NYSGA 1993
New York State Geological Association
65th Annual Meeting
John T. Bursnall, Editor
Field Trip Guidebook
Department of Geology
St. Lawrence University
Canton, New York, 13617
Published by the New York State Geological Association.
Additional copies may be purchased from the Executive Secretary,
Center for Earth and Environmental Science, State University of New York,
College at Plattsburgh, Plattsburgh, NY 12901
EDITOR'S PREFACE AND ACKNOWLEDGMENTS
The 65th Annual Meeting the NYSGA, held at St. Lawrence, is now behind us and the guidebooks are, at last, about to go out (!). But before they do I wish to thank the numerous people who helped with the planning, organization and running of the conference. In particular I should like to mention the trip leaders, since without their willing support the meeting would not have been possible; also all those who travelled the distance, on an unavoidably inconvenient weekend for some, and braved the characteristic vagaries of North Country weather at this time of year - bright sun (if not downright warm) on the first day and torrential rain (or was it sleet?) on the second. Particular thanks are also due to: Jim Olmsted, Executive Seecretary of the Association, for keeping us to appropriate deadlines early in the organizational process; Kurt Salzburg and the staff at St. Lawrence's Conference Services for their invaluable assistance; St. Lawrence Food Service for their great banquet; Alice Quackenbush for controlling the processing of applications, mailings, phone queries, and everything else; Mike Whitton for hours of , cutting and pasting'; and last, but far from least, all of the Geology Club members who willingly helped with registration, welcoming party, stuffing packages, and all the other time-consuming and sometimes onerous tasks that are necessary for the smooth running of a conference.
Finally, a separate note of thanks must go to Dave Franzi and Ken Adams who, together with Don Pair, put on a last minute trip when it was realized that Jim Street would not be able lead his intended trip - one that was to have included a summary of some of Jim's research over the past decade or more.
This short editorial piece is followed by the dedication of this volume in Jim's memory.
DEDICATION
John Bursnall
Canton, NY
We, the staff, students, and alumni of the Geology Department at St. Lawrence University wish to take the occasion of the 65th Annual Meeting of the New York State Geological Association to dedicate this Guidebook, and this conference, to our long time colleague, teacher and friend Dr. James S. Street. Jim's thoroughness, graciousness, and strong scholarly interest in his North Country surroundings are a model for us all, and have been so time and again.

A1: PRECAMBRIAN GEOLOGY OF THE NORTHWEST ADIRONDACK LOWLANDS: A STRATIGRAPHIC VIEWPOINT
WILLIAM F. DELORRAlNE
Geology Department
Zinc Corporation of America
Balmat, NY 13609
JAMES D. CARL
State University of New York
College at Potsdam
Potsdam, NY 13676
INTRODUCTION
The idea of widespread preservation of a coherent stratigraphic sequence in middle Proterozoic rocks in the Adirondack Lowlands has been challenged from several standpoints. Workers in the Adirondack Highlands, and elsewhere in high grade Grenville terrane, have drawn attention to the extent of tectonic realignment that has accompanied folding, ductile deformation and metamorphism. Rock units that were originally discordant have been swept into into parallelism to form "straight gneisses" that resemble a layered sequence. Sequences of metasedimentary rocks have been obscured by the size, volume and frequency of igneous intrusions. Contacts between intrusive and sedimentary rocks have been obliterated by tectonism, the acquisition of gneissic foliation and by metamorphic differentiation. Further complications are introduced where lithologic units have been disturbed or cut out by faulting, and where slivers of much older rocks have been thrusted into the terrane. Thrusting and stacking of crustal segments from southeast to northwest is proposed to have occurred in large parts of Grenville terrane in Canada (Davidson, 1986). For a general review of field and textural criteria used to recognize intense deformation and tectonic realignment, see the summary by Passchier and others (1990).
The Adirondack Lowlands consist chiefly of recognizable metasedimentary rocks and extensive units of fine grained gneisses whose protoliths are a matter of controversy. Meta-intrusive rocks here constitute a much smaller proportion of outcrops than in the Adirondack Highlands, and the intrusive bodies are generally smaller in size. Ductile deformation has been extensive in some rock types, particularly the marbles (now annealed?), Hyde School Gneiss and the Huckleberry Mountain granitic gneisses (Tewksbury and others, 1993, and this guidebook). Nonetheless, primary features have been preserved that include stromatolites in carbonates and cross bedding in quartzites. Dikes, apophyses, aplite veins, pegmatites and phenocrysts are preserved in certain meta-intrusive bodies. Highly ptygmatic and cross cutting migmatite veins have not been realigned to parallelism in Popple Hill Gneiss, and rocks in some of the fault panels mapped by Brown (1989) preserve a stratigraphic succession comparable with that elsewhere. The case for pervasive tectonic realignment that mimics, but does not represent, a true stratigraphic succession must be demonstrated for local areas in the Lowlands.
Stratigraphic principles are applicable where widespread rock units are shown to be older than the meta-igneous rocks that intrude them. Zircons from the widely distributed Popple Hill Gneiss, portions of which are regarded as meta-volcanic by Carl (1988), have a U-Pb age of 1214 +/- 21 Ma (Carl and Sinha, 1992) and a whole rock Rb-Sr age of 1297 +/- 41 Ma (Grant and others, 1984). Zircons from another possible meta-volcanic unit, the Hyde School Gneiss, range in age from 1219 +/- 52 Ma to 1284 +/- 7 Ma, but ages of 1236 +/- 6 Ma and 1230 +/- 30 Ma for unzoned zircons from two of the bodies have been considered representative (McLelland and others, 1992). Intrusive rocks in the Lowlands generally fall into the range of 1170-1130 Ma as is the case for anorthosite, mangerite, charnockite and granite members of the AMCG intrusive series in the Highlands (McLelland, 1986).
The above remarks are made in the aftermath of a large number (more than 40!) of published U-Pb zircon ages (McLelland and others, 1988; McLelland and Chiarenzelli, 1990; 1991; Chiarenzelli and McLelland, 1991; McLelland and others, 1992) which have had great influence on the understanding of Adirondack geology, particularly in the Highlands. The paper by McLelland and others (1992) on a major Lowland rock type, the Hyde School Gneiss, is of concern because it proposes to overturn a set of stratigraphic conclusions established over decades of field mapping and mining exploration. Hyde School Gneiss, long regarded as a basal stratigraphic unit throughout the Lowlands, is now proposed to be an intrusive igneous rock with no stratigraphic significance. The possibility that meta-volcanic rocks could constitute a large proportion of Adirondack rock types is relegated to the backwater of "phase II" in a three-phase summary of the history of Adirondack conceptual schemes (McLelland, 1991). That argument is the subject of a field trip to be held on the weekend following the 1993 NYSGA meeting. Interested readers can obtain copies of the guidebook from the organization known as Friends of the Grenville (FOG, which does not necessarily reflect the state of mind of its members). For the Lowlands and for this guidebook, we plan to "dress up" the corpse of "phase II" which is characterized by paradigms of stratigraphy and stratigraphic correlation. We address some of the issues in the field stops described below.

A1: PRECAMBRIAN GEOLOGY OF THE NORTHWEST ADIRONDACK LOWLANDS: A STRATIGRAPHIC VIEWPOINT

STOP 1. SW end of the Reservoir Hill body
Black Lake member of Lower Marble formation, SW end of the Reservoir Hill body of Hyde School Gneiss.
The purpose of this stop is to examine the Black Lake member of Lower Marble formation that overlies the Reservoir Hill body of Hyde School Gneiss. Marbles here are identical in lithology with those exposed west of the Beaver Creek lineament. The marble terrane west of the lineament was labelled the "Black lake Metasedimentary Belt" (Engel and Engel, 1953), and the lowermost member of Lower Marble derives its name from that area (deLorraine and Carl, 1986). Black Lake marbles are quite distinct from the marbles upsection. They are characterized by the presence of ribbed, rusty-weathered, calc-silicate gneiss bands, disseminated black tourmaline, feldspar grains, phlogopite and granular diopside (Fig. 1). Also common are coarse graphite, scattered quartz "eyes" and intercalated quartzites. Massive rusty diopside rocks and a thick, homogeneous calcitic marble unit occur west of the Beaver Creek lineament. Absent at stop 1 is the sillimanite-gamet gneiss that typically surrounds bodies of Hyde School Gneiss. It is informally labelled the Sawyer Creek gneiss after thick exposures near Sawyer Creek along the margin of the California body of Hyde School Gneiss (deLorraine and Carl, 1986).
Note the minor folds in the marbles. Are one or two phases of folds present? One might interpret an early phase defined by rootless, isoclinal intrafolial folds that are refolded by more or less upright to overturned disharmonic folds.
At first glance, one might regard Hyde School Gneiss at this locality as containing few amphibolite layers. When viewed from the rear, i.e. from the high bedrock knobs to the north, the massive outcrops of leucogneiss can be seen as steeply dipping slabs or layers, thanks to the presence of deeply weathered amphibolite layers. Foliation in the leucogneiss is folded about the Reservoir Hill anticline, suggesting that an earlier deformational fabric has been refolded. The anticline is interpreted as a doubly-plunging, southeast overturned, second phase sheath fold that is coeval with the Great Somerville anticline of Buddington and the Sylvia Lake syncline in the Balmat-Edwards mining district.
An important point to make here is the consistent and predictable appearance of Hyde School Gneiss below the Black Lake member of Lower Marble formation. Upsection of this member is a scapolite prism marble that separates the member from an overlying gray and white banded marble called the Marble City member (Fig. 1). The Marble City member will be examined in stop 3. It lacks the rusty weathering gneissic bands and disseminated feldspar observed in the Black Lake member.
We emphasize the contrasting carbonate and calc-silicate rock types because they might otherwise appear to constitute a homogeneous sea of undistinguished marbles. The marbles should not be dismissed simply as "tectonic grease." Stromatolites have been locally preserved, and the persistency of contacts between relatively thin members for great distances has provided information about the geometries of major folds. Mapping of the thin units is the basis for structural work and zinc exploration in the Sylvia Lake syncline. Unit 6 in the Upper Marble formation, for example, has several 10 to 30 ft thick subunits of distinctive texture and composition that can be traced around the Sylvia Lake syncline by drill core from Balmat to the Hyatt mine, a distance of at least 8 miles (12.9 km). Contacts between rocks of undoubted metasedimentary origin are conformable with each other and, in many cases, with the overlying and underlying gneissic formations. These contacts are interpreted as reflecting original compositional and lithologic differences; that is, they constitute a stratigraphic sequence.
Thus, the appearance of Hyde School Gneiss at a predictable horizon is regarded as the consequence of depositional patterns modified to various degrees by metamorphism, folding, ductile deformation, ductile faulting and partial melting. Stop 12 will add basaltic intrusion to the list, but these late dikes are not to be confused with an earlier amphibolite layering.

STOP 2. Scapolite marble with basalt dike
Scapolite marble member of the Lower Marble (with basalt dike).
Rock here overlies the carbonate and rusty gneiss of stop 1. This characteristically pitted, light gray member or horizon of the Lower Marble formation consists of scapolite- bearing, graphite-phlogopite marbles with quartz segregations. It can be traced southwest of the Gouverneur body of Hyde School Gneiss to aid in defining the "Great Somerville anticline" of Buddington that parallels Route 11 through Somerville village. Scapolite is gray because of finely disseminated graphite; it varies from coarsely bladed to small elongate crystals.
The 1 m thick basaltic dike within the scapolitic marble is N 60 E, vertical and undisturbed in contrast to the highly segmented and metamorphosed dikes to be seen at stop 3. These and other NE-trending Lowland dikes may have been produced by Late Precambrian rifting and the opening of the Iapetus Ocean basin. The dikes are generally vertical, fine-grained, undeformed, amygdaloidal, and show chilled borders against the wall rock. They must have intruded brittle rocks at shallow depths. Many have undergone saussuritization and contain epidote veinlets. They intrude all Precambrian rocks in the Lowlands, but do not intrude patchy remnants of overlying sedimentary rock such as the Cambrian Potsdam sandstone. They show deep weathering (some are altered to hematite) where exposed near the pre-Upper Cambrian unconformity.
Narrow dikes like this one are likely to be strongly saussuritized and to yield unreliable directions of paleomagnetization. Seven samples from thicker, well-crystallized dikes, however, show a grouping of north-seeking poles in the southeast quadrant of the lower hemisphere of an equal area net. Books and Brown (1983) were unable to match the grouping with data from dikes in Ontario.
A hydrothermal event (phase 4 of Brown, 1983) may have reset the ages of many basalt dikes. K-Ar ages from one dike of 405 +/- 11 and 440 +/- 10 m.y. obtained on feldspar and pyroxene respectively (Brown, 1975) are not compatible with the pre-Upper Cambrian age required by field relationships. Ages for Ontario dikes ranging from 600 to 800 m.y. (park and Irving, 1972) are likely to be representative of Lowland dikes, and the ages of 405 and 440 m.y. may approximate the time of hydrothermal activity (Brown, 1983). Hydrothermal activity is also proposed as the cause for alteration along joints that has produced epidote and reddish feldspar in some Lowland gneisses.
Badger (1993) has studied the largest of the Lowland dikes, a 14 km long, NE-trending dike that cuts Precambrian rocks including the Hyde School body of Hyde School Gneiss (see map of Brown, 1988). The dike shows alkalic affinities and has uniform chemical composition. Tectonic discrimination plots are indicative of within-plate magmatism and OIB-type (Ocean Island Basalt) mantle plume source. These dikes may be related in origin to late Precambrian, rift-related magmas of the Ottawa Graben, the eastern Adirondack Mountains and western Vermont.

STOP 3. Train Wreck outcrop
Marble City member of Lower Marble and the broken basaltic dike of the "train wreck outcrop."
The road cut is located just south of the SW end of a major regional fold hinge, the Reservoir Hill anticline. Numerous minor folds in the marble may reflect the proximity of that anticline. Reconstruction of a refolded isocline suggests an "S" asymmetrical sense when viewed to the north; the "S" is consistent with the location of the fold on the eastern limb of the Reservoir Hill anticline. Axial surfaces of many minor folds have shallow to moderate dips to the west, perhaps giving an indication of the degree of overturning of the anticline.
This massive, coarsely crystalline, blue-gray banded calcitic to slightly magnesian marble is graphic and phlogopitic. We correlate it with Brown's (1989) unit "mm" in the northern part of the Richville quadrangle and North Gouverneur area. Marbles at stops 1 and 2 are lower in the section.
This roadcut was proposed as the type section for a single northwest Adirondack carbonate-bearing formation named the Gouverneur Marble (Wiener and others, 1984). We regard it as a member of the Lower Marble Formation. The rock was quarried throughout the area for building stone in the early 20th century. Note the small town glory that once was Gouverneur (informally called "Marble City") as preserved in the upper levels of the downtown buildings.
The dike here is metamorphosed and disrupted in contrast to the dike at stop 2, but displacement is not great in view of the extensive folding in the marble. The antiform observed in the outcrop probably existed in its present form when the dike was intruded (Schoenberg, 1974; VanDiver, 1976). The lower part of the dike appears to have been a sill, whereas the upper part cuts across the banding in the marble. Possibly the subsequent refolding, as indicated by the shallow broad syncline to the right of the dike, may have caused brecciation and displacement of the dike blocks.
The dike blocks are recrystallized and re-equilibrated near the contact with the marble. They contain little or no plagioclase, abundant diopside and melonitic scapolite with lesser microcline, sphene, tremolite, biotite, quartz, opaque, tourmaline and apatite.

STOP 4. Steer's Head outcrop
Steer's Head outcrop where Antwerp-type granitoid gneisses have intruded the Lower Marble.
Gneisses of granite to granodioritic composition comprise a string of large, disconnected, boudin-like masses that extend from Antwerp village northeasterly for 40 km to Moss Ridge-Battle Hill near Gouverneur village. These rocks intrude chiefly the Marble City member of Lower Marble, but near Antwerp village they intrude Popple Hill Gneiss. Radiometric ages include an Rb-Sr whole rock age of 1197 +/- 53 Ma by Douglas Mose (in Carl and others, 1990), and a zircon U-Pb age of 1183 +/- 7 Ma by Jeff Chiarenzelli (in McLelland and others, 1992). These intrusions are slightly older than most anorthosite, mangerite, charnockite and granite (the AMCG intrusive suite of McLelland, 1986) in the Highlands.
Antwerp granite at this outcrop has surrounded and isolated a segment of cream colored marble that is shaped like a "steer's head" (resembling an illustration in a Zane Gray western novel). Major minerals include microcline, plagioclase, quartz, hornblende and biotite. Minor minerals include tourmaline, magnetite, ilmenite, apatite, zircon, titanite and secondary chlorite. Note the veins of quartz and tourmaline in symplectic intergrowth.
Intrusive origin is not easy to demonstrate for many Lowland gneisses, given the multiple deformation and high-grade metamorphism. Dikes and sills within marbles are especially susceptible to rupture, displacement and rotation, and many of the contacts are tectonic in origin. Selvage of scapolite, diopside, mica and quartz occurs between the meta-granite and marble at this outcrop, but the presence of selvage may be indicative of regional rather than contact metamorphism. Note at this outcrop a convolute, thin band of selvage that extends from the gneiss into marble (Fig. 6). The source of components in the band may lay within the meta-granite. Other features indicative of an igneous origin include aplite veins, cross-cutting relationships and the distribution of carbon and oxygen isotopes at the granite-marble contact.
Marble and granite have been analyzed for oxygen isotopes at the Steer's Head outcrop by Cartwright and Valley (1991). The marbles away from the contact have delta 18O values typical for Adirondack calcite (21-24 ‰). Antwerp gneisses away from the marbles have delta 18O values within the range of Grenville granitic rocks (11-12 ‰). Within a few meters of the contacts, however, delta 18O values increase in the metagranite and decrease in the marble. The result is a sigmoidal shaped delta 18O profile with the inflection points occurring near the contact. This steep gradient is believed to have formed by high temperature, fluid-hosted diffusion of oxygen isotopes from one rock into the other. The question is whether the profile formed during regional or contact metamorphism.
Cartwright and Valley (1991) also observe a change in marble mineralogy toward the contact with the metagranite. Phlogopite content decreases and the diopside content increases, possibly because of a shift to the right in the following reaction:
phlogopite + 3 calcite + 6 quartz = K-feldspar + 3 diopside + H2O + 3 CO2
This reaction buffers XH2O and is favored by increased temperature during contact metamorphism. Another XH2O buffering reaction involves tremolite as follows:
tremolite + 3 calcite + 2 quartz = 5 diopside + H2O + 3 CO2
Tremolite is described as disappearing towards the contact with the Antwerp metagranite, possibly as a result of a shift to the right in this reaction.
A change in the abundance and habit of graphite also is reported in the marble. Coarse (1-2 mm) crystalline flakes of graphite more than 1 m from the contacts give way to graphite free, or finer-grained, disseminated graphite near contact with the metagranite. This change probably resulted from oxidation during intrusion of the granite. Water diffusing from the granite probably caused the breakdown of graphite with the production of methane.
Cartwright and Valley (1991) argue that isotopic exchange occurred during contact metamorphism. Evidence includes the following: (1) Antwerp metagranite would have low porosity, and it is unlikely that enough grain boundary fluid remained in the granite to allow diffusion during regional metamorphism. (2) The systematic changes in marble mineralogy are indicative of contact metamorphism. The observed mineral assemblages also are stable at conditions of regional metamorphism, and little devolatilization would have occurred then. They argue that only during the contact metamorphic event was enough fluid available in the marble.
A larger conclusion drawn from this and other isotope studies at the contacts with meta-igneous rocks is that large volumes of pervasive metamorphic fluids have not infiltrated these localities during the regional metamorphism, or at any time thereafter. The sigmodal-shaped profiles would not have been preserved had this been the case (Cartwright and Valley, 1991).

STOP 5. Basal, sillimanitic Popple Hill Gneiss.
We are near the base of a thick gneissic unit called the Popple Hill Gneiss and near the contact with Lower Marble. Generally, the gneiss is migmatitic, gray and layered (see stop 6), but here it contains rod-like sillimanite up to 12% by volume (Hudson and others, 1986). Lineations defined by the sillimanite plunge 80 SW. Also present are feldspar porphyrob1asts and lenticular rotated garnets with helicitic textures defined by quartz and sillimanite inclusions (Ambers and Hudson, 1985).
This outcrop has been regarded by some as representing a pelitic protolith whose aluminous composition was appropriate for the growth of sillimanite. The presence of carbonate seams in the gneiss at Devil's Elbow and at Philadelphia village is compatible with an interpretation of a lime-bearing protolith. Stop 5, however, is proposed to be the site of ductile faulting that occurred during or near the peak of metamorphism, with the gneiss having moved northeasterly relative to the marbles in an essentially strike-slip motion (Hudson and others, 1986). In this model the presence of stress is believed to have influenced the growth of sillimanite, perhaps by shifting the following reaction to the right:
2 feldspar + 2 H+ = sillimanite + 5 SiO2(aq) + 2 K+ + H2O (Wintsch and Andrews, 1988)
The mylonites are described as Sr-depleted compared to layered Popple Hill Gneiss from which they are presumed to be derived. A whole-rock Rb-Sr isochron of 1177 ± 40 Ma is younger than ages obtained for the layered gneiss elsewhere and is interpreted as approximating the age of ductile deformation (Hudson and others, 1986). The age also approximates that of AMCG rocks in the Highlands and the Antwerp granite at stop 4; the age falls within the 1170-1130 Ma-interval of high grade metamorphism for the Lowlands as determined by Mezger and others (1991).
This mylonite zone has been extended to connect with the tectonic slide mapped by Foose (1974) near Moss Ridge. Informally called the Hailsboro ductile deformation zone, the mylonite zone may extend across the Lowlands. The Marble City member of Lower Marble lies against Popple Hill Gneiss at this outcrop, and stratigraphically higher members are absent. The gap depicted in our stratigraphic column at the base of Popple Hill Gneiss (Fig. 1) is based on this relationship and on mapping by Foose (1974). Ductile faulting also has disturbed the contact between Popple Hill Gneiss and the units within the Upper Marble in the zinc mines at Balmat. A tectonic slide on the lower limb of the Sylvia Lake syncline places unit 6 in contact with the Popple Hill Gneiss, units 1 through 5 having been excised (Fig. 5) Drill cores penetrating the gneiss generally show blastomylonitic fabrics whereas the overlying carbonate rocks generally are recrystallized "granoblastic mylonitic marbles."

