NYSGA 1971.kml

NYSGA 1971
GEOLOGICAL STUDIES OFTHE NORTHWEST ADIRONDACKS REGION
FIELD TRIP GUIDE BOOK
THE NEW YORK STATE GEOLOGICAL ASSOCIATION
GEOLOGICAL STUDIES OF THE NORTHWEST ADIRONDACKS REGION
Field Trip Guidebook
43rd Annual Meeting
New York State Geological Association
BRADFORD B. VAN DIVER
Editor
Department of Geological Sciences
State University of New York
College at Potsdam, New York
13676
Published by the New York State Geological Association. Additional copies available from the Permanent Secretary, Dr. Philip C. Hewitt, Chairman, Department of Geology and Earth Science, State University of New York, College at Brockport, New York 14420.
PREFACE
On behalf of the Department of Geological Sciences of the State University of New York, College at Potsdam. I extend a most cordial welcome to all participants in the 43rd annual meeting of the New York State Geological Association.
The area to be covered by the six field trips of this guidebook lies in the northwestern part of New York State approximately enclosed by the St. Lawrence River and a line from Alexandria Bay to Gouverneur to Edwards to South Colton to Massena. The area lies entirely within St. Lawrence County with the exception of a small portion of Jefferson County . Regional physiographic and tectonic location is shown in Figure 1 of this Preface. Field trips are principally in the Adirondack Lowlands, the St. Lawrence Lowland and the Frontenac Axis. Major observable rock assemblages of the area are shown in the form of a generalized stratigraphic column in Figure 2. The column may help to orient the visitor to the Northwest Adirondack region.

A: SOME ASPECTS OF GRENVILLE GEOLOGY AND THE PRECAMBRIAN/PALEOZOIC UNCONFORMITY, NW ADIRONDACKS, NEW YORK
James D. Carl and Bradford B. Van Diver
State university of New York
College at Potsdam, New York
ABSTRACT
This field trip will cover some of the outstanding characteristics of Grenville geology in the Lowlands of the Northwest Adirondacks, with emphasis on both small and large-scale structures. Trip stops will be as follows : 1) "The Snake" roadcut near Canton, a plastically folded, weakly foliated marble with a thin, persistent, similarly folded layer composed chiefly of microcline; 2) The Rock Island roadcut near Gouverneur, which exposes cavity fillings of Potsdam Sandstone in Grenville marble, a trachytic(?) amygdaloidal dike intruding the marble, complex brecciation in gneisses and schists, numerous shear zones, and pyritic mineralization; 3) and 4) The Hyde "phacolith" near Brasie Corners where the relationship between minor and major structures will be stressed, and the controversial question of phacolith origin will be discussed; 5) The Hailesboro roadcut, exposing plastically deformed marble containing gabbroic blocks apparently derived from dikes; 6) The Poplar Hill migmatite roadcut in quartz-biotite-oligoclase gneiss, one of the most extensive metasedimentary rock types in the Grenville of this region; and 7) The Edwards roadcut, a well-known mineral collecting site for diopside, calcite, phlogopite, K-feldspar and apatite .

STOP 1. The "Snake"
(Figs. 1,2,3)-Large marble roadcut on new section of highway 11 about four miles southwest of Canton. This stop illustrates a remarkable example of the plastic deformation so common in the Grenville marbles. The bulk of the roadcut is coarse-grained calcite marble with minor diopside, tremolite, muscovite and quartz veins. The "Snake" shown in Fig. 3, is a nearly continuous thin band, generally less than six inches across, which traverses about half the length of the east side of the cut, and describes numerous sinuous folds. The snake is more segmented at the northern end and a good example of a refold can be seen. Compositional banding in the marble near the Snake is folded similarly with the Snake. Mineralogically, the Snake consists of microcline with minor sphene, calcite, biotite, and opaque. It is framed by a darker border zone consisting of calcite with abundant diopside, and minor sphene, biotite, opaque, quartz, actinolite, and tourmaline.
The writers believe the Snake and adjacent compositional bands represent original bedding. The Snake itself apparently derives from a thin but persistent bed of clay, such as an illite-chlorite mixture. Metamorphic reconstitution fixed the clay-derived potassium in microcline. The symmetrically distributed diopside marginal to the Snake indicates outward migration of SiO and Mg, and reaction with calcite to produce the diopside.

STOP 2. Rock Island Roadcut
Located about three miles north of Gouverneur on the Rock Island Road just south of the Oswegatchie River. Cut exposes cavity fillings of Potsdam sandstone in Grenville marble; structurally and stratigraphically complex, dravite-rich Precambrian rocks; numerous shear zones; an amygdaloidal trachyte dike, and pyritic mineralization.
The following are considered by the authors as evidence for cavity filling of Potsdam sand in marble at south end of cut, and smaller sandstone pockets in other parts of the cut:
1) Outcrop pattern (Fig. 4, 7). The quartzites here identified as outliers of the Potsdam Sandstone form irregular outcrop patterns which bear no consi stent relationship to Precambrian structure. They have survived erosional stripping only where they fill deep solution pockets in the marbles.
2) Bedding attitudes (Figs. 4, 5). Gentle, inward-directed dips unrelated to compositional layering in the marble, which is generally steeply dipping and, in part, plastically folded. The inward-direction of dips is attributed
to compaction and slump. Cross-bedding is also present but not extensive.
3) Contacts (Figs. 5, 6, 7). Contacts with the marble are irregular and in part, dip steeply into the marble. They are characterized by breccias containing angular marble clasts derived by natural block caving of the marble by the contact, less conspicious clasts of quartzites, schists, gneisses, and alaskites derived from Grenville lithologies (probably nearby), and some autoclastic fragments of Potsdam Sandstone. The large marble block shown in Fig. 6 appears to be a joint block which has fallen only a short distance into the sand. Release joints in the marble are sub-parallel to the contact on the other (western) side of the cut (Fig. 5). The matrix as a whole is poorly sorted quartz sand with extensive iron staining that diminishes away from the contact. Pyrite is also abundant in the quartzite near the contact, and it occurs sporadically throughout the roadcut in the marbles and in shear zones in various other rock types. Bedding is obscure near the contact at the main exposure at the south end of the cut, but becomes well-defined 20 to 30 feet into the quartzite. The quartzite also becomes cleaner and better sorted away from the ccntact. On the east side of the cut (Fig. 6, sample 6) the upper part of the quartzite near the contact appears to be a reworked regolith with weathered fragments of all kinds, a dirty appearance, and many voids. Thin quartzite seams occur within the main marble and in marble clasts.
4) Petrography. The cleaner, axial portion of the large quartzite body consists of moderately well-sorted quartzose sand with well-rounded, overgrown grains, with the overgrowths commonly iron-stained. A very common minor accessory, dravite, is rounded, often fractured, and similar to the dravite found in the numerous Grenville lithologies at the north end of the cut. It probably has been derived from them or from similar rocks. The sand becomes poorly sorted near the marble contact, more iron-stained, locally pyrite-rich, and contains many fragments of Grenville rocks with crystalloblastic dravite. Calcite is a common cement for sparse, widely-spaced sand grains near the marble contact (samples 4 and 5. Fig. 6). These grains have little or no overgrowth and are partly resorbed. Such features suggest a pH fluctuation at the time of deposition or cementation of the quartzite, leading to alternate solution and deposition of calcite and quartz.
5) Conical, cylindrical or bowl-shaped structures in the quartzite. These are found in many exposures of Potsdam Sandstone north and south of the St. Lawrence River. In the Rock Island roadcut, several are exposed on the upper surface of the large quartzite body, although they are not as well defined as in some areas of northern New York (Fig. 7). It is now generally agreed that these are slump structures formed when unconsolidated sand dropped into solution cavities in the underlying marble (Dietrich, 1953).
We conclude that the large quartzite body exposed in the Rock Island roadcut, and the smaller bodies of similar lithology at stations 3 and 12 (Fig. 5) are remnants of Potsdam Sandstone. The sand was deposited in solution cavities in marble developed during erosion of the Precambrian metamorphic terrain. Marble blocks collapsed and mingled with the unconsolidated sand, and sand filtered into joint seams and smaller solutional voids, some of which appear to be post-depositional. Post-depositional solution of the marble underlying the large quartzite body probably accounts for the fairly steep (30°) inward dip of the bedding.
There has long been controversy over the origin of the many isolated quartzite bodies which occur in the Grenville complex of northern New York. The question is whether they are outliers of Cambrian Potsdam Sandstone or part of the Grenville complex itself. Certainly some are part of the Grenville, or Pre-Grenville for that matter. But the mapping of Potsdam outliers as Grenville lithologies may lead to great confusion, and the distinction is therefore a very important one. Here are some observations summarized by J. S. Brown (1967) that characterize the Potsdam Sandstone of this region.
1) The number of recognized Potsdam remnants in New York is inversely proportional to the distance from the St. Lawrence River and to the depth of the tributary valley in which the remnant is found (Fig. 2 of Trip B). The land surface is higher and the tributary valleys are deeper progressively away from the St. Lawrence River, leading to the conclusion that the Paleozoic cover has been more efficiently removed in that direction. Nearer the river, the outliers merge into large sheets covering both valleys and uplands.
2) Potsdam sandstone which overlies gneiss or granite is commonly flat-lying, white and lightly cemented. Where it overlies marble it is much more variable in attitude, color and particle size. It is generally agreed that the pre-Potsdam surface was a near-perfect peneplain where developed on gneiss, (Fig. 3,4,5, of Trip B), but was an irregular and lower surface where developed on marble.
3) Slump structures, sandstone dikes, and cavity fillings are common in Potsdam Sandstone resting on marble. These features apparently represent post-depositional collapse of sand into underlying sinkholes prior to silicification (Dietrich 1953).
4) Bedding in the Potsdam generally truncates structures of the underlying Grenville rocks.
5) Sedimentary textures and structures are generally well-preserved because they postdate the Grenville orogeny. Metamorphic minerals in some outliers may be either, a) resistant detritals, or b) residues of solution
derived from the underlying marble.
R. O. Bloomer (1965) mapped quartzite bodies in the DeKalb area which he considers to be part of the Grenville complex. His primary evidence is that they protrude down into the marbles in apparent concordant structural relationship, and contain apparently crystalloblastic dravite, phlogopite, K-feldspar, tremolite, apatite, diopside, and talc which are also found in the enclosing metamorphic rocks. The massive bodies of this quartzite, however, are not recrystallized and retain sedimentary textures. Preservation of original texture is attributed to differences in composition and competency. The flowage of adjacent rocks around the quartzite during the Grenville Orogeny was such to cushion the relatively rigid quartzites and to prevent extensive recrystallization.
Trachyte(?) Dike (Fig. 5, Station 1O) -A dark green dike about 5 feet thick intrudes the marble in the central part of the roadcut. Thin sections were cut from seven samples located across the contact as shown in Fig. 5. Texturally the rock is fine grained, felted, and porphyritic. It is, however, almost entirely chloritized and zeolitized so that the original mineralogy cannot be determined. Phenocrysts are lath-shaped, euhedral, and the pseudomorphously preserved form and twinning is suggestive of sanidine. The rock is arnygdaloidal, with amygdules primarily filled with chlorite. Color index ranges from about 5 to 25.
There is very little evidence of contact metamorphism, but there is a fine-grained, light green chill zone about one centimeter wide in places along the margins of the dike. Microscopic calcite veins are present in the dike and microscopic quartz veins occur in calcite adjacent to the contact. The distribution of tremolite, which is found in small quantities throughout the marble, appears unrelated to dike emplacement. In some parts of the contact there is a one-centimeter zone in which intrusive and marble are intimately interlayered parallel to the contact with numerous feather fractures in the dike material filled with calcite.
The dike clearly postdates the Grenville metamorphism. It was intruded in a rather viscous condition and the amygdaloidal character indicates a loss of volatile content at shallow depths of emplacement. Extensive hydrothermal alteration is indicated by chlorite and zeolite.
Metamorphic complex at north end of cut (Fig. 5, stations 6-9, 13) Because of its extreme complexity, this section of Fig. 5 is presented in a lithologically schematic manner. The exposure in general, consists of rather dark-colored,grey to purplish-brown rocks with a confusion of breccias, quartzites, gneisses, marble, albitite, a (Na) scapolitic rock, tremolite schist, and perhaps other lithologies, with northeasterly dipping foliation. In addition, the section is cut by numerous shear zones also dipping northeasterly. Additional shear zones are exposed at various localities up and down the river from here (Fig. 4). Fine-grained idioblastic dravite and some schorl(?), in measured amounts up to 25', is common to all of the rocks examined in thin section. Two breccia sections examined by the authors contain dravite-rich, angular clasts in a murky, highly oxidized crushed-rock matrix without dravite, indicating post-metamorphic brecciation.
The breccia problem here and elsewhere along the Oswegatchie River to the northeast and southwest, however, is not so simple. The writers are indebted to H. M. Bannerman (personal communication) for the following complex analysis.
Dr. Bannerman believes there are several types and several ages of breccias, in which some of the younger breccias appear to be superimposed upon the older.
"Many of the breccias exposed along the river in this part of the area appear to be autoclastic. The fragments in them are sharply angular and mineralogically composed of material similar to that of the matrix. Breccias of this kind are characteristically developed in, and in large measure restricted to the fine grained, dravite-bearing purplish-brown feldspar gneiss and its associated quartzites. In lateral distribution these particular breccias tend to parallel fold structures in the Grenville complex, and the brecciation is commonly accentuated along formational boundaries. Neither the mode nor the time of origin of these breccias has been precisely fixed. Conceivably they may not all have been formed in the same way or at the same time. They seem, however, to be Precambrian for at numerous points along the river breccias of this kind have been cut and re-crushed by the post-Precambrian faulting which has so profoundly affected the Grenville structures in this part of the area. In addition to these early breccias, various members of the Grenville assemblage throughout this area, superficially bear resemblance to skims and patches of fragmental rocks which I interpret as recomposed regolith. Areawise and bulkwise this type of material does not amount to much, but when imposed upon an older breccia it is both deceptive and confusing.
Briefly stated, this material is made up of a hodge podge of angular to subrounded fragments of metamorphic rocks, similar to and presumably derived from the underlying formation. The matrix is a mixture of quartz and low to medium grade authigenic silicates, and sometimes calcite, an assemblage compositionally quite unlike the minerals found in the unaltered portions of the fragments or in the underlying, parent rock. As indicated, this type of structure is relatively uncommon, but when found it seems always to be at, or near the projected position of, the interface between the Precambrian erosion surface and the basal members of the Potsdam represented in this area. It seems reasonable, therefore, to believe that this particular type of breccia-like material represents remnants of a residual soil which had been developed on the Precambrian landscape prior to the advance of the Potsdam sea.
By far the more impressive of the breccias found in the belt along the river however, are the fault breccias that are associated with and presumably born of a system of faults which, in the vicinity of Rock Island Bridge, trend northeasterly, approximately parallel to the course of the river. The breccias associated with these faults run the gamut from huge to small jumbled blocks, embedded in a crushed matrix, to crumpled fissile schists, to gouge.
The fault system, with which these structures are associated, intersect each of the Precambrian rock units that outcrop in this part of the area. The major faulting, hence the associated breccia, is Post-Precambrian in age, though one cannot overlook the possibility that this particular zone was the scene of recurrent faulting throughout at least some of the Grenville orogeny, thus that displacements of more than one age may be represented here. But be this as it may, some of the Post-Precambrian breccia exposed in the Rock Island Bridge road cut, contain fragments of earlier formed breccia. Note, for example, the blocks of autoclastic feldspar gneiss, and thin bedded quartzite that are caught up in the shear zones exposed in the east face of the road cut, just south of the river.
Younger than any of the above mentioned types are, of course, the collapse breccias referred to in paragraph 2 of this letter. Collapse structures similar to those exposed in the Rock Island Bridge road cut are fairly common features along the margins of sandstone karst fillings all over this area. Presumably they are caused, in the main, by natural block caving, incident to solution of the marble along the walls of the sandstone, though in all likelihood this process may have been augmented by crustal readjustments following the removal of the continental glaciers.
In my judgment, therefore, the breccias along the river in the vicinity of Rock Island Bridge are the result of several different processes, imposed at widely different times, and that in some instances the current mess is the result of a recurrence of brecciation events.
And, as though this was not enough, the rock outcrops in this belt have also suffered a considerable amount of weathering subsequent to the disappearance of the glaciers. As a consequence many of the brecciated parts of the section are now heavily stained, and some are infiltrated by Pleistocene and recent sands, silts, mud, humus and what have you. All of which serves to further mask their identity, confuse the issue and make more difficult the task of unravelling the history of the breccias."

