Geologic units in Johnston county, North Carolina

Terrace Deposits and Upland Sediment (Tertiary) at surface, covers 17 % of this area

Gravel, clayey sand, and sand, minor iron-oxide cemented sandstone.

Middendorf Formation (Cretaceous) at surface, covers 16 % of this area

Sand, sandstone, and mudstone, gray to pale gray with an orange cast, mottled; clay balls and iron-cemented concretions common, beds laterally discontinuous, cross-bedding common.

Yorktown Formation and Duplin Formation, Undivided (Tertiary) at surface, covers 13 % of this area

Yorktown Formation: fossiliferous clay with varying amounts of fine-grained sand, bluish gray, shell material commonly concentrated in lenses; mainly in area north of Neuse River. Duplin Formation: shelly, medium- to coarse-grained sand, sandy marl, and limestone, bluish gray; mainly in area south of Neuse River.

Black Creek Formation (Cretaceous) at surface, covers 13 % of this area

Clay, gray to black, lignitic; contains thin beds and laminae of fine-grained micaceous sand and thick lenses of cross-bedded sand. Glauconitic, fossiliferous clayey sand lenses in upper part.

Cape Fear Formation (Cretaceous) at surface, covers 12 % of this area

Sandstone and sandy mudstone, yellowish gray to bluish gray, mottled red to yellowish orange, indurated, graded and laterally continuos bedding, blocky clay, faint cross-bedding, feldspar and mica common.

Biotite Gneiss and Schist (Cambrian/Late Proterozoic) at surface, covers 10 % of this area

Inequigranular and megacrystic; in places contains garnet; interlayered and gradational with mica schist and amphibolite; includes small masses of granitic rock.

Felsic Metavolcanic Rock (Cambrian/Late Proterozoic) at surface, covers 7 % of this area

Metamorphosed dacitic to rhyolitic flows and tuffs, light gray to greenish gray; interbedded with mafic and intermediate metavolcanic rock, meta-argillite, and metamudstone.

Foliated to Massive Granitic Rock (Permian/Pennsylvanian) at surface, covers 6 % of this area

Megacrystic to equigranular. Rolesville suite, Wise and Lemon Springs (?) intrusives.

Phyllite and Schist (Cambrian/Late Proterozoic) at surface, covers 4 % of this area

Minor biotite and pyrite; includes phyllonite, sheared fine-grained metasediment and metavolcanic rock.

Metamudstone and Meta-Argillite (Cambrian/Late Proterozoic) at surface, covers 0.9 % of this area

Bedding plane and axial-planar cleavage common; interbedded with metasandstone, meta-conglomerate, and metavolcanic rock.

Castle Hayne Formation; Comfort Member and New Hanover Member, undivided (Tertiary) at surface, covers 0.2 % of this area

Comfort Member: bryozoan-echinoid skeletal limestone, locally dolomitized, solution cavities common. New Hanover Member: phosphate-pebble conglomerate, micritic, thin; restricted to basal part of Castle Hayne Formation in southeastern counties.

Injected Gneiss (Cambrian/Late Proterozoic) at surface, covers < 0.1 % of this area

Biotite gneiss and schist intruded by numerous sills and dikes of granite, pegmatite, and aplite; minor hornblende gneiss.

Amphibolite (Cambrian/Late Proterozoic) at surface, covers < 0.1 % of this area

Metamorphosed mafic extrusive and intrusive rock; includes hornblende gneiss, thin layers of mica schist, and small nonlayered masses of metadiorite and metagabbro.