STOP 6. Type locality of the Popple Hill Gneiss.
General:
This outcrop is typical of the migmatitic phase of the gneiss, and sillimanite is much less abundant here than at stop 5. Popple Hill Gneiss lies between two carbonate-bearing units, the Lower Marble of stops 1-4 and the Upper Marble in the Sylvia Lake syncline to the south (stops 7 and 8). The gneiss outcrops in a broad loop along the outer perimeter of the Sylvia Lake syncline and in the Balmat zinc mining district. It outcrops continuously across the Lowlands in a hard-to-farm landscape of bedrock knobs for 70 km from Philadelphia to Colton village.
Because much of the protolith may consist of volcanic ash, Carl (1988) urged that the name be changed from the Major Paragneiss (Engel and Engel, 1953) to the colloquial expression for poplar trees and the hill through which this section of Route 58 was cut (see the road sign). Here is exposed the typical gray, layered, fine grained plagioclase-K-feldspar-quartz-biotite-garnet-sillimanitic gneiss that is strewn with boudins and convolute (ptygmatic) quartzo-feldspathic veins, megacrysts of K-feldspar, layered amphibolites, sill-like bodies of leucogneiss, and other meta-intrusive rocks. Even a 1 cm thick seam of orthoquartzite extends vertically through the outcrop as a fracture-filling of Upper Cambrian Potsdam sandstone.
Geochronology:
A whole rock Rb-Sr isochron of 1296 ± 21 Ma (Grant and others, 1984) and a zircon U-Pb age of 1214 ± 21 Ma (Carl and Sinha, 1992) have been obtained for Popple Hill Gneiss. The discrepancy between the two ages has not been resolved. Both determinations were made on suites of samples from three outcrops that included one common locality here at Popple Hill. The 1.2-1.3 Ga-age of the gneiss must also apply to the Upper Marble whose stratigraphic position above Popple Hill Gneiss is well established by drilling.
The age of Popple Hill Gneiss is particularly important in view of the 1415 ± 6 Ma-age of a leucogneiss dike on Wellesley Island in the St. Lawrence River (McLelland and others, 1988; 1992). Host rocks there must be much older than Grenvillian, perhaps >1500 my, but the extent of their distribution is not known. If these older rocks are widely distributed, then the ca. 1230 Ma-age assigned to Hyde School Gneiss by McLelland and others (1992) would be a revelation. Hyde School Gneiss would be younger than the surrounding rocks and, therefore, intrusive in origin (McLelland and others, 1988; 1992). The previously accepted model would be rendered invalid, i.e. that the Hyde School Gneiss protolith was volcanic tuffs (Carl and VanDiver, 1975), that the bodies represented apical projections of a folded but continuous sheet, and that the gneiss lay near the base of a Lowland stratigraphic sequence (Carl and others, 1990). These recent age determinations of Popple Hill Gneiss, however, do not support an intrusive origin for nearby bodies of Hyde School Gneiss, and the argument regarding an intrusive origin has shifted to other grounds.
A 40 m thick body of metagranodiorite that we regard as intrusive into Popple Hill Gneiss occurs at the northern end of this outcrop. It has given a whole rock Rb-Sr isochron age of 1147 ± 35 Ma (Grant and others, 1984). This age indicates that the intrusion was contemporaneous with movement along the Hailsboro ductile deformation zone (stop 5) and with intrusion of the AMCG suite in the Highlands. Evidence for intrusive origin includes the young age, the presence of K-feldspar megacrysts (phenocrysts?), amphibolite that occurs as angular blocks (xenoliths?) rather than layers, and a more mafic composition than Popple Hill Gneiss. Contacts with the gneiss have been tectonized so that cross cutting relationships are not observed, or the body may be a sill. The intrusion is cut by numerous quartzo-feldspathic veins.
Migmatite and the Availability of Fluid during Metamorphism:
The belt of Popple Hill Gneiss crosses the isotherms of regional metamorphism that signify a transition from upper amphibolite to the granulite facies, from ca. 6400C in the SW to 7400C in the NE (Seal, 1986). Popple Hill Gneiss, thus, has the potential for study of mineral and chemical change as well as the availability of fluids during prograde metamorphism. The unit has been thoroughly sampled (Engel and Engel, 1953; 1958; Stoddard, 1980; Seal, 1986; Edwards and Essene, 1988; Ehrhard, 1986; Powers and Bohlen, 1985; Hoffman, 1982; see summary in Valley and others, 1990).
Quantitative estimates of the values for water activity are based on the equilibria of reactions that include:
(1) annite (biotite with Fe in octahedral sites) + sillimanite + quartz = almandine + sanidine + H2O, and
(2) muscovite + quartz = sanidine + sillimanite + H2O.
Calculated values of water activity range from 0.1 to 0.5 (Valley and others, 1990). Values are uniformly low, although not as low as in higher grade rocks in the Highlands. Values decrease from Gouverneur to higher grade metamorphic rocks to the NE near Colton.
Valley and others (1990) note that the gneiss is the largest migmatite unit in the Adirondack Mountains. The type locality here is replete with convolute quartzo-feldspathic leucosomes, some parallel to the foliation and others cross-cutting. The low values of water activity recorded for the gneiss can be used to argue that the leucosomes had formed by partial melting. Water produced during dehydration of mica and other minerals would be partitioned into the incipient melts, and the unmelted residue would be further dehydrated and made harder to melt. In support of this idea, Valley and others (1990) point to the local variability in water activity throughout the unit, suggesting that fluid compositions may have been internally buffered by solids or by melt. Buffering is consistent with the presence of migmatite and with partial melting.
Leucosomes within the gneiss, thus, may be locally derived and not introduced. Carl (1988) proposed an in situ origin on the basis of (1) the lack of leucosomes in either Lower or Upper Marble formation, (2) the presence of Ba-, Sr-, and Rb-rich leucosomes in Popple Hill Gneiss outcrops whose mesosome is enriched in Ba, Sr and Rb, (3) the presence of heavy REE-depleted leucosomes where mesosome is similarly depleted, and (4) the dominance of K-feldspar leucosomes in layered gneiss versus plagioclase leucosomes in the amphibolite layers. An origin by metamorphic differentiation was proposed for those leucosomes with exceptionally high K2O content that lacked minimum melt composition (Carl, 1988).
The studies of Valley and others (1990) are interpreted to rule out the passage of large amounts of fluids through Adirondack rocks during high grade metamorphism. On a local level, however, fluid migration into partial melts remains a possibility, and Popple Hill Gneiss may be unusual in that it retained much of the melt as leucosome (up to 25% at some outcrops). Higher grade gneisses in the Adirondack Highlands may have lost much of their melt fraction to consist chiefly of restite.
Minor folds are abundant in this outcrop. Many display overturned "s" asymmetries as viewed to the NE, suggesting that a major syncline lies to the east. In fact, the Sylvia Lake syncline is located east of this outcrop and may have influenced the orientation of minor folds. A number of folds, however, display "Z" asymmetries. Do these fold s suggest a separate or later fold event? Not necessarily. Note that many folded veins exhibit crosscutting relationships, and recall that fold asymmetries depend upon the orientation of the veins prior to folding. Thus, it is possible to have "S" and "Z" folds in the same outcrop that are coeval.

STOP 7. Stromatolites in Upper Marble, units 4 and 5.
NO HAMMERS AND NO SAMPLES, NOW AND FOREVERMORE (PLEASE).
Unit 4 of the Upper Marble (Fig. 7) in the Sylvia Lake syncline contains the first known biological remains described from the Adirondack mountains (Isachsen and Landing, 1983). This stromatolite-bearing rock is exposed in the woods above the roadcut. It consists of an alternating sequence of white dolomite, serpentinous-talcose diopside rock, and quartz lenses that may represent a chert-bearing, silty, peritidal dolostone intercalated between pure dolostones. Diopside formed by reactions between quartz and dolomite, and the rims of serpentine and talc owe their origin to retrograde metamorphism. Because the sequence is upside down, unit 5 underlies unit 4 in the roadcut. Unit 5 is a white to grayish, coarse-grained dolomite that contains sparse lenses of quartz and talcose diopside. Occasionally the dolomite is fetid.
The term stromatolite is applied to laminated carbonate sediment that occurs as bulbous heads or stacks. The laminations follow the outline of the structure and may be terminated at the edge of individual heads. Individual laminae may be thicker on the top and drape over the edge of the head to make a steep angle. Stromatolites are well displayed at this outcrop, and perhaps their late recognition can be attributed to an overturned position. The delay could also be attributed to frayed wiring in the twilight zone between the eye and brain of numerous observers, including your field trip guides who did not expect to see what they saw.
Stromatolites in unit 4 are domal SH-V stromatolites that occur as simple domes up to 12 cm high and 40 cm wide (Isachsen and Landing, 1983). They are composed of broad, convex laminae that consist of dolomite and iron-poor diopside (cream-colored rather than green), and they lack structural detail in thin section. The preservation of stromatolites may be due in part to their composition. Some are incompletely preserved with laminated quartz-diopside rock making up the preserved part. Silica replacement of algal structures during diagenesis can account for the preservation, whereas the unreplaced parts would recrystallize during metamorphism to coarse dolomitic marble. Fully replaced quartz-diopside mounds would form a rigid but minor structural buttress during deformation.
This outcrop lies on the upper, overturned limb of the Sylvia Lake isoclinal syncline. The stromatolites indicate that the upper limb is inverted and that this NNE-plunging complex fold is indeed a syncline as geologists of St. Joe Minerals (now ZCA) had proposed many years ago. Stromatolites have been recognized in units 4 and 11 of Upper Marble in recent years, and deLorraine has photographed domical stromatolites and finely laminated, possibly algal mat structures at the 2500 ft. level in the Balmat mine.

STOP 8. Units 14 and 15 of the Upper Marble fm
This newly completed roadcut (late 1992) in units 14 and 15 of the Upper Marble formation (Fig. 7) represents a rebuilding of Route 812 that followed collapse of the old road into an underground mine.
This roadcut occurs in the core of the Sylvia Lake syncline in the Upper Marble formation at Balmat. Subunits of unit 14 comprise the northern part of the cut, whereas the brownish and green rocks in the south part belong to unit 15, a phlogopite/tremolitic calcitic marble (Fig. 7). Unit 14 is composed of a variety of rock types including quartz-calcite marble (the "quartz-mesh limestone" of Buddington), thinly layered quartz-diopside rock, and serpentinous dolomite and calcitic marbles, to name a few. At the southern hinge of the Sylvia Lake syncline near Balmat, minor fold plunges are northerly or slightly west of north. Since the sides of the roadcut here are parallel to the plunges of minor folds, it is difficult to see many folds on the outcrop faces. On the southern end of the cut it is possible to see folds developed in unit 15. Minor folds associated with the Sylvia Lake syncline deform the schistosity in units 14 and 15 and, hence, the minor and major folds are interpreted as second phase isoclines. Down plunge (in the mines) the fold axes swing to the NE. At the other end of the syncline at Edwards, fold axes plunge to the NW. The overall geometry of the fold, thus, is lobate, and the Sylvia Lake syncline is interpreted as a sheath fold (Fig. 8).

Flat solution valley
Flat solution valley that surrounds the Hyde School body of Hyde School Gneiss which is in view straight ahead.

STOP 9. Amphibolite layering in the Hyde School body
Amphibolite layering in the Hyde School body of Hyde School Gneiss (Fig. 9).
Layering: Large and Small Scale
Hyde School Gneiss with numerous, thin biotitic-amphibolite layers is exposed in the smooth bedrock knobs overlooking a small pasture. We are located at the southern end of an F2 fold that parallels the Hyde School antiform (see map of Brown, 1988). The orientation of numerous minor folds in the amphibolite layers can be related to the Hyde School antiform, interpreted here as a major, second phase sheath fold. The antiform deforms an earlier fabric, including NW-SE trending lineations and rootless isoclines that may be related to Tewksbury's early shear fabric. Nearby are isoclinally folded amphibolite layers whose axes trend NW-SE, perhaps having been rotated into parallelism with the direction of early phase, NW -directed tectonic transport.
We are near the contact between two pink alaskite units of Brown (1988), one (aa) distinguished by thin parallel layers of biotitic amphibolite, and the other (a1) a massive unit with fewer layers (Fig. 9). Another mappable unit (pgd) consists of gneisses ranging in composition from biotite granite, trondhjemite, quartz monzonite, granodiorite to quartz diorite. All are foliated and contain amphibolite layers. Detailed mapping of the large-scale layering enabled Brown to interpret complex refold patterns, and we will discuss his work in the shade of a small tree.
Hyde School Gneiss, thus, differs from granitoid plutons of the Adirondack Lowlands in being compositionally zoned on a grand scale. Brown (1988) wrote that "the alaskite, granite, and diorite gneisses of the antiforms are a parallel-layered sequence that, despite abundant evidence of internal mobility and local melting, have not intruded each other or broken out of their elliptical structural shells as a melt." In contrast, the younger Lowland granitoid rocks show abundant evidence for intrusive origin. The Rockport granite and Gananoque syenite occur as dikes, sills and apothyses within metasedimentary rocks that outcrop along the St. Lawrence River. Even the oldest rock recorded so far, a 1415 Ma-old leucogneiss on Wellesley Island, is described as a dike within calc-silicate and tourmalinite layers (McLelland and others, 1988).
One objective of this stop is to observe the scale of the amphibolite layering, folding, and boudinage. These features are characteristic of Hyde School Gneiss. Note the absence of other lithologies or inclusions. No other granitoid bodies in the Lowlands exhibit layering like this, and most, if not all, have xenolithic inclusions of country rock attesting to their igneous provenance. Hyde School Gneiss is unique in being restricted to one stratigraphic horizon, containing layer-parallel amphibolites, and in the absence of xenolithic inclusions of the adjacent host gneisses. Feldspathic quartzites, calc-silicate and garnet-sillimanite gneiss occur within bodies of Hyde School Gneiss but, like the amphibolites, they also occur as parallel layers generally < 1 m thick.
Thus, Hyde School Gneiss consists of conformable lithologic layers on a large and small scale. Does the layering result from tectonism during intrusion, tectonism after intrusion, or is it a primary feature related to the deformation of ash and lava beds? Do the amphibolites represent basaltic dikes that were realigned prior to complete consolidation of the granitoid magma, so that igneous breccias and textures are preserved? Do the amphibolites represent dikes that were realigned strictly by solid state deformation? Do they represent slab-like sections of amphibolite wall rock that had been loosened during shearing and permissive intrusion of the granitoid magma? All scenarios have been proposed in one form or another.
A less complicated approach for the origin of Hyde School Gneiss begins with a layered complex of alternating ash-flow tuffs and minor metasediments, capped in some cases by outpourings of more fluid lavas and ash of trondhjemic and dioritic composition. Solid state deformation, with localized partial melting in low pressure sites, and late stage pegmatite intrusion, would account for features cited by others as evidence for intrusive origin. If the amphibolite layers were once basaltic dikes that had intruded the complex, then transposition to parallelism with the surrounding rocks had to occur prior to the 1170-1130 Ma period of high grade metamorphism in the Lowlands, because the amphibolite bodies were deformed after they had acquired the layered form. If the amphibolite layers represent original lithologies, e.g. protoliths of iron-rich, calcareous shales or basaltic ash, then deformation could have occurred simultaneously with high grade metamorphism.
High Temperatures and Contact Metamorphism?
The most compelling evidence for intrusive origin of Hyde School Gneiss cited by McLelland and others (1992) is the presence of perthite within the gneiss and the presence of a high grade mineral assemblage (garnet, sillimanite and spinel) in gneisses that surround Hyde School Gneiss. Perthite may form from exsolution of hypersolvus feldspar, the existence of which implies temperatures higher than those proposed for Lowland metamorphism.
It is interesting to note that the high grade mineral assemblage might have been used as evidence for higher temperatures of regional metamorphism had the assembly been found elsewhere than adjacent to Hyde School Gneiss. A search is underway to determine if the assemblage occurs in pelitic rocks elsewhere in the Lowlands. Given the paucity of Lowland pelitic rocks, and the remarkable selectivity that Hyde School Gneiss magma presumably has shown in intruding only pelitic horizons, we think it appropriate that the upper ranges of temperatures proposed for Lowland metamorphism be reconsidered. Also needed are U-Pb ages of garnet from the sillimanitic gneisses adjacent to Hyde School Gneiss. If the ages are >1200 my (similar to the age of the gneiss) then contact metamorphism is a possible cause. If the ages are <1200 my, then regional metamorphism is likely.
The proposal that stratigraphic principles cannot be applied in the Lowlands goes hand in glove with the model of intrusive origin for Hyde School Gneiss. Pelitic rocks can be conveniently distributed where needed as a host for granite intrusions. One may dismiss the present view of Popple Hill Gneiss as a lithologic/stratigraphic unit confined to the south-central Lowlands. It may be presumed to be distributed elsewhere, intruded by Hyde School Gneiss magma and partially melted so that the residue is left as a gamet-sillimanite gneiss that surrounds Hyde School Gneiss (McLelland and others, 1992).
On the other hand, we suggest that Hyde School Gneiss may represent a layered volcanic complex overlain by the lowest member of Lower Marble formation, whose pelitic composition was favorable for growth of garnet, sillimanite and spinel during the period of high grade regional metamorphism from 1170 to 1130 Ma.
A Stratigraphic View of Hyde School Gneiss:
The picture that emerges from detailed field mapping of members of Lower Marble formation is that the bodies of Hyde School Gneiss occur at the same stratigraphic horizon across the Lowlands. Each body is associated with the Black Lake member of the Lower Marble Formation. It is difficult to imagine how independent intrusions could acquire such similar surroundings unless the carbonate cover was deposited unconformably over each dome as proposed by Wiener and others (1984). Previous references to the gneiss appearing at various horizons across the Lowlands are incorrect. The California body of Hyde School Gneiss was cited as being in contact with Popple Hill Gneiss, with the inference being that the contact was intrusive in origin (Buddington, 1929; McLelland and others, 1992). However, the marble is exposed on the surface, and Zinc Corporation drill core shows that the Black Lake member of Lower Marble occurs between Hyde School Gneiss and Popple Hill Gneiss.
Xenoliths of adjacent metasedimentary rocks occur in Hermon-type and in most other meta-intrusive rocks throughout the Lowlands, particularly at the margins of a body. Diligent search has produced few xenolithic candidates in Hyde School Gneiss other than amphibolite. Cushing (1916) observed as much when he wrote of inclusions in Hyde School Gneiss as consisting of amphibolite "no matter what the nature of the bordering Grenville rock is" (p. 18).
The conformable amphibolite layers in Hyde School Gneiss have been interpreted as slabs that were stoped and separated along foliation planes by incoming magma (Levy and others, 1993). This process requires the fortuitous convergence of the following unrelated factors: (1) The necessary presence of vast quantities of amphibolitic material immediately below the Black Lake member of Lower Marble. (2) The necessary requirement that the batholith intrude but one stratigraphic horizon and that it stoped only the amphibolite layers. Apophyses, dikes and sills of Hyde School Gneiss are non-existent in the surrounding metasedimentary rocks. (3) The requirement that the magma be extremely fluid in order to incorporate slabs that vary in thickness from 1 to 60 cm or more. Many so-called slabs have uniform thicknesses for tens of meters. (4) The requirement that magma of stock-like to batholithic dimensions was confined to one or several substrata of appropriate pelitic composition that, in turn, could be subjected to contact metamorphism to produce the everpresent garnet-sillimanite gneiss.

STOP 10. The Pope Mills gabbro (Fig. 9)
Do not climb the outcrop to the right (E) onto the lawn of the trailer.
The purpose of this brief stop is to examine a folded and metamorphosed mafic intrusion within the Lower Marble formation as a prelude to examination of the Fish Creek body of Hyde School Gneiss. The Pope Mills gabbro was interpreted by Buddington (1934) as a relatively large mass of "pyroxenic amphibolite" that had been sheared prior to intrusion of syenitic magma. The intrusion of syenite into foliation planes, with the help of mineralizers, was believed responsible for the "migmatitic character" of the body, particularly the K-feldspar megacrysts and augen that are strikingly displayed at outcrops further to the south. The body was isoclinally folded and overturned towards the northwest with the dip of foliation varying from 55 to 70° SE (Buddington, 1934).
Xenoliths of banded, greenish calc-silicate from the Black Lake member of Lower Marble occur within the metagabbro. At least three phases of the gabbro are recognized: (l) sub rounded to angular and block-like forms of fine grained gabbro that are surrounded by (2) a slightly coarser grained gabbro matrix. Also present, but not at this outcrop, is (3) a biotite and K-feldspar megacrystic gabbro that Buddington regarded as a mixed rock. Examine the weathered horizontal surface on the west side of the road, and note the calc-silicate xenoliths that form a tectonically re-aligned intrusion breccia. Also note the deformed, fine grained gabbro ellipsoids whose long axes trend N 75 E.
Representative chemical analyses of the three gabbroic phases are given in Table 1. The coarser grained matrix (sample 223) is richer in total Fe, TiO2 and P2O5 than the finer grained phase (sample 222). We tentatively regard the finer grained gabbro as autoliths, and the coarser grained matrix as a later, more differentiated, iron-rich phase of the same magma.

