U.S. DEPARTMENT OF THE INTERIOR 

U.S. GEOLOGICAL SURVEY

Geologic Map of the Piedmont in the Savage and Relay Quadrangles, 

Howard, Baltimore, and Anne Arundel Counties, Maryland

By 

Avery Ala Drake, Jr. 1

Open-File Report 98-757

This report is preliminary and has not been reviewed for conformity with U.S. Geological 

Survey editorial standards or with the North American Stratigraphic Code. Any use of trade, 

product, or firm names is for descriptive purposes only and does not imply endorsement by the 

U.S. Government.

'Reston, VA

1998
GEOLOGIC MAP OF THE PIEDMONT IN THE SAVAGE AND RELAY 

QUADRANGLES, HOWARD, BALTIMORE, AND ANNE ARUNDEL

COUNTIES, MARYLAND

by

Avery Ala Drake, Jr. 

INTRODUCTION

The Piedmont in the Savage and Relay quadrangles (fig. 1) is largely in Howard County, 

Maryland. The northeasternmost part is in Baltimore County, Maryland and about 0.03 square 

miles is in Anne Arundel County. Most of the area is suburban and almost all outcrops are 

restricted to the Patapsco, Middle Patuxent, Little Patuxent, and other stream valleys. Crystalline 

rocks of the central Appalachian Piedmont within these quadrangles are overlain in many places 

by Coastal Plain deposits of Cretaceous age. Alluvium occurs along most streams. The geology 

of adjacent quadrangles on the west and south has been mapped by Drake (in press, unpublished 

data, 1991-1997) and J.N. Roen and A.A. Drake, Jr. (in press), and that to the north and east by 

Crowley (1976). The tectonics of the area were interpreted by Crowley (1976) and Drake (1995). 

Aeromagnetic and gravity surveys of the area were interpreted by Bromery (1968).

REGIONAL GEOLOGY

This part of the Maryland Piedmont is on the east limb of the Baltimore structural 

culmination, a major internal basement massif in the central Appalachian orogen (Drake and 

others, 1988; Rankin and others, 1989, 1993). This culmination exposes Mesoproterozoic 

basement and its Cambrian continental margin sequence cover in several antiformal windows 

through an obducted sequence of metamorphosed sedimentary and igneous rocks (fig. 1). These 

relations were mapped in the Clarksville (Drake, in press) and Sykesville (Roen and Drake, in 

press) quadrangles to the west (fig. 1). Here, the obducted sequence consists of the Loch RavenLaurel tectonic motif and the arc rocks of the Baltimore and Soapstone Branch thrust sheets. 

These rocks have been intruded by granitoids of Late Ordovician and Late Devonian age and a 

dike of Early Jurassic age.

LOCH RAVEN-LAUREL TECTONIC MOTIF

The Loch Raven-Laurel tectonic motif consists of a precursory sedimentary melange, the 

Laurel Formation (£1), and the Loch Raven thrust sheet, which are separated by the Burnt Mills 

thrust fault. The Loch Raven thrust sheet consists of the Loch Raven Schist (GZ1) and Oella 

Formation (GZo). The Laurel precursory melange contains fragments of the overlying Loch 

Raven thrust sheet that calved from it during its emplacement during the sedimentation of the 

melange matrix. The motif is a major tectonic unit in the Maryland Piedmont, the Loch Raven 

thrust sheet underlying about 400 square miles, and the Laurel Formation about 80 square miles.
Loch Raven Thrust Sheet

In this area, rocks of the Loch Raven thrust sheet were mapped as oligoclase-mica schist 

facies of the Wissahickon Formation by Cloos and Broedel (1940) and called Wissahickon 

Formation, eastern sequence by Hopson (1964). Throughout the Maryland Piedmont, these rocks 

were called the lower pelitic schist facies of the Wissahickon Formation (Southwick and Fisher, 

1967).

There are no outcrops of Loch Raven Schist (GZ1) in this map area. Fortunately, soil in arear 

underlain by this unit characteristically contains abundant flakes of coarse muscovite; therefore, 

it can be reasonably well mapped. In adjacent areas (Drake, 1998; unpublished data, 1991-1997) 

it consists mostly of quartz, muscovite, and biotite and much lesser plagioclase. Chemically, it is 

rich in alumina and alkalies, has a high Na-K ratio, and has a low silica content (Hopson, 1964). 

The schist contains meta-arenite beds identical to those in the overlying Oella Formation (GZo).

In the adjacent Clarksville quadrangle (Drake, in press) the Loch Raven Schist contains both 

mappable and unmappable layers of amphibolite as well as mappable blocks of serpentinized 

pyroxenite and amphibolite that have a spreading-center chemistry.

There is only one known outcrop of Oella Formation in this map area, but in adjacent areas 

(Drake, 1998, unpublished data, 1991-1997) it consists of meta-arenite and interbedded 

semipelitic schist and schist. The meta-arenite is fine grained and contains abundant quartz and 

plagioclase. In most exposures, it has a fair to good schistosity marked by aligned biotite flakes. 

The interbedded schist and semipelitic schist intervals are identical to those in the underlying 

Loch Raven Schist. Bedding can be determined easily at most places, particularly where metaarenite and schist are closely interbedded.

The meta-arenite is not graded, nor does it possess other sedimentary structures characteristic 

of turbidites. An extensive study of these rocks by Hopson (1964) showed that they have the 

composition of graywacke and subgraywacke.

The Oella also contains some light-gray quartzite that contains no relict detrital sand grains. 

Chemical analyses of quartzite (Hopson, 1964) compare well with those of chert, or possibly, 

highly siliceous shale. Some quartzose beds contain clinozoisite (Drake, 1998) and are probably 

metamorphosed calcareous cherty sediment.

As interpreted by Drake (1998), the Loch Raven Schist and Oella Formation must have been 

deposited in a deep, quiet basin as there is no evidence of current activity in the arenitic rocks. 

The schist is most likely a metamorphosed sodic shale. The quartzite is most likely a 

metamorphosed highly siliceous shale and (or) impure chert as it occurs in thin, continuous beds 

and lacks relict detrital sand grains. The interlayered amphibolite could be either metamorphosed 

basalt or basaltic tuff. The discontinuous few inch-thick interlayers demand a tuffaceous origin. 

The mappable bodies probably had the same origin.