STOP 3. East central part of Hyde School Alaskite body
Near the intersection of two different directions of major folding. Amphibolite layers are isoclinally folded.
Petrography of the Hyde Alaskite Body
Preliminary petrographic studies have been made by the authors of samples collected from two east-west and two north-south traverses across the Hyde Alaskite body (Fig. 14). These are part of a sampling grid which is the basis for broader petrographic and x-ray fluorescent studies of relict stratigraphy presently in progress.
The preliminary studies indicate a fairly well-defined compositional layering which approximately follows the structure contours established independently from field data (Fig. 11). The rock types observed are the following:
Granitic Alaskite (number of samples-13)
Quartz Monzonitic Alaskitic Gneiss (3)
Granodoritic Trondhjemitic Gneiss (6)
Quartz Dioritic Trondhjemitic Gneiss (3)
Oligoclasic Gneiss (80% oligoclase) (1)
Biotite Leucodioritic Gneiss (4)
Dioritic Gneiss (1)
(Classification after Peterson, 1961)
All of these rock types, with the exception of the dioritic gneiss, are leucocratic, and distinction among them is based primarily on different proportions of a small number of principle rock-forming minerals: alkalic feldspar, plagioclase, quartz and accessory biotite and hornblende. The different proportions, however, are remarkably consistent in the samples studied as are the concomitant changes in character of the alkali feldspar and anorthite-content of the plagioclase. Of particular interest are the alaskites, trondhjemites and leucodiorites because their distribution gives the best indication of mappable compositional layering. A summary of their mineralogy follows :
Granitic Alaskite | Quartz Monz. Alaskitic Gneiss | Granodioritic Trondhjemitic Gneiss | Quartz Dioritic Trondhjemitic Gneiss | Leucodiorite
50- 70% stringy
microperthitic
or microantiperthitic
microcline
35- 40% cryptoperthitic
10- 20% cryptoperthitic
orthoclase
0-10% orthoclase,
slightly
perthitic
0-15%
2-15% plagioclase
An9-14
20-30% plagioclase
An17-25
50-70% plagioclase
An17-27
An20-29slight zoning
Note: Distinction between microcline and orthoclase is made by optical means only. Microcline is grid-twinned and has a large 2Vα Orthoclase appears untwinned in thin section and has a smaller 2Vα. Distinction by X-ray diffraction is in progress.
Mineralogical and textural differences, if correctly mapped, are suggestive of relict sedimentary stratigraphy. Other features which also point to a metasedimentary origin are the following:
1) Xenomorphic textures, an almost total lack of euhedral crystal forms
2) Replacement textures
3) Symplectites of biotite and quartz
4) Crystallization schistosity of biotite, hornblende and quartz
5) High quartz contents typical of many sediments but atypical of igneous rocks
6) Well-rounded and locally clustered zircons.

STOP 4. SW nose of Hyde School Alaskite body
The blunt, southwest-plunging nose of the Hyde School Alaskite body to observe the topographic contrast between alaskite and surrounding marble solution valley. Amphibolite layers here are ruptured and only slightly displaced, and pegmatite occurs within ruptures. A short downhill walk will show an outcrop of sillimanite-garnet gneiss marginal to the alaskite.

STOP 5. Hailesboro Roadcut
2011: The Guidebook calls this Stop 4, but maps it correctly as stop A5.
(Fig. 15)-Located on new section of Highway 58 near Hailesboro.
This cut exposes a large section of plastically folded marble with local clusters of black, predominantly rectangular, blocks of a gabbroic rock. The striking rectangularity of the blocks and their clustering, suggest that these were tabular bodies, probably dikes, which behaved in brittle fashion during deformation of the marble. The position of the blocks indicates that they were carried along with the marble and, to some extent, rotated.
Dike blocks near the marble contact consist of about 60% diopside, 20% meionitic scapolite, with about 5% each of microcline, sphene, and tremolite, and minor biotite, quartz, opaque, tourmaline and apatite. Contact with the marble is gradational with decreasing calc-silicate minerals, increasing quartz, and increasing carbonate progressing into the marble. Low-temperature alteration is very minor, and the mineral assemblages appear well adjusted to the metamorphic conditions. Cataclastic textures are almost totally absent. The reactions suggested by the mineralogy of the contact zone are :
3 Ca Al2Si2 O8 + CaCO3 → Ca4 Al6 Si6 O24 CO3
Anorthite + Calcite → Meionite
and, calcite + biotite → Microcline + diopside + CO2 + H2O
There is no plagioclase in the contact zones of the dike rocks examined, presumably because it has been completely replaced by meionite and by-products.
The observed characteristics indicate that the dike was either pre-or synmetamorphic, and there has been sufficient post-deformational recrystallization for complete mineralogical adjustment between the dike blocks and the marble.

STOP 6. Migmatitic Quartz-biotite-oligoclase Paragneiss
2011: The Guidebook calls this Stop 5, but maps it correctly as stop A6.
(Fig. 16) Located in a long roadcut through Poplar Hill on a new section of Highway 58 about one mile northwest of Fowler, New York. This cut exposes the migmatitic phase of the quartz-biotite-oligoclase paragneiss which in all its phases, comprises one of the second most abundant metasedimentary rock types in the Grenville series (second to the marble-see Fig.2). In general, the Grenville metasedimentary stratigraphic section consists approximately of 8000' of basal marble, overlain by 3000' of paragneiss, overlain by 4000' of marble with feldspathic quartzite near its top. The paragneiss has been studied in detail by Engel and Engel (1953). The exposure lies on the northwest side of the Sylvia Lake-Edwards syncline just north of a large body of Hermon-type porphyritic or porphyroblastic granitic gneiss (Brown and Engel, 1956, Fig. 1).
Description
The paragneiss here consists of a fine-grained grey-brown·gneiss with variable foliation, and with extensive lit-par-lit granitic veining. The veins vary from a few millimeters to several feet wide and those which parallel the foliation are extensively boudinaged. Transverse veins, especially thin ones, form intricate ptygmatic folds which apparently result from the combined effects of flowage, shear folding, compaction, and recrystallization. The veins are coarse-grained to pegmatitic, and white to red in color with the thicker veins commonly having white borders with red cores.
The average mineral composition of the presumably isochemical phases of this unit, here and elsewhere in northwestern New York, consists of about 40% quartz, 39% plagioclase (An25-35), 1% K-feldspar, and 17% green-brown biotite (Engel and Engel, 1953). Garnet is locally present at this outcrop, especially adjacent to granitic veins. Elsewhere the unit contains sillimanite. The veinous granite primarily consists of coarse-grained K-feldspar and quartz with variable but generally small amounts of highly-sericitized plagioclase and red-brown biotite. Replacement textures, especially of K-feldspar after green-brown biotite, are exceedingly common along vein margins.
Origin
The composition of presumed isochemical phases of the quartz-biotite-oligoclase paragneiss is closest to that of a graywacke (Engel and Engel, 1953). The formational environment of a graywacke, however, is one of minimal weathering with rapid transport and deposition, and this is anathema to the environment demanded by thick sections of thin-bedded persistent marbles and clean quartzites which lie conformably above and below the paragneiss. Shale is the more compatible sediment, but the paragneiss has an unusually high Na2O:K20 ratio (1:3) not found in normal shales
(Na2O:K2O typically about 0.4). A mode of origin suggested by Engel and Engel (1953) is one in which shale is chemically modified, either during deposition or diagenetically, so as to yield the relatively high Na-content, perhaps by interaction with salty Precambrian seawater.
Feldspathization
Presumed isochemical phases of the quartz-biotite-oligoclase paragneiss throughout the northwest Adirondacks typically lie in areas farthest from large bodies of alaskitic granite of the Hermon type (a type transitional to Hermon gneiss). Furthermore, all gradations appear to exist from the isochemical phase to veinous migmatites to Hermon gneiss to Hermon-type alaskite. The migmatitic phase exposed in the Poplar Hill roadcut characterizes the incipiently to moderately feldspathized and injected gneiss. The Hermon-type inequigranular gneiss which appears to represent a more extensively feldspathized phase, occurs in numerous large and small bodies within the paragneiss (Fig. 2). It typically contains large, often sieved, euhedral to subhedral grains of microcline.
The Hermon-type alaskitic end-member, an exposure of which may be found near Hyatt, N.Y., is relatively equigranular and directionless.
These features suggest progressive granitization of the paragneiss. Mineralogically, the progression involves a marked increase in K-feldspar, largely at the expense of biotite, and an increase in the albite-content of plagioclase without much change in plagioclase mode. Quartz also appears to decrease slightly, but not linearly.
One of the most significant chemical aspects of the progression is the change in the Na2O/K2O ratio from 1.3 to less than 1.

