Geologic units in Mercer county, New Jersey

Additional scientific data in this geographic area

Stockton Formation (Upper Triassic) at surface, covers 18 % of this area

Predominantly medium- to coarse-grained, light-gray, light-grayish-brown, or yellowish- to pinkish-gray arkosic sandstone and medium- to fine-grained, violet-gray to reddish-brown arkosic sandstone; with lesser, reddish to purplish-brown, silty mudstone, argillaceous siltstone, and shale. Some coarse-grained sandstone in lower part contains thick beds of conglomerate (Trsc) which have been mapped in the vicinity of Stockton. Sandstone, deposited in high-gradient stream channels, is mostly planar bedded with scoured bases containing pebble lags and mudstone rip-up clasts. Upper part of channel beds are burrowed. Large-scale trough crossbeds occur in some very coarse grained sandstone beds; smaller scale trough and climbing-ripple cross lamination occur in the upper part of channel sequences and in finer grained sandstone beds. Typical floodplain mudstones are irregularly thin bedded and extensively burrowed. Floodplain beds are thicker and more numerous in the central Newark basin, near the Delaware River. Thickness of the unit (including Trsc) near Stockton is about 1,240 m (4,068 ft).

Passaic Formation (Lower Jurassic and Upper Triassic) at surface, covers 18 % of this area

Predominantly red beds consisting of argillaceous siltstone; silty mudstone; argillaceous, very fine grained sandstone; and shale; mostly reddish-brown to brownish-purple, and grayish-red. Red beds occur typically in 3- to 7-m (10- to 23-ft-)-thick, cyclic playa-lake-mudflat sequences and fining-upward fluvial sequences. Lamination is commonly indistinct due to burrowing, desiccation, and paleosol formation. Where layering is preserved, most bedforms are wavy parallel lamination and trough and climbing-ripple cross lamination. Calcite- or dolomite-filled vugs and flattened cavities, mostly 0.5 to 0.2 mm (0.02-0.08 in) across, occur mostly in the lower half. Sand-filled burrows, 2 to 5 mm (0.08-0.2 in) in diameter, are prevalent in the upper two-thirds of the unit. Desiccation cracks, intraformational breccias, and curled silt laminae are abundant in the lower half. Lake cycles, mostly 2 to 5 m (7-16 ft) thick, have a basal, greenish-gray, argillaceous siltstone; a medial, dark-gray to black, pyritic, carbonaceous, fossiliferous, and, in places, calcareous lake-bottom fissile mudstone or siltstone; and an upper thick-bedded, gray to reddish and purplish-gray argillaceous siltstone with desiccation cracks, intraformational breccias, burrows, and mineralized vugs. Thickness of the formation between Sourland Mountain and Sand Brook syncline is about 3,500 m (11,483 ft).

Lockatong Formation (Upper Triassic) at surface, covers 12 % of this area

Predominantly cyclic lacustrine sequences of silty, dolomitic or analcime-bearing argillite; laminated mudstone; silty to calcareous, argillaceous very fine grained sandstone and pyritic siltstone; and minor silty limestone, mostly light- to dark-gray, greenishgray, and black. Grayish-red, grayish-purple, and dark-brownish-red sequences (Trlr) occur in some places, especially in upper half. Two types of cycles are recognized: freshwater-lake (detrital) and alkaline-lake (chemical) cycles. Freshwater-lake cycles average 5.2 m (17 ft) thick. They consist of basal, transgressive, fluvial to lake-margin deposits that are argillaceous, very fine grained sandstone to coarse siltstone with indistinct lamination, planar or cross lamination, or are disrupted by convolute bedding, desiccation cracks, root casts, soil-ped casts, and tubes. Medial lake-bottom deposits are laminated siltstones, silty mudstones, or silty limestones that are dark gray to black with calcite laminae and grains and lenses, or streaks of pyrite; fossils are common, including fish scales and articulated fish, conchostracans, plants, spores, and pollen. Upper regressive lake margin, playa lake, and mudflat deposits are light- to dark-gray silty mudstone to argillitic siltstone or very fine grained sandstone, mostly thick bedded to massive, with desiccation cracks, intraformational breccias, faint wavy laminations, burrows, euhedral pyrite grains, and dolomite or calcite specks. Alkaline-lake cycles are similar to freshwater-lake cycles, but are thinner, averaging 3 m (10 ft), have fewer fossils (mainly conchostracans), and commonly have red beds, extensive desiccation features, and abundant analcime and dolomite specks in the upper parts of cycles. Thickness near Byram is about 1,070 m (3,510 ft). The formation thins to the southeast and northeast; thickness near Princeton is less than 700 m (2,297 ft).