In this area, rocks of the Loch Raven thrust sheet are at kyanite grade and typically contain 

large garnets. Fibrolite occurs sporadically. In adjacent areas (A.A. Drake, Jr., unpublished 

data), muscovite and garnet are oriented in the schistosity, whereas kyanite and fibrolite have 

grown randomly across the schistosity surfaces, suggesting that heating outlasted deformation in 

this area.
Laurel Formation

The Laurel Formation is the precursory melange of the Loch Raven-Laurel tectonic motif. It 

is very poorly exposed in this area, and outcrops are largely confined to major drainages. Much 

of the Laurel was mismapped as oligoclase-mica facies of the Wissahickon Formation by Cloos 

and Broedel (1940), perhaps because of the abundant coarse muscovite resulting from its high 

metamorphic grade.

The upper part of the Laurel (Glo) in the Washington West (Fleming and others, 1994), 

Kensington (Drake, 1998), and Clarksville (Drake, in press) quadrangles to the southwest 

contains more than 50 percent of previously deformed meta-arenite and schist olistoliths. That 

map unit was traced into and through this area on the basis of float.

BALTIMORE THRUST SHEET

In the Maryland Piedmont, the Baltimore thrust sheet consists of the Baltimore Complex. In 

Baltimore County, the Baltimore Complex consists of the Mount Washington Amphibolite, the 

Raspburg Amphibolite, and the Hollofield Ultramafite (Crowley, 1976). The Mount Washington 

and Raspburg are probably the same unit, but this could not be determined because of the Coastal 

Plain cover.

Mount Washington Amphibolite

In this area, the Mount Washington Amphibolite (Om) constitutes the Baltimore thrust sheet. 

The Mount Washington is the metamorphosed gabbro part of the Baltimore Complex (Crowley, 

1976; Higgins, 1977). The ultramafic part of the Baltimore Complex, the Holofield Ultramafite 

and the Raspburg Amphibolite crop out to the north and east (Crowley, 1976). There are 

excellent outcrops of amphibolite along the major drainages and essentially none on the uplands 

where its presence is marked by scattered cobbles and boulders of amphibolite in clay-rich, red 

soil. The amphibolite contains interlayers of metapyroxenite, and a body of soapstone (Omsp) 

was mapped along Soapstone Branch. The amphibolite commonly contains veins and sheets of 

plagiogranite. Bodies of plagiogranite (Omp) were mapped in a tributary to Soapstone Branch 

and along the railroad below All Saints Convent in the northwestern corner of the map.

Chemistry of the Mount Washington Amphibolite was presented by Hanan (1980). Two new 

analyses are given in Table 1. Chemically, the bulk of the unit is basalt, some is picrobasalt, and 

one trachybasalt was sampled (fig. 2).

A geophysical study of the Baltimore thrust sheet by Bromery (1968) found that it constituted 

a slab, about 10,000 feet thick, both contacts of which dipped steeply west. Bromery (1968) 

interpreted this slab to be an intrusive sill, as had all previous workers. Crowley (1976), 

however, in a major contribution to Appalachian geology, found that the Mount Washington 

Amphibolite and Hollofield Ultramafite constitute a thrust sheet. The principal evidence for a 

fault is the truncation of map units both within the Baltimore Complex and within the 

surrounding rocks. This fault, the Baltimore thrust fault, has overrun the Laurel Formation and 

the Burnt Mills thrust fault in the Ellicott City quadrangle to the north (fig. 1) where it also cuts
out the Hollofield Ultramafite (Crowley and Reinhardt, 1979). In addition, there is no evidence 

anywhere of contact metamorphism in the metasedimentary rocks adjacent to the Baltimore 

Complex.

SOAPSTONE BRANCH THRUST SHEET

In this area, the Soapstone Branch thrust sheet consists of the Druid Hill Amphibolite (Od), 

Relay Felsite (Or), and Carroll Gneiss (Oc).

Druid Hill Amphibolite

The Druid Hill Amphibolite (Od) originally was included in the Baltimore Complex (Mount 

Washington Amphibolite as used herein) by Knopf and Jonas (1925). It, however, is clearly 

layered, contains interlayered felsite, is finer grained than amphibolite of the Mount Washington 

Amphibolite, contains probable pillows, and clearly interfmgers and replaces the Carroll Gneiss 

to the northeast in the Baltimore West quadrangle (Crowley and Reinhardt, 1979). Crowley 

(1976), in another major contribution to Appalachian geology, recognized that the Druid Hill wa^ 

a volcanic rock and called it the Druid Hill Amphibolite Member of the James Run Formation. 

Drake (1998) removed the Druid Hill from the James Run Formation and promoted it to 

formational status. Outcrops of Druid Hill Amphibolite are restricted to the Patapsco Valley.

Two chemical analyses of Druid Hill Amphibolite were presented by Hanan (1980) and three 

new analyses are given in table 1. All rocks are basalt except for one dacite (fig. 2).

The contact of the Druid Hill Amphibolite with the Mount Washington Amphibolite, the 

Soapstone Branch thrust fault, is marked by mylonitic foliation. Abundant pegmatites appear in 

the Mount Washington north of the contact and are very sparse in the Druid Hill. Red soil has 

formed on the Mount Washington, whereas it has not on the Druid Hill.

Relay Felsite

The Relay Felsite (Or) originally was mapped as Relay Quartz Diorite by Knopf and Jonas 

(1925) and described as such by Hopson (1964). In addition, Hopson (1964) included in the unit 

the plagiogranite that has been intruded into the Mount Washington Amphibolite. Higgins 

(1972) interpreted the Relay to be a metamorphosed volcanic-volcaniclastic rock and assigned it 

to the James Run Formation. Crowley (1976) agreed with Higgins (1972) and named the unit the 

Relay Gneiss Member of the James Run Formation. Drake (1998) removed the Relay from the 

James Run Formation and promoted it to formational status as Relay Felsite. In this quadrangle, 

outcrops of Relay are restricted to the Patapsco Valley.

My study shows that although some of the Relay is fine grained and layered and passes down 

into the Druid Hill Amphibolite by interlayering, other parts are medium grained and unlayered 

and have all the characteristics of an intrusive rock. The Relay outcrop belt is linear (see fig. 1) 

suggesting a layered rather than an intrusive body. The Relay is here interpreted to consist of 

volcanic and subvolcanic rock that has intruded its own ejecta.
Chemistry of the Relay Felsite was published by Hopson (1964) and Higgins (1972). A new 

analysis is given in table 1. Chemically, the Relay Felsite is trondhjemite or quartz keratophyre 

(fig- 3).

