to strong pressures from the south-east,
thus resulting in the farthest westward advance between the
stationary pre-Cambrian protuberances.
During the period of compression, relief within the arc seems to have
assumed a fanlike pattern in en echelon reentrants. The change in trend
of the recntrants from northwest in Vermont to a more northerly direc-tion
in Canada, appears to be due to major structural controls. These
structural lines are betrayed topographically by the marked northwest
and northeast orientations of many lake basins and river courses, Lake
Memphrcmagog with its embayments and the St. Francis River system
being especially good examples (Fig. 1). From their patterns, it can be
seen that these structural lines of weakness comprise two systems with
acute angle intersection facing southeast in Vermont and south in
Canada. This is suggestive of stress application from these directions in
conformance with the rule of conjugate shearing planes (Bucher, 1920)
and, in addition, harmonizes with the direction of Appalachian pressures.
Bucher (1933, pp. 245-248) calls attention to a conjugate system of shear
planes in the Jura tectonic are described by Heim. Just as in the Jura
Mountains, the northeast side of the reentrant has moved northwestward
relative to the southwest side (idem., p. 247). This is well illustrated by
the Lake Memphremagog reentrant along which the rocks on the north-east
side do not match those directly opposite on the southwest side. In
Canada, Ambrose (1943) has mapped a fault which follows the valley
of the Tomifobia River and heads into the Lake Massawippi reentrant.
Cooke (1944) has indicated a fault in the Dudswell reentrant.
Divergences in the regional trend occur also in places other than those
56

cited. Recent field work in the Jay Peak quadrangle in the northern
Green Mountains, has disclosed a northwestward swing of 4 miles in the
regional strike in the vicinity of Hazens Notch. This westward swerve
has involved the Green Mountain anticlinal axis which is in turn shifted
to the west. Cooke (1937, P. 23) has found similar structures of cones-sponding
magnitudes in the Eastern Townships of Quebec. These in-stances
show that northwest deviations in the structural trends are
widespread in the region generally. In fact, related structures can be
traced westward beyond the northern Green Mountains to the eastern
part of the Champlain Valley, where a series of thrust slices involving
mostly Cambrian rocks, has been pushed westward (Keith, 1923b).
These structures lie within the scope of the Vermont-Quebec arc and,
in this relation, it is noteworthy that structures of great complexity
appear to be extensively developed in areas encompassed by these
structural arcs or "salients," as Keith called them. The southernmost
structural arc in the Appalachian system, which bends with a pro-nounced
convexity westward into Tennessee, also embraces a terrain of
highly complicated structures (Keith, 1907).
The location of the Monteregian Hills on the foreland of the Appa-lachian
folds in the greatest bend of the Vermont-Quebec are and with a
linear arrangement to the west, is particularly significant (National
Research Council, 1944; Dresser and Denis, 1944, p. 456, maps 703A
and 704A; Adams, 1913, map facing p. 32). The pattern resembles
similar structures in the Ouachita foreland, in which simple tension
fractures on a regional scale were developed along structural lines of
weakness, due to warping and longitudinal stretching. In the case of the
Monteregian Hills, the tension fractures are conceived to have had a
similar origin and, in addition, to have served as avenues of escape for
the igneous materials.
Of significance is the presence of intrusives on the southwest sides
of the reentrants (Plate 1). The intrusives in the several reentrants are
unlike in composition, increasing in basicity northeastward. Considered
individually their rock types are:
Reentrant Rock Type
Stony Hill Granite
Lake Memphremagog Granite and metadiorite
Lake Massawippi Serpentine'
Dudswell Rhyolite and basic lavas 2
'Ambrose, 1943 'Cooke, 1944
57

Laverdiêre (1935) also has mapped an intrusive on the southwest
side of the Dudswell reentrant, but gives a composition differing some-what
from that of Cooke.
The part played by the intrusives in the faulting is not clear, but it is
believed by the writer that the segments which they occupy might have
acted as relatively resistant, though not stationary, masses of the crust
while the segment bordering on the northeast moved in a northwest
direction. If the intrusions and faulting were synchronous, a differential
movement could be expected, in which case the intrusive side of the
fault must have taken an active part.
The en echelon displacements came into existence during the late
stages of the folding and were probably simultaneous with the develop-ment
of the Ware Brook thrust. The amount of displacement at the
Stony Hill reentrant is about 2 miles and considerably more in the Lake
Memphremagog reentrant, possibly between 3 and 4 miles.
Black River Fault
This fault is subparallcl to the Ware Brook thrust and represents a
subsidiary thrust slice. It follows the base of the 5-mile escarpment south
of Newport City and continues northeasterly close to the Barton River
core of the Indian Point syncline to the International Boundary at
Beebe Plain.
The existence of this fault is inferred mainly from the deficiency in
width of the North Neighborhood anticline bordering it on the east.
The thickness of the Ayers Cliff formation on the west limb of the Indian
Point syncline is too great to be accommodated in the narrowed area
occupied by the North Neighborhood anticline. This indicates that a
part of the western limb of the anticline has been cut out and, similarly,
much of the eastern limb of the Indian Point syncline, thus bringing the
synclinal axis close to the fault.
Along the fault younger beds have been thrust over older and piled
into a folded series presenting a precipitous escarpment to the east,
south of the city of Newport. Because it is nowhere exposed, nothing is
known about the fault itself, nor is its extent south of the village of
Coventry traceable. The writer is of the opinion that the Black River
fault is of the same age as the Ware Brook thrust.
Summary of Arguments for Structural Interpretations
1. a) Field evidence had long convinced the writer that the limestone
at Lake Park is similar to that of the Brownington belt, but the
58

latter contains more slate and other metamorphic rock types in
addition.
h) Similarly, the limestone west of Irasburg Village is essentially the
same as that of Lake Park.
2. East of the Brownington belt low dips prevail. West of it the dips
are higher.
3. The width of the low dip belt is so great that it suggests a dominant
right side up condition.
4. a) Points 1-3 demand that the Brownington belt be a syncline, and
that the Black River escarpment also be a syncline.
b) Without any structural hypothesis in mind the writer mapped
the Brownington section as growing wider northward, which
checks with the plunge of all observed minor folds.
c) The width of the Black River escarpment belt is also greater in the
north than farther south, suggesting a synclinal structure.
5. The highly sandy Westmore formation has no counterpart in the
western part of the area.
6. In the Cold Brook section in the southwestern rectangle of the
Island Pond quadrangle, the Westmore formation is seen to pass
downward into beds of whitish sandstone weathering into very
thin beds. These resemble the sandstone of the Shaw Mountain
formation in the Ware Brook section.
7. Points 5 and 6 suggest that:
a) The Westmore group is stratigraphically near the top of the Ware
Brook section southeastward.
b) If "a" is correct, then the slate beds and equivalent metamorphic
rocks should appear intercalated in the sandstone of the Cold
Brook section as one descends.
8. POints 6 and 7 fit perfectly into the structural picture developed
in points I to 5, and are essentially independent of the latter.
9. a) If 1 to 8 are correct, then the sequence of the larger pattern of the
stratigraphic succession of this area is cut out by an overthrust
in the northwestern part of the area.
b) This overthrust was not invented, for on the basis of the writer's
own correlations it was at first assumed that this contact was a
stratigraphic overlap, but he was driven by points 1 to 8 to the
interpretation that it is an overthrust and finds that in Canada an
overthrust had already been discovered. Other lines of evidence
for this overthrust have already been discussed.
59

