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Connecticut Bedrock Geology Polygon
SDE Feature Class - depgis.DEP.BEDROCK_GEOLOGY_POLY
FGDC, ESRI Metadata
DescriptionGraphicSpatialData StructureData QualityData SourceData DistributionMetadata
+ Resource Description
Citation
Information used to reference the data.
Title: Connecticut Bedrock Geology Polygon
Originators: State of Connecticut, Department of Environmental Protection (data compiler, editor and publisher)
Publisher: State of Connecticut, Department of Environmental Protection
Publication place: Hartford, Connecticut, USA
Publication date: 1985
Data type: vector digital data
Data location: http://www.ct.gov/deep
Other citation details:
The data source for this layer is the Bedrock Geological Map of Connecticut, Rodgers, 1985. The map is published at 1:125,000 scale. The layer was digitized from 1:50,000-scale compilation sheets for the 1:125,000-scale Bedrock Geological Map of Connecticut.
Larger Work Citation
Title: Bedrock Geology of Connecticut
Originators: John Rodgers, Compiler
Publisher: Connecticut Geological and Natural History Survey, Connecticut Department of Environmental Protection in cooperation with the U.S. Geological Survey
Publication place: Hartford, Connecticut
Publication date: 1985
Data type: map
Other citation details:
The Bedrock Geology of Connecticut map is published at 1:125,000 scale and is available for purchase at the Connecticut DEP Store.
Description
A characterization of the data, including its intended use and limitations.
Abstract:
Connecticut Bedrock Geology is a 1:50,000-scale, polygon and line feature-based layer describing the solid material that underlies the soil or other unconsolidated material of the earth for Connecticut. Bedrock geologic formations are described as polygons in terms of formation name (incorporating geologic age), rock type, and tectonic terrane association. Tectonic forces are responsible for the present day geologic configuration of the continents. Resulting terranes are regionally fault bounded rocks of a similar tectonic history. Each terrane is named after its plate tectonics ancestry. Geologic lines include contacts, faults, and terrane boundaries. Terrane boundaries are named for the faults involved. The geologic contacts and faults are delineated and classified by type. Polygon feature attribute information is comprised of codes to identify individual bedrock geologic units, their formation name, description and size. Line feature attributes identify, name and describe bedrock contacts, faults and terrane boundaries between these bedrock geologic units. Data is compiled at 1:50,000 scale and is not updated. A complete description of the bedrock mapping units with mineralogical descriptions and a brief history of Connecticut geology are included in the Supplemental Information Section for reference.

The data source is from John Rodgers, Bedrock Geological Map of Connecticut, 1985 (Connecticut Geological and Natural History Survey, DEP, in cooperation with the U.S. Geological Survey, 2 sheets, 1:125,000 publication scale). This datalayer was digitized from a set of 1:50,000 scale regional sheets used for compilation of the 1:125,000 scale published map. The regional sheets were compiled to a common publication base from 1:24,000 scale mylar originals prepared from geologic quadrangle mapping and other interpretations. A list of sources is included later in this document. Additional historical information is in the map notes section. For a stratigraphic correlation of bedrock units, major regional and statewide tectonic structures, and cross sectional views of the State's geology, please refer to the 1:125,000 scale Bedrock Geological Map of Connecticut. The Bedrock Geological Map of Connecticut is available for purchase at the DEP Store.
Purpose:
Connecticut Bedrock Geology is 1:50,000-scale data suitable for for geologic and environmental mapping and analysis purposes. Not intended for maps printed at map scales greater or more detailed than 1:50,000 scale (1 inch = 4,167  feet.). Not intended for site specific spatial analysis purposes.
Supplemental information:
Brief Bedrock Geologic History of Connecticut - Geologic regions (terranes) on this map reflect the role of plate tectonics in the geologic history of Connecticut. Each terrane is named after its plate tectonics history.

From 450 to 250 million years ago, during the Paleozoic Era, several crustal plates, including Africa and Eurasia, sequentially collided with the Proto-North American plate in a series of four mountain building events that ultimately created the Appalachian Mountains and the supercontinent Pangea. During these  collisions, Avalonia, a small continent believed to have been a part of the African plate, was thrust against the continent of Proto-North America, closing and collapsing the intervening Iapetos Ocean. The collisions deformed and metamorphosed both the continental rocks of Proto-North America and Avalonia and the oceanic rocks and sediments of the Iapetos Ocean floor. This process created the schists, gneisses and granites exposed today in eastern and western Connecticut. Features of these metamorphic and igneous rocks show this complex geologic history, confirming the continental and oceanic origins and the processes of plate tectonics.

Shortly after the collision ended, at the beginning of the Mesozoic Era or about 235 million years ago, plate tectonic processes reversed. Pangea began to break apart, initiating the opening of the Atlantic Ocean and leaving Avalonia welded to North America. In the early stages of this breakup, rift basins formed along and on both sides of the zone where the Atlantic Ocean finally opened. The Newark terrane in central Connecticut is the eroded remnant of one of these rift basins. It contains 200 million year old sedimentary rocks (brownstone) and lava flows and intrusions of basalt (trap rock).

Geologic Ages - Below is a list of Geologic ages represented in Connecticut rocks. The first letter represents the geologic age, which is the first portion of each bedrock unit code.

AGE CODE, GEOLOGIC AGE, DATE (mya = million years ago)

J, Jurassic, 140 - 205 mya, Youngest rocks in Connecticut
TR, Triassic, 205 - 240 mya
P, Permian, 240 - 290 mya
Carboniferous rocks (Pennsylvanian and Mississippian) are not present in Connecticut 
290 - 360 mya
D, Devonian, 360 - 410 mya
S, Silurian, 410 - 435 mya
O, Ordovician, 435 - 500 mya
C, Cambrian, 500 - 570 mya
Z, Proterozoic (PreCambrian), 570 - 800 mya
Y, Proterozoic (PreCambrian), 800 - 1700 mya, 'Y' Proterozoic are the oldest rocks in Connecticut (~ 1100 mya)

Simplified descriptions are given for rock terms used above. Descriptions include general and distinguishing characteristics of rocks as they commonly occur in Connecticut.

Alaskite gneiss: Light-colored, fine-to coarse-grained, banded metamorphic rock of granite-like composition with potassium feldspar as the major feldspar, and only a few percent dark minerals.

Amphibolite: Dark-colored, fine-to coarse-grained, massive to poorly layered metamorphic rock containing amphibole and plagioclase with little or no quartz.

Arkose: Red to brown, medium-to coarse-grained, sandstone-like, sedimentary rock containing quartz, feldspar, and rock fragments. It is the most common sedimentary rock of the Central Lowlands; locally known as brownstone. Brownstone was quarried for use as building stone.

Basalt: Dark-gray, orange-to brown-weathering, fine-grained, extrusive igneous rock, commonly fractured (jointed), containing calcium-plagioclase and pyroxene; occurs as lava flows in the Central Lowlands; locally known as traprock. Basalt is extensively quarried for use as crushed stone.

Diorite: Light and dark (salt and pepper), medium- to coarse-grained intrusive igneous rock, commonly massive-appearing, generally lacking layering or banding; composed primarily of plagioclase feldspar, quartz and dark minerals.

Dioritic gneiss: Light and dark, medium- to coarse-grained, compositionally banded metamorphic rock of dioritic composition.

Dolerite: Dark-gray, orange- to brown- to gray-weathering, medium- to fine-grained intrusive igneous rock, commonly fractured into well-developed columnar joints, compositionally similar to basalt; occurs as dikes and sills in both the lowlands and uplands; locally known as traprock. Dolerite is quarried for use as crushed stone.

Gabbro: Dark, medium- to coarse-grained, intrusive mafic igneous rock, commonly massive-appearing, generally lacking layering or banding; composed primarily of clinopyroxene and plagioclase; often altered.

Gneiss: Light and dark, medium- to coarse-grained metamorphic rock characterized by compositional banding of light and dark minerals, typically composed of quartz, feldspar, and various amounts of dark minerals; occurs with a variety of compositions and is a characteristic rock of the uplands.

Granite: Light-colored, medium- to very coarse-grained intrusive igneous rock, commonly massive-appearing, lacking layering or banding; composed of quartz, feldspar, and commonly muscovite mica with minor amounts of dark minerals. Granite and granitic gneiss were quarried for use as dimension stone. Very limited quarrying continues.

