A5: STRATIGRAPHY, STRUCTURE, AND TECTONICS OF NEW YORK CITY AS VIEWED THROUGH ITS PARKS
Charles Merguerian
Professor Emeritus
Geology Department, Hofstra University
Hempstead, NY 11549
Research Fellow
Yale University, New Haven CT 06520
Principal
Duke Geological Laboratory
Stone Ridge. NY 12484
J. Mickey Merguerian
Geologist
Stone Ridge, NY 12484
INTRODUCTION
Geological Setting
NYC is situated at the extreme southern end of the Manhattan Prong (Figure 1), a northeast-trending, deeply eroded sequence of metamorphosed Proterozoic to Lower Paleozoic rocks that widen northeastward into the crystalline terrains of New England. Southward from NYC, the rocks of the Manhattan Prong plunge nonconformably beneath predominately buried Mesozoic rocks, younger Cretaceous strata, and the overlying Pleistocene drift found capping much of the region including all of Long Island and much of Staten Island. This NYSGA paper and allied Trip A-5 field guide are intended to prepare and expose participants to our subdivisions of the venerable Manhattan Schist into three separable units by utilizing exposures in NYC parks including Isham, Inwood Hill and Central parks.
Previous Investigations
A detailed history of NYC bedrock investigations appears elsewhere (Merguerian and Sanders 1991) so the following is simply a brief excerpt and overview. In 1890 (p. 390), Merrill named the Manhattan Schist for the micaceous metamorphic rocks found on Manhattan Island and suggested, following the views of Professors W. W. Mather (1843) and J. D. Dana (1880), that they represent metamorphosed equivalents of the lower Paleozoic strata of southern Dutchess County, New York. Merrill (1890) confides that "the name Manhattan Group was proposed by naturalist R. P. Stevens, Esq., to include the rocks of New York Island".
Despite this acknowledgement, Merrill and others (1902) produced the United States Geological Survey New York City Folio (#83) and following Dana chose to use the name Hudson Schist (rather than Manhattan Schist) for the schistose rocks of NYC. This pioneering work by Merrill and coworkers set the stage for a series of detailed investigations by many geologists in the 1900's that helped define the details of NYC bedrock units and use of the term Manhattan Schist as the name locality for the unit. Merrill also extended "Group" status to include the Manhattan Schist, the Inwood "limestone" and the Fordham and Yonkers gneisses and correctly correlated the Fordham with Proterozoic sequences of the Hudson Highlands. Formal removal of the significantly older Fordham and Yonkers gneisses from the "Manhattan Group" had to await the refinement and application of radiometric dating techniques and detailed mapping in the 1960's by Leo M. Hall (1968a; b). Formal "de-Grouping" of the "Manhattan Group" took place after spirited debate at a Symposium on the New York City Group of Formations at the 1968 meeting of the New York State Geological Association at Queens College, Queens, New York. Our studies of the metamorphic rocks of NYC since 1972 have benefited from these early works and access to surface and subsurface construction sites.