MINOR STRUCTURES
FOLDS
Excellent folds may be seen in many places. Several well-defined folds
are exposed in the Ayers Cliff formation on Cove and Bell islands in
Lake Mernphremagog (P1. 12, fig. 2). A large fold in interbedded slates
and limestones of the Barton River formation, displaying bedding in
color differences on a glacially smoothed and striated surface which, to
some extent, is due to weathered pyrites in certain layers, is exposed in
a pasture 1 mile due south of Coventry School (P1. 12, fig. 3). Bedding
is also disclosed here by rows of minute pits left by the decomposition of
suiphides.
Excepting in the tract directly to the northwest of the central igneous
body where overturning is to the northwest, the folds are overturned
to the east and southeast. Axial planes dip anywhere from positions of
recumbency to verticality. The regional cleavage in the southern half
of the area changes from dips of more than 80 degrees in the town of
Coventry to dips as low as 13 degrees in the town of Westmore, indicating
the progressively more pronounced overturning of the structures to the
southeast. Away from igneous contacts the folds follow a general north-easterly
strike with an average plunge of 28° predominantly northeast.
An occasional plunge is as high as 80° or more, particularly in the vicinity
of the plutons. The changes in the orientations and attitudes of the folds
locally reflect the influence of the intrusions. Convergence of the fold
axes and plunges toward Beebe Plain in the northern portion of the area
is corroborative evidence that the intrusions are related to the deforma-tion
of the sediments.
Slip of the beds along bedding planes in folding has produced drag
folds in the less competent strata. Where slates or phyllites lie between
competent strata they are often folded in this manner. In some cases
thin beds of hard phyllite, lying between massive beds of limestone, are
squeezed into sharp-crested drag folds, the limestone on one side showing
perceptible flow structure leading into the troughs of the folds (P1. 13,
fig. 1). Apparently, the drag folds were originated before the adjacent
limestone attained the status of complete flow, as the flow structure in
the limestone shows no deformation to conform to that of the drag-folded
phyllite.
Folds are sometimes cut off longitudinally by shear planes, the beds,
especially in the region of the nose, ending abruptly against layers follow-
60

ing the regional strike. Where they are closely spaced, as in some folds
in the Ayers cliff formation, the shear planes traverse the many tightly-flexed
layers. Commonly small offsets are shown clearly by layers of
brittle quartz, simulating those in shear folds. Occasional shear planes
contain thin veins of quartz of a later date than that which is conformable
to the bedding (P1. 13, fig. 2).
Quartz veins frequently exhibit complex folds of the ptygmatic
variety. Good examples occur in limestones of the Ayers Cliff and slates
of the Barton River formations. They are prevalent in beds possessing
flow structure, occurring in a series of narrow loops resembling a con-xxxx
I 'I
X X
X X
I
x
X X X
i I
11
/ X X V XX x X
!
S X X
Figure 4. Shore of Lake Memphremagog at Lake Park. Ptygmatically folded
quartz veins in Ayers Cliff limestone. pegmatite. The sketch shows 8 feet of
width.
61

voluted length of rope (Fig, 4). Their association here with rocks that
have been in a plastic condition is significant, as it suggests an origin
similar to that advanced by Kuenen (1938). Here the previously em-placed
quartz vein appears to have suffered compression when the en-closing
strata behaved plastically. That the movements producing the
ptygmatic folds are restricted in scope, is indicated where veins remain
undisturbed in the adjoining beds (Fig. 4). Hills (1943, p. 84) classifies
this type with the flow folds.
FAULTS
Numerous transverse faults exist along strongly-developed northwest-trending
fractures. They involve beds, veins, sills and dikes, with lateral
displacements ranging from a few inches to several feet. Fault surfaces
are often coated with slickensided quartz and enclose quartz of varying
thicknesses, or even dikes. The faults are well defined in the more coin-petent
beds but soon die out after extending a short distance into the
adjacent limestone, indicating that the limestone must have been in a
plastic condition when faulting occurred. Where drag in the abutting
beds could be observed, it appeared to show that movement was pre-dominantly
northwestward. Cumulatively, these faults represent exten-sive
movement and they might be related in time to the major offsets
associated with the Ware Brook thrust, this in addition to a suggestive
structural connection.
At the margins of the large igneous bodies and in the neighboring
sediments are faults of small magnitudes caused by expansive action
of the intrusions (Fl. 13, fig. 3). These faults are usually distinct and, in
places, contain quartz veins. They involve aplites, pegmatites and strata,
the lattermost especially in the manifold sedimentary patches lying
within the areas of the plutons.
Longitudinal faults of the thrust type and contiguous beds indicate
an interesting series of events. Fig. 4, P1. 13 is illustrative of this type of
fault and shows a 6-foot longitudinal displacement of a thick layer of
phyllite. Thickening of the horizon by reverse faulting has caused the
thin bordering strata to bend. The marked attenuation of the confining
strata is, in part, due to lateral pressure exerted by the wedgelike move-ment
of faulting and, in part, to regional stretching during the period of
folding. Regardless of competency, all the beds are thinned, some pinch-ing
out altogether.
Noteworthy are the diagonally truncated ends of the faulted stratum,
62

indicated by the hammer and steel tape. The truncation at the chisel
end of the hammerhead fits that marked by the steel tape, suggesting
that both ends were joined here prior to faulting. The fact that the
truncations no longer face each other, precludes an explanation of de-formation
by thrusting alone. Rather, the displaced bed was brought
into its present position by separation along the strike sufficiently to
permit clearance of the ends before movement in the reverse direction
was instituted. Normally, the segments would be expected to lie with
their fault surfaces facing each other. Deformation was accompanied
both by stretching and shortening, during which the ruptured competent
bed had complete freedom of movement in the intervening plastic
limestone. If the fault was produced by dominantly linear movements,
tension stresses must have preceded those of compression, otherwise the
diagonal fault surfaces would not face away from one another as they
do at the end of each segment. Faulting may have been even more com-plex
but evidence for it is lacking. The longitudinal faults disclose both
elongation and shortening. One has only to imagine the behavior of
thinly-bedded, more or less, heterogeneous strata with innumerable
inherent planes of weakness than are present in heavy-bedded, homo-geneous
strata, to appreciate the effects of longitudinal stresses on such
rocks.
Fig. 1, P1. 14, which is located in the same outcrop and not many feet
away from that shown in Fig. 4, P1. 13, shows a feature that, in the
writer's opinion, depicts an early stage in the development of the longi-tudinal
fault discussed above. The diagonal fracture has begun to form,
its open end containing a wedge of the adjacent limestone. The V-shaped
fracture probably has an origin analogous to the fractures resulting
when a stick of shivery wood is bent to the breaking point, thus allowing
the plastic limestone to enter. An alternative explanation views the
plastic limestone, which is under confining pressures, as aggressively
wedging the fracture apart as it is forced to intrude.
BEDDING
Bedding is shown in different ways throughout the area mapped. It is
commonly recognizable, particularly in a succession of strata exhibiting
different lithologies (P1. 14, fig. 2). However, in thick sections of slates
and phyllites bedding has been either totally obscured or rendered
extremely difficult of detection by metamorphism. It is vaguely visible
upon close examination in shade differences of color and slight changes
63

