Qal
Alluvium
Quaternary
Well to poorly sorted, reddish-brown to grayish-brown mixture of unconsolidated rounded pebbles, cobbles, boulders, sand, silt and clay. These deposits form in stream channels, and on the flood plain adjacent to streams. Thickness varies from thin veneer
01-01-01-01
DMUHeader1
254 249 194
no pattern
DS1
Alluvial sediment
High
DMU_1
Qc
Colluvium
Unsorted, light-gray to reddish-gray, angular to subangular pebbles, cobbles, boulders and sand that accumulate on slopes below outcrops, in hillslope depressions, and are present at the foot of prominent mountain ridges. Formed by the slow downslope mov
01-01-01-02
248 215 147
Colluvium and other widespread mass-movement sediment
DMU_2
Qr
Residuum
Mixture of moderate reddish brown soil and rounded to angular pebbles, cobbles, and locally blocks of grayish-pink to white quartz. Thickness ranges from a veneer to 10 feet (3 m).
01-01-01-03
242 229 78
Residual material
DMU_3
Qt
Terrace deposits
Reddish-brown to light-brown, sandy and clayey mixture of rounded pebbles to cobbles of sandstone, vein quartz, and quartzite. Locally present on elevated low relief areas above creeks and drainages. Thickness ranges from a thin veneer to more than 10 fe
01-01-01-04
254 234 133
DMU_4
Mp
Purslane Formation
Mississippian
Light-gray, tan and reddish-brown, coarse-grained to conglomeratic, thick-bedded to cross-bedded sandstone and thin beds of gray shale and coaly shale. The Purslane is more than 300 feet (90 m) thick in western Washington County.
02-01-01-01
204 235 255
Clastic sedimentary rock
DMU_5
MDr
Rockwell Formation
Mississippian-Devonian
Interbedded, gray silty shale, light-gray to tan sandstone, and coaly and reddish shale. In Washington County, a reddish-brown to gray polymictic diamictite marks the base of the formation. The Rockwell Formation is more than 400 feet (120 m) thick in we
02-01-01-02
128 179 222
Sandstone and mudstone
DMU_6
Dh
Hampshire Formation
Devonian
Interbedded, reddish-brown to brownish-red, locally greenish-gray sandstone, reddish-brown siltstone, shale, and rooted claystone. The thickness of the Hampshire is more than 3,000 feet (900 m) in western Washington County.
02-01-01-03
179 179 255
Mostly sandstone
DMU_7
Df
Foreknobs Formation
Interbedded, olive-gray medium- to coarse-grained, cross-bedded sandstone and greenish-gray to dusky-red, fossiliferous shale and siltstone. Thick (>30 feet) sandstone intervals occur near the base and near the top of the formation. The Foreknobs is more
02-01-01-04
204 204 255
DMU_8
Dhbs
Harrell-Brallier-Sherr Formations (undivided)
The Harrell Shale is a dark-gray, fissile, calcareous, thinly laminated shale that weathers to thin, yellowish-gray shale chips. The base of the Harrell is marked by the black, very fissile Burket Shale Member. The Harrell grades eastward into the Bralli
02-01-01-05
166 179 242
Mudstone
DMU_9
Dm
Mahantango Formation
Medium-gray to olive-gray massive siltstone to fine-grained sandstone occurs near the base and top of the formation and is interbedded with siltstone, sandstone, with silty, hackly shale. Weathers brownish-gray to grayish-brown. The Mahantango Formation
02-01-01-06
179 204 255
DMU_10
Dnm
Needmore-Marcellus Shales
Medium to dark brownish gray to medium dark gray, calcareous, fossiliferous shale, with thin (30 cm) beds of dark-gray, argillaceous limestone. The upper Needmore Shale consists of approximately 35 feet (10 m) of interbedded, dark-gray, argillaceous lime
02-01-01-07
140 140 255
Mostly mudstone
DMU_11
Do
Oriskany Sandstone
Interbedded, medium- to dark-gray, siliceous shale and sandy and cherty limestone near the base (Shriver Shale Member), overlain by tan, fine-grained, calcareous sandstone, and then by light-gray, medium- to coarse-grained, thin- to thick-bedded, calcare
02-01-01-08
191 179 242
DMU_12
DSkh
Keyser-Helderberg Formations (undivided)
Devonian-Silurian
The Keyser Limestone consists of light-gray, coarsely crystalline, crinoidal limestone in the lower 50 feet (15 m), becoming medium- to dark-gray, medium- to thick-bedded, nodular, fossiliferous limestone containing dark-gray chert nodules. The upper Key
02-01-01-09
217 217 255
Limestone
DMU_13
Sto
Tonoloway Formation
Silurian
Medium- to light-gray, fine-grained, thinly laminated, mudcracked, dolomitic limestone with thin layers of medium-gray, fine-grained limestone, and tan laminated dolomite. The Tonoloway Limestone is approximately 400 feet thick (120 m).
02-01-01-10
204 179 255
DMU_14
Swc
Wills Creek Formation
Interbedded, greenish-gray to light-gray, calcareous shale and tan, dolomitic shale containing mud cracks, laminations, and salt and gypsum casts. The thickness of the Wills Creek is approximately 400 feet (120 m).