A5: STRATIGRAPHY, STRUCTURE, AND TECTONICS OF NEW YORK CITY AS VIEWED THROUGH ITS PARKS

Isham Park
Today’s field trip will start where bedrock is exposed in northernmost Manhattan in Isham and Inwood Hill parks (Figure 1). Northern Manhattan boasts the highest natural point of elevation at +265.5’ achieved atop rocky ridges in Bennett Park. The rocky ridges rise abruptly above the lowland plain to the east underlain by Inwood Marble. The adjacent prominent ridges are underlain by the venerable Manhattan Schist (OZm). Our analysis of the area departs a bit from published work in that we recognize schistose rocks in Manhattan aside from the Manhattan Schist. Indeed, in Inwood Hill Park representatives of all three ductile fault bounded schistose units can be found (Walloomsac [Ow], Manhattan [OZm] and Hartland [OCh] formations).
A cut-away cross-sectional view of northern Manhattan appears on a Google Earth basemap in Figure 2. Note the interpretation of the structure suggesting that the rocky ridges of northern Manhattan are controlled by overturned synforms of Manhattan Schist rooted by a major shear zone known as the St. Nicholas thrust which cuts both the Inwood Marble (OCi) and locally, the Walloomsac Schist (Ow). Below the flat plains of northeastern Manhattan, the Inwood is folded upward to the earth’s surface and beveled above two eroded F3 antiforms cored by Fordham Gneiss and an intervening F3 synform with all folds and most associated fabrics overturned toward the NW.
Isham Park contains near continuous exposure of white to blue-white Inwood Marble cut by high-angle conjugate joints which have facilitated the weathering process by allowing aqueous solutions to permeate the rocks (Figure 3). Several lithologies occur such as dolomitic marble, calcite marble, and foliated calc-schist, units that contain siliceous layers and calc-silicate aggregates that stand in relief on the weathered surface (Figure 4).
Depending on the amount of impurities the Inwood Marble weathers gray or tan and produces a sugary-textured surface on outcrops that ultimately develops into residual calcareous sand. Overall, the outcrops illustrate profound differential weathering with dolomite-silicate units standing in higher relief and calcite marble forming local depressions. With a bit of imagination, an overview of the entire outcrop at Isham Park allows a vision of mini-karst-like topography. Perched on this eroded surface are a number of Palisades diabase erratics and red-colored till, products of glacial advance from the NW.
A preliminary geological map of Isham Park is shown as Figure 5. Four major lithotypes are shown – white, coarse-textured calcite marble, white to gray dolomitic and calcite marble, marble, schist and calc-silicate rock and well-layered white to gray dolomitic marble. Although variable, the Inwood trends roughly N55°E, 73° SE in Isham Park and forms the eastern overturned limb of a large F3 synform which is cored to the west in Inwood Hill Park by the Manhattan Schist.
The marble, schist, and calc-silicate unit is intensely sheared and internally deformed by F2 tight- to isoclinal and F3 asymmetric folds producing complex interference patterns, boudinage and internal shearing of schistose boudins over a meter in dimension (Figure 6). Clearly, the marble + schist + calc-silicate sub-unit shows over-thickening and repetition of layers however most of the remaining carbonate sequence exposed in Isham Park appears to be homoclinal. Perhaps the over-thickening of the calc-schist unit is the result of the buttressing effect of the massive, well-layered marble that surrounds it. Asymmetric south-plunging F3 folds are locally developed in the Inwood of Isham Park (Figure 7). Abundant examples of boudinage of the quartzite and calc-silicate layers into lenses occur presumably the result of ductility contrast between the more competent siliceous rocks and the surrounding marble (Figure 8).
The broad outcrop-scale folding and warping of the S1 x S2 fabric is controlled not only by regional F3 folds but also are affected by open 2 m-wavelength SE-plunging F4 crenulate folds and open warps (∼ 55° plunge) with axial planar slip cleavage (S4), solution cleavage and joints trending ∼ N-S bearing moderate to steep dips.

Inwood Hill Park
The area of Manhattan north of Dyckman Street is known as the Inwood section. Except for Inwood Hill Park most of the region is underlain by the Inwood Marble marking the type-locality for that particular unit of NYC bedrock. This unit was originally called the Inwood Limestone by Merrill (1890). The geology of Inwood Hill Park is published elsewhere (Merguerian and Sanders 1991; Merguerian et al., 2011) but a brief summary is in order. Inwood Hill Park is located in the extreme northwest corner of Manhattan Island (Figure 22). The park is bordered by Dyckman Street on the south, the Hudson River on the west, Spuyten Duyvil (Harlem Ship Canal) on the north, and Payson and Seaman Avenues on the east. Isham Park occupies the flat area northeast of Inwood Hill Park extending eastward to Broadway between Isham and West 214th Streets.
We enter Inwood Park by following the path past the playground. The first prominent ridge to your left is composed of Manhattan Schist (OZm) which also dips steeply toward the SE, essentially parallel to the orientation of the Inwood Marble exposed in Isham Park. The S3 foliation in the schist is related to F3 folds with axial surfaces oriented N4l°E, 75°SE and south-plunging hinge lines. The F3 structures are superimposed on an older gently inclined S2 metamorphic layering which trends across Manhattan at roughly N50°W, 25°SW (Merguerian, 1983; 1996a). Both units are in contact but the contact is covered with soil. They form part of a huge south-plunging syncline with the Manhattan Schist preserved in the central core of the structure (Figure 10).
Strangely, the downfolds (synclines) hold up ridges and the upfolds (anticlines) underlie the flat valleys in northern Manhattan. Such inverted topography results from the marked contrast in weathering susceptibility afforded by the marble and schist. In the overall wet temperate climates such as we experience in this region, carbonate rocks (such as the Inwood Marble) weather and dissolve much more readily than do silica-rich rocks of the Manhattan Schist. As a result, structural synclines tend to be preserved to form topographically high ridges and structural anticlines are breached by weathering and erosion and commonly underlie the low valleys. (See Figure 2.) Such topographic inversions are well known in the folded central and northern Appalachians.