STOP 7. Edwards Roadcut
Brief stop if tine permits. This roadcut is well known to Mineral collectors in St. Lawrence County for green diopside, calcite of several colors, phlogopite, actinolite, apatite, molybdenite, pyrite and other sulfides and K-feldspar crystals.
This Irish green roadcut intersects one of several diopsidic marble units that are interlayered with feldspathic gneisses to the northwest of the outcrop face. These units are less than 100 feet thick with attitudes approximating N 50 E, 50 NW.
An outstanding feature here is the great quantity of green diopside, particularly in the form of coarse, well-parted crystals that extend into calcite veins. Contrast the occurrence of diopside here with that of Stop 1 southwest of Canton where the diopside is granular, disseminated within the marble, and partially a product of the reaction between marble and intrafolded silicic rock layers.
The outcrop consists chiefly of diopside except at the eastern edge of the roadcut where phlogopite-bearing marble with faint foliation can be seen. Megascopically, the diopside assumes several forms: (1) granular, green masses exclusive of marble, yet cut with calcite veinlets and with fine-grained, faintly foliated mica, (2) clusters or vein-like bladed diopside within granular diopside, and (3) large, parted crystals in the larger calcite veins typically oriented perpendicular to vein walls and surrounded more or less by gray calcite. Molybdenite, pyrite, phlogopite and apatite occur between diopside crystals. One molybdenite crystal collected here was 2 x 4 cm. in diameter and 2 mm. thick.
Diopside crystals measuring 2 feet 8 inches across in coarsely crystalline pink calcite masses were found with apatite and pyritohedral pyrite during road construction. Apatite crystals, 2 x 1/2 inches and doubly terminated with hexagonal bipyramids have also been reported in pink calcite.
Veins appear to be joint fillings by mobilized calcite accompanied by recrystallization of diopsidic host rock adjacent to the vein. Growth of crystals from the joint plane outward into the host rock is suggested in one vein. Note the vein with a sharp planar contact against granular diopsidic rock on one side (evidently the joint plane), and an irregular contact on the other side where coarse diopside crystals extend into the granular variety. In other veins, coarse diopside crystals extend only part way into the calcite matrix, and direction of growth appears to be inward toward the vein. Other diopside crystals are reported enclosed by marble with no apparent point of attachment.
Large diopside crystals show development of basal parting much better than cleavage, particularly where crystals extend into calcite matrix. Parting lamellae are generally of uniform thickness (about 2 mm) but may be wedge-shaped where crystals are bent (Fig. 17). Other crystals show lengthwise "feather" type parting, dividing the crystal into two unequal segments (Fig. 17). Broadly curved, concentrically parted segments are present in thicker diopside crystals.
Calcite is coarse, well cleaved, and shows pronounced color change from gray at vein margins in contact with diopside to pink toward the center of the vein. Gray calcite (by x-ray analysis) borders the larger diopside crystals (Fig. 17) and accentuates the margins of small veins. Bright orange calcite occurs on the hill behind the roadcut. It may occur as blotches of coarsely crystalline grains in a finer, lighter colored marble.
The hydrous minerals phlogopite and actinolite represent the more mobile, fluidized portion of vein filling. They are particularly abundant in the smaller veins or seams in granular diopside. Veins of calcite-phlogopite-pyrite-molybdenite (and other sulfides) extend outward from the larger joint fillings, and are usually devoid of diopside crystals. These veins contain phlogopite and pyrite which typically crowd the vein margins. Where the vein tapers to a thin seam, phlogopite is particularly abundant and the granular diopside host may be slightly discolored and impregnated with pyrite. Within the veins, pyrite is intergrown and often rimmed with an unidentified black metallic mineral. These smaller veins also have pink calcite cores and gray calcite margins.
Emplacement of hydrous minerals seems localized by foliation planes or tight joints. Actinolite occurs in clots or lenses, seemingly replacing the granular diopside host rock, but in crude alignment with the foliation. Or, the actinolite may occur as clots along calcite-phlogopite veinlets like knots in a rope. These clots vary from 1/2 to 2 inches in diameter and commonly consist of stubby, green, glassy actinolite crystals, phlogopite and pyrite. Coarse crystals of diopside, and perthitic K-feldspar (microcline?) occur several hundred feet northwest of the roadcut. The diopside and K-feldspar occur in aggregates enclosed by marble. Crystals often penetrate each other suggesting simultaneous growth of K-feldspar and diopside.

B: PRECAMBRIAN AND LOWER PALEOZOIC STRATIGRAPHY, NORTHWEST ST.LAWRENCE AND NORTH JEFFERSON COUNTIES, NY
by
William Kirchgasser,
The State University College at Potsdam
Potsdam, New York
and
George Theokritoff
Rutgers University
Newark, New Jersey
ABSTRACT
The field trip is designed to demonstrate general features of the lower Paleozoic sequence with emphasis on the stratigraphic relations with the Precambrian basement and environments of deposition. The strata form part of a complex upper Cambrian-Lower Ordovician transgressive sequence that blankets an erosion surface on the Precambrian of low but variable relief. Basal quartzose sandstones (Potsdam Sandstone), with local conglomerate and breccia, grade and inter-tongue seaward (eastward) through calcareous and dolomitic sandstones and sandy dolomites (Theresa and Bucks Bridge Formations) into purer dolomites in the Champlain Valley. In St. Lawrence County, the Theresa and the Bucks Bridge Formations are overlain by dolomites and sandy dolomites (Ogdensburg Dolomite). Sedimentological and paleontological features (particularly trace fossils and algal stromatolites) will be seen that document and refine the general interpretation of the various facies as shallow water shelf deposits.
The excursion is divided into Saturday and Sunday morning parts (Fig. 1). The Saturday trip begins with a brief examination of the complex flow folding in the Grenville marbles south of Canton followed by examination of outliers of Potsdam Sandstone within the marbles north of Gouverneur, in an area where there have been problems in the differentiation of Paleozoic and Precambrian quartzites and breccias. Lunch will be in a park at Alexandria Bay, overlooking the Thousand Islands; here we will discuss the influence of the Frontenac Axis on the distribution of the Paleozoic rocks.
In the afternoon, the trip continues at an excellent exposure of an angular unconformity between the Potsdam Sandstone and Precambrian metasedimentary rocks just east of Alexandria Bay. We will then proceed down the St. Lawrence valley and examine in stratigraphic succession 1). the Potsdam Sandstone and lower Theresa Formation near Chippawa Bay, 2). the Theresa Formation near Brier Hill and 3). the Ogdensburg Dolomite at Ogdensburg.
The localities to be visited on Sunday are 1). the Allens Falls Fanglomerate or "basal breccia" at Allens Falls, 2). the type exposure of the Potsdam Sandstone at Hannawa Falls and 3). the dendroid graptolite locality in the Bucks Bridge Formation near Madrid described by Berry and Theokritoff (1966).

STOP 3. Scenic View Park, Alexandria Bay, New York.
Lunch Stop; leuco-granitic (alaskitic) gneiss; Frontenac Axis.
The Frontenac Axis is a narrow southeastward extension of the Canadian Shield connecting the Laurentian Plateau with the "Lowlands" region of the Adirondack Mountains. This terrane of resistant Precambrian crystalline rocks forms the Thousand Islands where the axis is crossed by the postglacial St. Lawrence River a few miles from where the river spills out of Lake Ontario.
In the Thousand Islands area, the basement rocks are a highly folded and intensely metamorphosed complex of metamorphic rocks dominated by pink or red leucogranitic (alaskitic) gneiss (Alexandria Granite; Rockport-type granite in Canada) with white metaquartzites and a variety of layered gneisses; the sequence is broadly monoclinal, with a northwesterly dip (Wynne-Edwards, 1959, 1962, 1963).
The axis separates the lowermost Paleozoic strata of the Ottawa-St. Lawrence Lowland to the northeast from the similar but less complete succession of the Ontario Lowland to the southwest. It is difficult to document the influence of the axis on early Paleozoic sedimentation because of the scarcity of outcrop in the immediate area (Fig. 2). Numerous outliers of the Potsdam Sandstone (Nepean in Canada) and a few of the Theresa Formation indicate that the axis was covered by a westward-transgressing sea during Late Cambrian-Early Ordovician (Early Canadian) time. In the St. Lawrence Valley, the sandstones and dolomites of the Theresa-Bucks Bridge Formations (March Formation in Canada) are succeeded by the Ogdensburg Dolomite (Oxford Formation in Canada) of Medial and Late Canadian age; the Ogdensburg Dolomite is unconformably overlain by a Middle Ordovician linestone sequence of Chazyan (Rockcliff and St. Martin Formations) and Mohawkian (Ottawa Formation) age (Fisher 1968, p. 29).
West of the Frontenac Axis, the Ogdensburg Dolomite and Chazyan limestones are missing and here the limestone sequence of Mohawkian age (Black River and Trenton Groups) rests unconformably on the Theresa Formation and older rocks. The Black River and Trenton limestones were deposited in a transgressing sea that crossed the Frontenac Axis and entered the Ottawa-St. Lawrence basin from the southwest (Wilson, 1946, p. 7). There is no indication of later Paleozoic sedimentation over the axis. Any deposits that may have accumulated have since been removed by post-Ordovician erosion that has stripped the lower Paleozoic sequence away from the crest to leave a sequence of stair-like terraces and scarps.
Glacial deposits are rare and thin in the Alexandria Bay area and the Precambrian and Paleozoic rock display evidence of glacial erosion, especially on the Potsdam Sandstone. The features include glacial polishing, striae and grooves (direction to SW about parallel to the St. Lawrence River) and chatter marks (MacClintock and Stewart, 1965, p. 120).

STOP 4. Precambrian-Paleozoic angular unconformity at Alexandria Bay.
Roadcut on N. Y. 12, 2 miles east of Alexandria Bay, N.Y.
The east end of the roadcut exposes a knoll on the pre-Potsdam erosion surface formed on steeply inclined to vertical Precambrian metasedimentary rocks which are overlapped by nearly horizontal orthoquartzites of the Potsdam Sandstone (Figs. 3-5). The Precambrian rocks include medium-grained leucogranitic (alaskitic) gneiss which form resistant masses at the west and east ends of the outcrop. Between these rocks are darker layered gneisses, including red and pink leuco-quartz diorites, pink alaskitic gneiss and green and white diopsidic quartz diorites. The layered gneisses are mostly highly altered, especially in the intensely weathered zone in the first few feet below the erosion surface.
The basal Potsdam Sandstone is well bedded, medium-and thick-bedded, medium-grained, white orthoquartzite. The basal part of the sandstone sequence thins over the crest of the knoll, as the lowermost beds pinch out against the erosion surface. The quartz grains are mostly well rounded, highly spherical, and frosted and are thoroughly cemented by silica overgrowths in optical continuity with the grains, a feature for which the Potsdam Sandstone has long been noted. Cross-and horizontal laminae within the beds are defined by minor fluctuations in grain size from very fine-to coarse-grained texture and accessary mineral content. Heavy minerals are generally rare throughout the orthoquartzite facies of the Potsdam Sandstone; in this area tourmaline and zircon are the most common.
Above the basal strata the beds become more nearly horizontal and the bed thickness gradually decreases (medium-bedded). The beds include red, pink and white laminated, medium-grained orthoquartzite with conspicuous "dusty" hematite rimming the rounded quart grains. Similar, but less mature, friable, white, gray and pink, fine-to medium-grained orthoquartzites also occur which weather greenish-yellow. Tourmaline and hematite are conspicuous in these rocks, along with interstitial clay and occasional rock fragments. The red and pink "banded" sandstones continue to the top of the section. In the upper third of the section is a well defined band of large-scale, planar cross-stratified beds.
The high textural and mineralogical maturity and the absence of clasts of the Precambrian rocks in the lowermost beds suggests that the sediments described above were derived from reworking of fluvial sands (floodplain alluvium) by an encroaching sea. The detrital material carried seaward by currents accumulated on and eventually blanketed the irregular pre-Potsdam erosion surface. Sedimentary features in the sandstones (especially the laminated bedding) indicate deposition in the "low energy, littoral to nearshore environment" of the Potsdam Sandstone described by Otvos (1966); Fisher (1968, p. 16) interprets what appears to be a similar facies of the Potsdam Sandstone in the Champlain valley as, in part, the deposits of low energy outer intertidal and inner subtidal environments. The cross-stratified beds in the upper part of the section may indicate somewhat higher-energy conditions in which currents built solitary banks into shallow water just off a beach (Allen, 1963, p. 101).