Merchantville Formation (Upper Cretaceous, lower Campanian) at surface, covers 10 % of this area

Sand, glauconite, locally has high quartz content, very clayey and silty, massive to thick-bedded, grayish-olive-green to dark-greenish-gray; weathers moderate brown or moderate yellow brown. Mica, feldspar, and pyrite are minor sand constituents. Very micaceous at base. Locally, has extensive iron incrustations in near-surface weathered beds. Fossil molds are mostly phosphatic. Fossils typically occur in siderite concretions. No calcareous fossils were found in outcrop. The Merchantville forms a continuous narrow to wide belt throughout the map area. The unit is about 6 m (20 ft) thick in the northern part of the central sheet, about 20 m (66 ft) thick in the Trenton area, and 12 to 15 m (39-49 ft) thick throughout the southern sheet. The formation is best exposed in the Trenton East quadrangle, mainly in the tributaries on the western side of Blacks Creek and south of Bordentown, Burlington County, where the entire thickness of the formation can be seen in gullies (Owens and Minard, 1964b). The basal contact with the underlying Magothy or Cheesequake Formations is sharp and disconformable. At most places, a reworked zone about 0.3 to 1 m (1-3 ft) thick is present at the base. This basal bed contains reworked lignitized wood, siderite concretions as much as 13 cm (5 in) in diameter, scattered pebbles and coarse-grained quartz sand and is burrowed. Most burrows project downward into the underlying formations. The Merchantville is the basal bed of a lower Campanian transgressive-regressive cycle that includes the overlying Woodbury and Englishtown Formations. Merchantville faunas were analyzed by Sohl (in Owens and others, 1977) who concluded that northern fauna represented deposition on a lower shoreface or in the transition to an inner shelf, whereas the southern fauna was a deeper water assemblage, probably inner shelf. Macrofossils occur as internal and external molds and include the ammonites Menabites (Delawarella) delawarensis and Scaphites (Scaphites) hippocrepis III. The Scaphites is of the type III variety of Cobban (1969) and is indicative of the lower, but not the lowest, Campanian. More recently, Kennedy and Cobban (1993), detailing the ammonite assemblage that includes Baculites haresi, Chesapeakella nodatum, Cryptotexanites paedomorphicus sp., Glyptoxoceras sp., Menabites (Delawarella) delawarensis, M. (Delawarella) vanuxemi, Menabites (Bererella) sp., Pachydiscus (Pachydiscus) sp., Placenticeras placenta, Pseudoscholenbachia cf. P. chispaensis, Scaphites (Scaphites) hippocrepis III, Submortoniceras punctatum, S. uddeni, and Texanites (Texanites) sp., concluded that the Merchantville is of late early Campanian age. Wolfe (1976) indicated that the Merchantville microflora was distinct from overlying and underlying units and designated it Zone CA2 of early Campanian age.

Magothy Formation (Upper Cretaceous, middle and lower Santonian) at surface, covers 9 % of this area

