Geologic units in Westchester county, New York

Fordham Gneiss, undivided (Precambrian - Middle Proterozoic) at surface, covers 27 % of this area

fe: garnet-biotite-quartz-plagioclase gneiss, and amphibolite; fd: sillimanite-garnet schistose gneiss, quartzite; fc: biotite-hornblende-quartz-plagioclase gneiss, quartz-feldspar lenses, amphibolite, biotite and/or hornblende-quartz-feldspar gneiss; fb: amphibolite, biotite and/or hornblende-garnet-quartz-plagioclase gneiss; fa: garnet-biotite-quartz-plagioclase gneiss, amphibolite, biotite-hornblende-quartz-plagioclase gneiss, quartz-feldspar granulite.

Manhattan Formation, undivided (Ordovician?) at surface, covers 17 % of this area

Pelitic schists, amphibolite; Units ?Omb, ?Omc, and ?Omd may be Cambrian eugeosynclinal rocks thrust upon Oma; ?Omd - sillimanite-garnet-muscovite-biotite-plagioclase-quartz gneiss; ?Omc - sillimanite-garnet-muscovite-biotite-quartz-plagioclase schistose gneiss, sillimanite nodules, local quartz-rich layers; ?Omb - discontinous unit of amphibolite and ?Omc-type schist.

Fordham Gneiss (C and D member) (Precambrian - Middle Proterozoic) at surface, covers 11 % of this area

fc: biotite-hornblende-quartz-plagioclase gneiss, quartz-feldspar lenses, amphibolite, biotite and/or hornblende-quartz-feldspar gneiss; fd: sillimanite-garnet schistose gneiss, quartzite.

Inwood Marble (Early Cambrian - Lower Ordovician) at surface, covers 11 % of this area

Dolomite marble, calc-schist, granulite, and quartzite, overlain by calcite marble; grades into underlying patchy Lowerre Quartzite of Early Cambrian age.

Hartland Formation (Ordovician?) at surface, covers 9 % of this area

Basal amphibolite overlain by pelitic schists.

Biotite-quartz-plagioclase gneiss (Middle Proterozoic) at surface, covers 4 % of this area

With subordinate biotite granitic gneiss, amphibolite, calcsilicate rock.

Bedford Gneiss (Ordovician?) at surface, covers 3 % of this area

Biotite-quartz-plagioclase gneiss and interlayered amphibolite; in part with augen of andesine and microcline.

Biotite granite gneiss (Middle Proterozoic) at surface, covers 3 % of this area

Overprint signifies inequigranular texture.

Harrison/Ravenswood Gneiss (Ordovician?) at surface, covers 3 % of this area

Harrison Gneiss - in New York and Connecticut, Brookfield diorite gneiss in Connecticut, and Ravenswood Gneiss in Brooklyn - biotite-hornblende-quartz-plagioclase gneiss with accessory garnet and sphene; plagioclase commonly occurs as augen.

Yonkers Gneiss (Middle Proterozoic) at surface, covers 2 % of this area

Biotite and/or hornblende-quartz-feldspar gneiss.

Hornblende norite (Upper Ordovician) at surface, covers 1 % of this area

Hornblende is poikilitic.

Fordham Gneiss (B member) (Precambrian - Middle Proterozoic) at surface, covers 1 % of this area

fb: amphibolite, biotite and/or hornblende-garnet- quartz-plagioclase gneiss.

Biotite augite norite (Upper Ordovician) at surface, covers 0.9 % of this area

Biotite augite norite

Pyroxenite (Upper Ordovician) at surface, covers 0.9 % of this area

Pyroxenite

Fordham Gneiss (E member) (Precambrian - Middle Proterozoic) at surface, covers 0.9 % of this area

fe: garnet-biotite-quartz-plagioclase gneiss, and amphibolite.

Olivine pyroxenite (Upper Ordovician) at surface, covers 0.6 % of this area

In part with poikilitic hornblende; local peridotite.

