NEW YORK STATE GEOLOGICAL ASSOCIATION
60th Annual Meeting
FIELD TRIP GUIDEBOOK
JAMES F. OLMSTED
EDITOR
HOSTED BY:
THE CENTER FOR EARTH AND ENVIRONMENTAL SCIENCES
AND
THE CENTER FOR LIFELONG LEARNING
STATE UNIVERSITY COLLEGE
PLATTSBURGH, NEW YORK
PREFACE
Upon recalling my first thoughts of a teaching job at SUNY at Plattsburgh two impressions seem to have been important to me. One was the prospect of living in a pleasant place with interesting landscape and variable climate and secondly some interesting geology at the doorstep. Someone who considers himself a field petrologist is certain to be impressed with the notion of living and teaching with the Green Mountains a few miles to the east and the Adirondacks nearby in the other direction. Those thoughts could not begin to represent the richness and variety of the geology and its history to be found in the Champlain Valley. The fact alone that this college is hosting the NYSGA for the second time in less than twenty years is evidence of the interest in the geology of the Lake Champlain region.
All of the trips that are offered here reflect work that has been accomplished within the last ten years. Many of these works include efforts of students who have surely benefitted greatly as have the authors and, we hope, so will you. That this region continues to be a spectacular geological laboratory is supported by the variety of descriptions included herein.
I would like to thank all of those who contributed to this volume, in particular Dave Franzi who personally prepared much of two of the trips and solicited another and helped me in many other ways. Thanks is also due to Carolyn Turner who assisted with some of the typing and to Dave Lawrence who supervised production of the volume. Thanks is also due to the other faculty in the CENTER who helped in many ways and to Yngvar Isachsen who provided the cover design. Finally recognition is due to Tom Wolosz of our department, current NYSGA president and to Kate Chilton of the Center for Lifelong Learning, Plattsburgh State who ran the meeting. One does not have to read very far to realize that a number of important conclusions are reported here. The authors are to be commended, and I also wish to thank them here.
Finally that this is the SIXTIETH annual meeting of this organization attests to the vitality of the NYSGA and of geology as a profession in New York State. In reviewing previous guidebooks I am impressed with them as a resource of geological literature for New York and adjacent areas. The NYSGA provides important academic and professional service to the region and truly deserves this recognition.

A1:ASPECTS OF THE GLACIAL GEOLOGY OF KEENE AND LOWER AUSABLE VALLEYS, NORTHEASTERN ADIRONDACK MOUNTAINS, NEW YORK
JOHN A. DIEMER
Department of Geography and Earth Sciences
University of North Carolina at Charlotte
Charlotte, NC 28223
DAVID A. FRANZI
Center for Earth and Environmental Science
State University of New York at Plattsburgh
Plattsburgh, NY 12901
INTRODUCTION
The existence of Late Quaternary proglacial lakes in the Adirondacks has long been suspected (Taylor, 1897; Kemp, 1898; Ogilvie, 1902; Alling, 1916, 1919; Denny, 1974; Craft, 1976; Gurrieri, 1983; Diemer, et.al., 1984; Gurrieri and Musiker, 1988). Sedimentary deposits interpreted as dropstone-bearing varves and landforms interpreted as incised outlet channels, deltas and wave-formed beaches have been used as evidence for the existence of these intermontane proglacial lakes. On this trip, we propose to document some of these features in Keene and lower Ausable Valleys of the northeast Adirondacks. We will also discuss some constraints on the history of deglaciation of this region. Much work on the glacial geology of the northeast Adirondacks remains to be done and we hope you find this trip to be provocative.
FIELD AREA
Keene Valley extends northward 35 km (22 mi) from St. Huberts to Au Sable Forks (Figure 1). Waters from the Upper and Lower AU:sable Lakes feed the East Branch of the Ausable River which flows northward through Keene Valley. The elevation of the valley floor is 340 m (1117 ft) at St. Huberts (Figure 2), 254 m (833 ft) at Keene (Figure 3), and 170 m (558 ft) at Au Sable Forks (Figure 4). The West Branch of the Ausable River originates to the south of Lake Placid (Figure 1). It drops in elevation from 488 m (1600 ft) to 305m (1000 ft) as it flows through Wilmington Notch. At Haselton (Figure 5), the elevation is approximately 254 m (832 ft) . The confluence with the East Branch of the Ausable River is at the town of AuSable Forks. Below the confluence, the Ausable River flows east-northeast for 25 km (15.5 mi) through the lower Ausable Valley and empties into Lake Champlain (elevation 29 m (95 ft)) at Ausable State Park. · The mountains bordering Keene Valley are highest at the southern end (e.g. Giant Mountain to the east of St. Huberts is 1410 m (4627 ft)) and decrease in elevation northward (e.g. Bald Mountain southeast of Au Sable Forks is 652 m (2139 ft) (Figure I)). Major cots along the drainage divides separating Keene Valley from adjacent watersheds occur along lineaments. Two prominent sets of lineaments trend approximately NE-SW and NW-SE. The elevations of the cols decrease north ward.

A1: ASPECTS OF THE GLACIAL GEOLOGY OF KEENE AND LOWER AUSABLE VALLEYS, NORTHEASTERN ADIRONDACK MOUNTAINS, NEW YORK

STOP 1. Norton Cemetery
The borrow pits in the eastern part of the Norton Cemetery terrace contain stratified sand and gravel deposits. In the lower parts of the pits, horizontally stratified, trough cross-stratified and cross-laminated fine to medium sands in bedsets decimeters thick are common. Soft sediment deformation features are locally abundant. The terrace deposit coarsens upward to trough cross-stratified and channelized sands and gravels. Channels are decimeters to a meter or so deep and meters wide. Channels are filled with either stratified or massive sands and gravels. Channel margins have variable dips including nearly vertical.
Near the top of the Norton Cemetery terrace deposit, a sharp erosion surface is overlain by trough and planar cross-stratified sands and boundary gravels filling small channels. The channels intercut and are decimeters deep and meters wide. A concentration of boulders occurs immediately above the sharp erosion surface. Rounded, laminated, mud clasts occur locally both above and below the sharp erosion surface (Figure 70).
The terrace deposits are interpreted as a upwardly coarsening delta deposit. The lower part of the sequence consists of delta foreset beds with subaqueous channels, partly filled by sediment gravity flow deposits, at their upper ends. Steeply dipping channel margins may be due to channel incision into a frozen substrate. The prominent erosion surface is interpreted as the contact between delta foreset and fluvial topset beds. The trough and planar cross-stratification above the erosion surface are interpreted as the product of deposition by migrating dunes and small bars. The abundant intercutting channel forms an~ bar remnants suggest a braided stream origin. Rounded, laminated mud clasts are interpreted as either reworked, higher-level, lacustrine rhythmites or as floodplain muds.
A second locality at Stop 1 is at the end of the access road to Norton Cemetery. The access road to the south of the cemetery entrance has been closed as a result of slumping. In the landslide scar, climbing ripple cross-laminated very fine sand with abundant mud drapes can be seen. The bedding has been disturbed, either by soft-sediment deformation or by road construction. These sediments are the lowest accessible terrace deposits and are interpreted as the distal portion of delta foresets. A spring line marking the contact with underlying interlaminated muds and clays (rhythmites) is located a few meters downslope. The rhythmites are centimeter-scale ·and interpreted as lacustrine deposits formed in a setting close to a sediment source (i.e. a side valley tributary). Hence the rhythmites are interpreted as delta toeset beds.

STOP 2. D.O.T. Sand And Gravel Pit, Keene, N.Y.
The Department of Transportation operates a sand and gravel pit 1 km to the south of Keene, N.Y. The sediments are composed of stratified sands and gravels interbedded with diamictons. Grain size ranges from sand to boulders in both the stratified gravels and the diamicton. These sediments are interpreted as ice-contact glacial outwash in origin.

STOP 3. Rhythmite Sequence At Haselton, N.Y.
The sediments at Stop 3 are composed of a diamicton overlain by a rhythmite sequence. The diamicton contains boulders as large as 1 meter (Figure 8A). The top of the diamicton has decimeters of relief and is conformably overlain by millimeter to centimeter thick interlaminations of mud and clay (rhythmites). Dropstones are common (Figure 8B). The rhythmites are typically horizontally bedded, but may be locally deformed (Figure 8C). In places, rhythmites arc interbedded with cross-laminated sands which have sharp basal contacts and grade upward to asymmetrical ripple forms draped by mud laminations (Figure 8D). The sediments at this stop are interpreted a s glacial till or debris-flow deposits at the base (diamicton), overlain by lacustrine sediments (rhythmites). The rhythmites may have accumulated in a setting distant from a sediment source as they are fine grained. The interbedded cross-laminated sand layers may be due to turbidity currents. The deformed bedding may be a result of soft-sediment deformation on a low slope.

STOP 4. Black Brook Sand Plain
The Black Brook sand plain is a terraced accumulation of stratified drift at the distal end of a bedrock gorge north of the village of Black Brook. The surface of the sand plain is roughly triangular in map view and ranges in elevation from 329 m (1080 ft) at the mouth of the gorge to 275 m (902 ft) at the West Branch of the A usable River.
The exposures in a gravel pit 0.64 km (0.4 mi) east of Black Brook contain meter-scale beds of coarse sandy gravel to boulder gravel (Figure 9). The working face of the pit is oriented east-west and is approximately 40 m (130 ft) long and 4 to 6 m (13 to 20 ft) high. The surface elevation of the sand plain at this location is approximately 315 m (1 033 ft). The lower unit consists of horizontally stratified, and trough and planar cross-stratified sandy gravel, the base of which is obscured by slumping. The sandy gravel is overlain by a 2.0 to 2.5 m (6.6 to 8.2 ft) thick, massively bedded, very coarse boulder gravel layer. The gravel contains boulders over 1.5 m (5 .0 ft) in diameter, some of which are crudely imbricated. The gravel unit can be traced laterally across the working face of the pit. The gravel is overlain by 1.0 to 1.2 m (3.0 to 4.0 ft) of cross-stratified sandy gravel. The cross strata are centimeters to decimeters thick and commonly extend from the top to the bottom of the unit. Paleocurrent indicators indicate southward to southeastward flow throughout the section.
The Black Brook terrace deposits are interpreted as a fluvio-deltaic complex that was built into falling levels of preglacial lake in the lower Ausable Valley (Figure 10). Base level was probably controlled by the outlet channels in the vicinity of Colby, Sheep, Little, and Haystack mountains (outlet channels 5a, 5b, 5c, and 6, Figure 4).
The sand and gravel deposits at Stop 4 are probably glaciofluvial in origin and may represent deltaic topset beds. The sandy gravel facies probably represents fluvial deposition under near average meltwater discharges through the bedrock channel north of Black Brook. The boulder gravel facies is interpreted as a high energy, catastrophic flood deposit. Discharge of this magnitude may have been produced by the diversion of outflow from lakes in the Saranac Valley through the Black Brook channel (i.e. a limnic hlaup).

STOP 5. (Optional) Diamictons Near Ausable Forks
This stop includes roadside exposures along Ausable Drive, approximately 2.4 km (1.5 mi) southwest of Ausable Forks. The sediments consist of massive to crudely stratified diamicton with thin sand, gravel and silt interbeds. The diamicton beds are commonly decimeters to meters thick, light colored and have sandy matrices. The sandy interbeds are thin (centimeter-scale) and discontinuous and are either non-stratified or contain horizontal or ripple-drift laminations. The bedding is subhorizontal but may be deformed locally. These deposits probably accumulated in a ice-marginal, subaqueous environment.

STOP 6. Deltaic Deposits Near Clintonville
The gravel pit at Stop 6 is located on an extensive sand plain on the north side of the Ausable Valley between Clintonville and Ausable Forks (Figure 1). The surface of the sand plain slopes southward from approximately 204 m (670 ft) at its northern margin to 198m (650ft) near the Ausable River.
The lower portion of the pit contains approximately 5 to 6 m (16 to 20 ft) of southwardly dipping, fine to medium sand and sandy silt foreset beds. The bedsets are centimeters to decimeters thick and commonly contain horizontal laminations and ripple-drift cross-laminations. Thin silty deposits occur locally as draped laminae over ripple forms. The upper portions of the foreset beds are truncated and overlain by 1.0 to 1.5 m (3.0 to 5.0 ft) of horizontally stratified and trough and planar cross-stratified sand and gravel.
The sediments at the Clintonville gravel pit are interpreted as deltaic in origin. The erosional surface between the lower sandy facies and the upper gravel facies represents the contact between the subaqueous foreset beds and the fluvial topset beds. The elevation of the topset-foreset contact is approximately 198 m (650 ft) which indicates that deltaic sedimentation was graded to the level of Lake Coveville in the Champlain Valley (Denny, 1974). Southward-flowing meltwater streams from ice in the Little Ausable drainage basin north of Arnold Hill (Figure 1) provided much of the deltaic sediment in the eastern portion of the sand plain. The western portion of the sand plain was probably built by eastwardly flowing streams from the upper Ausable drainage basin. Southward drainage from proglacial lakes in the Saranac River Valley into the lower Ausable Valley via the Black Brook channel (Stop 4) may have contributed to delta construction near Ausable Forks (Denny, 1974).

STOP 7. Landslide Scar On The Ausable River At Keeseville
The section at Keeseville is exposed in a landslide scar on the south bank of the Ausable River at Keeseville. The river is deeply incised into deltaic terrace deposits which Denny (1974) correlated with Lake Fort Ann in the Champlain Valley. The surface elevation of the terrace is approximately 155 m (510 ft).
The base of the section consists of massive, compact, calcareous, gray diamicton with a silty to clayey silt matrix. The base of the diamicton is obscured by colluvium. The upper surface of the unit has a few centimeters of relief and is draped by 0.3 to 0.5 m (1.0 to 1.5 ft) of silt and clay rhythmites. The rhythmite sequence contains 11 silt-clay sediment couplets. The rhythmites are conformably overlain by approximately 6 m (20 ft) of fine to medium sand which coarsens upward to gravelly sand near the terrace surface. Spring sapping at the sand-rhythmite contact is responsible for slumping in the overlying sand unit.
The sediments at the Keeseville section record the ice recession from the mouth of the Ausable Valley. The diamicton is interpreted as a basal till and thus represents an interval of ice cover. The rhythmites are interpreted as varved lacustrine deposits that record the initial, deglaciation of the lower Ausable Valley and its subsequent inundation by Lake Coveville. The rhythmites, therefore, were probably deposited contemporaneously with the Lake Coveville deltas near Clintonville (Stop 6).
The overlying sandy deposits represent deltaic sedimentation by eastward flowing streams from the Ausable Valley into Lake Fort Ann. Regional lake level fell approximately 43 m (140 ft) in the Champlain Valley with the initiation of Lake Fort Ann. If the rhythmites are assumed to be Lake Coveville varves and the overlying sandy facies to be part of the Lake Fort Ann delta, then the time between the deglaciation of the mouth of the Ausable Valley and the initiation of Lake Fort Ann was about 11 years. The ice-front in the Champlain Valley may have receded northward to the mouth of the Saranac River at the time Lake Fort Ann was established (Denny, 1974).

Ausable Chasm

Surface of Champlain Sea delta (upper marine limit).

Surface of Champlain Sea delta (Port Kent Stage).

Entrance to Ausable Point State Park on the delta of the present Ausable River.

A2: GEOLOGY AND PETROLOGY OF MOUNTS JOHNSON AND ST.-HILAIRE, MONTEREGIAN HILLS PETROGRAPHIC PROVINCE
G. NELSON EBY
Department of Earth Sciences
University of Lowell
Lowell, MA 01854
INTRODUCTION
The Monteregian Hills petrographic province consists of a group of small igneous intrusions and associated dikes and sills which lie along a more or less linear East-West trend extending from the Oka carbonatite complex located 30 km west of Montreal to Mounts Shefford and Brame 70 km east of Montreal. These plutons cut a number of terranes: the Precambrian Grenville, the St. Lawrence Lowlands, and the folded rocks of the Appalachian orogen. Mount Megantic lies 100 km east of Mounts Shefford and Brome and its assignment to the Monteregian Hills province is somewhat problematical. Petrographically and chemically Mount Megantic shows stronger affinities with the White Mountain igneous province than with the Monteregian Hills. On this field trip we will visit two plutons located in the central part of the province which are representative of some of the major magmatic trends in the Monteregian Hills.

A2: GEOLOGY AND PETROLOGY OF MOUNTS JOHNSON AND ST.-HILAIRE, MONTEREGIAN HILLS PETROGRAPHIC PROVINCE

STOP 1. Exposures Of Hornfels Collar
Walk up the trail to the base of the waste-rock pile. Along the trail are numerous exposures of the Lorraine siltstone, now metamorphosed to the hornblende hornfels facies. The hornfels dips northward into the intrusion with increasing steepness as the base of the waste-rock pile is approached.

STOP 2. Quarry In Pulaskite
Excellent exposures of the pulaskite are found in this small quarry. The strong vertical foliation is clearly evident in the quarry wall. Climb up through this quarry to a slightly larger quarry located at higher elevation. Note the increase in the amount of amphibole in climbing from the first to second quarry. The rock apparently grades from pulaskite to essexite.

STOP 3. Quarry In Rhythmically Layered Essexite
This quarry is located in the coarse-grained, layered essexite, that comprises the outer edge of the core series. Along the road leading into this quarry are outcrops of hornblende-rich essexite which are typical of the essexite found in the peripheral series. This hornblende-rich essexite contains sphene while the essexite in the quarry does not carry sphene. In the quarry are found excellent exposures of rhythmically layered essexite with cross-beds and trough-like structures. Climbing up out of the quarry note the disappearance of the rhythmic layering. Continue on to the summit. Note the decrease in grain size as the summit is approached.

STOP 4. Summit Of Mount Johnson
At the summit the fine-grain size makes it difficult to distinguish the foliation which was clearly visible on the climb from Stop 3 to Stop 4. With the exception of the presence of olivine, the essexite at the summit and in the quarry at Stop 3 is petrographically and chemically identical. To the north of the summit is found an arcuate body of coarse-grained, amphibole-rich essexite. On a clear day the summit of Mount Johnson provides an excellent view of the Monteregian Hills. Return by the same route to the parking lot. It is once again worthwhile to look at the rocks to see if it is possible to distinguish any clear breaks between the various petrographic units.

