We have offered to lead this trip in order to lay before those interested in
Long Island geology some implications (we would go so far as to assert,
"far-reaching" implications) that follow from evidence we have discovered
during the past several years on Staten Island and in Westchester County,
chiefly, with respect to the number of and flow directions of the Pleistocene
glaciers. We are convinced that as many as 5 continental glaciers
spread into the
Proposition No. 1 in our interpretation may be paraphrased from a recent U.
S. Supreme Court ruling on voting rights: "one person, one
vote." In terms of tills, we would express this as "one
glacier, one flow direction." (Farther along, we discuss all the
caveats that go with this vision of "one glacier, one flow direction".
Suffice it to say here, that if this point is accepted, then a series of
drastic revisions in the Pleistocene geology of
Proposition No. 2 holds that the youngest of the Wisconsinan glaciers, the Woodfordian, flowed from the NNE to the SSW.
Proposition No. 3 holds that several pre-Woodfordian
glaciers flowed from NNW to SSE. In
BIG IMPLICATION: If ice flowing from the NNW to SSE deposited
the Harbor Hill moraine, then the age of that moraine must be pre-Woodfordian. We do not know its age exactly, but
concur with C. A. Kaye's (1964b) interpretation that the age of two prominent
moraines on Martha's Vineyard (correlatives of those on Long Island?) are
Early Wisconsinan and Illinoian. This
represents a major downward shifting of the age assignments of
Our next point is based on our new discovery at Garvies
Point of a till containing decayed granite erratics resting on the
Cretaceous. Without doubt, this contact is on a piece of material that
has been displaced upward by ice-thrust deformation and subsequent to that,
has slumped down to beach level. Nevertheless, whatever its post depositional
vicissitudes have been, we think this ancient till matches Fuller's Mannetto Gravel and that it is the product of a glacier
of Early Pleistocene age. We have found a comparably old till
containing decayed granitic stones on
Our approach to the study of
To date, our studies have led us to diametrically opposite conclusions from
all previous workers who have accepted the latest-glacial age for the
While we were pondering over how we could possibly put together a case strong
enough to instill some doubts in the minds of the "true believers"
and were in the midst of preparing the guidebook for our "On-The-Rocks"
We have summarized our interpretations on a new correlation chart (Table 1). Despite our lack of chronologic data, we present it as a logical statement of our current thinking and as a guide for others.
Our objectives for today's field trip for the Long Island Geologists are to take
the participants to 3 localities on the north
Specifically, our objectives are:
1. To examine the evidence for the proposition that the
Harbor Hill Moraine was deposited by a pre-
Woodfordian glacier which flowed from NNW to SSE.
This will involve us in a study of the erratics on
the north-shore beaches and discussions of their
2. To study an exposure of a till containing decayed
granitic stones (equivalent of Fuller's Mannetto
Gravel), and its contact relationships with the
3. To examine some exposed Cretaceous strata and to become
familiar with two distinctive varieties of Cretaceous
rocks, not exposed, that are common in the beach
gravels: (1) a hematite-cemented conglomerate
(erroneously identified by others as coming from the
Silurian Green Pond Conglomerate); and (2) a fine-
textured red sandstone (erroneously identified by
others as coming from the
4. To study the fans at the toes of the eroding bluffs and
how fan sediments and beach sediments are
interrelated. We shall use these fans as small-scale
models for interpreting the widespread outwash
So much for the introductory comments for today's trip. Now on to a
general summary of the bedrock geology to the northwest and north of
Viewed as a first approximation, any reasonable geologic intuition holds that
the erratic boulders found along the north
Rocks virtually identical with those of the
In the following paragraphs, we review the distinctive features of the
bedrock in southeastern
The bedrock geology of southeastern
Geotectonic map of western
Figure 3. Simplified geologic map of Manhattan Prong showing the distribution of metamorphic rocks ranging in ages from Proterozoic to Early Paleozoic. Most intrusive rocks have been omitted. (Mose and Merguerian, 1985).