Carroll Gneiss

The Carroll Gneiss (Oc) originally was mapped as Baltimore Gneiss by Knopf and Jonas 

(1925). Hopson (1964) recognized that these rocks differed greatly from the Baltimore Gneiss 

and called them paragneiss. Southwick (1969) recognized that these rocks were similar to the 

volcanic and volcaniclastic rocks in the James Run Formation and, therefore, were younger than 

the Baltimore Gneiss. Crowley (1976) accepted the volcanic origin of these rocks and named 

them the Carroll Gneiss Member of the James Run Formation. The Carroll Gneiss does not crop 

out in this quadrangle, but is important to an understanding of the regional geology.

INTRUSIVE ROCKS

The metamorphic rocks have been intruded by the Ellicott City Granodiorite (Oe) and related 

pegmatite (Op), the Guilford Granite (Dg) and related pegmatite (Dp), and a diabase dike (Jd).

Ellicott City Granodiorite

The Ellicott City Granodiorite is mostly granodiorite but has monzogranite phases (fig. 4). 

Of chemically analyzed samples, one is granite from the interior of a pluton, and one is * 

granodiorite from the border of a pluton (fig. 2). There are no exposures of Ellicott City 

Granodiorite in the large plutons in this quadrangle, but Hopson (1964) reported that 

monzogranite appears to be restricted to the interior of rock bodies presumably resulting from 

igneous zoning. Sheared rocks on the margins of rock bodies, such as along the Patapsco River, 

have microcline crystals growing across the foliation, suggesting K-metasomatism by fluids 

passing along the mylonitic foliation. This is similar to relations in the Kensington Tonalite to 

the south (Fleming and others, 1994; Drake, 1998). The abundant pegmatites (Op) that intrude 

the Mount Washington Amphibolite (Om) appear to be related to Ellicott City plutonism. A 

chemical analysis of pegmatite is given in Table 1. The contact zones between Ellicott City 

Granodiorite and Mount Washington Amphibolite are characterized by dikes of Ellicott City and 

screens of Mount Washington, making geologic mapping quite difficult as it follows the fold 

forms in the metamorphic rocks. This is particularly well shown in the adjacent Ellicott City 

quadrangle (Crowley and Reinhardt, 1980). The Ellicott City contains primary epidote (Hobbs, 

1889; Keyes, 1893, Hopson, 1964), suggesting that the granodiorite crystallized in a temperaturepressure regime of over 600°C and 8 kb (Zen and Hammarstrom, 1984).

Guilford Granite

The Guilford Granite (Dg) is monzogranite (fig. 3), although chemically some rock is 

granodiorite and quartz monzonite (fig. 2). The Guilford forms numerous elongate plutons in the 

western part of the map area. Most of these trend east-northeast to northeast but a few trend
north. In 1993, new construction along Route 29 near the north border of the map exposed a 

pavement outcrop within which a dike of Guilford Granite (Dg) could be seen within Ellicott 

City Granodiorite (Oe).

The Guilford magma apparently was quite fluid as pegmatite occurs as discordant and sparseconcordant seams, pods, and lenses within the granite. One pegmatite (Dp) has intruded the 

Laurel Formation (Gl). Some outcrops, such as one in the Middle Patuxent River about 3,750 

feet from the west margin of the map, contain dikes of aplite, some of which parallel the flow 

foliation. Other dikes fill joints that cut the flow foliation and parallel dikes. At least one quartz 

body (Dq) appears to be related to Guilford magmatism.

The Guilford Granite is clearly post-kinematic as it cuts the regional foliation, as well as the 

Baltimore thrust fault. There is no evidence of Devonian tectonism in this part of the Piedmont, 

so the Guilford probably formed by decompressional melting (Pitcher, 1982).

Diabase

One diabase dike (Jd) was mapped on the basis of float in the northwestern corner of the 

map. The rock is typical of other diabase dikes in the Piedmont.

STRUCTURAL GEOLOGY

The stacked thrust sheets in this map area have been obducted onto the Laurentian basement 

and continental margin sequence in the area to the west on the Loch Raven thrust sheet (Drake, 

1995, 1998, in press; Roen and Drake, in press). The thrust stack, bottom to top, consists of the 

Loch Raven-Laurel tectonic motif, the Baltimore thrust sheet, and the Soapstone Branch thrust 

sheet. Regionally most of these rocks dip west because they are on the overturned east limb of

+**

the Baltimore culmination.

Structures in the Loch Raven-Laurel Tectonic Motif

The Loch Raven Sheet and Oella Formation were emplaced above the Laurel Formation on 

the Burnt Mills thrust fault, which was first mapped in the Kensington quadrangle about 15 miler 

to the southwest (Drake, 1998). The Laurel was deposited during the emplacement of the thrust 

sheet as shown by abundant olistoliths of previously metamorphosed and deformed meta-arenite 

and schist. The Burnt Mills thrust fault, like the thrust faults in the other tectonic motifs in the 

Virginia-Maryland Piedmont, is visualized to have formed near the base of a trench slope where 

it was stretched over the thrust toe generating debris that slumped to the base of the scarp (Drake, 

1985a). With continuing deformation, the debris was overrun by the thrust fault, forming the 

tectonic motif.

There are far too few exposures of Loch Raven Schist and Oella Formation in this map area 

to permit mapping of macroscopic structures. Most outcrops of Laurel Formation have two 

foliations. At several places, one or both of these foliations have been folded into northnorthwest to northwest plunging, upright antiforms and synforms. These folds are here called 

Columbia folds for the "new town" of that name. Columbia folds may well be the same as Rock
Creek folds mapped in the Washington West (Fleming and others, 1994) and Kensington (Drake, 

1998) quadrangles fo the southwest. Rock Creek folds were interpreted to have formed by 

transpression related to dextral slip along the Rock Creek shear zone (Fleming and others, 1994; 

Fleming and Drake, 1998; Drake, 1998). I (Drake, unpublished data, 1992-1997) have been 

unable to trace the Rock Creek shear zone north of the Patuxent River, so it is uncertain if Rock 

Creek and Columbia folds are correlative.

One east-northeast plunging fold of foliation was mapped in the Laurel Formation between 

Jonestown and Oakland Mills. Similar folds were called Middle Patuxent folds in the Clarksville 

quadrangle to the west where they fold axial surfaces of northwest to north-northwest plunging 

folds (Drake, in press). Here, they probably post-date Columbia folds, but that cannot be proved.

