North Carolina State Library
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NORTH CAROLINA
DEPARTMENT OF CONSERVATION AND DEVELOPMENT
William P. Saunders, Director fo _ %*
DIVISION OF MINERAL RESOURCES
Jasper L. Stuckey, State Geologist
BULLETIN NUMBER 71
EXPLANATORY TEXT
FOR
GEOLOGIC MAP OF NORTH CAROLINA
By
Jasper L. Stuckey and Stephen G. Conrad
RALEIGH
1958
Norffe Carolir* St**
NORTH CAROLINA
DEPARTMENT OF CONSERVATION AND DEVELOPMENT
William P. Saunders, Director
DIVISION OF MINERAL RESOURCES
Jasper L. Stuckey, State Geologist
BULLETIN NUMBER 71
EXPLANATORY TEXT
FOR
GEOLOGIC MAP OF NORTH CAROLINA
By
Jasper L. Stuckey and Stephen G. Conrad
RALEIGH
1958
MEMBERS OF THE BOARD OF CONSERVATION AND DEVELOPMENT
GOVERNOR LUTHER H. HODGES, Chairman Raleigh
MILES J. SMITH, First Vice Chairman Salisbury
WALTER J. DAMTOFT, Second Vice Chairman Canton
CHARLES S. ALLEN ..__„___ Durham
W. B. AUSTIN Jefferson
F. J. BOLING Siler City
H. C. BUCHAN, JR North Wilkesboro
SCROOP W. ENLOE, JR Spruce Pine
VOIT GILMORE Southern Pines
R. M. HANES Winston-Salem
LEO H. HARVEY Kinston
CHARLES H. JENKINS - __..._...Ahoskie
AMOS R. KEARNS High Point
H. C. KENNETT Durham
R.W.MARTIN Raleigh
CECIL MORRIS Atlantic
HUGH M. MORTON Wilmington
W. EUGENE SIMMONS Tarboro
T.MAX WATSON Spindale
LETTER OF TRANSMITTAL
Raleigh, North Carolina
February 4, 1958
To His Excellency, HONORABLE LUTHER H. HODGES
Governor of North Carolina
Sir:
I have the honor to submit herewith manuscript for publication as Bulletin No. 71, "Explanatory
Text for Geologic Map of North Carolina". This text is an essential part of the new geologic map of
North Carolina.
The new geologic map and this explanatory text contain a summary of the best information pres-ently
available on the geology of North Carolina. This information should be of real value to mining
companies and individuals interested in the geology and mineral resources of the State.
Respectfully submitted,
WILLIAM P. SAUNDERS
Director
CONTENTS
Page
Abstract 7
Introduction 8
Acknowledgments 8
Map units 9
Dependability of the map 10
Structure and metamorphism 11
Description of rock units 12
Introduction 12
Igneous and metamorphic rocks 12
Gneisses and schists^ 12
Precambrian ( ?) 12
Mica gneiss 12
Mica schist 13
Hornblende gneiss 14
Granite gneisses 15
Precambrian ( ?) 15
Unnamed granite gneiss 15
Granite gneiss complex 16
Henderson granite gneiss 16
Cranberry granite gneiss 17
Blowing Rock gneiss 18
Max Patch granite gneiss 18
Beech granite gneiss 19
Granites and mafic igneous rocks 19
Paleozoic ( ?) 19
Dunite 19
Granite 20
Syenite 22
Mount Airy granite 22
Diorite-gabbro 23
Paleozoic 23
Toluca quartz monzonite 23
Cherryville quartz monzonite 24
Whiteside granite 24
Alaskite 24
CONTENTS—Continued
Page
Triassic ( ?) 25
Bakersville gabbro __ 25
Diabase dikes 25
Metavolcanic rocks 26
Precambrian or Lower Paleozoic ( ?) 26
Carolina Slate Belt 26
Felsic volcanics 27
Mafic volcanics 28
Bedded argillites (volcanic slate) 28
Upper Precambrian 29
Grandfather Mountain window 29
Linville metadiabase 29
Montezuma schist 29
Flattop schist 30
Metarhyolite 30
Mount Rodgers volcanic group 30
Metasedimentary rocks 30
Upper Precambrian (?) or Lower Paleozoic (?) 30
Stokes County and Kings Mountain belt 30
Kings Mountain group 30
Lower Cambrian ( ?) 31
Brevard belt 31
Brevard schist 31
Murphy belt 31
Brasstown schist 31
Valleytown formation 32
Andrews schist-Murphy marble 32
Sedimentary rocks 32
Upper Precambrian 32
Ocoee series 32
Snowbird formation • 34
Great Smoky conglomerate 35
Nantahala slate 36
Sandsuck shale 37
Undifferentiated 37
CONTENTS—Continued
Paye
Cambrian 37
Lower Cambrian 37
Unicoi formation 38
Hampton formation 39
Erwin formation 39
Shady dolomite 39
Rome formation 40
Triassic 40
Upper Triassic '_ 40
Pekin formation 41
Cumnock formation 41
Sanford formation 41
Undifferentiated 41
Coastal Plain _ 43
Cretaceous 43
Upper Cretaceous 43
Tuscaloosa formation 43
Black Creek formation 44
Pee Dee formation 44
Tertiary 44
Eocene (Middle and Upper) 44
Castle Hayne limestone 44
Miocene (Upper) 45
Yorktown formation 45
Quaternary 46
Pleistocene and Recent 46
Undifferentiated 46
References cited 48
ILLUSTRATIONS
Figure 1. Generalized geologic cross-section from Wilson,
N. C. to Cape Hatteras, N. C opposite page 47
State Library
EXPLANATORY TEXT FOR GEOLOGIC MAP OF NORTH CAROLINA
By
Jasper L. Stuckey and Stephen G. Conrad
ABSTRACT
A new geologic map of North Carolina, compiled from all available sources, is presented herewith.
The accompanying text describes the rock units shown on the map.
The classification of rock units is based more on rock type than age relations. However, where
possible formation names and age relations were used. The rocks were divided into the following four
groups: Igneous and Metamorphic Rocks, Metavolcanic Rocks, Metasedimentary Rocks and Sedimen-tary
Rocks.
Included in the Igneous and Metamorphic Rocks are gneisses and schists, granite gneisses, and
granites and mafic igneous rocks. The gneisses and schists occur mostly in the upper Piedmont and
Blue Ridge regions of the State and are presumably the oldest rocks present. With one exception, the
granite gneisses are restricted to the Blue Ridge region and probably represent ancient igneous and
sedimentary rocks that have been highly metamorphosed. The granites and mafic igneous rocks occur
throughout the Piedmont and Blue Ridge regions, but are most abundant in the Piedmont. Included in
this group are a wide variety of rock types that vary greatly in age, but all appear to be of igneous origin.
Metavolcanic Rocks occur in three distinct areas. The Carolina Slate belt occupies the largest area
and is present in two separate but parallel belts. The main belt lies across the central part of the State
in a northeast-southwest direction, and the second belt occurs along the western edge of the Coastal
Plain. The Grandfather Mountain window is the second area of metavolcanic rocks, and it lies partly
in the Blue Ridge and partly in the Piedmont Plateau in Avery, Watauga, Caldwell, Burke and McDow-ell
Counties. Third is the Mount Rodgers volcanic group which occupies a relatively small area in the
northwest corner of Ashe County. The Carolina Slate belt consists of volcanic-sedimentary formations,
composed of slates, breccias, tuffs and flows. These rocks vary from acid, or rhyolitic, to basic, or
andesitic, in composition and generally have a well developed cleavage. Rocks in the Grandfather
Mountain window include schists, altered basalt and amygdaloidal basalt, metadiabase, and metarhyo-lite.
The Mount Rodgers volcanic group is composed mostly of metarhyolite, including both tuffs and
flows.
Rocks more or less metamorphosed but retaining enough of their original characteristics to indi-cate
that they were sediments are classed as Metasedimentary Rocks. These rocks occur in four areas,
commonly referred to as the Stokes County area, the Kings Mountain area, the Brevard area, and the
Murphy area. The rocks in the Stokes County and Kings Mountain areas are much alike and are com-posed
mostly of quartzite, schist, conglomerate and marble. These two areas are classed as the Stokes
County and Kings Mountain belt. The other two areas are classed as the Brevard belt and the Murphy
belt, and they are composed mostly of schists with lesser amounts of marble.
The oldest Sedimentary Rocks occur along the western edge of the State. These rocks belong to
the Ocoee series and form much of the rugged topography in the Great Smoky Mountains. The Ocoee
series is a very thick sequence of detrital rocks of graywacke type that rest unconformably on the older
gneisses and granite gneisses. The Ocoee series is classed as Upper Precambrian in age. Overlying the
Ocoee series is a sequence of somewhat better sorted detrital rocks called the Chilhowee group that are
classed as Lower Cambrian in age. The Shady dolomite conformably overlies the Chilhowee group and
is overlain by the Rome formation. Both of these formations are classed as Lower Cambrian.
Triassic sedimentary rocks occupy two belts in North Carolina. The Deep River belt, the largest,
lies along the eastern edge of the Piedmont Plateau and extends from Anson County on the southwest
to near Oxford, Granville County, on the northeast. The Dan River belt lies in the north central part
of the Piedmont Plateau and extends from Davie and Yadkin Counties across Stokes and Rockingham
Counties into Virginia. The rocks of the two belts are very similar and consist of red, brown, purple
and gray claystone, shale, sandstone, conglomerate and fanglomerate, and some coal.
The eastern one half of the State is underlain by sedimentary deposits that range from Upper
Cretaceous to Recent in age. These sediments are commonly referred to as the Coastal Plain deposits
and consist largely of unconsolidated sediments that include gravels, sands, clays, limestone and marls.
The deposits of the Coastal Plain form a wedge-shaped block of sediments that increases in thickness
from a feather edge along its western border to approximately 10,000 feet at Cape Hatteras. The sedi-ments
rest unconformably on crystalline rocks of Precambrian (?) age.
INTRODUCTION
A new geologic map of North Carolina, compiled
from all available sources and supplemented by
several months of fieldwork, is presented here-with.
The accompanying text describes the rock
units shown on the map and indicates briefly the
importance of the units and their mineral deposits.
Prior to the preparation of the present map,
the only geologic map of the State of North Caro-lina
was one prepared by W. C. Kerr and pub-lished
as a part of his Geology of North Carolina,
Volume I, 1875. This map was revised slightly
by J. A. Holmes in 1887 and published as a part
of Ores of North Carolina by W. C. Kerr and G.
B. Hanna (1893). Modifications of these maps,
geologic maps of portions of the State found in
various state reports, geologic folios and other
reports of the U. S. Geological Survey, and a black
and white map of North Carolina modified from
the Geologic Map of the United States by the
U. S. Geological Survey, 1932, served as a basis
for interpreting the geology of North Carolina
until the present map was compiled.
ACKNOWLEDGEMENTS
The geologic map of North Carolina presented
herewith is a compilation from all available
sources, published and unpublished. It is supple-mented
by several months of fieldwork, during
which time areas of the State not previously cov-ered
were mapped on a reconnaissance basis, and
other areas were checked for accuracy of mapping
and to harmonize older maps. In addition to in-formation
obtained from older reports and from
geologists who have had experience in the State in
recent years, many others gave freely of their
time and knowledge in making the present map
possible. Thanks are gratefully expressed to all
who aided in the project, and where possible,
indebtedness for particular information is ex-pressed
below. An apology is hereby expressed
to any who have been overlooked.
First, thanks should be given to Luther H.
Hodges, Governor of North Carolina, who became
interested in the project and made funds avail-able
for the necessary fieldwork and for compiling
and publishing the map. Without his interest and
enthusiastic support the map could not have been
made available at the present time.
To Thomas B. Nolan, Director of the U. S. Geo-logical
Survey, and many members of the staff of
that agency, thanks are gratefully extended. The
U. S. Geological Survey cooperated informally by
making available unpublished geologic maps of
portions of the State, authorizing members of its
staff to evaluate much of the material used, and
furnishing the new base map on which the geology
was compiled and published. Robert A. Laurence
served as representative of the Survey in furnish-ing
unpublished material and gave valuable assist-ance
and advice on the map. Philip B. King re-viewed
the manuscript of the Piedmont and Moun-tain
areas of the State and made many valuable
suggestions. Jarvis B. Hadley edited the geology
of the Great Smoky Mountains area and furnished
valuable information on adjacent areas. W. C.
Overstreet, A. A. Stromquist, and Phil Choquette
contributed valuable data on the Central Piedmont
region. H. M. Bannerman, C. A. Anderson, R. H.
Lyddan, Harold Williams, J. P. Alders, and G. M.
Fitzgerald furnished valuable information as to
available maps and procedures to be used in the
preparation of the map. The geology of the
Coastal Plain is based on recent work of H. E.
LeGrand and P. M. Brown. Robert L. Moravetz
and his associates in the Office of Publications of
the Survey gave valuable instructions on the prep-aration
of the final manuscript and did photo-graphic
work that greatly reduced hand labor. The
8
Committee on Geologic Names checked the legend
and approved the names and ages of many of the
rock units and formations used on the map.
To make the map possible several areas in the
State not previously mapped were mapped on a
reconnaissance basis specifically for the project.
R. J. Council and C. M. Llewellyn, Jr., mapped
Alleghany, Wilkes, Surry, Yadkin, and parts of
Ashe and Caldwell Counties. D. B. Sterrett aided
Councill and Llewellyn and also mapped Alexan-der
County. V. I. Mann and S. S. Alexander map-ped
Franklin, Warren, and parts of Vance, Hen-derson,
Buncombe, and McDowell Counties and
checked several areas in the western part of the
State. W, A. White and E. C. Brett mapped Dur-ham,
Orange, and parts of Person and Granville
Counties. R. L. Ingram and O. B. Eckhoff mapped
Union, Stanly, and parts of Anson and Montgom-ery
Counties. S. D. Heron, Jr., and W. D. Reves
mapped Richmond and parts of Anson, Harnett,
Lee, Moore, Montgomery, and Randolph Counties.