STOP 11. SW margin of Fish Creek body (Fig. 9)
Park on Route 58 south of the Bishop road (right) and walk northward to the outcrop.
Hyde School Gneiss is exposed in the hinge/axial region of the Fish Creek anticline. Nowhere could a more challenging and complex outcrop be found, because these cuts expose highly deformed alaskitic and trondhjemitic gneisses with parallel layered amphibolites in the core of a regional "anticline that looks like a syncline" (i.e. a sheath fold) . Amphibolite layers may have undergone an early deformation that resulted in "chocolate-tablet" style boudinage before being refolded in the hinge of the Fish Creek anticline. Pegmatites with feldspar, green clinopyroxene and titanite assemblages intrude the suite of leucogneisses and also may appear at or near the contact with the overlying Black Lake member. Did the pegmatitic fluids derive some constituents from the carbonates up section? Mafic dikes, probably offshoots from the Pope Mills metagabbro, are present and superfically resemble the amphibolites. Other intrusive rocks also may be present in these outcrops.
The following scenario for the Fish Creek body is proposed by deLorraine: Begin with a "normal" sequence of Hyde School Gneiss, the trondhjemite phase in contact with overlying Black Lake metasediments that are exposed at the south end of the outcrop at Bishop road. Rocks are subjected to high grade metamorphism and deformation with temperatures at the higher end of those reported in the literature. The earliest phase of deformation produced chocolate-tablet boudinage in the conformable amphibolite layers, accompanied by partial melting in the neck zones ofboudins. Pegmatites are intruded, possibly channeled along the interface between Hyde School Gneiss and the Black Lake member. Offshoots of the Pope Mills metagabbro are intruded, and one wonders about contributions to the local heat budget that may have facilitated partial melting in Hyde School Gneiss.
Phase two isoclinal sheath folding then affected the region, producing the NE-SW regional grain. The second phase, sheath fold hinge in the SW end of the Fish Creek anticline resembles an "anticline that behaved like a syncline" because of the northerly plunges of a profusion of minor tight to isoclinal folds (see proposed sketch of the structure of the Fish Creek body, Fig. 10). "M and W" minor folds in the hinge of the anticline were superimposed on amphibolite layers that previously had undergone chocolate-tablet boudinage. Partial melting would be enhanced in the core of the Fish Creek anticline because it would be a low pressure site. Magmatic heat contributions from the sill and dikes offshoots of the Pope Mills metagabbro also may have facilitated partial melting. So-called "intrusion breccias," thus, are best interpreted in a regional framework as broken, boudinaged fragments of conformable amphibolite layers which have been refolded and deformed in the solid state by "M and W" folds. The best place to verify that the amphibolite layers are not randomly or chaotically distributed is to observe them from the top of the outcrop on the west side of the road. Look to the north down the plunges of minor folds.

STOP 12. Mafic layers in the Fish Creek body
Mafic layers in the Fish Creek body of Hyde School Gneiss, pasture of the Yoder farm (Fig. 9).
One purpose of this stop is to distinguish late dikes that may be related to the Pope Mills metagabbro (stop 10) from amphibolite layers of the Fish Creek body of Hyde School Gneiss. Metagabbro dikes are shown to post-date the foliated amphibolite layers and an early phase of isoclinal folding. Although the dikes have been deformed and metamorphosed (as is the case with the Pope Mills gabbro), they are clearly younger than the amphibolite layers.
The dikes and amphibolite layers have been regarded as coeval. Cross-cutting relationships as observed here have been used as evidence that all mafic layers had formed as dikes which, in turn, had been transposed shortly after their emplacement within Hyde School Gneiss magma (Mclelland and others, 1992). Phenocrystic plagioclase and coarse subophitic orthopyroxene have been used as evidence for an intrusive origin (Levy and others, 1993), but we believe it is the dikes that have been described rather than true amphibolite layers. The dikes have abundant orthopyroxene in various stages of alteration to hornblende. The amphibolite layers are chiefly amphibolite and biotite with little pyroxene.
The Fish Creek body was mapped by Dietrich (1954; 1957) who agreed with Buddington that the Hyde School Gneiss was intrusive in origin (he later changed his mind to an origin as in situ anatectic magma; Dietrich, 1963). The disrupted amphibolite layers were described as xenoliths throughout the 1957 report. In addition to the amphibolite layers, Dietrich recognized 18 tabular "amphibolitized melanocratic dikes," ranging from nearly 2 ft. to a few inches in width (see photos p. 57-58 in Dietrich, 1957).
We will examine several gabbroic dikes exposed in the pastures on both sides of Bishop road. One of the dikes cuts several amphibolite layers, including one that has been isoclinally folded. The dike has been realigned to near parallelism with the amphibolite layers at one end of the outcrop. A 1 m thick dike elsewhere in the pasture cuts several amphibolite layers at an acute angle. One layer can be traced into the dike where it reappears as ruptured fragments that are true xenoliths. Clearly the amphibolite had acquired its foliation and layered form prior to intrusion of the dikes.
We have observed these dikes only in the Fish Creek and Stalbird bodies of Hyde School Gneiss. They are particularly abundant in the Fish Creek body, perhaps because of the presence of the Pope Mills gabbro.
We compare the chemistry of (1) dikes in the Fish Creek body, (2) Hyde School Gneiss amphibolite layers, and (3) Pope Mills gabbro (Table 1). In general, Hyde School Gneiss amphibolites contain more MgO, Cr and Ni than the Pope Mills gabbro. Advocates of a meta-igneous origin for the amphibolite layers may regard enrichnent in these elements as indicative of a lack of olivine fractionation in their source. We have used plots of MgO vs CaO (Fig. 11A) and FeO-MgO ratios vs Cr (Fig. 11B) to distinguish Hyde School Gneiss amphibolite layers from Pope Mills gabbro. Fish Creek dikes plot with the gabbro.
Fish Creek dikes resemble the Pope Mills gabbro in a tendency toward iron enrichment. Both groups show increasing Zr (and TiO2 and P2O5) content and decreasing Cr and Ni (and CaO) content with increasing Fe-Mg ratio (Fig. 11C). In contrast, the amphibolite layers generally have lower Fe-Mg ratios and show relatively erratic changes in abundances of these elements with increasing iron content (Fig. 11D). We tentatively regard the dikes as fractionated, iron-enriched derivatives of the Pope Mills gabbro. More samples are needed.

STOP 13. Tourmalinites and quartzites
Tourmalinites and quartzites with a thinly layered appearance.
Exposed here are fine grained, gray to deep maroon, tourmaline-bearing metasedimentary rocks that include quartz-feldspar-mica-diopside gneisses, calc-silicates and quartzites. Note the inclined, 1 m thick layer of dark, glassy quartzite that contains tiny, vitreous grains of dark tourmaline. These grains could be overlooked or mistaken for biotite. We correlate the rocks with tourmaline-bearing gneisses and quartzites of unit "qmt" (Fig. 1) in the Beaver Creek area (Brown, 1989). Lithologically similar rocks have been intruded by the Rockport pluton in the Thousands Islands area, suggesting that "qmt" or its equivalents may be of widespread occurrence in southeastern Ontario.
Tourmalinite is abundant in the Lower Marble and may have crystallized from boron-rich basinal brines during diagenesis and metamorphism (Brown and Ayuso, 1985). Feldspathic quartzites and quartz-feldspar-mica granofels contain layers with up to 50% tourmaline whose composition is dravite-uvite with 0.85 to 4.25 wt.% Na2O, 0.39 to 4.04% CaO, and up to 13 .67% MgO (which is near end-member dravite composition). Li-rich compositions have not been found.
Tourmaline also occurs in sheet-like bodies of metagranite that intrude "qmt," but the tourmaline is compositionally distinct from that in the metasedimentary rocks (Brown and Ayuso, 1985). Ratios of FeO-(FeO+MgO) range from 0.55 to 0.75 in granites and pegmatites, compared to ratios of 0.15 to 0.58 for tourmalines in quartzites. Previous workers believed that the tourmaline in the metasedimentary rocks had originated from the granitic intrusions, but the reverse may be true. Intrusive rocks may have picked up (and compositionally modified?) the tourmaline from the metasedimentary rocks, as is suggested by the distribution of the tourmaline-bearing intrusions. Abundant tourmaline occurs in the metagranite that intrudes "qmt" rocks near Huckleberry Mountain (Richville quadrangle), whereas tourmaline is less common in granites that have intruded other rock units.
Some rock types within the unit "qmt" are intensely limonite-stained by the weathering of pyritic zones. Pyrite mining was carried out as a source of sulphur and sulphuric acid for the paper industry at Pyrites, Stellaville and elsewhere in northern New York in the late 19th and early 20th centuries.

STOP 14. Hermon-type granitoid gneiss of the Gray's School body.
At least two textural types of granitoid meta-intrusive rocks were mapped in the Lowlands at the turn of the century, a fine-grained, so-called "equigranular" gneiss of the Alexandria-type that included the Hyde School Gneiss, and a coarser grained, K-feldspar megacrystic gneiss called the Hermon-type (Cushing and others, 1910). The mapping of numerous small and isolated granitic bodies throughout the Lowlands eventually led to the adoption of local names and to the abandonment of the term "Alexandria-type" But the name Hermon-type is still applied to relatively small, sheet-like and irregularly shaped, K-feldspar megacrystic plutons that are scattered throughout the Lowlands.
Hermon gneisses are generally reddish, medium to coarse grained feldspar-biotite-hornblende-quartz-titanite gneisses of syenitic to granitic composition (note the paucity of quartz at this outcrop). They contain large K-feldspar megacrysts that occasionally are oriented transverse to foliation. This coarse grained rock may give way along strike to become a fine grained equigranular gneiss. Pervasive grain size reduction may be responsible, and K-feldspar augen, flaser structure and quartz ribbons are often observed in thin section in association with a mosaic textured groundmass.
Igneous textures have survived the metamorphism and ductile deformation. Concentrically zoned megacrysts of K-feldspar are observed in thin section to contain zones of patch or speckled or "fire flake" perthite that alternate with wider zones or bands of nonperthitic feldspar. Plagioclase grains and biotite flakes lie against the perthite zones and protrude outwardly from them. We interpret these grains to be Frasel or epitatic inclusions that originally adhered to the face of a K-feldspar crystal that crystallized from a melt The rims of fine grained pink feldspar that surround the phenocrysts were produced by ductile deformation.
Hermon gneisses generally occur as intrusions within the Lower and Upper marbles and the Popple Hill Gneiss. Conformity with the host rock, due in some cases to tectonism, has caused some to be mapped as lithologic units. They generally occur as sills and less often as dikes or apophyses. Xenoliths of amphibolite are common.
Each intrusive body of Hermon gneiss is characterized by a limited range in major element content. For example, samples from the Gray's School body (including this outcrop) are uniformly syenitic, low in SiO2 and rich in MgO (Fig. 12; see sample 101A in Table 2). Gneisses near Hermon village are of intermediate SiO2 content (sample 178), and samples of high SiO2 and low MgO content (sample 124) are characteristic of the Mott Creek body. We believe that these rocks represent a common intrusive series.
We compare Hermon gneisses with another Lowland metagranite, the "equigranular" Rockport gneiss which outcrops in the islands and along the shore of the St Lawrence River. Formerly called the Alexandria Bay Formation, this rock was cited by Wiener and others (1984) as equivalent to Hyde School Gneiss and, thus, was made to represent the basal stratigraphic unit in the NW Adirondacks. Rockport gneisses are quartz-feldspar-biotitic gneisses with less hornblende and titanite than Hermon gneisses. Fluorite is a notable accessory phase, as is tourmaline where tourmaline-bearing host rocks have been intruded (Brown and Ayuso, 1985). Rockport gneisses clearly show an intrusive origin as dikes, sills and stock-like masses. Geochemical and field differences suggest that they represent a more highly differentiated and less viscous magma than Hermon-type magma. Hermon gneisses show a tendency toward calc-alkaline character (Fig. 13A, B) that contrasts with a pronounced alkaline character for Rockport gneisses . Both gneissic groups plot chiefly in the field of "volcanic arc" granites on an Rb vs Y + Nb tectonic discrimination diagram (Fig. 13C) Plots of both gneisses are widely scattered among I, S and A-type granites (Fig. 13D). In contrast, granitoid rocks of the AMCG series in the Adirondack Highlands (Figs. 13C, D) plot chiefly as alkaline, A-type "within plate" intrusive rocks (McLelland, 1986; McLelland and Whitney, 1990; Daly and McLelland, 1991).

A2: THE POTSDAM-GRENVILLE CONTACT REVISITED (I)
JOHN BURSNALL
Department of Geology
St. Lawrence University
Canton, NY 13617
BILL ELBERTY
Department of Geography
INTRODUCTION
The purpose of this field trip is to examine the relationships at the boundary between Proterozoic Grenville gneiesses within the Adirondack Lowlands and overlying arenaceous rocks, presumed to belong to the Potsdam Sandstone of Upper Cambrian (?) age. It is the first of two that will explore the diverse mineralogy, lithology and structure of a number of arenaceous outcrops in the Canton-DeKalb-Gouverneur area and will provide an overview of the compositional and structural characteristics of some of these problematic rocks.
(Please note that trips A2 and B2 can be taken together, as a single long day sequence, or independently. This fieldguide includes a repeat in Trip B2 of Trip A2 stops 7 and 8 to conveniently provide a shorter day's review.)
The Potsdam-Grenville contact in the St. Lawrence valley represents a hiatus of some 500 Ma. Mineral assemblages within the Grenville gneisses indicate that perhaps 25 km of material was eroded prior to the deposition of the transgressive Cambro-Ordovician sequence, over an undulating Precambrian erosion surface. Many of the isolated, predominantly sandstone, bodies within the Grenville gneiss terrane of the Adirondack Lowlands can be confidently interpreted as outliers of Potsdam Sandstone. The focus of this field trip, however, is to question the affinity of those whose relationship to the Cambro-Ordovician sequence is equivocal. Such enclaves vary in composition from matrix supported breccias to equigranular orthoquartzites and their depositional environment has been variously interpreted as: pre-Potsdam solution pocket infills (related to a karst topography on a Grenville marble surface); fault related debris slides; fault breccias; and fault scarp talus accumulations. Some are seemingly crudely interlayered with the gneisses and are locally foliated. Rare sandstone/breccia dykes within the gneisses may be of significance in understanding the origin of these enigmatic, apparently sedimentary, clastic rocks.
This fieldtrip commences at exposures close to the St. Lawrence Seaway between Ogdensburg and Alexandria Bay - including the text book exposures of the Potsdam - Grenville unconformity east of Alexandria Bay (Fig. 1). This will take from 25 to 40 mins., depending on traffic conditions. We then head south towards the village of Theresa and start our investigation of the arenaceous enclaves within the gneiss terrane. In the process we will visit some of the classic outcrops of the St. Lawrence Valley and Adirondack Lowlands where arenaceous rocks in contact with demonstrable Precambrian are of uncertain age and origin. Some of these rocks are seemingly deformed along with late Grenville deformation (that is, exhibiting a qualitative strain level not seen in the Potsdam Sandstone; Trip B2) whereas others exhibit intrusive relationships to the gneisses (Trips A2 and B2), or lie structurally beneath them (Trips A2 and B2). The origin of these enigmatic relationships have variously been proposed as :
1) outliers of Potsdam Sandstone;
2) pre-Potsdam, post-Grenville in age;
3) Grenville in age, in that they have enjoyed at least the later stages of Grenvillian deformation.
It is likely that all of these relationships are represented on this fieldtrip - but the question we ask, since most relationships are at least superficially ambiguous, is - "how can we discriminate between them". We hope for fruitful discussion on outcrop that will lead towards a better understanding of the status of these "enclaves". Some of these outcrops have long been recognized as contentious and constitute a longstanding problem. It would be nice to move closer to solving it!

A2: THE POTSDAM-GRENVILLE CONTACT REVISITED (I)

STOP 1. Deformation in middle Theresa Formation
Gentle northeasterly-trending folds of Potsdam Sandstone and Theresa Formation are relatively common to the south and west of Theresa (Barber 1977). The examples in this road section are similar in geometry to those observed in that area. They are significant to this field trip in that they clearly demonstrate significant post Potsdam regional deformation. Folds in the Potsdam Sandstone north of Theresa will be seen (Stop 4, Figure 2, this trip) are considered likely to be the same age. A minor fault will be seen in the central part of this section.
Continue on Route 12 passing through some magnificent roadcuts of Theresa Formation and Potsdam sandston that are featured in Trips A3 (Erickson) and B2 (Selleck). Continue past the village of Chippewa Bay, across marshy ground on the southern shore of the St. Lawrence.

Very large outcrops on both sides of road
Very large outcrops on both sides of road with an obvious contact at their eastern end.

STOP 2. The Postdam Grenville unconformity at Alex Bay.
PLEASE WATCH FOR FAST MOVING TRAFFIC
This classic example of an unconformity shows typical, regularly layered, lowermost Potsdam Sandstone lying on deformed Grenville gneisses. Some slip has occurred along the contact resulting in small-scale buckling of a subvertical foliation within the gneisses on the north side of the road.
The nature of the unconformable relationship and the character of the Potsdam Sandstone immediately above the contact at this stop will provide a basis for discussion at subsequent outcrops and is typical of the basal Potsdam in this area, although no trace fossils have been observed (Selleck, this volume). Note the rare conglomeratic horizons and the well-defined bedding.

Up a sharp rise onto the plateau
Up a sharp rise onto the plateau underlain by the flat-lying Paleozoic sequence which is characteristic of this section of the St. Lawrence Valley.

Note exposures of gneisses in fields to the right.
The wooded higher ground ahead on both sides of Route 37 are underlain by sandstones.

An excellent example of the unconformity at their base

Note gneisses to the north, and escarpment ahead
Drive across a bridge, noting gneisses to the north, and head up the escarpment ahead.

STOP 3. Soft-sediment deformation close to the Precambrian erosion surface.
Unusual columnar structures within the sandstones of this region have been described from a number of localities (Van Diver, 1976; Dietrich, 1953). They measure from a few inches in diameter to 10 feet or more. Characteristically they possess a cylindical or conelike structure with a narrow structureless border zone that cross-cuts the bedding in the surrounding rocks. Concentric sub-vertical layering paralleling the margin may occur and, in the larger examples, the interior may be brecciated. This internal breccia may be comprised of laminated sandstone fragments set in a homogeneous sandstone matrix. This particular example, which must occur close to the Precambrian surface beneath well demonstrates these relationships. Abrupt truncation of bedding within the surrounding sandstone will be seen at the eastern margin of the structure and a brecciated central zone may be observed; individual clasts are typically poorly defined The origin of this and similar structures is not fully understood, but is thought most likely related to localized collapse of semi-consolidated sediment - that is the downward movement of a column of sand. A possible cause is settling or collapse of cavities in the underlying rocks - an hypothesis resulting from the observation that the location of these features is within sandstones seemingly overlying marbles within the underlying Proterozoic sequence. Subsequent stops will support this notion. The homogeneous sandstone matrix surrounding breccia fragments suggests a lack of grain coherence (and resulting aggregate fluidity) that may have been initiated by high pore fluid pressures. The details and mechanics of such an environment will be discussed at this and subsequent outcrops. Similar structures are common elsewhere within the Potsdam Sandstone of this region and in equivalent rocks of the Ottawa basin to the north (Grabs personal communication 1979).

STOP 4: Folds within the "Potsdam Sandstone" (Figure 2)
Outcrop of deformed "Potsdam Sandstone" on the east side of the road across a disused railroad line.
PLEASE NOTE THE POISON IVY AT THIS STOP
Further evidence of gentle large-scale folding within arenaceous rocks of presumed Potsdam age is exhibited here (Figure 2). These exposures of sandstone are typical for the area. Bedding is pronounced, with the rock taking on a 'flaggy' appearance locally. Hematite staining may accent layering, including cross-bedding, but also is apparently not controlled be internal structure in places cross-cutting the sedimentary structures. Such 'liesegang banding' is quite common throughout the Potsdam Sandstone in this region. Evidence for soft sediment deformation is present and a small monocline behind a pine tree in the center of the face could be a product of differential settling.
Barber and Bursnall (1978) described the folding in this outcrop as follows: "Bedding is folded in a manner typical of the lower part of the Potsdam Formation. Hinge -lines are tenuous and variable in orientation, and individual beds thicken and thin greatly through short distances. The most obvious fold at this locality is one of a series of irregular gentle undulations of bedrock, between which are small areas underlain by Grenville rocks or horizontal Potsdam strata. The hinge line of the fold trends approximately N40°E. Other folds in the area exhibit a similar trend ....... ". They suggested that the spatial relationship of many of these folds and internal soft sediment disruption of bedding to topographic highs of the Precambrian basement (in this case caused by a possible west-side down northeast-trending fault 2 miles to the southeast near Theresa village) might have produced "rapid downslope movement during and closely following sedimentation" (Barber and Bursnall, op cit.).

Drive up the hill (fault scarp referred to at Stop 4)
Drive up the hill (fault scarp referred to at Stop 4) into the center of Theresa.

STOP 5: Contact between Grenville gneisses and non-typical "Potsdam" sandstones.
Pass the reservoir for the Theresa village hydro plant and a large, overhanging outcrop on the right (unfortunately due for demolition).
This is Stop 5, but parking is restricted so continue across a bridge, find a convenient parking space and walk back to the outcrop.
This area exhibits considerable relief of the Proterozoic surface (consider the elevation change between this locality and Stop 4) and the local configuration of the unconformity reflects this. The contact between sandstone and weathered basement gneiss dips moderately to the east from a high point at the western end of the outcrop. Significant discordance in bedding attitude exists between the low dip of well-bedded and color banded "typical Potsdam" at the highest parts of the outcrop to moderate easterly dips at road level. A bluff overhanging the road exhibits well-bedded sandstone overlying a heterogeneous breccia of quartz-arenite at the base. The larger clasts are of quartz and sandstone and towards the base, within a few feet of the unconformity, thin pebbly horizons are present. The weathered surface suggests the possibility of large sandstone blocks or rafts encased in an otherwise structureless mass and healed microfaults are present towards the top of this lower section.
These features suggest a period of instability and possible slumping prior to the deposition of the well-bedded sandstones in the upper part of the exposure. Barber (1977) suggested that penecontemporaneous faulting might be the cause for the lower disrupted material and, although the gneiss-sandstone relationship here might be explained by initial dip of the Precambrian erosion surface, the existence of non-typical basal Potsdam Sandstone at this stop raises the possibility of a pre-Potsdam but post-Grenville depositional period accompanying fault-related deformation. This interpretation requires the existence of a cryptic depositional break within the outcrop and that the presumed slumping is not intraformational with respect to the present exposed section. <

Pass Payne Lake on the left at approximately 7.5 miles.
The complexly deformed Payne Lake alaskite body underlies the topographic high to the north (see Tewksbury, Trip A5, this volume).