Structures in the Baltimore Thrust Sheet

The Baltimore thrust fault has placed the Mount Washington Amphibolite and, to the north, 

the Hollofield Ultramafite (Crowley, 1976), onto the Loch Raven-Laurel tectonic motif. The 

Baltimore thrust fault is overturned from the point where it is covered by Coastal Plain deposits 

in the Laurel quadrangle to the south (A.A. Drake, Jr., unpublished data, 1993) to the point near 

Columbia where it becomes upright. The overturning is consistent with the steep west-dipping 

contact of the Mount Washington Amphibolite as interpreted from geophysical data by Bromery 

(1968). The thrust fault is overturned again in the Ellicott City quadrangle to the north (Crowley 

and Reinhardt, 1980). It remains overturned throughout Baltimore and Harford Counties to the 

northeast (Southwick, 1969; Crowley, 1976). To the north, it has overrun the Laurel Formation 

(Crowley and Reinhardt, 1980). Small horses of Laurel, called Sykesville Formation, were 

mapped between the Baltimore and Burnt Mills thrust faults in the Ellicott City (Crowley and 

Reinhardt, 1980) and Baltimore West (Crowley and Reinhardt, 1979) quadrangles. The Laurel 

Formation emerges from beneath the Baltimore thrust fault in Harford County, Maryland 

(Southwick, 1969), where it was called Deer Creek melange by Drake (1985b).

Bromery (1968), on the basis of geophysical data, interpreted that the rocks here called 

Mount Washington Amphibolite occupied a synform. He was correct. The axial trace of this 

synform passes about 1,000 feet west of Ilchester. It is a Columbia phase fold. A Columbia 

antiform and synform fold the Mount Washington Amphibolite and Ellicott Granodiorite east of 

that axis. Columbia synforms and antiforms also fold the Ellicott City Granodiorite just east of 

the Baltimore thrust fault.

The foliation in the Mount Washington Amphibolite and Druid Hill Amphibolite, and the 

overturned Soapstone Branch thrust fault were deformed by an anticline-synform pair. These 

folds are overturned to the east and plunge north. They are here called Patapsco folds for the 

Patapsco River. Their relation to Columbia folds is uncertain.

Zones of mylonite are common in the Mount Washington Amphibolite and Ellicott City 

Granodiorite along the Patapsco River. Mylonitization is especially severe near the north border 

of the map, Ellicott City Granodiorite being reduced to a material resembling quartzite. Most 

mylonite strikes west-northwest to northwest. It is impossible to trace these zones within this
map area. Mylonite was not mapped in the Ellicott City quadrangle to the north (Crowley and 

Reinhardt, 1980). It will not be possible to interpret this mylonite without additional work in the 

surrounding area.

Structures in the Soapstone Branch Thrust Sheet

The Druid Hill Amphibolite and Relay Felsite are folded together by several Patapsco folds. 

Mesoscopic folds and wedge structures confirm the clockwise rotation sense of these folds. 

Much of the Relay Felsite is sheared and contains numerous mesoscopic thrust faults that parallel 

the mylonitic foliation. Many of the thrust zones form mesoscopic duplexes. In the Baltimore 

West (Crowley and Reinhardt, 1979) and Baltimore East (Reinhardt and Crowley, 1979) 

quadrangles, rocks of the Loch Raven thrust sheet, called Jones Falls Schist, are exposed in a 

window through the Soapstone Branch thrust fault. It is uncertain at this time what the relation 

of the Soapstone Branch thrust fault to the Baltimore thrust fault is in the area beneath the 

Coastal Plain to the east of the outcrops along the Patapsco River.

TECTONIC SYNTHESIS

Recent geologic work in the northern Virginia-Maryland Piedmont (Drake, 1995), in part in 

the Savage and Relay quadrangles, led to the following synthesis. A stack of tectonic motifs was 

emplaced tectonically onto the Laurentian continental margin early in the Taconic orogeny. The 

tectonic motif and Laurentian basement and continental margin sequence rocks then were folded 

recumbently. In the south, rocks both east and west of the Mesoproterozoic core were intruded 

by numerous plutons that were interpreted to constitute a magmatic arc that had been built on the 

Laurentian margin (Drake and Fleming, 1994). This interpretation is supported by xenocrystic 

zircons from the intrusive rocks that yielded Mesoproterozoic ages (J.N. Aleinikoff, U.S. 

Geological Survey, written commun., 1996, 1997). The intrusive rocks range in age from 481 

Ma to 457 Ma, which constitutes early Taconic age as visualized by Drake and others (1989). 

That time agrees with the first appearance of flysch in the Martinsburg foreland basin in the 

central Appalachians (Drake and others, 1989).

The Baltimore thrust sheet appears to have been emplaced onto the Loch Raven-Laurel 

tectonic motif subsequent to the motifs obduction onto the Laurentian margin as it cuts out 

units, has nearly overrun the motif in areas to the north and east (Crowley, 1976) and does not 

appear on the west limb of the culmination. If the discrimination diagram (fig. 4), is accepted 

rocks of the Baltimore thrust sheet were generated within an ensialic basin.

The Soapstone Branch thrust sheet probably was emplaced onto the Baltimore thrust sheet 

subsequent to its emplacement onto the Loch Raven-Laurel tectonic motif because the 

Connewingo melange separates the thrust sheets along the Susquehanna River to the northeast 

(Southwick, 1969; Higgins and Conant, 1986). If the discrimination diagram (fig. 5) is accepted, 

rocks of the Soapstone Branch thrust sheet were generated within an island arc.

After all the thrust sheets were emplaced, they and the Laurentian basement and continental 

margin sequences rocks were backfolded into a major east-verging massif. The emplacement of 

the thrust sheets and recumbent folding was interpreted to be the result of the east-dipping
subduction of Laurentia beneath an oceanic sequence (Drake, 1995). This subduction, however, 

was aborted because of Archidmedic buoyancy leading to subduction flip (Roeder, 1973) and 

east-verging retrocharriage. This deformation was completed by 368 Ma, the age of the Guilford 

Granite, which crosscuts the Taconic structures.

10
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11
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Higgins, M.W., and Conant, L.C., 1986, Geologic map of Cecil County: Maryland Geological

Survey, scale 1:62,500. 

Hobbs, W.H., 1889, On the paragenesis of allanite and epidote as rock-forming minerals:

American Journal of Science, 3rd series, v. 38, p. 223-228. 

Hopson, C.A., 1964, The crystalline rocks of Howard and Montgomery Counties, in The geology

of Howard and Montgomery Counties: Baltimore, Maryland Geological Survey, p. 27-215. 

Horton, J.W., Jr., Aleinikoff, J.N., Drake, A.A., Jr., and Fanning, M.C., 1998, Significance of

Middle to Late Ordovician volcanic-arc rocks in the central Appalachians: Geological Society

of America Abstracts with Programs, v. 30, p. A125. 