J. M. Parker III and J. F. Conley mapped parts of
Granville, Wake, Harnett, Moore, Lee, and Chat-ham
Counties. J. L. Stuckey and S. G. Conrad
mapped parts of Johnston, Wake, Harnett, Chat-ham,
and Randolph Counties. S. D. Broadhurst
checked several areas and made valuable contribu-tinons
to the project. T. L. Kesler, chief geologist
of Foote Mineral Company, made available to the
project the results of his mapping in the Kings
Mountain district and offered valuable suggestions
on other areas. In addition to field mapping, the
men mentioned above, as well as E. Willard Berry,
G. R. McCarthy, W. H. Wheeler, and E. L. Miller,
Jr., gave valuable aid and criticism while the map
was being compiled.
MAP UNITS
A geologic map is no better than the rock units
or formations used. The map presented is not a
final summary of the geology of North Carolina
but a progress report in which an attempt has
been made to present the best information avail-able.
To give meaning to the map units, more
description is needed than can be presented in a
conventional map explanation. To meet this
need, the following descriptive text has been pre-pared
to indicate the relative dependability of the
map and point out areas where more work is most
urgently needed. There are enough such areas to
keep many geologists busy for a long time, and it
is hoped that this map will serve as a stimulus
and framework for increased geologic mapping in
North Carolina.
Since the present map is based on fieldwork that
is not sufficiently detailed to warrant a complete
revision of nomenclature, an attempt has been
made to show detail where detail exists and only
generalized units where information is lacking.
As a result, standardized units and names already
in use and approved by the Committee on Geologic
Names of the U. S. Geological Survey have been
used wherever possible instead of introducing new
ones.
Not all rock unit and formation names found in
the literature are retained on the present map. In
that portion of the Piedmont and Appalachian
regions covered by various folios and unpublished
maps of the U. S. Geological Survey are large
areas which were mapped as Carolina gneiss and
Roan gneiss. The formation names Carolina
gneiss and Roan gneiss are no longer accepted by
the U. S. Geological Survey and are not used on
the present map. Many of the rocks classed as
Carolina gneiss and Roan gneiss in older reports
are shown as mica gneiss, mica schist, and horn-blende
gneiss on the present map.
The same procedure was followed in the Caro-lina
Slate Belt of the Lower Piedmont. Prior to
the preparation of the present map, two methods
of classifying rock units in that belt had been
employed. Laney (1910), Pogue (1910), and
Stuckey (1928) mapped areas in the Carolina
Slate Belt and classed the rocks as acid volcanic
fragmental and flow materials, basic volcanic
fragmental and flow materials, and bedded slate.
Laney (1917) used the names Virgilina green-stone,
Aaron slate, Hyco quartz porphyry, and
Goshen schist for the volcanics in the Virgilina
district. For the preparation of the present map
it was not possible to do enough detailed fieldwork
to apply these formation names to the whole slate
belt ; instead, the rock-unit names Felsic volcanics,
Mafic volcanics and Bedded argillites (volcanic
slate) were used, as these units are more easily
recognized throughout the belt.
The Coastal Plain is doubtless the best mapped
part of the State, and the formation names in com-mon
use there have been retained with few
changes. In areas of the State, chiefly the Pied-mont
Plateau, where only limited mapping had
been done previous to the preparation of the pres-ent
map, rock units were set up and names most
descriptive of these units were used.
9
DEPENDABILITY OF THE MAP
In the order of dependability the Coastal Plain
is probably the best mapped part of the State.
This is true with respect to the formations estab-lished
and their age relations, but some of them
vary in thickness from place to place, and it is not
always easy to determine the exact limits of sur-face
exposures. The region west of longitude 81°
30' is the next best mapped part of the State, but
here variations in metamorphism and complex
structure make detail mapping difficult. East of
longitude 81° 30' and west of the western limits
of the Coastal Plain less detailed work has been
done, and the map is less complete. These three
areas are discussed below in the order of depend-ability.
The first detailed map of the Coastal Plain was
prepared by Clarke et al. (1912). In that report
Stephenson considered the oldest Cretaceous rocks
in North Carolina to be Lower Cretaceous and
classed them as Patuxent in age. In the same
report Miller considered the Trent formation to
be Eocene and older than the Castle Hayne lime-stone.
Cooke (1926) reclassified the Patuxent as
the equivalent of the Tuscaloosa of Upper Creta-ceous
age, and Kellum (1926) placed the Trent
formation in the Miocene. In subsequent years
other changes were proposed by different geolo-gists.
Berry (1947) compiled a geologic map of
the Coastal Plain from all available sources, which
has served until the present time. LeGrand and
Brown (1955) revised the geologic map of the
Coastal Plain and combined the Trent formation
with the Castle Hayne limestone. The present
map contains all the formations in the Coastal
Plain that are approved by the U. S. Geological
Survey.
Considerable mapping has been done in the
region west of longitude 81° 30', but all the earlier
work was highly generalized. Kerr (1875) divid-ed
the rocks of the region into three units, which
he classed as Lower Laurentian, Upper Lauren-tian,
and Huronian. The lower Laurentian cor-responds
to Paleozoic (?) granites of the present
map ; the Upper Laurentian corresponds to granite
gneisses and gneisses and schists of the present
map; and the Huronian corresponds to metavol-canics
and sedimentary rocks older than Triassic
of the present map. Holmes (1893 see Kerr and
Hanna 1893) used essentially the same classifica-tion
employed by Kerr but considered the three
units to be Archean in age.
Pratt and Lewis (1905) classed the gneisses,
schists, granites, diorite, and other crystalline
rocks of the region as Precambrian in age and the
conglomerates, quartzites, slates, etc., ac Ocoee
of Cambrian age. They considered the peridotites,
dunites, and related rocks as probably early Paleo-zoic
in age.
During a period beginning in 1888 and ending
about 1912, the U. S. Geological Survey mapped
the region being considered, except Polk and parts
of Henderson and Cleveland Counties, on 30-min-ute
quadrangles. Nine of these were published as
folios, and five were not published. The nine pub-lished
folios are: Keith (1895, Knoxville f. 16;
1903, Cranberry f. 90; 1904, Asheville f. 116;
1905, Mount Mitchell f. 124; 1907a, Nantahala f.
143 ; 1907b, Pisgah f. 147 ; 1907c, Roan Mountain
f. 151) , LaForge and Phalen (1913, Ellijay f . 187)
,
and Keith and Sterrett (1931, Gaffney-Kings
Mountain f. 222). The five unpublished maps
were: Keith (Cowee q. and Mt. Guyot q.) ; Keith
and Sterrett (Morganton q. and Lincolnton q.) ;
and Keith and Hayes (Murphy q.). The areal
geologic map of the Cowee, Mt. Guyot, Morganton,
and Murphy quadrangles were revised by Philip
B. King and placed on open file by the U. S. Geo-logical
Survey and were available for use during
the preparation of the present map.
In recent years, considerable mapping has been
done in the region by the U. S. Geological Survey
and the Tennessee Valley Authority, independent-ly,
and by the State of North Carolina in coopera-tion
with these agencies. Philip B. King, Jarvis
B. Hadley, and others of the U. S. Geological Sur-vey
mapped the Great Smoky Mountains and
vicinity, and R. G. Yates, W. R. Griffitts, and W.
C. Overstreet of the same agency mapped the
Shelby quadrangle and adjacent areas. The U. S.
Geological Survey in cooperation with the State
of North Carolina carried out extensive mapping
of mica mines in the area during World War II;
and under the same program J. C. Olsen (1944)
prepared a map of a part of the Spruce Pine dis-trict,
E. N. Cameron (1951) prepared a map of a
part of the Bryson City district, and J. M. Parker
III (1952) prepared a map covering the geology
and structure of a part of the Spruce Pine district.
More recently, Kulp, Brobst et al. (unpublished)
completed a geologic map of the Spruce Pine dis-trict
covering some 250 square miles.
Geologists of the Tennessee Valley Authority,
including Charles E. Hunter, Sam D. Broadhurst,
and E. C. Van Horn, did extensive geological work
10
in the region prior to 1941. Under cooperation
between the Tennessee Valley Authority and the
State of North Carolina, E. C. Van Horn (1948)
prepared a geologic map of the Murphy Marble
Belt, and S. S. Oriel (1950) prepared a geologic
map of the Hot Springs area. Under the same
cooperative agreement a number of other reports
on mineral resources were prepared, chief of
which were by Hunter, et al. (1942) , Murdock and
Hunter (1946), Hunter and Hash (1949), Hash
and Van Horn (1951), and Broadhurst and Hash
(1953). All of these, and other reports not men-tioned
here, were freely drawn upon in compiling
the map of the region west of longitude 81° 30'.
When compilation of the present map was be-gun,
less detailed mapping had been done between
longitude 81° 30' and the western limits of the
Coastal Plain than in any other part of the State.
Laney (1910 and 1917), Pogue (1910), and
Stuckey (1928) had prepared maps of a part of
the Carolina Slate Belt. Stone (1912), Campbell
(1923), and Reinemund (1955) had prepared
maps of the Dan River and Deep River Coal Fields.
Keith and Sterrett (1931) had mapped a part of
Cleveland County, and Overstreet et al. (1953)
had prepared a preliminary map of the Lincoln-ton
quadrangle. J. M. Parker III, under a coop-erative
agreement between the U. S. Geological
Survey and the State of North Carolina, had just
completed a map, not yet published, of the Hamme
Tungsten district covering parts of Granville and
Vance Counties. These and a number of maps
covering 50 to 100 square miles each, which had
been prepared by graduate students in connection
with theses problems, represented the only de-tailed
mapping in the region.
Considerable mapping, however, had been done
on a reconnaissance basis in connection with a
cooperative project between the U. S. Geological
Survey and the State of North Carolina for the
study of ground water in the State. Mundorff
(1946) prepared a geologic map of the Halifax
area covering Nash, parts of Halifax, Northamp-ton,
and Wilson Counties in the Piedmont. Mun-dorff
(1948) prepared a similar map of the
Greensboro area covering Alamance, Caswell,
Guilford, Rockingham, Forsyth, and Stokes Coun-ties.
LeGrand and Mundorff (1952) prepared the
same sort of map of the Charlotte area covering
Cabarrus, Mecklenburg, Gaston, Lincoln, Cleve-land,
Rutherford, and Polk Counties. LeGrand
(1954) prepared a similar map of the Statesville
area covering Alexander, Catawba, Iredell, Davie,
Rowan, and Davidson Counties.
The maps listed plus the new mapping in the
areas referred to under acknowledgments above
served as the basis for compiling the present map
of the State. Every possible precaution was taken
to make the best possible use of the available data,
but it should be pointed out that the map appears
much more accurate than it actually is. No one
is so well aware of its weak points and imperfec-tions
as the compilers are. A general precaution
is issued to all users not to consider it a finished
map, but a summation of the best information at
present available on the geology of North Carolina.
STRUCTURE AND METAMORPHISM
In an area as complex in geology as that found
in the Piedmont and Mountain regions of North
Carolina, structural features and metamorphism
of the rock units present many major problems.
After giving much thought to the structural fea-tures
of the rocks in the Piedmont and Mountain
regions of the State and discussing the subject
with many people who are more or less familiar
with the region, it was decided that enough de-tailed
information is not available to produce
structure sections of real value. It was also de-cided
that enough information is not available to
warrant any detailed discussion of faulting, fold-ing,
metamorphism, unconformities, and facies
changes. As a result, metamorphism is not dis-cussed
as such, and the only structural features
shown on the map are a few faults of regional
significance.
The U. S. Geological Survey is now engaged in
the detailed mapping of a strip from the western
edge of the Cumberland Plateau, across the Appa-lachian
Mountains, the Piedmont Plateau, and the
Coastal Plain. This strip is expected to cross a
part of North Carolina. Perhaps, when it is com-pleted,
a revised map of North Carolina will be
prepared which will contain more information on
structure and metamorphism than is now avail-able.
Structural features in the Coastal Plain are less
complicated than in the Piedmont and Mountain
regions. The formations generally strike north-east-
southwest and dip gently a few feet per
mile to the southeast. No faults or folds of any
significance have been found in the region. A
geologic cross-section across the Coastal Plain
11
with considerable subsurface data, obtained from
deep-well records, is presented below.
DESCRIPTION OF ROCK UNITS
INTRODUCTION
In the explanation listed on the map and dis-cussed
below, a three-fold grouping of rock units
has been used. First, the rock units have been
grouped as sedimentary rocks, metasedimentary
and metavolcanic rocks, and igneous and meta-morphic
rocks. Igneous and metamorphic rocks
have been grouped together because some of the
units used have characteristics of both igneous
and metamorphic rocks. Second, an attempt has
been made to group the rock units in the explana-tion
according to their geographic distribution in
the State. Third, as far as possible the sequence
in the explanation represents the stratigraphic
position of the rock units in the earth's crust.
This is thought to be correct for the sedimentary
rocks; however, in the case of metasedimentary
rocks, metavolcanic rocks, and igneous and meta-morphic
rocks, the sequence in the explanation may
not represent the true stratigraphic position. For
example, the rock units used in the metavolcanic
rocks of the Carolina Slate Belt are interbedded
and, as a result, are not distinctly different in age.
The exact ages of most of the granites listed as
Paleozoic (?) and Paleozoic are not known, and
as a result some may be the exact stratigraphic
equivalents of others. The same holds true for the
granite gneisses, as Eckelman and Kulp (1956)
classed the Cranberry granite gneiss and the Hen-derson
granite gneiss as stratigraphically equiva-lent.
Finally, the exact ages of the gneisses and
schists are not known, and it is quite probable that
the units used contain materials differing greatly
in ages.
IGNEOUS AND METAMORPHIC ROCKS
The gneisses, schists, and granite gneisses, list-ed
as Precambrian( ?) , present a major problem
in age classification. Many of these units in the
Blue Ridge area, according to King (personal
communication), are unconformable below Lower
Cambrian and Upper Precambrian units and
should be classed as Precambrian without the
query. However, the difficulty comes in going
southeast from the Blue Ridge area where similar
units have no certain stratigraphic relations to the
Cambrian or Upper Precambrian. The result is
that Precambrian (?) looks incongruous in the
Blue Ridge area where these rocks are in contact
with Upper Precambrian and Lower Cambrian,
but is well justified in the southeast. No simple
solution could be found for the problem, and it has
been left for map users to draw their own con-clusions.