in texture as, for instance, a crossbedded, sandy layer in the slates of the
Black River escarpment south of Newport City.
In some slates bedding appears as fractures (P1. 14, fig. 3). The writer
believes that, in some cases, curving fractures in vertical sections of
cliffs of slate horizons quite possibly represent bedding. In Fig. 4, P1. 14,
bedding is disclosed by a corrugated fracture and paralleling line of
solution pits formerly occupied by pyrites. The bedding surface exposed
in another part of the outcrop, displays a washboard structure. Con-trasting
examples in which bedding is manifest, are shown in P1. 15,
figs. I and 2; in the former the beds of slate are delineated by a series of
parallel grooves while the latter shows a succession of thin beaded ridges
in an exposure of hard, massive amphibolite, as though the beds were
welded together. The exceedingly smooth bedding planes in the whet-stone
phyllite of eastern Brownington, are parallel to the cleavage
(P1. 15, fig. 3).
BEDDING—CLEAVAGE RELATIONS
Bedding and cleavage comparisons are highly important in structural
studies in metamorphosed regions. They have aided enormously in the
determination of the major structures in this area and showed the beds
to be overturned with tops to the east in considerably more than half
of the area. The degree of overturning and the position on the fold is
clearly demonstrated where slates and phyllites are interhedded with
massive layers such as limestones, or in thick sections of slates in which
bedding is distinct (P1. 16, figs. 1 and 2). In slates where bedding and
cleavage relations are not well defined as, for example, on the limbs of
tight folds where both are essentially parallel, it became necessary to base
structural interpretations largely on observations made in adjacent
tracts.
SINu0sITY OF BEDS
The strata frequently display local rolls both along the strike and down
the dip, which, if not recognized, might seriously affect the accuracy of
strike and dip measurements (P1. 16, fig. 3). Sinuosity may be expected
in a region of tightly folded, comparatively thin, incompetent strata
such as those dealt with here. Locally, sinuous structures are the result
of expanded masses of quartz (P1. 12, fig. 1). Generally, however, they
result from unequal stresses of folding and dilation of igneous intrusions.
The small-scale sinuosities reflect those of greater magnitude flanking the
plutons and curving with the major folds.
64

PLASTIC FLOW OF THE CALCAREOUS ROCKS
Plastic flow in the limestones is widespread. It is expressed in the
bedding planes which appear as lines, often described by thin ridges of
the more resistant material due to weathering, and color distinctions
probably attributable to varying degrees of recrystallization. The flow
lines normally follow the bedding and occasionally curve around the
noses of folds. These folds are frequently cut off on one side by a shear
plane and apparently represent drag (P1. 16, fig. 4). Thin, steeply-dipping
slates sometimes occur torn apart and the slender pieces rafted to new
positions, still retaining their steep attitudes. In other instances, the thin
slate layers are molded into extremely complex small-scale folds, the
flow lines in the limestone core directed into the strongly crinkled, slate-bordered
salients. As suggested by its pattern, this peculiarly intricate
type of fold might appropriately be described as "birdsfoot" (P1. 17,
fig. 1).
In Fig. 2, P1. 17, the somewhat bulbous cores of two synclines are
composed of limestone displaying flow structure. The limestone, rendered
plastic under the intense stresses of folding, was forced into the synclinal
cores, producing the bulblike shape. Although most are ordinary drag
folds, a few folds of the flowage type were developed in the limestone
during its migration into the cores under confining pressures (Bain,
1931). Where overturned, some of the anticlinal folds are sharp crested
and bear a resemblance to the profile of a machete blade. Their upper
limbs sag and are thinned while the lower limbs display a more pro-nounced
sag and are greatly thickened. These features are all illustrative
of a flow condition in which there was a tendency for material to move
downward. Folds similar to these are described from the Vermont marble
belt by Dale (1902, p. 9). In places the flow structures resemble cross-bedding
where one set is truncated by another, or they appear as drag
at the contact with the enwrapping slates.
Not only were the limestones in an environment of deep burial but
they must also have been strongly affected by the igneous intrusions,
since most of the examples cited are located near their contacts. In some
folds at igneous contacts certain thin calcareous layers are completely
recrystallized to a white marble, while adjacent beds are partially
marbleized.
An occasional fragment of the intercalated, more competent rock
occurs embedded in limestone (P1. 17, fig. 3). Similar occurrences have
been reported from other localities (Balk, 1936, pp. 720-723; Adams and
65

Barlow, 1910, pp. 220-221). The presence of these erratic pieces in the
limestone matrix appears to be due to their dismemberment during
folding movements and subsequent inclusion. Behrc (1933, p. 148) has
described sedimentary fragments isolated in other strata and attributes
the phenomenon chiefly to settling movements sometime during di-agenesis.
That the "floating" fragments herein described have a tectonic
origin is evidenced by the cleavage and clean-cut transverse fractures
which they possess, the latter terminating segments which, therefore,
could readily be dislodged.
The free moldability of the limestone is further seen in the thickening
and thinning of individual beds along the strike. Although it is prominent
in the limestones, thickening and thinning is not confined to them but is
found in all types of layers, including granite sills and quartz veins.
Some beds are pinched out along the strike into lenses resembling horses
in faults; commonly slates and phyllites show this behavior between
limestone beds. Thicknesses of beds at the noses of folds are as much as
10 times greater than on the limbs.
Flowage of the limestone and associated structures are significant as
evidence showing that the rocks of the region were subjected to great
stress under conditions of considerable depth and to the influence of
igneous action.
BOUDINAGE
Beds, veins and thin sills or streamers are frequently found drawn
apart into separate units and the ensuing gaps filled with material from
the adjoining beds or by quartz. This structure was termed boudinage
by M. Lohest (1909), many examples of which have been cited in the
geological literature since. E. Cloos (1947) has reviewed the literature on
boudinage with a brief discussion.
In the bed of the Clyde River between the highway and railroad bridge,
1. 1 miles northwest of Barton Village, slate boudinage occurs in limestone
(Fig. 5). The slate beds are relatively thin and lie between thick beds of
limestone. Ostensibly, the weaker rock composes the boudins, which is
contrary to the competency relationships in the many occurrences
observed, but upon examination of the thicker limestone beds it is found
that they are thinly banded. The banding is much thinner adjacent to
the boudins than farther out in the limestone and parallels them (Fig.
5). Frequently the bands are bordered by thin, sinuous quartz veins
which occur singly or in parallel sets.
66

11
a
Figure 5. Bed of Barton River between highway and railroad bridge, mile east
of Country Club. Slate boudinage in limestone. Barton River formation. M & quartz.
The sketch shows 4 feet of width.
The banding in the limestone represents a flow structure, which is an
important factor in the explanation of the competency relationships
between the limestone and the slate. The slate is actually the more
competent while the limestone, which was effectively weakened by the
67

(lose SUC('eSSiOfl of shear planes, was prevented from behaving as a unit
when under stress. That a plastic condition prevailed during formation
of the boudinage structure, is exemplified, not only by the limestone,
but also by the shapes of the boudins themselves. They are drawn out
into tapering ends, much the same as taffy candy when pulled apart. The
cleavage in the slate is apparently older than the boudinage structure.
Two major stages in the formation of boudinage structure are illus-trated
in Fig. 2. In this exposure, located where the Pine Hill road
crosses Cobb Brook, three granite streamers, of which two exhibit varying
degrees of disruption, are elongated with the cleavage of the enclosing
slate. One of the streamers has suffered very little deformation, while its
neighbor has undergone segmentation on fairly evenly spaced transverse
fractures. Along its northwestward extension this streamer is progress-ively
more disrupted, the farthest segments showing incipient rotation.
The remaining streamer is completely disjointed into a series of boudins,
several showing rotation. In this developmental sequence the competent
layer is transversely fractured, along which the segments are displaced
and, apparently, rotated as they are longitudinally separated. Due to
friction caused by linear and rotational movements, the short, angular
blocks of the early stage have become lengthened and rounded in form.
The flow cleavage wraps around the isolated boudins and is lobed in the
gaps between them. It has already begun to bend around the displaced
angular segments in the middle streamer.
It is somewhat perplexing that competent layers lying only a matter
of feet or even less apart, should behave so differently under stress.
Selective differential movements, however, within the slates could
account for the structural differences in the three granite streamers.
Again, the time of intrusion relative to movements in the slate, might
explain the marked contrast between the practically undeformed and
completely dismembered streamers. The tension joints and offset rhombs
in the resistant layer in Fig. 2 suggest stresses causing a bending motion
as in folding. Boudinage is indicative of elongation and is a phenomenon
associated with layers that have been subjected to folding stresses.
In Fig. 6, which is from the same location as Fig. 5, a stratum of slate
shows both transverse offsets and boudinage, the faults and the bou-dinage
gaps being occupied by quartz. Although the flow structure in
the limestone curves into the gap between the boudins, it shows no
tendency to do so at the faults. Rather, it ends abruptly against them
and is even noticeably displaced; the displacements extend out into the
68