STOP 5. Camptonite Dike
Turn right out of the parking lot and continue northwesterly along the road to a lamprophyre dike cutting the Lorraine siltstone. Park on the west side of the road. The dike trends north-south along the western margin of Mount Johnson . It is of somewhat older age than the main pluton but may be petrogenetically related to the Mount Johnson magmas. The dike consists of phenocrysts of titanaugite, partly altered to a mixture of green amphibole, brown biotite and chlorite, and kaersutite in an intergranular groundmass of plagioclase, biotite, kaersutite, opaques, apatite, and trace sphene.

STOP 6. Exposures Of Igneous And Diatreme Breccias
Proceed north along the main trail which follows the valley between the two halves of the mountain. Pass Lac Hertel. On the left (west side) of the trail are scattered outcrops and boulders of both the igneous and diatreme-like breccias. Most of the lithologies of the pluton can be found as blocks and fragments in these breccias.

STOP 7. Gabbros And Diorites Of The Sunrise Suite
Retrace your path southwards to the intersection with the Pain de Sucre trail. Proceed up this trail (west) towards the summit of Pain de Sucre. Outcrops of gabbro and diorite of the Sunrise suite are exposed along this trail. In places the rocks are extremely coarse-grained and outcrops are found to carry clots of large radiating amphiboles. Foliation is generally poorly developed in this part of the suite.

STOP 8. Nepheline Diorites And Monzonites Of The Pain De Sucre Suite
Continue on to the summit of Pain de Sucre. In the immediate vicinity of the summit is an almost continuous exposure of relatively leucocratic coarse-grained rocks of the Pain de Sucre suite . The rocks usually have a bluish cast and visible laths of alkali feldspar. Olivine is present locally and nepheline occurs as an interstitial phase.

A3: FORELAND DEFORMATION AS SEEN IN WESTERN VERMONT
Rolfe S. Stanley
Department of Geology
University of Vermont
Burlington, Vermont, 05405
INTRODUCTION
Western Vermont is underlain by three distinctive sequences of rocks that range in age from Late Proterozoic to Middle Ordovician and are typical of the western part of the Appalachian Mountains. The lowest most sequence, which rest with profound unconformity on the Middle Proterozoic of.the Green Mountain and Lincoln massifs, largely consists of metawackes, mafic volcanic rocks and phyllites that represent a rift clastic sequence. These rocks grade upward into siliciclastic and carbonate rocks of the platform sequence which in turn are overlain by Middle Ordovician shales of the foreland basin sequence. The boundary between the two sequences is the based of the Cheshire Formation (fig. 1 ). North of Burlington, Vermont the platform sequence grades into shales, breccias and conglomerates of the ancient platform margin and eastern basin. These sequences have been studied by a number of workers in the past (Cady, 1945; Cady and others, 1962; Hawley, 1957; Erwin, 1957; Welby, 1961; Stone and Dennis, 1964i for example) and are receiving current attention by Mehrtens (1985, 1987) and her students (Gregory, 1982; Myrow, 1983; Teetsel, 1985; Bulter, 1986; MacLean, 1986, 1987). Agnew (1977), Carter (1979), Tauvers (1982), DiPietro (1983) and Dorsey and others (1983) have reexamined parts of the rift clastic sequence while Doolan and his students are currently working in the same sequence in northern Vermont and Quebec (Doolan and others, 1987; Colpron and others, 1987). Figures 1 and 2 illustrate the representative stratigraphic columns for western Vermont north of the latitude of the Lincoln massif where the field conference will be held. Additional information can be found in Welby (1961) and Doll and others (1961 ).
The structure of western Vermont is dominated by major, north-trending folds and imbricate thrust faults which are we ll d i s p 1 aye d on the G e o log i c Map of Vermont ( Do 11 and others, 1961). The rift clastic and platform sequences have each been displaced westward on major thrust faults that extend through much of Vermont. The larger of the two, the Champlain thrust, extends from southern Quebec to Albany, New York and places the older platform sequence over the younger foreland basin sequence. Estimates of westward displacement range from 15 km to 100 km. The smaller of the two, the Hinesburg thrust, places transitional and rift clastic rocks over the platform sequence and as such forms a boundary between the synclinorial rocks of western Vermont and the the Taconian Orogeny. This conclusion is based on regional considerations (Stanley and Ratcliffe, 1985) and the analysis of available isotopic data (Sutter and others, 1985). Mesozoic deformation in the form of extensional faults and igneous activity clearly affected the region (McHone and Bulter, 1984; Stanley, 1980). Available evidence, ho we ver, can not rule out limited Acadian or even Alleghenian deformation.
Participants of this field trip will see the change in structure and fabric as they cross the foreland from South Hero Island to the western margin of the hinterland at the Hinesburg thrust fault at Mechanicsville, Vermont.

STOP 1. West Shore of South Hero Island.
This stop illustrates the low level of deformation that characterizes much of the west shore of the Champlain Islands and the eastern shore of New York in the area of Plattsburgh. Local areas of moderate deformation, however, do exist where bedding plane faults and high-angle faults cut the bedrock. These outcrops of shale and thin micrite beds are in the Stony Point Shale. Note that the bedding, which is nearly horizontal, is cut by a poorly developed cleavage that is only developed in the shale beds. The cleavage dips very gently to the east and is interpreted to result from simple shear parallel to the bedding. Thin layers of calcite are present on some of the beds. Those layers that are marked by prominent slickenlines are bedding plane faults. As we will see at other outcrops today, the larger faults are marked by thicker layers of lineated calcite.

STOP 2. Lessor 's Quarry
This quarry is located in the fossiliferous Glens Falls Limestone. The quarry contains some of the finest evidence of pressure solution in western Vermont. The cleavage (S1), which is discontinuous and wavy, is a classical pressure solution feature with well developed selvedges that truncate fossils and offset bedding. A small anticline at the south _edge of the quarry contains adjustment faults at its hinge that end along cleavage zones with thick clay selvedges.
The major structures in the quarry are bedding-plane thrust faults. These faults are marked by calcite layers with west-trending slickenlines and a fault - zone cleavage (St).
Near the larger faults the S1 cleavage is rotated (Sr) toward the plane of the fault. Note that both St and Sr dip gently to the east and indicate that movement on the bedding faults was to the west. The St cleavage forms as a result of simple shear on the faults. The anticline along the south wall and edge of the quarry is formed from a small duplex. Unfortunately, the best evidence for this duplex has been excavated.
On the northeast side of the quarry (fig. 6) a syncline and an associated blind, synformal thrust fault are truncated by the major thrust fault that is continuous across the north wall of the quarry. The origin of this structure is not clear, but it is thought to be associated with a duplex or ramp below the level of the quarry floor.

STOP 3. "The Beam"
This is a superb outcrop that serves as a field laboratory for research and teaching of foreland deformation. Please study it. Use your cameras but not your hammers.
The outcrop is located in the Cumberland Head Formation approximately 5 miles (8 km.) west of the exposed front of the Champlain thrust fault or approximately 4600 ft. (1400 m.) below the restored westward projection of the thrust surface. The major questions that will be discussed are: 1. How do ramp faults form?, 2. Are there criteria to determine if imbricate thrust faults develop toward the foreland or hinterland?, 3. What is the relation between faulting and cleavage development?, 4. What processes are involved in the formation of fault zones?, 5. Are there criteria that indicate the relative importance and duration of motion along a fault zone?, 6. Is there evidence that abnormal pore pressure existed during faulting?, and finally 7. What is the structural evolution of the imbricate faults? The first six questions will be largely addressed by direct evidence at the outcrop. The last question will be answered by palinspastically restoring the imbricated and cleaved sequence to its undeformed state (fig. 9).
THE OUTCROP
Five imbricate thrust faults and associated ramps are exposed in profile section in a foot thick bed of micrite that extends 14 m along an azimuth of N 80 E (fig. 7a). The imbricate fault can be further classified as a central duplex of three horsts that are separated from two simple ramps at either end of the outcrop by approximately 2. 5 m of flats. The micrite bed is surrounded by at least 1.5 m of well-cleaved calcareous shale. Bedding plane faults are present along the upper and lower surface of the micrite where they merge with ramp faults that cut across the micrite bed at an angle of approximately 30 degrees. The lower bedding plane fault or floor thrust is relatively planar and the fault zone is thick compared to the upper bedding plane faults which are folded in the ramp areas, cut by ramp faults, and the fault zones are thin. The upper bedding plane fault forms the roof thrust for the central duplex. Along the intervening flats the upper faults are generally planar although they are cut by the S1 cleavage in many places. The lower bedding plane fault is the major decollement across the outcrop. Older bedding planes faults are also present throughout the shale where they are offset by the penetrative S1 cleavage.
All the fault surfaces are covered by layers of sparry calcite that vary in thickness from several millimeters to 4-6 cm. The thickest zone is found along the decollement or floor thrust whereas the thinest zone is found along the older bedding plane faults in the calcareous shale (fig. 7a). In all but the thinest layers, the calcite is arranged in distinct layers that are separated by discontinuous selvedge of dark gray shale. Each of the layers are marked by grooves or slickenlines that trends N 56 W and are essentially parallel from layer to layer (7b). In sections oriented perpendicular to the layering and parallel to the slickenlines the shale selvedges are more parallel to each other than in sections cut perpendicular to the slickenlines where the selvedges either anasatmose or conform to the cross section of the grooves. In the parallel sections, however, some of the selvedge layers are truncated by more continuous surfaces. One of these can be traced for 1.5 m or more along the decollement. At a number of places along the different fault zones small dikes of sparry calcite have intruded the lower part of the calcite-shale layers. The fault-zone fabrics are most clearly displayed along the decollement where the calcite-selvedge layers are more abundance.
Fractures are common throughout the micrite bed where they are oriented at either a high angle or low angle to the bedding. Most fractures are filled with sparry calcite. The most prominent fractures are arranged in en echelon arrays that climb either to the west or the east. Most of these arrays are located in ramps areas and along the west-facing limbs or small flexures. A few are present in the flat regions of the bed. The fractures in many of the arrays in the ramp regions are folded and some are cut by younger generations of en echelon fractures. In the eastern ramp the hanging wall and foot wall are cut by near-vertical fractures that are filled with fragments of the surrounding micrite embedded in sparry calcite so as to form clastic dikes.
Two, well developed, pressure-solution cleavages are present throughout the calcareous shale. The first and most conspicuous one, S1, strikes N 20 E and dips 60 to the east (fig. 7b). This orientation is an average based on measurements taken across the vertical face of the outcrop because the individual S1 surfaces are quite wavy along strike. As a result they form a distinct diamond - shape pattern on the bedding surface. The acute angle of the diamond pattern is approximately 30 degrees in the shale and 50 degrees in the micrite bed. This geometry indicates a moderate level of cleavage development according to the scheme of Alvarez and others (1976). S1 surfaces are covered by a black, carbon-rich selvedge of illite and kaolinite which is less than 0.5 cm thick. Although many of the cleavage surfaces are vertically continuous through the shale, some of them are short and discontinuous with tapered ends. The thickest selvedge occurs on the most continuous surfaces. The surfaces of the selvedge are not lineated although some are polished. The S1 cleavage offsets bedding and the older bedding-plane thrust faults with a down-to-the-east sense throughout much of the outcrop. This displacement is greatest where a selvedge is the thickest and it gradually is reduced to zero as a selvedge thins toward the tapered ends of the shorter cleavage surfaces. The average width of the microlithons between the S1 surfaces is 5.6 cm thick. The S1 cleavage not only cuts the older bedding-plane faults but cuts across most of the roof fault s on top of the micrite bed.
A second, well developed cleavage, St, is restricted to a foot-thick zone directly below the decollement (fig. 7a). The individual cleavage surfaces are thinner (about 1 mm thick), more closely spaced (about 1 cm or more), and are covered with a thin selvedge (less than 1 mm). Furthermore, St dips to the east at only 6 degrees compared to the steeper dip of S1. St is also developed along the roof thrust of the micrite bed, but the zone is thinner and it is more difficult to recognize because the roof faults have been folded in the ramp areas and deformed by S1. The St cleavage is definitely related to movement of the thrust faults because it is only found near the faults and it is absent away from them. In the zone near the decollement and the roof faults the S1 cleavage is rotated eastward so that the steeper 60 degree dip in the shale is reduced to 25 degrees (fig. 7b). The strike of the rotated S1 (hereafter referred to as Sr) is the same as S1 away from the faults. The counterclockwise rotation of S1 through an angle of shear of 35 degrees indicates that movement on the decollement was east-over-west along a direction of N 56 W as indicated by the slickenlines along the decollement. This sense of displacement is consistent with the orientation of St since the normal to St would correspond to the direction of maximum finite compressive strain.
Cleavage, similar to S1 and St, is totally absent from the micrite bed. In a few places, however, a very thin (less 1 mm), stylolitic to very irregular cleavage is oriented perpendicular to bedding in the micrite. This cleavage is not developed uniformly throughout the micrite. Where it is formed the cleavage surfaces are separated from each other by at least 6-10 cm. The form, orientation and limited distribution of this cleavage indicates that it formed very early in the deformation sequence while compression was essentially parallel to the planar micrite bed.

STOP 4. The Champlain Thrust Fault At Lone Rock Point, Burlington, Vermont -
The following discussion is reprinted from The Centennial Field Guide, Volume 5, of the Geological Society of America in 1986. All the figure numbers for this stop refer to those figures in the reprint. The reprinted discussion appears in Appendix 1. Figure 10 is a regional map showing the location of the Champlain thrust fault in 'western Vermont. The Long Rock Point locality is identified as "LRP". The Arrowhead Mountain thrust fault is located east of the Champlain thrust fault and is identified by the letters "AMTF".

STOP 5. The Hinesburg Thrust Fault At Hinesburg, Vermont
This is the classic and best exposed locality for the Hinesburg thrust fault (fig. 10, "HTFM"). It contains many fault related fabrics that have recently been studied by Strehle (1985) and published by Strehle and Stanley (1986) in a bulletin of the Vermont Geological Survey (Studies in Vermont Geology No.3). This publication also contains analyses of other fault zones of western Vermont which will not be seen during this conference. The reader is referred to this paper or an earlier NEIGC trip by Gillespie and others (1972).
The Hinesburg thrust fault separates the Cambrian-Ordovician rocks of the platform sequence from the older, highly deformed metamorphic rocks of the eastern hinterland. As shown in figure 4, the Hinesburg thrust fault developed along the overturned, sheared limb of a large recumbent fold. This fault probably broke out from the overturned limb of a fault-propagation fold (Suppe, 1985) and therefore is similar in origin to the Arrowhead Mountain thrust fault. To the south the Hinesburg thrust fault dies out somewhere in the overturned limb of the Lincoln massif (Tauvers, 1982; DiPietro, 1983; DelloRusso and Stanley, 1986).
At the Mechanicsville locality the lower 40 m. of the Cheshire Quartzite is structurally overturned along the base of the upper plate of the Hinesburg thrust fault. Higher up the cliff the quartzite grades into the Fairfield Pond Formation of Tauvers (1982). The lower plate rocks, which are poorly exposed, consist of carbonates of the Lower Ordovician Bascon Formation. Slivers of dark gray phyllite of the Brownell Mountain Phyllite are found at several localities along the fault trace. Chlorite, muscovite, and stilpnomelane are present in the quartzite. Muscovite and chlorite are present in the schist. Quartz is thoroughly recrystallized, but feldspar grains are fractured and bent. The following features should be studied here:
1) The change in fabric as the fault surface is approached. The quartzite grades from a protomylonite away from the fault to an ultramylonite near the fault. In thin section quartz becomes finer grained and quartz porphyroclasts decrease in number toward to fault.
2) The presence of east-over-west or "S" shaped asymmetrical folds. These folds are related to simple shear along the fault and are not related to the overturned limb of the older Hinesburg nappe. Parasitic minor folds related to this older structure would show a west-over-east or "Z" shaped asymmetry.
3) The prominent compositional layering. This layering is not bedding but represents the axial surface schistosity of the older parasitic folds related to the Hinesburg nappe. It is overprinted by a younger schistosity that is associated with the east-over-west folds. These two schistosities become a composite mylonitic schistosity as the fault surface is approached.
4) The prominent mineral lineation consisting of elongate quartz and quartz clusters.
5) "Z" shaped quartz veins that are associated with beds of quartzite. These structures are particularly interesting because the record progressive shear strain and mylonitization along the fault. The veins are confined to the metasandstone and metasiltstone layers and occur in at least 3 orientations. The least deformed veins are oriented either perpendicular to the layering or dip steeply to the west. They are filled with straight quartz fibers oriented perpendicular to the vein walls and show no signs of recrystallization except where they cross older "Z" shaped veins (Warren, 1988, pers. comm.). Here the fibers are reduced to smaller, nearly equant grains with undulose extinction. The most deformed veins are "Z" shaped and dip to the east. The older quartz fibers are completely replaced by fine grained, recrystallized quartz that forms a mylonite with distinct whitish layers oriented essentially parallel to the vein boundary. The third set is intermediate in orientation and deformation between the other two. The "Z" pattern develops because the shear strain (8.5 or an angle of shear of 84°) is higher in the pelitic units that surround the metasandstones where the shear strain is 1.48 (angle of shear of 56°). Strehle and Stanley (1986) suggested that these veins developed as shear fractures during east-over-west shear. This interpretation is not consistent with the fact that the youngest veins are vertical and consist of quartz fibers orientated essentially parallel to the layering (Warren, 1988, pers. comm.) It therefore appears that the veins formed as extension fractures during periods of vertical or near vertical loading. These periods of flattening (pure shear) were then followed by longer periods of east-over-west simple shear during which the veins were rotated westward and the characteristic "Z" pattern developed. The quartz, which was originally fibered, became progressively mylonitized as the extension veins were rotated into the favorable, east-dipping, shear position. Movement on these east-dipping veins continued even after they were cut by younger, unrotated veins because the fibered segments of the younger veins are deformed and recrystallized.
6) Rare west-dipping shear bands. These structures deform the younger schistosity which is parallel to the axial surfaces of the "s" shaped folds.
7) Westward displacement (N 75 W) of the upper plate of the Hinesburg thrust is documented by "s" shaped folds, "Z" shaped-quartz veins, quartz porphyroclasts, and late shear bands.
8) Late fractures and associated en echelon fracture arrays. These structures thought to be related to Mesozoic normal faults which cut the Champlain and Hinesburg slices. One of these faults is located about 1000 m. directly west of this locality.
The interpretation of these structures and the thin sections fabrics are discussed in Strehle and Stanley (1986).