Tectonic map of
Tectonic sketch map of southern
Cameron's Line, which skirts the New York - Connecticut state boundaries,
separates rocks of the Manhattan Prong to the west from coeval rocks to the
east that were deposited in a dramatically different paleogeographic
setting. Rocks to the west of Cameron's Line include the metamorphic
rocks of the Manhattan Prong consisting of the Proterozoic
Y Fordham Gneiss, the Proterozoic Z Yonkers and Poundridge gneisses and coeval rift-facies
strata mapped as the Ned Mountain Formation, the Cambrian Lowerre
(Cheshire) Quartzite, the Cambrian-to-Ordovician Inwood
(=Woodville, and Stockbridge) marbles, and overlying Middle Ordovician
Manhattan Schist (Unit A) and correlative Annsville
Phyllite. In addition, these basement-cover
rocks are structurally overlain by allochthonous
rocks of the Taconic sequence and their metamorphosed, dominantly massive
southerly equivalents (the Manhattan Schist and related amphibolite
(Units B and C), the Waramaug Formation, and
locally, the Hartland Formation). Farther north, beyond the
Hudson-Reading Prong in
Extending toward the southwest of the
Given the varied lithologies found in southeastern
The Western Terrane
(1) The western terrane includes mostly metamorphic rocks that form part of
the central crystalline core of the
We begin with the contrasting metasedimentary rocks found adjacent to
Cameron's Line and then summarize some of the distinctive mylonitic
rocks and igneous rocks. In westernmost
East of Cameron's Line, the bedrock formations differ significantly from
those of the Manhattan Prong to the west of this line. To the east, the
Cambrian-to-Ordovician Hartland Formation is the dominant formation
underlying the crystalline highlands of western
To the east of the panhandle area of southwesternmost
CM interprets Cameron's Line as a thrust fault within a deep-seated subduction complex that formed during the medial
Ordovician Taconic orogeny adjacent to the Early Paleozoic shelf edge of
The rocks along the Taconic suture (Cameron's Line) form an impressive zone of mylonitic rocks that experienced abnormally high shear strain under deep burial during the Taconic arc-continent collision. Mylonites, or ductile-fault rocks, bear unique metamorphic textures that can be easily identified in the field by their highly-laminated appearance and distinctive microtextures under the microscope.
With respect to the Taconic orogeny, local plutons are both synorogenic and post-tectonic. The older group of synorogenic plutons cut across Cameron's Line in western
The younger group of post-orogenic
intrusives include Devonian lamprophyre and
potash feldspar-phyric (meaning a porphyritic rock containing feldspar phenocrysts
to translate for those of who have not been exposed to the "new"
petrologic language) Nonewaug Granite. Other
plutonic rocks of still-younger ages include isolated bodies of Permian syenite, -adamellite, and -dacite porphyry. Of additional help, we are
investigating the distribution of economic ore deposits in the crystalline
terranes to the north- and northwest of
The Central Terrane
The rocks of the central terrane consist of Mesozoic sedimentary- and igneous
rocks filling the
Lithologically distinct, the strata filling the Mesozoic basins consist predominantly of east-dipping, red-colored sedimentary rocks and intercalated basalts with local intrusive mafic rocks (for example, the Buttress and West Rock dolerites). Correlative with the Upper Triassic to Lower Jurassic Newark Supergroup of New Jersey (On-The-Rocks Trip #5), the rocks of the Hartford and Pomeraug Basins include the New Haven, Shuttle Meadow, East Berlin, and Portland formations consisting of red- to maroon-colored micaceous arkose and quartzose sandstone and siltstone, shale, and local conglomerate and fanglomerate, together with subordinate black shale and local dolostone, and intercalated dark-colored mafic volcanic rocks of the Talcott, Holyoke, and Hampden basalts.