GNEISSES AND SCHISTS
PRECAMBRIAN(P)
The three units—Mica gneiss, Mica schist, and
Hornblende gneiss—used in this grouping repre-sent
essentially Carolina gneiss and Roan gneiss
in the areas mapped by Keith and similar mate-rials
outside these areas. The formation names
Carolina gneiss and Roan gneiss are no longer
accepted by the U. S. Geological Survey and are
not used on the present map. The three units as
presently constituted are too complex in compo-sition
to be given formation names, and it was
thought best to use the rock-unit names, Mica
gneiss, Mica schist, and Hornblende gneiss.
Mica Gneiss (mgn)
The Mica gneiss unit, as mapped, occurs over a
wider area and probably underlies more square
miles of the State than any other formation on
the map. It is especially abundant in the Blue
Ridge region and the western part of the Piedmont
Plateau where it covers large areas. It is less
abundant in the central part of the Piedmont Pla-teau
but is common along the eastern part of that
area. In the Blue Ridge and upper Piedmont
areas, the Mica gneiss unit consists largely of
Carolina gneiss as mapped by Keith (1903, 1904,
1905, 1907a, 1907b, 19007c, and 1931). In other
parts of the State the Mica gneiss unit is in all
respects comparable to that in the areas mapped
by Keith.
The Mica gneiss unit consists of an immense
series of mica gneiss, mica schist, and fine gran-itoid
layers in which mica gneiss predominates.
Most of these are light to dark gray in color,
weathering to dull gray, greenish gray, or yellow.
Varying amounts of garnet gneiss, garnet schist,
kyanite gneiss, granite gneiss, hornblende gneiss,
and crystalline limestone or marble are present
in the unit at many localities. There are also in-cluded
in the Mica gneiss unit younger bodies of
12
granite, diorite, and dikes and lenses of pegmatite
too small or not well enough known to show on the
map. Mica gneiss, which is the chief component
of the Mica gneiss unit, is composed chiefly of
quartz and feldspar with varying amounts of mica,
both biotite and muscovite, with biotite predomi-nating
in many localities. Much of the Mica gneiss
unit is doubtless metamorphosed sedimentary ma-terial,
while some of it resembles granite gneiss
and may well represent granite that has been
strongly metamorphosed. Rock of this type has
been quarried extensively around Asheville, Bun-combe
County; Hickory, Catawba County; Hen-derson,
Vance County ; and Raleigh, Wake County.
This material was used in the construction of the
present State Capitol in Raleigh, which was erect-ed
between 1830 and 1835.
Bands and lenses of mica schist, usually fine-grained
and composed of quartz, muscovite, a little
biotite, and very little feldspar are common in the
Mica gneiss unit. Closely associated with the mica
schist bands and lenses are extensive bands and
zones of garnet gneiss, garnet schist, and kyanite
gneiss. The garnet and kyanite gneisses and
schists are too widespread to describe in detail
here. Some of the better known garnet areas are
near Marshall, Madison County; on Sugar Loaf
Mountain near Willetts, the Savannah mine on the
headwaters of Betty Creek, and the Presley mine
near Speedwell in the upper Tuckaseegee valley,
all in Jackson County; and on Shooting Creek,
Clay County. An important belt of kyanite gneiss,
six to eight miles wide, extends along the line of
the Black and Great Craggy Mountains from
Swannanoa, Buncombe County, to Bakersville,
Mitchell County. The kyanite crystals vary in
length from a fraction of an inch to three or four
inches but average less than an inch. On weath-ered
surfaces, they often stand out in relief, giv-ing
the rock a porphyritic appearance. Small gar-nets
are often associated with the kyanite gneiss.
At many places throughout the Mica gneiss unit
there are thin, interbedded layers of hornblende
gneiss and schist, too small to show on the map.
These are in all respects similar to the Horn-blende
gneiss unit described below.
Bodies of crystalline limestone or marble are
present at many localities in the Mica gneiss unit.
The more important of these occur near Marshall,
Madison County; south of Bakersville, Mitchell
County ; eight miles northwest of Winston-Salem,
Forsyth County; and near Germanton, Stokes
County.
Included in the Mica gneiss unit at many places
are dikes and lenses of pegmatite which are dis-tinctly
younger than the enclosing rock. These
vary in thickness from a few inches to as much as
200 feet (Olson, 1946, p. 7) and are equally vari-able
in length. Most of the kaolin and feldspar
produced in North Carolina prior to 1945 came
from pegmatite bodies. Throughout the history
of mica mining in the State pegmatites have been,
and still are, the chief source of sheet mica. A
wide variety of commercially less important min-erals
are present in the dikes, and Olson (1944,
p. 26) stated, "At least 44 different minerals have
been reported from the Spruce Pine pegmatites."
Spodumene-bearing pegmatites, which are the
chief source of lithium in the United States, are
abundant in the Mica gneiss unit south of Lincoln-ton
in the Kings Mountain district.
The Mica gneiss is deeply weathered in most
places and is covered with a thick layer of resi-dual
clay. As a result, fresh outcrops and ledges
of solid rock are seldom seen except along streams,
on steep slopes, and in the more mountainous
areas. The residual clay contains fragments and
layers of schist, quartz, mica, and gneiss. The
cover of soil on the thick mantle of residual clay
and weathered rock is usually light and thin.
Mica Schist (msh)
The Mica schist unit occurs most abundantly
along the western border of the Piedmont Plateau,
just east of the Blue Ridge Mountains, and extends
intermittently completely across the State. In the
vicinity of Kings Mountain and around Gastonia
there are fairly large areas of mica schist, and
smaller areas are widespread throughout the Pied-mont
Plateau. The main occurrences of this unit
along the western border of the Piedmont Plateau,
the area around Gastonia, and the areas through-out
the lower Piedmont are essentially mica schist
of the Carolina gneiss as mapped on the various
folios of the U. S. Geological Survey.
North of the Yadkin River, the Mica schist unit
consists principally of a thinly foliated muscovite-sericite
schist. This unit also includes bands and
zones of muscovite-biotite schist and some areas
of mica gneiss, partly altered to mica schist. In-jections
of granite, too small to show on the map,
are also common east of the Blue Ridge, and small
amounts of hornblende gneiss and schist are pres-ent
at many places in the unit. At many places,
the Mica schist contains varying amounts of gar-
13
net, sillimanite, kyanite, magnetite, ilmenite, and
pyrite.
South of the Yadkin River, the Mica schist unit
consists basically of biotite schist. Three varie-ties
of biotite schist are common, namely, biotite
schist, biotite-muscovite schist, and sillimanite-biotite
schist. All gradations exist among the
three varieties. The sillimanite schist is in all
places more contorted and sheared than the other
varieties. A number of accessory minerals, in-cluding
garnet, graphite, chlorite, and pyrite are
present in the Mica schist unit. Pegmatites and
narrow quartz veins occur throughout the mica
schist. The pegmatites in general average less
than a foot in thickness and rarely exceed four
feet in length. Locally, they make up as much as
one-half of the sillimanite-biotite schist. Over-street
and Griffitts (1955, pp. 551-556) gave an
excellent description of the Mica schist unit and
related rock units and discussed their mineral
content in some detail.
Bands and zones of hornblende gneiss and horn-blende
schist, most of which are too small to show
on the map, are common throughout the Mica
schist unit. These hornblende rocks are generally
of simple mineral composition and locally may con-tain
varying amounts of garnet. Many bodies of
foliated to massive granite, too small to show on
the map, are present in the unit.
The Mica schist around Gastonia and in the
other areas of the Piedmont Plateau to the east
and northeast is essentially a fine-grained rock
composed chiefly of quartz, muscovite and sericite
mica. At places, the rock is a quartz-biotite
schist, while at others it becomes a quartz-sericite,
chlorite schist. The Mica schist evidently resulted
from the metamorphism of sedimentary rocks that
varied greatly in character from place to place.
Weathering has been extensive, and outcrops of
fresh rock are seldom seen except along streams
and on steep slopes. The thick layer of residuum
consists of clay mixed with fragments and layers
of schist, quartz, and mica. The clay varies from
yellow to dark red in color depending on the
amount of biotite in the schist. The soil cover is
usually light and thin.
Hornblende Gneiss (hgn)
The Hornblende gneiss unit is most abundant in
the mountain region west of the Blue Ridge and
north and northeast of Asheville. Several small
areas occur west of the Blue Ridge in Clay and
Macon Counties. In and parallel to the east side
of the Blue Ridge small areas occur almost com-pletely
across the State. In the central part of
the upper Piedmont, in the general vicinity of
Hickory and Statesville, there are some relatively
large areas. Smaller areas occur along the east-ern
edge of the Piedmont Plateau, particularly in
Wake County.
The Hornblende gneiss unit consists essentially
of Roan gneiss as mapped and defined by Keith
(1903). The type locality of the Roan gneiss is
Roan Mountain, which lies along the North Caro-lina-
Tennessee line and extends southward into
Mitchell County, North Carolina. Keith (1903)
stated, "The Roan gneiss appears to cut the Caro-lina
gneiss, but the contacts are so much metamor-phosed
that the fact cannot be proved." He con-sidered
the Roan gneiss as chiefly diorite and
smaller amounts of gabbro, which had been in-truded
into older rocks and metamorphosed to
hornblende gneiss and hornblende schist.
In recent years considerable attention has been
given to Roan gneiss, as mapped and defined by
Keith, and much of it is no longer considered to be
of igneous origin. Kesler (1944, 1955) pointed
out that bodies of hornblende gneiss in the Kings
Mountain district (See Kings Mountain group be-low,
p. 31) are metamorphosed, calcareous sedi-ments.
Parker (1952, p. 8) described the relation
of the hornblende gneiss to the mica gneiss in the
Spruce Pine district and concluded that certain
thin, interbedded hornblende gneisses and actino-lite-
tremolite rocks may have been impure dolo-mitic
limestones. He added: "The mafic min-eralogic
composition, however, coupled with the
conformable relations to mica gneiss, has led most
workers to believe that the ordinary hornblende
rocks are metamorphosed mafic volcanic extru-sives,
and perhaps, in part at least, are conform-able
intrusive sills," and concluded, "Perhaps some
of the hornblendic rocks are sedimentary in origin
and some are igneous."
Brobst (unpublished) concluded that the Roan-type
rocks (hornblende gneiss) are of sedimen-tary
origin and stated, "The hornblende rocks,
therefore, may represent the metamorphosed
equivalent of impure carbonate layers in the sedi-mentary
sequence." Overstreet and Griffitts
(1955, p. 553) considered the hornblende gneiss
between Kings Mountain and Marion, North Caro-lina,
to be in part of igneous and in part of sedi-mentary
origin.
14
The Hornblende gneiss unit consists essentially
of hornblende gneiss and hornblende schist layers
that vary from a fraction of an inch to many feet
in thickness. The thin layers of hornblende gneiss
and hornblende schist are interbedded with thin
layers of mica gneiss and mica schist to the extent
that portions of the Hornblende gneiss unit con-tains
considerable mica gneiss and mica schist,
and in the same way portions of the Mica gneiss
unit and portions of the Mica schist unit contain
considerable amounts of hornblende gneiss and
hornblende schist.
The hornblendic rocks of the Hornblende gneiss
unit include distinctly banded gneisses consisting
of alternating layers of hornblende and feldspar,
schistose rocks consisting almost entirely of coarse
to fine hornblende needles, and nearly massive am-phibolites
that lack distinct foliation. The gneisses
and schists are black to dark green and grade into
one another by feldspar content. Quartz, feld-spar,
and hornblende are the chief minerals pres-ent,
but varying amounts of biotite and chlorite
are present at places.
Garnet is less abundant than in the Mica gneiss
and Mica schist but at places becomes an impor-tant
constituent of the Hornblende gneiss. Peg-matite
dikes, some of which have furnished con-siderable
amounts of feldspar and mica, are pres-ent
at many places in the unit. Numerous bodies
of soapstone and talcose schist are associated with
the Hornblende gneiss unit especially in the Spruce
Pine district. These bodies, which vary from five
to 25 feet in thickness and consist of talc, soap-stone,
actinolite, biotite, chlorite, and vermiculite,
appear to have been formed locally by secondary
hydrothermal alteration of the hornblende gneiss.
In the more mountainous areas, the Hornblende
gneiss often crops out as ledges and bold ridges,
but at lower elevations it usually occupies broad,
flat areas or lower ground. It weathers readily
and is usually covered with a thick layer of resi-dual
clay mixed with rock fragments. This clay
has a strong, dark-red color and is covered with
a rich, fertile soil.
intruded by a number of rocks which he classed
as granites and granite gneisses (all highly meta-morphosed)
and named in various areas Cran-berry
granite, Henderson granite, Max Patch
granite, and Beech granite. One unit, the Blow-ing
Rock gneiss, he did not definitely class as a
granite, even though he considered it intrusive
into the older gneisses and the Cranberry gran-ite.
Little has been published on these rocks since
the work of Keith, but a number of workers in
the area have made observations that caused
them to doubt the validity of classing these units
as either intrusive in origin or true granites in
composition. This is true especially of the Cran-berry
and Henderson granites. Brobst (unpub-lished)
listed and described the Cranberry granite
as Cranberry gneiss. He discussed specifically
some layers, typical of the Cranberry gneiss, which
are interbedded with other metamorphic rocks
along the northwest and east borders of the
Bakersville-Plumtree area, Avery County, close
to the contact of the large body of Cranberry
gneiss that surrounds that part of the Spruce Pine
district on three sides (Kulp and Brobst, 1956).
Eckelman and Kulp (1956) considered the Cran-berry
and Henderson granites to be metasedimen-tary
in origin and stratigraphically equivalent.
During the preparation of the present map it
was not possible to restudy these units in detail.
As a result, in the areas covered by published
folios these units are shown as nearly as possible
as originally mapped. Outside the areas covered
by published folios, it is doubtful if the units cor-respond
in all details to those in the areas covered
by published maps. In view of the diversity of
materials in the units and the intense metamorph-ism
which has altered them, it was decided, after
discussing the problem with a number of workers
who have made observations in the field, to add
the word gneiss to each unit originally classed as
granite. As a result, each of these units originally
classed as granite becomes a granite gneiss on the
present map.