Glacial Potholes
Take the “high-road” path going southward to examine the dual potholes drilled into the east-facing slope of the westernmost synclinal ridge. The structure of the westernmost ridge is another south-plunging syncline overturned toward the northwest. (See Figure 10.) The S3 foliation in the Manhattan schist has transposed earlier fabrics and is associated with tight isoclinal F3 folds south-plunging hinge lines and axial surfaces oriented N41°E, 75°SE. At the north end of this ridge, we'll see the S2 foliation change trend from NE to NW to wrap around the synformal trough.
At the top of the trail, a bonus for glacial enthusiasts, two circular potholes produced by torrents of meltwater during the Pleistocene deglaciation are found (Figure 11). Clearly the potholes are cut into an already glacially polished rock outcrop. Here, we assume that resistant glacial drift boulders settled into a small depression (perhaps in ridge hugging drift) and then began to drill downward in response to vortices produced during turbulent flow from liberated glacial melt waters. A self-fulfilling prophesy, once the drilling begins the resistant boulders are trapped and constantly replenished by new boulders moved by water. In this case (Figure 11) the upper pothole merged to drill a second adjacent pothole. Since the potholes are developed on a sloping glaciated surface (pre-Woodfordian?), it may be tempting to envision that the potholes formed during a younger glaciation (Woodfordian?).
Farther up at the top of the trail past the potholes but before the trail bends into a hairpin turn to the right, note the highly polished outcrop of Manhattan Schist (Figure 12). The glacial striae and grooves are oriented N35°W to S35°E indicating the same glaciation that brought Palisades boulders from New Jersey. Sanders and Merguerian (1998) suggest this glaciation (from the NW to SE) was responsible for most of the deep glacial erosion in the NYC area and produced the prominent Harbor Hill moraine that extends across Staten Island, Brooklyn, Queens, and Long Island.

To Scenic Overlook of Hudson River
Continue up the trail on top of the westernmost ridge and jog left after awhile to get to the fine overlook across the Hudson to the Palisades ridge of New Jersey (Figure 13). Here, the columnar joints of the Palisades ridge are quite visible forming a steep wall of mafic rock that was intruded at shallow depth during the late Triassic-Early Jurassic split up of Pangea. Thus, we view across the Hudson, the products of a totally different type of tectonic activity than we have been viewing today. The metamorphic rocks of New York City were produced during deep-seated compressive deformation while the sedimentary and igneous rocks of New Jersey were produced by extensional tectonics associated with initial formation of the Atlantic Ocean basin. A cross sectional view from Manhattan to central New Jersey (Figure 14) shows that the entire Newark Basin is a rotated block of the earth’s crust with downward motion and westward tilting accommodated along the Ramapo fault. In this way the ancient Newark Basin is analogous to the modern rift basins of East Africa.
From the scenic overlook walk northward along trail toward the Henry Hudson Bridge and note that the foliation in the schistose rocks is oriented northwesterly and dips southward at the end of the trail before it heads downward. As mentioned earlier, this is the result of the wrapping of the early S1 x S2 foliation in the schist about the southward-plunging keel of the overturned F3 synform that holds up the westernmost ridge.
The contact between the middle and lower schist units (the St. Nicholas thrust) is exposed in a 20 m zone from beneath the Henry Hudson Bridge abutment to river level. Structurally beneath the Manhattan Schist, a 0.5 m layer of sheared (mylonitic) amphibolite is deformed by folds. Unlike the amphibolite in the schist unit above, which contains subidioblastic hornblende, this exposure of Manhattan amphibolite has been intensely sheared. Green hornblende porphyroclasts are set in a wavy, anastomosing foliation consisting of colorless amphibole, biotite, and quartz ribbons. The thrust zone is structurally complex consisting of intercalated lithologies of Walloomsac (Ow) and Manhattan Schist (OZm) together with mylonitic amphibolite. The Wallomsac is highly flattened and mylonitic at this location with a strong down-dip lineation, the result of localized shearing associated with the St. Nicholas thrust zone.