The basins are internally cut by a myriad of faults and, as discussed below,
trend southward and project into Mesozoic grabens in
the subsurface of Long Island and the New York Bight that have been
identified by samples from drill holes and data from geophysical surveys (Klitgord and Hutchinson, 1985; Hutchinson, Klitgord, and Detrick, 1986;
Hutchinson and Klitgord, 1988). The distinctive
color and lithology of these rocks make them ideally suited for use in
analysis as indicator stones and as sources for the generation of red-colored
tills but similarity with rocks of the
The Eastern Terrane
The crystalline rocks to the east of the basin-marginal fault along the east
side of the
The Ordovician rocks of the Bronson Hill - Ammonoosuc
volcanic terrane include the Monson Gneiss and overlying
Intrusive into these crystalline rocks are many plutons ranging in age from
Ordovician to Permian. The distinctive rocks among this group on the
Connecticut side of the Lake Char - Honey Hill Fault Zone include the
Ordovician Preston Gabbro (+/- diorite), the
Devonian Lebanon Gabbro (+/- diorite), and unnamed
Devonian norite, diorite, and granitoid
gneiss. In places where the mafic rocks are
in close proximity to the
Thus, given the complexities of the geology of the state of
DIRECTIONS OF GLACIER FLOW
The directions of flow of a former glacier can be determined easily and unambiguously in the field by recording the azimuths of features eroded on bedrock by the flowing ice (such as striae and grooves, and the long axes and slope asymmetry of roches moutonées and rock drumlins), by plotting the distribution of erratics (especially indicator stones), and by recording certain asymmetrical properties of glacial deposits (such as directions of orientations of elongate clasts and the long axes of drumlins).
In the nineteenth century, the raw data on ice-flow marks on the bedrock were
collected systematically. Indeed, many papers dealing solely with data on
striae on bedrock surfaces were published.
Before long, the novelty of such papers wore off. And a worn-off
geologic novelty is like yesterday's newspaper. Novel or not, the
straightforwardness of the directional data disappear when one begins to interpret
them. If all the flow-directional data in a given region are about the
same, interpretations are not controversial. But, if more than one set
of flow-directional indicators have been found, then that is another
story. In the following paragraphs, we review the evidence that in the
Glacial striae on bedrock surfaces
Perhaps the easiest of the ice-flow indicators to record are the directions
of striae and grooves on the bedrock. In
Details of Gale's observations are contained in our On-The-Rocks guidebook
for Trip 15 to
That great genius of
"In order to determine the direction of the diluvial currents, a particular knowledge of the local character (sic) of the rocks, as indicated in the account already given of the different local formations, is indispensable. Several of these local formations are so peculiar in the character (sic) of their rocks, that the latter cannot be mistaken, to whatever distance they may have been transported. These, by the distribution of their bowlders and fragments, furnish conclusive evidence that the more general (sic) direction of the diluvial current was S. S. E. (Percival, 1842, p. 454)
Despite the numerous examples he cited that demonstrate transport from NW to
SE, Percival reported that some rocks had been moved from NNE to SSW.
As did Gale in
"Although the general direction of the diluvial current was apparently S. S. E., yet in some instances, from local obstructions, its course was deflected to a S. S. W. direction. This is most distinctly obvious along the Western border of the larger Secondary formation, where blocks and fragments of the Trap and Sandstone of that formation are accumulated, sometimes quite abundantly, in such a direction from their apparent source." (Percival, 1842, p. 457).
Striated bedrock lending further support for glacial flow from the NW or NNW
to SE or SSE was found by Woodworth (1901) in
Hanley and Graff (1976) found numerous places in
Indicator stones implying flow from NW to SE have been found on
Sketch map of area west of
Sketch map showing lobate margin of a terminal
moraine (Harbor Hill?) in
Figure 7. Sketch map of the geology of Umpire Rock, Central Park, New York showing directions of glacial striae oriented NW to SE. (After Hanley and Graff, 1976, p. 43; modified by JES.)
Distinctive erratics found in till in New York City, (1) anthracite from
northeastern Pennsylvania, and (2) Green Pond Conglomerate from northern New
Jersey, support interpretation of rectilinear flow of glacier from NW to
SE. Stippled area, outcrops of anthracite coal;
After he had analyzed the Pleistocene stratigraphy of the
"The direction of ice flow in the
and adjoining uplands was studied by means of
the orientation of striations (sic) and grooves
on the bedrock surface, the orientation (sic) of
the long axes of drumlins, the direction of
transport of erratics in till, and the direction
of thrusting and and overturning of bedding in
glacially deformed drift. These data range
through 360° in azimuth. Analysis of this
confusing message shows the existence not of
an ever-shifting ice current but of at least
four separate and distinct ice currents of
different ages. Three of these flowed fairly
rectilinearly, but one (the last) was
multicomponent and marked by strong lobation"
(1982, p. 31).