A4: THE CAMBRIAN PLATFORM AND PLATFORM MARGIN IN NORTHWESTERN VERMONT
Charlotte J. Mehrtens
Department of Geology
University of Vermont
Burlington, Vt. 05405
The stratigraphy of northwestern Vermont is dominated by sedimentary rocks of the Cambro-Ordovician platform and basin sequence, which is part of an extensive belt of similar facies extending from Newfoundland to Alabama. These facies consist of carbonate and siliciclastic deposits characteristic of a shallow water platform, bordered to the east by a basinal sequence of shales and sedimentary breccias. Rodgers (1968) recognized this platform to basin transition as the margin of the Lower Paleozoic platform in eastern North America.
Cambro-Ordovician sediments were deposited on a passively subsiding shelf following late Precambrian rifting. These sediments accreted at a rate which kept pace with thermal subsidence as the shelf assumed the morphology of an accretionary rimmed platform during the Lower Cambrian. Examining the distribution of facies comprising the shallow water platform indicates that the interior regions were affected by tidal and wave processes whereas the shelf margin regions were subtidal and wave reworked (Gregory, 1982; Butler, 1986; Rahamanian, 1981; Myrow, 1983; Chisick and Friedman, 1982; Braun and Friedman, 1969). The adjacent deeper water basins accumulated talus, debris flows, and turbidites composed of detritus shed off the platform (Mehrtens and Dorsey, 1986; Mehrtens and Borre, 1987; Mehrtens and Hillman, in review).
The Cambro-Ordovician sequence in northwestern Vermont is unique in that the platform to basin sequence is intact and undisected by faults. Looking at the Cambro-Ordovician sequence throughout the Appalachians, only Pfeil and Read (1980) describe a platform to basin sequence, but it has been dismembered by faults and cannot provide information on the original geometric relations on the platform.
This field trip guide describes the facies and evolution of a portion of the Cambro-Ordovician carbonate platform in northern Vermont (Figure 1). The Cheshire Quartzite is the basal unit in the sequence (Figure 2), overlying Eocambrian rift-related sediments of the Pinnacle and Fairfield Pond Formations (Tauvers, 1982), and it will not be examined on this trip. The Cheshire is in gradational contact with the overlying Lower Cambrian Dunham Dolomite (Myrow, 1984), a carbonate unit which records sedimentation in peritidal, subtidal and platform margin environments (Gregory, 1982). The facies distribution and paleogeography of the Dunham Dolomite influenced the platform geometry and evolution in subsequent Cambrian deposits, consequently it will be examined in detail.
Overlying the Dunham Dolomite is the lower Middle Cambrian Monkton Quartzite, a mixed siliciclastic/carbonate unit which also records tidal flat to platform margin sedimentation (Rahmanian, 1981). The Middle Cambrian Winooski Dolomite has not been studied in detail, but a review of sedimentary and biogenic structures suggests that it also records peritidal to platform margin environments of deposition. The Upper Cambrian Danby Quartzite overlies the Winooski and contains a diverse suite of sedimentary structures documenting tidal flat, shallow subtidal, and platform margin environments, with significant storm overprinting (Mehrtens and Butler, in review).
This field trip will look at each of these units and examine evidence for their interpretation as shallow water platform deposits. The trip will also examine one basinal unit, the Rockledge Formation (Upper Cambrian). The Rockledge Formation is a limestone-clast conglomerate unit with associated massive sandstones and laminated siltstones interpreted to represent high and low density turbidity currents (Mehrtens and Hillman, in review).

A4: THE CAMBRIAN PLATFORM AND PLATFORM MARGIN IN NORTHWESTERN VERMONT

STOP 1. Abandoned quarry on the north side of Rt. 2
Park on the southwest (right) shoulder, cross Rt 2, and ascend overgrown driveway into quarry. The Champlain Thrust floors the quarry as the Dunham Dolomite is emplaced on the Middle Ordovician Stony Point Shale. The Dunham Dolomite exposed here is the basal facies of the Dunham, characterized by the rhythmic interbedding of dolomite (white) and silty dolomite (pink). This bedding style is interpreted to be the result of alternating sedimentation in a tidal flat setting, producing "ribbon bedding". Look for: undisturbed horizons of the dolomite and silt-rich dolomite, horizons of intraclasts, burrows, and cryptalgalaminites. Note that many of the clasts show rips and tears in their margins, others are bent. Many clasts are cored by calcite. Greiner (1982) recorded occurrences of gypsum in this facies in subsurface cores.

STOP 2. Shallowing-up cycles in the Dunham
This roadcut on the left (north shoulder) exposes 3 shallowing-up cycles within the Dunham. They are recognizable in the large roadcut because of the characteristic pink and white ribbon bedding of the peritidal caps of the SUC's. One SUC can be studied in detail on the northwest corner of the roadcut. The SUC (Figure 4) is composed of a basal subtidal dolomite overlain by the ribbon bedding of the peritidal cap. The cycles in the Dunham are similar to "muddy shallowing-up cycles" of James (1983) and they consist of 6-10 meters of bioturbated, sandy dolomite passing up into ribbon-bedded dolomite and silt-rich dolomite and local intra-formational conglomerate. What is the origin of the sand within the Dunham subtidal muds? SEM work led Gregory (1982) to suggest that frosting microtextures on quartz grains recorded an eolian history to the sediment. However, channels within the Dunham are sand-filled, and provide a mechanism for the transport of sand across the platform. This is similar to the tidal channels of Shark Bay, western Australia, where channels are infilled with a mixture of carbonate mud and quartz sand from eroded Pleistocene bedrock.

STOP 3. Dunham subtidal and platform margin facies.
Pull off about 100 yards beyond the speed limit sign on this long roadcut. At the base of this outcrop (west end) there are good exposures of the subtidal facies of the Dunham with the characteristic mottled texture, thought to be produced by burrowing. Burrow mottles are irregular in shape, 1 to 8 cm in diameter, and lack sand. The segregation of siliciclastic material is one property that implies bioturbation produced this mottled texture. Between the white burrows the red matrix is very clay and sand-rich, and Stone and Dennis (1964) attribute this color variation to differing concentrations of trace metals. Specimens of Salterella conulata (Mehrtens and Gregory, 1983) were found in this facies. The platform margin facies is exposed on the east end of the same outcrop. This facies is composed of chaotically bedded, laterally discontinuous horizons of breccia in a sand-rich dolomite matrix. Clast composition is highly variable, and includes chert pebbles, sandstones, sandy-dolostones, and dolomitic sandstones. Breccia beds are structureless and very poorly sorted. Graded beds of sandstone are also present.

STOP 4. Monkton Quartzite, subtidal and shelf edge facies
This roadcut exhibits the subtidal and shelf edge facies of the Monkton, as evidenced by the overall thickness of the individual beds, increasing amounts of shale between sandstone beds, presence of relict oolites in some dolomite horizons, and occurrences of large scale tabular cross stratification. Many of these beds probably represent shelf edge sand shoals. Note characteristics of the Monkton here for comparison to the shallower-water deposits seen at Stop 6.
Walk east 0.3 miles to the small knoll beyond the road sign. Here the polymictic breccia of the platform margin facies is exposed. The clasts are floating in a matrix of sandy dolomite and are interbedded with cross-bedded sandstones. Clast composition includes dolomite, sandstone and dolomitic sandstones. Beds are structureless and poorly sorted. These breccias are interpreted to represent talus deposits formed at the edge of the platform. These breccias can be traced to the north, where they form a rim around the St. Albans Reentrant. Mehrtens and Borre (1987) have documented that the Monkton passes laterally into the Rugg Brook Conglomerate within the basin. Return to cars and continue east on Route 2.

STOP 5. Winooski platform margin facies
Walk from the parking lot back to, and across the intersection, to the outcrop on the southwest side. This is an exposure of recrystallized dolomite, cross-bedded, and in places oolitic, of the upper most Winooski. Cross the road to the low-lying outcrop on the east side of Route 7. Note the variable clast composition and abundance of sand in the dolomite matrix in this Winooski platform margin breccia. These outcrops of Winooski at Chimney Corners and the adjacent I-89 exit ramps are the northernmost outcrops of Winooski Dolomite in northwestern Vermont. Immediately to the north on I-89 and Route 7 are exposures of the Rugg Brook Dolomite, a breccia deposit within the St. Albans Reentrant.

Outcrops of the Monkton Quartzite occur as roadcuts all along I-89.

First outcrop of Winooski Dolomite on the median of I-89

STOP 6. Salmon Hole - tidal flat facies of the Monkton, Winooski and Danby Fms.
Descend the pathway down to the broad bedding planes of the Monkton in the south bank of the river. This beautiful outcrop of Monkton is in danger of being destroyed by dam construction. Examine the multitude of rippled surfaces, and note the multiple paleoflow directions. Examine these rippled beds in cross section and note that they are composed of rippled dolomite, silty dolomite, and fine-grained sandstone with shale drapes, a typical tidal bedding style. Examining bedding planes again, look for both vertical and horizontal burrows. Mudcracks can also be found. The thick, structureless buff-colored dolomite bed near the top of the Monkton is interpreted to be supratidal in origin (carbonate mud washed up onto the tidal flat during a storm?). This implies that the section of Monkton just examined would be the upper portion of a shallowing-up cycle, which characterize the Monkton Quartzite. From having seen the subtidal and platform margin facies of the Monkton at Stop 4 you can now compare the features seen at the two outcrops. The tidal flat facies seen here and at other localities around the Burlington and Winooski areas were prograding northward towards the platform margin in the Milton region. The Monkton/Winooski contact is under water here but can be examined at Whitcomb's Quarry at the I-89 interchange. It is gradational over about 10 meters, with progressively decreasing amounts of sand up section into the Winooski.

STOP 7. Danby Quartzite and Winooski Dolomite
You are now on the bedding planes of the shallow subtidal facies of the Danby Quartzite (Figure 5), which is a dolomitic sandstone at this exposure. There are many exposures of sedimentary structures at this outcrop, including hummocky cross stratification, complexly-woven ripple bundles, bedding planes with interference ripples, and graded beds. Biogenic structures include small LLH stromatolites and oncolites. Most of these features suggest that the sediments of the Danby were frequently reworked by storm action, re-suspending and reworking the substrate, and rapidly depositing sediment during post-storm surge ebb flow.
During low water levels the entire Danby can be walked out from its contact with the Winooski on this side (upstream) of the bridge. The contact is gradational and is characterized by increasing amounts of quartz sand in dolomite until it becomes a dolomitic sandstone. The Winooski Dolomite does not exhibit many features but thin wisps of carbonaceous material with sand grains concentrated along the laminae are interpreted to be cryptalgalaminites.

STOP 8. Rockledge Conglomerate
In the field immediately to the north of the road are scattered outcrops of the Rockledge Conglomerate limestone clast facies. Examine exposures of the conglomerate and the poor sorting and angularity of clasts, and the sandy limestone matrix. Pods of the conglomerate, interpreted as individual flows of high density turbidity currents, are surrounded by the laminated siltstones of the Skeels Corners Slate.

Rugg Brook Formation
Small ridges 100 yards to the north are composed of massive dolomitic sandstone facies of the Rugg Brook Formation

A5: GRENVILLE CALC-SILICATE, ANORTHOSITE, GABBRO, AND IRON-RICH SYENITIC ROCKS FROM THE NORTHEASTERN ADIRONDACKS
ELIZABETH B. JAFFE and HOWARD W. JAFFE
Department of Geology and Geography
University of Massachusetts, Amherst
The Marcy anorthosite massif is delineated by a major NW-SE-trending lobe and a smaller N-S-trending lobe which coalesce to the S to form a heart-shaped outcrop pattern covering 5000km2. (Fig. 1). In section, the major NW-trending lobe approximates a piano bench or slab 3-4.5 km thick with two legs or feeder pipes extending at least 10 km down according to the geophysical model of Simmons (1964), whereas Buddington (1969) favored an asymmetrical domical shape based on extensive field mapping and other considerations. The massif consists of a coarsely crystalline core of apparently undeformed felsic andesine anorthosite thrust over a multiply deformed roof facies consisting of gabbroic-noritic anorthosite, gabbroic anorthosite gneiss, and quartz-bearing ferrosyenite-ferromonzonite facies (Pitchoff Gneiss). Remnants of a siliceous carbonate- and quartzite-rich metasedimentary sequence and associated garnet-pyroxene-microperthite granulites form discontinuous screens and xenoliths in the roof facies. Xenoliths of any kind are very rare inside the felsic anorthosite of the core, but abound in the gabbroic anorthosite of the roof facies.
We will visit ten outcrops which include all of the major rock types (Fig. 1) of the massif, and that lie principally in its multiply deformed roof facies.
That regional metamorphism took place at high pressure, in the range of 8-10 kbar at about 800°, is indicated by the occurrence of orthoferrosilite, Fs95 + quartz, and the absence of any vestiges of fayalite in the ferrosyenite facies of the Pitchoff Gneiss (Jaffe et al., 1978). Because recent Sm147-Nd143 age dating yields 1288 M.Y. for the age of magmatic crystallization of the Marcy anorthosite (Ashwal and Wooden, 1983), and older Pb-U age dating by Silver (1969) yields about 1130 M.Y. for crystallization and about 1100- 1020 for metamorphism, the Grenville orogeny may have spanned as much as 200 M.Y. and it is difficult to fix the peak of metamorphism with a specific thermal or tectonic event within this time span.

A5: GRENVILLE CALC-SILICATE, ANORTHOSITE, GABBRO, AND IRON-RICH SYENITIC ROCKS FROM THE NORTHEASTERN ADIRONDACKS

STOP 1. Fayalite-Ferrohedenbergite Granite, Locality Af-1-A
Iron-rich granitic-syenitic-quartz monzonitic rocks, ascribed to a charnockitic gneiss series, are abundant in the northeastern and central Adirondacks, where they occur in close association with anorthositic and metasedimentary calc-silicate rocks in the Marcy Massif. Most of these contain iron-rich orthopyroxene (eulite or orthoferrosilite) with quartz, an assemblage stabilized at the high operable regional metamorphic pressure of about 8 kbar, with T = 700-770°C (Jaffe, Robinson, and Tracy, 1978: Bohlen and Boettcher, 1981). Other members of this alkali-feldspar-rich series contain fayalite and quartz in place of orthoferrosilite and quartz. From tables 1, 2, 3, 4, and Fig. 9 and Table 7 from Jaffe, Robinson and Tracy (1978), (Appendix I) it is reasonable to assume that both of these rock types were recrystallized under similar metamorphic conditions. Work by Bohlen and Essene (1978) and by Ollilla, Jaffe, and Jaffe (1988) indicate that these rocks had igneous precursors that crystallized above 900°.
Here, at Stop 1, we will visit outcrops of the fayalite-ferrohedenbergite granite and later, at Stop 4, we will visit a culite-ferrohedenburgite syenite gneiss on Pitchoff Mt. in the 15' Mt. Marcy quadrangle.
A circular outcrop area, about 1 km in radius from the center of Ausable Forks village, was mapped by Kemp and Alling (1925) as an olivine-bearing quartz nordmarkite. They located several quarries within this outcrop area. On a fresh break, the rock shows the greenish cast typical of the ferrosyenites and charnockitic rocks of the northeastern and central Adirondack region. It is a medium-grained (1-5 mm) hypersolvus granite, in places gneissic, with a color index of 5-15. Similar fayalite-bearing granitic rocks were described by Buddington and Leonard (1962) from the Cranberry Lake quadrangle, near Wanakena, from the St. Lawrence Co. magnetite district of the central Adirondacks. At Wanakena, and very likely at Ausable Forks, eulite- or orthoferrosilite-ferrohedenbergite granitic-quartz- monzonitic gneiss is closely associated with the fayalite-ferrohedenbergite granitic rock. Fayalite and ferrosilite, together with quartz, have not thus far been found in the same specimen; if they were it would provide a precise geobarometric value for the pressure of regional metamorphism. From Fig. 9 and Table 7, Jaffe, Robinson and Tracy, (1978) (see Appendix I) it will be seen that the assemblage orthoferrosilite + quartz gives a minimum P, whereas fayalite + quartz gives a maximum P. A range of 7-9 kbar at 600° or 10-12 kbar at 800° outlines the extremes of the metamorphic P-T conditions. Recent work by Ollila, Jaffe and Jaffe (1988) indicates that the orthoferrosilite in Pitchoff Mt. syenite gneiss is actually an inverted pigeonite crystallized from a magma above 9 kbar and 900°c, conditions in excess of those accepted for the regional metamorphic peak.
In the Ausable Forks area, fayalite-ferrohedenbergite granite contains only trace amounts of hornblende: in outcrops where hornblende becomes abundant, fayalite is pseudomorphously altered to a brown fibrous serpentine or talc. The granitic rocks are cut by dikes of hornblende granite pegmatite and diabase.
The fayalite-ferrohedenbergite granite differs from the orthoferrosilite-ferrohedenbergite granitic-syenitic gneisses in several important aspects;
1) the fayalite granite is massive to poorly foliated, while the ferrosilite granitic gneiss is well foliated.
2) the fayalite granite is hypersolvus, carrying only a "strip" or "striped" microperthite that is slightly unmixed to sodic plagioclase and orthoclase, whereas the ferrosilite granitic gneiss is subsolvus, containing blebby and patchy microperthite more unmixed to sodic plagioclase and partly inverted to microcline, and this microcline microperthite coexists with an intermediate plagioclase,
3) the fayalite granite does not contain garnet because of the absence of intermediate plagioclase, whereas the ferrosilite granitic gneiss always carries garnet.
All of this suggests that the fayalite granite might be younger than the ferrosilite granitic gneiss. We concur with Buddington and Leonard (1962) who suggested that the fayalite granite could have originated from the fractional remelting at depth or the pyroxene granitic gneisses, with its intrusion occurring during the waning stages of deformation.