Keyes, C.R., 1893, Epidote as a primary component of eruptive rocks: Geological Society of

America Bulletin, v. 4, p. 305-312. 

Knopf, E.B., and Jonas, A.I., 1925, Map of Baltimore County and Baltimore City showing the

geological formations: Maryland Geological Survey, scale 1:62,500. 

Knopf, E.B., and Jonas, A.I., 1929, Geology of the crystalline rocks Baltimore County, in

Baltimore County: Maryland Geological Survey, p. 97-129. 

Landing, Ed, 1994, Precambrian-Cambrian boundary global stratotype ratified and a new

perspective of Cambrian time: Geology, v. 22, p. 179-182. 

LeBas, M.J., LeMaitre, R.W., Streckeisen, A., and Zanettin, B., 1986, A chemical classification

of volcanic rocks based on the total alkali-silica diagram: Journal of Petrology, v. 27, p. 745-

750. 

O'Connor, J.T., 1965, A classification for quartz-rich igneous rocks based on feldspar ratios:

U.S. Geological Survey Professional Paper 525-B, p. B79-B84. 

Pitcher, W.S., 1982, Granite type and tectonic environment, in Hsii, K.J., ed., Mountain Building

Processes: New York, Academic Press, p. 19-40. 

Plumb, K.A., 1991, New Precambrian time scale: Episodes, v. 14, no. 2, p. 139-140.

12
Rankin, D.W., Drake, A.A., Jr., Glover, L., Ill, Goldsmith, Richard, Hall, L.M., Murray, D.P., 

Ratcliffe, N.M., Read, J.F., Secor, D.T., Jr., and Stanley, R.S., 1989, Pre-orogenic terranes, in 

Hatcher, R.D., Jr., Thomas, W.A., and Viele, G.W., eds., The Appalachian orogen in the 

United States: Boulder, Colorado, Geological Society of America, The geology of North 

America, v. F-2, p. 7-100.

Rankin, D.W., Drake, A.A., Jr., and Ratcliffe, N.M., 1993, Proterozoic North American 

(Laurentian) rocks of the Appalachian orogen, in Reed, J.C., Jr., Bickford, M.E., Houston, 

R.S., Link, P.K., Rankin, D.W., Sims, P.K., and Van Schmus, W.R., eds.: Precambrian: 

Conterminous U.S., Boulder, Colorado, Geological society of America, The Geology of 

North America, v. C-2, p. 378-422.

Reinhardt, Juergen and Crowley, W.P., 1979, Geologic map of the Baltimore East quadrangle, 

Maryland: Maryland Geological Survey, scale 1:24,000.

Roeder, D.H., 1973, Subduction and orogeny: Journal of Geophysical Research, v. 78, no. 23, p. 

5005-5024.

Roen, J.N., and Drake, A.A., Jr., in press, Geologic map of the Sykesville quadrangle, Howard, 

Carroll, and Baltimore Counties, Maryland: U.S. Geological Survey Open-File Report, scale 

1:24,000.

Shaw, H.F., and Wasserburg, G.J., 1984, Isotopic constraints on the origin of Appalachian mafic 

complexes: American Journal of Science, v. 284, p. 319-349.

Sinha, A.K., Hannan, B.B., and Wayne, D.M., 1997, Igneous and metamorphic U-Pb ages from 

the Baltimore Mafic Complex, Maryland Piedmont, in Sinha, A.K., Whalen, J.B., and Hogan, 

J.P., eds., The nature of magmatism in the Appalachian orogen: Boulder, Colorado, 

Geological Society of America Memoir 191, p. 275-286.

Sinha, A.K., Hund, E.A., and Hogan, J.P., 1989, Paleozoic accretionary history of the North 

American plate margin (central and southern Appalachians): constraints from the age, origin, 

and distribution of granitic rocks, in Hillhouse, J.W., ed., Deep structure and past kinematics 

of accreted terranes: American Geophysical Union Geophysical Monograph 50, p. 219-238.

Southwick, D.C., 1969, Crystalline rocks, in Geology of Harford County, Maryland: Maryland 

Geological Survey, p. 1-76.

Southwick, D.C., and Fisher, G.W., 1967, Revision of stratigraphic nomenclature of the Glenam 

Series in Maryland: Maryland Geological Survey Report of Investigations, no. 6, 19 p.

Streckeisen, Albert, 1976, To each plutonic rock its proper name: Earth Science Reviews, v. 12, 

p. 1-33.

Williams, G.H., 1895, General relations of the granitic rocks in the middle Atlantic Piedmont 

Plateau: U.S. Geological Survey 15th Annual Report, p. 657-684.

Zen, E-an and Hammarstrom, J.M., 1984, Magmatic epidote and its petrologic significance: 

Geology, v. 12, p. 515-518.

13
Table 1 ~ Chemical analyses and C.I.P.W. norms of some rocks from the Savage and Relay quadrangles

Sample

Field No.

1

R-G-2-10

2

R-G-2-11

3 4 5

R-G-2-13 SA-A-2-6 SA-H-6-3

6

R-G-2-9

7

SA-H-6-1

Major oxide composition (weight percent)

SiO2 MA

Fe203

FeO

MgO

CaO

Na2O

K2O

H2O+

H2OTiO2

PA

MnO

CO2

Total

Q

C

or

ab

an

di

hy

to

ta

mt

hm

il

ap

cc

Total

50.6

16.5

2.6

5.7

8.5

11.3

2.4

0.2

1.4

0.1

0.5

0.05

0.2

0.10

100.15

0.7

--

1.3

20.2

34.3

17.3

21.1

~

3.8

0.9

0.1

_02

99.9

66.8

14.0

2.1

3.9

1.9

5.1

3.4

0.4

0.7

0.1

0.6

0.1

0.1

0.5

99.7

30.6

2.6

29.6

21.7

2.5

8.3

--

3.0

1.2

0.2

0.1

99.8

46.9 46.3 49.1

15.1 16.4 13.3

3.9 2.4 2.4

11.7 9.3 5.9

4.8 8.1 8.4

9.5 12.8 10.3

2.3 1.3 2.1

0.2 0.1 3.1

1.6 1.5 1.8

0.1 0.1 0.4

2.5 1.0 1.4

0.5 0.1 0.6

0.3 0.2 0.1

0.01 0.1 0.6

99.7 99.7 99.5

CIPW norms (weight percent)

Based on analyses recalculated

3.0

1.4 0.4 18.9

20.1 11.1 18.4

30.6 39.5 18.10

10.2 18.3 21.