Granitic gneiss: Light-colored, medium- to coarse-grained, compositionally banded metamorphic rock of granitic composition. Quarried for use as dimension stone (see granite).

Granofels: Light to dark, medium- to coarse-grained, massive to poorly layered metamorphic rock composed primarily of quartz and feldspar; lacking the compositional banding of a gneiss.

Greenschist: Light to dark, green, medium- to coarse-grained schist; typically consisting of the green minerals: chlorite, epidote, or actinolite.

Greenstone: Green to gray-green, fine- to coarse-grained, massive to poorly layered metamorphic rock composed of chlorite, hornblende, and epidote.

Lamprophyre: Dark-colored, medium-grained intrusive igneous rock occurring as dikes; composed of biotite, hornblende, pyroxene, and feldspars or feldspathoids.

Mafic rock: Dark-colored rock consisting of one or more dark (iron and magnesian) minerals as its major constituent.

Marble: Conspicuously white, or gray, medium- to coarse-grained, massive to layered metamorphic rock composed of calcite and/or dolomite. It is a metamorphosed limestone and underlies several major valleys in the Western Uplands. Marble is quarried for use as agricultural lime and for industrial uses.

Mylonite: Compact rock with streaky or banded structure, found in fault zones, and produced by extreme crushing and shearing of rocks during movement of a fault. It is particularly well developed along the Lake Char - Honey Hill fault zones of the Eastern Uplands.

Norite: Dark-colored, medium- to coarse-grained intrusive mafic igneous rock commonly massive-appearing, lacking layering or banding, composed of plagioclase and orthopyroxene; often altered.

Pegmatite: Light-colored, very coarse-grained intrusive igneous rock, composed of feldspar, quartz, and micas; frequently can be seen in highway roadcuts as light-colored parallel and cross cutting veins and lenses in the metamorphic rock of the uplands; occasionally is a host for gem minerals. Pegmatite is a common and economically important rock type in Connecticut. It occurs in bodies too small to show on a state-scale geologic map. The Branchville area of western Connecticut and the Middletown area of eastern Connecticut have pegmatites of particular significance.

Phyllite: Silvery, gray to dark-gray, fine- to very fine-grained, schist-like metamorphic rock.

Porphyry: Light-colored, fine-grained intrusive igneous rock with some conspicuously large crystals of quartz, feldspar, or biotite.

Quartzite: Light-colored to gray, massive to layered, medium-grained metamorphic rock. Very hard and resistant; a metamorphosed sandstone composed primarily of quartz.

Shale: Red to brown, locally gray to green, extremely fine-grained, strongly layered sedimentary rock composed of clay minerals; occurs in the Central Lowlands.

Schist: Light, silvery to dark, coarse- to very coarse-grained, strongly to very strongly layered metamorphic rock whose layering is typically defined by parallel alignment of micas. Primarily composed of mica, quartz, and feldspar; occasionally spotted with conspicuous garnets.

Schistose marble: Light-colored, fine- to coarse-grained, marble interlayered with schist or phyllite.

Syenite: Medium-gray, fine- to coarse-grained intrusive igneous rock, commonly massive-appearing, generally lacking layering or banding, composed primarily of potassium feldspar with minor dark minerals but little quartz.

Ultramafic rock: Dark-colored, medium- to coarse-grained intrusive igneous rock, commonly massive-appearing, generally lacking layering or banding and originally composed chiefly of olivine and pyroxene; commonly altered to serpentine and talc. Occurs as small intrusions in the uplands.
Dataset credit:
The compiler, John Rodgers, wishes to acknowledge his great debt to all the many geologists who have worked on the bedrock geology of the State over the years. But perhaps his deepest indebtedness is to the Report on the Geology of the State of Connecticut and the accompanying Geological Map of Connecticut published in 1842 by James Gates Percival. Connecticut had far less forest (or urban sprawl) and far more open country (fields and pastures) in Percival's day than ours, so that he almost certainly saw many more outcrops than anyone since; he was, moreover, an extraordinarily accurate observer with a retentive memory, so that his tracing of rock units from one part of the state to another is thoroughly reliable. His map is almost certainly more accurate than either subsequent geological map of the State (Gregory and Robinson 1906; Rodgers, Cameron, Gates, and Ross, 1956), but it is hardly usable because the map units are designated only by letters, numbers, Greek letters, and symbols keyed to the difficulty readable text. In more than one place, the compiler chose among diverse interpretations on the basis of Percival's mapping.

The compiler must further point out that, in order to produce a map consistent with itself and also with the Bedrock Geologic Map of Massachusetts (Zen and others, 1983), which was being compiled at the same time, he felt it necessary to depart significantly in some places from the source maps cited, as by using different units, correlating units differently, and occasionally introducing or suppressing contacts or faults. In those places of course the authors of the source materials are not responsible for the interpretation shown on this map within the quadrangles for which they are cited. In some cases, indeed, they strongly disagree with the compiler's reinterpretation, for which he must take the entire responsibility.

This compilation was begun at the suggestion of Joe Webb Peoples, then State Geologist. His persistence and encouragement helped carry the map through draft and redraft. Sidney Quarrier coordinated much of the work and brought the map to print two times; first a preliminary version at the scale of 1:250,000 in 1982, and now the final colored map at 1:125,000. He and his coworkers Robert Altamura and Margaret Thomas designed the format and material for this map. Nancy Davis, Craigh Dietsch, and Nat Gibbons drafted the original compilation.
Language of dataset: en
Point Of Contact
Contact information for the individual or organization that is knowledgeable about the data.
Organization: State of Connecticut, Department of Environmental Protection
Person: Margaret Thomas
Phone: 860-424-3540
Fax: 860-424-4058
Email: dep.gisdata@ct.gov
Hours of service: Monday to Friday, 08:30 to 16:30 Eastern Standard Time
Address type: mailing and physical address
Address:
79 Elm Street
City: Hartford
State or Province: Connecticut
Postal code: 06106-5127
Country: USA
Data Type
How the data are represented, formatted and maintained by the data producing organization.
File or table name: depgis.DEP.BEDROCK_GEOLOGY_POLY
Data type: vector digital data
Data format: SDE Feature Class
Native dataset environment: These data are maintained by the State of Connecticut using ArcGIS software developed by Environmental Systems Research Institute (ESRI) in a Microsoft Windows operating system environment.
Time Period of Data
Time period(s) for which the data corresponds to the currentness reference.
Date: 1985
Currentness reference:
publication date
Status
The state of and maintenance information for the data.
Data status: Complete
Update frequency: None planned
Key Words
Words or phrases that summarize certain aspects of the data.
Theme:
Keywords: geology, bedrock, lithology, rock type, geologic Age, geologic history, formation name, geologic terrane, plate tectonics, mineralogy, geologic sources
Keyword thesaurus: None
Theme:
Keywords: geoscientificInformation
Keyword thesaurus: ISO 19115 Topic Category
Place:
Keywords: Connecticut, CT
Keyword thesaurus: U.S. Department of Commerce, 1987, Codes for the Identification of the States, the District of Columbia and the Outlying Areas of The United States, and Associated Areas (Federal Information Processing Standard 5-2): Washington, DC, National Institute of Standards and Technology.
Place:
Keywords: United States of America, USA
Keyword thesaurus: U.S. Department of Commerce, 1995, Countries, Dependencies, Areas of Special Sovereignty, and Their Principal Administrative Divisions (Federal Information Processing Standard (FIPS) 10-4): Washington, D.C., National Institute of Standards and Technology.
Data Access Constraints
Restrictions and legal prerequisites for accessing or using the data after access is granted.
Access constraints:
None. The data is in the public domain and may be redistributed.
Use constraints:
No restrictions or legal prerequisites for using the data. The data is suitable for use at appropriate scale, and is not intended for maps printed at scales greater or more detailed than 1:50,000 scale (1 inch = 4,167 feet). Although this data set  has been used by the State of Connecticut, Department of Environmental Protection, no warranty, expressed or implied, is made by the State of Connecticut, Department of Environmental Protection as to the accuracy of the data and or related materials.  The act of distribution shall not constitute any such warranty, and no responsibility is assumed by the State of Connecticut, Department of Environmental Protection in the use of these data or related materials. The user assumes the entire risk related to the use of these data. Once the data is distributed to the user, modifications made to the data by the user should be noted in the metadata. When printing this data on a map or using it in a software application, analysis, or report, please acknowledge the State of Connecticut, Department of Environmental Protection as the source for this information. For example, include the following data source description when printing this layer on a map: Geology - From the Bedrock Geology layer, compiled and published by CT DEP and USGS. Source map scale is 1:50,000.
+ Graphic Example
Browse Graphic
Graphic illustration of the data.
Browse graphic 1
Open - Full view of Bedrock Geology - Bedrock Geology Polygon features symbolized by the (geologic) UNIT attribute
Graphic Image