02-01-01-11
179 153 235
DMU_15
Sb
Bloomsburg Formation
Interbedded, reddish-gray to brownish-gray, fine-grained sandstone and hackly shale to mudrock. The Bloomsburg Formation rarely exceeds 100 feet in thickness (30 m).
02-01-01-12
204 153 255
DMU_16
Sm
McKenzie Formation
Interbedded, greenish-gray, calcareous shale and medium- to dark-gray, thinly bedded, fossiliferous limestone. The McKenzie Formation is up to 300 feet thick (90 m).
02-01-01-13
230 179 235
DMU_17
Sk
Keefer Sandstone
Light-gray to yellowish-gray, fine- to medium-grained sandstone that weathers light-gray to yellowish-tan. The unit is thin-bedded in the lower part and thick-bedded in the middle and upper part, with lumpy and irregular bedding planes. The Keefer is mod
02-01-01-14
217 199 255
Conglomerate
DMU_18
Srh
Rose Hill Formation
Light-olive to pale reddish-gray, light-gray, greenish-gray, and deep purple shale, brownish-red sandstone, and thin reddish siltstone. The Rose Hill Formation is mostly fissile, papery shale, weathering to rusty chips. The shale is interbedded with thin
02-01-01-15
235 204 255
DMU_19
St
Tuscarora Sandstone
Light-gray, fine- to medium-grained, medium-bedded, dense sandstone. Locally, sandstone layers are interbedded with thin gray shale. The thickness of the Tuscarora Sandstone is less than 50 feet (15 m) in Washington County.
02-01-01-16
242 214 242
Sandstone
DMU_20
Oj
Juniata Formation
Ordovician
Interbedded, reddish-brown to brownish-red, fine- to medium-grained, medium- to thick-bedded, cross-bedded sandstone and micaceous siltstone and silty shale. The Juniata Formation is estimated at 200 feet thick (60 m).
02-01-01-17
224 112 222
DMU_21
Om
Martinsburg Shale
Medium- to dark-gray, fissile shale at the base, overlain by medium-gray, silty shale and thinly interbedded medium-grained sandstone, and then by thick-bedded, medium-grained, fining upward sandstone at the top of the formation. The Martinsburg is up to
02-01-01-18
255 128 222
DMU_22
Omu
Martinsburg Formation, upper member
Interbedded medium-gray shale and thin, light-gray to tan, silty sandstone at the base, grading upward into interbedded greenish-gray to medium-gray siltstone and silty shale with medium- to thick-bedded medium- to coarse-grained sandstone. Thickness est
02-02-01-01-01
242 140 230
DMU_23
Oml
Martinsburg Formation, lower member
Predominately medium- to dark-gray, silty, fissile shale with thin (<0.5 inches) siltstone interbeds. Dark-gray to black shale at base is equivalent to the Utica Shale. Thickness estimated at 1500 to 2000 feet (457 to 610 m).
02-02-01-01-02
235 128 204
DMU_24
Oc
Chambersberg Formation
Medium- to dark-gray, nodular- to medium-bedded, fossiliferous limestone. Nodular-bedded, shaly, highly fossiliferous limestone bearing the echinoderm Echinosphaerites occurs near the base of the formation. Top of the Chambersburg Formation is marked by
02-02-01-02
230 179 233
DMU_25
Osp
St. Paul Group (undivided)
Massive, light-gray lime mudstone containing fenestral fabric at the base (Row Park Limestone), overlain by interbedded, medium- to light-gray, medium-bedded limestone and laminated dolomitic limestone at the top (New Market Limestone). The thickness of
02-02-01-03
255 166 255
DMU_26
Ops
Pinesburg Station Dolomite
Light-gray to tan, medium-bedded, highly fractured, fine-grained dolomite. Weathers to a very light gray surface. Interbedded with very light gray, laminated dolomite. Thickness is 350 to 400 feet (107 to 122 m).