22.2 19.2 4.1

2.5 7.5

1.9 2.6

5.8 3.5 3.6

4.8 2.0 2.8

1.9 0.3 1.5

OQ2 0.3 1.4

100.02 99.0 100.1

78.8

12.1

0.3

0.5

0.5

0.2

6.5

0.09

0.2

0.03

0.07

0.05

0.01

0.1

99.4

39.9

1.2

0.5

55.6

0.09

1.7

--

0.4

0.1

0.1

0.3

99.8

73.5

14.3

0.2

0.1

0.1

0.1

1.8

9.6

0.06

0.1

0.03

0.05

0.1

0.01

99.9

26.1

1.0

57.0

14.9

0.03

0.4

--

0.4

_

0.06

0.1

0.02

100.0

14
Table 1 (cont.)

Trace-element abundances 

Large cations2

Rb

Ba

Sr

Th4

Zr2

Hf

Nb3

Ta

4

38

116

0.83

0.29

0.78

10

0.11

18

205

140

5.42

200

5.61

10

0.78

9.8

48

166

High

0.35

32

0.73

10

0.3

8

30

130

valence-cations

0.14

16

0.57

10

0.1

85

1200

1000

8.1

240

6.22

0.65

1.3

30

42

18.0

130

6.11

21

2.6

736

80

23

3.81

24

1.71

23

2.1

Metals4

Cr

Co

Ni

Cu

Sc

Zn

As

Mo

113

38.9

56.0

48

37.2

57

0.6

11

15.1

10

56

20

46

0.6

2.7

30.9

12

62

45.1

130

1.1

~

72.3

47.0

530

46

47.7

91

0.8

~

252

38.6

140

140

31.7

61

0.7

~

1.2

0.31

10

10

1.34

10

0.7

~

1.1

0.35

2.0

3.0

0.34

3.7

0.48

2

Rare-earth elements

La4

Ce4

Nd4

Sm4

Eu4

Tb4

Yb4

Lu4

Y2

3.3

6.4

6.5

1.38

0.47

0.31

1.3

.17

16

16.3

34.5

17

5.14

1.17

0.98

4.4

0.635

38

6.2

15

15

4.2

1.78

0.81

2.4

0.35

26

3.1

8.2

6.7

2.4

0.96

0.54

2.0

0.3

20

69.1

129

57

11

2.32

0.83

1.8

0.25

22

2.7

7.4

3.8

1.99

0.2

0.6850

6.3

0.9440

34.0

2.7

4.6

2.1

1.17

0.057

0.29

0.32

0.033

9

'XRF Analyses by D.F. Siems and J.E. Taggart, Jr. FeO, CO2, H2O+, H2O- analyses by J.W. Marinenko

2Analyses by J.K. Evans

3Analyses by M.W. Doughten

4Analysis of sample 4 by J.N. Grossman. All others by J.S. Mee

15
Table 1 (cont.)

Description of Samples

1. Amphibolite of Druid Hill Amphibolite from outcrop of interbedded amphibolite and metafelsite on 

southwest bank of the Patapsco River about 4,400 feet west-northwest of Interstate 1-95 bridge in the 

Relay, Md. 7.5-minute quadrangle at lat. 39°13'53"N. and long. 76°43'24"W.

2. Amphibolite of Druid Hill Amphibolite from outcrop of fine-grained amphibolite that contains some 

interlayered metafelsite on southwest bank of the Patapsco River about 700 ft west-northwest of sample 

1 in the Relay, Md. 7.5-minute quadrangle at lat. 39°13'35"N. and long. 76°43'34"W.

3. Amphibolite of Druid Hill Amphibolite from outcrop on southwest band of Patapsco River about 850 ft 

west-northwest of sample 2 in the Relay, Md. 7.5-minute quadrangle at lat. 39°13'41"N. and long. 

76°43'43"W.

4. Coarse-grained amphibolite of Mount Washington Amphibolite from outcrop in Hammond Branch 

about 6,750 ft N.86°E. from intersection of Interstate 95 and Route 198, Savage, Md. 7.5-minute 

quadrangle at lat. 39°07'48"N. and 76°50'20"W.

5. Coarse-grained biotite-hornblende metagabbro of Mount Washington Amphibolite from outcrop on 

west bank of Patapsco River at a right angle bend about 1,450 ft south of north border of Savage, Md. 

7.5-minute quadrangle at lat. 39°14'48"N. and long. 76°45'54"W.

6. Medium-coarse grained Relay Felsite from outcrops on southwest bank of Patapsco River about 1,200 

ft. west-northwest of Interstate 95 bridge in Relay, Md. 7.5-minute quadrangle at lat. 39°13'32"N. and 

long. 76°43'21"W. Rock probably is a trondhjemite intrusion.

7. Muscovite-albite-quartz-microcline pegmatite from outcrop on west bank of Patapsco River about 500 

ft south of the north border of the Savage, Md. 7.5-minute quadrangle at lat. 39°14'56"N. and 

76°45'56"W.

16
77

5 O 

I__I I I I I

5 NILE'S

Figure 1. Highly generalized geologic map of the east-central Maryland Piedmont showing the 

southern part of the Baltimore culmination.

17
EXPLANATION OF SYMBOLS 

Intrusive Rocks

Dg Guilford Granite (Late Devonian)

Ow Woodstock Granite (Late Ordovician(?))

Oe Ellicott City Granodiorite (Late Ordovician)

Obducted Rocks

Gs SykesviHe Formation (Cambrian)

Gl Laurel Formation (Cambrian)

GZ1 Rocks of the Loch Raven thrust sheet, undivided (Lower Cambrian and (or)

NeoproterozoicS-Includ65 Oella Formation, Loch Raven Schist, and Northwest

Branch Formation

GZs Soldiers Delight Ultramafite (Lower Cambrian and (or) Neoproterozoic) 

GZm Mather Gorge Formation (Lower Cambrian and (or) Neoproterozoic) 

GZu Ultramafic rocks (Lower Cambrian and (or) Neoproterozoic)

Laurentian basement and continental margin deposits

Gg Glenarm Group (Lower Cambrians-Includes Rush Brook Formation, Cockeysville

Marble, and Setters Formation 

Yb Baltimore Gneiss (Mesoproterozoic)

Magmatic Arc Rocks

Or Relay Felsite (Middle Ordovician)

Od Druid Hill Amphibolite (Middle Ordovician)

Om Mount Washington Amphibolite (Lower Ordovician)

 Contact

- y^- Thrust fault-Sawteeth on upper plate. BT, Brinklow thrust fault; BAT, Baltimore 

thrust fault; BMT, Burnt Mills thrust fault; HT, Henryton thrust fault; LT, Loch 

Raven thrust fault; PIT, Pleasant Grove fault; SBT, Soapstone Branch thrust fault 