Muscovite-biotite granodiorite (Upper Devonian) at surface, covers 0.5 % of this area

Muscovite-biotite granodiorite - of Peekskill Pluton.

Manhattan Formation (A Member) (Middle Ordovician) at surface, covers 0.5 % of this area

Sillimanite-garnet-muscovite-biotite-quartz- plagioclase schists; calcite marble and calcsilicate rock at base.

Poundridge Gneiss (Middle Proterozoic) at surface, covers 0.5 % of this area

Biotite and/or hornblende-quartz-feldspar gneiss, similar to Yonkers Gneiss and parts of Fordham C member.

Diorite with hornblende and/or biotite (Upper Ordovician) at surface, covers 0.4 % of this area

Diorite with hornblende and/or biotite.

Fordham Gneiss (A member) (Precambrian - Middle Proterozoic) at surface, covers 0.4 % of this area

fa: garnet-biotite-quartz-plagioclase gneiss, amphibolite, biotite-hornblende-quartz-plagioclase gneiss, quartz-feldspar granulite.

Garnet-bearing gneiss and interlayered quartzite (Middle Proterozoic) at surface, covers 0.4 % of this area

Contains varying amounts of biotite, garnet, sillimanite; minor marble, amphibolite, rusty paragneiss.

Amphibolite (Middle Proterozoic) at surface, covers 0.3 % of this area

Pyroxenic amphibolite, hornblende gneiss, commonly biotitic, garnetiferous; subordinate calcsilicate rock.

Muscovite-biotite granite (Upper Devonian) at surface, covers 0.3 % of this area

Muscovite-biotite granite - of Peekskill Pluton.

Poughquag Quartzite (Cambrian) at surface, covers 0.2 % of this area

(includes local Dalton Formation at base)-locally conglomeratic.

Glacial and Alluvial Deposits (Quaternary) at surface, covers 0.2 % of this area

Underlying bedrock geology unknown.

Gabbro or norite to hornblende diorite (Upper Ordovician) at surface, covers 0.1 % of this area

Rock complex with minor pyroxenite; Croton Falls and Peach Lake complexes in New York, and Mt. Prospect Complex in Connecticut.

Rusty and gray biotite-quartz-feldspar gneiss (Middle Proterozoic) at surface, covers 0.1 % of this area

Rusty facies contains variable amounts of garnet, sillimanite, cordierite, graphite, sulfides; minor marble and calcsilicate rock.

Serpentinite (Lower Ordovician) at surface, covers 0.1 % of this area

Serpentinite.

Balmville Limestone (Middle Ordovician) at surface, covers < 0.1 % of this area

Balmville Limestone

Calcitic and dolomitic marble (Middle Proterozoic) at surface, covers < 0.1 % of this area

Variably siliceous; in part with calcsilicate rock and amphibolite.

Hornblende granite and granite gneiss (Middle Proterozoic) at surface, covers < 0.1 % of this area

With subordinate leucogranite.

Garnet-biotite-quartz-feldspar gneiss (Middle Proterozoic) at surface, covers < 0.1 % of this area

Quartzite, quartz-feldspar gneiss, calcsilicate rock.

Stockton Formation (Upper Triassic) at surface, covers < 0.1 % of this area

(Kmmel, 1897) - Light-gray, light-grayishbrown, yellowish- to pinkish-gray, or violet-gray to reddish-brown, medium- to coarse-grained arkosic sandstone and reddish- to purplish-brown mudstone, silty mudstone, argillaceous siltstone, and shale. Mudstone, siltstone and shale beds thicker and more numerous in central Newark basin west of Round Valley Reservoir. Sandstones mostly planar-bedded, with scoured bases containing pebble lags and mudstone rip-ups. Unit is coarser near Newark basin border fault, where poorly exposed, reddish-brown to pinkish-white, medium- to coarse-grained, feldspathic pebbly sandstone and conglomerate (Trss) and pebble to cobble quartzite conglomerate (Trscq). Maximum thickness of formation about 1,240 m (4,070 ft).