Kay numbered these tills from I (oldest) to IV (youngest). Tills I, II, and III flowed from the NW to the SE, the mean direction being S23°E +/- 1° for Till I; S64°E +/- 18° for Till II; and S31°E +/- 2° for Till III. Till IV was from the NNE.
The regional geologic relationships in the
If one grants that the ice-flow indicators presented imply flow from both the NNW and the NNE, then several interpretations are possible. Three ideas are analyzed here: (1a) that changing meteorological conditions caused the sites of maximum snow accumulation to form "ice domes" on the top of the glacier and that flow direction responded to the changing zones of maximum ice thickness, thus enabling the flow directions within a single ice sheet to shift with time; (1b) that the margin of the ice sheet was characterized by lobes within which the ice flowed with contrasting directions; and (2) each set of flow directions was made by a single glacier having only one dominant flow direction.
(1a) Changing meteorological conditions and shifting ice domes.
The theoretical background in support of the concept that changing meteorological conditions could shift the locus of maximum snow accumulation to build ice domes and that as a result, one and the same continental ice sheet could display multiple flow directions was proposed at the time when the modern version of the Laurentide Ice Sheet was advocated (Flint, 1943).
(1b) Ice lobes at glacier margin.
Another version of how a single glacier could create flow indicators having several directions is based on the behavior of ice lobes. Such lobes characterize the terminus of a valley glacier that has spread beyond the confining bedrock valley walls. Although the main flow direction of ice in a valley glacier is parallel to the trend of the valley, within the terminal lobe, the spreading ice creates divergent flow paths.
(2) One ice sheet, one flow direction.
Our field studies made mostly off
We make no claim that we have proved that our interpretation is correct and that it should, therefore, supersede all others. Our scheme lacks a chronologic basis; we are vulnerable to all the pitfalls associated with that oft-used method of "counting down from the top." But, given the current state of affairs in local Pleistocene geology, we believe that our beliefs should be considered by the believers of contrasting sets of beliefs. Our interpretation contains specific, checkable consequences with regard to the provenance of the tills.
Rectilinear flow from NW to SE of glacier older than the latest
Wisconsinan. This glacier flowed across the
Inferred flow pattern of latest Wisconsinan glacier, down the
DESCRIPTIONS OF LOCALITIES ("STOPS")
Outwash, till, and loess in coastal cliff; fans and beach sediments at
Much of the present preserve was formerly part of the Sands Point U. S. Naval Station. To the west of the wooden stairs at the end of trail 3, archeological artifacts including arrowheads, coins (late 1700s), square hand-made nails, and pottery have been found.
Take trail #3 (numbers on painted markers) to beach past kettle lake. Note abundant erratics including possible blueschist boulders.
Four topics are of special interest here: (1) provenance of the erratics on the beach; (2) stratigraphy of the Pleistocene sediments, (3) erosion of the bluffs, and (4) relationships of the modern beach sediments to the older deposits and to sediments eroded from them.
Provenance of erratics on the beach
The most-diagnostic erratic we have found here so far is the block of middle Ordovician Normanskill graywacke (from the Appalachian-Hudson valley) near the place where the trail leads down to the beach. An early lesson that needs emphasizing here is how to distinguish between the blocks of concrete having local beach gravel as aggregate and the Upper Cretaceous hematite-cemented conglomerate. A careful search of the concrete will show that some of these hematite-cemented conglomerates were among the stones used in the aggregate. Notice that in these Cretaceous conglomerates, the rock usually breaks around the rounded, white quartz pebbles. This is a simple, but diagnostic way to tell these local Cretaceous conglomerates from the Lower Silurian Green Pond metaconglomerate in which the rock breaks across the quartz pebbles.
Other distinctive erratics whose provenance we have not yet established include mylonitic rocks and various granitic- and dioritic gneisses, schist, gneiss, amphibolite, and pegmatite.
Absent here are any Upper Triassic-Lower Jurassic rocks
(red sandstones, feldspathic conglomerates, dolerites, etc.) from the
Stratigraphy of the Pleistocene sediments
Beneath slope-wash cover, the cliff face consists of horizontally stratified outwash sand and -gravel with mafic minerals, and rounded white quartz pebbles. Outwash is overlain by till(?) and a layer of coarse reddish loess, 1 m thick, which undoubtedly was derived from a red till. We have not dug out this entire bluff, but have scraped away the slope-wash cover from near the top. We do not have anything definitive to say about the stratigraphy here but remind everybody that we are not far from the famous Port Washington sand pits, where Mills and Wells (1974) and Sirkin and Mills (1975) have described spectacular effects of ice-shove deformation involving both the Pleistocene and underlying Cretaceous.