Overturned thrust fault

Quadrangles

SY SykesviHe (Roen and Drake, in press)

E Ellicott City (modified from Crowley and Reinhardt, 1980)

BW Baltimore West (modified from Crowley and Reinhardt, 1979)

C Clarksville (A. A. Drake, Jr., unpub. data, 1993)

S Savage '(this report)

18
R Relay (this report)

Tectonic Windows

CW Clarksville MW Mayfield 

DW Dogwood SW Shepherds Lane 

FQW Folly Quarter WW Woodstock

19
S j 0Z (Weight- p

69 73 77

Figure 2. Total alkali-silica (TAS) plot (LeBas and others, 1986) of Druid Hill Amphibolite, o; 

numbered samples from this study, others from Hanan (1980). Mount Washington 

Amphibolite, x; numbered samples from this study, others from Hanan (1980).

20
/An

Or

Figure 3. Normative feldspar plot (O'Connor, 1965) for some rocks of the Relay felsite, ; 

Guilford Granite, x; and Ellicott City Granodiorite, o. Data from this study, Roen 

and Drake (in press), Higgins (1972), Hopson (1964), and Williams (1895).

21
Figure 4. Q-A-P plot (Streckeisen, 1976) plot of Ellicott City Granodiorite, , and Guilford 

Granite, x. Data from this study and Hopson (1964).

22
«M 

O

M0RBJAB

02. 0.4 0.6 0.8

Figure 5. Plot of TiO2 against (FeO/FeO+MgO) comparing Mount Washington Amphibolite

samples 8 and 9, o, presented herein with those reported by Hanan (1980), x, as well 

as samples of Raspburg Amphibolite, A, Hanan (1980). The fields for spreading 

center basalts (MORB), ensialic marginal basin basalts (EMB), and island arc basalts1 

(IAB) after Hannan and Sinha (1989). The dashed field is that of metagabbro of the 

Baltimore and State Line Complexes (Hannan and Sinha, 1989).

23
Figure 6. Plot of TiO2 against FeO/FeO+MgO comparing samples 1-3, , presented herein with 

amphibolites of the Bradshaw Amphibolite, x, (Hanan, 1980), and James Run 

Formation, A (Southwick, 1969). The fields for spreading center basalts (MORB), 

ensialic marginal basin basalts (EMB), and Island Arc basalts (IAB) after Hanan and 

Sinha (1989). The dashed field is that of volcanic amphibolites of the Baltimore and 

State Line Complexes (Hanan and Sinha, 1989).

24
CORRELATION OF MAP UNITS1 

SURFICIAL DEPOSITS

"Holocene

Unconformity 

COASTAL PLAIN DEPOSITS

^QUATERNARY

Lower 

Cretaceous

'CRETACEOUS

Unconformity 

INTRUSIVE ROCKS

Intrusive Contacts

Intrusive Contacts

Early Jurassic "/'JURASSIC

Late Devonian ^DEVONIAN

U J

Late Ordovician

Intrusive Contacts 

MAGMATIC ARC ROCKS

1

^>Middle Ordovician

^ORDOVICIAN

Soapstone Branch 

Thrust Fault

Om Early Ordovician

Baltimore Thrust Fault 

LOCH RAVEN-LAUREL TECTONIC MOTIF

Clo

Cl

Burnt Mills 

Thrust Fault

CZo

CZ!

'CAMBRIAN

LOWER

:AMBRIAN

AND (OR) 

NEOPROTEROZOfO

25
DESCRIPTION OF MAP UNITS' 

SURFICIAL DEPOSITS

Qal Alluvium (Holocene)--Sand, silt, gravel, and clay in lensoid layers underlying sinuous

floodplains along most streams. Sediments consist of yellowish-brown, fairly well bedded, 

poorly to moderately well-sorted, graded sand and silt deposits with gravel commonly filling 

scours at the base of up ward-fin ing sequences. Consists of micaceous silts and sands, and quartz 

and crystalline rock pebbles, cobbles, and boulders

COASTAL PLAIN DEPOSITS

K Cretaceous rocks undifferentiated Variegated gravel, sand, silt, and clay. Unconformably 

overlies crystalline Piedmont rocks

INTRUSIVE ROCKS 

Jd Diabase (Early Jurassic)~Medium- to dark-gray, fine-grained, largely equigranular diabase

Dg Guilford Granite (CIoos and Broedel, 1940) (Late Devonian)-Light-gray, medium- to finegrained, exceptionally homogeneous monzogranite. About equal parts of microcline, 

plagioclase, and quartz constitute about 90 percent of the rock. Remainder consists of equal 

amounts of biotite and muscovite and minor amounts of apatite, garnet, clinozoisite, zircon, and 

magnetite. Contains dikes and thin stringers of pegmatite and, at places, aplite that fill early 

formed joints or constitute ill-defined masses. The pegmatite has a nearly ideal granite 

composition, suggesting that it formed from residual Guilford magma. At places, the Guilford 

has a flow foliation, but neither a tectonic foliation nor lineation. Zircons from the Guilford 

have a SHRIMP II age of 368±4 Ma (J.N. Aleinikoff, U.S. Geological Survey, written commun., 

1997). This age is the weighted average of 16 spot analyses on 16 grains. Two other grains had 

ages of about 1.2 and 1.4 Ga showing that the Guilford magma had passed through 

Mesoproterozoic rocks

Dp Pegmatite (Late Devonian) Light-gray to pinkish-gray pegmatite petrographically identical to 

that associated with Guilford Granite

Dq Quartz body (Late Devonian)~Quartz probably related to Guilford magmatism

Oe Ellicott City Granodiorite (Late Ordovician) (Knopf and Jonas, 1929) Pinkish-gray, medium- to 

coarse-grained biotite granodiorite and lesser monzogranite. Rock contains primary epidote. 