STOP 2. Anorthosite Near Covered Bridge At Jay
Outcrops just beyond a covered bridge about 0.32 km E of Ausable Forks center show the characteristic textures of anorthositic rocks along the margins of the Marcy Massif. In the roadcut, anorthositic block structure shows up to 2 m blocks of coarse, cumulate-textured andesine anorthosite, and coarse hypersthene (to 25 x 1S cm) enclosed in a gabbroic anorthosite. Dark layers, up to 2.5 cm thick, occur within the country rock. Outcrops in the East Branch of the Ausable River are principally of coarse andesine anorthosite with a megacryst index of about 20-30 and a color index of only 1. Numerous shear veinlets crisscross the anorthosite, trending N40E and N10W for the most part.

STOP 3. Grenville-Anorthosite Hybrid Gneiss 3.4 Km S Of Upper Jay On Rte 9N
We are located in a 6.4 x 1.6 km north-trending section of Grenville strata consisting largely of calc-silicate-amphibolite-marble assemblages. Graphitic marbles occur across the Ausable River to the W of this roadcut. All these have been intruded and pervaded by sills of gabbroic anorthositic composition, resulting in the formation of Grenville-anorthosite-hybrid gneisses. Subsequently these were intruded by a sill of gabbro that forms the center of the E side of the large road cut on Rte. 9N (Fig. 2).
The section may be divided into three parts:
1) a lower unit consists principally of a mottled granular black and white sphene-augite-andesine calc-silicate gneiss discontinuously interlayered with black hornblendite-amphibolite lenses presumably of volcanic origin. The granular mottled host rock consists of white andesine, An32-39, black augite, and 5-10% of red-brown to yellow-brown sphene. The black amphibolitic layers contain mostly brown hornblende along with white plagioclase now altered to prehnite and calcite.
2) a central unit is a biotite-hornblende-hypersthene-augite-garnet-plagioclase metagabbro sill. The abundance of garnet, 20%, suggests that the gabbro sill may have been olivine-rich. The sill shows sharp contacts above and below with the anorthosite-calc-silicate-hybrid gneiss.
3) above the upper contact of the gabbro sill, the rock is augite-andesine An39-40 gabbroic anorthosite gneiss intercalated with dark amphibolite and calc-silicate layers.
Sporadic large garnets up to 6 cm in diameter occur along contacts of anorthositic and mafic layers.
The outcrop on the W side of the road shows a well-developed high strain pencil lineation, oriented N25E.

STOP 4. The Pitchoff Gneiss-Ferrosyenite Facies, PO-2
The foot of Lower Cascade Lake. Park at the lakeside in the second parking area on the left, just past a sign FALLEN ROCK 1 1/2 MILE. Be very careful cutting across traffic: this is a busy high-speed highway. Recross the road on foot, again with great caution. Walk back toward the FALLEN ROCK sign, to a rough trail up the talus just short of the sign. The talus and cliff are both steep and full of loose rocks: be considerate of those below and behind.
The prominent, southeast-facing cliff we are climbing to is a ferrosyenite gneiss that crystallized from a melt prior to its metamorphism. It is one of a group of quartz-poor, alkali-feldspar- and ferroan-pyroxene-rich igneous rocks that acquired their gneissic fabric during an episode of isoclinal and recumbent folding associated with the Grenville orogeny at about 1100 M.Y. The persistent proximity and intimate intercalation of these gneisses with "Grenville" supracrustal rocks suggests that they may have initially been iron-rich felsic volcanics, or perhaps sills, interlayered with siliceous dolomites, calcareous quartzites, marls and basaltic flows comprising a Proterozoic series of rocks deposited about 1350 M.Y. This Grenville age is estimated from Ashwal's (1983) recent Sm147Nd143 date of 1288 M.Y. believed to represent the age of crystallization of the Marcy anorthosite massif-core facies. Following the model of McLelland and Isachsen (1980) for the southern Adirondacks, we suggest that, in the High Peaks Region of the northeastern Adirondacks, a "typical" Grenville supracrustal sequence correlative with rocks of the Central Metasedimentary Belt (Wynne-Edwards, 1972) was buried in a plate-tectonic event or events to a depth of about 70 km (42 mi), that of a doubly thickened crust. Following Emslie (1977), we envisage the birth of an anorthositic magma from the fractionation of copious amounts of orthopyroxene from an already-fractionated Al-rich gabbroic magma. Under these deep-seated conditions, the high pressures and temperatures plus the availability of Grenvillestrata- derived CO2-rich fluids initiated the formation of potassium- and iron-rich, relatively quartz-poor, melts of syenitic to monzonitic composition (Wendlandt, 1981). Ascent, intrusion, and emplacement of the syenitic melt at levels on the order of 25-35 km (15-21 mi) and temperatures of 800-900° induced deep contact metamorphism of appropriate Grenville rock types. Here, at the easternmost part of the PO-2 outcrop, designated PO-2Gv (Fig. 3), a calc-silicate sequence infolded with the ferrosyenite contains the assemblage: wollastonite-diopside-grossularquartz. Because anorthosite is absent, the contact-metamorphic origin of the wollastonite must be attributed to the intrusion of syenitic melt. Further, because the ferrosyenite contains relict inverted pigeonite, which now consists of host orthoferrosilite, 100Fe/(Fe+Mg)=85-92, the melt must have crystallized at temperatures of 850-900° (Lindsley, 1983 and Ollila, Jaffe and Jaffe, 1988). Alternatively, shallow emplacement with crystallization of fayalite and quartz, later deeply buried and converted to orthoferrosilite and quartz, is conceivable, yet unlikely, because no relict olivine, whatsoever, has been observed by Jaffe or by Ollila in quartz-bearing syenitic rocks of the Mt. Marcy and the Santanoni quadrangles. Fayalite (Fa95) plus quartz, but with orthopyroxene absent, has been described from quartz-syenitic rocks in the Cranberry Lake quadrangle to the west (Buddington and Leonard, 1962, Jaffe et al. 1978) and in the Ausable Forks quadrangle to the northeast (Kemp and Alling, 1925 and Jaffe et.al., 1978). A deep emplacement with high pressure crystallization is consistent with field observations and experimental data for all of these rocks.
At the PO-2 outcrop, we will split into several smaller groups: the footing can be a bit tricky. Remember not to step back for a better look at the outcrops. The first or westernmost cliff consists of strongly foliated ferrosyenite gneiss, N45E,30W, with a large inclusion of shonkinite granulite (Fig. 4, Table 5). The foliation continues through the inclusion. The southwest end of the inclusion is sharply cut off by the gneiss but the northeast end fingers out. The inclusion is cut by a discordant vertical tongue of gneiss which becomes a subhorizontal pegmatite vein. At the northeast end of this cliff, the ferrosyenite gneiss is cut by an unfoliated aplite dike. Small amphibolite inclusions can be seen in the gneiss.
We will proceed cautiously about 300' (91.5 m) along the base of the cliff to the northeast, across a stream and a gully. Here we see several larger folded amphibolite inclusions in the ferrosyenite gneiss (Fig. 3). The axial planes of these folds are approximately parallel to the pervasive foliation. We will now crawl a few feet up the gully: in its cast wall are exposed marbles and calc-silicates intimately infolded in the ferrosyenite gneiss. Wollastonite occurs in these calcsilicate beds (Fig. 3). If we make allowance for the plasticity of the marble, these folds are also approximately parallel to the pervasive foliation. There is a cave in the marble a little higher up this gully. On the opposite side of Lower Cascade Lake, in the anorthosite, another cave can be found a few hundred feet higher up. Caves are common in New York State, but these two must be among the few in Precambrian rocks.

STOP 5. Grenville Marble-Syenite-Anorthosite Section South Of Keene
Drive five miles (8 km) northeast on Route 73 to the first right turn after a Gulf gasoline station and almost into Keene village center. Turn right (south) on the westernmost of two small roads that parallel both sides of the East Branch of the Ausable River. Drive about 0.75 (1.2 km) miles south on this western side of Hulls Falls Road and park judiciously along the edge of this little travelled road. Descend about 25' (7.6 m) to the bank of the river watching out to avoid standing or sitting in Rhus toxicodendron which commonly grows in Grenville marble terrain. A fine river outcrop of folded Grenville marble consists of calcite (white), diopside (green), fluopargasite (black), and minor glistening flakes of phlogopite (brown) along with less abundant graphite. Pink quartz leucosyenite and blackstreaked gray-white gabbroic anorthosite gneiss have been dragged into highly contorted syntectonic folds enhanced by the plasticity of the marble and the probable molten state of the quartz syenite and gabbroic anorthosite (Fig. 5). Occasional tongues of gabbroic anorthosite cross-cut the syenitic rocks. A major vertical fracture zone, the Keene Fault Zone runs parallel to the river in a N-S direction, and is well exposed about one-half mile (0.8 km) south in a granulated anorthosite outcrop. The Keene Fault has dragged the preexisting, gently north dipping, isoclinally folded strata into fairly steeply plunging folds at this locality. A late, brittle stage of movement on the same fault has granulated and retrograded all of the brittle rock types. Feldspar in syenite is sericitized, intermediate plagioclase in gabbroic anorthosite has been albitized and veined by calcite, grossular-diopside calc-silicate rocks have been prehnitized and chloritized, but marble merely goes along for the glide.
At the northernmost end of the outcrop, the diopsidic marble and the quartz syenite are transected by a 4' (1.2 m) wide N80W,90 trending lamprophyre dike (Fig. 5) which displays good chilled margins. It is a classic lamprophyre: a dark, dense, porphyritic dike rock in which the ferromagnesian minerals occur in two generations and in which only the dark minerals form the phenocrysts. It consists of 1-5 mm diameter phenocrysts of partially serpentinized magnesian olivine, and zoned clinopyroxene with augite cores and titanaugite rims, which display spectacular zoning, intense anomalous interference colors and dispersion, and hourglass structure. The groundmass contains a second generation of microphenocrysts of titanaugite, kaersutite, titanian biotite and abundant very thin needles of apatite in a quasi-isotropic base that has too high an index of refraction to be analcime or leucite; it has a mean index of refraction = 1.525 and is either untwinned anorthoclase or a zeolite. The dike may be classified as either a camptonite or a monchiquite, but exactly conforms to neither.

STOP 6. The 1063 Mylonite
On the west side of Route 73, 1.3 miles (2.1 km) south of the village of Keene Valley at BM 1063 and opposite the Beer Bridge across the Ausable River, the anorthosite is cut by a well-developed mylonitic zone about 2' (0.6 m) wide which trends N55E,35NW. Park on the west shoulder of the road south of the outcrop and walk back. The anorthosite here appears to be the normal gabbroic type; however, the mafic minerals occur in clots and aggregates of augite+apatite, many of which are bent into mini- and microfolds. These clots and the sparse megacrysts of labradorite form a foliation which trends N70W,70SW. The coarse grained contaminated felsic anorthosite and the mafic clots of partially assimilated augite+apatite represent either remnants of a Grenville phosphate-rich calc-silicate rock, or a mafic cumulate segregated from a gabbroic anorthosite melt. The iron content of the augite, 100Fe/(Fe+Mg) = 47, while too high for felsic anorthosite, is representative for anorthositic gabbro. Further, the profusion of "100" and "001" metamorphic pigeonite exsolution lamellae in the host augite (Jaffe et al., 1975) suggest that the clots may derive from anorthositic gabbro, where such are common, rather than from a Grenville calc-silicate lithology, where they are rare. Labradorite megacrysts in this rock are nevertheless higher in anorthite than felsic anorthosites of the Marcy region, and show An50.5_54 5 rather than the typical An46-48, suggesting a probable assimilation of calcium from the augite-apatite-rich clots of xenoliths. For this reason we classify such rocks as a percalcic subfacies of the gabbroic anorthosite facies. Just north of a small waterfall, the outcrop changes dramatically: the rough foliation gives way to fine layering along which the dark minerals occur as streaks and schlieren, though occasional megacrysts have escaped granulation and appear as flaser. The mylonite is focused in a 2' (0.6 m) zone which dies out gradually to the north after about 20' (6 m) giving way again to percalcic anorthosite. Just beyond a covered interval, the north end of the outcrop contains a mafic rock, in rudely vertical attitude, but somewhat bent about a sub-horizontal axis, perhaps earlier than the mylonitization. It has been named "aproxite" by one of the authors, in allusion to its bimineralic apatite + pyroxene composition, which is identical with that comprising the mafic clots in anorthosite host rock at the south end of the outcrop. The mineralogy thus suggests that the "aproxite" is a folded layer in anorthosite rather than a mafic dike.
The mylonitic zone does not retain any of its primary magmatic or high grade metamorphic mineralogy but is totally retrograded to a fine-grained mixture of albite, prehnite, sericite, quartz, chlorite, pumpellyite, epidote, and calcite. Labradorite is altered by the following probable retrograde reaction:
4 Lab + Or + Water
= 2[NaAlSi3O8] + Ca2Al[AlSi3O10](OH)2+ KAl2[AlSi3O10](OH)2 +SiO2
2 Ab + Prehrite + Sericite + Qz
Augites have been drawn out into elongate lenses, spindles, and schlieren, and totally retrograded to a mixture of fibrous, isotropic chlorite and pumpellyite with a little calcite. Apatite, alone, remains unaltered, appearing as microflaser in the mylonitized base (Fig. 6).
This wet assemblage is inconsistent with deep, ductile shear and suggests that the mylonitized zone originated by brittle shear or cataclasis in a wet, relatively shallow crustal setting.
That the shear zone was initially a deep, ductile mylonite, later retrograded, remains a possibility.

STOP 7. Chapel Pond Anorthosite
Outcrops on the E side of Rte. 73 consist of andesine anorthosite containing shear zones of scapolite gneiss and a garnetiferous aplite dike (Fig. 7). For a detailed description of these outcrops, see Kelly (1974). Most of the rock here is Marcy facies andesine anorthosite.
It consists of 30-40% dark blue-gray megacrysts of calcic andesine, An45-49, set in a matrix of white andesine, hypersthene, augite, and a little hornblende. Plagioclase makes up about 90% of the rock. A fine-grained aplite dike, up to l m thick, trends roughly parallel to the road where it may be seen to crosscut the foliation marked by aligned megacrysts of plagioclase in the anorthosite. The aplite contains about 60% microperthite, 25% quartz, 10% altered plagioclase, 3% magnetite, and 1% each of garnet and altered ferromagnesian silicates.
Along anorthosite-dike contacts, fracture zones in the anorthosite contain clear andesine, An44-47, abundant scapolite, Me36-47, dark olive hornblende, and a little hypersthene. Fluids carrying Cl and CO2 apparently migrated into fractures in the anorthosite to convert plagioclase into scapolite.
The abundance of the plagioclase megacrysts here and the overall texture of the rock is typical of the anorthosite that forms the core of the Adirondack high peaks to the west.

STOP 8. Gabbroic Anorthosite Protomylonitic Gneiss
The prominent outcrop on the W side of Rte. 9 is a gabbroic anorthosite protomylonite or straight gneiss located in one of the prominent northeast-trending fault zones that abound in the NE Adirondacks. Note that the size reduction and mylonitization of this gabbroic anorthosite are not so intense as that seen at Stop 6, the 1063 mylonite.
The rock consists of very fine crenulations and streaks of hornblende, garnet, ilmenite, and augite in a fine matrix of white andesine, An32, and anorthoclase. Recrystallization took place under dry conditions, and all minerals are fresh.
The high strain nature of the gabbroic anorthosite gneiss is evident, and is illustrated by the total granulation and virtual absence of plagioclase megacrysts. An occasional block or xenolith of felsic anorthosite is present. Punky grey veins of finely altered rock occur in fracture zones.

STOP 9. Multiply Deformed Layered Gabbroic Anorthosite Gneiss
The prominent cliff on the W side of Rte. 9 is a hydrothermally altered layered gabbroic anorthosite or leucogabbro located in one of the prominent northeast trending fault zones that abound in the NE Adirondacks.
The rock contains kaolinitized andesine, titanian brown hornblende, augite, and garnet, with a little ilmenite and apatite. Compositional layering is marked, with more mafic layers rich in augite and garnet, and more felsic layers richer in altered andesine and hornblende and without garnet. Many thin veinlets of white prehnite, calcite, and chlorite crosscut the gneiss. The layered gneiss was subsequently intruded by one or more aplite dikes, composed of altered albitic plagioclase, potassium feldspar, and quartz, along with garnet, and small amounts or apatite. Garnet is altered to chlorite. The rock is sliced on a mm scale, and slickensided, fracture surfaces often being coated with bright green pistacite.
The gneiss was recumbently folded under a high strain rate and then subjected to open folding (Fig. 8). Do the conspicuous open folds delineated by the pink aplite represent:
1) refolding of the recumbently folded gneiss?
2) a sheath fold squeezed or squirted up inside the gneiss? .
3) are there one or two aplite dikes, and does the aplite layer close into a fold hinge beneath the road?
Just across Rte. 9 on the E side, the rock has a completely different texture. About half the rock consists of 0.5-5 cm green, euhedral kaolinite pseudormorphs after plagioclase phenocrysts lying in a foliated matrix of brown hornblende, quartz, anorthoclase, augite, magnetite, and apatite. The fine black matrix is unaltered, in contrast to the large plagioclase phenocrysts. The green kaolinite pseudomorphs show good albite and Carlsbad twinning, but under the microscope only trace amounts of unaltered plagioclase remain. Compositionally, the rock is a quartz gabbro or quartz diorite. However, it may represent a porphyritic gabbro with its groundmass recrystallized to a metamorphic assemblage.