02-02-01-04
255 204 255
Dolomite
DMU_27
Orr
Rockdale Run Formation
Interbedded and cyclic limestone and dolomite, cherty in the lower 400 feet (120 m). Limestone intervals consist of medium- to light-gray, ribbony and thrombolitic to stromatolitic lime mudstone to boundstone. Locally, limestone layers are light-gray ool
02-02-01-05
235 153 214
DMU_28
Osdf
Dam Five Member
Stonehenge Formation, Dam Five Member
Medium- to dark-gray, medium-bedded, ribbony and oolitic, lime mudstone to packstone. Near the base of the member, ribbony lime mudstone predominates. Upsection, medium-gray, ribbony lime mudstone becomes interbedded with intervals of flat-pebble lime gr
02-02-01-06-01
255 222 255
Mostly carbonate rock
DMU_29
Osf
Funkstown Member
Stonehenge Formation, Funkstown Member
The lower part of the member is composed of massive, medium-gray, algal lime boundstone with some layers up to 7 m thick. Grading upsection into interbedded medium- to dark-gray algal thrombolites 1.5 to 2.0 m thick and medium-gray, thinly bedded to ribb
02-02-01-06-02
245 186 250
DMU_30
Oss
Stoufferstown Member
Stonehenge Formation, Stoufferstown Member
Dark-gray, argillaceous, thinly bedded to ribbony, lime mudstone with thin beds of flat-pebble lime grainstone conglomerate and hummocky, discontinuous, laminated limestone. A single, 10-foot (3 m) interval of massive, dark-gray, thrombolitic, algal boun
02-02-01-06-03
235 128 235
DMU_31
Ccsg
Shady Grove Member
Conococheague Formation, Shady Grove Member
Cambrian
Interbedded, medium- to light-gray, ribbony lime mudstone that weathers to flaggy to platy beds, and arenaceous grainstones exhibiting edgewise and flat-pebble conglomerates. Locally, thin pastel blue and pink marble strata are developed. Black or gray c
02-02-01-07-01
255 217 230
DMU_32
Ccz
Zullinger Member
Conococheague Formation, Zullinger Member
Predominantly cyclically bedded, medium- to dark-gray, thrombolitic limestone and gray, ribbony and laminated limestone and tan, laminated dolomite. Thrombolites range in thickness from 3 to 6 feet (1 to 2 m) within thrombolitic intervals to less than 1
02-02-01-07-02
255 191 217
DMU_33
Ccb
Big Spring Station Member
Conococheague Formation, Big Spring Station Member
Tan, massive dolomite interbedded with tan to light-gray, laminated dolomite; unit characterized by dark-brown weathering. At the type section on the western side of the Hagerstown Valley, this member is characterized by interbeds of light-gray, cross-be
02-02-01-07-03
255 166 204
DMU_34
Ce
Elbrook Formation
Lower part of the formation is very poorly exposed and contains interbedded tan, thin- to thick-bedded limestone and dolomite, which frequently weather shaly and are intercalated with medium-bedded, dark-gray limestone. Middle part of the formation conta
02-02-01-08
255 153 179
DMU_35
Cwac
Chewsville Member
Waynesboro Formation, Chewsville Member
Reddish-brown to chocolate-brown, silty shale, siltstone, and silty fine-grained sandstone, interbedded with white, calcareous, Skolithus-burrowed sandstone beds (2 to 6 cm thick) and tan to buff, medium-bedded, sandy dolostone. This unit usually is the
02-02-01-09-01
255 171 222
DMU_36
Cwak
Cavetown Member
Waynesboro Formation, Cavetown Member
Medium- to thick-bedded, medium- to coarse-grained, intraclastic grainstone; tan, laminated dolostone and dolomitic limestone; and medium-gray, oolitic, lime grainstone, ribbony carbonates, and burrowed-mottled dolomitic limestone. This unit is typically
02-02-01-09-02
255 133 207
DMU_37
Cwar
Red Run Member
Waynesboro Formation, Red Run Member
Interbedded, tan-weathering, punky, fine-grained sandstones; green-gray shale; gray sandy limestone; and laminated dolostone. Locally thin (0.6 to 5 cm) layers of red siltstone and sandstone are present. Typically, this unit forms a low ridge somewhat lo
02-02-01-09-03
255 110 163
DMU_38
Ct
Tomstown Formation
Predominantly buff-weathering, medium- to dark-gray dolomite, dolomitic limestone, and limestone. Divided into 4 members. Total thickness is 1,200 to 1,300 feet (366 to 396 m).
02-02-01-10
204 128 153
DMU_39
Ctd
Dargan Member
Tomstown Formation, Dargan Member
Interbedded and cyclical dolomite and limestone. Cycles consist of alternations of dark-gray, bioturbated dolomite and medium- to dark-gray, laminated dolomite, or dark-gray dolomite or limestone and tan, laminated, silty dolomite. Cycles of thin-bedded
02-02-01-10-01
252 204 179
DMU_40
Ctb
Benevola Member
Tomstown Formation, Benevola Member
Light-gray to white, massive to poorly bedded, highly fractured, sugary dolomite. The Benevola Member varies from white to very light gray, on both fresh and weathered surfaces. Bedding is rarely evident, except within polished slabs where faint ghosts o
02-02-01-10-02
242 158 179
DMU_41
Ctf
Fort Duncan Member
Tomstown Formation, Fort Duncan Member
Medium- to dark-gray, thick-bedded, mottled dolomite with white, void-filling, sparry dolomite. Weathered surface characterized by irregular, clotted to anastomosing network of algae. Layers of the white, sparry dolomite, 0.5 to 1.5 inches wide, fill voi
02-02-01-10-03
217 102 128
DMU_42
Ctbh
Bolivar Heights Member
Tomstown Formation, Bolivar Heights Member
The Bolivar Heights Member is characterized by three stratigraphically stacked lithologies. The basal lithology is a tan, vuggy dolomite that is in contact with the underlying Antietam Formation. This dolomite ranges from 10 to 40 feet (9 to 12 m) in thi
02-02-01-10-04
255 191 166
DMU_43
Ca
Antietam Formation
The lower part of the formation is greenish-gray, highly cleaved, slaty, phyllitic shale and siltstone interbedded with white, Skolithos-burrowed, and fine-grained sandstone. These lower strata grade upsection into medium-bedded, white, bioturbated and c
03-01-01-01
235 128 153
DMU_44
Ch
Harpers Formation
Brownish-gray to dark greenish gray, silty phyllitic shale to highly sheared phyllitic siltstone with intervals of brownish-gray, medium-grained, silty sandstone. On Catoctin Mountain: light brownish gray to light olive gray, sheared, muscovite(?)-serici
03-01-01-02
247 196 222
DMU_45
Chm
Harpers Formation, metasandstone
Commonly thin (1 inch to 16 feet; 3 cm to 5 m), dark green gray, fine to medium-grained, highly argillaceous metasandstones containing Skolithus burrows, especially near the top of the formation. Mappable metasandstone intervals are up to 30 feet (10 m)
03-01-01-02-01
217 110 159
Metasedimentary rock
DMU_46
Chma
Mont Alto Member
Harpers Formation, Mont Alto Member
Light-to medium-gray, coarse grained to conglomeratic, crossbedded quartzite, commonly less than 30 feet (10 m) in thickness.