Erosion of the bluffs
Herb Mills has been studying the rate of retreat of the coastal cliffs here. He told us about the history of the iron rods, 40 feet long, some of which can still be seen sticking out of the cliff sediments at the east end of the beach, but many of which have fallen down to the beach. These rods were buried at a shallow depth along the top of the bluff, at right angles to the trend of the bluff. Herb does not know their exact purpose, but infers that they were emplaced for the purpose of anchoring some structure or other. At any rate, in 1970, he first noticed that the ends of these rods were starting to stick out of the bluff. By 1990, the cliff had retreated southward approximately 40 feet, giving an average rate of 2 ft/yr.
Relationship of the modern beach to the older deposits and to sediments eroded from them.
Along the base of cliff exposing the Pleistocene sediments, a modern
beach has accumulated. At the mouths of each of the tiny watercourses
or larger channels, where rainwater is concentrated into surface flows that
erode the Pleistocene sediments, a fan is present. On
We think that these small fans are useful to study, not only for themselves
and their relationships to the eroding coastal bluffs and adjacent beach
sediments, but also because we think that they provide useful small-scale
models of what was happening during much of the Pleistocene when
Walk back to vans and prepare to go to Stop 2.
Restored profile-section from
Cretaceous clays and sands; Lower Pleistocene outwash and till; and
postglacial loess at
For permission to visit, contact Ms. Kathryne Natale [Chief; tel. (516) 671-0300
or Mr. Douglas Winkler (Asst. Curator) (same #)].
Many points of geologic interest are here, including numerous excellent
exhibits on the geologic history of
En route to the beach we shall make a brief stop at the three large erratics. We shall not bother with the interesting landforms, but proceed directly to the stairs leading to the beach.
Two chief features exposed in the slumped- and eroding bluffs south of the stairs here are: (1) the Cretaceous strata; and (2) the Lower Pleistocene till containing decayed granite clasts (the Manetto of Fuller). In addition, the boulders on the beach contain a large variety of erratics.
The exposed Cretaceous consists of varigated clays and sands with lignite seams and layers of charcoal (products of Cretaceous forest fires). Stratigraphy as found in slump block to south of wooden stairs is:
Yellow-brown sand with local cross strata, underlain by
Red-purple clay with local lignite at base, and
Lower Pleistocene sediments
The Cretaceous is overlain by a reddish till consisting of deeply weathered granitic boulders, Cretaceous ironstones, and manganiferous residue at contact with underlying outwash. At the right side of the face that we shall clean off for study is a large groove in the underlying Cretaceous. Of significant importance, the orientation of this groove indicates ice flow from the NW or even WNW.
In the currently fashionable "one-glacier-did-it-all" concept, Fuller's Jameco Gravel and Manetto Gravel, have been reassigned to younger ages. For example, Sirkin wrote:
These two units "probably do not represent pre-Wisconsinan glacial (sic) or interglacial deposits but may be Wisconsinan outwash. Another unit, the Gardiners Clay, was believed to represent an Early Pleistocene interglacial (Fuller, 1914) and was subsequently placed in the Sangamonian Interglacial Stage (MacClintock and Richards, 1936). In historical usage, a variety of fine-grained sediments of both fresh water (sic) and marine orgin have been called the Gardiners Clay. These strata, which have been observed in surface exposures and well sections, can vary considerably from the original fossiliferous marine sediments of the type section (Upson, 1968; Sirkin and Mills, 1975). Gustavson (1976) has shown that certain so-called Gardiners Clay units contain fossil faunas quite unlike the fauna from the type section, while Sirkin and Stuckenrath (1980) indicate that some strata identified as Gardiners Clay could be of Portwashingtonian age, particularly in the absence of radiometric ages for either the original or the presumably correlative units.
