| OBJECTID | MapUnit | Name | FullName | Age | Description | HierarchyKey | ParagraphStyle | Label | Symbol | AreaFillRGB | AreaFillPatternDescription | DescriptionSourceID | GeoMaterial | GeoMaterialConfidence | DescriptionOfMapUnits_ID |
|---|
| 1 | Qal | Alluvium | Alluvium | Quaternary | Grayish brown, light brown to reddish tan, poorly sorted, coarse to fine sand, silt, and clay with localized lenses of subrounded vein quartz cobbles. Locally, chips and angular cobbles of local bedrock are included. Thickness of this material ranges from a thin veneer up to 10 feet (3 meters). In smaller tributary streams alluvium has not been shown, but may still be present as a thin veneer overlying a bedrock channel. | 01-01 | DMU Unit 1 | Qal | 40 | 255,255,179 | None | MGS_LITTL2025.1 | Alluvial sediment, mostly coarse-grained | High | DMU001 |
| 2 | Qt | Terrace Deposits | Terrace Deposits | Quaternary | Reddish orange to light brown, sandy, clayey gravel with subrounded cobbles of quartz and local bedrock. Commonly occurs as a thin veneer that covers low-lands adjacent to present flood plains. Most extensively developed along Big Pipe Creek and Silver Run Creek. Thickness ranges from 0 to 10 feet (3 meters). | 02-01 | DMU Unit 1 | Qt | 71 | 255,235,102 | None | MGS_LITTL2025.1 | Alluvial sediment, mostly coarse-grained | High | DMU002 |
| 3 | Jd | Jurassic dike(s) | Jurassic dike(s) | Jurassic | Massive, medium to dark gray, fine- to medium-grained diabase, weathering orange brown. Occurs in dikes marked by rows of large, rounded, residual diabase boulders in the soil and at the surface. These dikes may be continuous and are shown as such. The age of the dikes in central Maryland and northern Virginia is early Jurassic (Kunk et al., 1992). | 03-01 | DMU Unit 1 | Jd | 01.03.02 | 255,0,0 | None | MGS_LITTL2025.1|GSA_AWP1992_24.2.25 | Coarse-grained, intermediate-composition intrusive igneous rock | Medium | DMU003 |
| 4 | Trn | New Oxford Formation | New Oxford Formation | Triassic | Interbedded pinkish gray, very coarse-grained, pebbly, trough cross-bedded, argillaceous, arkosic sandstones and reddish brown, silty rooted mudstone and laminated siltstone. Some reddish gray to gray arkosic sandstone (Trns) also occurs near the base of the formation. Sandstone vary from 5 to 15 feet in thickness, while siltstones range from 1 to 6 feet (30 cm- 2 m). Shales and mudstones are intensely rooted or fractures by closely spaced mudcracks that obscures primary bedding. The New Oxford Formation is best exposed in bluffs along Big Pipe Creek. Estimated thickness of the unit is about 1,000 feet (~300 meters). | 04-01 | DMU Unit 1 | ^n | 510 | 153,255,235 | None | MGS_LITTL2025.1 | Sandstone and mudstone | Medium | DMU004 |
| 5 | Trns | arkosic sandstone | arkosic sandstone subunit of the New Oxford Formation | Triassic | Reddish gray to gray arkosic sandstone (Trns) occurring near the base of the New Oxford Formation. | 04-01-01-01 | DMU Unit 3 | ^ns | 621 | 128,235,222 | None | MGS_LITTL2025.1 | Sandstone | High | DMU005 |
| 6 | Trni | Irishtown Member | Irishtown Member of the New Oxford Formation | Triassic | Localized massive to thick-bedded, grayish red conglomerates interbedded with reddish brown mudstone, shale, and siltstone. Clasts in the conglomerates are predominantly rounded to subrounded cobbles and pebbles of vein quartz and quartzite with maximum dimensions of 8 inches (20 cm) embedded in a reddish calcareous, mudstone matrix. The conglomerate beds creat loose and friable that weather free on the surface. Thickness of the member ranges from 0 to approximately 100 feet (30 meters) with an average of about 25 feet (8 meters). | 04-01-02 | DMU Unit 2 | ^ni | 705 | 102,153,255 | None | MGS_LITTL2025.1 | Conglomerate | High | DMU006 |
| 8 | CZscb | Sams Creek Formation metabasalt | Sams Creek Formation metabasalt | Late Proterozoic to early Cambrian | Olive green to dark greenish gray, foliated to flow banded, vesicular metabasalt. Basalt intervals appear to be interlayered with greenish gray to silvery gray, tuffaceous phyllite. Some beds are sheared and contain dark purple to black brecciated phyllite containing elongated clasts. | 05-01 | DMU Unit 1 | _Zscb | 344 | 204,179,179 | None | MGS_LITTL2025.1 | Mafic-composition lava flows | Medium | DMU007 |