03-01-01-02-02
255 176 231
Quartzite
DMU_47
Cwo
Owens Creek Member
Weverton Formation, Owens Creek Member
Dark to very dark gray, very coarse grained to conglomeratic, crossbedded graywacke. Although commonly crossbedded, the very coarse grained nature of this unit makes recognition of crossbedding difficult. Large (1 to 3 cm) white and pink quartz pebbles a
03-01-01-03-01
212 120 120
DMU_48
Cwm
Maryland Heights Member
Weverton Formation, Maryland Heights Member
Thin (less than 33 feet; 10 m), medium- to dark-gray quartzite and graywacke interbedded with very dark gray, highly cleaved siltstone and phyllitic shale. Shales and siltstones are very poorly exposed and individual quartzites and graywackes are only lo
03-01-01-03-02
247 153 153
DMU_49
Cwb
Buzzard Knob Member
Weverton Formation, Buzzard Knob Member
Light-gray to medium-gray, medium-bedded quartzite with dark-gray, argillaceous layers up to 4 cm thick separating the quartzite beds. Crossbedding within individual quartzite strata is pervasive. The Buzzard Knob Member has an estimated thickness of 50
03-01-01-03-03
255 222 209
DMU_51
CZl
Loudoun Formation
Late Proterozoic? Cambrian?
Medium- to dark-gray, medium-bedded conglomerate and black, tuffaceous phyllite. Lithology is very variable, ranging from a crossbedded quartz-pebble conglomerate to a highly cleaved polymictic conglomerate with a matrix of flattened phyllite pebbles. Th
03-01-01-04
240 179 179
DMU_52
CZlc
Loudoun Formation, conglomerate
Medium-bedded, medium light gray, grayish yellow green or dusky blue conglomerate that weathers light-gray and greenish-gray or dusky blue. Contains oval pebbles of quartz, quartzite, rhyolite, and granite(?) that are 0.5 to 4.0 cm long, and flattened, d
03-01-01-04-01
219 168 168
DMU_53
Zcr
Catoctin Formation, metarhyolite
Late Proterozoic
Undifferentiated bluish-gray metarhyolite in which no single variety is dominant.
03-01-01-05-01
193 135 77
Meta-felsic and intermediate rock
DMU_54
Zcra
Catoctin Formation, aphanitic metarhyolite
Aphanitic, bluish-gray metarhyolite that is massive and dense, and exhibits a conchoidal fracture. Rare phenocrysts, where present, comprise less than 1 percent of the rock. Weathers bone white to very light gray.
03-01-01-05-02
232 219 204
DMU_55
Zcrb
Catoctin Formation, metarhyolite breccia
Dusky blue-gray, metarhyolite breccia with angular to subrounded clasts that weather to a lighter color than the felsic matrix.
03-01-01-05-03
143 110 89
DMU_56
Zcrf
Catoctin Formation, flow banded metarhyolite
Flow-banded, bluish-gray metarhyolite containing nearly planar, locally convoluted flow bands 0.12 to 0.4 inch (3 to 10 mm) thick. Laminae are discontinuous and most prominent on weathered surfaces. Phenocrysts constitute less than 2 percent of the rock.
03-01-01-05-04
191 138 102
DMU_57
Zcrp
Catoctin Formation, porphyritic metarhyolite
Porphyritic, bluish-gray metarhyolite with conspicuous very light gray to very pale orange or pinkish-gray feldspar laths. Phenocrysts are up to 0.2 inches (6 mm) long and make up 2 to 5 percent of the rock.
03-01-01-05-05
179 130 110
DMU_58
Zcrr
Catoctin Formation, red metarhyolite
Grayish-red to dusky reddish purple, porphyritic metarhyolite. Phenocrysts make up 3 to 5 percent of the rock and are predominately euhedral, pink to light-gray feldspar and reddish quartz. Estimated thickness 200 to 300 feet (20 to 90 m).
03-01-01-05-06
204 150 128
DMU_59
Zcdf
Catoctin Formation, felsic dikes
Massive, light-gray to medium-gray felsite; weathers light orange brown. Contains very few small feldspar phenocrysts.
03-01-01-05-07
242 89 140
Fine-grained, felsic-composition intrusive igneous rock
DMU_60
Zcm
Catoctin Formation, metabasalt
Medium to dark greenish gray, chloritic, locally amygdaloidal, epidote-rich metabasalt. Some areas are composed of highly sheared chlorite schist. Epidote occurs as light-green veins and nodules. Thickness estimated at greater than 1000 feet by Fauth (19
03-01-01-05-08
222 204 179
Meta-mafic rock
DMU_61
Zcmp
Catoctin Formation, porphyritic metabasalt
Greenish-gray to bluish-green rock that weathers bluish-gray to dark greenish gray. Very prominent white to very light gray, randomly oriented lath-shaped feldspar (albite?) phenocrysts. Individual crystals or aggregates may range in length from 1 to 25
03-01-01-05-09
186 153 128
DMU_62
Zcp
Catoctin Formation, phyllite
Light-to medium-gray phyllite containing highly elongated light-gray flecks and blebs. Thickness of this unit appears to be less than 100 feet.