STOP 10. The Woolen Mill Gabbro And Anorthosite, Rte. 9N
On Rte. 9N about 1.6 km W of the intersection of Rtes. 9 and 9N at the golf course on the southern edge of Elizabethtown are outcrops of gabbro and anorthosite at the site of an old, long disused broken dam. Recent reconstruction of the dam and installation of a penstock along the Branch River just N of the road may limit our examination of a fine exposure of anorthosite block structure along the river.
On the S side of the road, a prominent cliff exposes the very irregular contact of a garnet- and magnetite-rich gabbro with a white gabbroic anorthosite in which almost all of the plagioclase megacrysts have been granulated. A rude foliation may be observed in both rocks. Modes of the gabbro and optically determined compositions of plagioclase, augite and hypersthene from the gabbro and anorthosite are given in Table 6. The contrast in Fs content of coexisting clino- and orthopyroxene in gabbro and anorthosite is marked. Note that the iron-rich gabbro has abundant garnet, while the relatively iron-poor anorthosite has none. The presence in the gabbro of isolated blue-gray, well-twinned (Carlsbad and albite) labradorite xenocrysts and occasional xenoliths, as well as contact relations, suggests that the gabbro has intruded the anorthosite before regional deformation. Toward the center of the roadcut, a pink aplite dike has intruded both the anorthosite and the gabbro.
The complexity of the contact relations here has led different geologists to different interpretations. Kemp and Ruedemann (1910) and Kemp (1921) reported that river outcrops showed "anorthosite tonguing in to the dark supposed gabbro" and suggested that the gabbros might represent "surviving inclusions of Grenville sedimentary gneisses impregnated with matter from the anorthosites." They suggested that the Woolen Mill gabbro was thus an old Grenville rock hybridized by later intrusion of anorthosite. Commenting on this interpretation, Miller (1919) assigned these plagioclase-megacryst-bearing gabbros to the Keene gneiss, which he believed to be a syenitic magma containing assimilated anorthosite! Buddington (1962) described the Woolen Mill gabbro as a typical olivine gabbro intrusive into anorthosite, in which olivine was extensively converted to garnet during regional metamorphic recrystallization. No evidence of relict olivine could be found under the microscope.
How would you interpret the outcrop relations?

A6: METASEDIMENTARY AND METAVOLCANIC ROCKS OF THE AUSABLE SYNCLINE, NORTHEASTERN ADIRONDACKS
Philip R. Whitney
Geological Survey, New York State Museum
James F. Olmsted
Center for Earth and Environmental Sciences
State University of New York College at Plattsburgh
On this trip we will examine two sections of granulite facies metamorphic rocks, exposed in stream cuts in the southern and central Ausable Forks 15' quadrangle. The first section is dominated by calc-silicate rocks, marbles, and quartzites, typical of metasedimentary rocks in the northeastern Adirondacks. The second includes both metasedimentary rocks and the Lyon Mountain Gneiss, an unusual lithologic unit comprising a diverse suite of rocks which we believe are chiefly metavolcanic. Points for discussion on the trip include possible protoliths, the tectonic and sedimentary environment at the time of deposition, the metamorphic environment(s), and contact relationships with olivine metagabbros and anorthositic gneisses. Both stops on this trip involve moderately long hikes along scenic Adirondack brooks. While the hikes are not particularly arduous, we recommend sturdy boots and the exercise of caution; some of the stream banks are quite steep, and frequent crossings of streams on slippery rocks will be necessary.

A6: METASEDIMENTARY AND METAVOLCANIC ROCKS OF THE AUSABLE SYNCLINE, NORTHEASTERN ADIRONDACKS

Clintonville.
This hamlet is a former iron mining town said to have had a population of over 10,000.

Unusual ferrohedenbergite-fayalite granite
Outcrops in roadcut on right are an unusual ferrohedenbergite-fayalite granite, first described by Buddington (1939). This may be a reduced facies of the Lyon Mountain Gneiss, or a subsequent intrusive rock.

Differing mechanical properties of various rock types "The Snake"
Stop at several small outcrops in a bank on the L (east) side of the road, directly downslope from a house. Cameras are a must at this stop, but no hammers, please. This informal stop illustrates the differing mechanical properties of various rock types, including marble, diopsidite, amphibolite, and granitic gneiss. This exposure has been called "The Snake", for obvious reasons.

Metanorthosite of the Jay Dome
Exposures on R in the bed of the Ausable River are metanorthosite of the Jay Dome, cut by several unmetamorphosed mafic dikes.

STOP 1. Gelina Basin.
The road forks at this point, with the R fork leading steeply uphill. There may be a gate across the L fork. This is private property, owned by Ward Lumber Co. in Jay. If you come here on your own, get permission. We will park here and proceed on foot up the R fork. If you have an altimeter, set it for 1280 feet. After about a half mile, the road ends at a hunting cabin in a clearing. Walk to the R of the cabin past the john, where you will find a trail that follows the top of a steep bank. Follow the trail S to about 1800 feet altitude, and work your way dawn the bank to the stream at the bottom. This unnamed, north-flowing stream drains a cirque (Gelina Basin on the 15' quadrangle map) on the north flank of Jay Mountain. We will attempt to hit the stream at about 1700 feet and traverse upstream over a well exposed section of NNE-striking metasedimentary rocks.
1730-1750' (altitudes approximate) Calcsilicate rocks with diopside and wollastonite, locally rusty weathered, with quartzite layers.
1750-1760' Strongly foliated amphibolite, overlain by coarse, rusty calcite-diopside-phlogopite-graphite marble.
1780-1820' First of three waterfalls. At the base of this falls, layered diopside-wollastonite calcsilicates (WoDi) and quartzite are exposed. The caprock is tremolite-bearing quartzite; just above this is Mg-rich enstatite-diopside-tremolite-quartz rock.
1830' 5' cascade over diopsidite and diopsidic marble with thin quartzite layers.
1840- 1870' Interlayered metasedimentary rocks (diopsidites and WoDi) and thin amphibolites.
1880-1900' Amphibolite, overlain by metasedimentary rocks, including a calcite-diopside-wollastonite-grossular-idocrase marble at the base of a second waterfall. The cap of this falls is a dark, feldspathic diopsidite with locally abundant sphene. The amphibolite here may be a sill or dike of olivine metagabbro satellitic to the larger body exposed just upstream.
1910-1960' Third falls. The lower part of the falls is a cascade over banded WoDi rock; the upper part is olivine metagabbro locally mixed with granitic gneiss. The gabbro contact here appears to have a steep easterly dip, truncating the more gently dipping metasedimentary layers. Thin sections of the WoDi rock here show thin rims of grossularitic garnet around wollastonite, possibly a result of the reaction wollastonite + plagioclase = grossular + quartz.

STOP 2. Clear Pond Park and Doyle Brook Gorge.
Park on R side of road. To reach the traverse up Doyle Brook we will walk along a private logging road (permission needed) that runs SW from Trout Pond Road. [Note: the 1953 USGS topographic map (1:62,500) is accurate in this area; the 1980 1:25,000 version is not]. Proceeding SW along the logging road, we will pass Copper Pond, which occupies a small basin in albite gneisses of the LAG and MAG facies. Just S of Nesbitt Pond, a short trail leads S to Doyle Brook. From here, we will traverse upstream. The stream gradient is small, so altitudes are not listed. The first rocks encountered in the streambed are amphibolites. A short distance upstream, Doyle Brook emerges from a slot formed at an ENE-trending fault here occupied by an unmetamorphosed mafic dike of indeterminate age that shows evidence of multiple episodes of intrusion. The walls of the gorge are MAG facies albite gneisses, with massive, banded, and megacrystic variants all present. Notice the complex folding in the banded gneisses.
After leaving this first slot, continue upstream along a flat stretch with occasional outcrops of the GG and LAG facies, same quite magnetite-rich. Then enter a second gorge, walled by heterogeneous, intensely fractured LMG, mostly of the GG facies. Shortly beyond the SW end of this gorge, the stream crosses a concealed contact between the LM3 and the under lying metasedimentary rocks. The first outcrop of the latter is a rusty-weathered, graphitic, sillimanite-garnet metapelite. Continuing upstream, the course of the stream swings around to a nearly NS direction, with outcrops of garnetiferous granitic gneiss. At the S (upstream) end of this segment are several marble outcrops, including a coarse white calcite marble with serpentine and graphite, and a nearly pure, gray, tan-weathering dolomite marble. A large spring marks the underground outlet of Lawson Pond, located just to the south and about 80' higher in elevation. The surface outlet shown on the map does not exist. The rocks here strike NNE and dip east; the marble overlies the granitic gneiss seen in the previous outcrop. Another bend in the stream leads first SW and then W (downsection) over outcrops of amphibolite and rusty calcsilicate rocks, back into garnetiferous granitic gneiss, followed by gabbroic anorthosite gneiss. The latter is part of a large, irregular lens of metanorthosite within the layered metamorphic rocks. At this point we will leave the stream and walk back to the access road, following the N rim of Doyle Brook gorge.

A7: IRON INDUSTRY OF THE EASTERN ADIRONDACK REGION
JAMES C. DAWSON
Center for Earth and Environmental Science
State University of New York
Plattsburgh, NY 12901
JOHN R. MORAVEK
Plattsburgh , NY 12901
MORRIS F. GLENN
Mapping and Charting Department
Defense Mapping Agency
u.s. Department of Defense
Washington , DC 20310
GORDON C. POLLARD
Department of Anthropology
Introduction
Developments in mining and iron smelting in the Adirondack-Champlain region commenced with effective American settlement after the 1812-1814 war, and in some instances preceded it. Iron ore had been observed on the lakeshore near Crown Point as early as 1749 by Swedish naturalist Peter Kalm (1770).
The crude ironworks on the manor of British military officer, Philip Skene, at Skenesborough (Whitehall, NY) at the head of Lake Champlain smelted ore from the vicinity of what later became the Cheever Mine a few miles north of Port Henry, NY (Morton, 1959). At the mouth of the Saranac River on Lake Champlain, Zephaniah Platt and associates operated a Catalan forge or bloomery in 1798 using ore from Vermont. In 1801, an ironworks was erected at Willsboro Falls on the Boquet River.

A7: IRON INDUSTRY OF THE EASTERN ADIRONDACK REGION

STOP 1. Lyon Mountain Mines
Lyon Mountain was the site of the Chateaugay ore beds. During its century-long life as a mining center, it produced more ore in aggregate than any other area in the Adirondack-Champlain Region , except for the Mineville-Witherbee complex of Essex County. The Prall Vein or Mine 81, an open pit situated two and a half miles to the southwest, was the probable source of ore that supplied a bloomery operating on the Chateaugay River to the north as early as 1803, but the Chateaugay deposits at Lyon Mountain were not discovered until 1822-1823. Development lagged for a full half century due to the remoteness of the area.
In 1868, a group of four Saranac Valley speculators purchased the ore beds and devised plans for an extensive enterprise. In 1873, this interest was transferred to the newly organized Chateaugay Iron Ore Company. Substantial quantities of ore were shipped to the large bloomery erected in 1872 at Popeville. The Chateaugay Railroad Company was formed to construct a railroad from Lyon Mountain east to the rail terminus from Plattsburgh at Clinton Prison in Dannemora. This was completed in 1879. The railroad, mining, and smelting interests were consolidated into a powerful new firm, the Chateaugay Ore and Iron Co. in 1881. This creation launched development on a great scale.
Our excursion will walk by the head frames of the later works and a former employee of Republic Steel who is familiar with the structures will describe their purpose at the time that operations were closed in 1967.
In Lyon Mountain, New York century-old residential structures border the mines, together with the 1920s-vintage standard "company" houses that line Route 374 (Belmont Street). Today's inhabitants, descendants primarily of Lithuanian, Polish, Russian, Italian, Spanish, Irish, and French-Canadian immigrants who labored in the mines and mills, are either retired or, if employed, commute to jobs on the outside, or since 1984, have found jobs on Belmont Street itself at the former public school house, now converted to a minimum-security state prison.

STOP 2. Site Of Catalan Forge At Standish
The Chateaugay Ore and Iron Company had an 8-fire bloomery at Standish by 1883. This was enlarged several times until it was shut down in 1907. In 1885 the company constructed a blast furnace at Standish to produce pig iron in addition to bloom iron (Linney, 1934). The trade name "Chateaugay" quickly gained a highly favorable reputation for excellence. Blooms, pigs, and the celebrated low-phosphorus magnetite were widely sought after, and commanded premium prices everywhere. The crude ore was/is rather lean, averaging only 26%-28% iron content, but was practically free from phosphorus, sulfur, and other chemical impurities, and could be readily beneficiated to 65-70% iron content. Iron and high-grade alloy steels made from Chateaugay ore were renowned for toughness and strength and widely used for the fabrication of wire rope, munitions, ordnance, and other specialties. For such purposes, it was considered unsurpassed in all the world, and steel cables made of Lyon Mountain's ore can be found today in such mighty and notable structures as the Brooklyn bridge, the Golden Gate Bridge in San Francisco, and the George Washington Bridge in New York City.

STOP 3. Caldwell Mine Site
Ore was discovered at the Caldwell site in 1840 and mining began in 1841. This was the first iron ore discovery in the Saranac River valley and it resulted in the establishment of a settlement named after the original property owner Leander Cadwell. Early newspapers and subsequent histories managed to misspell his name .
Leander Cadwell and Lawrence Myers erected four forges and a separator at the site in 1844. By 1846 this was expanded to six forges, two separators, two trip hammers and a finishing hammer. About 100 men were employed. Myers became the sole owner in 1855 and by 1860 the mine was yielding 1500 tons of iron ore per year. The property changed ownership in 1863 and again in 1873 and the mine was considered "mined out" and closed in 1881.
Historical archaeological research has been conducted by Gordon C. Pollard (Pollard, 1985). The research has produced a map of the eleven-acre site and has documented the mine, ore processing site, charcoal production and storage, residences and company store. Dr. Pollard will be on hand to guide this portion of the field trip.

STOP 4. Palmer Hill Mine Site
Iron ore was discovered at Palmer Hill, in the Town of Black Brook, in 1824-1825 by Zephaniah Palmer. In 1829 he sold a three-eights interest, the eastern extension of ore, to the Peru Steel and Iron Company. Later he sold the western five-eights interest to the J. and J. Rogers Iron Company of Au Sable Forks, NY.
Mining commenced about 1830 and continued to 1892-1893. The Palmer Hill Mines were initially excavated as open pits but as time passed increasing depth rendered impractical the removal of overburden, and drifts were developed as the companies followed bands of ore ranging in thickness from 10 feet to 20 feet. The deepest set of workings bottomed at a depth of 2,200 feet, down a dip slope that began at 60° and flattened to a nearly horizontal position at the bottom. Other pits extended to a depth of 1,000 to 1,200 feet down dips of roughly 30°. In some cases workings followed shoots of ore across the dip. The texture of Palmer Hill ore was rather fine, and in appearance and mode of occurrence resembled the Chateaugay ores at Lyon Mountain.
Our stop will briefly explore the honeycombed southern brow of Palmer Hill, with its numerous irregular openings and chambers and piles of rock and mine rubble. This site continues to hold a certain fascination, and remains potentially dangerous, to local explorers and students. In places the surface workings have caved in and are inaccessible, but numerous pits do allow access and invite cautious investigation. Deep water fills the lower parts of these "caves," and in some pits ice can be found at any time of the year.

STOP 5. Driving Tour Of Clintonville.
The Peru Steel and Iron Company was heavily engaged in smelting and iron fabrication in Clintonville, New York and reached its peak prosperity in the 1850s and 1860s when 900 men were employed (Moravek, 1976). The bloomeries, separator and rolling mill occupied more than a mile of the north bank of the Ausable River.
The national decline of the iron industry in 1873 was hard on Clintonville and by 1880 the activities of the Peru Steel and Iron Company at Palmer Hill and at Clintonville were over.

STOP 6. Fletcherville Blast Furnace And Sherman Mine.
Friend P. Fletcher joined with Silas H. Witherbee and Jonathon G. Witherbee to manufacture iron in a furnace on Fletcher's 4000 acres of land. Jerome B. Bailey of Plattsburgh, New. York built the blast furnace in 1864-1865. It was a stone stack 42 feet high, later increased to 61 feet, on a 42 foot square base. Nearby ten enclosed rectangular brick charcoal kilns were constructed, each capable of charring 65 cords at a time (Allen, 1975). The town that sprang up was known locally as Fletcherville, but people in Westport referred to it as Seventy Five because it was thought to be in Lot 75 in the Town of Elizabethtown. A survey showed that it was really in Lot 48 of Westport which then received the taxes.
In the early 1870s much of Fletcher's pig iron was shipped from Port Henry to Troy, New York where it was used in the experimental Bessemer steel process for railroad track (Witherbee, 1874). The early success began to fade in the 1870s and after Fletcher's death in 1874 the works closed down.
The Sherman Mine and other small mines on the Fletcher property were occasionally revisited with activity at the Sherman continuing as late as 1921.
Our visit will examine the remains of the blast furnace, charcoal beds, ore roasting kilns, various out buildings and perhaps the Sherman Mine.

STOP 7. Driving Tour Of Witherbee
The mines of the Mineville-Witherbee-Fisher Hill area in the Town of Moriah have been the most productive iron ore producers in the eastern Adirondacks. Our drive will circle through the sites of the "Old Bed," "21," "Barton Hill," "Harmony," and "Joker" mines of the extensive Mineville Group (Kemp, 1908). These mines were greatly expanded in the 1860s by the Port Henry Iron Ore Company after their initial discovery about 1825 (Warner and Hall, 1931). A variety of interests including the Witherbee, Sherman and Company operated in the area until Republic Steel Corporation took control from 1937 to 1971. Be sure to note the concrete block buildings that incorporate tailings material (Lincoln, 1909).

B1a: LATE WISCONSINAN LACUSTRINE AND MARINE ENVIRONMENTS IN THE CHAMPLAIN LOWLAND, NEW YORK AND VERMONT
David A. Franzi
Center for Earth and Environmental Science
State University of New York
Plattsburgh, New York 12901
Thomas M. Cronin
United States Geological Survey
M.S. 970 National Center
Reston, Virginia 22092
The Champlain Sea was a Late Wisconsinan marine incursion into the isostatically depressed St. Lawrence and Champlain Lowlands following ice recession from the eastern St. Lawrence Lowland (ca. 12.5 to 10.0 ka (kilo anno)). The marine episode followed a freshwater proglacial lacustrine interval in the Champlain and western St. Lawrence Lowlands (Fulton and others, 1987; Chapman, 1937). Sedimentary sequences containing till, ice-contact gravel, subaqueous outwash, and sparsely fossiliferous lacustrine sediment overlain by fossiliferous marine sediment record the transition from glacial to lacustrine to marine conditions in the basin.
This trip will examine the nature of the transition from freshwater to marine conditions and the paleoenvironments of the Champlain Sea as shown by the lithostratigraphic and biostratigraphic records in the Champlain Lowland. Faunal assemblages are used to reconstruct the areal and temporal distribution of water temperature and salinity within the basin. Emphasis is placed on the microfauna, particularly the ostracodes, and how changing microfaunal assemblages record environmental changes in this part of the Champlain Sea. The data summarized here are taken primarily from detailed faunal studies of foraminifers (Cronin, 1979) and ostracodes (Cronin, 1981) which concentrated in the southern arm of the sea in the Champlain Lowland of northwestern Vermont, northeastern New York, and southern Quebec. It should be stressed, however, that the sequence of faunas found in this region are not necessarily the same as those in other parts of the Champlain Sea where different hydrologic conditions caused a distinctly different sequence of paleoenvironments (Rodrigues and Richard, 1986; Rodrigues, 1987).