limestone only as far as the thin quartz filler extends. In this case, the
limestone appears to have possessed greater plasticity where the bou-dinage
was produced than it did along the faults. Apparently, the faults
are later in origin.
Quartz often occurs as boudins (P1. 15, fig. 4). The thin-bedded
limestones and slates have been bent inward to close the gaps between
the quartz lenses. The limestone layers in the gaps have been thickened
by flowage while those contiguous to the boudins have suffered attenua-tion.
However, these effects do not extend far into the enclosing strata
Figure 6. Bed of Barton River between highway and railroad bridge, mile east
of Country Club. Faulted bed of slate and incipient boudinage formation. Barton
River formation. quartz. The sketch shows 73/ feet of width.
(P1. 15, fig. 4). Boudinage is strikingly shown in the numerous patches of
thinly-bedded sedimentary rocks in the areas of the granite plutons.
Here the coarse, micaceous granite paste has flowed between the sepa-rated
beds.
69

LINEAR ELEMENT
Parallel streaks of minerals or their weathered products are common
on the planes of cleavage, schistosity and bedding. This linear parallelism
is shown by elongated mica flakes, amphiboles, sulphides and rust
streaks resulting from weathered sulphides. The suiphides are often
drawn out into a well-defined lineation and in some cases the biotites
and an undetermined, steel-colored mica exhibit definite oval shapes
with parallel elongation. The linear element is generally well developed,
but in many of the slates it is discerned with difficulty.
Orientation of the linear features over the whole area is shown in
Plate 1. The direction of the linear element is not the same everywhere
in the area, but for the most part it plunges northeast in the western
half and northwest in the eastern. Northwest plunges in the northern
part of the towns of Irasburg and southeastern Coventry, appear to be
the northwestward continuation of a similar plunge orientation in the
towns of Brownington and Westrnore. As a rule, the linear element
plunges more to the west in the southern than in the northern portion
of the eastern half of the area. Its many deviations have probably been
caused by nonuniform stresses generated during folding of the sediments
and emplacement of the plutons.
A study of the map reveals two major directions of the lineations,
namely, northeast and northwest. It has occurred to the writer that,
since there is a great deal of overturning in the area, the lineations also
might be overturned in one of the principal directions noted. Where the
beds are overturned to the southeast, which is the dominant attitude
of the beds northwest of the axial region of the Brownington syncline,
the trend of the lineation is markedly northwest. Near igneous contacts
it may deviate from the directions observed. Cloos (1946, pp. 21-22), in
discussing the age relations of the linear element, traces the probable
sequence of structural changes during the process of folding. He suggests
a stage when the process producing flowage and lineation is arrested
and followed chiefly by fracturing. These two succeeding stages are well
illustrated in Plate 5, figs. 1 and 2, in which a later "slip cleavage" has
been superimposed over an earlier flow cleavage. In strongly folded
rocks, such as those characteristic of this region, the lineation could
have become fixed in the fabric of the rock before overturning, so that
a lineation possessing an original northeast strike, was given a north-west
strike through reversal of the dip of the strata. For example, a bed
of slate whose linear element plunges to the northeast on a surface dip-
70

ping to the southeast is, with continued or renewed deformation, over-turned
to the southeast, thereby bringing the previous northeast plunge
of the linear element into a northwest orientation. Turner (1948, p. 282)
mentions changes in attitude of lineation by folding. In connection with
the above discussion, the question of the possible use of linear element in
determining reversal of beds where the usual criteria are totally lacking,
presents itself.
Lineation is both down the dip and parallel to the fold axes. It some-times
occurs on the same surface in more than one set, as in the axial
region of the Brownington syncline one mile southwest of Toad Pond.
Crenulations in at least two sets line the bedding surfaces and sometimes
are parallel to the plunge of the minor folds.
METAMORPHISM
General Statement
The rocks of the area were affected by regional metamorphism in
which the intrusives played a prominent part. They are assigned to
metamorphic zones according to grades on the basis of certain mineral
indicators (Billings, 1937, pp. 540-543) and also according to the zonal
subdivisions of Harker (1932, p. 209). All the formations east of the
Ware Brook thrust are in the middle-grade zone of metamorphism. The
minerals diagnostic of the intensity of metamorphism indicate an in-crease
toward the southeast. The high-grade zone is present in the
aureoles bordering the plutons. Northwest of the Ware Brook thrust
the rocks have not been studied petrographically, hence their place in
the zonal delimitation is not known, although general observation is
suggestive of middle-grade at most.
MINERALS
Chlorite—Chlorite is widely distributed in the area and, thus, has no
zonal significance. Much of the chlorite is the result of retrograde
metamorphism, replacing amphibole, augite and biotite. Where it con-tains
inclusions of zircon its origin from biotite is confirmed. Pale-colored
or "bleached" biotite flakes are associated with chlorite and a partial
alteration of hiotite to chlorite is not uncommon. Chlorite occurs as an
alteration product in the fractures of garnets, as in the six-rayed garnets
cited earlier in this paper.
Rectangular, well-defined porphyroblasts of chlorite, often of large
71

size, transgress the parallel structures, thus indicating a late develop-ment
of this mineral. They were formed either as the normal product of
progressive metamorphism, or in a lower temperature during retrogres-sive
metamorphism.
Biotite—Biotite occurs in the Ayers Cliff formation but is found in
greater amounts in the Barton River and Westmore formations. It is
present both as irregularly-shaped porphyroblasts and as well defined
crystals parallel to the banding in the rock or in random orientation.
Occasional large phantom crystals broken up parallel to the banding and
large porphyroblasts bent and broken to conform to a herringbone
structure, indicate the orientation effects of deformation. Flaser struc-tures,
many with frayed ends, composed of both oriented and unoriented
biotite, evince the effectiveness of dynamic metamorphism on these
rocks.
The concentration of biotite in rich bands and its development in
contact zones between sedimentary layers in the presence of muscovite,
calcite and quartz, is suggestive of hydrothermal action and possible
reactions among these minerals.
Garnet—Garnet occurs in the Barton River and Westmore formations,
including their contacts with intrusives where the high-grade metamor-phic
zone prevails. It is prominent as porphvroblasts which are especially
numerous in certain horizons, occurring in groups or as single crystals.
It is found with perfect crystal outline and also in irregularly shaped
masses which are often considerably corroded. In some porphyroblasts
corrosion has produced a poeciloblastic or "sieve" structure in which
quartz inclusions constitute as much as 50 per cent. Undistorted por-phyroblasts
in strongly crenulated schist indicate a late development.
Alteration in varying degrees is common in the garnets, the replacing
minerals quartz and sericite, and often chlorite, occurring at tufted ends
of garnets parallel to the schistosity, in bleached border zones in which
biotite, staurolite, and sulphides, in addition, are present, and in six-rayed
fractures. In some cases replacement has become so complete that
only phantom crystals remain. Finely disseminated carbon has rendered
some crystals a dark gray. Garnet occurs also in quartz and pegmatite
veins and in granites.
Andalusite—In the thin sections examined, andalusite appears to be
confined to sedimentary rocks bordering intrusives. It appears here, in
72