STOP 5. Chippawa Bay.
Upper Potsdam Sandstone and lower Theresa Formation exposed in roadcut on N.Y. 12, 0.2 miles northeast of intersection with Pleasant Valley Road, 2.7 miles east of Chippawa Bay, New York.
Potsdam Sandstone
The Potsdam Sandstone exposed at this locality is a thin-to medium-bedded, white orthoquartzite with minor cross-stratification and ripple marks, especially in the lower part of the section (Fig. 6). Vertical U-shaped organismal burrows (Diplocraterion?) occur in Horizon 5-1 (Stop 5, Horizon 1) and are well displayed in the southeastern wall at the southwestern end of the roadcut (Fig. 8). Simple vertical burrows are also seen at this level but these are believed to be U-shaped burrows that are only partly displayed by the available section.
Close examination shows that the burrows are Spreitenbauten (Seilacher, 1967, p. 418-421) as they display laminations reflecting the shape of the terminal bend that are indicative of a shift of the tube through the sediment. Some of the burrows are infilled and the infilling can be traced into the lowest part of the burrows; the burrows appear to be entirely protrusive in vertical direction and thus reflect a response to growth of the organism rather than a response to fluctuations in the depositional rate (Seilacher, 1967, p. 418-420). The rather deep penetration of the burrows at this horizon indicates a slowing down of the rate of sedimentation.
The organism that made these burrows can be postulated as an elongate animal that depended on the development of incurrent and excurrent water movements. It was thus a suspension feeder and its burrow a protective shelter. Currents above the sediment-water interface had sufficient turbulance to transport food particles and keep them in suspension, but not enough to introduce a significant amount of sediment or cause significant erosion. Such burrows are known from modern intertidal and shallow subtidal environments as well as more off-shore areas (Seilacher, 1967; Frey, 1970), and are made by a variety of organisms : amphipod crustaceans (Seilacher, 1967, p. 414, 422), polychaete annelids (Seilacher, 1967, p. 414; Rhoades, 1967, p. 464-467; Frey, 1970, p. 512-513) and hemichordates (Frey, 1970, p. 512). Studies by Rhoades (1967) and Seilacher (1967) indicate that deep burrows are generally characteristic of intertidal environments, in which the burrows provide shelter from fluctuations in temperature, salinity and dessication at the sediment-water interface. Such conditions might account for the relatively low density of burrows and the apparent absence of other fossils in Horizon 5-1 and elsewhere in the section. It thus seems a reasonable hypothesis that the white orthoquartzite facies of the Potsdam Sqndstone in this area records a nearshore intertidal environment.
Theresa Formation.
The lower Theresa Formation in this section consists of gray and blue-gray, fine-grained, feldspathic, calcareous and dolomitic sandstone. The original sedimentary fabric of the rock has been modified to varying degrees by burrowing and general bioturbation. Remarkably well rounded, spherical, medium-and coarse-grained quartz is scattered throughout the succession. The carbonate cement, which locally approaches 50% of the rock, is predominantly calcite which appears to have largely replaced an earlier dolomite cement. Locally the detrital grains float in a matrix of sparry calcite, forming the distinctive lustrous cleavage surfaces ("sand crystals" or "crystal sandstone") noted by early workers (Cushing and others, 1910; Cushing, 1916). The quartz grains, which appear frosted in hand specimen, are etched and corroded by the calcareous cement; siliceous overgrowths similar to those which characterize the underlying Potsdam Sandstone occur where the quartz grains are concentrated.
Relatively shallow vertical and nearly vertical burrows (Skolithos) infilled with calcite-cemented quartz are well displayed in Horizon 5-5. Lenses and lamellae of comminuted inarticulate brachipod debris (Lingulepis acuminatus) are concentrated at several levels in the lowermost horizons; the best material may be collected from Horizons 5-5 and 5-6 on the north side of the roadcut. Poorly preserved discoidal gastropods and grazing trails may be seen on some bedding surfaces in Horizon 5-4.
The immaturity of these sandstones and their carbonate content and fauna indicate accumulation in a relatively uniform low energy environment (possibly subtidal), offshore from the intertidal environment suggested for the underlying white orthoquartzites of the Potsdam Sandstone.

STOP 6. Brier Hill
Roadcut along N. Y. 12, just south of turnoff to Brier Hill and Jacques-Cartier State Park. Theresa Formation.
The outcrop exposes a gently folded and faulted section in the upper part of the Theresa Formation (Fig. 7) consisting of medium-grained, white orthoquartzites alternating with gray and blue-gray, coarse-, medium-and fine-grained, calcareous and dolomitic sandstones. The white orthoquartzites are like those of the upper Potsdam Sandstone seen at Stop 5. At Horizons 6-3 and 6-7, the quartzites are riddled with dark brown mottles and elongate patches of limonite-stained quartz floating in sparry calcite cement. These features trend nearly parallel to bedding surfaces and are interpreted as infillings of burrows.
The gray calcareous and dolomitic sandstones are thoroughly bioturbated (mottled) and original sedimentary fabrics have been nearly obliterated. Cut-and-fill structure may be seen at several levels, indicating relatively strong current activity. The rock consists of a mixture of about equal amounts of coarse-, medium-and fine-grained quartz, the coarser grains being remarkably well rounded, spherical, and frosted. The grains are notably etched and corroded by the predominantly calcitic cement, but optically conformable silica overgrowths occur where quartz grains are concentrated. The calcite appears to have almost completely replaced an earlier dolomite cement and the lustrous cleavage surfaces produced by pockets of sparry calcite cement (crystal sandstone) are a distinctive feature of the rock in the field (Horizons 6-2, 6-6). Inarticulate debris, detrital feldspar and rock fragments are less conspicuous in the Theresa Formation at this locality than at Stop 5.
The relatively thorough bioturbation of the gray and blue-gray calcareous and dolomitic sandstones (Horizons 6-2, 6-4, 6-6) again suggests that the sediments accumulated in a more offshore (subtidal) environment than that of the less biogenically disturbed orthoquartzites. Moore and Scrutton (1957) and Rhoades (1967) have noted that prolonged activity of subtidal bottom communities near the sediment-water interface under conditions of relatively slow sediment accumulation results in the complete reworking of the sediment.
Cushing (1916, p. 24) reported about 140 feet of Theresa Formation in this area and Dietrich (1957, p. 706) documented the variation in lithofacies within the unit. In addition to the types described above, Dietrich reported blue-gray, sandy limestones and buff and gray, sandy, dolomitic limestones. Chadwick (1915, p. 289) introduced the name Heuvelton Sandstone for a 0 to 20 foot thick lens of white orthoquartzite lying above the Theresa mixed beds in central St. Lawrence County. Although Cushing (19l6) used the name, the presence of the unit among the white orthoquartzites in the Brier Hill area is uncertain (Dietrich, 1957, p. 105). As noted above, Berry and Theokritoff (1966) regard the Heuvelton Sandstone as a member of their extended Bucks Bridge Formation. Although the Theresa Formation (northwesternmost St. Lawrence and Jefferson Counties) and the Bucks Bridge Formation (central St. Lawrence county) of Berry and Theokritoff (1966) occupy the interval between the Potsdam Sandstone and the Ogdensburg Dolomite, their precise stratigraphic relationships have yet to be established.

STOP 7. McConville, Inc. Quarry in Ogdensburg Dolomite on the west side of Ogdensburg.
Driving east on N.Y. 37 from Morristown, N.Y. turn left at the Ogdensburg bypass and follow the sign for downtown Ogdensburg. Continue on old N.Y. 37 for 0.8 miles and turn right at the fork onto Ogden Street. Proceed for two blocks and turn right onto Madison Avenue. Park in field opposite intersection with Gates Street (0. 1 miles). Ogdensburg Dolomite.
Introduction
Cushing (1916) recognized around 140 feet of Ogdensburg Dolomite in this region and measured sections from roadcuts and quarries (now mostly overgrown) between Morristown and Ogdensburg and northward to Red Mills, New York. In spite of scattered outcrop and apparent rapid facies changes, he pieced together the composite section summarized here, beginning at the base: 1. small thickness of basal sandy beds transitional with the underlying Theresa Formation 2. thick-bedded, blue, sandy dolomites (15 ft.) and thin-bedded, gray dolomites (20 ft.) 3. alternating thick-bedded, dark blue and gray, sandy dolomites, locally with abundant but poorly preserved gastropods (especially in the lower part) and occasional thin sandstones (white orthoquartzites) and Cryptozoon layers (80 ft.) 4. thin-bedded ("flinty" ) dolomites (20 ft.). The thirty foot section exposed in the abandoned southeast part of the quarry (Fig. 12; Appendix) represents the transition between intervals 3 and 4 described above. Detailed examination reveals a remarkably varied sequence with numerous structures of sedimentological and paleoecological interest especially in light of the wealth of data now avail able on the environments and characteristics of recent shallow water carbonate sediments. Walker and LaPorte (1970, p. 931-933) provide a concise review of the literature and a summary of lithologic, paleontologic and primary structural criteria for recognition of subtidal to supratidal carbonate environments in ancient rocks. Reconstructions of paleoenvironments must of necessity follow and build upon an understanding of regional stratigraphic relations (for example, LaPorte, 1969, Walker and LaPorte, 1970, Thompson, 1970) but in the case of the Ogdensburg Dolomite (and the Theresa and Bucks Bridge Formations as well) such a stratigraphic synthesis is not available. Perhaps in the case of the Ogdensburg Dolomite attempts to analyze sedimentological and paleoecologic features of local sections will stimulate new attempts to work out the regional stratigraphy. The horizons are briefly described in the Appendix and some tentative correlations are made with Cushing's (1916) sections.
Interpretation
The combination of various features in the section suggests that the sediments accumulated in a protected (high intertidal) carbonate flat environment. Fluctuations in physical conditions are indicated by evidence of alternating flooding (influx of quartz sand, oolites, pellets, shell debris and lime mud) and subaerial exposure.
Laminated, mudcracked, carbonate muds -Thin bedded to laminated (ribbon-laminated), mudcracked, finely crystalline to aphanocrystalline carbonates characterize the tidal flat environment where lime muds are subjected to subaerial exposure; the irregular and regularly laminated horizons (e.g. 7-2, 7-5, 7-6, Fig. 9, 7-10) are believed to indicate sediment trapping by algal mats. Flooding of the tidal flat during storms or extreme tides would tend to break up the limy crust and resediment the clasts, forming intra-formational breccias (7-9, Fig. 10).
Fossils, oolites, pellets -The lenses of fossil debris, especially the small gastropods (7 8, 7-12, 7-13, 7-17, Fig. 15) and the oolites (7-11, 7-13) and pellets (7-3, 7-5) as well, represent material transported in from, more seaward environments (low intertidal to subtidal) during times of flooding. A wind-blown origin of some of the quartz is indicated by frosted grains haphazardly distributed in some beds. The paucity of fossils believed to be indigenous to the deposits and the general lack of evidence of infaunal reworking also suggest the ecologically adverse conditions of the high intertidal environment (Walker and LaPorte, 1970); Hor1zons 7-3, and 7-5, however, show evidence of bioturbation and vertical burrows occur in Horizons, 7-14 and 7-15 (Fig. 14).
Algal stromatolites -Algal stromatolites are perhaps the least equivocal evidence of intertidal and supratidal environments although they have also been reported from recent subtidal environments (Gebelein, 1969). Studies of present day algal stromatolites indicate that most active mat growth and sediment binding requires subaerial exposure whereas prolonged wetting inhibits mat growth (Logan and others, 1964). Tidal and splash water accumulating in depressions on the mat surface leads to differentiation of the laminae into discrete domes and interareas. Linkage of the lamellae in the interareas between domes is further inhibited by scour-and-fill. Changes in stromatolite morphology with growth reflect minor fluctuations in the physical environment (Logan and others, 1964). For example, the change from initial space-linked hemispheroids (Collenia structure) to digitate vertically stacked hemispheroids (Cryptozoon structure) seen in Horizon 7-12 (Figs. 11, 13) indicate a change in environment from protected intertidal to a somewhat higher energy, more exposed intertidal environment. Larger, well differentiated, club-shaped, stacked hemispheroids (Cryptozoon structure) are known from other levels within the Ogdensburg Dolomite (Fig. 16) and in present day stromatolite environments these occur on exposed intertidal headlands (Logan and others, 1964, p. 80) _
Stromatolite growth ceased at Horizon 7-12 when the laminae were flooded and blanketed with skeletal debris and other sediment carried in from offshore. The relatively fossiliferous levels in the upper part of Horizon 12 and Horizon 13 may indicate subtidal deposits, with Horizons 14 and 15 (Fig. 14) marking a withdrawal of the sea and the return of the intertidal conditions.
Early dolomitization -Penecontemporaneous or early diagenetic dolomitization of carbonate sediments is known to occur in tidal flat environments, particularly supratidal, in areas of high aridity (Illings and others, 1965; Shinn and others 1965). Magnesium-rich brines developing on or just beneath the surface in the supratidal and high intertidal envircnments percolate through and replace the original carbonate sediment. Dolomitization of the original sediment in the Ogdensburg Dolomite appears to have been complete; the minor amounts of calcite occurring at several levels is interpreted as late diagenetic void-fillings (7-17, Fig. 15). Early dolomitizatLon in the Ogdensburg Dolomite is suggested by the similarity of texture of the intraclasts in the breccias and the dolomitic crusts from which they were derived (7-9, Fig. 10).
Vugs -Calcite-and dolomite-filled vugs are particularly conspicuous in the finely crystalline and aphanocrystalline dolomite in the upper part of the section. Some of the smaller voids (7-13) resemble birdseye structures (Shinn, 1968) although many cavities are clearly the result of leaching of shell debris. Studies by Shinn (1968) of recent birdseye formation demonstrate that the more planar vugs result from dessication of exposed sediments and are thus indicative of the supratidal and also intertidal environments.
Section in Ogdensburg Dolomite. From the top:
Unit | Thickness | Description
7-17, 18 | 2' 6" | Dark gray and brown, finely crystalline dolomite with abundant small gastropods, weathering light tan. Other clasts include fine-grained, sandy dolomite, oolites and rare orthocone fragments. This horizon represents the uppermost faunal assemblage (zone 4, Hormotoma zone) described by Cushing (1916, p. 41, 48) from the upper Ogdensburg Dolomite (Fig. 15).
7-16 | 0' 4" | Light and dark brown, cross-laminated, coarse- and medium-grained, calcareous and dolomitic sandstone, weathering tan. Similar to gray sandstones of Theresa Formation seen at Stop 6.
7-15 | 1' 0" | Tan, irregularly laminated and ribbon-laminated, very finely crystalline (aphanocrystalline), sandy dolomite. Quartz grains scattered through matrix, form dark lamellae or infillings of mudcracks or burrows. The quartz is mostly coarse-grained (well rounded and spherical) but ranges down to fine-grained. The rock also displays minor cross-lamination and cut-and-fill structures, and slump bedding (Fig. 14).
7-14 | 3' 3" | Dark brown, thin-bedded and laminated, aphanocrystalline, sandy dolomite, weathering light tan. Discontinuous and wavy laminae of very fine-grained quartz and silt-sized quartz are occasionally truncated by burrow-like structures. Conspicuous large, calcite-filled vugs.
7-13 | 2' 4" | Dark gray and dark brownish-gray, finely and medium crystalline dolomite, weathering light gray. Mosaic of dolomite rhombs masks abundant oolite and shell fragments. Conspicuous lenses of shell-molds and irregular vugs (resembling birdseye structure), partially or totally filled with yellowish dolomite, on weathered surfaces.
7-12 | 1' 1" | Light gray-brown, medium crystalline dolomite forming substratum to horizon of algal stromatolites that rise 2 to 3 centimeters above the floor (Figs. 11, 13). The stromatolite layer is overlain by dark gray and brown, medium crystalline dolomite with oolites, gastropod fragments and clasts of fine -grained, sandy dolomite. Vugs filled with calcite crystals are conspicuous in lower and upper parts of the horizon.
| | Description of stromatolites: Initial space-linked hemispheroids, with close-linked hemispheroids as a microstructure in constituent laminae (Collenia structure), passing upward into discrete digitate, vertically stacked, hemispheroids with laminae of close-linked hemispheroids (Cryptozoon structure). Interareas composed of finely and medium crystalline, sandy dolomite with patches and lenses of oolite, gastropod and orthocone fragments and clasts broken from the stromatolites. The quartz is scattered throughout and is medium-to coarse- grained and remarkably well-rounded and spherical (Figs. 11, 1 3). Believed to correlate with Bed 21 of Cushing's (1916, p. 41) Pythian Home section.
7-11 | 2' 0" | Dark gray, finely crystalline, sandy dolomite. Scattered quartz mostly coarse-grained with minor amounts fine- and medium-grained. Dolomite matrix in form of rhombs masking abundant and conspicuous relic oolites.
7-10 | 1' 11" | Dark brown and tan, thin-bedded to laminated, alternating finely crystalline dolomite (dark), and very fine -to fine-grained dolomitic sandstone (light). Sandy laminae are wavy and discontinuous.
7-9 | 0' 9" | Light gray, mudcracked, aphanocrystalline dolomite with lens of intraformational breccia at top. Breccia composed of rounded and angular intraclasts broken from dolomite and scattered in matrix of brown, finely crystalline, sandy dolomite. The quartz is mostly medium-grained, well-rounded, and spherical (Fig. 10).
7-8 | 2' 2" | Light gray to tan, medium crystalline, sandy dolomite with lenses of gastropod molds lined with dolomite crystals. Rock weathers light. Very fine-to coarse-grained quartz is mixed throughout the rock along with ovoid clasts of finely crystalline dolomite. Ghosts of gastropod shells are conspicuous in thin sections. This horizon appears to represent the Eccliomphalus (Eccliopterus) assemblage (zone 3) described by Cushing 1916.
7-7 | 2' 8" | Light gray, medium crystalline, sandy, calcareous dolomite, weathering light brownish-gray, with well rounded and spherical, medium-grained quartz (10%) and sparry calcite cement. Dark brown cores are conspicuous in the dolomite rhombs of the matrix and may be relic oolites.
7-6 | 2' 1" | Dark brown and gray, thin-bedded and laminated, finely crystalline dolomite with fine-grained, dolomitic sandstone filling mudcracks (Fig. 9 ).
7-5 | 1' 5" | Dark gray, irregularly laminated, finely crystalline and medium crystalline, sandy, dolomite weathering light brownish-gray. The quartz is fine-grained and angular to rounded. The dolomite rhombs have dark brown spherical cores which are believed to be relic pellets. Some slightly calcareous sandy laminae with calcite cement.
7-4 | 2' 10" | Light to medium gray, medium-grained, dolomitic sandstone, weathering light, with intraclasts of Horizon 7-3 in lower part. Quartz is mostly medium grained, rounded and spherical. Dolomite consists of very finely crystalline rhombs masking oolite and gastropod fragments.
7-3 | 0' 10" | Dark gray, irregularly bedded, mudcracked, finely crystalline, slightly calcareous, sandy dolomite with very fine-to fine-grained quartz. Dolomite matrix masks ghosts of fossil fragments, intraclasts of finely crystalline dolomite and pellets(?).
7-2 | 1' 5" | Dark brownish-gray to light gray, thin-bedded to ribbon-laminated, finely crystalline, sandy dolomite, alternating with very fine-grained, dolomitic sandstone.
7-1 | 1' 10" | White to light gray,coarse- to medium- grained, slightly calcareous, cross-laminated, orthoquartzite with dark gray clasts of sandy dolomite. Quartz grains well-rounded and spherical and cemented by silica over-growths. This distinctive white band, which can be traced in all the quarry walls, may correspond to Bed 9 of Cushing's (1916, p. 45) section the west side of Ogdensburg.
| | Base of section.