GRANITE GNEISSES
PRECAMBRIAN(P)
Along the western edge of the Piedmont Pla-teau
and throughout much of the Blue Ridge
Mountains area, according to Keith (see reference
above), the older gneisses and schists have been
Unnamed Granite Gneiss (gru)
In Jackson, Haywood, and Swain Counties, west
and north of Sylva, are areas of Unnamed granite
gneiss. J. B. Hadley, on a map of the Great Smoky
Mountains area furnished for use in the prepara-tion
of the present map, designated these rocks as
granite gneiss without formation or unit names or
15
age designations. Hadley et al. (1955, p. 402)
classed these rocks as Max Patch and Cranberry
as mapped by Keith (1904) and described them
as medium to very coarse genissic granites, gen-erally
gray but locally pink in color and containing
minor amounts of leucogranite, amphibolite, peg-matite,
and much blue quartz.
Cameron (1951, p. 10) described one of these
areas near Bryson City in some detail. He classed
the rocks of the area as granitic gneisses and de-scribed
them as predominantly fine- to coarse-grained
leucocratic and mesocratic gneisses, vary-ing
in composition from granitic to granodioritic
with well developed foliation and lineation. He
stated that the granite gneisses are cut by dikes
of fine-grained granite and by dikes of medium-gray
granite porphyry.
Granite Gneiss Complex (gnc)
Beginning a few miles northeast of Morganton
and extending in a southwest direction across
Burke, McDowell, Rutherford, and Polk Counties
is an area underlain with rocks classed as Granite
gneiss complex on the present map. About half
of this area, in Burke and McDowell Counties,
extending to latitude 35° 30' N. and longitude 82°
W. in Rutherford County, was mapped by Keith on
the Morganton quadrangle, which was not pub-lished.
He made field surveys in the Morganton
quadrangle in the years 1896, 1899, 1900, 1901,
and 1907 and was aided by D. B. Sterrett during
the last year. Traverse sheets available in the
U. S. Geological Survey files show complete cover-age
of the quadrangle. Based on these surveys,
Philip B. King edited a geologic map of the Mor-ganton
quadrangle, which appears to be a general-ization
by Keith of a more detailed map not at
present available.
The central part of the Morganton quadrangle,
as edited by King, is underlain with a rock unit
5 to 15 miles wide which is classed as "Cranberry,
Henderson (and other?) granites (Archean) (in-cludes
small areas of Roan gneiss)." Small areas
of the same unit are shown in the southeast corner
of the Morganton 30' quadrangle and in the Shelby
15' quadrangle. Rocks of this unit in Cleveland,
Lincoln and Burke Counties were named Toluca
quartz monzonite and classed as Ordovician in age
by Griffitts and Overstreet (1952).
The main area of Granite gneiss complex ex-tends
southwest from the Morganton quadrangle
across Rutherford County and well into Polk
County. LeGrand and Mundorff (1952) mapped
this unit in Rutherford County as mica schist and
granite with schist predominant, and hornblende
gneiss and granite interlain, and in Polk County
as granite gneiss interlain with hornblende gneiss,
and hornblende gneiss and granite interlain.
Attempts were made to harmonize the mapping
done by LeGrand and Mundorff in Rutherford and
Polk Counties with that done by Keith in the Mor-ganton
quadrangle. Attempts were also made to
determine if the granitic material in the Granite
gneiss complex as shown on the present map could
be correlated with the granitic rocks in the south-east
corner of the Morganton quadrangle and the
northeast corner of the Shelby quadrangle, which
Griffitts and Overstreet designated as Toluca
quartz monzonite of Ordovician age.
The problem was not fully recognized until com-pilation
of the map was well underway, and time
was not available to work out all the details. Two
field parties, working independently, spent several
days in the area and decided that the materials
mapped by LeGrand and Mundorff in Polk and
Rutherford Counties and by Keith in the Morgan-ton
quadrangle are essentially the same. It was
decided that in the time available no correlation
could be made between the granites in the area
and the Toluca quartz monzonite to the east and
southeast.
The rock unit shown on the present map as
Granite gneiss complex contains mica gneiss, mica
schist, and hornblende gneiss similar to that in
the gneisses and schists described above. In addi-tion
it contains granite gneiss similar to Hender-son
granite gneiss, and Cranberry granite gneiss
and also younger granite.
Henderson Granite Gneiss (hgg)
The Henderson granite gneiss unit on the pres-ent
map is essentially Henderson granite as origi-nally
named and described by Keith (1905) and
further described (1907b). The Henderson gran-ite
as mapped by Keith is not shown in contact
with Cranberry granite at any place on his maps.
On the present map the main area of Henderson
granite gneiss begins near Marion, McDowell
County, and continues southwest to the South
Carolina line. West of Marion, a narrow band
continues northeast along the west side of the
Shady dolomite and Erwin formation to the limits
of the Mount Mitchell quadrangle. Recently, Eck-elman
and Kulp (1956) extended this band north-
16
east to near Linville Falls, McDowell County,
where it makes contact with what they considered
the southern extension of Cranberry granite as
mapped by Keith in the Cranberry folio. They
considered the Cranberry granite and the Hender-son
granite to be metasedimentary in origin and
stratigraphically equivalent.
Keith (1905, p. 4) stated that the Henderson
granite extended eastward into the Morganton
quadrangle. A large area in the Morganton quad-rangle
(discussed above under Granite gneiss
complex) was mapped as Cranberry, Henderson
(and other?) granites No age relations are shown
between Cranberry and Henderson granites on
the Morganton quadrangle, but in the legend on
the Mount Mitchell folio, Keith placed Henderson
granite above Cranberry granite. The exact
origin and age of the Henderson granite is un-known.
The Henderson granite gneiss, whatever its
origin and age, is composed essentially of rocks
with a pronounced gneissoid structure. Min-eralogically,
the rock consists of orthoclase, pla-gioclase,
quartz, muscovite, and biotite, named in
the order of their abundance. Biotite varies a
great deal in amount but is usually subordinate.
The gneiss is usually gray in color but becomes
lighter on weathering. Porphyritic crystals of
feldspar are a prominent feature of the gneiss,
and at many places it is a typical augen gneiss.
The porphyritic varieties are not limited to any
particular areas or positions in the gneiss but are
generally irregularly distributed through it. Por-phyritic
varieties of the gneiss grade into even-grained
varieties, and the two varieties may be
seen in a single exposure. Even-grained varieties
of the gneiss are subordinate in amount to the
porphyritic varieties.
The rocks of this unit have been greatly changed
by metamorphism. In areas where the finer
grained beds did not contain porphyritic crystals
of feldspar, the rock has been metamorphosed into
gneisses and schists similar to those of the Mica
gneiss and Mica schist units. Areas of mica
gneiss, mica schist, and hornblende gneiss, too
small to show on the map, are included at many
places in the Henderson granite gneiss.
Weathering of the Henderson granite gneiss
varies greatly, and as a result the rock produces
a varying landscape with strong cliffs and ridges
in places and broad, flat areas in others. The
Henderson granite gneiss has not been much used,
but it offers an important source of dimension
and crushed stone.
Cranberry Granite Gneiss (cgn)
The Cranberry granite gneiss unit on the pres-ent
map consists essentially of Cranberry granite
as originally named and described by Keith
(1903), and further described (1904, 1905, and
1907c). The name Cranberry granite was first
given to well developed exposures at Cranberry,
Mitchell County, now Avery County. The rela-tions
of the Cranberry granite gneiss to the Hen-derson
granite gneiss have been discussed above
under Henderson granite gneiss.
Keith (references listed above) considered the
Cranberry granite as igneous in origin, Archean
in age, and intrusive into elder formations. He
described it as granite of varying texture and
color, and schists and granitoid gneisses derived
from granite. Included were small or local beds
of schistose basalt, diorite, hornblende gneiss, and
pegmatite.
As pointed out above, a number of workers in
the area have made observations that caused them
to doubt the validity of classifying the Cranberry
granite as either intrusive in origin or a true gran-ite
in composition. Brobst (unpublished) describ-ed
the unit as Cranberry gneiss, consisting of
white to gray gneisses, composed chiefly of micro-cline,
sodic plagioclase, and quartz, and stated that
in some layers biotite, muscovite, and rarely horn-blende
may be present in amounts in excess of ten
percent. He described the texture as cataclastic,
with rounded and fractured porphyroblasts of
microcline or plagioclase from three millimeters
to one centimeter across the longest dimension.
The Cranberry granite gneiss unit occurs as
strips and patches in the Mountain region along
the northwest border of the State. These begin
about the latitude of Asheville in Haywood and
Madison Counties and continue northeast to the
Virginia line. The strips and patches which make
up the unit have an elongation which conforms in
general with the northeast-southwest trend of the
mountains.
The Cranberry granite gneiss, whatever its
origin, is essentially a gneiss, which grades at
places into schist. Logs of cores from 12 drill
holes, varying in length from 400 to 1250 feet,
which were drilled at the Cranberry iron mine in
the type locality of the Cranberry granite in 1943-
1944, were examined during the preparation of
17
this report. These logs, which were prepared by
competent geologists, show the rock to be a typical
gneiss. In addition to gneiss, narrow bands' of
hornblende gneiss, chlorite schist, and pegmatite
were occasionally shown near the iron-ore veins.
Some of the gneiss in the area is coarse-grained,
but much of it is medium-grained and uniform in
texture. In color, it varies from light to dark
gray.
In general, the Cranberry granite gneiss is a
medium-grained, even-textured rock that varies
from light to dark gray in color. It is composed
of quartz, orthoclase, plagioclase, muscovite, bio-tite,
and occasionally hornblende. In some areas
the rock is more or less porphyritic, and in some
places it has a marked red appearance due to the
presence of red feldspar. The gneiss contains
many small areas of mica gneiss, mica schist, horn-blende
gneiss, schistose basalt, diorite, metadia-base,
metarhyolite, and pegmatite.
The Cranberry granite gneiss has been used to
a limited extent for chimneys, foundations, and
bridge piers, but no major quarrying operations
have developed. The rock withstands weathering
quite well in natural exposures. It takes a good
polish and should make an attractive building
stone. Quarry sites for crushed stone are avail-able
at many places.
Perhaps the most important mineral deposits
associated with the Cranberry granite gneiss are
the magnetic iron ores near Cranberry, Avery
County. The magnetite deposits, while surrounded
by the Cranberry granite gneiss, did not originate
with the gneiss. According to Bayley (1923) the
iron ore was brought up by pegmatites and depos-ited
in the gneiss. These iron-ore bodies have been
of interest for more than a hundred years. Sys-tematic
mining was carried on intermittently be-tween
1880 and 1928, and some 2,250,000 tons of
crude ore, which produced some 1,500,000 tons of
shipping ore containing 42 to 46 per cent iron, were
mined.
Blowing Rock Gneiss (brgn)
The main area of Blowing Rock gneiss is a
wedge-shaped body beginning a few miles north
of Blowing Rock, Watauga County, extending
southward almost completely across Caldwell
County and coming to a point at its southern end.
A small area is shown near Creston, Ashe County.
Keith (1903) named the unit Blowing Rock gneiss
because it is well developed near the town of
Blowing Rock. He classed it as an igneous rock,
intrusive into Cranberry granite and older forma-tions
and described it as chiefly dark, coarse, por-phyritic
gneiss.
The unit consists of two varieties, one contain-ing
large porphyritic crystals of orthoclase feld-spar
embedded in a groundmass of quartz, feld-spar,
biotite, and muscovite, and the other con-sisting
of the same minerals in grains of uniform
size. The porphyritic crystals vary in length from
three inches down to one-quarter of an inch and
are frequently twinned. Many layers of fine-grained,
black and gray schist are present in the
unit. Biotite is so abundant that both varieties
of the rock have a rather dark-gray color. The
unit as a whole has been so much altered by fold-ing
and metamorphism that while some of it is
gneissoid, much of it is distinctly schistose.
The rocks weather slowly, and outcrops are
abundant, as in the Blue Ridge near Blowing
Rock and south of Boone. Complete weathering
produces a reddish-yellow clay, which is usually
covered with light, well drained, fertile soil.
The Blowing Rock gneiss has been used locally
to a limited extent, but its importance as a build-ing
stone has not been realized. The formation
contains material suitable for ornamental and
building uses that can be obtained in great abund-ance.
Max Patch Granite Gneiss (mpgn)
Max Patch granite gneiss consists entirely of
Max Patch granite as mapped by Keith (1904 and
1905) . It was named for Max Patch Mountain in
Madison County, North Carolina, which may be
considered the type locality. In North Carolina
the unit is limited to Haywood and Madison Coun-ties,
with small extensions in Cocke and Unicoi
Counties, Tennessee. Keith classed the unit as
almost wholly coarse grained, in places porphy-ritic
and in places of uniform grain. It is com-posed
of orthoclase, plagioclase, quartz, biotite,
and a little muscovite. At many places crystals
of orthoclase feldspar more than an inch long are
present. The porphyritic variety is dull white to
light gray in color, while the even-grained variety
is darker in color due to the biotite present. An-other
variety of considerable extent is a coarse
red granite which gets its color from the red feld-spar
present. The red feldspars are often par-tially
altered to epidote, giving the rock an at-tractive
color. In places the feldspar has been
18
so far replaced by epidote that this mineral com-poses
one-third to one-half of the bulk of the rock.
The unit has been so completely metamorphosed
that most of it has a gneissic to schistose struc-ture,
and little, if any, true granite remains un-altered.
The porphyritic variety of the unit has
been altered to augen gneiss, while the even-grained
variety has been altered to gneiss or
schist.
Weathering reduces the surface of the unit
slowly, and as a result it commonly occupies higher
elevations and steep slopes. Complete decay re-sults
in a reddish or brownish clay of no great
depth. Where soils accumulate on gentle slopes,
they are rich and fertile.
Mineral deposits are scarce in the Max Patch
granite gneiss. A few small pegmatites near
Lemon Gap, Madison County, contain small
amounts of radioactive minerals. Some of the red
feldspars, partly altered to epidote, make beautiful
polished specimens, but the rocks of the unit have
not become important as building materials.
Beech Granite Gneiss (bgn)
Beech granite gneiss consists of Beech granite
as mapped by Keith (1903, 1905, and 1907c) and
named for Beech Mountain, Avery County, where
it is best developed. The largest area lies in and
around Beech Mountain in Avery County, and
extends westward into Carter County, Tennessee.
Three other small areas are shown on the map,
one around Blowing Rock in Watauga and Cald-well
Counties, another west of Roan Mountain,
Mitchell County, and extending into Carter Coun-ty,
Tennessee, and a third in the western part of
Yancey County, extending into Unicoi County,
Tennessee.