the high-grade zone, as a retrograde mineral which occurs in various
stages of alteration to quartz and muscovite. Large porphyroblasts of
the variety chiastolite, exhibiting symmetrically-arranged carbonaceous
inclusions, are greatly altered to quartz and muscovite, as is also a
strongly pleochroic colorless to rose-colored variety. Andalusite has
formed apparently in a retrogressive metamorphic environment of the
high-grade zone in argillaceous sediments, developing into the retrogres-sive
condition with falling temperatures.
Staurolite—Staurolite occurs generally in the Westmore formation,
and only at igneous contacts in the Barton River formation. It is found
in association with andalusite, which is rare according to Harker (1932,
p. 232). In this relationship, the staurolite is present as small porphyro-blasts
oriented to conform to a wavy schistosity which bends around
the much larger andalusite porphyroblasts that are considerably retro-gressed.
In this instance, the staurolite formed while deformation was in
progress and the andalusite at a later time of falling temperature. Many
large porphyroblasts of staurolite, variously oriented, are greatly frac-tured,
distorted and broken apart, which is suggestive of either a recur-ring
period of deformation or their development during the waning
stages of the main orogeny. The large porphyroblasts are profuse with
inclusions of quartz and carbonaceous matter, the latter sometimes
oriented parallel with the schistosity. Porphvroblasts that have suffered
little or no distortion, possess borders relatively free from inclusions.
Sülimanile—Sillimanite is restricted to contact areas of high thermal
metamorphism surrounding the plutons. In some places it occurs abun-dantly
in sheaf-like bundles and as isolated, needle-like crystals in
random orientation, in aluminous and highly quartzose sediments. It
is late to form and has grown at the expense of biotite and muscovite.
At the contact between a very fine-grained rock composed of quartz
grains and abundant carbonaceous material with phantom porphyro-blasts
of muscovite visible only under crossed nicols, fan-shaped groups
of slender sillimanite crystals extend into a bordering, medium-grained
quartz-calcite rock.
Lime-silicate Minerals—This group of minerals is here represented by
tremolite, actinolite, diopside, clinozoisite, some zoisite, wollastonite
and scapolite, and possibly vesuvianite. They occur almost exclusively
at igneous contacts in the calcareous rocks of the Barton River and
73

Westmorc formations. The development of these minerals at igneous
contacts is suggestive of the introduction of materials in addition to the
activation of the original constituents of the sediments, such as the clay
mineral impurities.
Tremolite ranges in size from fine grains to large euhedral crystals,
and sometimes occurs as phantom crystals. It is often associated with
quartz, calcite and diopside, in which relationship diopside has taken
the place of tremolite in an environment of rising temperature. Large
acicular porphyroblasts of tremolite and muscovite have, in some in-stances,
been observed with brush-like groups of tremolite crystals
attached to the ends of the rectangular muscovites. Actinolite accom-panies
tremolite in white, saccharoidal, highly siliceous, marbleized
layers of the limestones at igneous contacts.
Amphibole—Amphibole is common in the rocks of the middle- and
high-grade metamorphic zones. Colorless and yellow-green porphyro-blasts
are frequently found corroded by quartz and altered to chlorite
and epidote, and occasionally clinozoisite, suggesting a change to a
retrogressive metamorphic mineral assemblage. On the other hand,
hiotite partly altered to hornblende containing streaks of magnetite,
indicates a progressive metamorphic environment. The amphiboles have
a random orientation and, therefore, are considered to have formed
when the period of dynamo-metamorphism had subsided.
HISTORICAL GEOLOGY
The Memphremagog area lies within the Magog eugeosvnclinal belt
(Kay, 1937, p. 290; 1942, p. 1642; 1948, p. 1332) which subsided deeply
during early Paleozoic with accompanying volcanism, represented
sparsely by tuffs in the immediate section. The paleogeography and
sedimentation were strongly affected by deformation toward the west
in the later Ordovician, culminating in the Taconian orogeny. Deep
subsidence continued in a more restricted belt including the Mem-phremagog
area through Silurian and into early Devonian time, closing
with the severe folding, thrusting and plutonic invasions of the later
Acadian or Shickshockian orogenv. The sediments are generally poorly
sorted, dominantly argillaceous, with varying quantities of quartz and
calcareous constituents. Deposition was in waters of varying depths
having persistent source lands for terrigenous elastic sediments that
filled the rather rapidly subsiding geosynclines. Rapidly changing litholo-
74

gies in thin-bedded sections are frequent. Extensive conglomerates of
rounded quartz pebbles in lower formations, and crossbedding, frequent
in some units, indicate shallow water conditions at times. Most of the
argillites are quartz arenaceous, and much of the quartzite has argillace-ous
constituents, suggesting that subsidence proceeded too rapidly for
the debris to become well sorted by the currents that swept it in and
passed over it. Notwithstanding effects of subsequent metamorphism,
the rocks in many localities are sufficiently well preserved that fossils
should be found if originally common; few have been recognized con-fidently.
The area was occupied by medial Ordovician seas when the oldest
sediments in the area were deposited. The prevailingly silty muds laid
on a gravelly base, becoming sandy in higher horizons are represented in
the Cram Hill formation, suggesting progressive deepening, sinking
exceeding accumulation. After an erosional interval, perhaps representing
rise of a belt to the west, the seas advanced again over the area within
medial Ordovician time, beginning the deposition of quartz gravels that
with the succeeding sands interbedded with tuffaceous material and thin
calcareous zones, constitute the Shaw Mountain formation. Crustal
oscillations controlled the extent of erosion and deposition reflected in
the variable thicknesses of this formation, particularly of the con-glomerates.
Subsequently, with deepening water, dark, siliceous muds of the
Northfield slates were deposited, becoming more calcareous toward the
top and finally passing into the calcareous, somewhat sandy, muds of
the Ayers Cliff formation. The Taconian orogeny may be represented
in the conglomerate of sedimentary and igneous fragments at the base
of the succeeding Barton River formation and the unconformity at its
base. The succeeding beds are replete with abrupt changes in lithology
involving calcareous muds to sands, denoting shifting currents in the
shallow seas above the rapidly subsiding geosyncline. Similar conditions
of sedimentation continued throughout the span of the Westmore forma-tion,
but with the fine terrigenous clastics becoming progressively more
siliceous. Deposition of the Westmore formation may have extended into
early Devonian time (Doll, 1943, p. 57), though evidence is tenuous.
That this portion of the Magog trough was flooded by marine waters in
1)evonian time, is supported by the fossils in the Bernardston marble
far to the south in Massachusetts (Whitfield, 1883).
Although secondary structures were imposed upon the strata during
75