B1a: LATE WISCONSINAN LACUSTRINE AND MARINE ENVIRONMENTS IN THE CHAMPLAIN LOWLAND, NEW YORK AND VERMONT

Outcrop of the Cumberland Head argillite.

Outcrop of the Chazy Gp.

Korean Veterans Memorial Bridge (formerly Rouses Point Bridge).
The ruins of Fort Blunder (Ft. Montgomery), an American fort that was originally built on Canadian soil, can be seen on your left. The "blunder" was corrected by moving the border northward.

Outcrop of Stony Point argillite.

STOP 1. Town Gravel Pit, Isle LaMotte, Vermont
The predominant lithofacies consists of thinly bedded, molluscan-rich sand with minor gravelly sand and sandy to silty mud interbeds. The sands are generally medium to coarse grained and are cross bedded or horizontally laminated. Individual beds range from a few centimeters to about 20 cm thick and can be traced laterally for several meters. The sandy facies contains two biofacies, a Macoma balthica facies and a Mytilus edulus facies. The faunal assemblages were previously described by Cronin (1977 (loc. 11), 1979, 1981 (loc. 33)). Articulated valves of both species are commonly found in living position. Occurrences of Mytilus in living position in Champlain Sea deposits are rare since this mollusc usually lives attached to the substrate by a byssus and its two valves have an adont hinge that disarticulates easily.
Ostracodes and benthic foraminiferas are rare in these sands. The following species occur; Cyprideis sp.
Cythere lutea (Mueller, 1785)
Cytheromorpha macchesneyi (Brady and Crosskey, 1871)
Cytheropteron latissimum (Brady, Crosskey, and Robertson, 1874)
Cytherura gibba (Mueller, 1875)
Eucythere declivis (Norman, 1865)
Finmarchinella logani (Brady and Crosskcy, 1871)
Heterocypridcis sorbyana (Jones, 1857)
Hyocypris gibba (Rahmdohr, 1808)
Leptocythere quebecensis (Cronin, 1981)
Palmenella limicola (Norman, 1865)
Sarsicytheridea bradii (Norman, 1865)
Sarsicytheridea macrolaminata (Elofson, 1939)
Sarsicvtheridea punctillata (Brady, 1865)
Semicytherura cf. similis (Sars, 1865)
These deposits probably represent the latest phase of the Champlain Sea in this region known as the Mya arenaria Phase (Elson, 1969; Cronin, 1977). Mya arenaria is absent at this locality because it is usually found in clay substrates in low-lying a reas west of Lake Champlain. Based on modern temperature tolerances of the ostracode species, the annual temperature range is estimated to have been about 0° to 20°C. Salinities during the Mya Phase were oligohaline to mesohaline (1 to 18 ppt) and all the ostracode species occurring at the Isle LaMotte locality tolerate, and often thrive in brackish water environments.
A coarse gravel facies that contains decimeter-scale foreset beds that range from poorly sorted coarse pebbly sand to open-work cobble gravel was recently exposed in a small excavation at the south end of the pit. The facies contains marine fossils that are commonly disarticulated and fragmented. The gravel facies underlies the fossiliferous sand facies described above and may be related to coarse gravel in an excavation 0.5 km to the west. Gravel foresets at both localities indicate a southward to southeastward paleocurrent. It is difficult to reconstruct the sedimentary environment that existed at the time the gravel facies was deposited because of the limited extent of the exposure at this locality. The gravel facies may be related to a high-energy littoral marine environment during the late regressive phase of the Champlain Sea. Alternatively, it may represent ice-proximal subaqueous outwash that was deposited during ice recession or possibly an ice readvance. A readvance of this nature had been previously proposed by Wagner (1972) based upon stratigraphic evidence from northwestern Vermont.

Gravel pit.
Coarse gravel foresets indicating a southerly paleocurrent are exposed in the working face of the pit.

St. Anne's Shrine.

STOP 2. Beach Ridges of the Champlain Sea.
The ridges consist of coarse, flaggy gravel that is derived from the underlying Potsdam Sandstone. Outcrops of sandstone can be observed in drainage ditches nearby and presumably bedrock underlies the ridges at a shallow depth. These ridges were mapped and described by Denny (1970, 1974) who traced them over a distance of 0.3 km. They trend roughly north-south but curve westward at their northern ends along the margin of a former headland. The elevations of the ridge crests lie between 91 and 98 m.

W.H. Miner Agricultural Institute.
The Miner Institute is affliated with the Center for Earth and Environmental Science at P.S.U.C.

The road follows the crest of the Ingraham Esker.
Note that in places gravel operations have removed nearly all the esker material except for that under the road.

Lake Alice, named for Alice Miner.

Proceed southward along the crest of the esker.

The road follows the crest of the esker.

STOP 3. Ingraham Esker.
The sedimentology and stratigraphy of the Ingraham Esker was summarized by Denny (1972, 1974) and more recently by Diemer (in press). The esker consists predominantly of upwardly fining subaqueous outwash that was deposited in a series of esker fans at the terminus of the northward retreating ice front. The ridge is overlain by fresh water rhythmites which are in turn conformably overlain by a massive mud facies. Diemer (in press) attributes the massive mud facies to an early, transitional phase between fresh (Lake Fort Ann) and marine conditions (Champlain Sea). The section is unconformably overlain by coarse, fossiliferous gravel that probably represents wave-reworking of the previously deposited sediment during the marine regression. Denny (1972, 1974) attributed the low relief of the ridge to extensive wave erosion, however, Diemer (in press) suggests that the morphology of the ridge is a consequence of its origin as subaqueous outwash.
The faunal assemblages at this locality were described by Cronin (1977, loc. 18; 1979, 1981, loc. 4). Hazel studied ostracodes from several localities in the esker and found a total of nine species (in Denny, 1972). The esker's faunas represent the Hiatella artica Phase of the Champlain Sea (Elson, 1969; Cronin, 1977) which occurred between 11.6 to 10.6 ka The following ostracodes were found at this locality in the shelly marine gravels that cap the rhythmite facies.
Candona sp.
Cythere lutea (Mueller, 1785)
Cytheromorpha macchesneyi (Brady and Crosskey, 1871)
Cytheropteron champlainum (Cronin, 1981)
Cytheropteron latissimum (Norman, 1865)
Finmarchinella logani (Brady and Crosskey, 1871)
Heterocyprideis sorbyana (Jones, 1857)
Sarsicytheridea bradii (Norman, 1865)
Sarsicytheridea punctillata (Brady, 1865)
The annual range of bottom-water paleotemperature was probably 0° to 12°C and salinities were polyhaline, between 18 and 30 ppt, as indicated by the faunal assemblages. This salinity was the closest to normal marine conditions that was reached in this part of the Champlain Sea, at least for shallow-water environments.

Esker crosses the highway.

Point Au Roche State Park (beach and picnic area). Lunch.

STOP 4. Korths Farm Section.
This stop will involve two sections along the east bank of Ray Brook. Cronin (1977, loc. 34; 1979, 1981, loc. 84) described the faunal assemblages from the northern section approximately 100 m upstream from the Korths Farm road. Marine clays (formerly known as the Leda clay) overlie rhythmites and contain the mollusc Portlandia arctica and the following ostracodes;
Cytheromorpha macchesneyi (Brady and Crosskey, 1871)
Cytheropteron latissimum (Brady, Crosskey, and Robertson, 1874)
Heterocyprideis sorbyana (Jones, 1857)
Sarsicytheridea bradii (Norman, 1865)
Sarsicytheridea macrolaminata (Elofson, 1939)
Sarsicytheridea punctillata (Brady, 1865)
The faunas at this locality represent the Transitional Phase of the Champlain Sea (Cronin, 1977), which has been dated between 11.6 and 12.0 ka, however, the age for the earliest marine inundation in the region is not yet certain. The bottom-water temperatures ranged annually from about -2° to 10°C. Normal marine and polyhaline ostracodes are absent from the Transitional Phase and salinities fluctuated between 0 and 18 ppt. The term "Transitional Phase" was given to this interval because the faunas indicate a lacustrine to marine transition during which there was mixing of pre-Champlain Sea freshwater with the earliest influx of marine water that entered the region via the St. Lawrence estuary.
The southern section, 50 m downstream from the Korths Farm road, resulted from recent cutbank erosion. Approximately 3 m of flow-slide colluvium, derived primarily from the marine clay unit described above, overlie intact marine clay. The base of the colluvium is marked by an erosional unconformity that includes buried logs. The freshwater rhythmites were not observed at this section but may occur on or below the stream bed. Geomorphological evidence for other flow-slides exists throughout this part of the Ray Brook valley.

Roadbed is composed of wollastonite tailings from nearby mines in Willsboro.

STOP 5. Slump-earthflow.
The Whallonsburg slump-earthflow (Fig. 4) occurred during the night of 28 July, 1987, following localized, light to moderate thunderstorm activity. The slump involved the eastward displacement of 0.9 ha of Pleistocene lacustrine sediment on a cutbank of the Bouquet River. This portion of the Bouquet Valley has a history of landslide activity (Newland, 1938; Whitcomb, 1938; Buddington and Whitcomb, 1941). The 1987 Whallonsburg slump was described by Franzi, Bogucki, and Allen (1988).
The slump is roughly rectangular in plan with an average length of 85 m and an average width of 110 m. The crown is 16 m above stream level. A 0.2 ha toe bulge, composed of highly plastic clay and alluvial sediment, was raised to a height of 4.5 m in the stream channel. The slump consists of a primary mass that was involved in the initial slump and two smaller retrogressive slumps (Fig. 4).
The slump exposed 0.5 to 1 m of coarse sand and gravel over 4 m of nonfossiliferous lacustrine clay and silt at the headscarp. The lacustrine section is estimated to be 23 m thick based upon seismic refraction data from the crown. The clays are characterized by high plasticity and natural water content with low bulk density and shear strength (Fig. 5). The lacustrine unit grades upward from soft, blue-gray, thinly laminated, clay and clayey silt rhythmites to stiff , brown, thinly bedded silt and clay. The textural variation probably reflects the effects of shoaling or infilling during the waning stages of the lake's history. The overlying gravel is part of a large terrace that may be graded to Late Pleistocene marine deltas near Willsboro.
Hillslope reconstructions based on slide-deposit morphometry and laboratory analysis of the long-term shear strength of undisturbed clay samples were used to determine the geological controls on slope stability (Franzi, Bogucki, and Allen, 1988). The factor of safety (FS = resisting forces/driving forces) of the reconstructed preslide slope was calculated using the slope stability model STABR (Duncan and Wong, 1985) under a range of "likely" pore pressure conditions. The results indicate that the preslide factor of safety was close to the threshold value of 1.0 (range 1.0 to 1.2). Although the slump may have been triggered by the rainstorm activity, the actual cause is probably related to pore pressure conditions at the clay-bedrock contact and long-term processes such as cutbank erosion at the toe of the slope and fissure development in the upper, overconsolidated clay.

B1b: LATE QUATERNARY GLACIAL TO MARINE SUCCESSIONS IN THE CENTRAL ST. LAWRENCE LOWLAND
Cyril G. Rodrigues
Department of Geology
University of Windsor
Windsor, Ontario N9B 3P4
The Central St. Lawrence Lowland includes the area betwen the Ottawa and St. Lawrence Rivers, straddles the St. Lawrence as far as Quebec City, and extends a short distance beyond the north shore only (Bostock, 1970). Marine water from the Atlantic Ocean inundated the Central St. Lawrence Lowland and Champlain Valley during the final retreat of the Laurentide Ice Sheet from eastern North America, forming the Champlain Sea (Fig 1.) The purpose of this paper is to describe the lithologic and invertebrate faunal successions at two sites in the lowland and to discuss the sigifciance of the successions.

STOP 1. Sparrowhawk Point Site
A ten-metre section of glacial and marine sediments is exposed in the shore cliffs on the south side of the St. Lawrence River between Ogdensburg and Waddington (Fig. 1). The sediments are divided into the following units, (1) massive stony till, (2) rhythmically laminated silt and clay ("varves"), (3) massive mud, and (4) sand (Fig. 2). Unit 1 is equivalent to the Fort Covington Till of MacClintock and Stewart (1965) and is overlain disconformably by Unit 2. The contact between Units 2 and 3 is gradational and the contact between Units 3 and 4 is abrupt. The succession from till to massive mud was also reported by MacClintock and Stewart (1965) and Terasmae (1965) from sections exposed near Cornwall during the St. Lawrence Seaway Project.
Unit 1 is unfossiliferous. Ostracodes are present in Units 2, 3, and 4. Foraminifers are absent in Unit 2 and are present in Units 3 and 4. Invertebrate macrofossils are common in Unit 3 and in the lower part of Unit 4. Portlandia arctica (Gray) is the most abundant microfossil in Unit 3 and is accompanied by Cylichna alba Brown, Macoma calcarea (Gmelin), and Hiatella arctica (Linne). Macoma-balthica (Linne) is present in the lower part of Unit 4.
Radiocarbon dates, 11 900 ± 100 years BP (GSC-3767) and 11 300 ± 100 years BP (GSC-3788), were obtained for shells of Portlandia arctica from the lower part of Unit 3 and for shells of Macoma balthica from the lower part of Unit 4 respectively (Rodrigues and Richard, 1985). At one spot along the shore the laminated sediments are truncated and underlain by massive mud which in turn is underlain by laminated sediments. Rodrigues (1987) proposed that the presence of massive mud below laminated sediments is related to post depositional slumping. Radiocarbon dates of 11 900 ± 100 years BP (GSC-3767) for Portlandia arctica from the lower part of the massive mud overlying the laminated sediments and 11 900 ± 140 years BP (GSC - 4044) for the same pelecypod species from the massive mud below the laminated sediments, are consistent with the slumping hypothesis.
Three ecozones are recognized on the basis of foraminiferal and ostracode assemblages from 30 samples which were collected from 6 m of section (Fig. 2). Ecozone 1 is characterized by the ostracode Candona subtriangulata Benson and MacDonald and is restricted to the rhythmically laminated silt and clay (Unit 2). Ecozone 2 contains low numbers of the foraminifer Elphidium excavatum (Terquem) forma clavata Cushman and Candona subtriangulata; it is associated with the gradational interval between Unit 2 and the massive mud (Unit 3). Elphidium excavatum forma clavata-dominant foraminiferal assemblages characterize Ecozone 3. The foraminifers Cassidulina reniforme Norvang, Haynesina orbicularis (Brady) and Polymorphinids (species of the Family Polymorphinidae) are also present in Ecozone 3. The ostracodes Cytheromorpha macchesneyi (Brady and Crosskey) and Cytheropteron pseudomontrosiense Whatley and Masson are present throughout Ecozone 3, whereas Cytheropteron paralatissimum Swain occurs in the lower part and Roundstonia globulifera (Brady) occurs in the middle and upper parts of Ecozone 3. Portlandia arctica is the most common invertebrate macrofossil in Ecozone 3.
The laminated sediments (Unit 2) characterized by Candona subtriangulata (Ecozone 1) were deposited in a glacial lake which occupied the area during early stages of ice retreat (Fig. 3). The interval between Unit 2 and the massive mud (Unit 3) containing the Elphidium excavatum forma clavata - Candona subtriangulata assemblages (Ecozone 2) were deposited in low salinity bottom-water during the early part of the marine episode. The salinity of the bottom-water was highest (<25 o/oo) during deposition of Unit 3 which is characterized by Elphidium excavatum forma clavata - dominant foraminiferal assemblages and the pelecypod Portlandia arctica (Ecozone 3).
The inferred freshwater environment for the rhythmically laminated till and clay ("varves") is based on the modern and fossil occurrences of Candona subtriangulata. Congeners of Candona live in freshwater environments, i.e. lakes and rivers (Delorme, 1970 ). Identical Candona subtriangulata-assemblages were reported from the Late Pleistocene Sreboygan Member of the Lake Michigan Formation (Burke, 1987). The presence of Canadona subtriangulata and Elphidium excavatum forma clavata in Ecozone B (Fig. 2) indicates that C. subtriangulata can survive in marine environments characterized by low salinity. This does not imply that the varve-like rhythmites containing Candona subtriangulata were deposited in a marine environment. The distinction between freshwater and marine environments is based on the total fossil assemblage, rather than the presence of a single species in the assemblage. Thus, assemblages containing only Candona subtriangulata are related to freshwater conditions, whereas assemblages containing C. subtriangulata plus marine ostracodes and/or foraminifers are related to low salinity conditions during the early part of the Champlain Sea episode in the Central St. Lawrence Lowland. Cronin (1977) described assemblages containing 2, marine ostracodes, and foraminifers from deposits near the maximum extent of the Champlain Sea in the Champlain Valley. He also concluded that the assemblages are related to low salinity conditions during the early part of the marine episode.