"The inclusion of such strata in the Woodfordian moraines only show that they predate
(sic) the Woodfordian advance. As a surface
deposit, the Manetto Gravel, although well
weathered, is probably Woodfordian outwash (Sirkin,
1971), derived from deeply weathered granite and granite gneiss in
For reference, we include Fuller's original description (1914) of the Mannetto Gravel:
(p.80) Mannetto Gravel
"The Mannetto gravel was named from the Mannetto Hills (West Hills), on the crest of which just west of Melville some of the best exposures of this gravel on the island were found. (See section, p. 68.)"
"The Mannetto gravel, as is indicated in the table on page 21, is the earliest of the Pleistocene deposits. It consists of stratified (sic) and in some places cross-bedded gravels composed mainly of well-rounded pebbles of quartz from half an inch to an inch in diameter mixed with coarse yellowish quartz sand, but carrying everywhere a few deeply weathered granitic pebbles and scattered large bowlders of crystalline rock, also deeply weathered or disintegrated. It includes a few thin intercalated beds of yellowish clay. The granitic fragments can usually be crushed by the finger or by a slight blow of a hammer, and even the quartz is far more friable than fresh fragments. The quartzose (sic) and stained character (sic) of the gravels, the deep weathering of the pebbles, and the complex flow and plunge (sic) structure are the distinguishing features of the formation.
(p.81) Source of Material
"The great predominance of quartz in the Mannetto gravel is at variance with the composition of the later glacial deposits, in which granites are very abundant. It seems likely that this predominance arises from the nature of the formations of the Coastal Plain farther north. Highly quartzose Cretaceous beds probably extended across what is now Long Island Sound, overlapping the metamorphic rocks of Connecticut, and, being nearest, furnished a large part of the materials of the Mannetto gravel, as compared to the relatively small portion fornished by the more remote (sic) granitic rocks.
(p.82) Outcrops in the interior of the island
"Melville.--The finest exposure of the Mannetto yet found is that in the southern half of the West or Mannetto Hills, outside of the moraine. In these hills the Mannetto gravel appears to form an extensive terrace ranging from about 270 to 330 feet in height. The formation could be best seen in 1903 at the side of the road leading from Melville to the crest a mile west of that village. There 40 feet of somewhat irregularly stratified but not cross-bedded (sic) buff (sic) to orange-colored gravel, mainly quartz with a few rotten granite and ferruginous sandstone fragments, was found resting on the pre-Pleistocene deposits. Essentially horizontaly gravels of the same type, though somehwat less stained, are seen at intervals to the base of the hill, their relations (sic) being as shown in figure 57."
"South end of Mannetto Hill.--Many sections of
the Mannetto can be seen about the south end of the
Mannetto Hills, especially in the vicinity of
"Among the points at which the Mannetto gravel was recognized were the small projecting ridge east of the road half a mile northwest of Plainview, the sand pit just northeast of the Bethpage clay pit, sections on the east-west road a mile south of Plainview, and the cut made by the east-west road through the till a quarter mile north of Bethpage Junction. At the last-named locality a fine unconformity, marked by a zone stained by iron and manganese, was seen between the Mannetto and the overlying Manhasset. The steeper slopes of the Mannetto Hills are commonly covered with talus defying identification."
Half Hollow Hills.--From road sections it seems probable that a large part of the mass of the Half Hollow Hills also is made up of the Mannetto gravel, although no typical outcrops were discovered. Yellowish sands, however, such as occur in this formation at many places, were seen in several road cuts. The top of these hills appears to consist of later Pleistocene material, abounding in large and relatively fresh granitic fragments."
(p.83) Outcrops on the coast
"Lloyd Neck.--On the north side of Lloyd Neck the Mannetto
was apparently removed by the erosive action of the Montauk ice, no
indication of it being seen over the Cretaceous outcrops at that place.
Back of the south end of the beach southwest of
Section north of Lloyd Beach Feet
Montauk till member of Manhasset formation (?): Interstratified yellowish clay
and sand with an occasional erratic up to 6 inches in diameter . . . . . . . . . . . . . . . . . . . . . . . 2
Dark-gray clay . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.5
Bright-yellow clay . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
Yellow clay with ferruginous sand and pebble layers . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
Fine quartz gravel with iron and manganese stains; weathered granitic pebbles . . . . . . 5
"The beds are folded on east-west axes, the dips ranging from 5° to 30°."