the earlier stages of the geosynclinal development, it was not until the
late Devonian that the present structures, revealing a deformation of
great intensity, were formed. This was the Acadian or Shickshockian
disturbance. The formations were squeezed into strongly folded and
faulted structures with northeast trends, the structures notably ac-centuated
by the forceful invasions of the magmatic bodies which shoved
the beds from the earlier acquired northeast trends to a perimetric
orientation in proximity to the plutons. The final emplacement of the
igneous bodies lagged behind the dynamic phase of the orogeny which
produced the folded and faulted structures, but that they were actively
rising during the period of deformation is shown by sills infolded with
the sediments. The intrusions were definitely related to the orogeny and
very possibly played an important part in the evolution of the en echelon
reentrants, in which they occupy "cornerstone" positions. The thrust
faults originated during the final stages of the folding and probably long
before the intrusives had ceased to be active. A solitary basic dike affirms
the occurrence of post-orogenic injections.
Metamorphism is intimately associated with the deformation and
igneous intrusions. It is both deformational and thermal, the latter
producing widespread recrystallization of high rank. Although recrystal-lization
began early in the deformation, it probably had not established
a zonal pattern until the arrival of the more advanced intrusive stage of
the orogeny. This is substantiated by the proximal relationship of the
high-grade metamorphic zone to the intrusives. Besides heat, the in-trusives
sent gases and liquids far out into the enclosing rocks, resulting
in the development of a variety of new minerals in the easily altered
argillaceous and calcareous sediments.
Later Devonian time introduces a long span characterized chiefly by
erosion and intermittent uplifts, the warping of the late Tertiary herald-ing
the Great Ice Age or Pleistocene epoch. The glacial ice modified the
earlier landscape, rasping material from the higher elevations and
distributing it over the surface generally as till, but to greater thick-nesses
in the valleys. Much of these deposits was reworked by the
meltwater liberated by the waning ice sheet and in the major valleys
was submerged under the waters of marginal glacial lakes, of which
Glacial Lake Memphremagog was the most extensive (Hitchcock,
1907-1908, p. 641).
Post-glacial history is principally one of uplift with continued erosion,
76

in which time the major streams have incised themselves to form scenic
gorges in places.
ECONOMIC GEOLOGY
Granite quarries and prospects at many places in the plutons bear
•witness to a time of extensive activity in this industry. The granite
probably found local use mostly as foundations for bridges and houses.
The Willey Granite Quarry in Derby appears to have been in produclion
longest and, after a period of inactivity, is again in operation. For a time
this quarry furnished stock for gravestones, as may be seen in the
cemeteries in Newport. In the past, phyllite of whetstone grade from the
upper part of the Westmore formation was a natural resource of some
note. Several openings are located on the slopes north of Lake Willoughby
and east of East Brownington School. The chief source of whetstone
stock was the large quarry located on the westerly slope half a mile
east of the junction of state highway route nos. 58 and 5A. The phyllite
was fashioned into whetstones at a mill on the Willoughby River in
Evansville about 3 miles west of the quarry. Phyllites have also found
local use as foundation stone and flagging.
Gold and copper have been reported in the area (Richardson, 1907-
1908, p. 289); the former in hardly more than a trace and the latter in
small samples in combined form. The quest for these metals in the past
is revealed by pits in pyritized rock and openings in quartz veins.
A generous supply of gravel is being exploited in the various towns
for road metal and other uses.
77

REFERENCES USED
ADAMS, C. B.: 1845, First Annual Report on the Geology of Vermont, Burlington, p.49.
ADAMS, C. B.: 1846, Second Annual Report on the Geology of Vermont, Burlington, p.
241.
ADAMS, F. D. and BARLow, A. E.: 1910, Geology oft/ic Haliburton and Bancroft Areas,
Memoir No. 6, Canada Dept. of Mines, Geol. Survey Branch.
ADAMS, F. D.: 1913, The Monteregian Hills, Guide Book No. 3, Geological Survey,
Canada, pp. 29-80.
AMBROSE, J. W.: 1943, l'reliminary Map 43-12, Stanstead; Stanstead and Brome
Counties, Quebec: Geological Survey of Canada.
BAlK, G. W.: 1931, Flowage Folding, Amer. Jour. Sci., vol. 22, pp. 503-530.
BALK, ROBERT: 1925-26, A Contribution to the Structural Relations of the Granite
Intrusioni of Bethel, Barre, and Woodbury, Vermont, Report of the Vermont State
Geologist, pp. 38-96.
BALK, RoBERT: 1936, Structural and Petrologic Studies in Dutchess County, New York,
Bull. Gaol. Soc. Am., vol. 47, pp. 685-774.
BARRELL, JOSEPH: 1902, The Physical Effects of Contact Metamorphism, Amer. Jour.
Sci., vol. 13, pp. 279-296.
BEI-JRE, C. H.: 1933, Slate in Pennsylvania, Topographic and Geologic Survey, Bull.
Mb, 400 pages.
BILLINGS, M. P.: 1929, Structural Geology of the Eastern Part of the Boston Basin,
Amer. Jour. Sci., 5th ser., vol. 18, pp. 97-137.
BILLINGS, M. P.: 1937, Regional Metamorphism of the Littleton-Moosilauke Area,
New Hampshire, Bull. Gaol. Soc. Am., vol. 48, pp• 463-565.
BUCHER, W. H.: 1920, The Mechanical Interpretation of Joints, Jour. Geol., vol. 28,
pp. 707-730.
BUCIIER, W. H.: 1933, The Deformation of the Earth's Crust, Princeton, 518 pages.
CLARK, T. H.: 1934, Structure and Stratigraphy of Southern Quebec, Bull. Geol. Soc.
Am., vol. 45, pp. 1-20.
CI.ARK, T. H., and FAIRBAIRN, H. W.: 1936, The Bolton Igneous Group of Southern
Quebec, Trans. Royal Soc. Canada, 3rd ser., vol. 30, pp. 13-18.
CLoos, ERNST: 1946, Lineation, a critical review and annotated bibliography, Mem. 18,
Geol. Soc. Am., 122 pages.
CLoos, ERNST: 1947, Boudinage, Trans. Am. Geophysical Union, vol. 28, No. 4, pp.
62 6-632.
CohEN, C.: 1900, Summlung von Mikrophotographien zur Veranschaulichtung der
Mikroskopischen Struktur von Mineralien und Gesteinen, 3. Auflage, Stuttgart.
COOKE, H. C.: 1937, Thetford, Disraeli, and Eastern Half of Warwick Map-areas,
Quebec, Memoir 211, Gaol. Surv. Canada, 160 pages.
COOKE, H. C.: 1944, Preliminary Map 44-33, Dudswell; Richmond, Wolfe and Compton
Counties, Quebec; Geological Survey of Canada.
COOKE, H. C.: 1948, Age of the Bolton Lavas, Il[e,nphremagog District, Quebec, Trans.
Royal Soc. Canada, 3rd ser., vol. 42, pp. 17-27.
CURRIER, L. W., and JAHNS, R. H.: 1941, Ordovician Stratigraphy of Central Vermont,
Bull. Gaol. Soc. Am., vol. 52, pp. 1487-1512.
78