STOP 2. Casselman Site
About 17 m of glacial and post-glacial sediments are exposed along the west bank of the South Nation River, northwest of the town of Casselman (Fig. 1). The sediments rest unconformably on Ordovician carbonate rocks. The glacial and post-glacial sediments are divided into the following units, (1) till, (2) rhythmically laminated silt and clay ("varves"), (3) massive mud, and (4) red- and grey-banded mud (Fig. 4) . The contacts between Units 2 and 3 and Units 3 and 4 are gradational. The succession from Unit 2 to Unit 4 was described by Fransham and Gadd (1977) and Gadd (1977, 1986) from boreholes in the deeper parts of the lower Ottawa Valley.
Unit 1 is unfossiliferous. Foraminifers are absent in Unit 2 and are present in Units 3 and 4. Ostracodes occur in Units 2, 3 and 4. The pelecypods Macoma calcarea, Mytilus edulis Linne, Portlandia arctica and Yoldiella sp., and the sponge Tethya logani Dawson are present in Unit 3. Invertebrate macrofossils were not observed in Units 2 and 4.
Six ecozones are recognized on the basis of foraminiferal and ostracode assemblages from 22 samples which were collected from Unit 2 and Unit 3 and the gradational interval between the units (Fig. 4). The varve-like rhythmites (Unit 2) and the lower part of the gradational interval between Unit 2 and the massive mud (Unit 3) are assigned to Ecozone A which is characterized by the ostracode Candona subtriangulata. Foraminifers and ostracodes are present in low numbers in Ecozone B which is restricted to the upper part of the gradational interval between Unit 2 and Unit 3. Ecozones C to F are associated with Unit 3. Cassidulina reniforme and Islandiella helenae Feyling-Hanssen and Buzas are the characteristic species of foraminiferal assemblages from Ecozone C. Cassidulina reniforme, Elphidium excavatum forma clavata and Haynesina orbicularis are the most abundant species in Ecozones D and E. The abundance of Cassidulina reniforme is lower and that of Elphidium excavatum forma clavata is higher in Ecozone E by comparison with their abundances in Ecozone D. Cassidulina reniforme is absent and Haynesina orbicularis is the most abundant species in Ecozone F. Portlandia arctica is the most common invertebrate macrofossil and ostracodes are rare in Ecozones C to F. Foraminifers and ostracodes are present in low numbers in the upper part of Unit 3 and in the lower part of the colour-banded mud (Unit 4).
The Candona subtriangulata assemblages of Ecozone A are related to fresh water conditions (Fig. 5). Marine conditions are inferred for Ecozones B to F which are characterized by foraminifers. Ecozone B represents a transition from freshwater to maximum salinity conditions. Salinity was <25°/oo in Ecozone Band from the upper part of Ecozone D to Ecozone F. Maximum salinity conditions (25-34°/oo) existed from Ecozone C to the lower part of Ecozone D.
The rhythmically laminated silt and clay (Unit 2) was deposited in a glacial lake which occupied the area during the early stages of deglaciation. The massive mud (Unit 3) and the upper part of the gradational interval between Unit 2 and Unit 3 were deposited during the Champlain Sea episode. Low salinity water replaced freshwater during the deposition of the gradational interval between Unit 2 and Unit 3. Maximum salinity conditions were followed by decreasing salinity during deposition of Unit 3. The lower part of colour-banded mud (Unit 4) was deposited under relatively low salinity conditions during regression of the Champlain Sea.
A radiocarbon date of 11 460 ± 70 years BP (TO-702) was obtained for foraminifers from the base of Unit 3, i.e. the base of the maximum salinity Ecozone C (Fig. 5). The date indicates that maximum salinity water arrived at the Casselman site ca. 11 500 to 11 400 years BP. TO-702 is younger than the date of 11 900 ± 100 years BP (GSC-3767) for Portlandia arctica from the lower part of the massive mud (Unit 3, Ffg. 3) which overlies varve-like rhythmites at the Sparrowhawk Point Site.

B2: DIKES OF THE NORTHEAST ADIRONDACK REGION - INTRODUCTION TO THEIR DISTRIBUTION, ORIENTATION, MINERALOGY, CHRONOLOGY, MAGNETISM, CHEMISTRY, AND MYSTERY
Y.W. ISACHSEN and W.M. KELLY
New York State Geological Survey
C. SINTON and R.A. COISH
Middlebury College
M. T. HEIZLER
SUNY Albany
INTRODUCTION AND SCOPE
More than 1300 dikes in the Adirondack region have been compiled on a map at 1:250,000 (Isachsen and Wright, in press). Figure 1 is a severe reduction of this map. While 1300 may seem a large number of dikes, the sparsity of reck exposures in the region suggests that it represents at most a few percent of the total mnnber actually present. Most dikes are exposed over a length of only a few meters or less, and are a meter or so thick. Several, however, are exposed intennittently for distances up to 15 km, and are as much as 10 m thick. Twenty-four types are represented, five of which are metamorphic. Mafic dikes clearly predominate. Their prominence, in decreasing order, using the names given in the literature, are as follows: diabase, "mafic dike", basalt, gabbro, metagabbro, metadiabase, hyperthene metadiabase, and garnet metadiabase. Next most prominent are lamprophyres and granite pegmatite dikes. Rose diagrams of dike orientations (Isachsen and Wright, in press) show these dominant strike directions: 1) NNE-NE for the basalt, diabase, gabbro and "mafic" dikes, 2) WNW to E-W for the lamprophyres, and 3) NS to NNW for the metamorphic dikes. The northeasterly strikes of most of the unmetamorphosed mafic dikes corresponds to the predaninant trend of faults and zero-displacement crackle zones that account for the great number of linear valleys in the southeastern half of the Adirondacks (Isachsen and McKendree, 1977; Isachsen and others, 1983). The easterly-westerly trends of the larrprophyre dikes correspond to the trends of similar dikes in Vermont . (McHone and Corneille, 1980, McHone, 1984). Their radiometric dates are similar as well.
This trip will include two stops to see lamprophyre dikes and one to see the most impressive concentration of dikes in the Adirondacks - the Rand Hill dike swarm. Here, more than 100 dikes, up to 180 m in exposure length, are exposed in three cross-cutting orientations. Diabase, olivine diabase, and trachyte porphyry dikes intrude gabbroic anorthosite gneiss.
Subjects for discussion will include: dike orientations vs regional fracture patterns, magnitude of extensional strain, dike propagation mechanisms, relative and radiometric ages (and problems), paleomagnetism and apparent polar wander path, geochemical characterization, and plate tectonic inferences
"For the structural geologist, eroded dykes may be viewed as the remnants of full-scale tests of the fracture strength of the Earths crust. If field observations are properly interpreted, they will provide important constraints on the process of dyke emplacement." David Pollard, 1987

B2: DIKES OF THE NORTHEAST ADIRONDACK REGION - INTRODUCTION TO THEIR DISTRIBUTION, ORIENTATION, MINERALOGY, CHRONOLOGY, MAGNETISM, CHEMISTRY, AND MYSTERY

Pass Plattsburgh Quarries on left.

STOP 1. Lamprophyre Dikes
Two lamprophyre dikes cutting a tilted fault block of Crown Point Limestone (Middle Ordovician) of the Chazy Group. The dikes strike N55-73W and dip 83-85 NE, parallel to the prominent joint set here. They are about 50 cm thick and display chilled margins. They contain calcite amygdules, clinopypoxene phenocrysts and local xenoliths of gabbroic metanorthosite. The subject of lamprophyres has recently been reviewed by Rock (1987). The name covers a number of alkalic rock types that form dikes or sills, and rarely lavas. They are defined by their content of abundant euhedral to subhedral phenocrysts of mafic minerals such as olivine, amphibole, biotite, clinopyroxene, apatite or oxides, but not felsic phenocrysts; the groundmass may be mafic, felsic or glassy. Silica content and Na/K ratio vary widely.
In the field, lamprophyres may be difficult to distinguish from diabase dikes, but a careful examination of textures shows lamprophyres to lack the familiar ophitic or diabasic texture with its visible laths of plagioclase. Instead, lamprophyres have a pronounced panidiomorphic-granular (sugary) texture with mafic phenocrysts of various sizes in a fine-grained alkali groundmass. Spherical, calcite-bearing amygdules are common. They, and mafic phenocrysts, may weather preferentially to produce a pitted weathering surface. Although similar weathering also characterizes olivine diabase and olivine basalt, these show the lath-shaped crystals of plagioclase, commonly of phenocryst size.
The dikes at this locality are rich in amygdules filled with calcite. One dike shows an equigranular texture of biotite, plagioclase laths, subhedral and skeletal opaques, and olivine micro-phenocrysts, with some apatite and amphibole. Two samples taken fran the southern side of the road show a characteristic porphyritic, texture, with large euhedral to subhedral phenocrysts of zoned clinopyroxene. The groundmass consists of essential biotite, plagioclase, subhedral opaques, apatite, and possibly amphibole. Alteration of the rock is minimal, but some of the mafic phenocrysts have been altered to chlorite and calcite. The presence of rounded anorthosite xenoliths suggests possible contamination of the magma.
From the whole rock chemistry (Table 1) these rocks can be classified as alkaline lamprophyres, according to Rock (1987). Note the high concentration of alkalis, particularly K2O. The SiO2 contents of the dikes are similar to those of the camptonites of the Champlain Valley studied by McHone and Corneille (1980). Rock (1987) notes that lamprophyres have distinctly higher concentrations of Ba and Sr relative to other silicate igneous rocks, and this is shown here. The lamprophyres have Sr values ranging from 879 to 2016 ppm and Ba values of 800 to 1631 ppm (Table 1), as compared to the diabase dikes at Stop 2 (Rand Hill) which have Sr values of 334 to 706 ppm and Ba values of 373 to 496 ppm (Table 1).
These dikes are probably related to other lamprophyres of Mesozoic age found within the Champlain Valley which have been associated with the alkalic syenite gabbro intrusions of the Monteregian Hills of Quebec (e.g. McHone and Corneille, 1980; deBoer and others, 1988).

STOP 2A. Rand Hill Dike Swarm
Road cuts along Rt. 190 immediately south of Murtaugh Hill Road. Examination will be made first of the roadcuts here which provide fresh 3D exposures of the several dike types that make up the Rand Hill dike swarm. Very extensive exposures will then be examined in the largely open area that extends half a kilometer to the west, STOP 2B. The intruded country rock is gabbroic anorthosite gneiss.
The Rand Hill swarm is located at the eastern foot of Rand Hill. It was first described by H.P. Cushing (1898) who called attention to three localities in the northeastern Adirondacks with "exceedingly numerous dikes": Rand Hill, Dannemora Mountain, and the shores of Upper Chateaugay lake. The Rand Hill dikes are nearly all vertical or sub-vertical, and consist of three types: diabase, olivine diabase, and trachyte porphyry (the "red syenite porphyry" of Cushing). Cushing noted that the thinner diabasic dikes are almost without exception porphyritic, and that the same applies to the borders of the wider dikes. In thin section, he found two generations of plagioclase and augite but only one of olivine. Biotite was observed in about 25 percent of the dikes.
Nineteen dikes are intruded into gabbroic meta-anorthosite in these road cuts. Their thicknesses range from 1 cm to 7 m. Some contain xenoliths and blocky plagioclase xenocrysts derived from incorporated host rock. The dikes are chilled at both their margins and along their contacts with xenoliths.
The distribution, dimensions, orientations, and classification of all dikes thicker than 40 cm is shown in Fig. 10. Dike identifications are based on field examination, including staining for K-feldspar, and then corroborated by thin section study. Numerous geochemical analyses were made in order to evaluate possible plate tectonic settings of the intrusions, as was discussed under Geochemistry.
The dominant dike type at Rand Hill is olivine diabase. Typically, altered olivine phenocrysts are concentrated in the central part of the dike by flow differentiation. The phenocrysts are altered to blackish serpentine clots (check hardness). The selective weathering of these clots accounts for the characteristic pitted surface. Although the olivines, with a specific gravity of 3.3 are concentrated in the centers of the dike by flow differentiation, the less dense plagioclase phenocrysts with a specific gravity of 2.7 are not; in fact they are generally concentrated in the finer grained border zones.
A 2.4 m wide trachyte porphyry dike with flow-aligned laths of Carlsbad-twinned plagioclase and K-feldspar is exposed near the southern end of the roadcut (sample numbers 6182-6188). It is typical of this group, although the color of these dikes vary: they may be either red, greenish, or gray to black. Cushing (1901) identified 19 trachyte porphyry dikes at Rand Hill and summarized their petrography. The essential minerals are microperthite and biotite, and accessory minerals are magnetite or specular hematite, hornblende, quartz, albite, orthoclase, microcline, apatite, and sphene; secondary minerals are chlorite, calcite, sericite, epidote,and hematite. Microperthite and biotite or chlorite are the only two minerals found in all dikes examined. Staining here shows that both K-feldspar and plagioclase laths are up to 1 cm long but vary in size and abundance. Total feldspar makes up about 55 percent of the rock, chlorite-altered biotite about 40 percent, and opaque minerals plus apatite needles the remainder. Note small blocky xenocrysts (?) of gray plagioclase and incorporated angular fragments of mafic dike rock. As discussed under Geochronology and Geochemistry, the diabase and trachyte dikes at Rand Hill are coeval, and presumably derived from a common magma source.
The northern contact of this dike is faulted, as indicated by shearing of the dike (probably cataclasis) and the introduction of anastamosing, hematite-stained calcite veins.
A small xenolith(?) of coarse-grained diabase or fine-grained gabbro (sample site 6194) adjoins the 7 m-wide olivine diabase dike at its southern margin (Fig. 10). The xenolith(?) is crosscut by a thin diabase dike that is chilled against it.
Relict ophitic texture is visible in the xenolith(?) although the rock is pervasively stained by oxides. It contains about 50 percent subhedral plagioclase and 20 percent relict orthopyroxene, most of it altered to serpentine and chlorite. Its similar composition (Table 1) suggests that it may be a cognate inclusion (autolith) brought up from a deeper level in the same magma system.

STOP 2B. Rand Hill Dike Swarm
Turn left (west) onto Murtaugh Hill Rd. and park. Walk across the road onto open hillocks that expose at least 100 mafic dikes in gabbroic anorthosite gneiss (Fig. 11). This locality, at the eastern foot of Rand Hill, is by far the best exposed mafic dike swarm in the Adirondacks. Dikes are intermittently exposed for lengths in excess of 150 m. Their thicknesses range up to at least 5 m. Ramble westward, in a zig-zag course across the dike swarm to the end of the exposure area about 350 m to the west. Exposures extend beyond the map area to the south and west .
Dikes here have three trends (Fig. 11), all crosscutting the N30E strike of foliation in the host rock. The large irregular EW dikes bear alkali feldspar as shown by Kf staining. They are the "syenite porphyry dikes" of Cushing (1898). The N60-70E dikes are prophyritic olivine diabase dikes that show clear evidence of flow differentiation. Olivine phenocrysts that formed at depth have been concentrated in the centers of the rising magma by flow. The olivines are generally highly to completely altered, and weather out to produce the characteristic pitted surface. A N40E set is sparsely represented.
Note these interesting features of dikes during your ramble, and recall that basaltic dikes are emplaced almost instantaneously, the average velocity of propagation being 0.4-0.5 m/sec (Delaney and Pollard, 1982):
1) Chill borders against host rock.
2) Dikes may be straight, stepped, segmented.
3) Joints within the dikes do not penetrate the host rock: cooling cracks? compression features?
4) Dike walls may be even, irregular, cusped, and may have horn-like extensions or irregular apophyses.
5) Dike terminations may be tapered, blunt, rounded or irregular, and may have narrow extensions or "squirts".
6) Some dikes are composites of two sheeted dikes. The boundary between such dike pairs is a thin line of preferential erosion between the two adjacent chill borders. In at least one locality southwest of the mapped area, a sheeted dike pair bifurcates along strike around a slabbed inclusion of wall rock.
7) Relative age and direction of opening can be determined by analysis of dike intersections. These and en echelon configurations can also permit reconstruction of stress axes during emplacement. En echelon dikes indicate a reorientation of principal stress trajectories at the fingered propagation front of intrusive sheets (e.g. Delaney and Pollard, 1981).
8) Dike-parallel joints generally are absent in the host rock. This suggests that emplacement was not along pre-existing fractures but along an opening created and propagated by magma pressure in advance of the dike tip, in a plane perpendicular to the least compressive stress axis.
9) Concentration of olivine phenocrysts toward the center by flow differentiation.
10) Concentration of plagioclase phenocrysts near the margins rather than in the center.
11) Flow-aligned plagioclase laths indicate direction of magma propagation.
12) The amount of extensional strain produced by intrusion was significant in this swarm, reaching a magnitude of 18.8 percent north of Station C. A number of the dikes measured in this section could not be shown on the map of Fig. 11 because of its small scale.

STOP 3. Camptonite Dike
NO HAMMERS; cameras instead. Xenolith-filled augite camptonite dike, Martin Bay. Private property; permission required of landowner.
The dike makes a low garden wall that strikes N80W. It is 0.5 m thick, and exposed over a length of 7m.
The place to concentrate on, however, is along the shore, where an isolated block of dike rock, 70 cm thick, has weathered out of its host rock, the Cumberland Head Argillite (Middle Ordovician). Note the parallel dike walls bordering the 10 cm-thick fine-grained chill margins. Note also the striking number of xenoliths concentrated in the 50 cm-thick central part of the dike by flow differentiation. These subangular to round xenoliths constitute about 50 percent of the dike, and appear megascopically to have sharp boundaries with the dike material. They range in diameter from 1 mm to 9 cm, most exceeding 2 cm. Lithologies include pyroxene syenite gneiss, gabbroic metanorthosite, metagabbro, and trachyte, as well as one ultramafic xenolith and a round xenocryst of hornblende. Note the slight flow alignment of elongate xenoliths.
In crushed grains and thin sections D.H. Newland (in Hudson and Cushing, 1931) found that the syenitic inclusions contain microcline, microperthite, much-altered greenish pyroxene, and iron-stained grains that may be hornblende, biotite or both, along with small amounts of quartz, and occasional garnet crystals. The dike material is a fine-grained holocrystalline lamprophyre with phenocrysts of clinopyroxene and olivine in a felted groundnass of plagioclase, augite and opaque oxides. Staining indicates about 20% K-feldspar in the groundmass.
The xenoliths are typical of Adirondack rock types, so their source along the path of intrusion is easy to visualize. What is unusual is the fact that 1) among the 250 lamprophyre and trachyte dikes in the lake Champlain area of New York and Vermont (McHone and Corneille, 1980) such xenoliths are extremely rare, and 2) the xenoliths are so remarkably rounded. Does the abundance in this one dike suggest that the magma advanced through a brecciated and fragmented fault zone? through a basal Paleozoic conglomerate? If the latter, the xenoliths are considerably larger than the pebbles in the rare exposures of basal Potsdam in the eastern Adirondack region. If the former, was the rounding produced by mechanical abrasion of incorporated breccia? by melt abrasion or partial resorption?
This particular dike gives a K/Ar date of 131+5 Ma (Greg McHone, written comm., 2-19-85) which falls in the age range of the NY-Vt. lamprophyres and corresponds to the oldest ages of the Monteregian Hills intrusions of Quebec (McHone and Corneille, 1980).
A similar xenolith-laden dike is well exposed farther south, in Indian Bay, Willsboro Point. It is an augite camptonite dike, more than 2 m thick, intruding Canajoharie Shale (Middle Ordovician). It is pictured and described by Buddington and Whitcomb (1941). McHone (written comm., 2-19-85) reports a K/Ar age of 119+5 for this dike.
The narrow range of strike of the lamprophyre and trachyte dikes, in the Lake Champlain valley, as well as the consistency of Cretaceous ages, suggest that they are a cogenetic suite, perhaps a mafic-felsic pair formed by an immiscible liquid mechanism from mantle-derived camptonitic magma (McHone and Corneille, 1980)

B3: MIDDLE ORDOVICIAN STRATIGRAPHY AND SEDIMENTOLOGY - SOUTHERN LAKE CHAMPLAIN VALLEY
Bruce Selleck
Colgate University
David Maclean
Con-Test, Inc.
The Middle Ordovician strata (Chazy, Black River and Trenton Groups) of the Champlain Valley record the latter stages of passive margin deposition on the early Paleozoic continental margin of eastern North American. The onset of foredeep development, in response to loading of this portion of the continental margin during the late Medial Ordovician Taconic orogeny, in also recorded in the this section by development of generally deepening-upward facies patterns in the Black River and Trenton Groups. The goals of this trip are to examine these units in the Southern Champlain Valley, interpret the depositional environments represented, and to assess the importance of tectonic controls upon regional facies patterns.