The unit consists of three varieties of granite
gneiss. One is a coarse-grained, usually porphy-ritic
rock, another is medium to fine grained, while
the third is a coarse, red variety. In the porhy-ritic
variety, crystals of orthoclase feldspar as
much as two inches in length are often present.
The chief minerals present in the unit are ortho-clase
and plagioclase feldspar, quartz, biotite, and
a little muscovite. The porphyritic variety is dull
white to light gray in color, the medium- to fine-grained
variety is darker in color due to the pres-ence
of biotite mica, while the red variety gets its
color from many pink or red feldspar crystals
present.
The unit has been greatly changed by meta-morphism.
The mineral composition is essentially
that of a granite, but the rocks composing the unit
have a decided gneissic structure often becoming
schistose with an increase of mica. The rocks of
this unit are not too readily attacked by weather-ing
and usually underlie higher ground. On
complete weathering they produce a thin, brown-ish
clay containing much sand. On gentle slopes
where soils develop, they are strong and fertile.
Mineral deposits are not known to occur in the
Beech granite gneiss. The unit contains rock
varieties that should make excellent building and
crushed stone, but due mainly to location, they
have not been developed.
GRANITES AND MAFIC IGNEOUS ROCKS
Rocks of definite igneous origin that have under-gone
varying amounts of metamorphism and pos-sess
textures ranging from massive to gneissic are
classed as Paleozoic (?), Paleozoic, and Trias-sic(?)
on the present map. The units classed as
Paleozoic (?) could probably be classed as Paleo-zoic
without the query, as most of them, except
the dunites, have been considered for years as late
Carboniferous in age and were shown on the 1932
Geologic Map of the United States as Carbonifer-ous
( ?) . However, little has been done to prove or
disprove this classification since 1932, and it was
thought best to show them on the present map as
Paleozoic (?).
PALEOZOIC?)
There are five rock units in this group, four of
which consist of granite, syenite, and diorite-gabbro.
The fifth is classed as dunite and con-sists
essentially of peridotite and pyroxenite, part-ly
altered to talc, soapstone, and serpentine. The
positions of these units in the column is arbitrary.
Dunite (du)
Dunite bodies are most abundant in the Blue
Ridge Mountains where more than 250 outcrops
occur in a northeast-southwest trending belt ap-proximately
175 miles long. A few small bodies
occur in the western half of the Piedmont Plateau,
but the most important bodies outside the Blue
Ridge Mountains are found in the northern part
of Wake County. Only a few of the larger bodies
in the Blue Ridge Mountains and those in Wake
County are shown on the map. In the mountains
19
the bodies vary greatly in size. The smallest,
near Otto, contains 1500 square feet, while the
largest, near Swannanoa in Buncombe County, is
four miles long with a maximum width of nearly
one mile. One of the most interesting is a ring
dike near Webster, Jackson County, with a major
axis six miles long and a minor axis about four
miles long. In Wake County the deposits vary in
length from a few hundred feet to nearly two
miles.
The age of the dunites is not definitely estab-lished.
Keith (folios listed above) classed the
dunites as Archean in age. He considered them
intrusive into and closely related to the Roan
gneiss but older than Cranberry and other gran-ites
which he classed as Archean in age. Pratt
and Lewis (1905, p. 159) suggested that they may
have been formed during the Taconic revolution
at the end of the Ordovician period. Parker
(1952), Probst (unpublished) and King (1955)
classed the dunites as Paleozoic in age.
The dunites consist chiefly of peridotite and
pyroxenite, in part altered to talc, soapstone, and
serpentine. Some deposits consist almost entirely
of olivine, and some contain small amounts of
pyroxene minerals, but most of them have been
altered extensively by metamorphism and hydra-tion.
Many of the deposits in their present state
consist of talc, soapstone, serpentine, asbestos,
chlorite, vermiculite, and varying amounts of car-bonate.
Unlike most metamorphosed rocks they
show only minor schistosity. Amphibole minerals,
such as tremolite and actinolite, often form
bunches and radiating clusters in soapstone.
The dunites in general weather slowly and often
stand out as hills and ledges with much barren
rock exposed at the surface. Final decay leaves a
stiff yellow clay of little depth, and soils derived
from this clay are of no value. Many of the de-posits,
particularly in the Blue Ridge Mountains,
are covered sparsely with a stunted vegetation.
The dunites contain a wide variety of minerals
that have been of interest at different times for
many years. Many of the deposits contain varying
amounts of chromite; and, while the production
has been limited, much prospecting has been car-ried
out for this mineral. At a few places,
especially near Webster and Democrat, nickel sili-cate
veins are conspicuous in the dunite, and con-siderable
prospecting was carried out for nickel
at Webster more than fifty years ago. The dunites
contain varying amounts of corundum. Between
1871 and 1905, North Carolina was an important
producer of corundum, most of which came from
dunites. Talc and soapstone, associated with the
dunites, have been of interest for many years, and
small amounts have been produced. The most
important period of activity was during World
War II, when considerable amounts of ground talc
and crayons were produced around Marshall, Mad-ison
County. In recent years, considerable inter-est
has developed in the olivine associated with
the dunites. Hunter (1941) described some
twenty-five deposits in the Blue Ridge Mountains
that contain 230 million tons of high-grade olivine
and more than one billion tons of partly altered
olivine. Varying amounts of vermiculite are as-sociated
with some of the dunites, and vermiculite
production, which began in North Carolina in
1933, has continued intermittently since that time.
Granite (gr)
The rocks included in this unit are abundant
along the western edge of the Coastal Plain and
throughout the Piedmont Plateau. They were
divided into three belts by Watson and Laney
(1906), as follows: (1) Eastern Piedmont and
Western Coastal Plain Belt ; (2) Central Piedmont
Belt (Carolina Igneous Belt) ; and (3) Western
Piedmont Belt.
The rocks of the three belts are essentially gran-ite
according to the commonly accepted meaning
of the term. They consist in general of quartz,
orthoclase, plagioclase, biotite, a little muscovite,
and varying amounts of accessory minerals, such
as chlorite, epidote, titanite, zircon, and mag-netite.
On the basis of accessory minerals, varie-ties
such as biotite granite and biotite-hornblende
granite may be recognized. Councill (1954), on
the basis of microscopic studies of the feldspars
present, pointed out that in addition to granite,
granodiorite is present, and quartz monzonite is
common. He stated: "Many of the so-called
granites of North Carolina approach more closely
the mineral composition of granodiorite and/or
quartz monzonite than normal granite."
Each of the three belts listed above contains
distinctive granites that seem to justify a brief
description.
The western boundary of the Eastern Piedmont
and Western Coastal Plain Belt is formed by sedi-mentary
rocks of Triassic age. In general the
granites of this belt are massive, even-granular
rocks, that show little effects of metamorphism.
Jointing is common but not excessive at any place.
20
The textures present are chiefly medium to coarse
grained. Porphyritic texture, though not abund-ant,
is present at many localities, while fine-grained
texture is seldom found. Two basic
colors, one a light to medium gray and the other
light to medium pink, sometimes approaching red,
predominate. Outcrops, while not abundant, are
common throughout the belt. Along stream val-leys,
outcrops form elongated masses and ledges
;
while in rolling topography, large boulders are
often found. Away from streams in relatively flat
topography, flat to dome-shaped masses often oc-cur.
Where it has not been removed by erosion,
the granites are covered with a residuum varying
from a few inches to as much as 25 to 40 feet
thick. This residuum varies in color from buff,
yellow, and red to reddish-brown, depending on
the weathering of the underlying granite.
The granites of the Central Piedmont Belt
(Carolina Igneous Belt) occupy a region several
miles wide in the central part of the Piedmont
Plateau. In this belt bodies of granite, varying
greatly in shape and size, have intruded older
rocks. On the basis of work by Mundorff (1948)
and LeGrand and Mundorff (1952), the granites
of this belt can be divided into three distinct geo-graphic
areas.
In one area, the granite, which Mundorff (1948)
mapped as Sheared granite, crops out as an irreg-ular
and interrupted zone across northern Ran-dolph
County, southeastern Guilford County, most
of Alamance County, the southeastern corner of
Caswell County, and into central Person County.
The granite is most commonly a coarse-grained
rock of light-pink color, composed chiefly of ortho-clase,
plagioclase, quartz, and biotite. At a few
places, it is light gray and medium grained, with
plagioclase as the chief feldspar. The granite is
badly crushed and broken with the development
of a schistose or gneissic structure.
Basic dikes that vary from green to brown in
color occur nearly everywhere in the granite in
great numbers. Rarely does an outcrop of 200
to 300 feet of granite fail to expose one or more
dikes, and at many places 10 to 12 dikes cut a
granite body of that size. The dikes are more
numerous and closely spaced along the margins of
the granite. In some marginal exposures dike
material is more abundant than granite. The dikes
are fine grained, schistose in structure, and com-posed
chiefly of chlorite, biotite, plagioclase, and
augite. The granites of this area were intruded
into basic volcanic rocks, largely of andesitic ori-gin.
Councill (1954, p. 56) described these gran-ites
as containing inclusions of basic volcanic
rocks, probably of andesitic composition. It is
probable that the dikes described above are in part
dikes and in part inclusions from the basic vol-canic
rocks into which the granite was intruded.
In the second area, the granite, which Mundorff
(1948) mapped as Porphyritic granite, crops out
as irregularly shaped masses and elongated bodies
in the southeastern corner of Rockingham County,
across northwestern Guilford County, and in the
southeastern half of Forsyth County. The granite
in this area is coarse grained to porphyritic in tex-ture
and usually medium gray in color. Porphy-ritic
crystals of orthoclase feldspar up to eight
inches in length have been observed in this granite.
The groundmass consists of feldspar, quartz, and
biotite. At many places dikes and fingers of
granite can be seen cutting the surrounding gneiss
and schists parallel to the regional strike. The
granites have intruded these rocks much more
complexly than could be shown on the map. Ex-cept
for gneissic structure around the margins of
the bodies, which was probably inherited from the
gneisses and schists into which the granite was
intruded, no effects of shearing or metamorphism
are present.
In the third area, the granite, which LeGrand
and Mundorff (1952) and LeGrand (1954) map-ped
as Granite and Granite-diorite complex, be-gins
about the Forsyth-Davidson county line, lies
west of the Gold Hill fault, and continues south-west
to the South Carolina line. Mundorff and
LeGrand mapped the rocks of this area as Granite
;
Granite and diorite, granite predominant; and
Diorite and granite, diorite predominant. On the
present map, the first two of these have been com-bined
in one unit, Granite. The diorite and gran-ite,
diorite predominant unit has been included
in the Diorite-gabbro unit, which is discussed as
a separate unit. In using this subdivision, the
boundaries between the Granite unit and the Dio-rite-
gabbro unit are necessarily somewhat indef-inite.
In this area granite occurs in some places
as distinct bodies and in other places interlayered
with diorite. Large bodies composed essentially
of granite, occur in northern Davidson and eastern
Davie Counties, in Rowan County, and in southern
Iredell and Catawba Counties. Large areas of
granite-diorite complex, in which granite predom-inates
and which are shown as granite, occur in
Davidson, Davie, Rowan, Cabarrus, Mecklenburg,
and eastern Gaston and Lincoln Counties. In the
21
granite-diorite complex, the relations of the gran-ite
and diorite are uncertain. At many places,
relations suggest that granite has intruded dio-rite,
while at others it appears that diorite has
intruded granite. In western Gaston and Lincoln
Counties, granite has been intruded into gneisses
and schists, forming a complex. Where granite
predominates, this complex has been mapped as
Granite. As a result, considerable gneiss and
schist are included in the granites in Gaston and
Lincoln Counties.
The granites of this area vary from fine grained,
through medium grained to porphyritic in texture,
with medium-grained and porphyritic texture pre-dominating.
Porphyritic granites are common
along the western part of the area in Gaston, Ire-dell,
Rowan, and Davie Counties and northwest
of Concord, Cabarrus County. The other granites
of the area vary from medium to fine-grained in
texture, with medium-grained texture predomi-nating.
Outcrops are common and vary from
large boulders to flat-surface areas. Colors vary
from almost white through various shades of gray
and pink to almost red. Minerals present consist
of orthoclase, plagioclase, quartz, biotite, musco-vite,
and various accessory minerals. Where gran-ite
is associated with diorite, hornblende often
occurs in the granite. Jointing is widespread but
not excessive at any place in these rocks. The
larger bodies, composed essentially of granite,
show little metamorphism, but where granite has
been intruded into gneisses and schists and in the
granite diorite complexities, gneissic structure is
often found. The rocks of this area react readily
to the forces of weathering, and as a result the
residuum varies in thickness from a few inches to
many feet. The residuum covering the granites
varies from buff through yellow to reddish-brown
in color, while that covering the granite-diorite
complex is much darker in color.
The granites of the Western Piedmont Belt con-sist
of numerous bodies of varying size and shape
lying between the Central Piedmont Belt and the
Blue Ridge, exclusive of the Mount Airy granite
in northern Surry County. The granite in north-ern
Stokes and eastern Surry Counties are largely
porphyritic. The others are medium to fine grain-ed,
with medium-grained rocks predominating.
Most of these rocks may be classed as biotite
granite, since biotite is common in all the outcrops.
They are composed of orthoclase, plagioclase,
quartz, biotite, a little muscovite, and minor ac-cessory
minerals. They vary from massive gran-ite,
showing no metamorphism, as in Stone Moun-tain,
Wilkes County, to gneissic and schistose rock,
where granites have been intruded into gneisses
and schists. Outcrops are in the form of boulders
and flat-surface exposures. Stone Mountain in
northern Wilkes County, is a barren, granite
monadnock, 500 to 600 feet high and measuring
three to four miles in circumference at the base.
The residuum in the various areas is similar in
composition and color and equally as thick as that
found in other granite regions of the State.
The rocks of the Granite unit as a whole have
intruded a wide variety of older rocks. As a result,
many small bodies and lenses of these older rocks,
chiefly in the form of gneisses, schists, and meta-morphosed
volcanics, are included in the Granite
unit. The rocks of this unit contain quartz veins,
pegmatite dikes, and dikes of granite, quartz por-phry,
aplite, diorite, gabbro, and diabase, which
vary in amounts and sizes from place to place.