Marble with calc-silicate nodules
Directly beneath the bridge, where a dirt trail leads down to the river, a coarse-textured gray-white calcite marble with differentially eroded calc-silicate nodules is exposed at low tide. It is unknown whether the marble exposed at the low-tide mark is an interlayer in the Walloomsac schist (Ow) or the Inwood Marble (OCi). Unquestionably, the Inwood Marble lurks nearby as it wraps around the westernmost ridge of Manhattan Schist and underlies the Spuyten Duyvil, Marble Hill in the Bronx, and the Hudson River and was penetrated by a utility tunnel found east of and parallel to the Broadway Bridge. As a geometric result of the southward plunge of the major folds, the oldest unit of the NYC bedrock (Fordham Gneiss) projects up to the surface in the Bronx in a huge vertical exposure immediately across the Harlem Ship Canal. Here, in the Bronx, the Fordham is painted blue with the Columbia University “C”.

STOP 1. SE of Zoo work shed, Hartland formation.
OHM 2020: The UTM coordinates in the Guidebook have been corrected to WGS 84.
The exposure consists of gray- and locally brown-weathering muscovite-biotite schist and thin interlayers of biotite granofels, rocks typical of the Hartland formation (OCh) in New York City. The S2 foliation, which predominates at this exposure, consists of parallel thin laminae and local syntectonic granitoid veins oriented N80°W, 34°SW. F3 z-folds are also obvious with traces of axial surfaces oriented N42°E, 88°SE and F3 axes plunging 35° into S17°W. Abundant pegmatite veins (some with large books of muscovite) and veinlets create a nubby weathering appearance, but should not be confused with the aluminosilicate-induced nubby weathering of the OZm unit of the Manhattan Schist. Some of the pegmatite veins have been folded by the F3 folds. Local 10-cm thick quartzose segregations are present. An amphibolite, 15 cm thick, can be found at the south end of the exposure near 63rd Street.
Evidence for SE-directed glacial flow is obvious in the glacially sculpted exposure in the form of large- and small grooves oriented N30°W to N35°W wrapping around the south end of the exposure and at an azimuth of N40°W on top of the exposure.

STOP 2. Mylonitic Hartland formation cut by glacial grooves.
E of walkway just N of 65th Street Transverse Road
OHM 2020: The UTM coordinates in the Guidebook have been corrected to WGS 84.
The exposures of Hartland here consist of slabby, gray-weathering vitreous quartzite layers (thicknesses usually 4 to 5 cm, but locally up to 30 cm), granofels, minor schist and amphibolite with a laminated fabric developed parallel to a composite S2 foliation. S2, subparallel S1 and bedding (S0), are strongly transposed (oriented N56°E, 45°SE) because of the effects of F3 z-folds with axial surfaces trending N50°E, 85°SE. The F3 folds and associated lineations plunge 24° into S21°W. Away from the limbs of minor F3 folds, at the NE corner of the first exposure, the S2 fabric returns to its typical orientation, roughly N53°W, 28°SW. Pegmatites, up to 2 m thick, containing K-feldspar megacrysts up to 30 cm in size, have been intruded parallel to S3 . Vertical healed joints cut the exposures at a high angle (N42°W) and show positive relief producing a reticulate pattern with the dominant lithologic layering and parallel metamorphic fabrics.
All of the scattered outcrops show the effects of glacial rounding and polish. Glacial grooves are oriented N47°W to S47°E; they resulted from ice flowing toward the SE.

STOP 3. Mylonitic Hartland formation and glacial grooves
OHM 2020: The UTM coordinates in the Guidebook have been corrected to WGS 84.
E of walkway near "X" crossing of paths S of "The Dene;" .
Similar to the last exposure (still in view toward the S), here the Hartland possesses a pronounced mylonitic fabric because we are approaching Cameron's Line. The composite S2 + S3 foliation is oriented N70°E, 49°SE (the combined effect of transposition by F3 fold and late warps) and has been intruded by numerous foliated lit-par-lit granitoids. In fact, two generations of granitoids cut the bedrock: 1) an older foliated generation, as mentioned above, and 2) a younger sinuous granitoid that cuts across the metamorphic layers.
Glacial grooves are here oriented N25°W to N32°W; they are products of a glacier that flowed SE.