03-01-01-05-10
204 179 128
Slate and phyllite, of sedimentary-rock origin
DMU_63
Zcp1
Catoctin Formation, phyllite unit 1
Poorly exposed, lustrous, light-gray to medium dark gray, olive-gray phyllite, or mottled yellowish-gray and medium-gray phyllite. Commonly contain numerous light-colored, flattened and elongate blebs from 1x10 to 10x20 mm in size. Unit thickness is esti
03-01-01-05-11
153 128 89
DMU_64
Zcp2
Catoctin Formation, phyllite unit 2
Light greenish gray, moderate greenish gray and very light gray streaked phyllite; may be silicified. Weathered surfaces commonly soft and soapy. Lithologically similar to parts of the lavender phyllite exposed in adjacent parts of the Myersville 7.5-min
03-01-01-05-12
214 201 158
DMU_65
Zcp3
Catoctin Formation, phyllite unit 3
Medium dark gray, medium bluish gray, or light-gray phyllite containing blebs 2 to 4 mm long. Weathers to light-colored, flat or platy fragments up to 15x40 cm in size. Estimated thickness between 30 and 60 feet (9 and 15 m).
03-01-01-05-13
191 166 128
DMU_66
Zcpl
Catoctin Formation, lavender phyllite
Pale purple to grayish red-purple or very light gray phyllite. Locally, color is mottled with red quartz grains and light-gray to yellowish-gray porphyroblasts of feldspar. Estimated thickness of 30 to 50 feet (9 to 15 m).
03-01-01-05-14
217 196 184
DMU_67
Zcb
Catoctin Formation, basaltic dike
Dark greenish gray, locally phyllitic and chloritic basalt. Commonly has strongly developed cleavage. These bodies are present in the basement gneiss complex and appear to represent dikes that once contacted the main Catoctin outcrop belt.
03-01-01-05-15
204 179 179
Extrusive igneous material
DMU_68
Zcd
Catoctin Formation, mafic dikes
Typically dark greenish gray to grayish olive green, fine- to medium-grained metadiabase or metabasalt. Commonly occurs as dikes and sills(?) intruding rocks of basement gneiss complex. Crosscutting relationships with older, gneissic structure discernibl
03-01-01-05-16
191 77 115
DMU_69
Zsr
Swift Run Formation
Medium gray brown, silty sandstone with intervals of very light gray, foliated, micaceous marble. Marble locally quarried for agricultural purposes. Thickness estimated at 0 to 200 feet (0 to 60 m).
03-01-01-06
204 128 179
Meta-carbonate rock
DMU_70
Zsrp
Swift Run Formation, phyllite
Very light gray, dusky yellow green and very light greenish gray, lustrous quartz sericite(?) phyllite that weathers grayish-orange to very light gray. Quartz occurs as medium to coarse detrital grains either uniformly disseminated throughout the rock or
03-01-01-06-01
217 166 191
DMU_71
Zsrq
Swift Run Formation, quartzite
Very light gray, thin-bedded, laminated and cross-laminated sericitic quartzite that weathers light greenish gray to light-gray; and medium light gray, thick-bedded, coarse-grained, laminated quartzite, weathering light-gray. Locally, a white to very lig
03-01-01-06-02
236 206 218
DMU_72
Ygl
Basement gneiss complex, leucocratic gneiss
Middle Proterozoic
Fine- to medium-grained, tan to very light gray, massive, finely banded to indistinctly foliated chlorite-quartz-microcline-plagioclase gneiss. Very light gray to yellowish-gray granitic rock weathers very pale orange, grayish-pink, and grayish-orange to
03-01-01-07-01
161 189 138
Medium and high-grade regional metamorphic rock, of unspecified origin
DMU_73
Ygt
Basement gneiss complex, garnet gneiss
Fine- to medium-grained, very light gray, finely banded to indistinctly foliated quartz-microcline-plagioclase gneiss. Similar to leucocratic gneiss, but with scattered garnets. Weathers light-gray to yellowish.
03-01-01-07-02
199 215 158
Schist and gneiss, of sedimentary-rock origin
DMU_74
Ygb
Basement gneiss complex, biotite gneiss
Fine- to medium-grained, very light gray to yellowish-gray granitic rock that weathers very pale orange, grayish-pink, and grayish-orange to pale brown. Usually massive, but a faint foliation is commonly discernible. Quartz occurs in prominent grayish-bl
03-01-01-07-03
179 204 128
DMU_75
Ygh
Basement gneiss complex, hornblende gneiss
Medium-grained, granular, massive or poorly foliated biotite-hornblende-plagioclase gneiss that weathers light olive gray, pale olive, or greenish-gray. May contain prominent greenish-black hornblende porphyroblasts 5 to 10 mm long. Hornblende, grayish-b
03-01-01-07-04
204 204 153
DMU_76
Ygp
Basement gneiss complex, paragneiss
Fine- to medium-grained, tan to rusty red, highly foliated micaceous-quartz-garnet paragneiss to schist. Weathers to a yellowish-brown or very pale orange, schistose rock.