Drive through the village of Oxbow.
Continue on Route 25, which continues as Route 52 in St. Lawrence County, passing through Wegatchie and closely following the path of the Oswegatchie River. Note that the flow is to the southwest here - at a position upstream of a major change in direction at Oxbow, from where the river heads northeastwards to the St. Lawrence at Ogdensburg.

Pass the "mint-with-the-hole" statue and the village park on your right.

STOP 6: The Rock Island Roadcut
Complex relationships of sandstone to gneiss.
This outcrop is perhaps one of the most intriguing in the North Country. It is featured in Van Diver's "Rocks and Routes of the North Country" and is a common stopping point for field parties visiting the area. Our main interest here is to characterize the relationship of the presumed Potsdam Sandstone to the Grenvillian gneisses which at the upper part of the roadcut are calcitic marbles. This deep roadcut provides magnificent exposure and is one of the better outcrops in illustrating the variety of marble - sandstone relationships present in the region.
At the southeast end of the cut, a well-bedded quartzarenite illustrates the attractiveness of the Potsdam sandstone erosional remnant interpretation. However, the very complex relationships of the sandstones with the "underlying" marbles invite alternative explanations to a simple erosional unconformity relationship. Moderate dips (30°), angular marble clasts in quartzarenite, thin sandstone dikes extending outwards and upwards from contacts, and changes in composition of the sandstones close to the marble have all contributed to a karst surface depression infill (Van Diver, 1976). Some of the contact relationships in this section have been used as evidence for structural control of deposition and basement remobilization (Bannerman in Carl and Van Diver, 1971).
Contact zones need to be carefully examined. Iron oxides and iron pyrites armor many of the surfaces, and the potential significance of angular marble fragments, subtle brecciation features particularly in the northern sections (perhaps, autobrecciation), matrix supported conglomerates (upper west side of northern section), etc., are easily overlooked. A spectacular tourmaline-rich breccia in the latter area further suggest a protracted and complex history for this section. Evidence of significant post-arenite deformation is present at many localities.

STOP 7. The Richville breccias.
BEWARE OF FAST MOVING TRAFFIC!
Please note that description of this stop is repeated in Trip B2
Cross the road and visit the moderately high exposures on the northwest side first.
Karboski et al. (1983) described this outcrop this as containing a "flow breccia" at its base, followed by a densely consolidated breccia with an overlying highly deformed metaquartzite, overlain by an "orthoquartzite", which contains pebble-sized quartz clasts - possibly derived from the underlying metaquartzite. The breccias contain quartz clasts set in a hematite stained, medium grained arenite. Large (0.5 m) phacoidal blocks of the breccia are enveloped by thin shaly borders, the whole giving the impression of a shear zone.
This outcrop certainly inhibits any notion that the unconformity between Precambrian basement and overlying cover is a simple one!
Points to concentrate on are:
1) Possible shear fabrics in the lower part of the outcrop, in part defining the borders of coherent blocks of breccia
2) Compositional variation of clasts in the breccias
3) The relationship between and the textural character of the each of the recognized rock types
If the upper part of this outcrop is indeed comprised of rocks which are part of the Grenville basement as supposed by Karboski (1976) and Karboski et al. (1983) then the current disposition of lithologies seems not to be satisfied by a model that involves karst infill alone (Van Diver, 1976) as seems possible at Rock Island Road. It is possible, however, that the wall collapse of a large solution depression may have allowed a slab of basement to slide into the argillite filled basin. The presence of shear fabrics within the breccia may be accommodated by this model provided that these rocks were only partially lithified at the time.
Cross over to the vehicle and investigate the southern end of the outcrop on the southeast side of the road. Here, a narrow zone of sandstone breccia dips steeply through marble. One of the contacts is sheared indicating high angle faulting. Is there evidence for displacement sense?
[Note: if time permits an outcrop of marble on the nortwest side of Route 11, a few hundred yards to the south should be visited. It contains narrow subvertical veinlets of arenite at the northeast end, which provide good evidence for solution cavity infill.]

STOP 8. Southwest of East Dekalb.
Please note that description of this stop is repeated in Trip B2.
Roadcuts due south of Dekalb further illustrate the complexities within these post-Grenville rocks. A long series of low exposures on the northwest side of the road contain well-layered marble (reclined folds at the north end) to the north which in the central section give way to a complex steep contact with rusty weathered arenaceous rocks. A number of small sandstone breccia wedges penetrate downwards into the marble in the vicinity, again supporting the solution-pocket infill model for the larger scale relationships seen elsewhere (e.g. Rock Island Road). Evidence for sulfide mineralization is present at some contacts, in common with the Rock Island Road locality (Elberty and Romey, 1990).
Bedding in the sandstone is irregular and breccia/conglomerates are common, particularly lower in the section a hundred yards to the south and at the base of the southernmost outcrop on the northwest side of the road. A poorly defined cylindrical structure exists in the latter section and may be seen on the top of a low outcrop of compect, rusty weathered, quartzarenite (compare with Stop 3).
Similar conglomerate and breccia occur in a large outcrop on the southeast side of Route 11. Quartz, quartz-arenite, and metaquartzite are common clast compositions and are similar to those at Stop B3 (Stop 9 in Fig. 1). In both the western and southeastern outcrops shaly zones could have been generated by shear and at the northern end of the latter bedding dips are steep (>60°; Karboski, 1977), yet again supporting the notion of significant post-depositional deformation .

A3: CAMBRO-ORDOVICIAN STRATIGRAPHY, SEDIMENTATION, AND ICHNOBIOLOGY OF THE ST. LAWRENCE LOWLANDS - FRONTENAC ARCH TO THE CHAMPLAIN VALLEY OF NEW YORK
J. MARK ERICKSON
Department of Geology
St. Lawrence University
Canton, New York 13617
INTRODUCTION
This trip is being offered for the purpose of introducing students of geology to some of the interesting and important relationships to be found in the first Cambrian(?) rocks to be "properly" described on this continent. Indeed, the name Potsdam is the oldest recognized stratigraphic name in North America accepted under the terms of the Code of Stratigraphic Nomenclature. The unit is, however, not strictly homogeneous, nor are its age and stratigraphic relationships known throughout its geographic distribution. The aim of this field trip is to point out some of the stratigraphic, sedimentologic, paleontologic, and paleoenvironmental variety that has been included under the label of "Potsdam Sandstone" in the region of the type area, northern New York.
This field trip will span the North Country from Chippewa Bay to Champlain, New York, (Figure 1) and will emphasize the basal units in the Paleozoic sedimentary cover of the basement. During its progress the guide will attempt to point out relationships between bedrock and the activities and deposits of the Wisconsinan glaciation which covered the entire field area. The trip will be entirely within the St. Lawrence Lowlands physiographic province as used by Fisher, 1977 (Figure 2).
Please note that the articles in support of this trip (Erickson & Bjerstedt; Erickson; and Erickson et al.) follow this road log.
ROADLOG
In this road log one will find, associated with each stop description, a number of questions that are best addressed by relationships at that particular stop. To stimulate thought and discussion participants are encouraged to make their own observations in an attempt to answer these and any others that arise in the process. The author assures you that he does not have answers to most of these!
Questions to be raised by this field trip:
1. What is meant by "Potsdam" - how well defined is the unit? Is the name being applied properly? Is misapplication preventing better understanding of regional tectonic and depositional histories
2. What is the age of the Potsdam Sandstone?
3. What depositional environments are involved in the Potsdam Fm.?
4. What are the relationships between the Potsdam-Theresa-Ogdensburg Formations?
5. What was the biota of the Potsdam-Theresa interval?
6. What was the paleoecology of the ichnotaxa (and of the trace-making organisms) found in these rocks?
7. Is the first appearance of trace fossils in regional rocks indicative of evolutionary change or of depositional environment?
8. What are the stratigraphic relationships of the formation?

A3: CAMBRO-ORDOVICIAN STRATIGRAPHY, SEDIMENTATION, AND ICHNOBIOLOGY OF THE ST. LAWRENCE LOWLANDS - FRONTENAC ARCH TO THE CHAMPLAIN VALLEY OF NEW YORK

STOP 1. St. Lawrence County Court House. (Figure 3)
Photo stop - no hammers please! The field trip begins appropriately at this classic structure because it contains most of the impressive elements of the Potsdam Sandstone as it occurs in the stratigraphic/lithographic type locality in the vicinity of Potsdam, N.Y., 10 miles to the East. The edifice also demonstrates many of the uses of the Potsdam and the skills of the quarry craftsman.
Emmons (1838, p. 214; 1842) named this unit in the Report of the Survey of the 2nd Geological District of New York. Quarries of the Potsdam are no longer accessible; however, the lithologic character of the "type" Potsdam is easily seen in this structure.
The rock is a fine-to-medium grained, well-rounded, well sorted, laminated, plane bedded or cross-stratified, hematitic, silica cemented orthoquartzite. It has very unique decorative properties because quartz grains were individually coated by hematite before the silica cement was introduced. For this reason the red coloration is protected from weathering, thus facades do not become streaked or stained as is the case with some hematitic or limonitic building stones having calcitic cement that contains the oxides or with pyritiferous limestones and sandstones.
The gray ashlar blocks of the courthouse are a Precambrian unit known as Gouverneur Marble. Red trim is all Potsdam Sandstone. Both were produced in St. Lawrence County. Please note that the newly completed addition to the courthouse attempts to use the same color themes but employs man-made materials rather than native building stone.
Questions to be raised at Stop 1, in particular are:
1. What are the lithologic properties of the Potsdam Sandstone?
2. What depositional environments are represented in the "type" Potsdam Sandstone?
3. Do the rocks contain fossils - either ichnofossils or body fossils?
4. What primary sedimentary structures are present?

Note sandstone facade on Canton Municipal Building on left.

Cross Grass River
The Grass River is one of several northward-flowing rivers whose headwaters are in the Adirondack Highlands. These are tributary to the St. Lawrence River approximately 20 miles to the North. Several have major power dams or paper mills on them thus being developed to the degree that the original character and fishery of the river has been lost. Canton's water supply is drawn from the Grass River.

The route passes along the Canton phaccolith
The route passes along the Canton phaccolith, a body composed of alaskite and surrounded by marble and paragneiss, all presumably Grenvillian age (Bloomer, 1965; 1967).

Outcrops of Canton Alaskite are visible at crest of hill.

Whalebacks of alaskite and gneiss
The entire region has been glaciated multiple times, most recently during the Wisconsinan Stage of the Pleistocene. Topography of both bedrock and surficial material reflect that process. Outcrops of alaskite and gneiss having smooth glacial polish and protruding from surrounding till are referred to as "whalebacks" because of their appearance and morphology.

Prominent valleys through the alaskite-gneiss terrain
Differential scouring of softer marble and subsequent valley filling by alluvium and bog deposits has produced prominent valleys through the alaskite-gneiss terrain. The bus will cross such a valley at the given mileage. The next stop lies within such terrain.

STOP 2. Potsdam Outlier Or Grenvillian Quartzite? (Figure 4)
Bus will turn onto gravelled parking strip on W. side of the highway. Disembark and carefully cross this busy highway to examine low outcrops in roadcut on east side.
In the North Country no trip in the Potsdam would be complete without visiting one of the region's outcrops of enigmatic sandstone. Cushing (1916) included this hill as an OUTLIER of Cambrian Potsdam Formation overlying Grenvillian marble.
Bloomer (1965,1967), after structural mapping and petrographic studies of included minerals, concluded that the quartzites mapped as outliers were in structural and mineralogical equilibrium with enclosing Grenvillian rocks, implying for the sandstones a Precambrian age as well. Others (eg. Brown, 1967) have considered the quartzites to be collapse fillings of, or deposition in, a karst developed on Grenvillian marbles, or fillings of cavities created by hot, high-pressure, acidic brines conducted through the porous Potsdam (see trips by Selleck, and by Bursnall and Elberty in this volume for further discussion). As one examines this outcrop bear in mind that the type Potsdam is an outlier of quartzite on Grenvillian rocks!
Careful examination of the outcrop will reveal at least six lithologic units (including those to be seen in the continuation of the roadcut approx. 75 yards to the north). The lowest unit is white, buff-weathering, fine- to-coarse grained, laminated, trough cross-stratified quartz sandstone, 3+ feet thick dipping NE at 28 degrees.
Unit 1 is overlain disconformably(?) by laminated, plane bedded, more friable, pink and white quartz sandstone. Unit 2 persists through thickness of approximately 20" grading into unit 3, a more massive expression of the same lithology. A 3" set of trough cross-strata that occurs 4" below top of unit 2 may be filling a channel. Unit 2 contains laminae packaged in coursening-upward bundles one to three inches thick.
Tracing unit 2 toward to South end of the outcrop reveals at least two instances where it is brecciated and fills vertical interstices on planes of displacement(?). Flow lamination in the sand matrix parallel (?) to the plane of movement suggests deposition of the matrix by fluid but indices for the direction (stratigraphically up or down) of fluid motion are lacking. Such autobreccias constitute a 4th unit. Lest there be question regarding structural motion on these surfaces, there are well-developed, if a bit weathered, slickensides in the upper portion of the south end of the outcrop.
Walking northward will bring one to a low outcrop of siliceous autobreccia and finally to a second laminated sandstone, the exact relationship of which is unclear.
Coloration in the Potsdam Sandstone is often a point of interest, even contention. Lower surfaces of pink, hematitic(?) color bands on this outcrop sometimes transgress bedding planes and show sharp boundaries having micro-irregularities similar to those of stylolites. Coloration seems diagenetic not primary depositional in origin in this case. Such may not always be the case for Potsdam coloration, therefore each outcrop should be examined without prejudgment in the matter of color.
Stratigraphic relationships of many sandstone outliers, including those of the type Potsdam (Reed, 1934), to the main lithosome are unknown. Most workers today discuss informally the red, pink (or peach in Canada), pink and white, and white Potsdam. The terms lower and upper Potsdam are used as well. Although relationships among these units are unclear, paleoenvironmental interpretations are likely to eventually afford means for distinction.
At this outcrop consider the following questions:
l. What depositional environments are represented by the various units?
2. What are the structural relationship of the outcrop?
3. What might the sources of coloration in the sandstones be?
4. Are trace or body fossils present?
5. What is the age of this sandstone?

Cross Oswegatchie River.

Note road cut exposure of Precambrian granite gneiss.

Village of Heuvelton.
This region of St. Lawrence County has been settled by Amish groups so it is probable that we will see horsedrawn buggies or other farm equipment while driving along the south side of Black Lake. These gentle folk are superior craftspersons who contribute much to the diverse culture of this county.

Note stone house in Federal architectural style on right.

Pink and white orthoquartzite
Note outcrops of pink and white orthoquartzite on both sides of the road. There are no fossils in this rock and it resembles some of the laminated units seen at the last stop. Note the terrain change ahead as bus crosses into metamorphic country rock.

Grenvillian gneiss.

White, poorly bedded sandstone.

Gray gneiss with granitic dikes cutting outcrop.

Pope Mills.
Note outcrop of marble in the village as bus turns toward North.

Cross Black Lake at Edwardsville.

North Shore of Black Lake
The north shore of this long, narrow lake marks the edge of rather flat-lying, Paleozoic sediments

Exposure of Paleozoic sandstone.

Note use of stone in the new house on the right at corner.

Bedding plane exposure of white orthoquartzite
On left is a bedding plane exposure of white orthoquartzite having a striated, polished surface. It reveals no bed features, nor any fossils. Please note its elevation with respect to the outcrop of Precambrian gneiss 0.1 mi. ahead and to the left side of the road.

Escarpment cut in Paleozoic sediments
While driving note the escarpment cut in Paleozoic sediments on the right in the trees and the wide valley to the left in which Precambrian granitic gneiss whalebacks stand as evidence of proximity to the Precambrian-Paleozoic contact.

Climb through the outcrop to be visited.
It is a road cut made where Hwy. 12 crosses the escarpment just viewed. Take this opportunity to preview the outcrop which we will spend some time examining.

STOP 3. "White" Potsdam and Theresa fm. are exposed in this important outcrop (Figure 5).
PLEASE USE PROFESSIONAL CARE - WATCH FOR TRAFFIC AND FOR LOOSE ROCK ON THE OUTCROP.
This outcrop provides one of the most complete exposures of the Precambrian-Potsdam-Theresa transitions in the northwestern St. Lawrence Adirondack Lowlands on the American side of the St. Lawrence River. That is not to say that the section is chronostratigraphically complete; almost certainly it is not, because the more angular, poorer sorted, ferrugenous, often arkosic and siliceous-cemented sandstone facies generally associated with the older (lower) Potsdam are not present in the immediate vicinity. The red rocks exposed approximately 0.3 miles to the SE are Precambrian alaskitic gneiss. Pleasant Valley intervenes between the exposure now being examined and the Precambrian outcrop leaving the possibility that the lower Potsdam section has been removed by erosion.
Other local sections, however, preserve the transition into white Potsdam Sandstone through a few to several feet of quartz cobble conglomerate which marks a marine transgression that is probably younger than Dresbachian in this region. Its precise age is not yet well constrained (Fisher, 1977) in this location, yet lithologic relationships in northeastern New York (Fisher, 1977; 1982) and recent ichnobiostratigraphic studies by Yochelson and Fedonkin (1993) infer a Franconian or even a Trempealeauan age for rocks not containing species of the ichnogenus Climacticnites. No Climacticnites sp. have yet been recovered from the "white" Potsdam sandstones locally.
The trip first examines a relatively unweathered exposure of Potsdam-Theresa deposits created as a roadcut approximately 25 years ago. This section includes units 3 through 8 on the composite stratigraphic column given herein (Erickson and Bjerstedt). The Potsdam is white, cream or buff, brown-weathering, moderately sorted, fine to coarse, medium-to thick bedded, cross-stratified or laminated, calcite- or silica-cemented orthoquartzite. Current ripples and "herringbone" cross-strata suggest deposition under tidal conditions (see Erickson and Bjerstedt herein). Contact between Potsdam and Theresa is taken to be at the inception of dominant calcareous cement in grey, buff-weathering, more poorly sorted ferrugenous, thin- to medium-bedded, limey sandstones and sandy dolostones. Biotiurbation becomes a controlling element of preservation of primary sedimentary structure at this point. Iron is often present as pyrite framboids. Originally these sediments were very rich in organics. Much of that original food resource was removed by trace-making organisms leaving rocks of the unique "Theresa aspect" in which bedding planes are formed between bioturbated sedimentation units seen in this outcrop.
Cross-strata and presence of Skolithos sp. suggest that the white Potsdam lithofacies originated as sandwaves built across expansive tidal flats subsequently reworked by shifting tidal currents. Varying eustatic conditions resulted in recurrence of such conditons a number of times during Theresa deposition. Thus a "white Potsdam" lithofacies of rather clean quartz arenite can be found in the Theresa repeatedly. The Skolithos ichnofauna is not, however, always contained in it. It seems the Potsdam lithofacies does not always carry the Potsdam Ichnofacies.
At this outcrop the two styles of ichnofaunal development - infaunal suspension feeders and infaunal deposit feeders - are recognized. Bjerstedt and Erickson (1989) and Erickson and Bjerstedt (herein) discuss these trace fossil relationships, particularly as they relate to energy of depositional environment and depth of burrowing. Here it is emphasized that body fossils are essentially absent from this unit so that knowledge of the biota is developed from the ichnofauna. The Potsdam was unable to support deposit-feeding organisms as it was too well-sorted, reflecting high energy conditions of deposition on the tidal platform. Theresa sediments, on the other hand, must have held a rich admixture of organic matter within their more muddy matrix. These are burrowed extensively to depths of more than 5 cm by a wide variety of trace-making organisms. These are illustrated in the accompanying article by Erickson and Bjerstedt (herein).
Questions to be considered at this stop:
1. What were the depositional environments of the Potsdam and Theresa Formations.
2. Why are there no body fossils in these rocks?
3. What is the significance of the depth of burrowing in the Theresa? (Does it reflect ability of the Burrowing organisms, food content of sediments, sedimentation rates, oxygen content, or other environmental factors.)
4. What types of organisms were the likely trace-makers?
5. What was the source for the organics being utilized by deposit feeding ichnofauna?

STOP 4. Weathered Theresa Formation. (Figure 5.)
In the weathered bedding plane exposures found along this roadcut and the scarp to the SE one finds a diverse ichnofauna preserved in hyporelief, or occasionally in epirelief, on bed soles and surfaces. Examples of Monocraterion sp., Phycodes flabelliforme, Planolites sp., Roselia socialis and perhaps of Cruziana sp., will be found here. Weathering along the scarp face represents approximately 10,000 years of development, whereas that along the roadcut may be much less. Apply the same questions examined at Stop 3.

STOP 5. St. Lawrence Sea Way Senic View. (Figure 5)
Photo pause - 10 minutes. Islands in the St. Lawrence River are formed by Precambrian (Grenvillian) granitic gneiss which is elevated along the Frontenac Arch, a structural high that links the Adirondack Dome to the Canadian Shield proper. This view of the region is probably not unlike that which one would have seen during the Cambrian as the Sauk marine transgression crossed the region. Knobs of grenvillian metamorphic basement became islands about which conglomerate, and subsequently sandstone, were deposited as tidal currents swept between the islands.
The St. Lawrence River, now a "seaway" for ocean-going vessels, flows NE draining the Great Lakes of Canada and the U.S. The international boundary passes up the middle of the river here, but east of Massena, NY the river lies entirely in Canadian territory.
Note boulders of local and regional rock types.