STOP 4.Two sets of cross-cutting glacial features on polydeformed Hartland formation.
Outcrop W of "The Dene"
This large polished exposure contains rocks similar to the last three stops and shows the effects of superposed F2 and F3 folds. The composite S2 + S3 foliation is oriented N53°E, and is vertical (90°) or dips steeply SE. The bedrock has been cut by two generations of healed fractures, an older one trending N40°W and a younger one, N-S.
Obscured by post-glacial weathering on the E end of the exposure a partial pothole greets the observant student of geology. Nearby, glacial grooves are oriented N35°W again, supporting our earlier observations, indicating a SE-directed glacial ice-flow direction. At the NE end of the exposure a glacial treat awaits our eyes. Here, a subdued roche-moutonnée structure oriented N37°E is cut by N36°W-trending glacial grooves. Thus, one of our older glacial advances has left its indelible mark on the bedrock. (See Table 1.)

STOP 5. Beginning of the Cameron's Line shear zone, and glacial features
By "Platform" (outcrop E of "The Dene" and N of playground)
At this exposure, we will try to convince you that deep-seated mylonitic faults such as Cameron's Line are not unique single surfaces of dislocation but rather zones of imbricated lithologies (termed mélange) bearing mylonitic fabrics. Here, we see commingled gray-weathering quartzite- and granofels-bearing schist of the Hartland (OCh) and rusty-weathering schist and gneiss of the Manhattan (OZm) formations in fault rocks bearing a highly penetrative S1 + S2 mylonitic foliation. Lithologies typical of unit OZm are mostly found near the north end of the exposure. Although variable because of F3 folding, at the south end of the exposure, the S1 + S2 mylonitic foliation strikes N68°E and dips 22°SE and can be traced parallel to the axial surfaces of F2 folds of the S1 foliation in quartzites. The F2 folds are reclined and plunge 25° into S10°W. Elsewhere, the enveloping S2 mylonitic foliation is oriented N46°W, 27°SW.
At the north end of the large exposure, where rusty-weathering OZm predominates, OCh granofels layers, 30 to 50 cm thick, can be seen "floating" in a schistose matrix (Figure 23). Such intermixing is perhaps the product of shearing and imbrication related to the formation of mélange within the Cameron's Line thrust zone. Here the S2 foliation swings to N75°W, 35°SW. The folds and fabrics related to the F2 and older folds are strongly reoriented by F3 folds. Tight- to isoclinal F3 folds plunge 25° into S15°W with axial surfaces oriented N28°E, 68°SE. Beautiful examples of F2 x F3 interference patterns are found in this exposure.
Glacial plucking has here been facilitated by joints oriented N85°E, 70°NW. A broad roche-moutonnée structure oriented N10°E occurs at the north end of the exposure and glacial grooves and troughs are found elsewhere oriented N32°W but crosscutting relationships were not observed. Based on what we saw at Stop 4, we suspect that the NW-trending grooves are younger than the roche-moutonnée structure.

STOP 6. Typical Hartland Formation away from the Cameron's Line thrust zone.
At USGS bench mark S of The Pond
OHM 2020: Picked location from topo sheet overlay - not UTM coords.
Rocks of the Hartland formation here consist of typical gray-weathering, highly muscovitic schist and massive, structureless granofels in an exposure at the SE corner of "The Pond", across from the Plaza Hotel. The granofels layers are quite numerous; their thickness varies from 3 cm to 50 cm and they are separated by schistose layers, 3 cm to 4 cm thick, exceedingly rich in muscovite (only about 5% biotite). Bedding is thus preserved and our interpretation is that the protoliths of the granofels layers were turbidites. With a little imagination, relict grading indicates that bedding tops toward the NW with S0 and parallel S2 and S3 oriented N48°E, 70° to 80°NW.
Upright F3 synformal folds of S0 and S2 plunge 20° into S45°W with axial surfaces oriented N45°E, 85°SE. A marked difference in mechanical behavior is indicated as the granofels layers show only large-scale warping at the hands of F3 folds yet the schistose interlayers are strongly folded and crenulated. Glacial grooves are oriented N32°W indicating SE-directed glacial-ice flow.

STOP 7. Folded and glacially polished Hartland formation.
W of the Pond, opposite the Avenue of the Americas access to Park
Muscovite schist and interlayered granofels of the Hartland are cut by open warps of the composite S2 + S3 foliation. These folds, which must postdate the F3 folds, plunge southward at 51° with NE-trending axial surfaces. A minor shear zone in the center of the exposure cuts through a 10-cm-thick layer of amphibolite and an F2 reclined fold refolded by F3 occurs on the south end of the exposure.