STOP 1. Westport, New York
These roadcuts expose approximately 24 meters of the Glens Falls Formation of the Trenton Group. Stratigraphically, we are located in the middle and upper portion of the Glens Falls, within the zone of Cryptolithus tesselatus. The Glens Falls at this exposure consists of two major facies. The lowermost three meters, and the uppermost ten meters of the section are characterized muddy packstone beds, often capped by Chondrites burrows. The limestone beds are separated by thin calcareous shale interbeds. Each limestone bed consists of a couplet, with the basal portion of the bed characterized by whole-shell and fine bioclastic grainstones, and the upper portion consisting of slightly fossiliferous mudstones. This facies is interpreted as a storm surge ebb current deposit, resulting from the turbidity current-like flows generated as storm wave surge resuspended mud and shell debris on shallower portions of the shelf. Fossils are relatively abundant in this facies, and include the typical Trenton brachiopods, bryozoans and rare trilobites.
The middle ten meters of the exposure consists of somewhat more regularly bedded argillaceous micrites, with relatively thick (2-20 cm.) shale interbeds. The argillaceous mudstone beds show limited size grading, and are often highly bioturbated. Fossils are scarce in the limestone beds, but interbedded shales may contain bryozoans and other bioclasts. This facies is interpreted as a hemipelagite, resulting from deposition of suspended lime and terrigenous mud in a setting unaffected by wave and storm driven currents. The abundant shales in this facies indicate a sudden increase in the influx of terrigenous sediment to the shelf at this time. Insoluble residues from the limestone beds often contain abundant silt-size euhedral quartz, plagioclase and sanidine crystals, suggesting that volcanic ash was supplied, perhaps from the Taconian island arc system to the east. This facies is traceable to the east in sections on the Vermont side of Lake Champlain.

STOP 2A. Redoubt Fort east of N.Y. 8
Approximately 6 meters of variously burrowed, slightly dolomitic, thin to medium bedded bioclastic packstones are exposein this section. The dolomite occurs in shaly weathering wisps and laminae and in burrow fills. Abundant "Girvanella" algal oncolites (algal accretionary grains) are present in beds approx. 4 meters from the base of the section. Rounded dark calcite grains (abraded gastropod fragments) form the cores of the oncolites, and are scattered in other beds. Fossils are relatively abundant and best seen on bedding surfaces. Trilobite fragments, brachiopods, bryozoans, pelmatozoan plates, nautiloids and large Maclurites magnus are present. The relatively high faunal diversity, abundant lime mud and burrowing argue for a normal marine, low energy shallow subtidal carbonate environment. A possible modern analogue is found in the mixed mud and sand shelf to the west of the emergent Andros Island tidal flats, as described by Bathurst (1971) and Purdy (1963). The 5-10 cm thick beds of "oncolite conglomerate" and other more well-sorted grainstone beds may represent periods of storm winnowing of the bottom, with transportation of abraded sand from adjacent sand shoal environments (e.g. Locality 2B). The wavy, irregular dolomite laminae appear to result from post-depositional dolomitization of lime mud, followed by compaction and local pressure solution of calcite, producing irregular, clay- and dolomite-rich stylocumulate seams. Preferential dolomitization of burrows may be due to contrasts in porosity or permeability of burrow-fill versus burrow-matrix sediment. The burrow-fill sediment may have retained permeability longer during diagenesis, permitting pervasive dolomitization. This sort of fabric selective dolomitization is common throughout the Chazy and Black River Groups in the southern Lake Champlain Valley.

STOP 2B. Ledge immediately NE of gate to Historic Site
Cross-stratified coarse lime grainstones with bipolar crossbed dip directions are well-exposed near the entrance road. Siliciclastic sand grains (angular quartz and feldspar up to 2 mm in diameter) are locally concentrated along prominent stylolite seams. The carbonate particles are dominately subrounded, abraded pelmatozoan plates, plus gastropod and brachiopod fragments. Large Maclurites fragments and grainstone intraclasts are present on the upper bedding plane surfaces of the ledge.
We envision the environment of deposition of this facies as shallow subtidal wave and/or current reworked sand bars. Active transport of abraded grains may have been accomplished by tidal currents as suggested by the bipolar cross-beds. The lack of burrows and well-preserved fossils may be due to the inhospitable shifting sand substrate. This environment may have been rather like the unstable sand shoal environments described from the Bahamas Platform by Bathurst (1971) and Ball (1967). The scale and style of cross-stratification present here are similar to that predicted by Ball from his studies of the bed forms and primary structures of the Bahamian sand bodies. Similar Chazyan facies in the Northern Champlain Valley contain abundant oolites (Oxley and Kay, 1959).

STOP 2C. Low Ledges on entrance road approx. 50 meters north of 2B
Brown weathering, slightly shaley dolostone exposed here contains small lenses and stringers of fossiliferous lime packestone. Trilobites, small brachiopods and Maclurites fragments are common. This exposure resembles the shelf lagoon facies of Stop 2A, although dolomitization is more pervasive.

STOP 2D. East point of British Fort, by horizontal water tank and south moat
Approximately 3 meters of thickly laminated limestone and dolostone is exposed in the southeast "moat" of the British Fort. The dominant facies here consists of alternating 0.5-2 cm thick laminae of limestone and dolostone - often termed a "ribbon rock". The limestone ribbons are mudstones and appear blue-grey on slightly weathered surfaces and as indentations on highly weathered surfaces. The more resistant dolostone weathers tan to brown. An erosional surface with 10-20 cm of relief is exposed near the base of the southwall. Abundant Maclurites shells occur in a shell bed on this surface. Lateral accretion cross-strata consisting of gently dipping ribbon rock are present above the erosional surface. Dolomitized burrows transect the limestone ribbons in the lower 1 meter of the section. On the less-weathered prominence on the SE corner of the moat, shallow scours containing a shell hash of brachiopods and gastropod debris are present, along with intraclasts of lime mudstone in dolostone and "Mexican Hat" structures (rolled intraclasts or pseudoclasts with a dolomitized burrow center).
We interpret this sequence as a tidal flat facies. The rhythmic limestone/dolostone "ribbon" fabric is interpreted as representing alternating slightly finer (lime mudstone) and coarser (dolostone) "tidal bedding" similar to that described by Reineck and Singh (1980) from the clastic mud/sand tidal flats of the North Sea. The Maclurites shell bed may mark the basal erosional level of a tidal channel, with the cross-stratified ribbon laminites forming by draping on the channelled surface. Variations in degree of burrowing record subtle differences in degree of subaerial exposure of the flat and/or reworking by tidal currents. Limited in situ faunal diversity is also expected in the stressed tidal flat environments. The absence of mudcracks and any indication of evaporite minerals suggests that we are seeing only the lower portion of a wet intertidal flat system preserved here.

STOP 2E. Enter Parade Grounds by barracks.
Around 1916, gunite was sprayed on the interior walls to protect the mortar from deteriorating. Starting in 1976, the N.Y. State Division for Historic Preservation began extensive maintenance, removing loose gunite, replacing rotted stones and repainting the stone walls.
In the outer wall of the first barracks, note at about eye level the stones that are nearly white-weathering. These are lime mudstones from the "Lowville" facies of the Orwell Limestone, exposed at Stop 2F.
The broad limestone outcrop west of the barracks is a cross-stratified lime grainstone with scattered subrounded quartz and feldspar sand grains. Trough cross-strata and "herringbone" co-sets of planar-tabular cross-strata are visible on the low vertical face. Large angular clasts of slightly dolomitic lime grainstones and Maclurites magnus shells are present on the uppermost bedding surfaces.
We interpret this facies as a current-dominated sand shoal environment rather similar to the exposures at Stop 2B.
Westward across the parade grounds there is a massive, bioturbated, brown weathering dolostone unit (similar to Stop 2C), overlain by 0.5 meters of very coarse-grained bioturbated, slightly dolomitic feldspathic quartz sandstone. This sandstone forms the summit of the Chazy Group (Crown Point Formation). The abundant angular quartz and feldspar granules in the sandstone suggest derivation from a relatively close granitic (Adirondack?) source terrane. These sands were apparently transported from the west during an interval of relative emergence of the carbonate platform and were briefly reworked in a shallow marine setting. The basal dolostone bed of the Black River is exposed immediately atop the sandstone.

STOP 2F - Moat Walls at North Entrance to British Fort
The section from here to locality I is within the Orwell Limestone. The basal beds consists of thick-bedded to massive lime mudstones with vertical spar-filled burrows (form - genus Phytopsis) and rare ostracodes. Fossil abundance and diversity increase in the overlying beds, with gastropods (Loxoplocus), corals (Lambeophyllum, Foerstephyllum) and brachiopods appearing. Grain size increases upsection, with sporadic appearance of intraclast grainstones and ripple cross-lamination. Overall this section is similar to the Lowville Limestone of the type Black River Group of the Tug Hill region. The facies pattern here suggests a progression from restricted (tidal or lagoonal?) mud flats (Phytopsis lime mudstones) to more open marine mixed mud/sand shelf environments.
The summit of the moat outcrop exposes a horizon of black chert nodules which can be traced laterally across the road to locality G.

Stop 2G. Ledges extending from service road to lake shore.
Watch for poison ivy!
These exposures closely resemble the Chaumont (House Creek Limestone of Fisher, 1977) facies of the Black River type section. Thick-bedded to massive richly fossiliferous lime packstones and wackestones document a normal marine, relatively low energy carbonate shelf environment. In addition to the forms mentioned earlier, the large stromatoporoid (calcisponge) Stromatocerium, the high-spired gastropods Hormotoma and Subulites, the nautiloids Actinoceras and Geisonoceras, plus bryozoans, brachiopods and pelmatozoan material are common. On some bedding surfaces, black chert nodules follow large horizontal burrows. The chertification here is post-depositional and involved dissolution and reprecipitation of siliceous skeletal material (sponge and radiolarian). The uppermost bed in this set of ledges is a black chert bed approximately 2 cms thick. This bed can be traced to the lake shore where a similar section can be seen. Glacial abrasion obscures much of the detail that is exposed on more weathered surfaces.

STOP 2H. Blocks and Quarry Walls by Lake Shore
The quarry was established in 1870 by the Fletcher Marble Co. in an unsuccessful attempt to find a source of "black marble" dimension stone. The quarry is reportedly only 1 meter or so deep. The narrow spit going north was built to load blocks on barges, but evidently no blocks were shipped. The quarried blocks consist of medium to thick-bedded fossiliferous packstones and wackestones with some ripple cross-laminated grainstone beds visible in the north quarry bench. Strophomenid brachiopods, bryozoans, pelmatozoan stems and fragments of the trilobite Isotelus are present. The environments represented here are similar to those at 2G. As we continue north and walk along the lake shore, more exposures of the upper part of the Orwell can be examined. The bedding surfaces contain abundant opercula of Maclurites logani, and scattered Forstephyllum, Lambeophyllum and Stromatocerium are found. The byssate bivalve Ambonychi is also present.
The transition from the Orwell to overlying Glens Falls Limestone is covered by beach gravels as we continue west along the lake shore.

STOP 2I. Exposures of Glens Falls is separated by intervals of beach gravels
STOP 2I. The contact between the Orwell Formation and the basal Glens Falls Limestone is covered by beach gravels. The lower 16 meters of the Glens Falls lies below the first occurrence of Prasopora. Cryptolithus appears approximately 20 meters from the base of the section. Thus, only the uppermost 10 meters of section are time equivalent to the Westport exposures seen at Westport. The Glens Falls at Crown Point consists of the same muddy packstone facies seen at Westport. Limestone beds typically have shelley basal portions which rapidly grade upward into muddy packstones. Thin calcareous shale interbeds define the bedding. This facies is again interpreted as storm surge-ebb current deposits with intervening shale suspension rainout. There is a slight tendency for the bedding style in the lower portion of the section to be more wavy or lenticular, perhaps suggesting that storm wave scour occurred. The upper portion of the section is slightly thinner bedded, and bryozoans become relatively more abundant. Fine examples of the various trace fossils which characterize this facies are to be found on the bedding surfaces, including Chondrites.
Fossils are abundant and rather diverse. Trilobites (usually fragmental) include Isotelus, Flexicalymene and rare Cryptolithus; the brachiopods Sowerbyella, Rafinesguina; Dinorthis and Dalmanella; bryozoans Prasopora, Eridotrypa and Stictopora; plus orthocone cephalopods and pelmatozoan debris. Gastropods, which are so abundant in the underlying Orwell limestone are exceedingly rare in the Glens Falls.
The Glens Falls here records the continuing deepening of the Middle Ordovician shelf that began with the deposition of the Phytopsis lime mudstones at Stop 2F. The shale interbeds and generally more argillaceous character of the Glens Falls document increase in terrigenous mud input, perhaps derived from the rising Taconic Orogenic complex to the east. Quartz and feldspar grains of volcanic origin are also common in insoluble residues of Glens Falls limestones, suggesting increased eruptive activity at this time.

B4: GEOLOGY OF THE WILLSBORO WOLLASTONITE MINE
JAMES F. OLMSTED
S.U.N.Y. Plattsburgh
Plattsburgh, NY 12901
PAUL W. OLLILA
Vassar College
Poughkeepsie, NY
The wollastonite deposits of this region are the world's major source of of this important industrial mineral. Several occurrences of coarse wollastonite gneiss that is potential ore are known throughout the Willsboro and Ausable Forks quadrangles but to date only this and the Lewis deposit have been exploited. We have chosen this, now inactive, mine as the site for the trip because of excellent exposure of related rock types as well as unmatched display of structural and metamorphic features. The presently active Lewis mine is located at the other end of a fifteen kilometer long belt of metasediments that overlie the Westport anorthosite dome. Topics of particular interest are the mineralogy of the wollastonite unit, petrography of related units, mineralogical and textural relationships at contacts and the structural geology of the metasedimentary belt.
The trip will consist of a walking traverse in which we will study the lower half of the Willsboro metasedimentary belt. We begin at the lower portal of the mine and proceed north about 600 m. where we encounter the base of the "Midsection Anorthosite" a thick sill-like unit that divides the section into lower and upper parts. We will then cross the section in a westerly traverse to a point about a kilometer west of the lower portal where we will examine the wollastonite and the amphibolitic unit at the top of the Westport anorthosite dome. We then return along strike to the mine site where you can collect samples of the ore and related rocks. The entire hike is about three kilometers through wooded terrain but with one exception (a steep descent) it is not particularly difficult.
GEOLOGIC SETTING
Throughout the northeast Adirondack Mountains metasedimentary shelf type deposits are in contact with anorthosite dome-like structures. The infolded metasedimentary rocks include marble, calcsilicates of a variety of compositions, quartzite and gneisses that range from amphibolite to quartzo-feldspathic in composition. Many of the latter two are thought to be of volcanic origin although some may have been intrusive. Emplaced into these units are intrusive rocks that range in composition from granite to gabbro and include anorthosite and related rocks. All of these have been subjected to granulite facies metamorphism which has altered the primary petrographic and structural features. Buddington and Whitcomb (1941) indicate the temporal sequence to begin with Grenville metasediments intruded by anorthosite, gabbro and granitic rocks all of which were deformed and metamorphosed. Our mapping indicates the metagabbro to be the younger rock type. It occurs as dikes and sills and cuts the other three rock types. In this area we have mapped a large metagabbro sill that has intruded the metasediments above the wollastonite gneiss. We will examine its textural and contact relationships with surrounding rocks for the purpose of understanding influence it may have had on their formation.

B4: GEOLOGY OF THE WILLSBORO WOLLASTONITE MINE

STOP 1. Wollasonite Mine
Park on right if gate is closed or continue up road to first portal.
From the east end of the lower portal of the mine we will climb up over the exposed bedrock, carefully examining the rock types as we climb. In the immediate area of the mine they include; wollastonite ore, garnetite, gabbroic anorthosite gneiss, syenitic gneiss and a very mafic appearing calc silicate gneiss. We will point out several structural features as we move up the hill. Higher in the woods we will see evidence of repetition of the wollastonite rock in the form of another garnetite unit. The northernmost extent of the traverse will be indicated by an anorthositic unit that forms a prominent ridge. At this point we turn southwesterly back across the valley where we encounter more mafic calcsilicates, then up the hill to a large exposure of metagabbro. We will continue southwesterly over Bristol Mountain and down into the next valley where we will examine among other things, the base of the wollastonite unit, it upper contact and the underlying rocks of the Westport Dome. We will then walk easterly along strike of the wollastonite unit past the mine area where you may collect ore samples to your heart's content and back to the cars.
Optional stops may include the westward extension of the Willsboro belt where it crosses the Adirondack Northway and the Deerhead location which is another similar wollastonite occurrence that can provide additional structural insight as well as opportunity to examine other rocktypes in the section.