STOP 8. Allens Falls Fanglomerate or "basal breccia"
Located from index map, the pages were missing from the Guidebook pdf.

STOP 9. Type exposure of the Potsdam Sandstone at Hannawa Falls
Located from index map, the pages were missing from the Guidebook pdf.

STOP 10A. Bucks Bridge
Outcrops on east bank of Grasse River at confluence of Nettle Creek at Bucks Bridge; Chadwick's (1920) locality 55. Canton 15 minute quadranqle; Morley 7 1/2 minute quadrangle. Bucks Bridge Formation.
The strata consist of buff-weathering, thin-bedded to massive, gray, dolomite-cemented sandstone with rounded quartz grains. Many bedding surfaces show asymmetric ripple-marks, having a wave-length of 1.5-2 inches and an amplitude of 0.25-0.5 inch. Other bedding surfaces exhibit shrinkage cracks. There are many poorly preserved discoidal gastropods.
Berry and Theokritoff (1966, p. 876) inferred that deposition was "...in shallow, near-shore waters, possibly intertidal. The ripple marks and shrinkage cracks as well as the well-sorted, well rounded nature of the sand grains at this locallty are considered indicative of possible intertidal conditions. Many types of snails are found today in intertidal areas... "

STOP 10B. Trout Brook
Outcrops in Trout Brook north of railroad bridge; Chadwick's (1920) locality 12. Canton 15 minute quadrangle; Hewittville 7 1/2 minute quadrangle. Bucks Bridge Formation.
Dendroid graptolites were recorded by Chadwick (1920, p. 33) from this locality in Trout Brook; Berry and Theokritoff (1966) erected a new species, Dictyonema potsdamense, to accommodate these dendroids. The graptolites are most abundant in a 2 1/2-3 inch-thick bed of medium-grained, dolomitic sandstone in the east bank of Trout Brook. Most are fragmented but a few have small discs, probably used for attachment to the substrate, at the apical end of the rhabdosome. A few discoidal gastropods, similar to those at Stop 10A, occur in the same bed as the graptolites, as well as in strata above and below.
The strata at this locality are similar lithologically to those in Nettle Creek (Stop 10A) but lack the ripple-marks and shrinkage cracks. However, they are laced with many tubular structures, ovoid to round in cross section, that are composed of compact, dolomite-cemented sand lacking all signs of bedding laminae. The tubes are unbranched, overlap one another at all angles forming an open mesh, and none crosses from one bed to the next. They disrupt bedding laminae that may be seen preserved between them. Although the tubes are moderately numerous in the graptolite-bearing bed, they are very abundant in underlying and overlying strata, comprising as much as 80 per cent of some beds.
Berry and Theokritoff (1966) inferred that the tubes were made by an organism that tunneled through the most recently deposited, relatively soft sediment; the weight of the most recently deposited sediment led to the expulsion of water from the underlying layers of sediment and so probably made these layers impenetrable to the organism. The abundance of the tubes suggests that the sediment originally contained a considerable amount of organic matter.
Berry and Theokritoff (1966) considered "that the graptolite-bearing strata were formed in relatively shallow water, albeit possibly more distant from shore than were the strata at Nettle Creek. The qraptolites themselves were inferred to have lived in small clusters or "gardens" attached to the sea floor; colony growth was possibly terminated when the sea-floor supporting the graptolite clusters was disrupted by organismal tunneling.

STOP 10C. Outcrops along railroad
Outcrops along railroad west of bridge over Trout Brook and east of Townline Road.- Chadwick's (1920) locality 11. Canton 15 minute quadrangle; Hewittville 7 1/2 minute quadrangle. Ogdensburg Dolomite.
The strata along the railroad here are light-gray-weathering, slightly sandy, gray calcareous dolomite. They contain algal stromatolites.
Berry and Theokritoff (1966, p. 873) assigned these strata to the Ogdensburg Dolomite and placed the lower contact with the Bucks Bridge Formation at approximately the elevation of the railroad track at the western bridge abutment. This contact dips northerly and crosses Trout Brook approximately 250 feet north of the graptolite locality.

C: SOME ASPECTS OF ENGINEERING GEOLOGY IN THE ST. LAWRENCE VALLEY AND NORTHWEST ADIRONDACK LOWLANDS
W.P Harrison & E.T. Misiaszek
Clarkson College of Technology
Potsdam, New York
ABSTRACT
The purpose of this field trip is to illustrate the interdependence of geology and civil engineering by means of several examples from the St. Lawrence Valley and the Lowlands of the Northwest Adirondacks. We will make seven stops in the vicinity of Norfolk, Massena, Potsdam, and South Colton, New York.
Stop 1 will be at a limestone quarry where the rock is processed for Portland cement and asphalt concrete aggregate. Here we will emphasize the interrelationship between the bedrock type and the physiography. Stops 5 and 7 will be at gravel quarries of very different geologic and physiographic character. The relationship of physiography and bedrock to gravel characteristics will be stressed. Stop 6 will be at concrete gravity dams on the Racquette River, for which much of the crushed stone and concrete aggregate was taken from the gravel pit at stop 5. We will indicate some of the desirable and undesirable properties of this fill for use in this particular dam project. At stop 2 we will visit the site of a landslide in the sensitive Leda Clay. Stops 3 and 4 will be in the Moses-Saunders Power Dam and Eisenhower Lock, respectively. Here the geologic parameters and problems of construction will be stressed.

STOP 1 -Barrett Allied Chemical Pit, Norwood, N.Y.
The ten to fifteen feet of glacial cover can be clearly seen at the southern end of the pit, and the fairly clean character of the overlying till is evident, as is the thin soil cover at the grass line near the top.
The rock is drilled, blasted, broken down further by the large steel ball, and trucked to the primary crusher, where it is sized, recrushed and stocked in piles according to size for use as Portland cement aggregates, asphalt concrete aggregates, and general engineering use as fills, drains, etc.
The rock which usually is hard and dense, probably extends 100 feet deeper than the present base of the pit.
Its denseness is apparent on the west side of the pit, where minimum pumping operation is required to keep out the water infiltrating from the river just over the hill, and whose elevation is considerably higher than the base of the pit.