Browse graphic 2
Open - Detail view of Bedrock Geology and Bedrock Contacts - Bedrock Geology Polygon features symbolized by the (geologic) UNIT together with Bedrock Geology Line features symbolized by CLASS_COD attribute values.
Graphic Image

Browse graphic 3
Open - Full view of Geologic Terrane - Bedrock Geology Polygon features symbolized by the Geologic Terrane (TERRANE) attribute together with Bedrock Geology Line features symbolized by the Terrane Boundary (TERR_BNDRY) attribute.
Graphic Image
+ Spatial Reference Information
Horizontal Coordinate System
Reference system from which linear or angular quantities are measured and assigned to the position that a point occupies.
Projected coordinate system:
Name: NAD 1983 StatePlane Connecticut FIPS 0600 Feet
Map units: survey feet
Geographic coordinate system:
Name: GCS North American 1983
Coordinate System Details
Map projection
Map projection name: Lambert Conformal Conic
Standard parallel: 41.200000
Standard parallel: 41.866667
Longitude of central meridian: -72.750000
Latitude of projection origin: 40.833333
False easting: 999999.999996
False northing: 499999.999998
Planar Coordinate Information
Planar coordinate encoding method: coordinate pair
Coordinate representation:
Abscissa resolution: 0.000250
Ordinate resolution: 0.000250
Planar distance units: survey feet
Geodetic model
Horizontal datum name: North American Datum of 1983
Ellipsoid name: Geodetic Reference System 80
Semi-major axis: 6378137.000000
Denominator of flattening ratio: 298.257222
Vertical Coordinate System
Reference system from which vertical distances (altitudes or depths) are measured.
Altitude system definition:
Altitude resolution: 1.000000
Altitude encoding method: Explicit elevation coordinate included with horizontal coordinates
Spatial Domain
The geographic areal domain of the data that describes the western, eastern, northern, and southern geographic limits of data coverage.
Bounding Coordinates
In Projected or local coordinates
NAD 1983 StatePlane Connecticut FIPS 0600 Feet
BoundaryCoordinate
Left730529.813000 (survey feet)
Right1263094.375000 (survey feet)
Top944279.188000 (survey feet)
Bottom544018.813000 (survey feet)
In Unprojected coordinates (geographic)
GCS North American 1983
BoundaryCoordinate
West-73.742107 (longitude)
East-71.781365 (longitude)
North42.052612 (latitude)
South40.949970 (latitude)
+ Data Structure and Attribute Information
Overview
Summary of the information content of the data, including other references to complete descriptions of entity types, attributes, and attribute values for the data.
Entity and attribute overview:
Bedrock Geology polygon features describe 157 geologic units for arkose, basalt, gneiss, granite, marble, shist, shale and other rock types. The information encoded about the geologic unites includes the formation name, description, geologic terrane, and age. Use the UNIT attribute as the key field that identifies and differentiates bedrock units. Refer to the FORMATION attribute for the name of the geologic unit. Label a map with either the UNIT or FORMATION attribute. Refer to the DESCRIPTION attribute for a brief explanation of the geologic unit. For cartographic purposes, symbolize polygon features on a map using either the UNIT or TERRANE attribute, depending on the desired level of detail. Use the LITHO1, LITHO2, LITHO3, LITHO4, and LITHO5 for information about the lithology of the geologic unit. The Bedrock Geology layer also describes 17 classes of geologic boundaries, contacts and faults. Line feature attributes are primarily for cartographic purposes. For example, when symbolizing polygon features on different UNIT attribute values, also uniquely symbolize line features on the CLASS_COD or DEFINITION attribute to emphasize the various boundary types. When symbolizing polygon features on different TERRANE attribute values, also uniquely symbolize line features on the TERRB_COD or TERR_BNDRY to emphasize the terrain boundaries.
Entity and attribute detailed citation:
Bedrock Geology of Connecticut (Rogers, J., State of Connecticut, Department of Environmental Protection, 1985, scale 1:125,000)
Direct spatial reference method: Vector
Indirect spatial reference method: State of Connecticut, United States of America
Attributes of Connecticut Bedrock Geology Polygon
Detailed descriptions of entity type, attributes, and attribute values for the data.
Name: depgis.DEP.BEDROCK_GEOLOGY_POLY
Type of object: Feature Class
Geometry type: Polygon
Number of records: 1892
Description:
Bedrock Geology map units represented as polygon features.
Source:
State of Connecticut, Department of Environmental Protection
Attributes
OBJECTID
Definition:
Internal feature number.
Alias: OBJECTID Type: OID Width: 4 Precision: 10 Scale: 0
Attribute values: Sequential unique whole numbers that are automatically generated.
Attribute definition source:
ESRI
SHAPE
Definition:
Feature geometry.
Alias: SHAPE Type: Geometry Width: 4 Precision: 0 Scale: 0
Attribute values: Coordinates defining the features.
Attribute definition source:
ESRI
UNIT
Definition:
Geologic Unit - Represents the map unit symbol for bedrock geology polygon features. Upper case letters in the map unit represent the geologic age of the formation. Lower case letters in the map unit represent the formation. Map units (Geological Formations) with more than one upper case letter denote a geologic age range represented by the formation (i.e. DSts, The Straits Schist, denotes Devonian and Silurian aged rock unit). Use of the question mark indicates uncertainty about the age or the identification of the geologic formation. For example: D?d denotes uncertainty about the designation of D (Devonian) for the age of the geologic formation. Jb? denotes uncertain identification of the formation, with the most closely associated formation symbol used for the map unit. C is used for the Cambrian age rocks ~ 500 mya - 570 mya. There are no Cretaceous age rocks in Connecticut.
Alias: UNIT Type: String Width: 20 Precision: 0 Scale: 0Output width: 20
Attribute domain values
ValueDefinition
Cc
Cheshire Quartzite (Lower Cambrian) - Mainly pure, white, glassy, tough quartzite
Definition Source:
compiler
Cd
Dalton Formation (including Poughquag Quartzite and Lowerre Formation) (Lower Cambrian and perhaps partly older) - Gray, tan-weathering, medium grained, generally well layered gneiss or feldspathic quartzite, composed of quartz, microcline, plagioclase, muscovite, biotite, and generally tourmaline; some schistose micaceous layers have sillimanite, commonly as quartz-sillimanite nodules rimmed with muscovite. Layers of purer quartzite in many areas, especially near the top or where the formation is thin
Definition Source:
compiler
Ce
Everett Schist (Cambrian?) - Grayish to greenish (some rusty-weathering), fine-to medium-grained, foliated but poorly layered schist or phyllite, composed or quartz, albite or oligoclase, muscovite, garnet, staurolite or chloritoid, and generally chlorite. Local layers are dark-gray to silvery schist or phyllite
Definition Source:
compiler
Ch
Hoosac Schist (Cambrian?) - Light-to medium-gray, rusty-weathering, fine- to medium-grained schist and poorly layered schistose gneiss, composed of quartz, biotite, plagioclase, muscovite, and generally garnet and sillimanite or kyanite
Definition Source:
compiler
Cm
Manhattan Schist (including Waramaug Formation and Canaan Mountain Schist) - (Cambrian?) - Dark-gray to silvery, rusty-weathering, generally coarse grained, foliated but poorly layered to massive gneiss or schistose gneiss, composed of quartz, oligoclase, microcline, biotite, and muscovite, and generally sillimanite and garnet. Amphibolite layers locally, especially near base where in places separately mapped as unit Cma
Definition Source:
compiler
Cma
Amphibolite-bearing unit of Manhattan Schist (Cambrian?) - Like Manhattan Schist but with numerous lenses and layers of amphibolite
Definition Source:
compiler
Cmcl
Lower slice of Canaan Mountain Schist (Cambrian?) - Dark-gray, rusty-weathering, coarse-grained, well-foliated and moderately well layered schist composed of quartz, plagioclase, biotite, muscovite, and generally garnet and sillimanite (or minor staurolite). Amphibolite layers rather rare
Definition Source:
compiler
Cmcu
Upper slice of Canaan Mountain Schist (Cambrian?) - Dark-gray to silvery, generally rusty weathering, medium- to coarse-grained, well-foliated, massive to well-layered schist and schistose gneiss, composed of quartz, plagioclase, biotite, muscovite, and generally garnet and sillimanite; also layers of amphibolite
Definition Source:
compiler
Cmcub
Basal member of upper slice of Canaan Mountain Schist (Cambrian?) - Gray, generally rusty- or tan-weathering gneiss, composed of quartz, plagioclase, microline, biotite, and muscovite, interlayered with feldspathic quartzite
Definition Source:
compiler
Csa
Unit a [of Stockbridge Marble] (Lower Cambrian) - White to pale-gray, massive, smooth-weathering dolomite marble
Definition Source:
compiler
Csb
Unit b [of Stockbridge Marble] (Upper and Middle? Cambrian) - White, pink, cream, and light-gray, generally well-bedded dolomitic marble interlayered with phyllite and schist and with siltstone, sandstone, or quartzite, commonly dolomitic
Definition Source:
compiler
Csc