Sand, quartz, fine- to coarse-grained, locally gravelly (especially at the base), white; weathers yellow brown or orange brown, interbedded with thin-bedded clay or dark-gray clay-silt mainly at the top of the formation. Muscovite and feldspar are minor sand constituents. Large wood fragments occur in many clay layers. Clay weathers to gray brown or white. Formation characterized by local vertical and lateral facies changes. The Magothy is best exposed and thickest (about 80 m (262 ft)) in the Raritan Bay area. The outcrop belt is widest in the north and narrows to the southwest. The formation is about 25 m (82 ft) thick or less in the southern sheet. The formation is poorly exposed because of its sandy nature and its widespread cover by younger sediments. The old geologic map of New Jersey (Lewis and Kmmel, 1910-1912, revised 1950) showed the Magothy to consist of only one lithology (Cliffwood beds at Cliffwood Beach, Monmouth County). Subsequent pollen studies of the Magothy and the underlying Raritan Formation showed most of the Raritan to be the same age as the Magothy. Wolfe and Pakiser (1971) redefined and considerably expanded the Magothy. Kmmel and Knapp (1904) had already recognized that the Magothy, as used here, contained a large number of lithologies. At the time of their study, the Magothy was extensively mined for clay and sand and was well exposed. Their subdivisions had economic designations (for example, Amboy stoneware clay). Barksdale and others (1943) later gave geographic names to these subdivisions, discussed individually below. The lower contact of the Magothy in the Delaware River valley is difficult to place because the lower part of the Magothy is lithically similar to the underlying Potomac Formation. The contact is placed at the base of the lowest dark-gray clay in the Magothy. The best faunas from the Magothy were obtained from siderite concretions and slabs in and near Cliffwood Beach representing only the top of the formation. These faunas were discussed in detail by Weller (1904, 1907) and supplemented by Sohl (in Owens and others, 1977). The presence of Ostrea cretacea in the Cliffwood Beach fauna suggests that the upper part of the Magothy is late Santonian in age. Wolfe and Pakiser (1971) and Christopher (1979, 1982) discussed the microfloral assemblage in the Magothy. Christopher subdivided the Magothy into three zones: Complexipollis exigua-Santalacites minor (oldest), Pseudoplicapollis longiannulata-Plicapollis incisa (middle), and Pseudoplicapollis cuneata-Semioculopollis verrucosa (youngest). The oldest zone, originally considered to be as old as Turonian, was subsequently considered to be post-Coniacian Christopher, 1982). The middle and upper zones are also probably Santonian. Christopher (1979) followed the nomenclature for the subdivisions elaborated upon earlier. The Cliffwood and Morgan beds, and, presumably the upper thin-bedded sequence, would include the youngest pollen zone; the Amboy Stoneware Clay Member and perhaps the uppermost part of the Old Bridge Sand Member, the middle pollen zone; and the lower part of the Old Bridge Sand Member and South Amboy Fire Clay Member, the oldest pollen zone. The Magothy is considered herein to be of Santonian age. Cliffwood beds - Typically very sandy, horizontally bedded to crossbedded, mainly small-scale trough crossbeds. Thin layers of dark, fine, carbonaceous matter are interbedded with sand. Carbonaceous units are conspicuously micaceous; the sand is less so. Sand is typically fine to medium grained and locally burrowed. Burrows include the small-diameter Ophiomorpha nodosa and some that are not clay lined. Slabs of dark-reddish-brown siderite were common at the base of the bluff at Cliffwood Beach before the outcrop was covered. Some of these slabs had many fossil molds, typically a large number of pelecypods. Lower in the section, between high and low tide level, there is a pale-gray clay-silt about 1.5 m (5 ft) thick with many small reddish-brown siderite concretions. These concretions have many fossils that were described in detail by Weller (1904). The Cliffwood beds are about 7.5 m (25 ft) thick in outcrop. Equivalents of the Cliffwood beds are exposed near the Delaware River between Trenton and Florence, Burlington County. These beds are mainly sand, as are those at Cliffwood Beach, but they tend to have more crossbedding than the typical Cliffwood strata and no burrows or marine fossils. In addition, beds of quartz gravel are present in the Cliffwood near Riverside, Burlington County. Morgan beds - Occur only in the northern part of the central sheet. They consist of interbedded, thin, dark-colored clay and fine-grained, light-colored, micaceous sand. Clay is locally more abundant in the Morgan than in the Cliffwood beds. Sand ranges from massive to locally crossbedded and locally has fine organic matter. This unit is exposed only in the South Amboy quadrangle where it is as much as 12 m (39 ft) thick. It grades downward into underlying clay. Amboy Stoneware Clay Member - Crops out only in the South Amboy quadrangle in the central sheet and is mainly dark-gray, white-weathering, interbedded clay and silt to fine-grained quartz sand. Clay has abundant, fine, carbonaceous matter and fine mica flakes. Small cylindrical burrows are abundant in this unit. Locally, the clay is interbedded with sand and contains large pieces of lignitized, bored (Teredolites) logs. Large slabs of pyrite-cemented sand are associated with the woody beds. Amber occurs in some of the wood. Unit is approximately 7.5 m (25 ft) thick, but pinches out along strike. The Amboy Stoneware is disconformable on the underlying sand. Old Bridge Sand Member - Predominantly a light-colored sand, extensively crossbedded and locally interbedded with dark-gray laminae; clay is highly carbonaceous, woody, in discontinuous beds, especially near the base. The scale of crossbedding varies from small to large. Locally, small burrows are present. Unit is as much as 12 m (39 ft) thick and rests disconformably on the underlying unit. South Amboy Fire Clay Member - Basal member of the Magothy Formation. Unit resembles the Amboy Stoneware Clay Member, particularly in its lensing character. Unit is best exposed in the central sheet in the South Amboy quadrangle and in the Delaware River valley at the base of the bluffs at Florence. The South Amboy is a dark, massive to finely laminated clay, locally oxidized to white or red. Unit fills large channels and has local concentrations of large, pyrite-encrusted, lignitized logs. Some of the clay is slumped, suggesting post-depositional undercutting during channel migration. The clay is interbedded with fine- to medium-grained, crossbedded sand. The basal contact with the underlying Raritan is well exposed in the Sayre and Fisher Pit in Sayreville, Middlesex County, where the contact is marked by a deeply weathered gravel zone.