STOP 2 -Landslide in Leda Clay
Landslide in Leda Clay on the Massena Springs Road Near the Massena Airport (Racquette Cemetery Site)
The general area of the Racquette cemetery site has been exposed to many earthquakes, the most severe that of September 5, 1944. Many smaller tremors have been recorded prior to and after this shock.
Structures founded on the marine (Leda) clay were most affected by earthquake shock, while those founded on glacial till showed much less response. The epicenter of the 1944 earthquake was located in Massena Springs, approximately one mile north of the cemetery site.
The last glacial ice sheet deposited many very dense glacial till moraines near the St. Lawrence River. Streams with their headwaters in the Adirondacks encountered these moraines, and generally cut through glacial outwash deposits and the clays, these offering the least resistance.
The cemetery site consists of marine clay deposited between two moraines. The moraines existed prior to the formation of Lake Iroquois, which deposited clay in the valley between the moraines. The highest points of these moraines are 250 feet and 230 feet above sea level for the south and north shore respectively.
Soil borings performed at the site on the north shore indicated a clay layer thickness of about 65 feet, where surface elevation was 200 feet. Since till was encountered below the clay, the valley between the moraines was at or below 140 feet. The clay offered very little resistance so that the water was confined between these two moraines.
The clay at the site is rather strong and somewhat pre-consolidated in the undisturbed state, but remolding causes a drop in shear strength to a very small value. If one looks closely at the surface topography immediately adjacent to the river as the bus proceeds along the road to this stop, old landslide scars will be evident in the form of small surface scarps.
The landslide located at this stop resulted from the combination of heavy loads on top of the slope (logs from cut elms, sand piles), and erosion of the clay by the river at the foot of the slope. Many graves were lost and the trees near the river were tilted. The small island nearest the cemetery is probably a remnant of an old slide.
Mr. Spencer Thew of Clarkson College has placed observation wells in the slide area, and has taken samples of the undisturbed clay. The failure plane of the slide can be seen in the field, and it is possible that the soil strength parameters existing before the slide occurred can be inferred from the data he will collect. Such studies of field failures may make it possible to prevent future slides and property damage and personal injury. Note how close the next group of houses to the right of the cemetery is to an apparent old slump scarp.

STOP 3 - Moses-Saunders Power Dam
The location map is shown in Fig. 4. This dam provides approximately 912,000 kilowatts of power. The dam has a head of 81 feet, and behind it is Lake St. Lawrence, with its fine marina and Barnhart Island Beach. A section through the Moses Power Dam is shown on Fig. 5, and of the Long Sault Control Dam on Fig. 6.
A thirty minute film will be shown in the auditorium at the dam, which will illustrate the methods and problems of construction.
A tour of the dam will be made, and from the top of the building Lake St. Lawrence can be clearly seen, with some of the zoned and rip-rapped dikes bounding it composed of compacted glacial till with dry densities on the order of 140 pcf (concrete is 150 pef).

STOP 4 -Eisenhower Lock, St. Lawrence Seaway
This structure enables ships traveling the St. Lawrence River to pass around the Moses Saunders Power Dam and, along with Snell Lock five miles farther east, lowers the ships through a total of 95 feet of elevation. Both locks have dimensions of 860 feet by 80 feet and are of concrete construction. The locks are huge bathtubs in a sense, with openings along the sides into a passageway (about 13' wide by 15' high) on each side which slopes to the upstream end of the lock. When a ship comes down the St. Lawrence River and through the canal to the lock, the lower lock gates are closed, and the water is at the upper canal elevation. The ship moves slowly into the "bathtub", the upstream gates are closed, and then the water is let out of the locks through the openings in their sides, down the passageway on either side and discharged below the lock. A system of
baffles on the downstream end prevents excessive turbulence.
When a ship comes upstream to the lock, the upper gates are closed and the water level is at the same elevation as the water surface downstream from the lock. The ship moves into the lock, the lower gates are closed, and water is introduced into the side passageways from the upstream end of the locks flowing into the lock through the side openings, thus filling the lock and raising the ship to the elevation of the canal on the upstream side. Then the upper gates are opened and the ship moves out of the lock upstream. Recently, some deterioration of the lock concrete has been observed, and an extensive study has been made by the Corps of Engineers, which is resulting in appropriate remedial measures.
Since the overburden materials and lock location problems at Eisenhower and Snell Lock are very different, Figures 7 through 10 are included to show, for Eisenhower Lock, boring locations, exploratory core borings, some laboratory test data on overburden material and geologic sections. Figures 11, 12, 13a, 13b, 14 and 15 show the same data for Snell Lock. Note the difference in the overburden at the two sites 5 miles apart. Also note in Figure 11b boring 0-1302, which shows evidence of a possible fault at the site. This fault area is shown in Figure 12.

STOP 5 -The Martin Gravel Pit, "The Plains", South Colton
This pit is twenty miles from Potsdam on Route 56 towards Tupper Lake in the Adirondack Physiographic Province. The pit is part of a Kame Terrace deposit of very clean and uniform quality, largely composed of reddish brown gneiss. Excellent quality fine and coarse aggregate are produced from this pit. Due to its proximity to the construction site, most of the aggregate used in the construction of the five Niagara Mohawk dams on the Racquette River, completed in 1957, came from this pit.
At the site of the pit the company installed a large crushing, screening and washing plant for producing the aggregates for making concrete. This plant also produced several sizes of unwashed material for use in road and dike construction.
The processing plant was about 400 feet long and 100 feet wide covering about 2 acres. Stock piles of sand and various sizes of processed stone surrounded the plant, some of which were 100 feet in diameter, forty feet high, and contained as much as 8000 tons of product. The plant had a capacity of 200 tons per hour, and 15 men worked full time.
The operation starts with the "run of the bank" gravel and rocks which are fed into one end of the plant. As this material moves along the plant conveyor belts, the sand is separated and the rocks crushed, screened to size and washed. Waste material is screened out and the balance runs the gamut of vibrating screens, scrubbers and washers until there are a number of neat piles of various sized crushed stone and sand.
The crushed stone for the concrete was divided into 3 stockpiles, one with stone graded from 1/2" to 1"; one from 1" to 2"; and one with sand which varied from near a #200 sieve-size to 1/4".
Trucks took the various materials to the job sites where it was handled in batch plants as its first step towards becoming concrete for one of the project structures.
It is estimated that for the entire project about 400,000 tons of washed sand and gravel were used. This required excavating about 600,000 tons from the gravel pit and crushing about 300,000 tons of rock.

STOP 6 -The Niagara Mohawk Power Corporation Dams
The Niagara Mohawk Power Corporation Dams, South Colton to Carry Falls
The Racquette River Power Development Project added five new hydro-electric plants which boosted Niagara Mohawk Power Corporation's production capacity to almost 1 billion kilowatt hours of electricity per year. This is enough power to supply the needs of more than 400,000 homes. The project cost $33,000,000 and resulted in the creation of six new lakes and public areas for boating and fishing. Figures 16 and 17 show the plan and statistics of the project. (also Table 2).

STOP 7 -Bicknell Gravel Pit, West Parishville, New York
This site is also a Kame Terrace deposit, but the rock utilized for crushed gravel and sand shows different geologic characteristics from the Martin Pit of stop 5.
Cross bedding of sand, boulder pavements (concentrations of large cobbles in one area of the deposit), the effects of water-working and a wide variety of rock types can be seen here, allowing comparison to be made between different physiographic areas visited, the very different types of engineering material types and their relation to the area geology.
Sandstone, quartzite, gneiss, limestone can be observed at this pit, contrasting markedly with the uniform material at the Martin Gravel Pit.

D: ECONOMIC GEOLOGY OF INTERNATIONAL TALC AND BENSON IRON MINES
Willlam T. Elberty and Peter Lessing
St. Lawrence University
Canton, New York
Since 1964 International Talc Co. has mined commercial talc from its open pit at Fowler, New York. The minable product 1s tremolite-talc schist, a Grenville metasedimentary unit of the Balmat-Edwards district. Production of 80,000 tons annually accounts for 45 percent of New York State talc. The mineralogy of this complexly folded, Mg-rich unit is typical greenschist facies. The petrogenesis is complex and speculative, but replacement and/or isochemical metamorphism is suggested.
Iron ore, principally magnetite and hematite, are extracted by open pit methods at Benson Mines, New York. The 2.5 mile-long pit is located in the overturned eastern limb of a northerly-plunging syncline. Ore occurs disseminated in Grenville gneisses that average 23 percent iron. Average annual tonnage is 1.1 million, which yields a concentrate of 62 percent iron. A metasedimentary or replacement origin is postulated.

STOP 1. International Talc Open Pit
New York talc was originally discovered by Colonel Henry Palmer and in 1878 he opened the first commercial talc mine in New York at Talcville. Over the past 93 years talc has steadily grown in economic importance. Commercial talc from the Balmat-Edwards district is the only source in New York State and accounts for 22 percent of U.S. production or approximately 200,000 tons per year.
All of the producing and abandoned talc mines were underground operations until 1964 when International Talc started production from their open pit at Fowler. All mining operations in the district are confined to unit 13, a tremolite-talc schist that varies in thickness from 0 to 400 feet. It can be traced more or less continuously from Balmat to Edwards, some 10 miles.
Regional Geology
The Balmat-Edwards belt is a northeast-trending marble belt approximately 10 miles long and 1/2 to 2 miles wide. It is part of the Grenville metasedimentary sequence of northern New York. Within the marble belt ~6 lithologic units have been identified (Brown and Engel, 1956). These stratigraphic units can be traced with a fair degree of accuracy, the entire length of the belt. They are numbered 1 to 16 with number 1 presumably oldest (Table 1, Fig. 2). All units have been extensively folded and there is abundant evidence of cross-folding, flowage, and intricate contortions. The interested reader is referred to Brown and Engel (1956), Buddington and Leonard (1962), and Lea and Dill (1968) for complete descriptions and detailed maps. The area has been subjected to regional metamorphism of the upper amphibolite and lower granulite facies. This high grade metamorphism is characteristic of the silicate gneisses that surround the Balmat-Edwards marble belt. However, the marble itself exhibits a mineralogy typical of greenschist and lower amphibolite facies.
Mine Geology
Structure
The International Talc Co. open pit is located in the tremolite-talc schist of unit 13 of the Balmat-Edwards district (Fig. 2). Initial stripping of overburden was begun in 1962 and production started in 1964. Since that time the pit has been expanded to its present size of 1200 x 450 feet with a depth of approximately 60 feet.
Unit 13 strikes northeast and is overturned to the southeast. Dips generally vary from 45 to 50 degrees.The tremolite-talc schist persists to a proven depth of at least 1000 feet and probably greater. Alone strike to the south are remains of abandoned shafts to Wight, Woodcock and American mines and the producing Gouverneur Talc mine. There is evidence of fracturing, faulting, complex folding, and boudinage in many of the exposed surfaces. Minor and major folds plunge north at 15 to 50 degrees.
Mineralogy & Chemistry
Unit 13 is generally referred to as tremolite-talc schist, these being the major minerals present. All of the common minerals found in unit 13 are listed in Table 2. Mineral compositions of unnit 13 are given in Table 3.
Table 1. Stratigraphic units of the Balmat-Zdwards district (presumably oldest at bottom).
16 | Median gneiss
15 | Rusty marble
14 | Calcitic-dolomitic marble
13 | Tremolite-talc schist
12 | Dolomitic marble
11 | Dolomitic-diopside marble
10 | Anhydrite-gypsum marble (not exposed)
9 | Dolomitic marble
8 | Silicated dolomite
7 | Dolomitic marble
6 | Silicated dolomite
4 | Silicated dolomite
2 | Pyritic schist
Table 2. Common minerals of unit 13.
Diopside | CaMgSi2O6
Tremolite | Ca2Mg5Si8O22(OH)2
Anthophyllite | Mg7Si8O22(OH)2
Serpentine | Mg6Si4O10(OH)8
Talc | Mg3Si4O10(OH)2
Dolomite | CaMg(CO3)2
Calcite | CaCO3
Quartz | SiO2
Anhydrite | CaSO4
Biotite | K(MgFe)3(AlSi3)O10(OH)2
K-feldspar | KAlSi3O8
Phlogopite | K(Mg)3(AlSi3)O10(OH)2
Pyrite | FeS2
Table 3. Mineral composition of talc unit (volume %). (after Brown and Engel, 1956 )
| 1 | 2 | 3
Anthophyllite | 7 | 38.4 | 4.5
Dolomite | tr | tr | -
1. Average of talc unit, 5th level., Woodcock Mine.
2. Commercial talc, Woodcock Mine.
3. Average of talc unit, Balmat zinc mine.
Table 4. Chemical analyses of channel samples across 5 commercial talc zones in the Balmat-Edwards district, (after Engel, 1962).
* = Total loss on ignition (includes CO2)
** = Contamination ( ? )
The mineralogy represents typical hydrous assemblages of the greenschist facies. Distinction between tremollte, anthophyllite, and fibrous talc generally requires x-ray diffraction and/or optical examination. Most mineral percentages vary greatly throughout the schist. In general, however, the footwall (east) is tremolltic with tan serpentine (antigorite?), and the hanging wall (west) is enriched in fibrous and scaly talc.
Chemical analyses of 5 channel samples are given in Table 4. SiO2, CaO, MgO, and H2O total more than 98 percent.
Pleistocene
Of interest to "The Friends" are some extraordinary glacial features exposed in the pit. A conglomeratic "cement" no more than 0.25 inch thick is plastered over much of the polished and striated bedrock, even in places where the glaciated surface is vertical or overhanging.
On the northwest end of the pit the overburden is typically gravel, while at the southeast it consists of a thixotropic clay. This facies change is rather abrupt and needless to say presented difficulties during stripping operations. A more complete discussion of the Pleistocene at this locality can be found in the field Trip E guide.
Economic Geology
At the northern end of the pit are the remains of the old Arnold Mine. This underground operation had 15 levels, 45 to 65 feet apart, branching from a shaft that followed the dip for 850 feet (Engel, 1962). International Talc purchased the Arnold Mine property from Loomis Talc in 1956 and began production via open pit methods in 1964.
Mining methods are relatively simple. Talc ore is drilled, blasted, and truck-hauled to the jaw crusher, which is located just north of the pit. The Telesmith jaw crusher is 36 inches wide and 20 inches between adjustable jaws. At a 6 inch spread, the crusher has a maximum capacity of 500 tons per hour. Usual runs at the pit are approximately 100 tons per hour, or lower if smaller sizes are required.
The crushed ore is screened and separated usually at 4 inches with coarser material stored and the finer material hauled to the mill. The coarse-ground ore is trucked to the mill when supply warrants.
International's pit produces an average of 80,000 tons per year. This represents 45 percent of New York talc and 9 percent of U.S. production. The value varies depending on grade. Coarse commercial talc (80 percent less than 325 mesh or 44 microns) runs $30 per ton.
Top grade talc ore (average 1.4 microns) and fiber products sell at $90 per ton. Most of the products go to the paint and ceramic industries.
Petrogenesis
The origin of the tremollte-talc schist represents a complex problem as does that of the zinc deposits so intimately associated with the schist. There are no definitive answers, but certain facts place limits on interpretations.
1. The Balmat-Edwards district is predominantly dolomite and associated Mg-silicates.
2. The stratigraphy is reliable throughout the length of the belt.
3. Associated anhydrite, gypsum, and halite suggest an evaporite sequence.
4. Metamorphic foliation and primary layering are generally in good agreement.
5. Tremollte-talc ore was present prior to deformation.
6. Commercial talc is only found in unit 13.
Engel (1962) suggests that the talc unit is a product of the replacement of a siliceous dolomite. He notes that relict carbonate layers and lenses in the talc support this interpretation. If such a replacement occurred it was remarkably selective since tremolite and talc are almost exclusively restricted to unit 13. No other units of presumably similar composition contain commercial tremolite and calc.
Any hypothesis regarding petrogenesis must consider original composition and the stability of the present assemblage. Major variablea that must be considered are T, P, PH2O, and PCO2. Geothermometry in the district (Engel, 1962; Lessing and Grout, 1971) indicates metamorphic temperatures of approximately 50°C. Pressures are more difficult to determine, but PCO2 was probably high as suggested by coexisting quartz and dolomite and lack of dissociated carbonate. Water is a minor phase suggesting low PH2O. The stability of anthophyllite at Balmat (Greenwood, 1963) also supports a low water pressure; perhaps only 2-3 bars. Load pressure is estimated at 2-4 kilobars.
The chemical composition of the schist is essentially a hydrous calcium-magnesium silicate. A replacement origin is certainly possible as Engel has suggested. However, the stratigraphic restriction of unit 13 may indicate a metasedimentary origin that was essentially isochemical. A possible parent material of siliceous dolomite with trapped connate water would provide the necessary chemistry. Metamorphism of this unit would require the loss of CO2 while retaining H2O. The separation of CO2 and H2O may be controlled by permeability and/or osmotic pressure.
Brown and Engel (1956) have pointed out a retrograde metamorphic sequence tremolite → anthophylllte → serpentine → talc. Elsewhere, Elberty and Lessing have noted the reaction diopside → serpentine and excellent examples of dedolomitization (Fig. 3) in which Mg has been removed from dolomite to make diopside, and leaving a selvage of calcite. This phenomenon is common in diopsidic dolomites. The characteristic greenschist assemblage is in large part due to retrograde metamorphism that did not noticeably affect the surrounding gneisses.