Paleozoic calcareous sandstones of the Theresa Formation
You will be traveling on a surface held up by Paleozoic calcareous sandstones of the Theresa Formation. Note the appearance of this St. Lawrence Lowlands topography; it is typical of landscapes with very thin, or no, glacial drift remaining on it.

Note Precambrian gneiss.
Where loop closes on itself Precambrian gneiss lies NE of road and Potsdam SS has SW forming ledge behind garage. Contact not exposed but quartz pebble cpnglomerate occurs in wooded area to ENE of the side roads.

STOP 6. Section At Oak Point. (Figure 6)
The drive around the Oak Point loop has provided a typical example of many of the exposures along both Canadian and American sides of the St. Lawrence River in this immediate region. Exposures along the frontage road contain the Potsdam-Theresa contact.
This outcrop offers another opportunity to investigate the burrowing depths, bioturbation thicknesses, and trace fossil taxa involved in the transition to carbonate rich mudflat sedimentation in lower energy conditions (?) upsection. This section is noteworthy because it has produced one example of an arthropod trackway of large size probably assignable to the ichnogenus Protichnites as is discussed herein by Erickson and Bjerstedt. The trackway will be available for examination and discussion at this stop.

Note white sandstone bed in blue-gray Theresa
Note white sandstone bed in blue-gray Theresa Formation on right of road.

Slight deformation of Paleozoic strata
Slight deformation of Paleozoic strata can occasionally be seen in roadcuts such as that near Brier Hill.

Several exposures of Theresa Formation
Several exposures of Theresa Formation form roadside outcrops here.

Stone fences of upper Theresa Fm.
Stone fences constructed of slabby, upper Theresa Fm. begin to be a local hallmark in this region. They will be emphasized in the "Stone Fence Motel" that will be seen in about 15 miles on the LEFT (NW) side of the road.

Scotch Bush Road.
A small quarry opened in the "white Potsdam" (or Heuvelton) Sandstone lies 1.3 miles south along this road. It is now being used to store rubble, but it once presented a fine view of this unit.

Bedrock now is Ordovician limestone and dolostone.
Stratigraphically the trip has traversed the Theresa-Ogdensburg contact. Bedrock now is Ordovician limestone and dolostone. The highway here passes through a small (no admittance) private, abandoned quarry in the Ogdensburg Formation in which can be found domal stromatolites. The depositional setting of these rocks was described by Kerans (1977) and conodont faunas from two larger quarries in the formation were investigated by Judson (1981).

Stone Fence Motel on left.

Quarry in the Ogdensburg Fm.
Pass a large stone quarry (behind berm on left) in the Ogdensburg Formation (See Kirchgasser and Theokritoff, 1971). It is beyond scope of this trip.

Cross the Oswegatchie River
Cross the Oswegatchie River the confluence of which with the St. Lawrence lies in the city of Ogdensburg. Note the "Golden Dome", a highschool hockey arena.

Bridge to Prescott, Ontario, CANADA.
Frequent views of the St. Lawrence Seaway and terraine formed on glacial Lake Iroquois sediments will be seen between Ogdensburg and Massena, NY.

Full view of Iroquois Dam to north.
Full view of Iroquois Dam, a waterlevel control structure, can be seen to the north.

Sucker Brook drowned valley
Construction of the St. Lawrence Seaway raised water levels in the valley greatly. Many St. Lawrence River tributaries now have drowned valleys above their confluence. That of Sucker Brook, crossed here, and Brandy Brook are typical.

Valley of Brandy Brook.

Cole's Creek, the drowned valley now being crossed
Cole's Creek, the drowned valley now being crossed, marks a former channel of the Grass River drainage which was pirated eastward after the marine waters of the Champlain Sea were excluded from the St. Lawrence Lowland by isostatic rebound. Development of the present drainage followed.

To the LEFT (N) view a coffer dam
To the LEFT (N) view a coffer dam constructed across another abandoned channel of the Grass River. This dam is designed to keep the valley from being flooded by waters of manmade lake St. Lawrence.

Village of Massena.
There are several items of geological interest associated with Massena. It was the site of a major rapids in the St. Lawrence River which became the site for the Moses-Saunders power dam of the NY Power Authority and Ontario Hydro. Massena was also the epicenter of the 1944 magnitude 4.0 (Richter) earthquake of regional significance. The Massena Clay, a blue, marine clay deposited in the Champlain Sea, underlies much of the region. This deposit contains the marine bivalve mollusks Macoma baltica and Hiatella arctica, a modest foraminiferid (Katz, 1981) and ostracod (Erickson et al., 1984) fauna, and to the south at Norwood, N. Y, the skeleton of a Beluga whale was recently recovered by Bill Kirchgasser (Kirchgasser and Steadman, 993).

Visitor center of Eisenhower Lock
To the left is the visitor center of Eisenhower Lock, one of the sites where zebra mussels (Dreissena polymorpha) were first introduced to U.S. waters. Robinson Bay, northeast of the lock, will be the site of the $14 million St. Lawrence Aquarium and Ecological Center.
Inexpensive electric power from the NYPA project has made this the site of ALCOA, Reynolds, and GM plants producing and using aluminum. Some serious environmental problems have also been generated: the large earth moving project on the left is part of a PCB mitigation effort.

Biomass Poplar Plantation
Biomass Poplar Plantation, are experimental, quick-growing strain of the poplar to be used for wood chips which fire a heating plant. This project was spawned by the energy crisis of the 1970's when some institutions like Clarkson University installed wood-fired heating plants.

View of the Raquette River to the right.

Cross Raquette Rlver.

Enter Akwasasne the Mohawk Nation.

Cross St. Regis Rlver.

Cross Little Salmon Rlver.

Village of Ft. Covington
At confluence of Little Salmon and Salmon Rlvers.

Westville. The Salmon Rlver here flows on bedrock.

Cross Salmon River.

Begin to climb onto the platform of a major delta
Terrane begins to "roll" at the approaches to the town of Malone and begins to climb onto the platform of a major delta built into the Champlain Sea (Clark and Karrow, 1984).

Cross the Salmon River
Cross the Salmon River, and begin to ascend hill on E. side of town.

STOP 7. Meagan Residence. (Figure 7)
Field trip members are the guests of the Michael Meagan Family. Walk up driveway and enter backyard through gate in fence. Please stay on path. Mr. Michael Meagan is the owner of the unusual Malone dubiofossils which we are here to view. The specimens, which are displayed near the pool, were discovered during excavation in 1992, and were recognized by Mr. Meagan to be unusual. He permitted removal of the specimens to St. Lawrence University where they were studied by Erickson.
Preliminary findings presented herein interpret these structures as slighly-transported fragments of algal mat with included trapped sediments. Please examine the specimens which are part and counterpart of a single block of laminated Potsdam Sandstone. During examination one may wish to keep the following questions (and others!) in mind.
1. What conditions were required to produce such an algal mat?
2. How much transport might they withstand?
3. Were there no animals present in the environment of deposition?
4. Could these be something other than algal/sediment features?
5. What is the age of this specimen?
6. Similar structures seem to be restricted to the Cambrian and very late Precambrian - why?

Malone delta built into glacial Lake Iroquois
You will climb again onto the plain of the Malone delta built into glacial Lake Iroquois (Clark and Karrow, 1984). From this vantage there is a commanding view of the St. Lawrence Valley to the North - the former basin of Lake Iroquois and later the Champlain Sea.

Entering Burke Center.
The careful viewer will see to the north-northeast a prominent elevation across the St. Lawrence Valley. This may be Covey Hill, a Potsdam Sandstone ridge against which glacial ice lay to dam glacial Lake Iroquois. The lake drained between approximately 12,000 and 11,500 B.P. (Pair and Rodrigues, 1993).

Cross an abandoned drainage through a deltaic platform
Again, cross an abandoned drainage through a deltaic platform related to the ancestral Chateaugay(?) River.

STOP 8: HIGH FALLS PARK. (Figure 8)
NO HAMMERS PLEASE.
This scenic stop affords the opportunity to view a more easterly exposure of the Potsdam Sandstone. Comparison with the sections seen previously at Pleasant Valley Road and Oak Point in St. Lawrence County will support the idea that the sandstone of the Potsdam thicken northeastward across the Laurentian Platform. Here more than 100' of section is exposed. As thickening occurs it is probable that age relationships within the formation become increasingly complicated. Trace fossils have assisted stratigraphers to make regional correlations and paleoenvironmental intrepretations in the absence of body fossils.
At this stop one may wish to examine character of the Potsdam lithologies, bedding characteristics and contacts, weathering profile, and trace fossil content of the rocks. What paleoenvironments are suggested? Time allowed 1/2 hour. Please return to bus promptly when requested.

Cross Chateaugay River.

Rising out of ancestral Chateaugay River Valley
Rising out of ancestral Chateaugay River Valley, note retaining wall constructed of local sandstone. On the upland there is another view northward toward the St. Lawrence Valley and Canada. South of the highway lies a newly constructed substance abuse center, one of several penal facilities that have proliferated northward in the past decade.

Cross North Branch of Great Chazy River
The trip has crossed into the basin of the Great Chazy River, the North Branch of which is crossed here.

Trip crosses a deltaic sand plain
Again the trip crosses a deltaic sand plain, probably an element of the ancestral Chazy River system.

Cross Great Chazy River in Mooers Forks.

Modern floodplain of the Great Chazy River
Route winds eastward once gain at edge of the village where the modern floodplain of the Great Chazy River can be seen well developed south of the highway.

Cross Great Chazy River once more

Travel on surface held up by Potsdam Sandstone
Travel on surface held up by Potsdam Sandstone which underlies glacial deposits.

STOP 9. CLINTON FARM SUPPLY. (Figure 9)
Exposed in the north half of the parking lot and surrounding an abandoned quarry to the rear of the Clinton Farm Supply are bedding planes of the Potsdam Sandstone. Rocks here are assumed to be in the upper or Keeseville Member. These are medium bedded, cream to white, plane and cross-stratified, quartz arenites (Fisher, 1968).
This outcrop affords an exceptional opportunity to examine bedding plane features, including large scale ripple marks, trough cross strata, sand waves and associated ichnofossils. The unusual and abundant trace fossils are of particular interest. Some aspects of these rocks are very similar to the white sandstone facies seen at Pleasant Valley Road (Stop 2) and within the Theresa Formation at Oak Point (Stop 3) this morning. At first look the traces fossils seem unique, however.
Some of the paleoenvironmental and ichnological features of this outcrop are described in the accompanying paper (Erickson, Connett, and Fetterman, this volume) resulting from studies by the 1993 St. Lawrence Paleoecology Class. Relationships here give insights into some questions raised at previous stops as well as spawning new questions such as:
1. What organism produced the large traces?
2. What controlled their distribution?
3. How deeply did they burrow?
4. What is the relationship, if any, of burrows to the ripples in both space and time?
5. How did the trace makers feed, on what, and where? (e.g., were they filter feeders, suspension feeders, or deposit feeders?)
6. Is this Potsdam Sandstone? What age is it? Examine the outcrop thoroughly. Several bedding planes are preserved but the lowest surface, that displaying the ripples, is the most interesting. It continues on the south side of the road where some brittle-fracture patterns are present as well.

Climb again onto rich soils of the Malone paleo-delta.
Once a major potato-growing area, the presence of Popeye on the sign denotes that spinach is now the major crop. It is frozen on site for sale to several brands. Rotation of fields assures nearly steady production during the growing season.

East Branch of the Little Salmon River

Nicholville, NY on the St. Regis River.
The Nicholville Conglomerate Member (Postel, et al., 1959) of the Potsdam Sandstone crops out along the river near here. It is overlain by orthoquartzite which occurs along Hopkinton Brook, .75 mi N of Village of Hopkinton. Stratigraphic relationship between members are uncertain and distribution is local. As such, the Nicholville is one of three or four difficult-to-define, restricted, basal conglomeratic units that may be "Potsdam," but are more likely Precambrian. The Allens Falls Fanglomerate (Harris, 1988) is another such unit. Their examination is beyond the scope of this trip.

Cross West Branch of St. Regis River.

Note use of true Potsdam Sandstone in buildings
Note use of true Potsdam Sandstone in buildings of Clarkson University and the village museum and library. This rock came from quarries south of the village that are no longer available for study.

Cross the Raquette River.
Note church of Potsdam Sandstone on left when crossing island.

A4: THE LATE GLACIAL ORIGIN OF THE CLINTON COUNTY FLATROCKS
David A. Franzi, Kenneth B. Adams
Center for Earth and Environmental Science
State University of New York
Plattsburgh, New York 12901
Donald L. Pair
University of Dayton
The Clinton County Flat Rocks comprise a discontinuous, 5-kilometer wide belt of bare sandstone areas that extend approximately 30 km southeastward into the Champlain Valley from Covey Hill, near Hemmingford, Quebec (Figure 1). Created by catastrophic floods from the drainage of glacial Lake Iroquois and younger post-Iroquois proglacial lakes in the St. Lawrence Lowland more than 12,000 years ago (Denny, 1974; Clark and Karrow, 1984; Pair et a1., 1988), the exposed sandstone today provides a nutrient-poor, drought-prone habitat that is often covered by jack pine (Pinus banksiana) barrens. The relatively low-diversity jack pine community is maintained by fire, which has an important role in ecosystem regeneration. We will examine the deglacial events leading to the origin of the Flat Rocks by following the path of late glacial meltwater drainage from the divide between the St. Lawrence and Champlain drainage basins. We will also address on-going efforts to understand the linkages between the hydrogeology and ecology of the jack pine barrens and document the recent history of anthropogenic development in the Flat Rocks region. The trip will feature a visit to several sites in the southeastern portion of Altona Flat Rock on property owned by the William H. Miner Agricultural Institute. The area contains the remains of the "Million-Dollar Dam", part of a failed hydroelectric project begun by William Miner in 1910. Additional stops will examine the deposits and landforms that record deglacial events leading to the catastrophic drainage of Lake Iroquois and subsequent formation of the Flat Rocks. The text of this field guide is an expanded version of a previous field guide (Franzi and Adams, 1993) that was concerned exclusively with the geology and ecology of Altona Flat Rock.

A4: THE LATE GLACIAL ORIGIN OF THE CLINTON COUNTY FLATROCKS

STOP 1. Lake Fort Ann Beach Ridges.
Park at the gate at the entrance of the Miner Institute property and continue northward on foot along Barnaby Road approximately 100 meters (320 ft). Turn left into woods and proceed west for 150 to 200 meters (500-750 ft) up the eastern flank of Cobblestone Hill. The beach ridges occur at elevations between 175 and 205 meters (580 and 670 ft) above sea level (Denny, 1974).
The beach ridges on Cobblestone Hill were first described by Woodworth (1905a) and later by Denny (1974). The beaches consist predominantly of moderately rounded to well rounded, pebble to cobble gravel that is deposited in multiple, elongate, low-relief ridges that extend along the northern and eastern flanks of Cobblestone Hill between 175 and 205 meters a.s.l. (Figure 7). Individual deposits are typically as much as 1 meter high and 30 meters wide, and often extend laterally for more than 400 meters (Denny, 1974). The gravel is almost exclusively composed of Potsdam Sandstone that was presumably derived from the alluvial cobble to boulder gravel that composes Cobblestone Hill.

Cobble gravel that comprises the Lake Fort Ann beach ridges.
Low roadside excavations approximately 75 meters (250 ft) west of the gate expose the cobble gravel that comprises the Lake Fort Ann beach ridges. Near the crest of the ridge the angular, 1.3 to 1.2 meter (1 to 4 ft) diameter boulders that comprise the core of Cobblestone Hill can be observed at the surface. The remains of the "Million-Dollar Dam" can be seen on the right just southwest of the hill crest.

STOP 2. The "Million-Dollar Dam".
The "Million-Dollar Dam" and hydroelectric generation plant was completed on 11 March, 1913 and operated intermittently from 21 January, 1915 until its closure in 1922. A large hole was blasted in the dam shortly after William Miner's death in 1930 to permit Cold Brook to drain freely through the former reservoir. The Flat Rock sandstone pavement is exposed southwest of Cold Brook. The change from mixed deciduous, primarily oak, forest on Cobblestone Hill to jack pine barrens on Flat Rock is characteristically sharp at this location.
...establish an instrumented field station for undergraduate research and instruction in geology and environmental science at the Miner Dam site. A monitoring-well network, consisting of nine wells ranging in depth from 10 to 25 meters, was completed in May, 1992 between the northeastern portion of the former Million-Dollar dam reservoir and the Skeleton Dam (Figure 7). Water-level measurements were begun in late July, 1992 (Figure 8). Future plans include the installation of a weather station, an inflow stream gaging station, and expansion of the monitoring-well network. The field station will provide an important linkage between traditional and applied educational opportunities that addresses some of the unique geological and ecological aspects of the Flat Rock region.

STOP 3. "THE SCARPIT".
The "scarpit" is the local name given to the desolate landscape created by efforts to grout the porous boulder gravel slope of Cobblestone Hill (Figures 6 and 7). The surface consists of a thin (1.2 to 2.5 cm) layer of cement that was poured and raked between large boulders composed predominantly of Potsdam Sandstone. The trench that was dug for the grout curtain (Figure 4) can be observed approximately 100 meters west of the concrete road that parallels the former shoreline of the reservoir.

The first of nine observation wells
The first of nine observation wells drilled in May 1992 can be observed to the left near the treeline at the edge of the grout surface. The wooded area beyond the well is part of minor southeast-facing bedrock riser. The slope of Cobblestone Hill steepens and the boulder size increases to the northwest.

The concrete road ends
The concrete road ends and the access road bears sharply northeast and continues on the bedrock surface through the jack pine barrens.

The road crosses a surface-water supported wetland.
The road bed is deeply rutted where it crosses a wetland that contains 0.2 to 1.0 meters of organic soil. Observation wells located approximately 50 meters northeast and 70 meters southwest of the wetland indicate that the water table is usually more than 7.5 meters below the surface.

The road crosses a small channel
The road crosses a small channel that contains a large wetland. A concrete wall on the left (south) side of the road was constructed to prevent water impounded behind the "Million-Dollar Dam" to escape northward through this channel.

STOP 4. The "Skeleton Dam".
The partially completed "Skeleton Dam" was designed to augment flow to the reservoir impounded behind the "Million-Dollar Dam" (Figure 7). The dam impounds "Chasm Lake" (Gooley, 1980), presumably named for the deep gorge cut into a prominent sandstone riser at its northwestern edge.
The water level of Chasm Lake dropped more than 2 meters below the spillway of the Skeleton Dam during the summers of 1991 and 1992. What little surface flow reached the basin during the summer months was lost by evaporation and ground-water seepage from the basin. Water level measurements from nearby observation wells since late July, 1992 indicate that steep, eastwardly directed hydraulic gradients exist at the southeastern flank of Chasm Lake, providing support for the hypothesis that some water is being lost from the reservoir by groundwater seepage.

STOP 5. The Ellenburg Moraine.
The gravel pit at this stop is excavated into the eastern (ice-proximal) side of the moraine. The pit contains approximately 10 to 12 meters of interbedded sand, gravel and diamicton that overlies Potsdam Sandstone. Bedset thickness generally ranges from about a decimeter to just over a meter. The maximum elevation of the upper surface of the moraine at this location ranges between 290 and 297 meters a.s.l.

STOP 6. The Ellenburg Moraine.
The exposure at this location is on the west (ice-distal) side of the moraine. The exposure contains approximately 10 to 12 meters of interbedded fine to medium sand with minor gravel and silt interbeds. Bedsets range from a centimeter to a few decimeters thick and are commonly horizontally laminated or ripple-cross laminated. Thin silt or silty fine sand deposits occur locally as draped laminae. Ripple azimuths and the gentle dip of the strata indicate a westerly paleocurrent. The moraine deposits were probably deposited in a proglacial lake west of the moraine in the upper North Branch valley. A small sandplain at an elevation of about 290 meters a.s.l. at Ellenburg may represent a delta that was built by the North Branch into the western end of the proglacial lake.

Route 11 crosses the Chazy-Chateaugay drainage divide.
The most easterly of the Chateaugay Channels can be seen adjacent to and crossing the road over the next few miles.

STOP 7. Discussion Of The Chateaugay Channel System.

Cross the Chateaugay River

The Chateaugay channels are on the right.

STOP 8. Chateaugay Channels.
This stop is alongside one of a series of underfit stream channels referred to as the Chateaugay Channels by MacClintock and Stewart (1965). These channels are eroded in till and bedrock and trend east-west across the low relief of the south slope of the St. Lawrence Valley. The channels are present from elevations of about 400 m (1300') to 315 m (1040') and are graded to the west.
MacClintock and Stewart (1965), Denny (1974), and Clark and Street (1984) concluded that the channels were eroded along a retreating ice front and emptied into Lake Iroquois to the west. These channels do appear to be graded to the highest level of Lake Iroquois in the vicinity of Malone (Pair and Rodrigues, 1993).
Discussion at this stop will focus on the channel morphology, nature of the ice-marginal drainage, and the possible duration of the drainage events.

Village of Dickinson.
11B passes through morainal topography identified as the Fort Covington Moraine by MacClintock and Stewart (1965).

STOP 9. The St. Regis Esker-Fan Complex And Nicholville Channels.
This stop will illustrate the sequence of deglacial landforms characteristic of ice margins in this part of the St. Lawrence Lowland. Moraines and an esker-fan complex in the St. Regis River valley indicate that a lobate ice margin extended southward and ended in a local proglacial lake. The esker ridge attached to the subaqueous fan complex is 80 to 90 feet high and extends northward 2 miles. Esker-fan complexes are present in many of the north-south valleys along the northwestern flank of the Adirondacks. Moraines in the region were attributed by MacClintock and Stewart (1965) to their Fort Covington readvance. They suggested that this ice advance was equivalent to the Port Huron stade. Our studies suggest that the ice margin here is probably recessional in nature and post-dates the Port Huron stade.
Continued ice retreat along the Adirondack flank uncovered the north end of the St. Regis River valley and the water level of the local proglacial lake dropped. Northwest of St. Regis Falls at Nicholville, the ice margin was still grounded and a series of progressively lower ice-marginal channels (from 1050-950') carried drainage westward and emptied into Lake Iroquois. We are standing in the bottom of one of these channels. Subsequently, a northward-flowing stream constructed the Iroquois delta at Nicholville.
Discussion at this stop will center around the time-transgressive nature of ice retreat, the proglacial water bodies in this region, and the morphology of the characteristic landforms.