03-01-01-07-05
204 235 153
DMU_77
Jd
Jurassic Dikes
Jurassic
Medium- to dark-gray, medium- to fine-grained diabase, weathering to rusty orange-brown spheroidal boulders and cobbles. Diabase dike(s) range in thickness from 3 to 15 feet (1 to 5 m).
04-01-01-01
255 77 0
Fine-grained, intermediate-composition intrusive igneous rock
DMU_78
JTrtm
Thermally metamorphosed rocks
Triassic
Medium- to olive-gray, hard, brittle, and fractured hornfels and meta-arkose, adjacent to diabase intrusions. Includes dark-gray to olive-black hornfels in contact metamorphic zones that are a few feet wide adjacent to narrow dikes but may be hundreds of
04-01-01-02
140 167 189
Contact-metamorphic rock
DMU_79
Trg
Gettysburg Formation
Reddish-brown to reddish-gray, locally greenish-gray, medium-grained siltstone, claystone, mudstone, and fine-grained sandstone. Sandstone beds exhibit sharp bases, shale pebble-lag conglomerates, and fining upward character. Claystone intervals are thor
04-02-01-01
158 209 209
DMU_80
Trgc
Gettysburg Formation, conglomerate
Limestone conglomerate marks the western edge of the Gettysburg Basin in Maryland and is similar in appearance and position to the Leesburg Formation in the Culpeper Basin. Thickness is in question, but may be as much as 2438 m (8000 feet).
04-02-01-01-01
194 232 232
DMU_81
Trgh
Heidlersburg Member
Gettysburg Formation, Heidlersburg Member
Interbedded gray calcareous siltstone and shale; laminated, mudcracked, and brecciated limestone; and dark grayish brown to reddish-brown siltstone and shale. Bedding is defined by cycles of gray siltstone and shale grading upward into gray, laminated li
04-02-01-01-02
27 183 222
DMU_82
Trn
New Oxford Formation
Brownish-red to dark reddish brown, argillaceous to silty sandstone and micaceous siltstone with subordinate interbedded silty shale and mudstone. Some reddish-gray to gray arkosic sandstone also occurs. Claystone intervals are thoroughly root-mottled an
04-02-01-02
153 245 240
DMU_83
Trns
New Oxford Formation, sandstone
Interbedded, light reddish gray to reddish-brown sandstone. Sandstones exhibit sharp bases with shale-pebble lag conglomerates, and fining upward character.
04-02-01-02-01
128 235 224
DMU_84
Trni
Irishtown Member
New Oxford Formation, Irishtown Member
Light reddish gray, subangular to subrounded, quartz and limestone conglomerate. Clasts are predominately gray limestone, tan dolostone, or quartz pebbles with a matrix of reddish-brown, calcareous mudstone. Poorly exposed, and thickness is in question (
04-02-01-02-02
102 207 204
DMU_85
Trl
Leesburg Formation
Light-gray to light reddish gray, very thickly bedded, boulder conglomerate. Clasts are mainly subangular to subrounded limestone and dolostone of Cambrian and Ordovician age, but locally Triassic age siltstone and sandstone are prevalent. Thickness rang
04-02-02-01
102 191 204
DMU_86
Trb
Balls Bluff Siltstone
Brownish-red to reddish-brown, argillaceous, massive siltstone with thin fine-grained sandstone interbeds. Thickness is estimated at 200 to 4500 feet (61 to 1372 m).
04-02-02-02
140 217 230
DMU_87
Trmp
Poolesville Member
Manassas Formation, Poolesville Member
Reddish-brown to reddish-gray, locally greenish-gray, medium-grained sandstone and reddish, variegated claystone. Sandstone beds exhibit sharp, convex-down bases, shale-pebble lag conglomerates, and fining-upward character. Claystone intervals are thorou
04-02-02-03-01
166 204 230
DMU_88
Trmps
Poolesville Member, sandstone beds
Manassas Formation, Poolesville Member, sandstone beds
Medium-grained sandstone beds exhibiting sharp, convex-down bases, shale-pebble lag conglomerates and fining upward character.
04-02-02-03-01-01
102 166 204
DMU_89
Trmt
Tuscarora Creek Member
Manassas Formation, Tuscarora Creek Member
Light-gray to light reddish gray, subangular to subrounded, limestone and dolomite conglomerate. Clasts are predominately tan dolostone, but locally reddish siltstone, sandstone, and some limestone clasts are prevalent. Matrix is a reddish-brown calcareo
04-02-02-03-02
189 219 235
Carbonate rock
DMU_90
Ogw
Woodsboro Member
Grove Formation, Woodsboro Member
Thin-bedded, dark-gray, fine-grained limestone interbedded with medium-bedded, bioturbated, dark-gray, fine-grained limestone, and thin, wavy bedded limestone with tan, dolomitic partings. Top of Woodsboro Member not exposed because it is covered by the
04-02-03-01-01
DMU_91
Ogf
Fountain Rock Member
Grove Formation, Fountain Rock Member
Very thickly bedded, medium light gray, locally sandy, thrombolitic and stromatolitic algal limestone and medium-gray, laminated dolomitic limestone and olive-gray dolomite. Thickness is in question, but may range from 1000 to 3300 feet (305 m to 1006 m)
04-02-03-01-02
255 179 255
DMU_92
Ogfs
Fountain Rock Member, sandstone
Grove Formation, Fountain Rock Member, sandstone
Two cross-bedded sandstone units recognized in the middle of the formation were identified and traced.