STOP 8. Hartland rocks sheared along F3 limbs and glacial features.
On S side of West Drive, near SW boundary of Park
The effects of shearing along the limbs of F3 folds here produce a penetrative foliation oriented N32°E, 90° in highly muscovitic rocks of the Hartland formation. The effects of rounding and smoothing of the bedrock surface here are quite obvious as are glacial grooves oriented N38°W.

STOP 9. Hartland rocks exhibiting bedding.
On N side of West Drive near bridge over walkway from 7th Avenue
Pronounced interlayering of granofels and muscovite schist here typify the Hartland formation. Bedding (S0) and the S2 foliation are oriented N43°W, 30°SW near the vicinity of an F3 antiformal hinge area (7th Avenue Antiform of Figures 16 and 18). The F2 folds here show z-fold symmetry indicating we are on the eastern side of the south-plunging antiform.

STOP 10. Hartland rocks "safe at home" (Umpire Rock) .
Umpire Rock is the most-spectacular natural exposure in the southern part of Central Park. Here, rocks of the Hartland formation show the superposed effects of F2 and F3 folds, abundant syn- and post-tectonic pegmatite intrusives, brittle faults, and numerous glacial features. The rocks consist of interlayered muscovite schist and granofels that have been cut by numerous granitoids. F2 fold hinges are locally preserved but the glacial smoothing of the outcrop surface inhibits direct measurement of plunge orientation. The S2 axial-planar foliation is strongly folded here but displays an average enveloping surface of N77°W, 21°SW.
F3 z-folds vary from open- to tight- to isoclinal in profile and plunge 22° into S25°W with axial surfaces oriented N35°E, 72°SE. Beautiful interference patterns result from the superposition of F2 and F3 folds. Late-stage open warps with southward plunges are locally developed. Some pegmatites are syntectonic (foliated) and were intruded parallel to S2. Other granitoids are thin aplites oriented N50°E and crosscut all structural fabrics. Yet younger micaceous pegmatites cut the aplites. At least two brittle faults oriented N32°E cut the exposure; the one on the eastern edge of the outcrop shows a crumbly gouge zone roughly 3 m thick.
Perhaps the most-obvious geologic features here are of glacial origin. At the NW edge of the exposure, glacial meltwaters have modified spectacular glacial troughs oriented N28°W. These troughs are related to the overall SE-directed roche-moutonnée shape of the exposure with its steep drop off toward the playground area. A potpourri of glacial erratics can be found on this outcrop. We identified erratics of Palisades diabase and hornfelsic Lockatong Formation from the Newark basin W of the Hudson River, granite, and diorite.
Around the steep, north-facing wall of the exposure, note the glacial grooves oriented N46°W and the grooves oriented N35°W on the eroded outcrops immediately north of the north-facing wall. Of additional structural interest, the north-facing wall offers a rare glimpse at the shallow dip of the S2 foliation and a sub-parallel granitoid sill, all folded by F3? or younger open warps.

STOP 11. Pegmatite erratic on glacially polished Hartland rocks.
E side of walk E of Heckshcer Playground
The most-obvious feature of this stop is the 2m-high K-feldspar megacrystic pegmatite erratic but we can not be sure whether the erratic has been placed there during park construction or renovation. The “erratic” rests on rocks of the Hartland that have been scored by N38°W glacial grooves. F3 s-folds are locally found in the exposure.

STOP 12. Mylonitic Hartland rocks.
E of junction of walks N of Stop 11
The Hartland formation here shows some evidence for lithologic mixing; rocks of the Manhattan formation are present in the form of tectonic inclusions consisting of wisps- and shreds of aluminosilicate-bearing, rusty- to maroon-weathering schist. The outlines of the wisps and shreds are masked by shearing along S2 and S3. S2 is well developed here and is oriented N68°W, 42°SW. F3 folds are not hard to spot with their typical southward plunges and steep NE-trending axial surfaces.

STOP 13. The Manhattan formation, by the Carousel
The exposure of rocks immediately west of The Carousel show the rusty- to maroon-weathering typical of the Manhattan Formation (OZm). Layers and lenses of kyanite+quartz+magnetite weather in positive relief and outline the S2 foliation which is largely mylonitic. Here, S2 is variable but oriented N70°E, 25°SE because of pervasive F3 folds plunging 34° into S25°W. The F3 axial surfaces trend N42°E, 68°SE. We map this area as the beginning of the Cameron's Line thrust zone and links these exposures to those found at our earlier Stop 5.