Proceed across the sand plain of the Iroquois delta towards Nicholville.

A5: RETHINKING GRENVILLE-AGE DEFORMATION - DUCTILE SHEAR IN GRANITIC GNEISSES OF THE LOWLANDS
BARBARA J. TEWKSBURY
Hamilton College
Clinton, NY 13323
Grenville-age metamorphic rocks exposed in New York State are customarily divided into two regions, the Northwest Lowlands and the Adirondack Highlands (figure 1). The Lowlands are dominated by upper amphibolite to lower granulite facies metasedimentary lithologies; the Highlands are dominated by lower granulite to granulite facies metaigneous units. The Highlands-Lowlands Boundary lies along the Carthage-Colton Mylonite Zone, a major shear zone that juxtaposes the two terranes and exhibits evidence of a complex motion history. The youngest motion along the Carthage-Colton Zone has recently been dated at approximately 1098 Ma by Mezger et al. (1992).
Despite the dominance of metasedimentary lithologies in the Lowlands, a number of metaigneous units have figured prominently in various models for the structural history of the Lowlands. Chief among these are the 14 large bodies of leucogranitic gneiss collectively referred to in the recent literature as the Hyde School Gneiss, after exposures in the Hyde School body (Carl et al., 1990, Whitney et al., 1989; Mclelland et al., 1992) (figure 1). The Hyde School Gneiss bodies are complex domical structures scattered throughout the Lowlands. U/Pb zircon geochronology indicates that protoliths for the Hyde School Gneiss in a majority of these bodies formed ca. 1225-1230 Ma (Mclelland et al., 1992).
Traditional views portray the structural evolution of Proterozoic rocks in the Northwest Lowlands as a series of folding events at scales ranging from microscopic to regional as part of a series of contractional orogenic events stretching from Texas to Labrador over a time period from some time between 1300 and 1200 Ma to about 1050 Ma. These models attribute complex patterns in the distribution of lithologic units to the interference of fold wave forms of different ages and orientations. Shearing, when recognized at all, has been relegated to discreet and narrow zones and has not been previously thought of as a major kinematic element in evolution of Lowlands structures.
Over the past several years, I have evolved a very different view of deformation in the Lowlands, one in which regional ductile shear played a major role, and have argued that models for the formation of structures in the Lowlands must be consistent with the manner in which microscopic through macroscopic structures evolve when rocks undergo deformation involving a large component of ductile shear. Evidence for the importance of regional ductile shear has come from examining several bodies of Hyde School Gneiss, as well as a series of younger granitic gneisses in the Lowlands. The introductory paper for this field trip will first compare published models for the evolution of Lowlands structures, then briefly outline an alternative model consistent with structural features of the Hyde School Gneiss, and finally explore the evidence compelling us to think seriously about regional shear.

A5: RETHINKING GRENVILLE-AGE DEFORMATION - DUCTILE SHEAR IN GRANITIC GNEISSES OF THE LOWLANDS

Hyde School Gneiss of Canton body on the left.

The famed Snake Roadcut.
The marbles exhibit complex fold patterns, some of which may be sheath folds.

Good views of cliffs of Hyde School Gneiss
Payne Lake Fishing Access Site, where there are good views of cliffs of Hyde School Gneiss on the eastern margin of the Payne Lake body. Fields east of the Payne Lake body are largely underlain by marble.

STOP 1. Main foliation (Sm) in the Hyde School Gneiss
Main foliation (Sm) in the Hyde School Gneiss along the eastern limb of the Payne Lake body (figure 7).
Park at the gate on the west side of the road, and walk west along the State access at the edge of the field to the outcrops of Hyde School Gneiss (HSG) visible from the road.
The contact is not exposed but lies between non-resistent metasediments and resistant HSG at the west edge of the field. The best exposures lie along a very small stream bed in the first set of outcrops immediately south of the fishing access path. The stop description begins in the stream bed at the first set of HSG outcrops.
The HSG at this stop is a lineated and well-foliated pink leucogneiss with interlayered amphibolite. The main foliation (Sm) is subvertical and strikes parallel to the margin of the body, and the lineation (Lm) plunges steeply in the main foliation plane. Because the outcrops are dominantly quasi-horizontal glacially polished surfaces, the lineation is difficult to see. One of the only vertical foliation surfaces exposed at this stop lies in the stream bed, where it is clear that the lineation is a very nice quartz ribbon lineation.
Thin sections show that the main foliation is a well-developed shear fabric displaying sigma grains with core and mantle texture, quartz ribbons ramping from shear plane to shear plane, and dynamically-recrystallized grains. The fabric is well-recovered and shows polygranular quartz ribbons, no grain shape preferred orientation of fine quartz grains, and generally straight grain boundaries. Sense of shear is east side up.
The HSG contains abundant coarse-grained granite and pegmatite, and it is clear at outcrops such as this one that granitic liquids were present throughout the shearing history of the HSG. Some pegmatites are thoroughly sheared, streaked out parallel to Sm as bumpy chains of coarse K-feldspar porphyroc1asts in the main foliation plane. Other coarse granitic phases are discordant and show no fabric at all. A particularly nice example of an intermediate state occurs on the flat part of the outcrop above the lineated surface along the stream bed. Here, coarse-grained granite is clearly discordant to the main foliation but is itself weakly foliated.
While much of the HSG in the Payne Lake body is devoid of amphibolite, localities such as this one at the margin of the body typically contain abundant interlayers of amphibolite. Amphibolite interlayers lie parallel to the main foliation, and have been sheared out and streaked out parallel to the foliation. It cannot be overemphasized that the current relationship between amphibolite and leucogneiss is structural.
Amphibolite layers are discontinuous along strike and are commonly segmented. Some of the layer terminations are clearly isoclinal fold hinges. A fine example of such a fold occurs in the stream bed immediately east of the large patch of junipers separating the stream bed from the higher outcrops extending to the south. Here, a biotitic amphibolite layer has been folded into an isoclinal fold with the main foliation lying parallel to the axial plane.
Outcrops stretching to the south show other important features of the interlayered amphibolites. As in many of the other bodies of the HSG, amphibolite layers are divided into blocky segments separated by medium- to coarse-grained granite. The granite separating the blocks is typically unfoliated or less well-foliated than the adjacent leucogneiss. A number of amphibolite interlayers in this large exposure show fold terminations, and many of the fold sets are not simple trains of isoclinal folds. While none are unequivocally sheath folds, many have outcrop patterns that couid reflect sheath folding.

Ask permission to visit stops 2 and 3
Ask permission to visit stops 2 and 3 at the Raymon Farm on the corner of New Connecticut Road and County Route 22. Resistant rocks of the Hyde School Gneiss form a prominent knobby, wooded rise across the fields to the north of New Connecticut Road. The southern contact of the Payne Lake body with surrounding metasediments lies approximately at the break in slope below the wooded rise.

Newly excavated roadcut of serpentinized marbles.

STOP 2: Discordant foliation in the Hyde School Gneiss
Discordant foliation (Sd1) in the Hyde School Gneiss along the southern end of the Payne Lake body (figure 7).
Park along the road, and walk north across the field. Follow the farm track that rises from the field diagonally up across the contact at the break in slope marking the transition to more resistant HSG. Proceed to the top of the rise immediately west of the farm track. The stop description begins in the HSG outcrops at the top of the rise.
Figure 7 shows clearly that this locality lies at the southern end of the Payne Lake body, where the main foliation (Sm) in the HSG, as well as the compositional layering and the contact between HSG and surrounding units, swings around the end of the body. At this locality, Sm and the contact dip very steeply south and strike approximately N35W.
The most prominent feature in the dark pink leucogneiss at the top of the rise is a well-developed, steeply-plunging quartz ribbon lineation that is well exposed on quasi-vertical surfaces. Close examination of the outcrop shows a striking thing. The lineation is associated with a weak, sub-vertical foliation striking approximately N55E, parallel to the length of the Payne Lake body, not parallel to the margin of the body. The main foliation (Sm) is difficult to locate in this exposure, where the lineated fabric is well-developed and where there is no compositional layering in the HSG. Interlayered amphibolite is exposed to the northwest below the crest of the rise, and the orientation of the foliated amphibolite makes it very clear that the prominent lineated fabric is discordant to both the main foliation (Sm) and the compositional layering. We have named the well-lineated, discordant fabric Sd1 (the subscript "1" derives from the fact that we find a second discordant fabric of slightly different character but similar orientation in the Dodds Creek body, as described in the log for stop 4).
Thin sections show that Sd1 like Sm, is a well-developed shear fabric displaying sigma grains with core and mantle structure, quartz ribbons ramping from shear plane to shear plane, and dynamically-recrystallized grains. The fabric is well-recovered and shows polygranular quartz ribbons, no grain shape preferred orientation of fine quartz grains, and generally straight grain boundaries. Sense of shear is east side up. Sd1 is a distributed shear fabric but is not equally well-developed at all localities around the southern margin of the Payne Lake body. In some areas of outcrop, the most prominent fabric in the rock is the well-lineated Sd1 fabric; in other areas, the most prominent fabric is Sm.
In summary, the Payne Lake body exhibits two distinct shear fabrics, one parallel to the margins of the body (Sm) and one parallel to the long dimension of the body (Sd1). Along the eastern and western limbs of the body, the two fabrics are parallel to one another and are consequently particularly well developed, especially along the eastern margin (e.g., at the previous stop). We have interpreted Sm to have been the earlier fabric developed in a subhorizontal regional shear zone. As sheath folds grew, Sm was folded into very large folds with highly recurved hinges. Figure 1 shows the geometry of the Payne Lake sheath. Sd1 developed with a shear sense consistent with earlier shear directions as a younger shear fabric parallel to the axial plane of the growing sheath. Along the limbs of the sheath, Sd1 lies parallel to Sm (figure 4b); in the hinge region at the north and south ends of the body, Sd1 is discordant to Sm.

STOP 3. Sheath folds and late dike
Sheath folds and late dike with mylonitic fabric in units adjacent to the Hyde School Gneiss (figure 7).
This property is owned by the Raymon family at the corner of New Connecticut Road and County Route 22; ask permission before visiting this locality. Park along the road, and walk north across the field. The contact between the Payne Lake body and adjacent units lies at the prominent break in slope at the edge of the wooded area. This stop description covers exposures of units adjacent to the Payne Lake body in outcrops on the low shoulder north of the field but south of the Payne Lake body itself. The stop description begins in the cluster of outcrops at the top of the rise.
A variety of metasediments, including feldspathic quartzites, marbles, and garnet-sillimanite gneiss, are interlayered with leucogneiss in these outcrops. The contact here between HSG and surrounding metasediments gives every appearance of being gradational.
Compositional layering and the main foliation (Sm) in these units dip steeply and strike approximately N80W, parallel to the margin of the Payne Lake body. In the flat outcrops at the top of the rise, garnet-sillimanite gneiss exhibits both eye-shaped folds several centimeters across and refolded isoclinal folds. We interpret the eye-shaped folds as sheath folds. Sheath fold long axes and isoclinal fold hinges plunge steeply in the foliation plane, parallel to quartz ribbon stretching lineations in adjacent HSG. The presence of mesoscopic sheath folds provides additional supporting evidence for interpretation of the Payne Lake body as a large sheath fold.
Refolds in isoclinal intrafolial folds and tight to open folds in Sm also occur in this outcrop. A moderately well-developed foliation is locally developed parallel to the axial planes of these folds. The folds plunge steeply, and the axial plane foliation is subvertical and strikes approximately N50E, subparallel to Sd1 and to the long dimension of the Payne Lake body.
Walk east to the last major set of outcrops before the ground drops away to the farm in the distance to the southeast. A sub-vertical dike approximately 15 cm thick and striking N60E cuts interlayered metasediment and leucogneiss. The dike displays a prominent mylonitic fabric that is best developed within the dike itself but that does occur in the country rock on either side of the dike. The mylonitic fabric is subvertical and strikes approximately N50E, subparallel to the long dimension of the Payne Lake body and at a high angle to Sm in the outcrop.
Thin sections of the mylonitic fabric of the dike show sigma grains with core and mantle structure, quartz ribbons, and dynamically-recrystallized grains. The fabric in this dike is the least-recovered of the fabrics at Payne Lake. Serrated grain boundaries are common, and some grain shape preferred orientation of fine quartz is present. Some later cataclasis is also evident. Orientations of outcrop surfaces makes it impossible to locate the stretching direction of quartz ribbons in the field. Multiple sections, however, show that quartz elongation is best developed in vertically-oriented sections, suggesting a steep stretching lineation. Shear sense is east side up, consistent with shear sense on both Sm and Sd1. Based upon shear sense and orientation, the argument could be made that this fabric, and the axial planar fabric in the sheath fold outcrop, are likely Sd1 fabrics. The fact that the mylonitic dike fabric is relatively poorly-recovered suggests that it represents a late phase in development of Sd1.
The features at this stop have two implications. First, shear in the Payne Lake body apparently had a long history, developing from a major shear zone with regional shear fabrics (Sm) to sheath folds with axial planar shear fabrics (Sd1) to late, discreet zones of shear with poorly-recovered mylonitic fabrics (late phase Sd1 or Sd2). Second, intrusion of granitic liquids persisted until the latest phases of shear, and some were clearly important in localizing melt-enhanced shear. This raises the question of the importance of melt-enhanced. deformation in the overall development of the Payne Lake sheath fold.

Good views of the northern end of the Payne Lake body to the SW.

Bridge over the Indian River.
The river channel follows the Pleasant Lake Fault Zone (PLFZ), a major late brittle structure (figure 1). Slip along the PLFZ has removed half of the Dodds Creek body, leaving the body with a steepsided, half-dome shape. Cataclasis along the PLFZ significantly reduced the resistance of gneisses along the fault. Swamp and floodplain cover the entire width of the fault zone, and rocks within the fault zone itself are not exposed anywhere along the Indian River. Mylonites in the Lowlands, on the other hand, are not typically more weakly resistant than unmylonitized lithologies.

Good view of the N end of the Dodds Creek body
Good view of the north end of the Dodds Creek body "at 2:00". The contact between the HSG of the Dodds Creek body and the weakly resistant metasedimentary lithologies underlying adjacent fields lies at the base of the knobby exposures of pink leucogneiss.

STOP 4. Main fabric (Sm) and discordant foliation (Sd2) in the HSG
Main fabric (Sm) and discordant foliation (Sd1) in the Hyde School Gneiss along the northern end of the Dodds Creek body (figure 7).
This property is owned by Mr. Edmon Phalen in the farm next door; please ask permission to visit this locality. Park along the road, and walk to the outcrops on the knoll west of the road.
The HSG at this stop near the margin of the Dodds Creek body is a pink, medium- to fine-grained leucogneiss with abundant interlayers of amphibolite. Flat outcrops on the north side of the knoll near the barnyard have abundant interlayers of quartzite several centimeters thick. While both the Dodds Creek and Payne Lake bodies have been previously mapped as consisting entirely of leucogneiss and interlayered amphibolite, we have established that both bodies, in fact, contain significant metasedimentary interlayers. The Dodds Creek body contains both thin interlayers of metasediment, as at this stop, and two wide swaths of interlayered marble, quartzite, and garnet-sillimanite gneiss (the concentric half-rings in figure 1). The Payne Lake body also contains a prominent metasedimentary inter layer with a peculiar "ear" shape (also shown in figure 1).
The HSG at this stop is well-foliated parallel to compositional layering, and thin sections from outcrops at the top of the knoll show that this main foliation (Sm) is a shear fabric, as it is at Payne Lake. Fabrics display sigma grains with core and mantle structure, quartz ribbons ramping from shear plane to shear plane, and dynamically-recrystallized grains. The fabric is well-recovered and shows polygranular quartz ribbons, no grain shape preferred orientation of fine quartz grains, and generally straight grain boundaries.
Sm at this stop is sub-vertical and strikes N95E, parallel to the margins of the Dodds Creek body. Stretching lineations plunge moderately steeply in the Sm foliation plane. At the southern margin of the Dodds Creek body, quartz ribbon lineations have a somewhat more variable orientation, consistent with reorientation during development of a large sheath fold in Sm. Along the margins of the body, quartz ribbon lineations plunge steeply. Sense of shear along the margins is east side up, as it is at Payne Lake.
A number of prominent discreet ductile shear zones several centimeters thick occur in the HSG at this stop and elsewhere in the Dodds Creek body. These zones are sub-vertical and strike N40E, approximately parallel to the long dimension of the Dodds Creek body. At the north and south margins of the Dodds Creek body, the mylonitic fabric of these zones is clearly distinct from the main shear fabric (Sm), because it is discordant to Sm. As at Payne Lake, the two fabrics can be difficult to distinguish from one another where they are quasi-parallel along the long margins of the Dodds Creek body. There are four significant differences between the main foliation (Sm) and the younger discordant mylonitic fabric. First, Sm is a distributed shear fabric, moderately well-developed to well-developed over zones 10's to 100's of meters wide. The discordant fabric, one the other hand, is distinctly domainal, occurring in ductile shear zones several centimeters thick. Second, the discordant fabric is clearly a mylonitic fabric in outcrop; the taffy-like appearance stems from abundant quartz ribbons and dynamically-recrystallized grains. Despite the fact that Sm is not as clearly mylonitic in outcrop, thin sections show unequivocal shear fabrics. In fact, when one is hunting for foliations in lichen-covered outcrops without amphibolites in the Dodds Creek body, it is very easy to latch onto the discordant fabric as the main fabric, because it is so easy to see. One must be careful to look for both fabrics. Third, the discordant fabric is only poorly-recovered. Serrated grain boundaries are common, and pronounced undulose extinction and grain shape preferred orientation of fine quartz are present. Fourth, and most interesting, the sense of shear in this discordant fabric is opposite from shear both on the main foliation (Sm) in the Payne Lake and Dodds Creek bodies and on the discordant fabric (Sd1) in the Payne Lake body. Every sample we examined from the discreet ductile shear zones shown west side up and slightly oblique sense of shear. We named this fabric Sd2, presuming from its un-recovered character and opposite shear sense that it is younger than Sd1 at Payne Lake. Figure 4c shows the geometry of Sd2in the Dodds Creek body.
As at Payne Lake, melt-enhanced deformation seems to have been important in late shearing at Dodds Creek. Several of the ductile shear zones at this stop are developed in what appear to be granitic dikes injected across Sm roughly parallel to Sd2.
We have found only limited evidence at Dodds Creek for an older pervasive discordant fabric (Sd1) similar to the one discovered in the Payne Lake body. At this stop, HSG exposed on the sloping outcrop surface below the phone pole shows a very weak pervasive fabric discordant to Sm and roughly parallel to the long dimension of the Dodds Creek body. Exposures along the Indian River immediately adjacent to a spur of the Pleasant Lake Fault Zone at the northern end of the Dodds Creek body show fabrics of similar orientation related to folds much like those at stop 3 in the Payne Lake body. Thin sections show that these are weakly-developed shear fabrics.
The HSG at this stop and at many places in the Dodds Creek body is laced with fracture swarms oriented approximately parallel to the Pleasant Lake Fault Zone. Thin sections show nice cataclastic textures. It is important to note that, while intensity of cataclasis does increase with proximity to the Pleasant Lake Fault Zone, intensity of ductile shear fabric development does not.
Evidence from the Dodds Creek body reveals an even more protracted history of ductile shear than that suggested by work in the Payne Lake body. Fabrics in the Dodds Creek body are consistent with development of Sm in a regional subhorizontal shear zone. Sheath fold development followed, with production of weak axial planar fabric (Sd1). Shear sense reversed, and discreet ductile shear zones developed but did not have time to recover before they were affected by cataclasis. Shear sense reversal and progression to brittle deformation is consistent with late extensional unroofing in the Lowlands.

Good views of the Pleasant Lake Fault Zone
Good views of the Pleasant Lake Fault Zone to the right of the road, with rocks east of the PLFZ underlying the wooded rise beyond the river.

Farm for permission for STOP 5.