Unit c [of Stockbridge Marble] (Upper Cambrian) - Gray, generally massive dolomite marble, commonly contains quartz grains, locally beds of sandstone; may be calcitic near top
Definition Source:
compiler
Cwb
Waterbury Gneiss (Proterozoic Z or Cambrian or both) - Medium- to dark-gray, fine- to medium-grained, generally irregularly foliated and lenticular rather than regularly layered schist and schistose gneiss, composed of biotite, quartz, oligoclase, kyanite (or sillimanite), and garnet, also locally microcline, irregularly mixed with granitoid gneiss, composed of oligoclase or andesine, quartz, biotite, and commonly microcline and muscovite
Definition Source:
compiler
D?d
Foliated quartz diorite (Devonian in part, probably Ordovician in part) - Mainly dark-gray, medium-grained, well-foliated gneiss (locally strongly sheared, especially near contacts), composed of plagioclase, quartz, biotite, and hornblende, locally also pyroxene (? denotes uncertainty about the designation of D (Devonian) for the age of the geologic formation).
Definition Source:
compiler
DSs
Scotland Schist (Devonian or Silurian or both) - Gray to silvery, locally rusty, fine- to medium-grained schist, composed of quartz, muscovite, biotite, staurolite, and oligoclase, locally with kyanite or sillimanite; interlayered, especially below and to the west, with quartz-oligoclase-biotite schist and granofels and locally with quartzite
Definition Source:
compiler
DSsq
Quartzite unit [in Scotland Schist] (Devonian or Silurian or both) - Quartzite, generally micaceous, interlayered with mica schist
Definition Source:
compiler
DSt
The Straits Schist (= Goshen Formation of Massachusetts) (Devonian or Silurian or both) - Silvery to gray, non-rusty, coarse- to very coarse grained, generally poorly layered schist, composed of quartz, muscovite, biotite, oligoclase, garnet, and commonly staurolite and kyanite or sillimanite; graphitic almost throughout
Definition Source:
compiler
DSts
Southington Mountain Member [of The Straits Schist] (Devonian or Silurian or both) - Gray to silvery, non-rusty, medium-grained, well-layered alternating schist and granofels, composed of quartz, oligoclase, muscovite, biotite, and garnet, commonly with staurolite and kyanite (or sillimanite); schist commonly graphitic
Definition Source:
compiler
DSw
Wepawaug Schist (Devonian or Silurian or both) - Medium- to dark-gray, medium- to fine-grained, well-layered schist or phylite and metasiltstone, composed of quartz, muscovite or sericite, plagioclase, biotite, and in appropriate metamorphic zones chlorite, garnet, staurolite, and kyanite. Schist or phyllite generally graphitic
Definition Source:
compiler
Dbl
Littleton Formation (Devonian) - Gray to silvery, generally non-rusty, medium-grained, massive to well-layered alternating schist and micaceous quartzite, composed of quartz, muscovite, biotite, garnet, and oligoclase, also staurolite, graphite, and ilmenite, and in certain areas kyanite or sillimanite in schist
Definition Source:
compiler
Dbl?
Littleton Formation - see Dbl (? denotes uncertain identification of the formation, with the most closely associated formation symbol used for the map unit).
Definition Source:
compiler
Dblm
Mount Pisgah Member of Littleton Formation (Devonian) - Gray, medium-grained, well-layered (locally graded) granofels or micaceous quartzite with some schist, composed of quartz, oligoclase, biotite, garnet, and sillimanite
Definition Source:
compiler
Dc
Canterbury Gneiss (may be equivalent to Ayer Granite of Massachusetts) (Devonian) - Light-gray, medium-grained, variably foliated, locally strongly lineated gneiss, composed of quartz, oligoclase, microcline, and biotite, locally also muscovite or epidote, and generally with megacrysts 1 to 2 cm long of either or both feldspars
Definition Source:
compiler
Dce
'Eastford gneiss phase' [of Canterbury Gneiss] (Devonian) - Mainly light gray, medium-grained, foliated to strongly lineated gneiss, composed of quartz, microcline, oligoclase or albite, biotite, and muscovite
Definition Source:
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De
Erving Formation (Devonian) - Gray, medium-grained, well-foliated and generally well layered granofels and schist, composed of quartz, plagioclase, and biotite, also muscovite in schist, and accessory garnet and kyanite
Definition Source:
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Dgg
Foliated granitic gneiss (Devonian?) - Light-gray, coarse-grained, strongly to weakly foliated gneiss, composed of phenocrysts of K-feldspar in a groundmass of plagioclase, quartz, K-feldspar, and biotite, with accessory sillimanite and garnet
Definition Source:
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Dl
Lebanon Gabbro (Devonian) - Dark, speckled, coarse-grained, massive but locally sheared gabbro, composed of hornblende, labradorite, and opaques. Some bodies contain biotite and quartz; some smaller ones are nearly pure hornblende with local augite
Definition Source:
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Dld
Dioritic phase [of Lebanon Gabbro] (Devonian) - White to black, streaked, medium-grained, foliated or sheared gneiss, composed of plagioclase, biotite, quartz, and generally hornblende
Definition Source:
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Dlp
Lamprophyre (Devonian?) - Dark-gray to greenish, fine-grained, badly altered dike rock, composed of biotite, augite, K-feldspar, and accessory apatite and sphene, plus secondary minerals
Definition Source:
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Dm
Maromas Granite Gneiss (Devonian?) - Light-gray to buff, medium- to fine-grained granitic gneiss, composed of quartz and microcline with minor plagioclase and biotite. Central body is massive, but outlying strips are foliated and have accessory hornblende or garnet. Massive parts may be young anatectic intrusive rocks; foliated parts may include older felsic metavolcanic rocks belonging to unit Ochv. Pegmatite bodies are common in the vicinity
Definition Source:
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Dn
Hornblende norite (Devonian?) - Dark, coarse-grained, massive rock, composed of bytownite, hornblende, and hypesthene
Definition Source:
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Dng
Nonewaug Granite (Devonian) - White to pink, fine- to very coarse grained (commonly pegmatitic), massive to layered granite composed of albite, microcline, quartz, and muscovite, with minor biotite and garnet. Microcline commonly graphic; quartz and muscovite commonly in plumose aggregates
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Jb
Buttress Dolerite (Middle? Jurassic) - Dark-gray to greenish-gray (weathers brown or gray), medium- to fine-grained, commonly porphyritic, generally massive with well-developed columnar jointing, grading from basalt near contacts to fine-grained gabbro in the interior, composed of plagioclase and pyroxene with accessory opaques and locally devitrified glass, quartz, or olivine
Definition Source:
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Jb?
Buttress Dolerite - see Jb (? denotes uncertain identification of the formation, with the most closely associated formation symbol used for the map unit).
Definition Source:
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Jeb
East Berlin Formation (Lower Jurassic) - Maroon siltstone, silty and sandy shale, and fine-grained silty sandstone, generally well laminated and commonly well indurated, alternating with dark fissile shale; dolomitic carbonate common in cement, concretions, and thin argillaceous laminae. Local arkose; grades eastward into coarse conglomerate close to eastern border fault
Definition Source:
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Jha
Hampden Basalt (Lower Jurassic) - Greenish-gray to black (weathers bright orange to brown), fine- to medium-grained, grading from basalt near contacts to fine-grained gabbro in the interior, composed of pyroxene and plagioclase with accessory opaques and locally olivine or devitrified glass
Definition Source:
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Jho
Holyoke Basalt (Lower Jurassic) - Greenish-gray to black (weathers bright orange to brown), fine- to coarse-grained, grading from basalt near contacts to gabbro in the interior, composed of pyroxene and plagioclase with accessory opaques and locally olivine or devitrified glass
Definition Source:
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Jp
Portland Arkose (Lower Jurassic) - Reddish-brown to maroon micaceous arkose and siltstone and red to black fissile silty shale. Grades eastward into coarse conglomerate (fanglomerate) 'Meriden Formation' of Krynine (1950) (Lower Jurassic)
Definition Source:
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Jsi
Silicified rock and mylonite along Mesozoic faults (probably mainly Jurassic) - Close network of quartz veins and veinlets cutting each other and older rock, which is mostly replaced by very fine grained quartz. In places, incompletely replaced rock shows strongly mylonitic texture.
Definition Source:
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Jsm