Potomac Formation, unit 3 (Upper Cretaceous, lower Cenomanian) at surface, covers 9 % of this area

Sand, fine- to coarse-grained, locally gravelly, crossbedded, light-colored, interbedded with white or variegated red and yellow, massive clay, and rarely dark-gray, woody clay. The Potomac Formation crops out only in the Delaware River valley where the river and its tributaries have eroded away the overlying formations. The Potomac has been mapped in a broad belt parallel to the inner edge of the Coastal Plain. Although mapped in a broad belt, the Potomac is very poorly exposed because of the widespread cover of surficial sediments. The best exposures occur where surficial material is mined away in the Camden area. Unit is about 45 m (148 ft) thick. Contact with the overlying Magothy Formation is difficult to pick where the basal Magothy also contains variegated clays. Most of the basal Magothy has more dark-colored clay, and the contact was drawn by using this criterion. The basal contact of the Potomac with the underlying crystalline rock is not exposed in New Jersey. Biostratigraphically, the Potomac has been separated into pollen zones I, II, and III (Doyle, 1969; Doyle and Robbins, 1977). Samples from the Potomac Formation in the Camden area and along the Delaware River nearby contain pollen assemblages of early Cenomanian age (Zone III) (Les Sirkin, written commun., 1988).

Woodbury Formation (Upper Cretaceous, lower Campanian) at surface, covers 7 % of this area

Clay-silt, dark-gray; weathers brown and orange pink. Iron oxides fill fractures or form layers in the most weathered beds. Unit is massive except at the base where thin quartz sand layers occur. Locally, thin stringers of pale-greenish-brown, smooth-surface glauconite occur near the top. Unit conspicuously micaceous throughout and contains finely dispersed pyrite, carbonaceous matter, and small pieces of carbonized wood as much as 30 cm (12 in) in length. Small siderite concretions are abundant in the Woodbury in the northern part of the outcrop belt. Unit forms a broad belt in the central sheet from Sandy Hook Bay, southwest to area around East Greenwich, Gloucester County, where it pinches out or changes facies. The Woodbury maintains a thickness of about 15 m (49 ft) throughout most of its outcrop belt. Fossil imprints are abundant. An extensive Woodbury macrofauna was described by Weller (1907) from siderite concretions from a tributary to the Cooper River in the Camden quadrangle. This assemblage is unusual in that it is the only existing outcrop of the Woodbury where calcareous and aragonitic shells are still intact. Most fossils are small, fragmented, and concentrated in small pockets, but larger intact calcareous fossils are scattered throughout the Woodbury. Weller (1907) recorded 57 species from this locality. In addition, this is the same locality that contains fossils of the dinosaur Hadrosaurus foulkii. Pollen collected from the Woodbury was assigned to the CA3 Zone by Wolfe (1976). Biostratigraphic data suggest that the Woodbury is of early Campanian age.

Englishtown Formation (Upper Cretaceous, lower Campanian) at surface, covers 5 % of this area

Sand, quartz, fine- to coarsegrained, gravelly, massive, bioturbated, medium- to dark-gray; weathers light brown, yellow, or reddish brown, locally interbedded with thin to thick beds of dark clay. Abundant carbonaceous matter, with large lignitized logs occur locally, especially in clay strata. Feldspar, glauconite, and muscovite are minor sand constituents. Sand is extensively trough crossbedded particularly west of Mount Holly, Burlington County. In a few places in the western outcrop belt, trace fossils are abundant, typically the burrow Ophiomorpha nodosa. Unit is pyritic, especially in the carbonaceous-rich beds where pyrite is finely disseminated grains or pyritic masses as much as 0.6 m (2 ft) in diameter. Lowest part of unit is a massive sand that contains small to large, soft, light-gray siderite concretions. The Englishtown underlies a broad belt throughout the map area and ranges from about 45 m (148 ft) thick in the northern part of the central sheet to 30 m (98 ft) thick in the western part of the central sheet to 15 m (49 ft) in the southern sheet. Best exposures occur along Crosswicks Creek in the Allentown quadrangle and along Oldmans Creek. The basal contact with the underlying Woodbury Formation or Merchantville Formation is transitional over several meters. The age of the Englishtown in outcrop could not be determined directly but was inferred from stratigraphic position and pollen content. Wolfe (1976) designated the microflora of the unit as Zone CA4 and assigned it to the lower Campanian.