STOP 5. Shear fabrics in biotitic augen gneiss
Shear fabrics in biotitic augen gneiss and surrounding metasedimentary lithologies immediately west of the Beaver Creek Fault Zone (figures 1 and 5).
Park on the right hand side of the road. This property is owned by the Amish farm on the north side of the road and back about 0.6 miles; please ask permission to visit this locality.
Walk into the field to the south of the road to the crest of rounded knobs of granitic gneiss about 1600' from the road, bypassing the wooded knoll approximately 1050' from the road.
Figure 5 shows a condensed and generalized geologic map of the Beaver Creek region based on an excellent and detailed map by Brown (1989). Several aspects are pertinent to this stop. First, granitic gneisses of two different ages appear in the region. The ca. 1225-1230 Ma Hyde School Gneiss is exposed in two bodies, the larger Hyde School body and the smaller Hickory Lake body. The other granitic gneisses in the region are younger than the HSG, having been intruded ca. 1150-1170 Ma. Second, while controversy rages over whether the HSG was originally plutonic or volcanic, no one disputes the plutonic origin of the younger granitic gneisses in the Beaver Creek region. Third, the region is divided into a number of elongate zones by northeast-striking faults, including the Hickory-Mud Lakes Fault, the Beaver Creek Fault and the Pleasant Lake Fault (the northern extension of the fault that cuts off the Dodds Creek body, as described at stop 4). Fourth, outcrop patterns of both metasedimentary and metaplutonic units lying immediately west of the Beaver Creek Fault Zone (BCFZ) are attenuated and elongated NE-SW, while similar units have larger, more irregular outcrop patterns farther northwest, suggesting the possibility of major ductile shear in the zone west of the BCFZ. Fifth, both the granitic gneisses and the metasedimentary units immediately west of the Beaver Creek Fault Zone are well foliated and display the "main regional foliation". This stop will give us a chance to study the character of the main regional foliation in several lithologies other than the Hyde School Gneiss.
At this stop, we will examine the most northerly of a series of seven elongate granitic gneiss bodies lying immediately west of the Beaver Creek Fault Zone (figure 5). This granitic gneiss is not only different in age from the HSG but also different in character, being a pink to grayish-pink, coarse-grained biotite-quartz- oligoclase-microcline gneiss with distinctive microcline augen.
These gneisses are spectacularly lineated - quartz ribbons lie like pieces of linguini on the steeply-dipping foliation surfaces exposed on the knoll. The lineations are best viewed on the sub-vertical faces of the east side of the knoll. Lineations plunge approximately 25, 40E.
The foliation carrying the lineation is the main regional foliation and shows characteristics that indicate formation by ductile shear. In thin section, the foliation shows clear fabric asymmetry in sigma grains and ramping quartz ribbons. Relatively coarse grain size in porphyroclast tails suggests a period of annealing following development of the main shear fabric. By contrast, the early shear fabric in the HSG of the Payne Lake and Dodds Creek bodies is recovered but not well-annealed. Shear sense in the Beaver Creek granitic gneisses shows consistent sinistral strike slip with a small component of east side down motion along subvertical planes striking approximately N40E. The fact that the gneiss bodies are elongate parallel to the main shear fabric in the rocks suggests that the individual bodies may have been intruded into a developing shear zone. Several of the bodies farther southwest (figure 5) that show only poorly-developed shear fabrics may have been intruded either relatively late or into zones that did not experience as much subsequent shear strain.
As in the Payne Lake and Dodds Creek bodies of the Hyde School Gneiss, the granitic gneisses west of the Beaver Creek Fault Zone show evidence in thin section of additional shear fabrics younger than the shear fabric of the main regional foliation. Some samples show a younger well-recovered but unannealed shear fabric. This fabric displays classic core and mantle structure around sigma porphyroclasts, polygranular quartz ribbons, and grain size reduction. This younger fabric appears to lie parallel to the main foliation. Shear sense consistently shows a component of sinistral strike slip.
Some thin sections show a third shear fabric, this one an unrecovered fabric. This fabric is characterized by quartz grain shape preferred orientation, biotite fish, and rare feldspar sigma grains. Sense of shear is opposite that shown by earlier phases and has a component of dextral, rather than sinistral, strike slip.
Interestingly enough, the dextral shear sense observed on this youngest shear fabric is, in fact, the sense of shear that one might infer from the geometry of the sigmoid east of the Beaver Creek Fault Zone (figure 5), and it is also the same as the sense of shear that we have suggested for the Pleasant Lake Fault Zone where it truncates the Dodds Creek body farther southwest. Late formation of the sigmoid is consistent with the results of our reconnaissance work in the sigmoid, which suggest that formation of the sigmoid postdates development of the main foliation and lineation in that region.
Multiple shear fabrics suggest a protracted history of ductile shear, much as we observed in the Payne Lake/Dodds Creek region. Changes in shear direction also suggest a complicated kinematic picture.
Walk 240' southwest from the crest of the knoll. While the contact itself between granitic gneiss and surrounding metasediments is not exposed, outcrops of metasediment lie very close to granitic gneiss on the east side of the knoll. As you walk southwest, examine the character of the foliation in the marbles. The foliation in the marbles and calc-silicate gneisses is defined primarily by compositional layering and lies parallel to the prominent lineated foliation in the augen gneiss. One of the striking aspects of these rocks is that spectacularly lineated granitic gneisses with well-developed shear fabrics lie within centimeters of metasedimentary lithologies that show absolutely no microfabric evidence of ductile shear.
The only fabric asymmetry that we noted in the metasediments occurs in the outcrop of marble 240' southwest of the knoll where we first examined the granitic gneiss. This rock is a marble with quartz lozenges several millimeters to centimeters in size floating in a sea of coarse, equant calcite grains. While the calcite aggregate preserves absolutely no record of the shear that produced the spectacular lineations in the adjacent granitic gneisses, many of the quartz lozenges have a distinctly asymmetric shape. The lozenges are sigmoidal in shape and ramp from one foliation plane to another. Shear sense is left lateral with a small component of down-to-the-east motion. This sense of slip is consistent with that observed for the earliest microfabrics in the granitic gneiss.
Well-lineated rocks with good kinematic indicators appear to occur primarily in the granitic gneisses of the region. The metasediments we examined here and elsewhere in the Beaver Creek region preserve essentially no kinematic indicators, even in locations within centimeters of highly-sheared granitic gneiss. Several factors may be involved. If melt-enhanced deformation was important during shear, the granitic material may have concentrated the shear, leaving adjacent metasediments with comparatively low shear strains. Second, quartzofeldspathic aggregates are ideal for preserving the kinds of kinematic indicators associated with ductile shear. Marble-bearing metasediments may, in fact, have accumulated as much shear strain as adjacent granitic gneisses, but shear fabrics may have annealed completely in the metasediments. Regardless of the cause, the effect is an important one to note and suggests that trying to sort out the history of regional shear in the Lowlands by examining the metasedimentary lithologies may well be an exercise in frustration.
In summary, the "main regional foliation" is clearly a shear fabric in both the well-foliated and lineated granitic gneisses we observed in the Beaver Creek Region and in the Hyde School Gneiss of the Payne Lake and Dodds Creek bodies, despite the fact that the Hyde School Gneiss is considerably older. Granitic gneisses of both ages also show conspicuous evidence for protracted ductile shear with complex shear histories. All of the evidence points toward the importance of ductile shear across the Lowlands over a protracted period of time in development of both major and minor structures.
Walk approximately 200' toward Beaver Creek to small, rounded outcrops of gray to white marble. You are standing right at the edge of the Beaver Creek Fault Zone, which is very much like the Pleasant Lake Fault Zone that we saw at stop 5 - no outcrop and lots of creek and swamp. Close examination of the marbles in these outcrops reveals little in the way of fault zone features, despite proximity to the Beaver Creek Fault Zone. The lack of major cataclastic features in outcrops immediately adjacent to the Beaver Creek Fault Zone is also reminiscent of the Pleasant Lake Fault Zone.

Cross Beaver Creek and the Beaver Creek Fault Zone.
The lack of outcrop in the weakly-resistant cataclastic rocks of this late fault zone is similar to that along the Pleasant Lake Fault Zone.

Cross the Oswegatchie River.

Crossing the "Race Track".
This low area of fields and swamps sweeping in a broad arc marks the weakly resistant metasedimentary rocks bordering the more resistant Hyde School Gneiss of the Canton body. The road climbs out of the Race Track onto HSG, which crops out in abundant rounded knobs.

STOP 6. Low pink outcrop on the east side of the road.
Lineated Hyde School Gneiss of the Canton body (figure 7).
If time permits, we will stop briefly to examine well-lineated Hyde School Gneiss of the Canton body at this locality.
HSG in the Canton body is lithologically similar to that in the Payne Lake and Dodds Creek bodies, but the orientations of lineations are conspicuously different. Lineations in the Payne Lake and Dodds Creek bodies plunge very steeply, consistent with the vertical orientations of the sheaths. Lineations in the Canton body, on the other hand, plunge moderately to shallowly throughout much of the body. Lineations at this locality plunge approximately 25, S60W, an orientation consistent with the overall shallow plunge of the complex Canton body finger.
Some publications have portrayed the Canton body as a south-southwest plunging structure, e.g., Foose's "Loch Ness Monster" model that interprets the Canton body and the Gouverneur body as two eroded "humps" connected in the subsurface (figure 2). Orientations of both foliations and lineations in the Canton body, however, suggest that a shallowly west-southwest-plunging overturned structure is a better interpretation (figure 1). Preliminary data from our on-going work on the Canton body show shear fabrics similar to those in the Payne Lake and Dodds Creek bodies, and we would argue that a shallowly west-southwest-plunging sheath fold is a better interpretation for the large-scale structure of the Canton body. Preliminary thin section analysis on samples collected during summer 1993 suggests that shear sense in much of the Canton body is top side down to the west.
Work in progress shows fabrics in this part of the Canton body to be more like those in the Beaver Creek region than those in either the Payne Lake body or Dodds Creek body. Fabric asymmetry is present in ramping quartz ribbons and relict sigma grains with coarse asymmetric tails, but fabrics are strongly annealed, as they are in granitic gneisses of the Beaver Creek region. Fine, dynamically recrystallized grains, so common in the Payne Lake and Dodds Creek bodies, are rare in the Canton body.

STOP 7: Hyde School Gneiss of the Canton body
Hyde School Gneiss of the Canton body and garnet-sillimanite gneiss in adjacent metasediments (figure 7).
Outcrops in the field to the west of the road. Ask permission at the Theron Stacey farm (west side of the road, first farm to the north across the creek). Park on the side of the road, and walk through the gate. Walk a short distance into the field along the farm track, and then proceed approximately 135' south to the first knoll.
This locality lies along the southern edge of a narrow, curved inlier of metasedimentary rock that gives the Canton body its famous "double fish hook" appearance. The inlier dips shallowly southwest beneath the westsouthwest to west-plunging tip of the Canton body (figures 1 and 7).
At this stop, we will examine the garnet-sillimanite gneiss that commonly (but not ubiquitously) occurs at or near the margins of the Hyde School Gneiss bodies. Similar garnet-sillimanite gneiss borders inliers of metasedimentary rock within both the Payne Lake and Dodds Creek bodies.
The small outcrop approximately 135' south of the farm track displays well-lineated porphyroblastic garnet-sillimanite gneiss. Lineations plunge approximately 25, S75W, parallel to quartz ribbon lineations in adjacent mylonitic HSG.
Walk 40' farther south to a small knoll consisting of HSG south of the contact. This outcrop nicely displays a characteristic feature of well-lineated and sheared HSG. Many outcrops of HSG are better lineated than they are foliated, and the appearance of the HSG varies considerably with the orientation of the outcrop surface. Surfaces oriented parallel or nearly parallel to the stretching lineation typically appear streaky and "well foliated". Surfaces oriented perpendicular or nearly perpendicular to the stretching lineation typically appear "poorly foliated" or even massive. This results, of course, from the fact that much of the "foliated" appearance arises from the lineation. Some exposures of HSG are essentially L-tectonites (lineation but no foliation, like a bundle of pencils); in such exposures, the foliation is impossible to locate on surfaces oriented perpendicular to the lineation. Understanding the variation in appearance with orientation can be very useful in outcrops where glacial erosion has sculpted rounded knobs and where there are no foliation surfaces to examine for stretching lineation orientation. Studying the outcrop for the "streakiest" surfaces can give a clue to the approximate stretching direction.
This locality exhibits other interesting features that we will not have time to examine during this trip. Roughly 800' northwest along strike from the knoll where we examined the HSG, dip slopes on the main foliation (Sm) have prominent southwest-plunging corrugations 0.5-1.0 m in wavelength. Examination of west-facing outcrop surfaces reveals that these corrugations are erosional features marking the intersection of slightly less resistent HSG with slight more resistent shear zones 1-2 cm thick. The shear zones dip steeply west at a high angle to Sm. The shear zones have a prominent mylonitic fabric and a component of down-to-the-west slip. As in the Payne Lake, Dodds Creek, and Beaver Creek gneisses, younger shear fabrics such as these attest to prolonged and complex ductile shear in the Lowlands.

Crossing the Little Race Track.
The stream valley marks the location of a weakly resistant, curved "finger" of metasedimentary rock that gives the Canton body its well known double fish hook map pattern (figure 1).

First outcrops of HSG in the North Pyrites body.

STOP 8. Low outcrops on the right side of the road.
Spectacularly lineated Hyde School Gneiss of the North Pyrites body (figure 7).
This outcrop displays fabulously lineated Hyde School Gneiss near the northern margin of the North Pyrites body. Quartz ribbons in this outcrop are many centimeters long and plunge shallowly northwest (approximately 10, N60W). The foliation carrying the lineation dips shallowly north (N89W, 18NE).
The power pole at the east end of the outcrop is rip-rapped with locally derived lineated HSG containing mafic tongues highly elongate parallel to the stretching lineation. The origin of these tongues is not clear at this outcrop. In a spectacular series of outcrops in the yard and gardens of the house across the road and to the west, however, features clearly show that the mafic material occurred originally in layers and has since been isoclinally folded and disrupted by shear. The tongues may very well have sheath-shaped geometries, although this is difficult to prove in these glacially-polished outcrops. We will not visit this locality during the field trip, because the gardens could easily be trampled. The owners, the French's, have been kind enough to give individuals permission to view the outcrops and could be approached for permission if a group is very small.
Unlike the annealed fabrics in rocks of the Canton body, fabrics in many samples from the North Pyrites body are recovered but not annealed. In addition, fabrics in some samples from the North Pyrites body are spectacularly un-recovered and display highly strained porphyroclasts and serrated grain boundaries, suggesting, once again, a complex and protracted shear history in the Lowlands.

STOP 9. Outcrops to the south of the road
Outcrops to the south of the road between the road and the woods.
Discordant shear fabric in the Hyde School Gneiss along the eastern margin of the North Pyrites body (figure 7).
This exposure of lineated and foliated Hyde School Gneiss lies along the eastern margin of the North Pyrites body. Unlike the HSG at stop 8, the HSG at this locality displays well-developed compositional layering oriented approximately N20W, 7OSW. The prominent lineation in the outcrop does not, however, lie in the plane of the compositional layering. Rather, the lineation is carried in a foliation that dips shallowly northwest, discordant to the compositional layering. This discordant foliation has the same kinds of distinctive asymmetric structures characteristic of shear fabrics that can be seen in the HSG of the Payne Lake, Dodds Creek, and Canton bodies, and we have termed this discordant foliation Sd. The lineation at this locality plunges approximately 20, N50W.
The orientations of Sd and the associated lineation Ld vary somewhat across the North Pyrites body, but Ld generally plunges shallowly NW. Shear sense determined from preliminary examination of thin sections appears to be top side down to the northwest.
Based on both the shape of the North Pyrites body and on the presence of prominent shear fabrics, we tentatively suggest that the North Pyrites body is a sheath fold plunging shallowly northwest (figure 1). We would interpret the lineated foliation, Sd, in much the same way as we have interpreted the discordant foliation in the Payne Lake body, as an axial plane foliation that developed parallel to the sheath fold axial surface as the sheath fold grew in a major shear zone. Where the earlier fabric, Sm, lies at a high angle to the axial plane of the sheath, as it does at this locality, Sd is clearly discordant to Sm and to compositional layering.

B1: BEDROCK EROSIONAL FORMS PRODUCED BY GLACIAL PROCESSES, NO.2 MINE, GOUVERNEUR TALC CO., GOUVERNEUR, NEW YORK.
DONALD L. PAIR
Dept. of Geology
University of Dayton
JAMES S. STREET
Canton, NY, 13617
FRED R. TOTTEN and JOHN E. KREIDER
Gouverneur Talc Co.
Gouverneur, NY, 13642
This trip takes place at the No. 2 (Arnold) open pit mine of the Gouverneur Talc Co. NYSGA last visited this location in 1971 on a trip led by J.S. Street (St. Lawrence University). He described a number of highly polished grooves, flutes, crescentic fractures, and striations present on bare bedrock surfaces (Street, 1971). Stops on this field trip will focus on the geologic setting of the region, history of pit operations, and a re-examination of the intriguing erosional forms present on both horizontal and vertical exposed bedrock surfaces. Our discussion will center on the nature and classification of these erosional forms, field evidence suggesting their possible origin, relationship to regional ice flow patterns, and their possible implications regarding subglacial processes and conditions.

B1: BEDROCK EROSIONAL FORMS PRODUCED BY GLACIAL PROCESSES, NO.2 MINE, GOUVERNEUR TALC CO., GOUVERNEUR, NEW YORK.

STOP 1. North end of pit
At this stop mine geologists will discuss the tectonic framework of the Northwest Adirondack Lowlands, provide a overview of the mineralogy and stratigraphy at the pit, and summarize the history of mining operations.
2015: Mine closed in 2008. Considerable reclamation since then. GE has good image from 1997.

STOP 2: South end of pit.
NOTE: Please stay otT the bedrock faces directly above the open pit. Beware of slippery footing on the vertical face. Many of the forms are best viewed from the road!
At this stop we will examine the bedrock erosional forms present on both horizontal and vertical surfaces at this end of the No. 2 Mine. Discussion will focus on the regional glacial setting, proposed classification of the forms, the possible origin of these intriguing forms.
Possible questions for discussion:
1. Do differences in the bedrock lithology control the location and distribution of the various bedrock erosional forms?
2. Can embedded 'tools' frozen in the ice abrade with smooth, sharp surfaces and produce all of the erosional forms present?
3. What do these forms say about the plastic nature of glacial ice at several scales?
4. What is the significance of these erosional forms occurring on the sides of the linear, rock-walled valley that includes the No. 2 Mine?
2015: Mine closed in 2008. Considerable reclamation since then. GE has good image from 1997.

STOP 3: Pulpit Rock.
Discussion at this stop will address the possible origin of the well known Pulpit Rock.

Linear, rock-walled valley
We are in the bottom of another of the linear, rock-walled valleys common to this region.

B2: THE POTSDAM-GRENVILLE CONTACT REVISITED (II)
JOHN BURSNALL
Canton, NY 13617
BILL ELBERTY
Department of Geography
This field trip continues the review, initiated in Trip A2 (Bursnall and Elberty, this volume), of outliers and enclaves of younger arenaceous rocks in contact with Grenvillian gneissic basement. The trip will concentrate on relationships between this basement and cover rocks, or enclaves, in the Dekalb and Richville areas whose affinity with the Upper Cambrian (?) Potsdam Sandstone is equivocal.
Repeats of Stop 7 and 8 of Trip A2 (described below) provide a basis for the trip, which includes an investigation of a newly exposed section in Dekalb (Stop 3). This exhibits somewhat similar relationships to those seen at the Rock Island roadcut (A2, Stop 6) which have been proposed as originating from burial of a karst topography - specifically the infill of solution pockets in marble on the Precambrian erosion surface (Carl and Van Diver, 1971). Outcrops of quartzarenite, "metaquarzite", and conglomerate to the south of Dekalb which were seen by Bloomer (1965, 1967) as being inseparable from the surrounding Grenville will also be visited. These, or very similar lithologies are contained as clasts in some of the sandstones (e.g., Stop 8, A2 and Stop 3, this trip).
"The Potsdam-Grenville contact in the St. Lawrence valley represents a hiatus of some 500 Ma. Mineral assemblages within the Grenville gneisses indicate that perhaps 25 km of material was eroded prior to the deposition of the transgressive Cambro-Ordovician sequence, over an undulating Precambrian erosion surface. Many of the isolated, predominantly sandstone, bodies within the Grenville gneiss terrane of the Adirondack Lowlands can be confidently interpreted as outliers of Potsdam Sandstone. ........ Such enclaves vary in composition from matrix supported breccias to equigranular orthoquartzites and their depositional environment has been variously interpreted as: pre-Potsdam solution pocket infills (related to a karst topography on a Grenville marble surface); fault related debris slides; fault breccias; and fault scarp talus accumulations. Some are seemingly crudely interlayered with the gneisses and are locally foliated" (Bursnall and Elberty, this volume).
The age of these enigmatic rocks have variously been proposed as:
1) outliers of Potsdam Sandstone
2) pre-Potsdam, post-Grenville remnants
3) Grenville in age, in that they suffered at least the later stages of Grenvillian deformation

B2: THE POTSDAM-GRENVILLE CONTACT REVISITED (II)

STOP 1: East Dekalb (Stop 8, Figure 1)
For convenience, the following description is taken from Trip A2 of this volume.
"Roadcuts due south of Dekalb further illustrate the complexities within these post-Grenville rocks. A long series of low exposures on the northwest side of the road contain well-layered marble (reclined folds at the north end) to the north which in the central section give way to a complex steep contact with rusty weathered arenaceous rocks. A number of small sandstone breccia wedges penetrate downwards into the marble in the vicinity, again supporting the solution-pocket infill model for the larger scale relationships seen elsewhere (e.g. Rock Island Road). Evidence for sulfide mineralization is present at some contacts, in common with the Rock Island Road locality (Elberty and Romey, 1990).
Bedding in the sandstone is irregular and breccia/conglomerates are common, particularly lower in the section a hundred yards to the south and at the base of the southernmost outcrop on the northwest side of the road. A poorly defined cylindrical structure exists in the latter section and may be seen on the top of a low outcrop of compect, rusty weathered, quartzarenite (compare with Stop 3).
Similar conglomerate and breccia occur in a large outcrop on the southeast side of Route 11. Quartz, quartz-arenite, and metaquartzite are common clast compositions and are similar to those at Stop B3 (Stop 9 in Fig. 1). In both the western and southeastern outcrops shaly zones could have been generated by shear and at the northern end of the latter bedding dips are steep (>60°; Karboski, 1977), yet again supporting the notion of significant post-depositional deformation." (Bursnall and Elberty, this volume).

STOP 2. The Richville breccias (Stop 7, Figure 1)
Please note that description for this stop is taken from Trip A2, this volume
"Karboski et al. (1983) described this outcrop this as containing a "flow breccia" at its base, followed by a densely consolidated breccia with an overlying highly deformed metaquartzite, overlain by an "orthoquartzite", which contains pebble-sized quartz clasts - possibly derived from the underlying metaquartzite. The breccias contain quartz clasts set in a hematite stained, medium grained arenite. Large (0.5 m) phacoidal blocks of the breccia are enveloped by thin shaly borders, the whole giving the impression of a shear zone.
This outcrop certainly inhibits any notion that the unconformity between Precambrian basement and overlying cover is a simple one!
Points to concentrate on are:
1) Possible shear fabrics in the lower part of the outcrop, in part defining the borders of coherent blocks of breccia
2) Compositional variation of clasts in the breccias
3) The relationship between and the textural character of the each of the recognized rock types
If the upper part of this outcrop is indeed comprised of rocks which are part of the Grenville basement as supposed by Karboski (1976) and Karboski et al. (1983) then the current disposition of lithologies seems not to be satisfied by a model that involves karst infill alone (Van Diver, 1976) as seems possible at Rock Island Road. It is possible, however, that the wall collapse of a large solution depression may have allowed a slab of basement to slide into the argillite filled basin. The presence of shear fabrics within the breccia may be accommodated by this model provided that these rocks were only partially lithified at the time.
Cross over to the vehicle and investigate the southern end of the outcrop on the southeast side of the road. Here, a narrow zone of sandstone breccia dips steeply through marble. One of the contacts is sheared indicating high angle faulting. Is there evidence for displacement sense?
[Note: if time permits an outcrop of marble on the nortwest side of Route 11, a few hundred yards to the south should be visited. It contains narrow subvertical veinlets of arenite at the northeast end, which provide good evidence for solution cavity infill.] " (Bursnall and Elberty, this volume).