Mineral deposits as such are not abundant in the
Granite unit, but the granites of the unit are the
basis of an important quarrying industry. Quar-ries
too numerous to discuss here, but which have
been described by Councill (1954) , are widespread
throughout the unit and furnish a large produc-tion
of dimension and crushed granite.
Syenite (sy)
The only discrete body of syenite in the State
is a ring dike, approximately 22 miles in circum-ference,
located in the west-central part of Cabar-rus
County, LeGrand and Mundorff (1952). The
outcrop of this syenite body varies in width from a
few hundred feet at its southern limits to more
than a mile along its western border, where it is
crossed by Rocky River. The Syenite is more re-sistant
to erosion than the surrounding rocks and
stands out strongly in relief. The area of outcrop
is generally marked by large boulders and pedistal
rocks. The rock is an augite-syenite, composed
largely of bluish-gray feldspar and augite. It is
uniformly of coarse texture and massive in struc-ture
showing no effects of metamorphism. The
absence of a fine-grained matrix permits the sye-nite
to disintegrate into a residual granular ma-terial
that makes excellent road metal.
Mount Airy Granite (mag)
The name, Mount Airy Granite, is introduced by
the writers for a body of granite approximately
eight miles long and four miles wide, which is
22
located around Mount Airy in northeastern Surry
County. Much of the granite in this area is deeply
weathered and covered with a thick layer of resi-dumm.
The most important outcrop is located one
mile north of Mount Airy, where a body of fresh
granite more than five thousand feet long occupies
the crest of a prominent hill. The rock is a very
light gray, nearly white, biotite granite of medium
texture, composed of orthoclase, plagioclase,
quartz, biotite, and minor amounts of apatite, zir-con,
muscovite, chlorite, and epidote. On the basis
of the feldspar content, it is best classed as a
quartz monzonite. The rock contains no injurious
minerals and is free of joints and the effects of
metamorphism. Quarrying was started at Mount
Airy in 1890 and has continued uninterrupted
since that time. Over the years, the quality and
attractiveness of the rock has made Mount Airy
granite a popular building stone. The absence of
joints and lack of metamorphism have made pos-sible
the production of dimension stone of almost
any desired size. The rock is used extensively for
the construction of mausoleums, bridges, statues,
and as architectural stone and curbing. Large
amounts of crushed stone are produced also.
Diorite-Gabbro (digb)
Rock of the Diorite-gabbro unit are confined
largely to the Central Piedmont Plateau, where
they are associated with granites of the Central
Piedmont Belt (the Carolina Igneous Belt), dis-cussed
above. They are most abundant west of
the Gold Hill fault and south of Forsyth and Yad-kin
Counties, but a few small bodies are found in
southeastern Guilford County, southern Caswell
and Person Counties, and in the northeastern cor-ners
of Person and Granville Counties. The rocks
of this unit range locally from diorite to gabbro
but, as a whole, are intermediate between true dio-rite
and gabbro. Some rocks consisting of diorite
and granite, diorite predominating, are included
in the unit. Areas of relatively true diorite and
gabbro have been designated on the map, but most
of the rock is shown as Diorite-gabbro. Bodies of
almost normal diorite occur in southeastern Guil-ford,
southern Caswell, and Person Counties.
Bodies of nearly normal gabbro are found in
northeastern Granville and Person Counties, in-side
the syenite ring dike in Cabarrus County, and
from a short distance north of Barber south to
Bear Poplar in Rowan County. The Diorite-gab-bro
is a coarse-textured rock that is distinctly
massive and not closely jointed. It is composed
chiefly of hornblende or pyroxene, plagioclase, and
varying amounts of quartz and accessory min-erals.
In some places it is exposed as rounded
boulders or flat outcrops that are not much weath-ered,
but in most places it is deeply weathered,
and covered with a thick layer of soil that is
deep red or brown and relatively fertile. At sev-eral
places, both on interstream areas and along
valleys, shallow depressions resembling sinks in
limestone are present. These appear to be the
result of weathering and solution of the Diorite-gabbro.
PALEOZOIC
The four units in this group have been studied
and described by Olson (1944) , Griffitts and Over-street
(1952), Parker (1952), and Overstreet
and Griffitts (1955) and classed as Paleozoic.
These workers did not agree completely as to the
position the units occupy in the Paleozoic, but they
were in agreement in classing them as Paleozoic
in age. Two of these, Toluca quartz monzonite
and Cherryville quartz monzonite, consist in part
of Whiteside granite as mapped by Keith and
Sterrett (1931).
ToSuca Quartz Monzonite (tqm)
Toluca quartz monzonite consists of numerous
bodies of varying shape and size, occupying a belt
extending across central and western Cleveland
County, western Lincoln County, and into southern
Burke County. It was named by Griffitts and
Overstreet (1952) for the town of Toluca in the
western edge of Lincoln County. Individual bod-ies
vary from a few inches to several thousand
feet thick and from a few feet to ten miles long.
In general, these are parallel to the foliation of
the mica gneiss into which they were intruded but
occasionally cross it. Outcrops are not abundant
as the rock is deeply weathered and underlies
broad areas of light-gray soil. Toluca quartz
monzonite is typically a medium gray, moderately
gneissic rock. Usually, the smaller bodies are
more strongly foliated than the larger, which,
while gneissic throughout, are more strongly fol-iated
near the margins. Chief minerals are oligo-clase,
microcline, orthoclase, quartz, and biotite.
Minor amounts of garnet and muscovite and small
amounts of apatite, zircon, ilmenite, and monazite
are present. The rock is characterized by a wide
variation in texture and composition. The texture
23
is everywhere gneissic, but the size, shape, and
arrangement of the grains vary widely.
Monazite-bearing pegmatites genetically associ-ated
with the quartz monzonite inject it and occur
parallel to the foliation of the surrounding gneiss.
These dikes vary from a few inches to several feet
in thickness and often attain lengths of several
iiundred feet. Overstreet and Griffitts (1955, p.
556) classed the Toluca quartz monzonite as early
Ordovician in age.
Cherryville Quartz Monzonite (cqm)
Cherryville quartz monzonite occupies a broad
belt across eastern Cleveland, western Gaston, and
central Lincoln Counties. The unit was named by
Griffitts and Overstreet (1952) for Cherryville,
Gaston County. Outcrops are not abundant as the
rock underlies thick layers of light-gray soil.
South of Cherryville, the belt is parallel to the
structure of the older rocks, but north of Cherry-ville,
it bends eastward and crosses the structures
of the older rocks. The Cherryville quartz mon-zonite
contains many inclusions of country rock.
It is essentially a gray, even-grained, massive to
slightly gneissic rock, consisting chiefly of two
varieties, one containing muscovite and biotite
and the other containing muscovite but no biotite.
It is, in general, a medium-grained rock, composed
of oligoclase, microcline, quartz, muscovite, and
biotite, with minor amounts of zircon, ilmenite,
and apatite. Overstreet and Griffitts (1955, p.
556) classed the Cherryville quartz monzonite as
probably Devonian in age.
Two major varieties of pegmatite dikes, spod-umene-
bearing and mica-bearing, are related to
the Cherryville quartz monzonite. Spodumene-bearing
pegmatites are restricted to the tin-spod-umene
belt that lies along the east side of the
Cherryville quartz monzonite bodies. These dikes
are most commonly in gneiss, but some extend into
the quartz monzonite bodies. These dikes vary
from zoned and nongneissic, north of Kings Moun-tain,
to gneissic and nonzoned, south of Kings
Mountain. Mica-bearing pegmatites that are well
zoned occur in the northern part of the Lincolnton
and Shelby quadrangles. These form dikes that
cross the foliation of the enclosing gneiss and also
the Toluca quarts monzonite.
Whiteside Granite (wg)
The Whiteside granite unit on the present map
is essentially Whiteside granite as originally nam-
24
ed and described by Keith (1907b) . It was named
for the cliffs of Whiteside Mountain, Jackson
County, where it is well developed. On the pres-ent
map, it is shown as several areas of varying
sizes and shapes, along the southern boundary of
the State in Henderson, Transylvania, and Macon
Counties. The granite is a light-gray, even-grain-ed,
massive rock, composed of orthoclase, plagio-clase,
quartz, muscovite, biotite, and minor
amounts of magnetite, ilmenite, and garnet. Bio-tite
varies in amount and is often absent. The
granite was injected into older rocks, parallel to
their foliation, and often contains inclusions of
gneiss and schist. Two varieties were described
by Keith. One is fine to medium grained and
massive, the other contains a decided flow banding.
Outcrops vary with topography, and much of the
granite is covered with thick layers of light red
to yellowish soil mixed with sand.
ABaskite (a!)
The Alaskite unit consists essentially of a
coarse-grained pegmatitic granite that crops out
near Spruce Pine, Mitchell County, as a number
of bodies varying greatly in size and shape. The
rock, which has been of interest to miners in the
Spruce Pine district for several years, was desig-nated
by Hunter (1940) as alaskite. It consists
essentially of oligoclase, quartz, microcline, and
muscovite, listed in the order of abundance. Dark-colored
minerals are almost absent, but small
amounts of biotite and garnet occur at places near
inclusions or contacts with country rock and are
apparently products of contamination. The rock
is not true alaskite, but the name is so well estab-lished
in the Spruce Pine district that it is used
here. The alaskite masses are granitoid in tex-ture
and uniform in grain size and mineral con-tent.
Much of the rock is sufficiently coarse-grained
to be called pegmatite, but its uniformity
and wide extent make the name Alaskite appro-priate.
The alaskite bodies contain many inclu-sions
of gneiss and schist near their margins, but
internally they are relatively free of such. Alas-kite
bodies containing inclusions of gneiss and
schist often grade into gneiss and schist, contain-ing
numerous bands and lenses of alaskite. Most
inclusions, as well as alaskite bands and lenses,
are parallel to one another and to the foliation of
the country rock.
Pegmatites occur in all parts of the alaskite, but
the average size and number is greater near the
margins of the alaskite bodies. The pegmatites
in alaskite and in the surrounding gneisses and
schists are important sources of mica, feldspar,
kaolin, and other minerals, for the production of
which the Spruce Pine district is widely recogniz-ed.
Sheet mica is obtained almost exclusively
from pegmatites. For many years, feldspar and
kaolin were produced from fresh and weathered
pegmatites. As the demands for these minerals
increased, attention was directed to alaskite, and
it is now the chief source of feldspar, kaolin, and
flake, or scrap, mica. Large bodies of unaltered
alaskite serve as a source of feldspar by flotation.
In many places, the alaskite is deeply weathered,
often to depths approximating a hundred feet.
Many of these weathered deposits are rich in
kaolin and contains considerable flake mica. Most
of the kaolin and a large part of the flake mica
produced in the State are being obtained from
weathered alaskite. Economically, Alaskite is
one of the most important rock units shown on
the present map.
TRSASSICC?)
Two units, Bakersville gabbro and Diabase
dikes, are shown as Triassic(?) on the present
map. Diabase dikes have been considered of pos-sible
Triassic age for many years and probably
should be classed as Triassic without the query;
however, there is some question as to the exact
age of the Bakersville gabbro. Keith (1903) first
named this unit and described it in the text as
Juratrias(?) but showed it in the legend on the
geologic map as Juratrias without the query. The
unit has received considerable attention in recent
years, but its exact age is still in doubt. Kulp and
Brobst (unpublished) showed Bakersville gabbro
on an unpublished geologic map of the Spruce
Pine district as Devonian. Brobst (1955, pp. 584-
585) described the unit briefly and pointed out
that it is considered younger than the alaskite and
pegmatites. As to age, he stated, "The Bakersville
might have been emplaced between the late Ordo-vician
.or early Silurian and the Triassic." The
Committee on Geologic Names of the U. S. Geo-logical
Survey recommends Triassic (?) for the
Bakersville gabbro, and it is so shown on the
present map.
Bakersville Gabbro ("Rg)
Bakersville gabbro outcrops are shown on the
map near Bakersville, Mitchell County, and south
and west of Elk Park and Cranberry, Avery
County. The major outcrop near Bakersville is
roughly triangular in shape, with a maximum
length of five miles and a maximum width near the
base of the triangle of about three miles. The
outcrop near Elk Park and Cranberry is about two
miles long and one mile wide. A number of out-crops
too small to be shown on the map are found
in the general area. Keith (1903) named the unit
for Bakersville, Mitchell County, and described it
briefly. It is a dense, hard, unmetamorphosed
rock, nearly black when fresh but becoming red-dish
brown on weathering. It is composed chiefly
of plagioclase, hornblende, and pyroxene in crys-tals
of medium size, with small amounts of mag-netite,
epidote, and garnet as accessory minerals.
The texture is usually massive and granular but
occasionally becomes aplitic. Outcrops consist of
spheroidal masses and boulders mixed in a dark-brown
clay.
Diabase Dikes (lid)
Diabase dikes of probable Triassic are widely
distributed throughout the Piedmont and Moun-tain
regions of North Carolina. They are most
abundant in and adjacent to sedimentary rocks of
Triassic age along the eastern and central Pied-mont
region, but become less common in the west-ern
Piedmont and are found sparingly in the Blue
Ridge region. They also occur frequently along
the western edge of the Coastal Plain where pre-
Triassic rocks are not covered by younger sedi-ments.
Because of the wide distribution and
limited area of outcrop, Diabase dikes are shown
in only two localities on the map. One of these
is the Deep River basin in Chatham, Lee, and
Moore Counties, and the other is an unusually long
dike northeast of Morganton, Burke County. In
the Deep River basin, according to Reinemund
(1955), who gave an excellent description of the
diabase intrusives in that basin, dikes, sills, and
sill-like masses occupy about four percent of the
Triassic rocks. Diabase dikes in the Deep River
basin vary in width from less than an inch to 320
feet and in length from a few feet to nearly seven
miles. Most dikes in the area are between 20 and
75 feet wide and are fairly constant in width for
several thousand feet of length. Sills and sill-like
intrusives of diabase are abundant in the Deep
River basin Triassic sediments and range in thick-ness
up to 400 feet. In the Morganton area, an
unusual diabase dike extends in a northwest-south-east
direction with minor interruptions for nearly
twenty miles.