Shuttle Meadow Formation (Lower Jurassic) - Maroon to dark-gray, silty shale, siltstone, and fine-grained silty sandstone, generally well and thinly laminated. In the southern part of the State includes a layer, up to 5 m thick, of blue, commonly sandy, fine-grained limestone or dolomitic limestone, grading laterally into calcareous siltstone. Coarser and more arkosic to east and south, grading into conglomerate near the eastern border fault
Definition Source:
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Jta
Talcott Basalt (Lower Jurassic) - Greenish-gray to black (weathers bright orange to brown), fine- to medium-grained, grading from basalt near contacts to fine-grained gabbro in the interior, composed of pyroxene and plagioclase with accessory opaques and locally olivine or devitrified glass. Pillows in may places; volcanic breccia with fragmentary pillows in others
Definition Source:
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Jwr
West Rock Dolerite (Lower Jurassic) - Dark-gray to greenish-gray (weathers bright orange to brown), medium- to fine-grained, grading from basalt near contacts to fine-grained gabbro in the interior, generally massive with well-developed columnar jointing, composed of plagioclase and pyroxene with accessory opaques and locally devitrified glass, quartz, or olivine
Definition Source:
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Jwr?
West Rock Dolerite - see Jwr (? denotes uncertain identification of the formation, with the most closely associated formation symbol used for the map unit).
Definition Source:
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OCr
Rowe Schist (Lower Ordovician or Cambrian or both) - Light-gray to silvery, fine- to medium-grained, generally poorly layered schist composed of quartz, muscovite, biotite, oligoclase, and generally garnet, staurolite, and kyanite or sillimanite. Layers of granofels common; also some layers of amphibolite, quartz-spessartine rock (coticule), and calc-silicate rock
Definition Source:
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OCr+OCra
 Rowe Schist and Amphibolite unit in Rowe Schist undivided -  see OCr and OCra
Definition Source:
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OCr?
Rowe Schist - see OCr (? denotes uncertain identification of the formation, with the most closely associated formation symbol used for the map unit).
Definition Source:
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OCs
Stockbridge Marble (including Inwood Marble (Lower Ordovician and Cambrian) - White to gray, massive to layered marble, generally dolomitic but containing calcite marble in upper part, locally interlayered with schist or phyllite and with calcareous siltstone or sandstone
Definition Source:
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Oa
Allingtown Metavolcanics (Middle? Ordovician) - Green, fine-grained, massive greenstone, composed of epidote, actinolite, albite, and chlorite, commonly with abundant megacrysts of saussurite, interlayered with minor green phyllite, generally containing quartz and sericite. Dark amphibole in western outcrops
Definition Source:
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Oa+Oma
 Allingtown Metavolcanics and Maltby Lakes Metavolcanics undivided -  see Oa and Oma
Definition Source:
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Ob
Brookfield (dioritic and granodioritic) Gneiss (including Newtown Gneiss of Crowley, 1968) (Middle? Ordovician) - Dark and light, commonly speckled or banded, medium- to coarse-grained, massive to poorly foliated gneiss, composed of plagioclase, biotite, and hornblende, generally with quartz and K-feldspar, the latter commonly as megacrysts 1 to 3 cm across (also plagioclase megacrysts in darker rocks), locally associated with amphibolite or hornblende schist
Definition Source:
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Obr
Brimfield Schist (includes Hamilton Reservoir Formation) (Upper? and Middle Ordovician) - Gray, rusty-weathering, medium- to coarse-grained, interlayered schist and gneiss, composed of oligoclase, quartz, K-feldspar, and biotite, and commonly garnet, sillimanite, graphite, and pyrrhotite. K-feldspar partly as augen 1 to 3 cm across. Minor layers and lenses of hornblende and pyroxene-bearing gneiss, amphibolite, and calc-silicate rock
Definition Source:
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Obr?
Brimfield Schist - see Obr (? denotes uncertain identification of the formation, with the most closely associated formation symbol used for the map unit).
Definition Source:
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Obrg
Gneiss (metavolcanic) member [of Brimfield Schist] (Upper? and Middle Ordovician) - Medium-gray, medium-grained, layered gneiss and schist, composed of oligoclase, quartz, and biotite; some gneiss and most schist layers contain garnet and sillimanite; some gneiss layers contain garnet, hornblende, or pyroxene or grade into amphibolite or calc-silicate rock. Probably includes metavolcanic rocks
Definition Source:
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Obs
Bristol Gneiss (Middle? Ordovician) - Light, medium-grained, massive to well-layered gneiss, composed of plagioclase, quartz, and biotite, also muscovite and garnet in many layers, interlayered in places with dark amphibolite
Definition Source:
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Oc
Collinsville Formation (Middle Ordovician) - Mixture of rock types as described for the two members; in many areas felsic and mafic striped metavolcanic rocks predominate
Definition Source:
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Ocg
Hornblende gneiss member [of Collinsville Formation] (Middle Ordovician) - Dark, fine- to medium-grained, well-layered amphibolite and hornblende gneiss, composed or hornblende and plagioclase, commonly with biotite, garnet, or epidote, interlayered with light-gray felsic gneiss and pink quartz-spessartine rock (coticule). Grades into Bristol Gneiss
Definition Source:
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Och
Collins Hill Formation ( = Partridge Formation of New Hampshire) (Upper? and Middle Ordovician) - Gray, rusty-weathering, medium- to coarse-grained, poorly layered schist, composed of quartz, oligoclase, muscovite, biotite, and garnet, and commonly staurolite, kyanite, or sillimanite, generally graphitic, interlayered with fine-grained two-mica gneiss, especially to the west, and with calc-silicate and amphibolite layers, also rare quartz-spessartine (colicule) layers
Definition Source:
State of Connecticut, Department of Environmental Protection
Ochv
Metavolcanic member [of Collins Hill Formation] (Upper? and Middle Ordovician) - Ranges from mafic to felsic, from dark layered amphibolite and hornblende schist, locally with garnet or epidote, to light-gray (in places purplish), laminated gneiss, composed of quartz, oligoclase, and biotite, in which some layers contain garnet (generally manganiferous) and hornblende or cummingtonite
Definition Source:
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Ocm
Cobble Mountain Formation (Middle Ordovician) - Gray to silvery (not rusty), medium- to coarse-grained, generally layered schist and granofels, composed of quartz, oligoclase, muscovite, biotite, and garnet, and locally kyanite and staurolite or sillimanite. Some amphibolite layers
Definition Source:
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Ocs
Sweetheart Mountain Member [of Collinsville Formation] (Middle Ordovician) - Gray and silvery (not rusty), medium- to coarse-grained, poorly layered schist, composed of quartz, oligoclase, biotite, muscovite, and garnet, and in places kyanite or sillimanite. Amphibolite layers common; also layers of quartz-spessartine rock (coticule)
Definition Source:
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Og
Ordovician(?) granitic gneiss (including local terms Ansonia, Mine Hill, 'Tyler Lake', 'Siscowit') (Middle Ordovician?) - White, light-gray, buff, or pink, generally foliated granitic gneiss, composed of sodic plagioclase, quartz, microcline, muscovite, and biotite, and locally garnet or sillimanite. Commonly contains numerous inclusions or layers of mica schist and gneiss
Definition Source:
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Og?
Ordovician? granitic gneiss - see Og (? denotes uncertain identification of the formation, with the most closely associated formation symbol used for the map unit).
Definition Source:
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Ogh
Golden Hill Schist (may be equivalent to part of Trap Falls Formation) (Lower? Ordovician) - Gray to silvery, medium- to coarse-grained, generally layered schist and granofels, composed of quartz, muscovite, biotite, plagioclase, and garnet
Definition Source:
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Ogh?
Golden Hill Schist - see Ogh (? denotes uncertain identification of the formation, with the most closely associated formation symbol used for the map unit).
Definition Source:
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Ogl
Glastonbury Gneiss (Middle? Ordovician) - Gray, medium- to coarse-grained, massive to well-foliated granitoid gneiss composed of oligoclase, quartz, microcline, and biotite, (as patches), also epidote and hornblende in many areas, commonly associated with layers of amphibolite; elsewhere minor muscovite and garnet
Definition Source:
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Oh
Harrison Gneiss (including Prospect Gneiss) (Middle? Ordovician) - Interlayered dark- and light-gray, medium-grained, well-foliated gneiss, composed of andesine, quartz, hornblende, and biotite (also locally K-feldspar as megacrysts 1 to 5 cm long). Thought to be metavolcanic equivalent of unit Ob
Definition Source:
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Oh?
Harrison Gneiss - see Oh (? denotes uncertain identification of the formation, with the most closely associated formation symbol used for the map unit).
Definition Source:
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Ohb
Beardsley (hornblendic) Member [of Harrison (Prospect) Gneiss] (Middle? Ordovician) - Gray to dark-gray, medium-grained, lineated gneiss
Definition Source:
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Ohc
Hawley Formation (carbonaceous schist facies) (Middle Ordovician) - Gray, rusty-weathering, fine- to medium-grained, generally layered schist and granofels, composed of quartz, oligoclase, and biotite; some muscovite and graphite, rare garnet and kyanite or sillimanite. Layers of quartz-spessartine rock (coticule) common
Definition Source:
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Ohn
Nodular member [of Harrison Gneiss] (Middle? Ordovician) - Harrison Gneiss containing prominent quartz-sillimanite nodules
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Ohp
Pumpkin Ground (porphyritic) Member [of Harrison (Prospect) Gneiss] (Middle? Ordovician) - Medium- to light-gray, medium- to coarse-grained, well-layered and foliated gneiss, composed of oligoclase, microcline, quartz, and biotite; some layers have numerous microcline megacrysts 1 to 5 cm across; others have hornblende. Minor layers of garnetiferous schist and gneiss
Definition Source:
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Ol
Litchfield Norite (Middle? Ordovician) - Dark, medium- to coarse-grained, mostly massive mafic rock (olivine norite, quartz norite, hypersthene pyroxenite), composed of labradorite, hypersthene, augite, and olivine in varying proportions, also hornblende and biotite (and minor quartz in quartz norite). Associated with small mineral deposits of pyrrhotite, pentlandite, and chalcopyrite
Definition Source:
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Om
Middletown Formation ( = Ammonoosuc Volcanics of New Hampshire) (Middle Ordovician) - Heterogeneously interlayered dark- to light-gray, generally medium grained gneiss and granofels, ranging from quartz-biotite gneiss through felsic amphibolite gneiss to amphibolite and characteristically containing anthophyllite or cummingtonite with or without hornblende. Also layers of calc-silicate rock and of biotite gneiss with quartz-sillimanite nodules
Definition Source:
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Om?
Middletown Formation -  see Om (? denotes uncertain identification of the formation, with the most closely associated formation symbol used for the map unit).
Definition Source:
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Oma
Maltby Lakes Metavolcanics (Middle? Ordovician) - Green to gray-green, fine-grained, massive to well-foliated and layered greenstone, greenschist, and schist; also dark amphibolite to west and southwest
Definition Source:
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Omal
Lower part [of Maltby Lakes Metavolcanics] (Middle? Ordovician) - Gray-green to green, fine-grained, generally well foliated greenschist, greenstone, and schist or phyllite, composed of albite and chlorite, plus quartz and sericite or epidote and actinolite, mixed metavolcanic and metasemidentary rocks
Definition Source:
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Omau
Upper part [of Maltby Lakes Metavolcanic] (Middle? Ordovician) - Green to gray-green, fine-grained, layered and foliated to massive greenstone and greenschist, composed of epidote, albite, actinolite, and chlorite, and locally minor quartz, sericite, garnet, pyrite, or calcite. Mainly metavolcanic
Definition Source:
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Oml
Lower member [of Middletown Formation] (Middle Ordovician) - Dark- to medium-gray amphibolite and hornblende gneiss, commonly with garnet, diopside, or epidote, interlayered with light-gray gneiss composed of oligoclase, quartz, biotite, and generally one or more amphiboles, also garnet
Definition Source:
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Omm
Massive mafic rock [in Middletown Formation] (Middle Ordovician) - Dark, coarse-grained, massive amphibolite and metagabbro, composed of hornblende and plagioclase; in places with quartz and epidote, in others with patches of actinolite or anthophyllite, chlorite, and epidote or garnet. May be intrusive
Definition Source:
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Omo
Monson Gneiss (may be equivalent to part of Waterford Group) (Middle or Lower Ordovician?) - Interlayered light to dark, mostly medium to coarse-grained gneiss and amphibolite; gneiss composed of plagioclase, quartz and biotite, with hornblende in some layers and microcline in others; traces of garnet, epidote, and magnetite
Definition Source:
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Omu
Upper member [of Middletown Formation] (Middle Ordovician) - Light-gray, generally rusty weathering, well-layered gneiss and granofels, composed of oligoclase, quartz, biotite, and amphibole (cummingtonite, anthophyllite, gedrite, or hornblende, or several of these), also garnet and chlorite. Many layers of amphibolite and biotite gneiss throughout
Definition Source:
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Oo
Oronoque Schist (Lower? Ordovician) - Gray to silver, medium- to fine-grained, well-layered to laminated schist and granofels, composed of quartz, oligoclase or albite, muscovite or sericite, biotite or chlorite, and in western belt local garnet, staurolite, and kyanite. Small lenses of amphibolite or greenstone
Definition Source:
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Op
Preston Gabbro (Middle Ordovician or older) - Dark, medium- to coarse-grained, mainly massive gabbro, composed of labradorite, augite, and opaques, generally with hornblende, locally hypersthene or olivine or both
Definition Source:
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Op+Oq
 Preston Gabbro and Quinebaug Formation undivided -  see Op and Oq
Definition Source:
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Opd
Dioritic phase [of Preston Gabbro] (Middle Ordovician or older) - Medium- to dark-gray, streaked or speckled, medium-grained diorite and quartz diorite, gneissic where sheared near contact, composed of plagioclase, hornblende, and biotite, and locally quartz and relic pyroxene
Definition Source:
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Oq
Quinebaug Formation (Middle Ordovician or older) - Medium- to dark-gray, commonly greenish, medium-grained, well-layered gneiss, composed of hornblende, andesine, biotite, and epidote, commonly with quartz or garnet, interlayered with amphibolite
Definition Source:
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Oqb
Black Hill Member [of Quinebaug Formation] (Middle Ordovician or older) - Gray, medium- to fine-grained, well-layered schist and granofels, composed of oligoclase, quartz, and biotite, commonly with hornblende or muscovite, and locally with calcite, garnet, or epidote
Definition Source:
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Oqf
Felsic gneiss member [of Quinebaug Formation] (Middle Ordovician or older) - Light- to medium-gray, fine- to medium-grained gneiss, composed of plagioclase, quartz, biotite, and muscovite, commonly with K-feldspar
Definition Source:
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Or
Ratlum Mountain Schist (Lower? Ordovician) - Gray, medium-grained, interlayered schist and granofels, composed of quartz, oligoclase, muscovite (in the schist), biotite, and garnet, also staurolite and kyanite in the schist. Numerous layers and lenses of amphibolite; also some of quartz-spessartine (coticule) and calc-silicate rock
Definition Source:
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Or+Ora
 Ratlum Mountain Schist and Amphibolite unit in Ratlum Mountain Schist undivided -  see Or and Ora
Definition Source:
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Or?
Ratlum Mountain Schist - see Or (? denotes uncertain identification of the formation, with the most closely associated formation symbol used for the map unit).
Definition Source:
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Ora
Amphibolite unit [in Ratlum Mountain Schist] (Lower? Ordovician) - Black or mottled, generally massive amphibolite and hornblende gneiss, composed of hornblende and andesine, commonly with minor quartz and magnetite, and locally with garnet, biotite, and epidote
Definition Source:
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Ose
Units e and d [of Strockbridge Marble] (Lower Ordovician) - White to gray massive calcite marble, commonly mottled with dolomite and locally interlayered with dolomite marble and calcareous siltstone and sandstone
Definition Source:
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Osg