STOP 3. Large outcrop on the west side of the road
Large outcrop on the west side of the road at the entrance to Dekalb (gentle left-hand bend)
Note: the best parking is approximately 100 yards to the south along a disused section of Route 812, opposite an Amish farm.
STOP 3. (Stop 9 in Figure I)
This outcrop possesses a newly exposed surface resulting from road-widening and contains a number of irregular sandstone bodies within well-layered Grenvillian marble.
A number of sub-vertical arenaceous zones, varying in width from less than one to greater than ten feet in width occur throughout the outcrop. In the largest of these fragmentation and "stoping" of the marble wall rock is evident but relatively few areas exhibit "permissive veining" relationships - where separated marble fragments could be pieced together in their pre-fragmentation configuration. In places, it is possible that injection of sand could have occurred from below. In addition to marble, abundant angular quartzarenite fragments similar to the foliated quartzite of Stop 4 are present.

STOP 4. Deformed quartzarenites of possible Grenville age
Where this road curves sharply to the left, continue and park on the right. Stop 4 is in the woods on the right (west).
STOP 4. Deformed quartzarenites of possible Grenville age (Stop 10 on Figure 1). Outcrops of conglomerate and foliated quartz arenite occur 75 yards into the woods (stay close to an old fence on the left until these outcrops are visible). These rocks were thought by Bloomer (1965, 1967) to belong to an infolded sequence within the Precambrian gneisses and to have been affected by probably the latest stages of Grenvillian deformation. Foliated and folded metaquartzite (best seen on the top of the ridge) is petrographically very similar to clasts at the previous stop and at Stop 1. Fold style here, however, and the nature of the conglomerate (at the base of this outcrop), suggests that these rocks may not have experienced the full Grenvillian deformation sequence but could represent a post-Grenville, pre-Potsdam, depositional period.

It includes a quarry on the east side of the road

STOP 5. et seq. (Stop 11 on Figure 1)
The section referred to above extends from the northern part of Dekalb village to the Oswegatchie bridge near Kendrew Corners (at 3.25 miles from the junction of Routes 812 and 17). It includes a quarry on the east side of the road (at 0.8 mi.) and conglomerates exposed on the Oswegatchie River at Coopers Falls (at 1.3 mi.). To reach the falls ask permission at the house opposite the intersection of the Old Canton Road and follow the track that passes the house to the south. For additional description of a part of this section see Trip A3, Stop 2 in this volume.

B3: SEDIMENTOLOGY AND DIAGENESIS OF THE POTSDAM SANDSTONE AND THERESA FORMATION, SOUTHWESTERN ST. LAWRENCE VALLEY
BRUCE W. SELLECK
Colgate University
Hamilton, NY 13346
The lower Paleozoic strata in the southwestern St. Lawrence Valley consist of the Late Cambrian-Early Ordovician Potsdam Sandstone, Theresa Formation and Odgensburg Dolostone. This sequence totals approximately 120 meters in thickness, and is the age equivalent of the considerably thicker passive margin carbonate sequence of eastern New York and western Vermont. In the area of this field trip, the lower Paleozoic sequence is well-exposed along the St. Lawrence River from the vicinity of Ogdensburg to Alexandria Bay, New York. In this area glacial sedimentary cover is thin or absent, and outcrop exposures are common in streams tributary to the St. Lawrence, and as roadcuts. The contact between the basal Potsdam Sandstone and the Late Proterozoic metamorphic and igneous rocks of the Grenville province is well-exposed in the area. The so-called Frontenac Axis is a topographic high in the Grenville rocks, and trends NNW-SSE. Regionally, Paleozoic strata dip gently to the ENE to the east of the Frontenac Axis and to the WSW to the west. The Medial Ordovician Black River Group overlies the Theresa Formation to the southwest of the area of this field trip. To the north and east Early Medial Ordovician Chazy Group strata overlie the Ogdensburg Dolostone and its equivalents.

B3: SEDIMENTOLOGY AND DIAGENESIS OF THE POTSDAM SANDSTONE AND THERESA FORMATION, SOUTHWESTERN ST. LAWRENCE VALLEY

STOP 1. Upper portion of the Theresa Formation.
Roadcuts on both sides of Route 37 expose tidal flat facies of the upper portion of the Theresa Formation. The basal beds here consist of sandy dolostone with irregular voids containing authigenic dolomite, calcite, quartz, barite and sulfides. Other lithofacies present here include laminated silty dolostones, burrowed dolomitic sandstones and cross-laminated sandstones exhibiting well-developed bipolar cross-sets.

STOP 2. Middle portion of the Theresa Formation
The roadcuts at this stop expose the middle portion of the Theresa Formation. The rhythmic interbedding of yellow-white cross-laminated sandstones and darker, burrowed dolomitic sandstones is typical of this portion of the Theresa Formation. The burrowed units are often capped by a few centimeters oflaminated dolostone. The cross-laminated sandstones are interpreted as low tidal flat deposits, the burrowed dolomitic sandstones as upper intertidal, capped by algal-stromatolitic carbonate mud. These sequences are tidal flat cycles, and their origin may reflect both high-order sealevel change and tidal flat progradation that produced slight but sudden deepening followed by shallowing due to progradation.
Note the apparent soft-sediment deformation represented by the intraformational folds near the northeast end of the outcrops. Note also the more general low-amplitude folding and the high-angle faults.

STOP 3. Contact between Potsdam and Theresa fms.
The contact between the uppermost Potsdam Sandstone and basal Theresa Formation is exposed on the south side of Route 12 near the southwest end of the outcrop. The contact is marked by the change in color (potsdam = white-grey-yellow; Theresa = grey-brown), the abrupt increase in carbonate content in the basal Theresa Formation, and the change in bedding thickness from the thick to massive beds of the Potsdam to the thin beds of the basal Theresa. The lower Theresa in this area consist of2-10 cm. beds of plane-laminated or ripple cross-laminated fine sandstones/siltstones that are capped by calcareous and dolomitic fine sandstones/siltstones. Escape burrows that traverse the laminated beds record attempts of organisms to return to the sediment surface following a sudden influx of sediment. The environment of the lower Theresa is interpreted as a subtidal, near wave base shelf lagoon setting characterized by sporadic sediment influx and physical disturbance of the bottom (storms). These events produced laminated and cross-laminated sheets of sand and silt, the tops of which were subsequently colonized by organisms, producing the bioturbated tops on each bed.
The upper Potsdam Sandstone at this stop consists of burrowed calcareous sandstones and laminated and cross-laminated sandstones that generally resemble the middle portion of the Theresa Formation seen at the last stop. The trace fossil Diplocraterion is common in the burrowed units, and a alternating low tidal flat - high tidal flat environment is envision for these facies. Fragments of the brachiopod Lingulepis are common in the upper Potsdam and lower Theresa at this stop. The lower Theresa here also contains scattered pebbles and cobbles of quartzite that were clearly derived from a Proterozoic basement knob exposed approximately 300 meters south of this outcrop.

STOP 3a. Replicates last stop
This stop replicates the sequence observed at our last stop, and we will only stay a short time to examine the features of the upper Potsdam Sandstone, which are somewhat better exposed here. Very well-preserved examples of Diplocraterion are present in the upper Potsdam on the southeast side of the outcrop.
Note the outcrop of Proterozoic basement immediately to the southwest along Route 12.

STOP 4. Contact between lower and upper Potsdam Sandstone
The contact between the lower and upper portions of the Potsdam Sandstone is exposed in the roadcut on the southwest side of Route 12. The lower section of the outcrop consists of medium-bedded, cross-laminated, medium-grained sandstones typical of the lower Potsdam. The upper, massive calcareous sandstone bed is highly burrowed, and is the base of the upper Potsdam. This facies of the lower Potsdam is interpreted as a shallow, wave and tidal current dominated shelf.
The contact between the lower and upper Potsdam represents a depositional hiatus of some duration. Networks of vertically-oriented cracks, brecciated sandstone and kaolinite-cemented concretions are common along this horizon, which is widely traceable throughout the St. Lawrence Lowlands, and clearly represents a sealevel lowstand. As noted in the text, the lower Potsdam may be Dresbachian, based upon the occurrence of Climactichnites, whereas the upper Potsdam is Tremadocian, suggesting that a portion of the upper Cambrian is absent due to non-deposition, or erosion, prior to deposition of the upper Potsdam.

STOP 5. Proterozoic/Potsdam unconformity
The unconformity between the basal Potsdam Sandstone and underlying Proterozoic gneisses is exposed in the roadcut on the southeast side of Route 12. The time interval represented by this contact is some 600 million years. The basal sandstones here exhibit large-scale low-angle planar-tabular cross-bedding, and are devoid of fossils. The depositional setting for this facies is problematic, although shallow marine tidal inlet, shoreface, and perhaps even aeolian dune environments are possible facies models.
Considerable variation in color pattern is evident in the lower Potsdam here, with the basal meter or so consisting of white to light grey sandstone, and the remainder of the outcrop showing pink, red, orange and salmon colors often seen in the Potsdam used as building stone. The colors here are due to finely crystalline hematite, goethite and anatase (=leucoxene) which form pigments around the detrital grains and within secondary quartz and illite cements. The iron and titanium for these pigments were derived from the breakdown of detrital magnetite and ilmenite grains in the original sediment. Paleomagnetic studies at this outcrop suggest that the iron-bearing minerals were precipitated in late Paleozoic time. The white sandstones at the base of the Potsdam contain no hematite or anatase, although limonite-goethite halos of relatively recent origin are developed around some magnetite grains.
Note the alteration of the underlying gneisses immediately beneath the Potsdam. The alteration assemblage here consists of illite, Fe-chlorite (or berthierine), siderite and quartz.

STOP 6. Typical lower Potsdam Sandstone
The roadcut on the southeast side of Route 12 exposes typical lower Potsdam Sandstone. Plane-bedded medium- and fine-grained sandstones underlie and overlie a one meter thick bed of cross-bedded medium sandstone. The dominant cross-bed dip direction is SSW. Above the thick cross-bedded unit small-scale cross-strata dip to NNE. As with many exposures of the lower Potsdam, the environment of deposition is difficult to assign, Although the flatbedded sandstones lack trace or body fossils, a shallow marine environment is suggested by the continuity of individual beds, the lack of upward fining or coarsening trends, and the lack of channel form geometry. However, definitive primary structures are absent. The thick cross-bedded unit was produced by a bedform of perhaps two or three meters in amplitude. Stoss-side erosion beveled the upper portion of the structure as it migrated, leaving behind a scoured lag deposit of granules at the updip termination of the cross-strata. A structure of this size and geometry could be produced by tidal currents or by wind during a period of emergence.

STOP 7. Proterozoic/Potsdam unconformity
The unconformity between the basal Potsdam Sandstone and Proterozoic gneisses is again exposed in these large roadcuts on both sides of Route 12. The dominant facies here is typical of the lower portion of the Potsdam, Flat-stratified medium- and fine-grained sandstones are interrupted by 0.2 to 1.0 meter thick sets of cross-strata, The lack of trace and body fossils again makes assignment of a depositional environment somewhat difficult.
Note the altered gneiss immediately beneath the contact. illite, Fe-chlorite, and siderite form the alteration assemblage. The sandstones immediately above the contact contain abundant authigenic illite, which has been K-Ar dated at 355-360 million years.

STOP 8. Conglomerates in the Potsdam formation
These long roadcuts on Interstate Route 81 expose a sequence of conglomerates and pebble-cobble sandstones in the Potsdam Sandstone. The quartzite cobbles in these exposures were derived from a basement quartzite ridge immediately to the south. At least some of the conglomerate beds here were emplaced by mass flow mechanisms, perhaps as sandy debris flows. Wave reworking of the tops of mass flow beds indicates that the sands and gravel were deposited in a marine setting. Near the top of the exposure the contact between the lower and upper Potsdam is present, and burrowed calcareous sandstones succeed the conglomeratic facies.

B4: SOME CLASSIC MINERAL COLLECTING SITES IN ST. LAWRENCE COUNTY
MICHAEL A. WHITTON
St. Lawrence County Rock and Mineral Club/
Geology Department
Canton, NY 13617
SCHUYLER ALVERSON
St. Lawrence County Rock and Mineral Club
P. O. Box 112
Rensselaer Falls, NY 13680
Introduction
The St. Lawrence County Rock and Mineral Club is a local organization who meets once a month and organizes collecting field trips as well as trips to rock and mineral shows. We have members from as far away as New Hampshire, Ohio and Canada. All meetings and trips are open to the public. It is our pleasure to welcome you to Canton and to lead you on this field trip of classic mineral localities in St. Lawrence County.
If you would like more information about our club for attending some of our meetings or trips, you may write to our club president Gary Stacy, 148 Rowley St., Gouverneur, NY 13642, vice-president Michael Whitton, 24 Miner St., Apt. 1, Canton, NY 13617, or Schuyler Alverson at the above address. Michael will be along on this trip as one of the principal guides. He will be happy to take a business card or take down your name and address to include you in the club's next newsletter.
We will be departing Canton, from St. Lawrence University at 8:30 AM on Sunday, September 26. Our first stop will be at Benson Mines in Star Lake. At one time, this was the largest open pit magnetite mine in the world. Our second stop will be in West Pierrepont at a tremolite locality. Our last stop will be the world famous Powers' Tourmaline Locality in Pierrepont. This site has been known for over 100 years since George Kunz wrote about it in 1892. We will learn more about each stop later. At the end of this road log will be a list of suggested readings for these stops if you would like to find more information about them.
We will be eating en route to our second stop to save time. We will spend a good deal of the morning travelling to Star Lake and back. You may eat at any time you wish, but we want to be sure to have everyone back to Canton on time so that they will not miss their rides or their scheduled time of departure. The map on the next to last page of this trip log shows our route and the stop locations.

B4: SOME CLASSIC MINERAL COLLECTING SITES IN ST. LAWRENCE COUNTY
Michael A. Whitton and Schuyler Alverson

Climb up Waterman Hill toward Degrasse.
There will be a radio tower in a field on the right on top of the hill. Notice the vista over Canton behind you.
Michael A. Whitton and Schuyler Alverson

This intersection is known as the Turnpike Crossing.
If you'll notice the tavern on the corner you will understand why.
Michael A. Whitton and Schuyler Alverson

STOP 1. J & L STEEL CORP. BENSON MINES. STAR LAKE. NY
History of the Mines The ores were first discovered in 1812 when a military road was being built in the region. It became known as the Chaumont Ore Bed. In 1883 the Magnetic Iron Ore Co. was formed. Byron D. Benson, a large land owner in southern St. Lawrence County sells the company the mineral rights on 2,201 acres of the Brodie Tract in the town of Pitcairn. In 1886, a railroad is started from Carthage to Jayville in the town of Pitcairn and additional mineral rights on 40,000 acres in the southern part of the county are obtained by the Magnetic Iron Ore Co.
In 1887 and 1888, the company purchased minerals rights for magnetite iron ore on Vrooman Ridge in the Town of Fine and all the mineral rights (9,185 acres) in the southeast comer of Chaumont Township (later part of Clifton Township) including the Chaumont Ore Bed. In 1888-89, work was done on the Jayville mines in the town of Pitcairn. From 1889-93 the Magnetic Iron Ore Co. shipped 150,000 tons of high grade concentrates (magnetite iron ore) to Pennsylvania.
In 1906, Benson Mines Company formed and leased Benson Mines (Chaumont Ore Bed). From 1907-1919, sporadic mining occurred at Benson Mines and in 1922 the Benson Mines Co. gave up its lease and sold its plant to the Magnetic Iron Ore Co., owner of the mineral rights.
Later in 1922, the Benson Iron Co. Inc. was formed, but did not do much mining. In 1941, Jone & Laughlin Ore Co. leased Benson Mines and built a $7,000,000 mill and upgrade of the mine. In 1946, the Benson Iron Co. Inc. and Magnetic Iron Ore Co. (both belonged to the Benson family) consolidated to form the Benson Iron Ore Corporation, and by 1950, it was the largest open pit magnetite iron ore mine in the world.
In 1978 Benson Mines shut down. The St. Lawrence County Development Corporation tried to find a buyer or lessee without success. Lumbering is the only thing going on in the mine area now that is bringing in any money, but just barely enough to pay the taxes. Of the 3,200 acres now owned by the company, only 1,200 are cut in a 15 year cycle to that allows for replenishment. There is some sale of waste rock, but the income from this is negligible. The mine used to employ 1,000 people and pump 2,000,000 gallons of water a day .
Geology The Benson Mines ore body is not of simple origin. Sillimanite gneiss, metagabbro and pegmatitic units are located throughout the pits. Small, localized fault zones rich in secondary mineralization provide the areas of greatest interest to the crystal collector.
Minerals The primary ores mined here are magnetite and martite. Samples of each abound. The sillimanite crystals from here are unparalleled in their size. The sunstone, relatively common in the pegmatitic zones, may be fashioned into cabochon and used to make attractive jewelry. Probably the most desired species from this mine is the dark green fluorite cubes, found about 30 years ago in a fracture zone and associated with various other secondary minerals. These, needless to say, are only rarely found. The following minerals can usually be collected, many in crystal form: aragonite, azurite, bornite, calcite, chalcopyrite, chlorite, gamet, hematite, hornblende, magnetite, malachite, martite, microchne, molybdenite, muscovite, pyrite, quartz, sillimanite, sunstone, tourmaline, and others.
The tools that will be most helpful here are a crack hammer, chisel and small pick. Be sure to bring something (sample bags, boxes) to store your specimens in on the trip . Collecting is by clubs or groups only. Permission may be obtained and arrangements made by writing in advance. The person to talk to, his address and phone numbers are listed here. He will send you a release form for everyone to sign and return before going to the mine. Please respect the common courtesies expected of you.
David H. Ackerman
Benson Mines, Inc.
100 Bay Street
Glens Falls, New York 12801

STOP 2. TREMOLITE LOCALITY. WEST PIERREPONT. NY
History of the Site This site has also been known for many years. It was discovered by prospectors looking for iron ore. Ours was one of the first rock and mineral clubs to visit the site in 1965; Originally, the amphiboles were called actinolite. However, Dr. George Robinson identified them as tremolites by electron probe.
Geology Tremolite-actinolite crystals are commonly found in the calcium silicate rocks associated with the county's Grenville Marble deposits. The rock here appears to be a tremolite-quartz schist, with varying amounts of calcite, diopside and pyrite. A large body of leucogranitic rock nearby, if representing an igneous intrusion, may have provided the necessary physiochemical conditions to recrystallize the adjacent sediments.
Minerals Doubly terminated crystals of tremolite-actinolite occur in pockets and fissures throughout the outcrop. Other nearby outcrops have furnished dravite, diopside, pyrite and quartz crystals.
Notes The best crystals are in the cracks and crevasses in the ledges. Hammers, chisels, crowbar and small digging utensils will prove useful.

STOP 3. POWERS' FARM. PIERREPONT. NY
The collecting site is just a short hike along the brook. Stay on the farm lane until you come to a path. Turn left onto the path and twenty-five yards or so ahead is the collecting area.
History of the Site As stated above, George Kunz wrote about this locality in 1892. It was known to collectors for some years before that. It was originally the Ryland Clary Farm. An aggressive mineral collector by the name of Charles D. Nims would drive his horse and wagon to the site from Canton where he worked for the railroad for 10 years. He would remove baskets full of crystals.
Around 1910, Bower Powers, Sr. bought the land. In 1921, William Agar wrote about the occurrence. Just prior to 1962 the top of the hill had been bulldozed. In 1993, due to littering, people sneaking in, burning fires and digging on the hillside next to the stream, Bower Powers, Jr. closed the site to individuals. It is still possible to arrange in advance club or group trips as long as you abide by the rules. There are still many nice crystals to be found.
Geology The geology of this PreCambrian Grenville site is very complex. The interesting minerals occur in veins and along contacts between the Grenville marble and other metamorphic rocks including a mica-tourmaline-quartz schist, an amphibolite, and other rocks locally rich in pyroxene or scapolite. Additional evidence of an origin through recrystallization is provided by the frequent presence of uralite, a pseudomorph of actinolite after diopside. The field relationships are buried by overburden . The mineral paragenesis is complicated and not worked out.
Minerals The uvite tourmaline crystals found here are indeed world famous. They contain a relatively high percentage of iron. These dark, magnesian tourmalines are typified by their lack of prismatic striations and short c axes. Figure 1 below illustrates the most commonly encountered forms: trigonal prism (m), ditrigonal prism (a), rhombohedra (e) and (r), basal pedion (c), and trigonal pyramids (0). Other minerals to be found here in excellent representations include: uralite, rennselaerite, diopside, pyrite, pyrrhotite, quartz, apatite, micas, chlorite, calcite, actinolite, titanite and scapolite.
Notes Although small single crystals may be found in the soil, the better specimens lie deeper and occur most often in pockets and seams in the solid tourmaline-quartz rock, especially where it is in contact with the calcite. Often, good specimens can be obtained by removing the calcite from the matrix rock with dilute hydrochloric acid.
Useful tools for this location include shovels, crowbars, sledge hammers, wedges, and other heavy tools will be needed to reach the deeper crystal bearing areas, but hand tools will also be useful.