| 9 | None | Ijamsville Formation | Ijamsville Formation | Late Proterozoic to early Cambrian | Gray, bluish gray, silvery gray, and greenish gray phyllite and limestone containing thin beds of tuffaceous sandstone. Individual mapped units contain varying combinations and percentages of each type of phyllite so that the named lithology is borne by the dominant phyllite. | 06-01 | DMU-Heading1 | None | None | None | None | MGS_LITTL2025.1 | Lower-grade metamorphic rock, of unspecified origin | Medium | DMU008 |
| 10 | CZisp | slaty phyllite | slaty phyllite subunit of the Ijamsville Formation | Late Proterozoic to early Cambrian | Dark gray, grayish purple, and dark bluish gray phyllite with local light gray streaks and layers of greenish gray tuffaceous phyllite. Unit parts in regular, millimeter-thick layers reminiscent of slaty cleavage. Contains common intervals of bluish gray, thin- to medium-bedded, locally laminated, argillaceous, ribbony Silver Run Limestone (CZisr). Stratification in limestone strata is up to 10 cm (4 inches) thick and highly contorted. This phyllite unit is partially equivalent to the Silver Run Limestone (srl) of Fisher (1978) and Sams Creek Silver Run Limestone (CZscsr) of Reger et al. (2004) in the New Windsor quadrangle, and the Silver Run Limestone of the Marburg Formation (mfs) of Edwards (1986) and Silver Run Limestone of the Sams Creek Formation (CZscsr) of Reger and Edwards (2006). Owing to deformation and inconsistent bedding indicators thickness is undeterminable. | 06-01-01 | DMU Unit 2 | _Zisp | 221 | 222,235,222 | None | MGS_LITTL2025.1|USGS_NEWWI1978|MGS_NEWWI2004.1|MGS_UNION1986|MGS_UNION2006.1 | Slate and phyllite, of sedimentary-rock origin | High | DMU009 |
| 11 | CZisr | Silver Run Limestone | Silver Run Limestone subunit of the slaty phyllite subunit of the Ijamsville Formation | Late Proterozoic to early Cambrian | Common intervals of bluish gray, thin- to medium-bedded, locally laminated, argillaceous, ribbony Silver Run Limestone (CZisr) within the slaty phyllite subunit of the Ijamsville formation. Stratification in limestone strata is up to 10 cm (4 inches) thick and highly contorted. | 06-01-01-01 | DMU Unit 3 | _Zisr | 434 | 179,179,204 | None | MGS_LITTL2025.1 | Meta-carbonate rock | High | DMU010 |
| 12 | CZimp | muscovite-chlorite-phyllite | muscovite-chlorite-phyllite subunit of the Ijamsville Formation | Late Proterozoic to early Cambrian | Light greenish gray to grayish green, and tan to silvery phyllite. The micas and chlorite are typically segregated into prominent pinstripe laminations spaced 1 to 3 cm (0.4 to 1.2 inches) apart and parallel to cleavage. Resistant to weathering; crops out extensively and commonly forms low ridges capped by a thin sandy soil. Locally, light gray, discontinuous, tuffaceous sandstone can be mapped (CZiq). Corresponds to the Ijamsville mica-chlorite-quartz phyllite (ijqp) of Fisher (1978) that crops out west of the Avondale Fault and to the Gillis Formation (gf) of Edwards (1986). | 06-01-02 | DMU Unit 2 | _Zimp | 201 | 222,235,255 | None | MGS_LITTL2025.1|USGS_NEWWI1978|MGS_UNION1986 | Lower-grade metamorphic rock, of unspecified origin | Medium | DMU011 |
| 14 | CZiq | discontinuous tuffaceous sandstone | tuffaceous sandstone subunit of the muscovite-chlorite-phyllite and the chlorite phyllite subunits of the Ijamsville Formation | Late Proterozoic to early Cambrian | Locally, light gray to greenish gray, discontinuous, tuffaceous phyllitic sandstone. Can be found within both the muscovite-chlorite-phyllite (CZimp) subunit and the chlorite-phyllite (CZicp) subunit of the Ijamsville Formation. | 06-01-02-01 | DMU Unit 3 | _Ziq | 75 | 255,153,102 | None | MGS_LITTL2025.1 | Quartzite | Medium | DMU013 |