STOP 2. Benson Mines Iron Ore Deposit.
STOP 2. Benson Mines Iron Ore Deposit (Fig. 1). The Benson Mines magnetite-hematite deposit is located on the northwest slope of the Adirondacks in the Grenville province of the Canadian Shield. Knowledge of the deposit dates back to about 1810. Production of magnetite began around 1889 and the deposit was worked intermittantly until 1941 when it was leased by Jones and Laughlin Ore Company. In 1952, a merger formed the New York Ore Division of Jones and Laughlin Steel Company. At the present time, the plant facility has an annual production capacity of about 1,100,000 long tons of magnetite and 700,000 long tons of hematite concentrates. The deposit is 400 to 600 feet thick and about 2.5 miles long making it the largest known deposit of its kind.
Much of the following information was obtained from Leonard and Buddington (1964); Crump and Buetner (1968) and Palmer (1970). The reader is referred to these sources for more detailed discussion.
Regional Geology
Magnetite and hematite ores are confined to a relatively narrow horizon within a sequence of paragneisses which are infolded into granitic rocks of the Adirondack Highlands. Figure 4 shows the general geology of the area around Benson Mines. Palmer (1970, p. 31)recognizes four major units in the paragneiss sequence.
1. Mixed garnet-and pyroxene-feldspar gneiss.
2. Garnet-and sillimanite-quartz-feldspar gneiss (ore and mineralized horizon)
3. Migmat1tic plagioclase gneiss.
4. Pyroxene-Quartz-feldspar gneiss.
The surrounding crystalline rocks consist of alaskite and hornblende granites and their gneissic equivalents.
Mine Geology
The paragneisses comprise a large, structural synform overturned to the west and plunging north about 20° in the vicinity of the mine. The paragneisses are subdivided into six lithologic units: 1) hanging-wall gneiss, 2) disseminated-garnet gneiss, 3) sillimanite gneiss, 4) ferromagnesian gneiss, 5) blotchy garnet gneiss, and 6) biotite gneiss. Important concentrations of ore are confined to units 2, 3, and 4, and some ore is found in unit 5. Thicknesses, mineral composition, and appearance of the units vary considerably. Sequence is an important aid to identification within the mine. Rocks similar to those exposed in the Benson Mine have been traced approximately 8 miles along the strike.
Hanging-wall gneiss. An extremely heterogeneous unit composed of a variety of different rock types including diopside, marble, quartzite, and hornblendite in bands 5 to 50 feet thick. Most of the unit consists of pink or gray hornblende and/or pyroxene gneiss. A pink, microcline pegmatite marks the immediate hanging wall throughout the deposit. Hornblendite and diopside rock are encountered in drill holes. Minerals include quartz, orthoclase, microcllne, perthite, oligoclase, biotite, muscovite, hornblende, pyroxene, chlorite, with local garnet and sillimanite near the ore contact. Common accessory minerals are apatite, zircon, leucoxene, magnetite, and hematite.
Disseminated-garnet gneiss. Largely a potash feldspar-quartz gneiss with disseminated grains of garnet. Quartz with magnetite and adisseminated garnet and biotite characterize the contact with the hanging-wall gneiss. Other minerals are pyroxene, hornblende, chlorite, muscovite, sillimanite, biotite and accessory apatite, zircon, pyrite and sphene. The ore is largely magnetic and the highest-grade ore in the southern half of the ore body was concentrated in this unit. The unit varies in thickness from zero to 350 feet.
Sillimanite gneiss. This unit is generally composed of orthoclase or microcline with low quartz and ferromagnesian content. Sillimanite is a common constituent of many sections, but there are thick sections exposed in the pit and in drill cores which do not contain sillimanite. The unit averages 350 feet thick with a maximum of 650 feet. It is absent locally in the northern end of the pit. Sillimanite gneiss contains most of the non-magnetic ore and the nature of the gneiss changes with the ratio of magnetic to non-magnetic ore. Biotite, chlorite, muscovite, and accessory apatite, zircon, sphene and leucoxene may be present.
Biotite-garnet gneiss. A light-gray, coarse-grained, orthoclase-quartz-biotite rock with knots or blotches of garnet. The rock is similar to the disseminated garnet gneiss and forms the footwall of the Benson Mines ore body. Pyrite, pyrrhotite, sillimanite, magnetlte, apatite and zircon are present.
Ferromagnesian gneiss. This unit contains the high-grade magnetite ore of the northern part of the mine. It is lens-shaped with a strike length of about 3300 feet, an average width of 200 feet, and it pinches out in depth. The rock contains orthoclase and quartz with the quantity of hornblende, biotite, and pyroxene varying inversely to the quantity of magnetite. Other minerals present, 1n more or less abundance, are garnet, pyrite, pyrrhotite, sillimanite, and accessory zircon, spinel, and apatite.
Biotite gneiss. A medium-to fine-grained quartz-feldspar gneiss with biotite and local disseminations of garnet, sillimanite, chlorite, and hornblende.
There are no sharp boundaries between any of the above units. Units containing important concentrations of ore minerals may be traced for considerable lengths. Magnetic and non-magnetic ore are generally confined to specific lithologic units (Crump and Beutner, 196&, p. 66).
Assuming some potassium metasomatism as evidenced by the presence of K-feldspar pegmatites, Palmer (1970, p. 37-38) postulates "illiitic siltstones, calcareous silt or sandstone and carbonate lenses with either graywacke or soda shale" as original sediments.
In addition to the minerals mentioned 1n the description of the gneiss units, copper occurs rarely as native copper, chalcopyrite, chalcocite, bornite, covellite, azurite and malachite. Molybdenite occurs in pegmatite dikes and disseminated in some ore zones (Crump and Beutner, 1968, p. 61). Fluorite is present in some pegmatites.
A generalized plan and section of the major structure is given in Fig. 4 and a more detailed plan of the mine showing the distribution of the various units in Fig. 5. The ore body is located on the eastern limb of a synform, the Benson Syncline, which is overturned towards the west "and plunges 20° to N30°E. Smaller folds plunge 12° to S30°W and form an anticline and syncline in the overturned east limb of the Benson Syncline. They are of economic significance because they more than double the volume of ore-bearing rock. The Amoeba pit (Fig. 5) is interpreted as the bottom of one of the subsidiary synclinal rolls developed in the eastern limb of the Benson Syncline (Crump and Beutner, 1968, p. 53-54). It is the only place where the blotchy garnet gneiss (unit 5) has been found to contain sufficient iron mineralization to constitute ore.
Palmer (1970, p. 32) recognizes two stages of folding. Flow folding is shown by thickening and axial-plane schistosity in fold hinges, with accompanying mineral lineations. The latter were deformed by flexure-slip folding.
Ore is found where the stratigraphic footwall is overturned to form the structural hanging-wall. Ore stops at both the northern and southern ends of the pit where this hanging-wall relation ceases. Drilling, however, has penetrated 35 feet of ore-grade rock, resting on "hanging-wall" gneiss where there is no overturning (Crump and Beutner, 1968, p. sq).
Many of the relationships discussed above are illustrated in Fig. 6-10, with section lines given in Fig. 5.
Ore
Ore minerals are magnetite and hematite. The are is classified as magnetic if 80 percent or more of it is magnetite, and non-magnetic if magnetite comprises less than 80 per cent. Average grade is a function of economics. The distribution of the magnetic and non-magnetic ore is shown in Fig. 5 and a summary of their characteristics is given in Table 5. Table 6 gives representative analyses of the two kinds of ore and their respective concentrates.
Although the Benson Mines deposit is considered non-titaniferous, there is enough TiO2 present in the concentrate obtained from the Humphrey spirals to constitute a metallurgical problem.
Ore Genesis
Palmer (1970) discusses three possible origins for the magnetite-hematite ore in the Benson Mines deposit. 1) as a product of metamorphic differentiation. 2) as an epithermal replacement in the metasediments, and 3) as a metamorphosed iron-rich sediment. Each of these origins can explain the confinement of the ore to a restricted lithologic horizon; the fact that the ores have apparently been present during deformation and recrystallization of the host rock (Hagni, et al., 1968; Palmer, 1970); the presence of hematite and magnetite in different areas of the ore deposit; etc. Leonard and Buddington (1964), Buddington (1966), and Crump and Beutner (1968) favor a hydrothermal origin, because of the lithologic heterogeneity of the host rocks; the presence of skarn, a low-angle, cross-cutting relation between the ore and the host rocks; and the presence of veins of fluorite, calcite, quartz, and other minerals typically associated with hydrothermal activity. Palmer (1970) rejects both metamorphic differentiation and hydrothermal replacement in favor of a syngenetic, metasedimentary origin. Palmer feels that the confinement of the ore to a specific horizon within the paragneiss sequence, the relatively great lateral continuity of this horizon; the lack of any evidence of replacement of the host rock by magnetite or hematite, and the apparent presence of ore prior to deformation and metamorphism is best explained by metamorphism of iron-rich sediments.
Mining and Processing
Mining is carried out by open-pit methods. Magnetic and non-magnetic ores are differentiated by diamond drilling and are mined selectively. Operating faces are generally about 50 feet high. Blast-hole drilling is done with rotary drills. Ammonium nitrate explosives are used. Crude ore is loaded by 6-yard, electric shovels into 85-ton dump trucks for transport to the primary crusher. The plant is capable of handling 16,000 tons of ore per day.
Figure 11 illustrates by flow diagram the methods used to concentrate the magnetic and non-magnetic ores. Magnetic ore is concentrated by magnetic separators, with the final concentrate (minus 20 mesh) containing 63 to 65 percent iron. Non-magnetic ore is concentrated by gravity methods with auxiliary magnetic separation to collect magnetite, or by flotation to collect hematite and magnetite fines (minus 100 mesh). The concentrates are transported to the sintering plant where they are thoroughly mixed with fine anthracite coal, lime, and sinter fines in the ratio of 64 per cent concentrate: 5 per cent anthracite: 1 per cent lime : 30 per cent sinter fines. The sintering cycle takes about 11 minutes.
Sinter is shipped by rail to the Jones and Laughlin steel plants at Pittsburgh and Aliquippa, Pa. and Cleveland, Ohio.
Table 5. Summary of ore characteristics (after Crump and Beutner, 1968)
MAGNETIC | NON-MAGNETIC
1) Generally difficult to crush | Friable
2) Distribution generally confined to lithologic horizons | Same
3) Occurs in all lithologic horizons | Not found in ferromagnesian gneiss and only to minor extent in disseminated garnet gneiss
4) Generally high quartz gangue | Generally low quartz gangue
5) Sulfides present | Sulfides absent but with many limonite-filled vugs of a size corresponding to sulfides
6) Sphene present | No sphene but some leucoxene
7) Contains green or colorless, untwinned, potash feldspar | Contains pink or colorless, twinned and strained, potash feldspar
8) Rare labradorite grains in ferromagnesian gneiss ore | No plagioclase
9) Has fairly uniform gneissic structure and texture | Ptygmatic folding and pegmatitic lenses are quite common
10) Average grain size 1mm | Same
Table 6. Representative chemical analyses (after Crump and Beutner, 1968 and Palmer, 1970)
MAGNETITE
| Crude | Conc. | Crude | Conc. | A*
* Average of 8 whole rock analyses of ore (Palmer, 1970).