04-02-03-01-02-01
255 153 255
DMU_93
Ogc
Ceresville Member
Grove Formation, Ceresville Member
Medium light gray to medium-gray, thick-bedded and cross-bedded, arenaceous limestone and sandy, dolomitic limestone with thin interbeds (1 ft or 0.3 m) of medium light gray, sandy, thrombolitic dolomite. Thickness is approximately 150 to 200 feet (46 to
04-02-03-01-03
255 128 255
DMU_94
Cfu
Frederick Formation, undivided
Medium- to dark-gray, thin- to medium-bedded, pyritic, argillaceous limestone and shaly limestone. Contains intervals of tan-weathering dolomitic shale and sandy brecciated limestone. In the Emmitsburg Quadrangle, the Frederick Formation is highly sheare
04-02-03-02
255 145 114
DMU_95
Cfa
Adamstown Member
Frederick Formation, Adamstown Member
Thinly interbedded, medium dark gray to dark-gray, argillaceous, fine-grained limestone and dusky yellow to medium dark gray, silty dolomite. Limestone beds range from 0.1 to 2.0 inches (0.3 to 5.1 cm) in thickness. Several thin (6.0 to 30 feet or 1.8 to
04-02-03-02-02
255 204 204
DMU_96
Cfl
Lime Kiln Member
Frederick Formation, Lime Kiln Member
Interbedded, thinly laminated to thinly bedded, dark-gray, fine-grained limestone, calcareous shale, and medium-bedded, fine-grained limestone near the base, becoming more thickly interbedded toward the top with medium dark gray, fine-grained limestone w
04-02-03-02-01
240 153 166
DMU_97
Cfr
Rocky Springs Station Member
Frederick Formation, Rocky Springs Station Member
Interbedded dark-gray, thinly bedded, lime mudstone and black dolomitic shale, massive, medium-gray polymictic breccias, medium-gray sandy limestone, and dark-gray, flaggy lime mudstone. Top of the member is mapped at the top of the stratigraphically hig
04-02-03-02-03
255 166 140
DMU_98
Cfrb
Rocky Springs Station Member, breccia
Frederick Formation, Rocky Springs Station Member, breccia
Massive, medium-gray, polymictic breccias on the western flank of the synclinorium but are not evident on the east flank.
04-02-03-02-03-01
255 120 120
DMU_99
Cfm
Monocacy Member
Frederick Formation, Monocacy Member
Thickly interbedded, black, platy shale, rubbly, dolomitic breccia, laminated lime mudstone, and black shale. A laterally continuous black shale marks the top of the member. Thickness of this member is approximately 200 feet (61 m).
04-02-03-02-04-02
255 143 133
DMU_100
Cfms
Monocacy Member, shale bed
Frederick Formation, Monocacy Member, shale bed
Black shale that marks the top of the Monocacy Member and is more than 50 feet (15 m) thick.
04-02-03-02-04-01
255 179 128
DMU_101
Car
Araby Formation
Thickly bedded, greenish-black to grayish-black, very fine grained to fine-grained, burrow-mottled silty sandstone, interbedded with medium-gray to grayish-black, phyllitic shales 1 to 3 m thick. Top of the formation consists of grayish-black phyllitic s
04-02-03-03
255 166 184
DMU_102
CZi
Ijamsville Phyllite
Dusky blue, grayish-blue, very dusky red-purple, greenish-gray to pale olive phyllite, phyllonite, and minor slate. Phyllite contains mostly muscovite and chlorite. Lustrous sheen from mica and dark color results from abundant hematite dust.
04-03-02-03
235 173 194
DMU_103
CZiq
Ijamsville Phyllite, quartzite
Yellowish-gray, fine- to medium-grained, sericitic quartzite locally intervenes between phyllite and metabasalt.
04-03-02-03-01
191 128 128
DMU_104
CZib
Ijamsville Phyllite, metabasalt
Dark-green and schistose metabasalt composed of chlorite, epidote, and quartz. Rare pillows locally preserved. Mapped as thin unit east of Martic thrust fault contact with Urbana Formation; one small body mapped in fault slice near confluence of Potomac
04-03-02-03-02
189 190 129
DMU_105
CZic
Ijamsville Phyllite, conglomeratic metagraywacke
Light-gray and green, medium- to coarse-grained metagraywacke with white quartz pebbles, variegated phyllite, and green chloritic matrix.
04-03-02-03-03
217 140 166
DMU_106
CZil
Ijamsville Phyllite, metalimestone
Light bluish gray to medium light gray, thin-bedded, laminated, carbonaceous and argillaceous metalimestone; and minor, medium dark gray, finely laminated, carbonaceous phyllite. Thin unit mapped from confluence of Potomac and Monocacy Rivers for about 5
04-03-02-03-04
151 127 102
DMU_107
CZim
Ijamsville Phyllite, marble
Light olive gray, sandy limestone and dusky red, calcareous quartzite occurs within phyllite locally.
04-03-02-03-05
204 140 179
DMU_108
CZip
Ijamsville Chlorite Phyllite
Light olive gray and greenish-gray, chlorite phyllite and metasiltstone.