| 13 | CZicp | chlorite-phyllite | chlorite phyllite subunit of the Ijamsville Formation | Late Proterozoic to early Cambrian | Pale green to greenish gray phyllite. Contains subordinate amounts of paragonite and muscovite phyllite. Chloritic laminae commonly alternate with white mica-albite-quartz layers up to 5 mm (0.2 inch) thick; most of these layers parallel axial-plain cleavage and must be tectonic in origin, but some may be relict bedding laminations (Fisher, 1978). Locally, light gray, discontinuous, tuffaceous sandstone can be mapped (CZiq). Corresponds in part to the Sams Creek chlorite phyllite (sccp) of Fisher (1978) and the tuffaceous phyllite [also CZitp] of the Union Bridge quadrangle. | 06-01-03 | DMU Unit 2 | _Zicp | 311 | 204,235,235 | None | MGS_LITTL2025.1|USGS_NEWWI1978|MGS_UNION2006.1 | Lower-grade metamorphic rock, of unspecified origin | Medium | DMU012 |
| 15 | CZitp | tuffaceous phyllite | tuffaceous phyllite subunit of the Ijamsville Formation | Late Proterozoic to early Cambrian | Dark gray, grayish red, reddish purple, and bluish gray, silty, granular tuffaceous phyllite with light gray lapilli streaks and blebs. Intermixed with intervals of greenish gray to gray, tan-weathering, tuffaceous phyllite and silty tuffaceous phyllite. Contains intermixed variegated and lustrous to dull, purple to reddish gray hematitic muscovite phyllite and tan to green chlorite muscovite phyllite. Corresponds to parts of the Urbana Formation of Edwards (1986), tuffaceous phyllite of Brezinski et al. (2004), and Ijamsville Phyllite of Reger and Edwards (2006). Owing to deformation and inconsistent bedding indicators thickness cannot be determined. | 06-01-04 | DMU Unit 2 | _Zitp | 403 | 179,204,255 | None | MGS_LITTL2025.1|MGS_UNION1986|MGS_UNION2006.1|MGS_WALKE2004.1 | Intermediate-composition pyroclastic flows | Medium | DMU014 |
| 16 | CZu | Urbana Formation | Urbana Formation | Late Proterozoic to early Cambrian | Dull, olive gray to light olive gray, silty, sandy, phyllite, metasiltstone, and argillaceous sandstone. Stratification obscured by deformational fabrics, but often preserve primary textures including grading, cross-bedding, ripple marked, and bioturbation. Discontinuous fine- to medium-grained, light olive gray and light brownish gray metasandstone (CZus) are friable, lenticular, and intensely cleaved. Interpreted to be partially equivalent to the Harpers Formation of Jonas (1928). Thickness is indeterminable. | 07-01 | DMU Unit 1 | _Zu | 24 | 255,191,191 | None | MGS_LITTL2025.1|MGS_CLGEO1928 | Lower-grade metamorphic rock, of unspecified origin | Medium | DMU015 |
| 17 | CZus | metasandstone | metasandstone subunit of the Urbana Formation | Late Proterozoic to early Cambrian | Discontinuous fine- to medium-grained, light olive gray and light brownish gray metasandstone. Can be found within the Urbana Formation (CZu). | 07-01-01-01 | DMU Unit 3 | _Zus | 35 | 255,166,166 | None | MGS_LITTL2025.1 | Quartzite | Medium | DMU016 |
| 18 | CZmb | Marburg Formation | Marburg Formation | Late Proterozoic to early Cambrian | Predominately greenish gray, pale olive gray, silvery gray, silty, sandy phyllite. Some intervals are dark gray, to dark greenish gray, exhibiting pinstriped foliation where phyllite layers are folded with light gray, quartz-rich layers. Minute (>0.01mm) disseminated flakes of hematite and pyrite are abundant. Formation contains localized layers of quartzose metasandstone to metagraywacke (CZmbs) vary from light to medium olive-gray, are medium- to coarse-grained, and can be foliated, blocky, or massive. Massive intervals of metasandstone can be up to 3 feet thick and comprised of subrounded quartz grains surrounded in a quartz and mica matrix. This interval is equivalent to the Urbana Formation of Edwards and Glaser (1993), and the Harpers Formation of Jonas (1928). | 08-01 | DMU Unit 1 | _Zmb | 244 | 222,179,179 | None | MGS_LITTL2025.1|MGS_LITTL1993|MGS_CLGEO1928 | Lower-grade metamorphic rock, of unspecified origin | Medium | DMU017 |
| 19 | CZmbs | quartzose metagreywacke/metasandstone | quartzose metagreywacke/metasandstone subunit of the Marburg Formation | Late Proterozoic to early Cambrian | Localized layers of quartzose metasandstone to metagraywacke (CZmbs) vary from light to medium olive-gray, are medium- to coarse-grained, and can be foliated, blocky, or massive. Massive intervals of metasandstone can be up to 3 feet thick and comprised of subrounded quartz grains surrounded in a quartz and mica matrix. Can be found within the Marburg Formation (CZmb). | 08-01-01-01 | DMU Unit 3 | _Zmbs | 404 | 179,179,255 | None | MGS_LITTL2025.1 | Quartzite | Medium | DMU018 |