We think that the till containing the decayed granitic stones correlates with Fuller's Mannetto gravel. We concur that the Mannetto is of Early Pleistocene age (based on the state of decay of its stones) and thus find no merit in Sirkin's assertion that the age of the Mannetto gravels is Woodfordian.
As for the MacClintock and Richards (1936) reassignment upward to the Sangamonian of the Gardiners Clay (assigned to the Yarmouth Interglacial by Fuller), which has become established "dogma," we refer the reader to Ricketts (1986).
The beach is littered with boulders of great variety and distinctive types include:
plagioclase-phyric gabbro with xenoliths,
potash feldspar phyric granitic gneiss,
mylonitic granitoid gneiss,
potash felspar pegmatite,
mica-rich red shale (Cret.),
hematite-cemented conglomerate (Cret.),
and many others.
As at Sands Point, no erratics of Triassic-Jurassic Newark-type basin fill rocks are present.
Unfortunately, we do not yet know the provenance of these boulders, some of
which are very distinctive. The augen gneiss may be from the Bedford
Gneiss of Westchester County and the epidote amphibolite is probably from the
STOP 3 - Target Rock - Tills, outwash, hogwash, loess and erratic boulders. UTM coordinates = 632.0E/4531.8N, Lloyd Harbor 7-1/2 minute quadrangle.
In our pre-trip visit to Target Rock, we were not able to study these exposures that were described in 1975 by Sirkin and Mills. We are eager to have a look at them, but if we do get to all of them, we will be seeing them for the first time. From what we did see, we disagree with the provenance of the stones inferred by Sirkin and Wells. We include extensive quotations from Sirkin and Mills (1975, Trip B-5, p. 316-322).
Guide to trip from stairway to the beach and extending NW along the
Stop 1: Ca. 100 m NW of stairway.
Beach upward: outwash, till, outwash, and loess.
From top downward:
Loess: ca 1 m. thick.
Outwash: "Stratified sand and gravel (outwash?) forms a lens pinching out to the southeast and thickening to about 2m to the northwest. The height of the cliff diminishes southward as this unit pinches out."
Till: "A compact, brown till (a sandy loam with abundant cobbles and boulders) about 1 m thick overies the outwash."
Glacial outwash: "approximatley 5m of glacial outwash composed of stratified sand and gravel."
"On the beach there is an abundance of cobbles and boulders.
Diabase and purple-red puddingstone conglomerate erratics, along with till
fabrics and other rock compositions suggest a northwesterly
source are for the till. The diabase may be derived from the
"Between Stops 1 and 2, cobbles begin to appear in the loess and the stratified unit above the till thickens and then thins until the loess is nearly resting on the till."
Stop 2. Actively slumped section in the topographic high; added relief supplied by thickening to about 8 m of sediments above the till.
"These //(p.320) stratified layers exhibit small scale (sic) cross bedding and bedding rippled by translational waves overturned to the southeast. This unit is characterized by clay, silt, and fine sand at the abase which is somewhat obscured by slumping. It coarsens upward into fin and medium sized (sand). Overall this unit probably represents sedimentation in a proglacial lake that aformed between the ice just to the north and the upland to the south."
"On the beach a number of predominantly dark colored (sic) erratics of mafic composition have been eroded from the till.
Some of these rocks resemble the Harrison Gneiss found to the north and
northwest in southern
Stop 3: in two parts, A and B.
Stop 3A: "low cliff where well exposed (sic) lake silts may be observed."
"Here the basal unit of interbedded, fine grained (sic) silts and sands are well exposed. These beds are somewhat disturbed and have small folds that are overturned to the southeast, and represent additional evidence of minor glacial deformation due to overriding by the ice."
Stop 3B: (description omitted).
Stop 4: The low cliff at the northern point of the beach.
Two tills exposed here; erratics are more felsic than farther south.
"This upper till is of limited extent and seems to grade southward into proglacial deposits. It was probably deposited
during the 'Necks' stillstand, with
a different source areas than the underlying till. While (sic)
correlation with other local tills has not been resolved, the lower till may
be the equivalent of the upper or late Wisconsinan till (the Roslyn Till) in
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