DALE, T. N.: 1902, Structural Details in the Green Mountain Region and in Eastern
New York (Second Paper), Bull. U. S. Geol. Surv., No. 195, pp. 9-22.
DOLL, C. G.: 1941-1942, An Abandoned Valley at West Charleston, Vermont, Report
of the State Geologist, pp. 20-25.
DOLL, C. G.: 1943, A Paleozoic Revision in Vermont, Amer. Jour. Sci., vol. 241, pp.
57-64.
DOLL, C. G.: 1943-1944, A Preliminary Report on the Geology of the Strafford Quad-rangle,
Vermont, Report of the State Geologist, pp. 14-28.
DRESSER, J. A. and DENIS, T. C.: 1944, The Monteregian hills, Geology of Quebec,
Dept. of llhines, Quebec, Geological Report 20, vol. 2, pp. 455-482.
ELI.s, R. W.: 1894, Report on a portion of the I'rovince of Quebec, southwest sheet of the
"Eastern Townships," Geol. Surv. of Canada, Ann. Rpt., new series, vol. 7, pt. J,
pp. 1-92.
HALL, S. R.: 1871, Geology and Mineralogy of Orleans County, Archives of Science and
Transactions of the Orleans County Society of Natural Sciences, vol. 1, January,
1871, pp. 71-78.
HARKER, ALFRED: 1932, Metamorphism, Methuen and Co., London, 360 pages.
HILLS, E. 5.: 1943, Outlines of Structural Geology, Nordeman Publishing Company,
New York, 172 pages.
HITCHCOCK, C. H.: 1905-1906, The Champlain Deposits of Northern Vermont, Report
of the Vermont State Geologist, pp. 236-253.
HITCHCOCK, C. H.: 1907-1908, Glacial Lake Memphremagog (abstract), Bull. Geol.
Soc. Am., vol. 18, pp. 641-642.
HITCHCOCK, EDWARD: 1861, Report on the Geology of Vermont, vol. 2, 988 pages.
JACOBS, E. C.: 1919-1920, The Geology of Lake Willoughby, Report of the Vermont
State Geologist, pp. 280-298.
JACoBS, E. C.: 1921-1922, The Geology of Westmore, Brownington and Charleston,
Report of the Vermont State Geologist, pp. 93-108.
JOHNSON, D. W.: 1925, The New England-A radian Shoreline, John Wiley and Sons,
New York, 608 pages.
KAY, C. M.: 1937, Stratigraphy of the Trenton Group, Bull. Geol. Soc. Am., vol. 48,
PP. 233-302.
KAY, G. M.: 1942, Development of the Northern Allegheny Synclinorium and Adjoining
Regions, Bull. Geol. Soc. Am., vol. 53, pp. 1601-1658.
KAY, G. It.: 1948, Paleozoic Volcanic Geosynclines and Island Arcs (abstract), Bull.
Geol. Soc. Am., vol. 59, p. 1332.
KEITH, ARTHUR: 1907, Description of the Roan Mountain quadrangle (Tenn. - N. C.),
Roan Mountain Folio, No. 151, Geologic Atlas of the United States, U. S. Geologi-cal
Survey, 11 pages.
KEITH, ARTHUR: 1923-a, Outlines of Appalachian Structure, Bull. Geol. Soc. Am., vol.
34, PP 309-380.
KEITH, ARThUR: 1923-b, Cambrian succession in northwestern Vermont, Amer. Jour.
Sci., 5th ser., vol. 5, PP. 97-139.
KERR, F. A.: 1923, Manuscript on the geology of the Memphremagog quadrangle,
Canada, Dept. of Geology, McGill University (unpublished).
79

KUENEN, P. H.: 1938, Observations and experiments on ptygmatic folding, Comm. Geol.
Finlande, Bull. 123, pp. 11-28.
LAVERDII'RE, J. W.: 1935, Géologie des environs de Marbleton, Canton de Dudswell,
Comlé de Wolfe, Service des Mines, Quebec, Partie D, pp. 33-44.
LOGAN, W. H.: 1852, On the Age of the Copper-bearing Rocks of Lake Superior and
huron, and various facts relating to the Physical structure of Canada, Amer. Jour.
Sci., vol. 14, pp. 224-229.
LOGAN, W. H.: 1863, Geology of C'anada, Geol. Surv. of Canada, 983 pages.
L0FIEsr, MAX: 1909, Dc l'origine des veines et des géodes des terrains primaires de
Beigique, Ann. Soc. Ghol. Belgique, vol. 36, B, pp. 275-282.
NATIONAL RESEARCH COUNCIL: 1944, Tectonic Map of the United States, The American
Association of Petroleum Geologists.
RENARD, A.: 1882, Les roches grenatifères et amphiboliques de la region de Bastogne,
Bull. Mus. Roy. Hist. Nat. Beig., vol. 1, pp. 1-47.
RICHARDSON, C. H.: 1905-1906, The Areal and Economic Geology of Northeastern
Vermont, Report of the Vermont State Geologist, pp. 63-115.
RICHARDSON, C. H.: 1907-1908, The Geology of Newport, Troy and Coventry, Report
RICHARDSON, C. H. and CONWAY, H. F.: 1911-1912, The Terranes of Irasburg,
Vermont, Report of the Vermont State Geologist, pp. 146-161.
RICHARDSON, C. H. and CAMP, S. H.: 1917-1918, The Terranes of Northfield, Vermont,
RICIIARoS0N, C. H.: 1919-1920, The Geology and Mineralogy of Braintree, Vermont,
RICHARDSON, C. H.: 1927-1928, The Petrography of the Irasburg Conglomerate, Report
RUEDEMANN, RUDOLF: 1919, Paleontologic Contributions from the New York State
Museum, Bull. 227, 228, pp. 63-130.
RUEDEMANN, RUDOLF: 1947, Graptolites of North America, Memoir 19, Geol. Soc.
Am., 652 pages.
'rHoMPsoN, ZADOCK: 1848, Geography and Geology of Vermont, Burlington, 220 pages.
TURNER, F. J.: 1948, Mineralogical and structural evolution of the metamorphic rocks,
Mem. 30, Geol. Soc. Am., 342 pages.
WHITFIELD, R. P.: 1883, Observations on the Fossils of the Metamorphic Rocks of
Bernardston, Massachusetts, Amer. Jour. Sci., vol. 25, pp. 368-369.
ME

I S*S • role
- • ,. S... - ,•
-. ;<
• T S - _J'..
S •r •.' 1i
V ' .0 .# • • ,.- -
'-
...
JAW
S -. .J• 5-.
- 0 '.5 • -_, ,•• • -". '
-.
w
7 a Ile •
• 4. '.
•t& .1.
ri.
ro
-
PLATE 2
Figure 1. Surface of an arenaceous limestone pock-marked by parallel solution
cavities, bordering road at farmhouse, 1 mile southwest of Bemis School (Island
Pond quadrangle).
Figure 2. Thick phyllite layer in escarpment of Black River south of Newport
City, exhibiting spheroidal weathering.
82

I'LATE 2
Figure 3. "Tombstone" weathering of phyllite, 3' mile northwest of Brownington
Village.
Figure 4. Glacial erratic of pillow lava belonging to the Bolton igneous group, in
pasture 2 miles north of Orleans and still within sight of its home.
83

!'LATE 3
Figure 1. Metacrysts of six-rayed garnets and bent and broken arnphiboles in
Barton River phyllite. (Vt, 366).* Nicols not crossed. (X 25).
84

IV
g-.. 4.
•' •-•.:
1
•:.
1
. - -q
l'I'l'E
Figure 2. Advanced stage in alteration of six-rayed garnet in Barton River phyllite.
355)•*
(Vt.
Nicols not crossed (X 30).
*These accompanying numbers in the illustrations refer to slide collections at the
University of Vermont.
85

c
4
PLATE -I
Figure 1. Andalusite metacrysts in Barton River phyllite showing longitudinal and
transverse sections, the latter considerably altered to a skeletal frame. (Vt. 421).
Nicols not crossed. (X 24).
86

!
:07
I f
I
LAlE 1
Figure 2. Sheaf-like bundles and isolated acicular crystals of sillirnanite in impure
quartzite of the Barton River formation (Vt. 368). Nicols not croced. (X 180).
87

I'LATE 5
Figure 1. Quartz-sericite-biotite schist of the Barton River formation showing mica
and suiphides bent with the herringbone structure illustrating slip cleavage." (Vt.
479). Nicols not crossed. (X 24).