25
The diabase intrusives are massive, crystal-line,
unmetamorphosed rock that varies in color
from dark gray, grayish black to nearly
black. The minerals and textures present are
those commonly found in normal diabase, except
some of the larger sills which more nearly ap-proach
gabbro in composition. In general, the
dikes form low ridges and divides, but in the Deep
River basin, they are an important influence on
drainage patterns. The direction of flow of sev-eral
streams in the area is determined in part by
the trends of the dikes. Many springs occur
along these dikes, and it has been learned from
experience that water-well sites located near dikes
are more likely to furnish good yields. Outcrops
are common in the form of boulders, which were
produced by spheroidal weathering along the
joints in the rock. Two types of soil, one a brown
or grayish-brown, silty loam and the other a dark
red to brownish-red heavy clay loam, occur over
areas of diabase. Both soil types are underlain
with yellow to dark red, sticky clays.
METAVOLCANIC ROCKS
Metavolcanic rocks occur in three distinct geo-graphic
areas in North Carolina. First and most
important is the Carolina Slate Belt which actually
consists of two belts, one lying across the central
part of the State, and the other lying along the
eastern edge of the Piedmont Plateau and western
edge of the Coastal Plain. Second is the Grand-father
Mountain Window, which lies partly in the
Blue Ridge area and partly in the Piedmont Pla-teau
in Avery, Watauga, Caldwell, Burke, and Mc-
Dowell Counties. Third is a relatively small area
known as the Mount Rogers volcanic group which
lies in the northwestern corner of Ashe County.
PRECAMBRIAN OR LOWER PALEOZOICt?)
CAROLINA SLATE BELT
Rocks of the Carolina Slate Belt, because of
their complex character and well defined cleavage,
have been called slates. Actually, they consist of
volcanic-sedimentary formations, composed of
slates, breccias, tuffs, and flows. The flows are
interbedded with the breccias and tuffs, while the
tuffs pass gradationally into slates. These rocks
vary from acid or rhyolitic to basic or andesitic in
composition and generally have a well developed
cleavage, which gives them a slaty appearance.
Rocks of the Carolina Slate Belt series actually
form two belts in the State. The first and most
important of these, and the one which Olmstead
(1825) first called the Great Slate Formation,
crosses the central part of the State in a northeast
direction from Anson and Union Counties on the
south to Granville and Person Counties on the
north. This belt varies in width from 25 to 60
miles and consists of metavolcanic rocks intruded
at many places by younger granites, described
above. The second belt, in which metavolcanic
rocks are exposed as irregular bodies of varying
size and shape, lies along the eastern edge of the
Piedmont Plateau and western edge of the Coastal
Plain. This belt, in which Kerr (1875, p. 131)
first recognized rocks similar to those of the Great
Slate Formation of Olmstead, begins in Richmond
County on the south, varies greatly in width, and
continues in a northeast direction to Northampton
County on the north.
Olmstead (1825), Emmons (1856), and Kerr
(1875) considered the rocks of the slate belt as
sedimentary in origin but described them as slates,
containing beds of porphyry, hone or whetstone
slate, breccia, and conglomerate. Emmons (1856)
placed the rocks in the Taconic System, while Kerr
(1875) classed them as Huronian in age, which,
according to his geologic column, is a division of
the Archean. Williams (1894) recognized for the
first time the presence of volcanic rocks in the
slates. He described exposures of volcanic flows,
breccias, and tuffs, which had been sheared into
slates by dynamic metamorphism. Nitze and
Hanna (1896) recognized volcanic rocks in the
slate belt and considered the Bedded argillites
(volcanic slate) of the present map as younger
than the volcanics and called them Monroe slates.
It is now recognized that the Monroe slates repre-sent
a better bedded, less metamorphosed portion
of the slate-belt rocks.
Following the work of Williams (1894) , reports
by Laney (1910 and 1917), Pogue (1910), and
Stuckey (1928) emphasized the importance of
volcanic rocks in the slate belt but did not over-look
entirely the presence of sedimentary material.
These authors considered the rocks of the slate
belt to be largely of volcanic derivation but recog-nized
the presence of considerable sedimentary
(nonvolcanic) material and classed the whole se-ries
as laid down by sedimentary processes.
Mapping carried out for the compilation of the
present map tended to verify the above findings.
Rocks which may be classed as flows, breccias,
26
tuffs, and shales or slates were found to be present.
All of these, except flows, contain considerable
amounts of nonvolcanic materials. The flows,
breccias, tuffs, and slates are all interbedded and
do not occupy any definite stratigraphic positions
in the series. The flows vary from rhyolite,
through andesite, to basalt. The rhyolites and
andesites vary from fine grained to coarsely por-phyritic,
while the basalts are often amygdaloidal.
The breccias vary from rhyolitic to andesitic in
composition and in size from an inch to nearly a
foot in diameter. The fragments of the breccias
are, in turn, fragmental, apparently of a pyro-clastic
origin. Some of the fragments in the
breccias are sharply angular, while many are
rounded, indicating transportation and deposition.
The tuffs are generally of acid composition and
composed of fragments less than an inch in diam-eter.
These fragments, which vary from angular
to rounded, are embedded in much fine-grained
material apparently of nonvolcanic origin. Be-ginning
at Siler City, Chatham County, and con-tinuing
southwest for 15 to 20 miles are several
beds of quartz conglomerate, varying in width
from a few inches to 250 feet and of unknown
length. The quartz pebbles are less than an inch
in diameter and well rounded, further indicating
sedimentary processes. The shales or slates, which
are generally well bedded, are composed of fine-grained
volcanic material and much land waste.
Finally, much of the finer material in the breccias,
tuffs, and portions of the shales or slates strongly
resembles metasiltstone and metagraywacke of
some of the metagraywacke rocks in other areas,
further indicating sedimentary origin.
In view of the above facts, there is a strong
trend on the part of some workers to drop the
term metavolcanic and use one that defines the
rock more nearly as sediments. That idea was
considered for the present map but was discarded
in favor of metavolcanics, since the rocks of the
slate belt are largely of volcanic origin, and the
terminology has been in the literature for more
than sixty years.
No fossils have been discovered in the slate belt,
and the age of the rocks is not known. For many
years they were classed as Precambrian, while
in recent years there has been a trend towards
classing them as lower Paleozoic. On the present
map, they are classed as Precambrian or Lower
Paleozoic (?). They have been divided into three
units, Felsic volcanics, Mafic volcanics, and Bed-ded
argillites (volcanic slate).
Felsic Volcanics (fvs)
Rocks of the Felsic volcanics unit occupy about
half of the Carolina Slate Belt in the central part
of the State and are the only rocks shown in that
portion of the belt lying along the eastern part
of the Piedmont Plateau and western part of the
Coastal Plain. In the central part of the State,
rocks of the Felsic volcanics unit occupy much of
the eastern part of the Carolina Slate Belt north-east
of Anson, Richmond, and Stanly Counties.
The rocks of the Felsic volcanics unit are com-posed
largely of materials of volcanic flow or frag-mental
origin. The flows are essentially rhyolite,
while the fragmental materials vary from rhyo-litic
to dacitic in composition. The fragmental
rocks consist of breccia and coarse and fine tuff,
with coarse and fine tuff making up the greater
portion of the unit. Lenses of bedded slate and
mafic volcanics, too small to show on the map, are
present in this unit.
The rhyolite occurs as narrow bands and lenses
interbedded with the breccia and tuff. It is dense
and indistinctly porphyritic with a dark gray to
bluish color, and, on fresh surfaces, shows a greasy
luster. Flow lines are often present and are best
seen on weathered surfaces, while amygdaloidal
structure is also present. In porphyritic speci-mens
the minerals are plagioclase, orthoclase, and
quartz. None of the rhyolite outcrops show any
effects of metamorphism.
The fragmental rocks consist of breccia and
coarse and fine tuff. The coarse tuff predominates
and contains the breccia and fine tuff as interbed-ded
bands and lenses. The fragments composing
these rocks are angular to well rounded and vary
in size from nearly a foot to a fraction of an inch
in diameter. The larger fragments are internally
fragmental, while the finer material grades into
Bedded argillites (volcanic slate) . At places,
within a few inches, fine fragmental rock grades
into a rock showing bedding planes. When freshly
broken, the rock proves to be made up of quartz
and feldspar grains and rock fragments, some of
which show a flow structure, set in a dense bluish
or greenish groundmass. In general, the rocks of
this unit have a light gray to greenish color.
In the central part of the State, the rocks of
the Felsic volcanics unit vary from massive to
schistose. At places, the fragmental texture of
the rock may be seen, but much of the rock has
been strongly metamorphosed and possesses a
well denned slaty cleavage that strikes northeast-
27
southwest and dips to the northwest in the south-ern
part of the area and to the southeast in the
northern part. The felsic volcanics weather to a
light gray soil usually underlain by yellow to light-red
clay. The layer of soil and clay is usually
thick, and outcrops of fresh rock are not abund-ant.
Along the eastern part of the Piedmont Plateau
and western edge of the Coastal Plain, all the
raetavolcanics of the Carolina Slate Belt are shown
as the Felsic volcanics unit on the present map.
The rocks are deeply weathered and covered by a
thick layer of soil. As a result, outcrops of fresh
rock are scarce, and mapping is difficult. Mun-dorff
(1946) showed these rocks on the legend of
his map as Slates, schists, and metamorphosed
volcanics. He considered the series as metamor-phosed
sedimentary and igneous rocks, including
lavas, tuffs, and breccias. He did not mention
rhyolite or rocks of a mafic character but did refer
to a coarse breccia near Roanoke Rapids. In the
course of fieldwork for the present map no rhyo-lite
was seen, but small amounts of breccia and in
one or two places small outcrops of mafic volcanics
too small to show on the present map, were ob-served.
In general, the rocks of this area consist of
coarse to fine tuff and bedded slate, with which
bodies of gneiss and schist are present in many
places. The tuffs and bedded slates are present
throughout the area in about equal amounts. In
some places, bedded slate predominates, and in
others tuffs predominate. These rocks are usually
altered near igneous intrusions to garnetiferous
mica schist, mica hornblende schist, or biotite
schist. Some bodies of gneiss and schist not ap-parently
related to igneous intrusives are present
and probably represent metamorphosed nonvol-canic
sediments. Six miles west of Smithfield,
Johnston County, on the east side of U. S. High-way
70, is a large outcrop that resembles quartzite
and contains kyanite crystals. It may be siliceous
sediment metamorphosed to quartzite, or it may
be a silicified tuff. Similar outcrops, except for
the kyanite, are found north of Princeton in the
eastern part of Johnston County. The bedded
slates are dark blue to greenish gray when fresh
and become various shades of yellow and red when
weathered, while the tuffs, gneisses, and schists
are generally gray, yellow, or brown. All these
rocks have been moderately metamorphosed and
contain a cleavage that strikes northeast and
stands nearly vertical.
Mafic Volcanics (mvs)
Rocks of the Mafic volcanics unit are shown on
the present map only in the northern two-thirds
of Carolina Slate Belt in the central part of the
State. They are scattered throughout the area
but are more abundant along the western side.
The rocks of this unit consist largely of flows and
fragmental materials of volcanic origin. The
flows vary from andesite to basalt, while the frag-mentals
are generally andesitic in composition.
Lenses of bedded slate and felsic volcanics, too
small to show on the map, are present in this unit.
The andesite and basalt occur as narrow bands
and lenses interbedded with the fragmentals. The
andesite is dark green in color, usually massive or
fine grained, but occasionally coarsely porphyritic.
A coarse porphyritic variety, with hornblende
crystals up to two inches long, occurs in western
Randolph County. The basalt is dark to nearly
black and often amygdaloidal. Both the andesite
and basalt are characterized by the lack of a well
defined cleavage. Minerals present consist of
epidote, plagioclase, quartz, secondary calcite, and
iron oxides. Epidote is the most abundant min-eral
present, giving the rock its green color.
The fragmentals consist of breccias and tuffs of
andesitic composition, often intermixed with much
fine-grained material. In places these rocks are
fine grained and lack the fragmental appearance.
In such areas, one of which may be seen along
U. S. Highway 64 for a mile west of Haw River,
the rock strongly resembles a graywacke. The
breccias and tuffs contain much epidote and often
have a greenish color. Other colors vary from
dark gray to nearly black. In addition to epidote,
plagioclase, and quartz, secondary calcite and iron
oxides are present. The mafic fragmentals are not
as strongly metamorphosed as the felsic frag-mentals
but contain a cleavage that strikes north-east
and dips to the northwest in the southern part
of the area and to the southeast in the northern
part. These rocks are usually covered with a thick
layer of dark-red residuum.
Bedded Argillifes (Volcanic Slate) (ar)
Bedded argillites (volcanic slate), commonly re-ferred
to as slate, bedded slate, or volcanic slate,
occur in the southern part of the Carolina Slate
Belt in the central part of the State and extend
north as far as the central part of Davidson and
Randolph Counties. A few small areas are shown
on the east side of the belt in Montgomery, Moore,
28
and Chatham Counties. There are also some small
areas east of the Jonesboro fault in Anson and
Richmond Counties.
The unit as shown on the map is chiefly bedded
argillites or bedded slate, but many lenses of felsic
and mafic volcanics, too small to show on the map,
are included. The Bedded argillites (volcanic
slate) consist chiefly of dark-colored or bluish
shales or slates, which are usually massive and
thick bedded. However, the beds occasionally
show very .finely marked bedding planes. Contacts
between the slates and the tuffs are usually grada-tional,
and often a single hand specimen will show
gradation from a bedded slate to a fine-grained
tuff. Much of the slate is massive and jointed,
showing little effects of metamorphism, while in
other places it has been strongly metamorphosed
and shows a well defined, slaty cleavage. The
cleavage, or schistosity, does not in most places
correspond to the bedding planes of the rock. In
places, especially near igneous intrusive and min-eralized
zones, the slate is highly silicified and
often resembles a chert. The slates are deeply
weathered, and good outcrops of fresh rock are
seldom seen. In general, they are covered with a
thick layer of residuum, which consists of light
soil on top and yellowish, decomposed slate be-neath.
The rocks of the Carolina Slate Belt have fur-nished
mineral resources of considerable impor-tance
for many years. Between 1800 and 1860,
the slate belt produced important amounts of
gold. Gold mining is no longer important, but
many quartz veins in the area contain varying
amounts of silver, lead, zinc, and copper. The
production of these metals has never been large,
but the veins continue to attract the attention
of individuals and mining companies. Important
deposits of pyrophyllite occur in Moore, Randolph,
Alamance, Orange, and Granville Counties, from
which large amounts of pyrophyllite are being
mined. The Bedded argillites (volcanic slate)
are deeply weathered in many places to clay and
shale, suitable for the manufacture of clay prod-ucts.