Units g and f [of Strockbridge Marble] (Lower Ordovician) - White to gray massive calcite marble with layers and laminae of dolomitic marble
Definition Source:
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Ot
Taine Mountain Formation (Lower? Ordovician) - Gray, medium-grained, generally fairly well layered to well-laminated ('pin-stripe') gneissic or schistose granofels, composed of quartz, oligoclase, biotite, muscovite, and garnet, and locally staurolite and kyanite or sillimanite
Definition Source:
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Ot+Oc
Taine Mountain and Collinsville Formation undivided - see Ot and Oc
Definition Source:
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Ota
Tatnic Hill Formation (Upper? and Middle Ordovician) - Medium- to dark-gray, medium-grained gneiss or schist composed of quartz, andesine, biotite, garnet, and sillimanite, locally kyanite, muscovite, or K-feldspar, interlayered with locally mappable units and thinner layers of rusty-weathering graphitic pyrrhotitic two-mica schist, amphibolite, and calc-silicate rock
Definition Source:
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Otaf
Fly Pond (calc-silicate) Member [of Tatnic Hill Formation] (Upper? and Middle Ordovician) - Light-gray, medium-grained, layered to massive calc-silicate gneiss, composed of andesine, quartz, hornblende or actinolite, epidote, and commonly diopside, biotite, and scapolite; some layers are calcitic
Definition Source:
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Otay
Yantic Member [of Tatnic Hill Formation] (Upper? and Middle Ordovician) - Medium- to dark-gray, fine- to medium-grained schist, composed of quartz, oligoclase, biotite, and muscovite, some layers with garnet, staurolite, and kyanite or garnet and sillimanite, local epidote or K-feldspar; some layers of rusty-weathering graphitic, pyrrhotitic, two-mica schist
Definition Source:
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Otb
Basal member [of Taine Mountain Formation] around Waterbury dome (Lower? Ordovician) - Differs from rest of Taine Mountain Formation in being especially well layered and generally less micaceous and schistose
Definition Source:
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Otf
Trap Falls Formation (may be equivalent in part to Golden Hill Schist) (Middle or Lower Ordovician) - Gray to silvery, partly rusty weathering, medium-grained, generally well layered schist, composed of quartz, sodic plagioclase, biotite, muscovite, and garnet, locally with sillimanite or kyanite, interlayered with two-mica gneiss and granulite and with amphibolite
Definition Source:
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Otf+Og
 Trap Falls Formation and Ordovician? granitic gneiss undivided -  see Otf and Og
Definition Source:
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Otfc
Carringtons Pond Member [of Trap Falls Formation] (Middle or Lower Ordovician) - Interlayered medium- to dark-gray, rusty-weathering, medium-grained schist and light-gray, fine- to medium-grained gneiss, composed of quartz, sodic plagioclase, biotite, muscovite, and garnet; schist locally contains sillimanite or kyanite; gneiss locally contains K-feldspar; amphibolite layers common
Definition Source:
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Otfg
Schist and granulite member [of Trap Falls Formation] (Middle or Lower Ordovician) - Interlayered gray to silvery, medium- to coarse-grained schist and fine-grained granofels, composed of quartz, sodic plagioclase, biotite, and muscovite; garnet common in schist
Definition Source:
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Otfs
Shelton (white gneiss) Member [of Trap Falls Formation] (Middle or Lower Ordovician) - White, light-gray, or buff, fine- to medium-grained, generally well foliated granitic gneiss, composed of sodic plagioclase, quartz, microcline, muscovite, and garnet (in tiny almost ubiquitous grains), also commonly minor biotite; generally interlayered with mica schist, biotite gneiss, and calc-silicate rock. Thought to be metavolcanic equivalent of unit Og
Definition Source:
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Ots
Scranton Mountain Member [of Taine Mountain Formation] (Lower? Ordovician) - Gray, rusty-weathering, medium-grained schist, composed of quartz, muscovite, biotite, plagioclase, garnet, and generally kyanite
Definition Source:
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Otw
Wildcat Member [of Taine Mountain Formation] (Lower? Ordovician) - Gray, medium-grained, generally fairly well layered to well-laminated ('pin-stripe') gneissic or schistose granofels, composed of quartz, oligoclase, biotite, muscovite, and garnet, and locally starolite and kyanite or sillimanite
Definition Source:
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Otwv
Whigville Member [of Taine Mountain Formation] (Lower? Ordovician) - Gray, medium-grained, generally fairly well layered to well-laminated ('pin-stripe') gneissic or schistose granofels, composed of quartz, oligoclase, biotite, muscovite, and garnet, and locally staurolite and kyanite or sillimanite
Definition Source:
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Ow
Walloomsac Schist (Middle Ordovician) - Black to dark-or silvery-gray, rarely layered schist or phyllite, composed of quartz, albite, and commonly garnet and staurolite or sillimanite (locally strongly retrograded to chlorite and muscovite). Locally feldspathic or calcareous near the base
Definition Source:
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Owm
Basal marble member [of Walloomsac Schist] (Middle Ordovician) - Dark-gray to white, massive to layered schistose or phyllitic calcite-phlogopite marble
Definition Source:
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Pn
Narragansett Pier Granite (Permian) - Pink to red, medium- to coarse-grained (commonly pegmatitic), generally massive (not gneissic) granite, composed of microcline, oligoclase, quartz, and biotite and accessory muscovite and magnetite. Considerable associated pegmatite
Definition Source:
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Pnm
Mafic phase [of Narragansett Pier Granite] (Permian) - Gray to reddish, medium-grained, generally massive granite, like Pn but with more biotite and locally hornblende
Definition Source:
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Pp
Porphyry (dacite or rhyolite) (Permian) - Light-colored, very fine grained, massive porphyry with phenocrysts of quartz, feldspar, and biotite; muscovite and accessory fluorite in ground mass
Definition Source:
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Ppa
Pinewood Adamellite (Permian) - Light-gray, medium-grained, massive adamellite, composed of microcline, albite, quartz, and muscovite with accessory fluorite. High radioactivity
Definition Source:
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Ps
Syenite (Permian) - Medium-gray, massive syenite, composed of microcline, amphibole (arfvedsonite), and biotite with accessory apatite and sphene
Definition Source:
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Pw
Westerly Granite (Permian) - Light-gray, pink-weathering, fine-grained, massive, aplitic granite, composed of oligoclase or albite, quartz, and K-feldspar, with minor biotite and accessory muscovite, magnetite, allanite, and sphene
Definition Source:
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Pzmy
Mylonite along Paleozoic faults (Upper or Middle Paleozoic) - Mylonite, blastomylonite, and blastomylonitic gneiss, composed of intensely granulated quartz, plagioclase, biotite, and epidote, in places with hornblende or microcline and commonly with secondary minerals. In places has later been silicified (compare unit Jsi)
Definition Source:
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SObl
Lower member [of Bigelow Brook Formation] (Silurian or Ordovician or both) - Chiefly gray, medium-grained, well-layered granofels, composed of quartz, oligoclase, and biotite, commonly with garnet and sillimanite, interlayered with thinly fissile sillimanitic, graphitic, pyrrhotitic biotite schist and with calc-silicate rock
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SObm
Middle member [of Bigelow Brook Formation] (Silurian and perhaps Ordovician) - Greenish-gray, medium-grained calc-silicate rock, composed of plagioclase, quartz, and diopside (locally hornblende and scapolite), interbedded with schist and granofels composed of plagioclase, quartz, biotite, and commonly garnet and sillimanite
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SObu
Upper member [of Bigelow Brook Formation] (Silurian and perhaps Ordovician) - Chiefly gray, rusty-weathering, medium-grained, generally well layered and locally fissile schist, composed of plagioclase, quartz, biotite, garnet, and sillimanite, locally with K-feldspar or cordierite, fissile layers commonly with graphite and pyrrhotite, interlayered with quartzose granofels with less biotite but with calc-silicate minerals
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SOh
Hebron Gneiss (Silurian and Ordovician) - Interlayered dark-gray, medium- to coarse-grained schist, composed of andesine, quartz, biotite, and local K-feldspar, and greenish-gray, fine- to medium-grained calc-silicate rock, composed of labradorite, quartz, biotite, actinolite, hornblende, and diopside, and locally scapolite. Local lenses of graphitic two-mica schist