PLATE 5
Figure 2. Barton River quartz-mica schist with herringbone structure illustrating
"slip cleavage" and a rod of suiphide bordered by a halo of secondary biotite. Strut-like
appearance of suiphide and curvilinear groundmass at its right end, indicate a
late development of the sulphide. (Vt. 483). Nicols not crossed. (X 23).
89

,2
.:
9.
PLATE 6
Figure 1 Pleochroic partly rose-colored (gray areas in the porphyroblasts) anda-lusite
porphyroblasts. Andalusite schist of the Barton River formation. (Vt. 422).
Nicols not crossed. (X 25).
90

!r * .
VII
:. . -
..— _.? .'
t
r
P1..A'l'E
Figure 2. Porphvroblasts of chiastolite disp1a ing geometru-alIv-arranged car-honaceous
inclusions. Barton River formation. (Vt. 412). Nicols not crossed. (X 24).
91

a..
.4.
or..
PLATE 7
Figure 1. Quartz-mica schist of the Westrnore formation displaying parallel augen
composed of biotite and scattered muscovite. (Vt. 464). Nicols not crossed. (X 37).
92

7 - - -
M.
.- •.-.w. .•"F'•
4 . .
PLATE 7
Figure 2. Garnet-mica schist; corroded amphibole showing rhombic cross sections
of cleavage. Garnet porphyroblast with corroded border and numerous inclusions.
Westmore formation. (Vt. 465). Nicols not crossed. (X 51).
93

'4. 1
jAA IN
I
(* :
J'LA'l'E 8
Figure 1. Staurolite porphyroblast dark with carbon inclusions. Staurolite schist,
Westmore formation. (Vt. 489). Nicols not crossed. (X 24).
94

A-
- - -- -
, .
PLATE 8
Figure 2. Garnet porphyroblast surrounded by bleached zone of quartz, muscovite
and biotite. Mica schist of Westmore formation. (Vt. 489a). Nicols not crossed.
(X 84).
95

M •
,r Ii
/
3
!'L.A'FE 9
Figure 1. Shore of Lake iIemphremagog at Holbrook Bay. Granite inclusions in
basic rock of the Bolton igneous group.
Figure 2. Bordering brook just off west side of road southwest of Maxfield Light.
Reticular weathered surface of metadiorite. Bolton igneous group.
96

AL
'½
IV
PLATE 9
Figure 3. Northeast slope of Sugar Hill, in pasture at sharp bend in road. Meta-morphosed
sediments of Barton River formation lying upon granite in synclinal
depression.
Figure 4. 9.4 mile east of Sugar Hill. Tabular inclusion of sediment in granite
hoghack. Note divergent fractures at the sharp corners of the xenolith.
97

ç: . ... .•. . . F t -
- . JPW - .
PLATE 10
Figure 1. Steel) Part of west slope of Sugar Hill, opposite elevation 1226. Lime-stone
of Barton River formation dipping beneath granite cliff.
Figure 2. North side of road near brook, V2 mile southeast of Cobb Pond. Gap in
sediments (point of hammer) filled by flowage of coarse-grained granite.
98

S -
AMU-aw.
1A
•. i• . •'..
ILATE 10
Figure 3. In pasture on side of road opposite location of Fig. 2. Resistant meta-morphosed
shell and hollow interior of an inclusion.
Figure 4. Southwest slope of Wilcox Hill, Y4 mile northeast of Morgan. Age rela-tions
of two granites cut by pegmatite dike.
99

- '
I'LA'fE II
Figure 1. Vest slope of 1600-foot hill, 1 mile southeast of West Charleston. Brec-ciated
dark granite.
Figure 2. Escarpment along the Black River south of Newport City, above eleva-tion
692. Granite sill folded with sediments. Barton River formation.
100

p -.•------ ' : .
S S
5%
• •;•
i tm 'ka
'n
PLATE 11
Figure 3. Granite knob on northwest side of Barton Mountain, 3/ mile southeast
of Baird School. Two generations of pegmatite and an earlier aplite vein showing
displacements.
Figure 4. On east slope, 3j mile east of elevation 1003 in southern part of west
rectangle, south of Coventry Center School. Milky quartz vein in Barton River
formation. Man is 6 feet tall.
101

:
. ,
PLATE 12
Figure 1. Low bill 1 mile directly west of Echo Pond. Mass of quartz causing
curve in strata of Westmore formation.
Figure 2. Cove Island in Lake Memphremagog, Minor fold in Ayers Cliff forma-tion
plunging northeast.
102

PLATE 12
Figure 3. South of Coventry Center School, Y8 mile northeast of elevation 1003.
Fold in Barton River slates plunging northeasterly.
103

'ON O "
Lv ILP
l'I'fE 14
Figure 1. Barton River ' mile north of Country Club. Sharp drag-fold of phyllite
layer in limestone. Barton River formation.
Figure 2. Shore of Lake Memphreniagog, Lake Park. Fold in limestone traversed
by (losely-sl)aced shear planes. Ayers Cliff formation.
104

1LATE 13
Figure 3. Shore of Lake Memphremagog at Eagle Point. Marginal fractures and
faults at border of granite pluton.
Figure 4. Clyde River at lower bridge, West Charleston. Longitudinally displaced
bed of phyllite. Barton River formation.
105

4p: A"
,l ~A
PLATE 14
Figure I. Clyde River at lower bridge in West Charleston. Diagonal wedge-shaped
fracture in phyllite layer filled with adjacent limestone. Barton River formation.
Figure 2. Below dam at Clyde Pond. Typical bedding in Barton River formation.
106

,
).'
PLATE 14
Figure 3. West slope of hill south of Breezy Hill, Y2 mile northeast of elevation
960. Bedding appears as folded fractures in slates. Barton River formation.
Figure 4. Southwest corner of Memphremagog quadrangle, 3 32 miles west of
Barton Village. Bedding disclosed by open fracture and solution holes. Slates in
Barton River formation,
107

,i
--'r-
PLATE 15
Figure 1. Northwest end of Stony Hill, Y4 mile north of Brighton School. Bedding
delineated by parallel grooves in slate. Hammer on highly contorted slate within
5 feet of granite contact.
Figure 2. Clyde River Valley, Y2 mile north of Toad Pond. Bedding in amphibolite
revealed by beaded divisions between beds.
108

71
-
"V
..----
4— -
-
PLATE 15
Figure 3. Scythstone quarry, Y4 mile southeast of East Brownington School.
Smooth bedding in phyllite of whetstone quality. Wcstmore formation.
Figure 4. Beside brook off Highway No. 5, 1 mile east of Newport City. Boudins
of quartz in limestone of Barton River formation.
109

(I
I'
,.c.-
-- a
I: All
--'
-
PLATE 16
Figure 1. Coventry Station. Bedding-cleavage relations in interbedded slates and
limest ones of Barton River formation.
Figure 2. Indian Point, L mile south of elevation 721. Steeply-dipping bedding
and practically horizontal cleavage in slates. Barton River formation.
110

;
.
I
TT '
/ .t.
I
Figure 3. North side of road, Y8 mile south of Day School. Rolls in beds of lime-stone.
Barton River formation.
Figure 4. At lower bridge on Clyde River at West Charleston. Flow fold in lime-stone
of Barton River formation.
111

9
4
di 4r)
iupui'
Figure 1. Shore of Lake Memphremagog at Lake Park. Intricate folds of thin slate
layers in limestone of Ayers Cliff formation.
Figure 2. Abandoned road metal quarry beside Highway No. 5, 2 miles north-east
of Derby P. 0. Limestone cores of synclinal folds overturned to northeast.
Barton River formation.
112

4. .
4
PLATE 17
Figure 3. In pasture southeast of Orcutt Brook and mile northwest of Morgan
Gore School. Sedimentary 'inclusion" in limestone. Barton River formation.
113

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