Unit has a well-developed flow foliation where not sheared. Monzogranite appears to be 

restricted to the interior parts of Ellicott City bodies. The granodiorite has an upper intercept UPb age of 458 Ma (Sinha and others, 1989). A regression of Sinha and others (1989) data, 

however, shows that the 458 Ma age has a MSWD of 50 (J.N. Aleinikoff, U.S. Geological 

Survey, written commun., 1996)

Op Pegmatite (Late Ordovician) Light-gray to pinkish-gray muscovite-microcline-albite-quartz 

pegmatite. Locally contains minor amounts of biotite, tourmaline, allanite, monzonite, 

magnetite, and pyrite. Most of the microcline is microperthite. The pegmatite is probably 

related to the Ellicott City Granodiorite

26
MAGMATIC ARC ROCKS

Or Relay Felsite (Middle Ordovician) (Knopf and Jonas, 1929; Drake, 1998)--Well-foliated, fine- to 

medium-grained, grayish-orange-pink plagioclase-quartz-biotite felsite that at places contain 

minor amounts of chlorite, epidote, muscovite, and garnet. Some of the rock is layered, but 

other parts are more massive and coarser grained suggesting that the unit consists of both 

metamorphosed quartz-keratophyre and subvolcanic trondhjemite. Much of the rock has been 

sheared and silicified. Grades down into Druid Hill amphibolite, the contact being placed abov« 

the highest amphibolite layer. Apparently grades upward and laterally into Carroll Gneiss. Th^ 

Relay has a single crystal SHRIMP II U-Pb age of 461 ±5 Ma (weighted average of 13 grains, 

MSWD=l.l)(Horton and others, 1998)

Od Druid Hill Amphibolite (Middle Ordovician) (Crowley, 1976; Drake, 1998)-Dark-green to

black, fine- to medium-grained, well-foliated, layered amphibolite. Contains interlayered felsite 

identical to the Relay Felsite. Layers range from a few inches to a few feet in thickness. Grades 

northeastward into Carroll Gneiss (Crowley, 1976)

Oc Carroll Gneiss (Middle Ordovician) (Crowley, 1976) (Shown in section only) Fine- to mediumgrained oligoclase-quartz-biotite gneiss and granofels that at places contains muscovite and (or) 

magnetite. The felsic rock is interlayered with subordinate amphibolite. Rock layers range from 

an inch to more than 20 feet in thickness. Unit is a facies equivalent of both the Druid Hill 

Amphibolite (Od) and Relay Felsite (Or). The Carroll has a single crystal SHRIMP U-Pb age of 

464±5 Ma (weighted average of 16 grains, MSWD=0.732) (Horton and others, 1998)

Omp Mount Washington Amphibolite (Lower(?) Ordovician) (Crowley, 1976) Fine- to mediumOmps Om grained, dark-green to black amphibolite and minor pyroxene amphibolite. At places, contains 

thin interlayers of clinopyroxenite. Contains one mappable body of steatized pyroxenite 

(Omps). Commonly contains thin veins and two mappable bodies of plagiograntte (Omp). Most 

of the amphibolite is well foliated and recrystallized, but at places, relict gabbroic textures have 

been preserved. Shaw and Wasserburg (1984) published a model Nd-Sm isochron age of 

490±20 Ma for rocks equivalent to the Mount Washington, which they interpreted to be an 

igneous crystallization age, but noted that it might record a metamorphic event. More recently, 

Sinha and others (1997) obtained an U-Pb upper intercept age of 489±7 (MSWD=0.75) for 

zircons from the Mount Washington Amphibolite. The Mount Washington is here considered to 

be Lower Ordovician in age

LOCH RAVEN-LAUREL TECTONIC MOTIF

Clo Laurel Formation (Cambrian) (Hopson, 1964) Light- to medium-gray, medium- to coarseCl grained, moderately to well-foliated sedimentary melange consisting of a quartzofeldspathic

matrix that contains quartz "eyes" and fragments of meta-arenite (+) and schist (D). Typically 

spangled with very large muscovite porphyroblasts. Upper part of unit (Clo) contains more than 

50 percent olistoliths of metaarenite and schist. Thickness is indeterminate

CZo Oella Formation (Lower Cambrian and (or) Neoproterozoic) (Crowley, 1976)~Light-gray,

medium-grained, well-bedded quartz-plagioclase-biotite meta-arenite and lesser quartzite and 

calc-silicate rock. Beds range from 5 in to 4 ft in thickness. Contains interbedded schist similar 

to the underlying Loch Raven Schist. Both the meta-arenite and quartzite have a good 

schistosity marked by biotite flakes. Thickness is indeterminate

27
GZ1 Loch Raven Schist (Lower Cambrian and (or) Neoproterozoic) (Crowley, 1976)--Thin-bedded, 

medium-gray, lustrous, medium- to coarse-grained quartz-muscovite-biotite-plagioclase schist 

that at places contains garnet and (or) staurolite and (or) kyanite. Contains some interbedded 

semipelitic schist and meta-arenite similar to the overlying Oella Formation (GZo) into which it 

grades. Thickness is indeterminate

'The term "Neoproterozoic" follows the usage of Plumb (1991) and applies to rocks ranging in age from 1000 Ma tc 

-544 Ma (base of Cambrian following Bowring and others, 1993; and Landing, 1994)

28
EXPLANATION OF MAP SYMBOLS 

Contact Dotted where concealed

Distribution and concentration of structural symbols indicates degree of reliability 

Faults Dotted where concealed 

Thrust Sawteeth on upper plate

Overturned thrust-Sawteeth in direction of dip; bar on tectonically higher plate 

Small fault seen in outcrop showing dip

FOLDS 

(Dotted where concealed)

Fold phases are designated from oldest to youngest: PA, Patapsco; MP, Middle 

Patuxent; CL, Columbia

4 T Antiform Showing crest line and direction of plunge

Overturned antiform Showing trace of axial surface, direction of dip of limbs, and 

direction of plunge

* Synform Showing trace of trough line and direction of plunge

Overturned synform Showing trace of axial surface, direction of dip of limbs, and 

direction of plunge

MINOR FOLDS 

(F indicates fold of foliation)

//- ^ ^ Minor asymmetric fold Showing bearing and plunge of axis, and rotation sense viewed 

down plunge

10 4 ^_ Minor M-shaped fold Showing bearing and plunge of axis 

Minor anticline Showing bearing and plunge of axis

 C-3 Layering

PLANAR FEATURES 

(Symbols intersect at point of observations. May be combined with linear features)

Strike and dip of crystallization foliation

Inclined

Vertical

Mylonitic foliatioa

"29
Flow foliation

 £* Inclined

 B Vertical

IS 

U- u II Shear band foliation-Showing relative movement

t ' Schistosity

ui Spaced schistosity

Strike and dip of joints

80

 m Inclined

-* Vertical

LINEAR FEATURES 

(May be combined with planar features)

l» 4. Mineral lineation

/£< Elongation lineation 

e.

OTHER FEATURES

7\ Abandoned quarry Building stone, bs; Crushed stone, cs 

Mil Location of chemically analysed sample 

Location of isotopically dated sample 

Float

30