E: SOME PLEISTOCENE FEATURES OF ST. LAWRENCE COUNTY, NEW YORK
James S. Street
St. Lawrence University
Canton, New York
The field trip route from Potsdam to International Talc's open pit mine at Fowler crosses uneven ground moraine and a series of ice contact features. The latter have been mapped as part of the frontal Fort Covington Moraine. Kames, kettles, discontinuous eskers, and extensive sand plains are well displayed. Stop 1 will examine the core of one of these ice contact features, in Elm Creek Valley north of Edwards, New York.
Stop 2, at the International Talc open pit, will provide an opportunity to examine striae, gouges, and the remnants of highly polished flutes preserved on the bedrock surface. Patches of sand and gravel cemented to the rock surface form an unusual pavement. Drift exposures adjacent to the pit show Fort Covington sand, gravel and clay deposits. Stop 2 of this trip is same as Stop 1 of Trip D.
INTRODUCTION
Pleistocene glacial events of a major part of St. Lawrence County have been interpreted by MacClintock and Stewart (1965). Their report on the St. Lawrence Lowland gives an excellent summary of previous investigations in the area and presents substantial evidence supporting the concept of two ice flow directions in the St. Lawrence Valley during the late Wisconsin Stage.
Using glacial striations and till fabrics as primary criteria for flow direction, MacClintock and Stewart identify an ice mass moving from northeast to southwest (Malone Glaciation) which, at maximum extent, spread over the Adirondack mountains. A later ice mass (Fort Covington Glaciation) radiating from a new source on the Ottawa Highlands moved from northwest to southeast. Malone drift, described as red-brown till and assorted ablation debris, is said to be leached usually 5 to 8 feet, whereas Fort Covington drift is grey-buff till and other debris that are leached only a foot or two. The southern boundary of Fort Covington drift extends diagonally across St. Lawrence County from Nicholville to Harrisville (Fig. 2). This uneven boundary forms many loops and re-entrants in a typically lobate pattern marked in places by strong frontal moraine topography (MacClintock and Stewart, 1965). Deglaciation accompanied by the draininq of ice-dammed lakes in the lowland was followed by a westward incursion of marine water.

E: SOME PLEISTOCENE FEATURES OF ST. LAWRENCE COUNTY, NEW YORK

Broad, ridge-like hills of till
The field trip route along U.S. 11 between Potsdam and Canton traverses an uneven till-covered surface with several broad, ridge-like hills of till having long axes oriented approximately northeast-southwest. The hills are part of a broad belt of similarly-oriented topographic features which cover the northern portion of St. Lawrence County. Interpreted by MacClintock and Stewart as part of the recessional Fort Covington drift sheet, the hills are described as having formed perpendicular to the flow of Fort Covington ice. The hills have cores of Malone drift that have been "pushed into place" (1965, p. 7-B). Exposures into these features have not been found in the vicinity of the trip route.

Series of ice contact features
Southwest of Canton the trip follows N.Y. 87 to Hermon thence via Marshville and Stalbird toward Edwards along a series of ice contact features trending approximately north-south parallel to Elm Creek valley. Where internal structures are exposed, there are varying degrees of sorting and a chaotic arrangement of stratified drift. Precambrian rock types predominate but a variety of sedimentary rocks can be found in the gravel.
These deposits lie a long the Fort Covington frontal moraine and are composed of Fort covington Drift (MacClintock and Stewart, 1965, p. 102-105).

STOP 1. Ice contact debris south of Stalbird.
This stop provides an opportunity to examine the structure and composition of a "textbook" example of ice contact debris.

STOP 2. Open pit mine of International Talc Co.
Several glacial erosional features are preserved on the bedrock surface. Mineralogy and petrology of the mine are discussed in detail under trip D of this guidebook.
In several places the bare bedrock surface shows broad, highly polished grooves trending northeast-southwest (N 20°, azimuth). Prominent striations having a parallel orientation are well displayed in the grooves. A major set of fractures from 2-12" long can be seen across the rock surface. The fractures strike N 8° at the northeastern end of the pit but their orientation gradually swings more easterly (N 20°) toward the crest of a 15' bedrock rise. A second fracture zone west of the crest produces a series of small step-like features, some of which are slightly curved, having a strike of N 280° nearly perpendicular to both the more easterly set of features and the prominent striations. The orientation of these step-like features, and some of the associated fractures might stimulate discussion on the origin and directional properties of crescentic marks.
Patches of cemented sand and gravel adhere tightly to the bedrock in several places. Usually 1/4 inch thick, these patches are remnants of a pavement which covered the entire surface prior to the mining operation. Several flutes in the bedrock show the cemented material preserved in a vertical position.
Exposures of drift at the edges of the pit show approximately 5 feet of red-brown till overlain by oxidized sand and laminated silt and clay totalling some 30 feet. The stripping operation combined with slump of the walls prevents a clear understanding of drift relationships.

F: MINERAL COLLECTING IN ST. LAWRENCE COUNTY
George Robinson
Fort Jackson, New York
The purpose of this trip is to visit some of the classic mineral collecting sites of St. Lawrence County, observe their geology, and collect specimens. Stops will be made at: 1) the Bower Powers farm in Pierrepont, a world-famous locality for doubly-terminated tourmaline; 2) the West Pierrepont actinolite locality; 3) the gem diopside locality near DeKalb; and 4) the Gomer Jones farm in Richville, a well-known occurrence of dravite. Other minerals which may be found at these stops are apatite, biotite, calcite, chlorite, pyrite, quartz, schorl, tremolite and uralite.
The mineral collecting sites of St. Lawrence County may be classified as: 1) those of sedimentary origin; 2) those formed by fracture filling and 3) those of metamorphic and complex origin. These will be briefly discussed, as will their typical mineralogy and their collecting history.
General
The trip will consist of four stops which are located on the stop map, (Figure 1). Please note that nearly all the stops are on privately owned land. Please do not litter, and kindly abide by any restrictions or regulations set forth by the land owners regarding the use of their properties.

STOP 1. Bower Powers farm, Pierrepont, N. Y.
This locality is one of the world's most famous for doubly terminated black tourmaline crystals. The tourmaline appears to be of metamorphic origin, and occurs in contacts between Grenville Marble, and a quartz-tourmaline-biotite schist. Nearly perfect crystals are observed both within the quartz-tourmaline rock and separated from it, enclosed by marble. Often crystals are found loose in the soil where they have freed from the marble. It is interesting to note the absence of feldspar at this tourmaline deposit.
Mineralogy
1) Tourmaline | occurs as near perfect trigonal crystals with shortened c-axes and lacking the usual prismatic striations typical of the species. Riggs' analyses indicate this is an iron-magnesium tourmaline (Clarke, 1899). Crystals and crystal aggregates are commonly found associated with quartz and uralite. The common habit includes the following forms illustrated by Fig. 5 : trigonal prism (m), ditrigonal prism (a), rhombohedra (e) and (r), basal pedion (c), trigonal pyramids (o), and more rarely ditrigonal pyramids and second order hexagonal prisms (not shown).
2) Quartz | is typically milky and shows poor development, but occasionally clear to smoky crystals are found associated with the tourmaline. They are commonly prismatic, with hexagonal prisms and terminating rhombohedra being the only faces developed. The physical development of these crystals does not illustrate enantiomorphism.
3) Uralite | is an amphibole replacement of pyroxene. Actinolite commonly replaces diopside, and is a relatively common phenomenon in metamorphic rocks. However, complete, free-standing pseudomorphs are uncommon and the ones from this locality are well known for their perfection and sharp definition. They are usually associated with the tourmaline. Occasionally they grade into unaltered diopside or more rarely into rensselaerite.
4) Apatite | is uncommon, but sometimes is found in the calcite as small hexagonal prisms seldom over an inch long. The most common color is light green to brown.
5) Biotite | Pseudohexagonal sheets approaching four inches in diameter may be found. It is interesting to note that in areas where the mica abounds, tourmaline is not common.
6) Others | Chlorite, pyrrhotite, pyrite, calcite, scapolite, and diopside are also likely to be encountered here, but usually not as desirable specimens

STOP 2. Actinolite locality, near West Pierrepont, N.Y.
Most commonly observed as radiating fibers, or matted masses of acicular crystals, actinolite is seldom seen as large, perfectly developed euhedra. At this stop actinolite occurs in the latter mentioned form, and is found in a marble-calc-silicate rock. A few crystals of pyrite, quartz, and dravite have been found here, but are relatively uncommon. The most striking feature here is a fifteen foot outcrop of solid actinolite crystals. Each crystal is remarkably well formed and was probably formerly in contact with marble which has since eroded away.
Figure 5 illustrates the typical habit of the actinolite here. The following forms are usually well developed: orthopinacoid (a), prism (m), prism (e), clinopinacoid (b), and clinodome (r).

STOP 3. Gem Diopside locality, near DeKalb, N.Y.
This is the famous Calvin Mitchell farm to which all mineralogy texts refer when citing DeKalb, N.Y. as a noted locality for diopside. The crystals from here are without any doubt the world's finest gem diopsides. They occur in seams and pockets within the diopsidic host rock which is part of a long ridge composed chiefly of interbedded quartzite and silicated marble. The ridge trends northeast-southwest, and dips 45° to the northwest.
A typical diopside crystal is shown in F1gure 7. The common forms include orthopinacoid (a), clinopinacoid (b), prism (m), pyramid (u), and basal pinacoid (c). The pyramids (u) are typically heavlly etched, whereas all the other faces are smooth and glassy. Sometimes an asbestiform tremolite is observed growing into and parallel with the diopside, as if it were in the process of replacing it. A few complete tremolite pseudomorphs after diopside have been found here. Unlike other diopside in the Grenville rocks, this diopside seldom shows basal part1ng, and always exhibits good cleavage (11O).
Note: This locality is presently being mined for gem diopside, and mineral collecting is NOT permitted anywhere on the property.

STOP 4. Gomer Jones farm. Richville, N.Y.
Nearly all the famous large brown dravite crystals labelled as coming from Gouverneur, N.Y., probably came from this locality. Here coarse white tremolite crystals, as much as a foot in length, form a major part of the calc-silicate-marble bedrock. Associated with these large tremolites are white pyroxene crystals, apatite, and dravite. Mineralogy
1) Dravite | occurs as masses, grains, and complete crystals scattered locally throughout the deposit. The largest and best crystals are usually in intimate association with the tremolite and coarsely crystalline calcite. Occasional small, free growing crystals are found in the marble, and loose in the soil. The habit is similar to the Pierrepont tourmalines, with the exception of a few longer, more prismatic crystals.
2) Pyroxene | occurs as small, white to light tan colored crystals in veins in the hard calc-silicate rock. They are presumably diopside, but lack the familiar green color.
3) Apatite | has been found enclosed in the coarse calcite in the floor of the pit at the east end of the hill. The crystals are sharp hexagonal prisms of blue color, and are not commonly encountered.