Diabase (Jurassic) at surface, covers 4 % of this area

Concordant to discordant, predominantly sheet-like intrusions of medium- to fine-grained diabase and dikes of fine-grained diabase; dark-greenish-gray to black; subophitic texture. Dense, hard, sparsely fractured rock composed mostly of plagioclase (An50-70), clinopyroxene (mostly augite), and magnetite-ilmenite. Orthopyroxene (En75-80) is locally abundant in the lower part of the sheets. Accessory minerals include apatite, quartz, alkali feldspar, hornblende, sphene, zircon, and rare olivine. Diabase in the map area was derived primarily from high-titanium, quartz-tholeiite magma. Sedimentary rocks within about 300 m (984 ft) above and 200 m (656 ft) below major diabase sheets are thermally metamorphosed. Red mudstone is typically altered to indurated, bluish-gray hornfels with clots or crystals of tourmaline or cordierite. Gray argillitic siltstone is typically altered to brittle, black, very fine grained hornfels. Sills are 365 to 400 m (1,197-1,312 ft) thick. Dikes range in thickness from 3 to 10 m (10-33 ft) and are many kilometers long.

Gneiss granofels and Migmatite (Middle Proterozoic) at surface, covers 3 % of this area

Gneiss and granofels range in composition from felsic to intermediate to mafic; intermediate compositions predominate. Contains a wide variety of rock types including graphitic schist and marble. Many rocks were injected by a granitoid that has blue quartz and augen of potassic feldspar and are arteritic migmatites. One body of gneiss contains a 1 m by 0.5 m (3 by 2 ft) phacoid of gabbro that is interpreted to be an olistolith. Unit probably represents a sequence of meta-sedimentary and metavolcanic rocks that have been heavily injected and migmatized by felsic magma.

Passaic Formation gray bed (Lower Jurassic and Upper Triassic) at surface, covers 2 % of this area

Upper Triassic gray lake deposits (Trpg) consist of gray to black silty mudstone, gray and greenish- to purplish-gray argillaceous siltstone, black shale, and medium- to dark-gray, argillaceous, fine-grained sandstone and are abundant in the lower half of the Passaic Formation. Gray lakebeds occur in groups of two to five cycles although they also occur as single cycles in some parts of the formation. Several lakebed sequences consisting of one or two thick groups of drab-colored beds as much as 30 m (98 ft) thick or more can be traced over tens of kilometers. Many gray-bed sequences are locally correlated within fault blocks; some can be correlated across major faults or intrusive rock units. Thickness of the (entire Passaic) formation between Sourland Mountain and Sand Brook syncline is about 3,500 m (11,483 ft).

Wissahickon Formation (Lower Cambrian and Late Proterozoic) at surface, covers 2 % of this area

Fine- to medium-grained biotite-quartz-plagioclase schist and gneiss that contains thin amphibolite layers. Schist and gneiss in alternating layers suggest a turbidite sequence of shale and graywacke. The rocks are at high metamorphic grade, and, in places, the more pelitic parts have partly melted forming veins of migmatite. Some exposures show evidence of polymetamorphism as micaceous minerals occur both within the schistosity and as static porphyroblasts.

Gabbro (Middle Proterozoic) at surface, covers 0.7 % of this area

Medium- to coarse-crystalline, medium- to dark-gray foliated rock composed principally of plagioclase (An35) and clinopyroxene. Contains minor amounts of garnet, biotite, and sulfide. The rock is more siliceous than typical gabbros.

Trenton Gravel (Quaternary) at surface, covers < 0.1 % of this area

Gray or pale-reddish-brown, very gravelly sand interstratified with crossbedded sand and clay-silt beds; includes areas of Holocene alluvium and swamp deposits.

