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Geologic units in Anne Arundel county, Maryland

Chesapeake Group; Calvert Formation (Miocene) at surface, covers 36 % of this area

Chesapeake Group; Calvert Formation - Plum Point Marls Member: Interbedded dark green to dark bluish-gray, fine-grained argillaceous sand and sandy clay; contains prominent shell beds and locally silica-cemented sandstones; and Fairhaven Member: Greenish-blue diatomaceous clay, weathers to pale gray; pale brown to white, fine-grained argillaceous sand; and greenish-blue sandy clay; total thickness 0 to 150 feet.

Lithology: sand; clay or mud; sandstone

Lowland Deposits (Quaternary) at surface, covers 15 % of this area

Lowland Deposits - Gravel, sand, silt, and clay. Medium- to coarse-grained sand and gravel; cobbles and boulders near base; commonly contains reworked Eocene glauconite; varicolored silts and clays; brown to dark gray lignitic silty clay; contains estuarine to marine fauna in some areas (includes in part Pamlico, Talbot, Wicomico and Sunderland Formations of earlier reports); thickness 0 to 150 feet.

Lithology: gravel; sand; silt; clay or mud

Magothy Formation (Cretaceous) at surface, covers 11 % of this area

Magothy Formation - Loose, white, cross-bedded, "sugary", lignitic sands and dark gray, laminated silty clays; white to orange-brown, iron-stained, subrounded quartzose gravels in western Anne Arundel County; absent in outcrop southwest of Patuxent River; thickness 0 to 60 feet.

Lithology: sand; clay or mud; gravel

Matawan Formation (Cretaceous) at surface, covers 10 % of this area

Matawan Formation - Dark gray micaceous, glauconitic, argillaceous, fine-grained sand and silt; absent in outcrop southwest of Patuxent River; thickness 0 to 70 feet.

Lithology: sand; silt

Monmouth Formation (Cretaceous) at surface, covers 9 % of this area

Monmouth Formation - Dark gray to reddish-brown, micaceous, glauconitic, argillaceous, fine- to coarse-grained sand; basal gravel in Prince Georges County; thickness 0 to 100 feet.

Lithology: sand; gravel

Potomac Group, including Raritan and Patapsco Formations, Arundel Clay, and Patuxent Formation (Cretaceous) at surface, covers 8 % of this area

Potomac Group - Interbedded quartzose gravels; protoquartzitic to orthoquartzitic argillaceous sands; and white, dark gray, and multicolored silts and clays; thickness 0 to 800 feet. Includes Raritan and Patapsco Formations - Gray, brown, and red variegated silts and clays; lenticular, cross-bedded, argillaceous, subrounded sands; minor gravels; thickness 0 to 400 feet; Arundel Clay - Dark gray and maroon lignitic clays; abundant siderite concretions; present only in Baltimore-Washington area; thickness 0 to 100 feet; and Patuxent Formation - White or light gray to orange-brown, moderately sorted, cross-bedded, argillaceous, angular sands and subrounded quartz gravels; silts and clays subordinate, predominantly pale gray; thickness 0 to 250 feet.

Lithology: gravel; sand; silt; clay or mud

Pamunkey Group; Nanjemoy Formation (Eocene) at surface, covers 6 % of this area

Pamunkey Group; Nanjemoy Formation - Dark green to gray, argillaceous, glauconitic, fine- to medium-grained sand; minor gray to pale brown clay; total thickness 0 to 125 feet; Marlboro Clay member at base: Pink to gray, homogeneous plastic clay with local lenses of very fine-grained white sand; thickness 0 to 30 feet; present west of Chesapeake Bay only; total thickness 0 to 125 feet.

Lithology: sand; clay or mud

Upland Deposits (Western Shore) (Quaternary) at surface, covers 5 % of this area

Upland Deposits (Western Shore) - Gravel and sand, commonly orange-brown, locally limonite-cemented; minor silt and red, white, or gray clay; (includes Brandywine, Bryn Mawr, and Sunderland Formations of earlier reports); lower gravel member and upper loam member in Southern Maryland; thickness 0 to 50 feet.

Lithology: gravel; sand; silt; clay or mud

Pamunkey Group; Aquia Formation (Paleocene) at surface, covers 0.5 % of this area

Pamunkey Group; Aquia Formation - Dark green to gray-green, argillaceous, highly glauconitic, well-sorted fine- to medium-grained sand; locally indurated shell beds; thickness 0 to 100 feet.

Lithology: sand

Baltimore Gabbro Complex (Late Precambrian (?) - Early Paleozoic ) at surface, covers 0.2 % of this area

Baltimore Gabbro Complex - Hypersthene gabbro with subordinate amounts of olivine gabbro, norite, anorthositic gabbro, and pyroxenite; igneous minerals and textures well preserved in some rocks, other rocks exhibit varying degrees of alteration and recrystallization with a new metamorphic mineral assemblage.

Lithology: gabbro; norite; pyroxenite

Metagabbro and Amphibolite (Early Paleozoic (?)) at surface, covers < 0.1 % of this area

Metagabbro and Amphibolite - Weakly to strongly lineated metagabbro and epidote amphibolite.

Lithology: gabbro; amphibolite