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SOs
Southbridge Formation (Silurian or Ordovician or both) - Dark- to light-gray, locally rusty, fine- to medium-grained interlayered granofels and schist, composed of quartz, plagioclase, and biotite, with muscovite in schist and amphibole, calc-silicate minerals, or K-feldspar in certain layers; also locally mappable units and thinner layers of calc-silicate rock, amphibolite, and sillimanite-garnet and sillimanite-graphite-pyrrhotite schist
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SOs?
Southbridge Formation -  see SOs (? denotes uncertain identification of the formation, with the most closely associated formation symbol used for the map unit).
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SOsp
Porphyritic member [of Southbridge Formation] (Silurian or Ordovician or both) - Light-to medium-gray, fine-grained porphyritic massive to layered gneiss, composed of quartz, oligoclase, microcline, and biotite, with megacrysts 1 to 2 cm long of microcline
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Sbc
Clough Quartzite (Silurian) - White, medium-grained, glassy to granular, well-layered quartzite and muscovitic quartzite, locally with garnet; conglomeratic (commonly with tourmaline) in lower part
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Sbf
Fitch Formation (Silurian) - Gray, fine- to medium-grained calc-silicate rock, composed of quartz, biotite, calcite, actinolite, diopside, microcline, and locally garnet, scapolite, or epidote, interlayered with two-mica schist
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Stb
Basal member [of The Straits Schist] ( = Russell Mountain Formation of Massachusetts) (Silurian) - Distinguished by presence of layers of amphibolite, marble, calc-silicate rock, and quartzite within more uniform schist like that on either side. Minor, unevenly distributed mineralization in W, Bi, Cu, Ni, and other metals
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TRnh
New Haven Arkose (Upper Triassic; possibly Lower Jurassic at top) - Red, pink, and gray coarse-grained, locally conglomeratic, poorly sorted and indurated arkose, interbedded with brick-red micaceous, locally shaly siltstone and fine-grained feldspathic clayey sandstone
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TRnh+Jb
 New Haven Arkose and Buttress Dolerite undivided -  see TRnh and Jb
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Yg
Gneiss of Highlands massifs, (including Fordham Gneiss) (Proterozoic Y; may contain some older rocks) - Mixture of rock types described below, where not separately mapped
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Yga
Augen gneiss (including local term 'Danbury Gneiss', equivalent in part to Tyringham Gneiss of Massachusetts) (Proterozoic Y) - Medium-gray to spotted, fine- to medium-grained, porphyritic, foliated and lineated granitic gneiss, composed of microcline (largely as megacrysts or augen up to 10 cm long), quartz, albite, or oligoclase, biotite and minor hornblende
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Ygh
Hornblende gneiss and amphibolite (Proterozoic Y) - Dark-gray to mottled, fine- to medium-grained, massive to foliated amphibolite and gneiss, composed of hornblende and plagioclase, also commonly biotite and minor quartz; commonly interlayered with banded felsic gneiss. Locally contains calc-silicate rock or diopsidic calcite marble
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Ygn
Layered gneiss (Proterozoic Y) - Gray, medium-grained, well-foliated and generally well layered, light and dark, but locally wispy gneiss, composed of quartz and plagioclase, with microcline locally in the light layers and abundant biotite and common hornblende in the dark layers; garnet or epidote locally. Layers and lenses of calc-silicate rock and amphibolite in some areas
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Ygr
Pink granitic gneiss (Proterozoic Y) - Light-pink to gray, medium- to coarse-grained, foliated but generally massive or poorly layered granitic gneiss, composed of quartz, microcline, oligoclase, and either biotite or muscovite or both, also locally amphibole or epidote
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Ygs
Rusty mica schist and gneiss (equivalent in part to Washington Gneiss of Massachusetts) (Proterozoic Y; may contain some older rocks) - Dark-gray, rusty-weathering, well-foliated and well- to poorly layered schist and gneiss composed of quartz, plagioclase, biotite, muscovite, sillimanite, and locally garnet; some layers of feldspathic quartzite and garnetiferous amphibolite
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Zl
Light House Gneiss (Proterozoic Z?) - Light-pink or gray to red, medium-grained, generally well foliated granitic gneiss, composed of K-feldspar, oligoclase, quartz, biotite, and magnetite, with local muscovite but no garnet
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Zp
Plainfield Formation (Proterozoic Z?) - Interlayered light-gray, thin-bedded quartzite, in places with feldspar, mica, graphite, or pyrite, light- to medium-gray gneiss composed of quartz, oligoclase, and biotite (rarely microcline), medium- to dark-gray schist composed of quartz, oligoclase, biotite, sillimanite, and garnet, dark-gray or green gneiss composed of plagioclase, quartz, biotite, and hornblende (commonly with diopside), amphibolite, diopside-bearing quartzite, and calc-silicate rock. In places contains quartz-sillimanite nodules
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Zp+Zsc+Pn
 Plainfield Formation, Stony Creek Granite Gneiss and Narragansett Pier Granite undivided -  see Zp, Zsc and Pn
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Zp+Zsph+Pn?
Plainfield Formation, Potter Hill Granite Gneiss and Narragansett Pier Granite undivided -  see Zp, Zsph and Pn (? denotes uncertain identification of the formation, with the most closely associated formation symbol used for the map unit).
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Zpq
Quartzite unit [in Plainfield Formation] (Proterozoic Z?) - Light-gray, glassy, generally thin bedded quartzite, also feldspathic and micaceous quartzite containing quartz-sillimanite nodules
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Zpq+Zsc+Pn
 Quartzite unit in Plainfield Formation, Stony Creek Granite Gneiss and Narragansett Pier Granite undivided -  see Zpq, Zsc and Pn
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Zsc+Pn
 Stony Creek Granite Gneiss and Narragansett Pier Granite undivided -  see Zsc and Pn
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Zsh
Hope Valley Alaskite Gneiss (Proterozoic Z?) - Light-pink to gray, medium- to coarse-grained, locally porphyritic, variably lineated and foliated alaskitic gneiss, composed of microcline, quartz, albite or oligoclase, and minor magnetite, and locally biotite and muscovite. Lineation formed by rods of quartz. Locally contains quartz-sillimanite nodules
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Zsp
Ponaganset Gneiss (Proterozoic Z?) - Dark-gray, coarse-grained, porphyritic, well-foliated gneiss, composed of oligoclase, quartz, microcline (mostly as megacrysts up to 8 cm long), biotite, magnetite, and generally hornblende; also garnet and muscovite where hornblende is absent
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Zsph
Potter Hill Granite Gneiss (Proterozoic Z?) - Light-pink to gray, tan-weathering, fine- to medium-grained, rarely porphyritic, well-foliated (not lineated) granitic gneiss, composed of microcline, quartz, oligoclase (or albite), biotite, and magnetite, minor muscovite, and local garnet
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Zsph+Pn
 Potter Hill Granite Gneiss and Narragansett Pier Granite undivided -  see Zsph and Pn
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Zspp
Porphyritic phase [of Potter Hill Granite Gneiss] (Proterozoic Z?) - Light- to medium-gray, fine- to medium-grained, porphyritic, well-foliated (note lineated) granitic gneiss, composed of microcline (much of it as megacrysts up to 4 cm long), quartz, oligoclase, biotite, and magnetite
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Zss
'Scituate' Granite Gneiss (Proterozoic Z?) (probably not equivalent to type Scituate in Rhode Island, which is probably Devonian) - Light-pink to gray, medium- to coarse-grained, generally porphyritic, well-lineated and locally foliated granitic gneiss, composed of microcline, quartz, albite or orthoclase, biotite, hornblende, and magnetite. Megacrysts of microcline up to 3 cm long; lineation formed by splotches of biotite or by rods of quartz
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Zw
Waterford Group (may be equivalent in part to Monson Gneiss) (Proterozoic Z?) - Interlayered part (but layers locally distinct) of Waterford Group, light to dark, generally medium grained gneiss, composed of plagioclase, quartz, and biotite, with hornblende in some layers and microcline in others. Some layers of amphibolite
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Zw+Zb
 Waterford Group and Branford Gneiss undivided -  see Zw and Zb
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