Brick and tile are being produced in large
amounts from these materials. Lightweight ag-gregate
is being produced in Stanly County from
semiweathered slate. Rocks of the Carolina Slate
Belt were first used for building purposes at Hills-boro
in colonial days. More recently, both felsic
and mafic volcanics were quarried near Hillsboro
and used in the construction of the buildings on
the West Campus of Duke University. Bedded
slate is being quarried in southern Davidson
County and southern Montgomery County and
used as building stone and flagstone. When fresh
and unweathered, the bedded slate makes an ex-cellent
crushed stone, and large amounts are be-ing
produced.
Upper Precambrian
grandfather mountain window
The Grandfather Mountain window area is
nearly surrounded by the Grandfather Mountain
fault and lies partly in the Blue Ridge and partly
in the Piedmont Plateau in Avery, Watauga, Cald-well,
Burke, and McDowell Counties. Keith
(1903) mapped and described four units in that
area, as follows : Linville metadiabase, Montezuma
schist, Flattop schist, and Metarhyolite. His
names and descriptions have been retained on the
present map.
Linville Metadiabase (Imd)
Linville metadiabase occurs as irregular out-crops
associated with Montezuma schist, Flattop
schist, Cambrian quartzite, and as narrow bands
in Cranberry granite gneiss. It occurs as flows,
which came up through cracks in older rocks, such
as those now filled with metadiabase in the Cran-berry
granite. The metadiabase contains plagio-clase,
largely altered to epidote, chlorite, and
quartz. Other original minerals, olivine and augite,
are largely replaced by hornblende, epidote, and
chlorite. Epidote sometimes occurs as grains and
masses as much as six inches in diameter. The
rock has been much metamorphosed, but at places
its original character is retained. It is generally
of a dull-yellowish color, due to epidote, chlorite,
and hornblende. The metadiabase weathers read-ily
and usually is covered by a thick layer of dark-red
and brown clay.
Montezuma Schist (mtsh)
The Montezuma schist consists of fine-grained
epidotic and chloritic schists and amygdaloidal
beds and is rather uniform in appearance. Orig-inally
it was probably a basalt, but it has been
so completely metamorphosed that only a few
traces of flow banding remain. Amygdaloidal
beds are the commonest evidence of its original
nature. The color of the rock when fresh is bluish
black, gray, or green, becoming more green and
yellowish green on weathering. The chief min-
29
erals are chlorite and feldspar in abundance and
muscovite, epidote, and quartz in small amounts.
The schists weather slowly and usually form high
ledges and cliffs, while the amygdaloidal beds
weather more readily and are covered with thick
clay of yellow or red color.
Flattop Schist (fsh)
This unit, named for Flattop Mountain, Watau-ga
County, consists of black, dark-blue, bluish-green,
and greenish-gray schists, which weather
to a yellow or greenish-gray color. The schist is
commonly banded. The bands, which are seldom
more than half an inch thick, consist of quartz
and feldspar grains of varying size, and the rock
strongly resembles a sandy slate of sedimentary
origin. Where not banded, the schist contains
pyrophyritic crystals of feldspar and amygdules,
indicating that it is volcanic in origin. Originally,
the rock was probably a lava flow, but it has been
strongly metamorphosed, and most of the original
minerals have been replaced by secondary quartz,
feldspar, and mica. The Flattop schist resists
decay and forms ridges and mountains. Final
decay produces a reddish, sandy clay.
Metarhyolite (mry)
This unit consists mainly of fine metarhyolite
but occasionally contains layers which show por-phyritic
crystals of feldspar and quartz. When
fresh, the rock is dark blue, dark gray, and bluish
black; but, when weathered, it becomes dull yel-low
and yellowish gray. It occurs as intrusive
sheets and dikes in older rocks and as surface
flows. The unit has been greatly metamorphosed,
but flow banding and amygdules are occasionally
poorly preserved. The rocks of this unit vary
from rhyolite, little altered, to a well defined
schist, depending on the original nature of the
rocks and the amount of metamorphism. These
rocks weather slowly, but final decay produces a
thin layer of fine yellow and red clay.
MOUNT ROGERS VOLCANIC GROUP (mr)
The Mount Rogers volcanic group, named by
Stose and Stose (1944, pp. 410-411) for Mount
Rogers, the highest point in Virginia, underlies
a small area in the northwest corner of Ashe
County, North Carolina, adjacent to Tennessee
and Virginia. Jonas and Stose (1939, pp. 590-
591) and Rogers (1953, p. 23) have summarized
very well the characteristics of the group. The
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unit consists of purplish and greenish metavol-canic
rocks, chiefy metarhyolite, but apparently
contains tuffs as well as flows. The rock has been
strongly metamorphosed and possesses a slaty
cleavage. Some of it is good slate; but, despite
the foliation, much of the rock forms massive
ledges and blocks. The foliation of the more mas-sive
rock is interrupted by small, irregular masses
of quartz, while the slaty rock commonly contains
small, very thin lenses of chlorite and epidote.
Interbedded with the volcanic rocks are layers of
conglomerate, graywacke, and nonvolcanic silty
shale or slate. The rocks of the group often crop
out in large masses, and at places in Tennessee and
Virginia, they form high, rough mountains. They
weather to a thin, very strong, light soil.
METASEDIMENTARY ROCKS
Rocks more or less metamorphosed but retaining
enough of their original characteristics to indicate
that they were originally sediments are classed
as metasedimentary rocks on the present map.
They occur in four areas, commonly known as the
Kings Mountain area, the Stokes County area, the
Brevard area, and the Murphy area. The rocks
in the Stokes County area and the Kings Mountain
area appear to be much alike and stratigraphically
equivalent. On the present map, these two areas
are classed as the Stokes County and Kings Moun-tain
Belt, while the other two are classed as the
Brevard Belt and the Murphy Belt. The ages of
the rocks in these three belts are not definitely
known, but it is assumed that their position in
the explanation is essentially correct.
Upper precambrian(?) or lower paleozoic?)
stokes county and kings mountain belt
Kings Mountain Group (kmg)
The rocks of this unit fall into two natural
groups, one of which consists of highly siliceous
rock, while the other consists largely of calcareous
rock. The siliceous group consists in the Kings
Mountain part of the belt, of slate, rhyolite, vol-canics,
quartzite, and conglomerate, and, in the
Stokes County part of the belt, of mica schist,
quartz mica schist, and quartzite. In the Kings
Mountain area, the slates and phyllites are essen-tially
sericitic schist. Pyroclastic textures are not
abundant but are common enough to indicate that
volcanics make up an important part of the group.
Quartzite and conglomerate are present in beds
that crop out prominently at many places. In the
Stokes County area, the chief rocks are quartzite,
mica schist, and quartz mica schist, apparently
interbedded. At a few places in the Stokes County
area is found a flexible sandstone, consisting of
fine, interlocking quartz grains and mica flakes.
Throughout the Stokes County and Kings Moun-tain
Belt, the siliceous rocks form the higher ele-vations
and prominent ridges, often called moun-tains.
The calcareous group is confined largely to the
Kings Mountain part of the belt and consists of
crystalline limestone, dolomite, and calcareous
metashales. In the southern part of Catawba
County and the northern part of Lincoln County,
interesting amounts of hornblende gneiss are
found, apparently interbedded with quartzite, that
probably represent metamorphosed calcareous
shales. One important body of crystalline lime-stone
occurs near Siloam, Yadkin County, in the
Stokes County part of the belt. Other limestone
bodies, mentioned above, occur in mica gneiss
along the southern border of the belt in Yadkin
and Stokes Counties, that may or may not belong
in this group.
The limestone and dolomite of the belt have been
quarried intermittently for years, and a large
quarry is in operation near Kings Mountain. The
quartzite in the Kings Mountain part of the belt
contains interesting amounts of kyanite, but it has
not been mined in North Carolina.
LOWER CAMBRIAN(?)
BREVARD BELT
Brevard Schist (bv)
The Brevard Belt begins in North Carolina at
the state line, southwest of Brevard, for which it
was named by Keith (1907b), crosses Transyl-vania,
Henderson, and Buncombe Counties, and
ends in McDowell County, a short distance north-west
of Old Fort. The Brevard schist, the only
unit in this belt, consists mainly of schist and
slate. Schist, which predominates, is of a dark-bluish-
black, bluish-black, black, or dark-gray
color. Lenses of limestone, varying from a few
hundred feet to more than a mile in length and
up to 250 feet in thickness, are scattered widely
throughout the belt. Thin layers of quartzite and
conglomerate are occasionally found. Graphite is
widely disseminated as small flakes through large
masses of the rock and occasionally forms lenses
that are graphite schist. The schists are composed
of quartz and muscovite, through which are scat-tered
numerous small grains of iron oxides, while
garnets are occasionally found. The slates are
essentially clay slates. The rocks are all essen-tially
fine grained except for occasional layers of
quartzite and conglomerate.
Some years ago graphite was produced from the
northern part of the belt, west of Old Fort but
none has been mined in recent years. Considerable
amounts of crystalline limestone have been pro-duced
for lime, agricultural lime, and aggregate
near Fletcher, Henderson County. At the present
time, crushed stone for aggregate is the chief ma-terial
being produced. Near Etowah, Henderson
County, a clay slate weathered to a shale is being
used for the manufacture of brick.
MURPHY BELT
Rocks of the Murphy belt occur in the southwest
corner of the State, where Keith (1907a) mapped
a synclinal structure and named the following
formations: Tusquitee quartzite, Brasstown
schist, Valleytown formation, Murphy marble, An-drews
schist, and Nottely quartzite. The Tusqui-tee
quartzite and Nottely quartzite could not be
shown on the present map due to the limited area
each covers. They are much alike and consist
essentially of v/hite quartzite. On the present map
the Brasstown schist and Valleytown formation
are shown as separate units, while the Murphy
marble and Andrews schist are combined as one
unit due to the limited area each covers.
Brasstown Schist (bt)
The Brasstown schist consists of schists and
slates more or less banded. The greater part of
the formation consists of banded ottrelite schist,
but some of it is banded slate with little or no
ottrelite. All the rocks are dark colored and vary
from dark blue or bluish black to dark gray. They
are usually marked by a fine banding of light and
dark-gray colors. The light layers are often sili-ceous
and sometimes grade through sandy slate
into sandstone. The slates are argillaceous, while
the schists are more siliceous. The most outstand-ing
mineral is ottrelite of dull-bluish or greenish-gray
color, but varying amounts of garnet and
staurolite are present at many places. The rocks
31
weather to thin, yellow and brown clay soils of
poor fertility.
Valleyfrown Formation (vfr)
The rocks of the Valleytown formation vary
widely from place to place but consist mainly of
mica schist and fine-banded gneiss. However, in
many areas, mica slate, argillaceous slate, gray-wacke,
feldspathic sandstone, and occasionally
beds of coarse quartzite are present. These rocks
are usually dark colored, varying from dark gray
to grayish black. In most of the rocks the min-erals
that can be identified in hand specimens are
quartz and mica in the mica schist and feldspar
and quartz in the feldspathic sandstone ; however,
bands of ottrelite schist and garnet schist are
often present. The rocks of this unit are resistant
to weathering and stand up as knobs and ridges.
Final decay produces a thin soil, full of rock frag-ments,
which is of little value.
Andrews schist—Murphy Marble (ma)
Because of limited areal extent, the Murphy
marble and Andrews schist have been combined
into one unit on the present map. The Murphy
marble is found in two areas, one along the Nan-tahala
and Valley Rivers in Swain and Cherokee
Counties, and the other along Peachtree and Little
Brasstown Creeks in Cherokee County. The rock
consists entirely of marble, rather fine grained but
completely crystalline. The predominant color
is white, but a large part of the marble is dark
gray or blue, and many layers consists of banded
or mottled blue and white. In the Red Marble
Gap some of the layers have a rose-pink color.
Van Horn (1948 pp. 12-13) established a zoning
or stratigraphic sequence in the marble, based on
color and secondary minerals. The Murphy mar-ble
passes by gradation into the Andrews schist
and often contains bands of schist. Other than
crystals of calcite and dolomite, the marble con-tains
mica, quartz, garnet, and ottrelite along
gradational zones and talc and tremolite at many
places. Much of the marble underlies low ground
and is covered with stream deposits of sand and
gravel.
The Andrews schist consists essentially of thin
beds of calcareous schist of relatively light-gray
color. It is characterized by a large number of
ottrelite cyrstals, which lie at right angles to the
bedding. Muscovite and biotite occur frequently,
lie parallel to the bedding, and are the chief cause
of the schistose planes in the rock. The Andrews
schist weathers readily and usually underlies low
ground. It is usually covered wit ha residual,
micaceous clay, that grades downward into fresh
rock.
The Murphy marble is an attractive rock, and
over the years considerable dimension and crushed
stone have been produced from it. Building, mon-umental,
and crushed stone are being produced
near Marble, Cherokee County, and crushed aggre-gate
and agricultural limestone are being produced
near Hewitts, Swain County. A white, fine-grain-ed
dolomite, occupying the approximate center of
the marble, often contains deposits of high-grade
talc. This talc has been mined for years and is
presently being produced about one mile south-west
of Murphy. Iron ore in the form of limonite
occurs at many places, usually associated with the
Andrews schist. Production was carried on for
many years with maximum development and min-ing
taking place between 1917 and 1920. No pro-duction
has been made since 1921.
SEDIMENTARY ROCKS
Upper precambrian
OCOEE SERIES
Along the western boundary of the State, in
Cherokee, Graham, Swain, Haywood, and Madi-son
Counties and smaller areas in Clay, Jackson,
and Mitchell Counties, occurs a thick sequence of
clastic, nonfossiliferous sedimentary rocks. These
rocks were named the Ocoee conglomerate and
slates by Safford (1856) from the exposures
along the Ocoee River between Parksville and
Ducktown, Tennessee. Keith (1895, 1896, 1904,
and 1907c) mapped and named a number of forma-tions
within the series ; however, his formations
differed considerably from one folio to another.
Rodgers (1953), in his compilation of a geologic
map of East Tennesse