Metabasalt (Late Proterozoic) at surface, covers < 0.1 % of this area

Sequence of conformably layered volcanic rocks of fine-grained to aphanitic, greenish-gray, retrogressively metamorphosed greenstone, greenschist, and basalt. Greenschist contains clots and lenses of blue quartz and abundant sulfide. Unit does not crop out and is known only from subsurface borings and artificial exposures. Interpreted to be Late Proterozoic by Volkert and Drake (1993) on the basis of geochemical similarity to Late Proterozoic metadiabase dikes in New Jersey Highlands.

Amphibolite (Middle Proterozoic) at surface, covers < 0.1 % of this area

Medium-grained, very dark gray to black, and foliated; consists of hornblende and andesine. Some exposures exhibit crosscutting bodies of white plagioclase pegmatite

Manhattan Schist (Lower Cambrian and (or) Late Proterozoic) at surface, covers < 0.1 % of this area

(Hall, in press) - Medium-dark gray, medium- to coarse-grained schist and gneiss composed of biotite, muscovite, quartz, and plagioclase, and local accessory minerals sillimanite, kyanite, tourmaline, and garnet. Contains some interlayered amphibolite. Unit is not exposed in the map area, but is present in boring logs.

Passaic Formation (Lower Jurassic and Upper Triassic) at surface, covers < 0.1 % of this area

(Olsen, 1980) - Reddish-brown to brownish-purple and grayish-red siltstone and shale (JTrp) maximum thickness 3,600 m (11,810 ft). At places contains mapped sandy mudstone (JTrpms), sandstone (JTrps), conglomeratic sandstone (JTrpsc) and conglomerate containing clasts of quartzite (JTrpcq), or limestone (JTrpcl). Formation coarsens up section and to the southwest. Quartzite conglomerate unit (JTrpcq) is reddish-brown pebble conglomerate, pebbly sandstone, and sandstone, in upward-fining sequences 1 to 2 m (3-6 ft) thick. Clasts are subangular to subrounded, quartz and quartzite in sandstone matrix. Sandstone is medium to coarse grained, feldspathic (up to 20 percent feldspar), and locally contains pebble and cobble layers. Conglomerate thickness exceeds 850 m (2,790 ft). Limestone conglomerate unit (JTrpcl) is medium-bedded to massive, pebble to boulder conglomerate. Clasts are subangular dolomitic limestone in matrix of brownish- to purplish-red sandstone to mudstone; matrix weathers light-gray to white near faults. Maximum thickness unknown. Conglomeratic sandstone (JTrpsc) is brownish-red pebble conglomerate, medium- to coarse-grained, feldspathic sandstone and micaceous siltstone; unit is planar to low-angle trough cross laminated, burrowed, and contains local pebble layers. Unit forms upward-fining sequences 0.5 to 2.5 m (1.6-8 ft) thick. Conglomeratic sandstone thickness exceeds 800 m (2,625 ft). Sandstone (JTrps) is interbedded grayish-red to brownish-red, medium- to fine-grained, medium- to thick-bedded sandstone and brownish-to purplish-red coarse-grained siltstone; unit is planar to ripple cross-laminated, fissile, locally calcareous, containing desiccation cracks and root casts. Upward-fining cycles are 1.8 to 4.6 m (6-15 ft) thick. Sandstone beds are coarser and thicker near conglomerate units (JTrpcq, JTrpcl). Maximum thickness about 1,100 m (3,610 ft). Sandy mudstone (JTrpms) is reddish-brown to brownish-red, massive, silty to sandy mudstone and siltstone, which are bioturbated, ripple cross-laminated and interbedded with lenticular sandstone. To southwest where similar lithologic units also occur, they have not been mapped separately, but have been included in undivided unit JTrp. Rhythmic cycles 2 to 7 m (7-23 ft) of thick gray-bed sequences (Trpg), termed Van Houten cycles by Olsen (1985), contain basal thin-bedded to finely laminated shale to siltstone, which grade upward through laminated to microlaminated, locally calcareous mudstone to siltstone and finally into massive silty mudstone. Lowest part of cycle has some desiccation features and local fossils; middle part has highest organic content and the most fossils; highest part contains mudcracks, burrows, and root casts. Gray-bed cycles are abundant in lower half of Passaic Formation and less common in upper half. Rocks of the Passaic Formation have been locally thermally metamorphosed to hornfels where in contact with the Orange Mountain Basalt, diabase dikes, and sheetlike intrusions. Total thickness of formation ranges from 3500 to 3600 m (11480-11810 ft).