04-03-02-03-06
209 153 163
DMU_109
CZmb
Marburg Formation
Buff to light olive green quartz-muscovite phyllite with subordinate silvery gray quartz-paragonite-muscovite-chlorite phyllite and muscovite-quartz phyllite. Contains abundant limonite cubes, up to 2 cm across, that are pseudomorphs after pyrite. Hemati
04-03-02-04
191 153 179
DMU_110
CZmbq
Marburg Formation, quartzite
Tan to reddish quartzite. Beds of quartzite 15 to 60 cm thick (6 to 24 inches) interbedded with muscovite and chlorite phyllites. Very resistant to weathering. Corresponds to the parts of the Ijamsville quartzite of Fisher (1978) that are associated with
04-03-02-04-01
149 152 128
DMU_111
CZscb
Sams Creek Formation, metabasalt
Dark greenish gray to medium bluish gray, aphanitic to porphyritic, massive to schistose metabasalt composed of chlorite, epidote, quartz, altered plagioclase, actinolite, hornblende, and albite; igneous texture is locally preserved and pods of epidosite
04-03-02-02-01
151 182 221
DMU_112
CZschp
Sams Creek Formation, hematite phyllite
Bluish-purple, hematite-rich phyllite, resembles Ijamsville Phyllite (Southworth et. al, 2008).
04-03-02-02-02
162 178 196
DMU_113
CZscm
Sams Creek Formation, marble
Brownish-gray to grayish reddish purple, massive to thin-bedded, calcitic and dolomitic marble containing quartz sand. Includes minor calcareous metasiltstone.
04-03-02-02-04
120 136 197
DMU_115
CZscmp
Sams Creek Muscovite Phyllite
Light bluish gray, dusky yellow, and moderate orange pink, muscovite-chlorite phyllite containing albite porphyroblasts, quartz, and hematite dust. Contains minor metasiltstone. Lithologically distinct from rocks of the Ijamsville Phyllite and Marburg Fo
04-03-02-02-05
208 205 207
DMU_116
CZscq
Sams Creek Formation, quartzite
Light-gray to grayish-green, medium-grained, thin-bedded to massive quartzite and minor calcareous sandstone. Contains detrital plagioclase, orthoclase, and polymictic quartz. Bedding is defined by concentrations of heavy minerals. Light-gray, medium- an
04-03-02-02-06
162 119 169
DMU_117
CZscqp
Sams Creek Formation, quartzite within phyllite subunit
Light-tan to light grayish green to light silvery gray. The micas and chlorite are typically segregated into prominent pinstripe laminations spaced 0.4 to 1.2 inches (1 to 3 cm) apart and parallel to cleavage. Resistant to weathering; crops out extensive
04-03-02-02-07
167 145 187
DMU_118
CZscs
Sams Creek Formation, metasiltstone
Metasiltstone, phyllite, quartzite, and metagraywacke, undifferentiated. Light-brown metasiltstone interbedded with quartzite and calcareous metasandstone. Bedding can be recognized except where transposed in shear zones adjacent to faults. Muscovite phy
04-03-02-02-08
141 130 159
DMU_119
CZscsr
Silver Run Limestone Member
Sams Creek Group, Silver Run Limestone Member
Medium to dark bluish gray, fine-grained, thin-bedded to laminated, siliceous to argillaceous or micaceous limestone, interbedded with minor amounts of black to silvery gray phyllite. Bedding ranges from 1/4 inch to 4 inches (0.5 to 10 cm) in thickness a
04-03-02-02-09
217 217 217
DMU_120
CZsctp
Sams Creek Formation, tuffaceous phyllite
Grayish red-purple and bluish-gray, variegated, vesicular phyllite with light-gray streaks and blebs of tuffaceous phyllite.
04-03-02-02-10
209 219 244
DMU_121
CZwm
Wakefield Marble
Predominately white to gray, massive to banded or bedded crystalline marble, but also contains dark-gray, bluish-gray, pale green, and purple marble and interbeds of green and purple phyllite. Some zones or layers of the marble are made up primarily of c
04-03-02-01
199 207 237
DS21
DMU_122
Cu
Urbana Formation
Predominately moderate olive brown to light olive gray, calcareous metagraywacke and metasiltstone. Poorly sorted, graded, cross-bedded, and ripple marked. Contains light olive gray and light brownish gray very calcareous metasandstone and quartzite. Fin
04-03-01-01
255 191 191
DMU_123
Cuq
Urbana Formation, quartzite
Light olive gray and light brownish gray, coarse-grained, thin- to medium-bedded, cross-bedded, pitted, vuggy, friable, lensoidal, and discontinuous quartzite.
04-03-01-01-01
255 166 166
DMU_124
Csq
Sugarloaf Mountain Quartzite
Pinkish-gray to white, fine-to medium-grained granular quartzite. Medium-bedded to massive, well-sorted, graded, crossbedded and ripple marked. Quartzite, interbedded with seldom-exposed moderate-brown quartzose metasiltstone and dusky blue laminated met
04-03-01-02
255 184 209
DMU_125
CZscl
Sams Creek Formation, metalimestone
Light-gray, thinly layered, argillaceous metalimestone (Southworth et. al, 2008).
04-03-02-02-03
144 153 177
DS4
DMU_127