THE GEOLOGY OF THE ST. DOMINIQUE RIDGE,
BAGOT COUNTY, QUEBEC
A Thesis
Submitted to the Faculty of Graduate Studies and Research
in Partial Fulfilment of
the Requirements for the Degree of
Master of Science
in the
Department of Geological Sciences
McGill University
by
John L. Usher
MONTREAL
April, 1947 TABLE OF CONTENTS
Page
Introduction 1
Location 1
Physical Features 2
Culture 3
Transportation 4
Previous work and the Present Study 4
General Geology 10
Formations of the St. Dominique Ridge 15
Beldens Formation 15
Fauna and Correlation 22
St. Dominique Formation • 24
Fauna and Correlation •• 32
Formations of the Black River Group 41
Formations of the Trenton Group ••••• 46
The Cryptolithus Beds 47 The Rosemount Formation • 43
The Higher Trenton Beds 49
Utica-Lorraine Shales ..... 50
Structure 54
Folds and Faults 54
Cleavage • 61
Gash Veining ..... 62
Geologic History of the St. Dominique Ridge 64
Summary and Conclusions •• • 77
Bibliography of References Cited 81 FIGURES AND CHARTS
Page
Table of Formations 14
Correlation Chart of the St. Dominique Limestone F&una. . 38
Follows Page
Figure 1 - Location of St. Hyacinthe Map-Area 2
Figure 2 - Western Half of the St. Hyacinthe Map-Area . 9
Figure 3 - Map of St. Dominique Ridge 13
Figure 4 - St. Pie Hill 19
Figure 5 - Map of Abandoned Quarry South of La Carriere 40
Figure 6 - Quarries at La Carriere 44
Figure 7 - Paleogeographic Maps of the Positions of the Chazy Bnbayment 63 THE GEOLOGY OF THE ST. DOMINIQUE RIDGE,
BAGOT COUNTY, QUEBEC
INTRODUCTION
The ridge of Ordovician rocks at St. Dominique, Quebec, abounds in problems of stratigraphical, paleontological and
structural importance, yet, in spite of its nearness to Montreal,
it has so far received only cursory attention from geologists.
Because of these features the present writer considers himself
fortunate to be able to devote himself to this nearby though
practically untouched field.
LOCATION
The St. Dominique Ridge, so named after the village of
St. Dominique, Bagot County, Quebec, is located in the western
half of the St. Hyacinthe map-area (Department of National Defence,
sheet 31H, 1940, delimited on the north and south by latitudes
45°50f and 45°30f respectively and on the east and west by 72°45f and 73° respectively). It stretches from near the village of St. Pie - 2 -
for almost eight miles towards the north-northeast and
constitutes the first rise of land separating the nearly flat
plain of the St. Lawrence Lowlands to the west from the hilly
country of the eastern half of the map-area. St. Pie is
situated on the north bank of tne Black River about a mile
south of the southern tip of the ridge. The road from
St. Dominique to St. Hyacinthe, running northwest-southeast
cuts across the middle of the ridge. Along this road, at the
junction of the plain and ridge, is the village of La Carriere.
The accompanying index map (Fig. 1) indicates the position of the
ridge in the St. Hyacinthe map-area,
PHYSICAL FEATURES
As mentioned above, the western margin of the ridge is
the dividing line which separates the almost featureless plain of
the St. Lawrence Lowlands to the west from the hilly rolling
country to the east. From an elevation of 125 feet at the base of
the ridge, the Lowlands slope down gently towards the west.
Beginning as a hill nearly 100 feet high above the plain near
St. Pie, the ridge stretches north, widening to the extent of
one mile some 3 miles from its southern extremity. It disappears
as a prominent feature south of the stream which flows through
St. Rosalie. It is steepest on the west, being almost precipitous J
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K - 3 - in places, while its eastern side grades down imperceptibly into the St. Dominique plain which continues as far as the
Granby thrust. Along the road from St. Hyacinthe to
St. Dominique the ridge rises to its greatest height, more than
200 feet above sea level. Other than the Yamaska River, which drains northward past St. Hyacinthe, and its tributary, the
Black River whose headwaters are to the east and which circum vents the southern tip of the ridge at St. Pie, there are no waterways of any consequence.
CULTURE
Most of the population outside of the to?/ns are engaged in mixed farming, for the country is but sparsely wooded. St. Hyacinthe is a thriving city of 15,000, owing its location to rapids across the Yamaska River. St. Pie, the largest village in the area, is also situated beside rapids, this time in the Black River. St. Dominique is a limestone producing centre.
Quarrying has been carried on for more than a hundred years and the numerous quarries still in operation point to the importance of the area as a limestone producer. Most of the quarries are close to the highway between St. Dominique and St. Hyacinthe.
Whereas formerly the stone was used for building purposes and engineering construction in the neighboring towns, the present day products are largely crushed stone, flux and stone for lime - 4 - burning. All but one of the quarries are worked on a small
scale. Gravel deposits in the eastern part of the area have been found suitable for road construction and cement making and are being used for that purpose.
TRANSPORTATION
Access to the area is gained by a system of good roads,
few of which are paved. The new Sir Wilfred Laurier highway passes
through St. Hyacinthe as does the main line of the Canadian
National Railways from Montreal to Halifax. Transportation along
the above mentioned rivers is prohibited by fluctuating waters and
the presence of boulder-strewn rapids during the low water seasons
of the year.
PREVIOUS WORK AND THE PRESENT STUDY
Despite the fact that the St. Dominique ridge is not identified by name on the present topographic map, it is an out standing physiographic feature. For this reason and also because parts of the St. Dominique ridge are well settled and because it has been of economic interest as far as stone for building purposes is concerned, it is amazing that no detailed geological work has been done upon it. Nonetheless, rocks in the area have not hitherto been described in detail nor have any extensive collections of fossils been made. - 5 -
Logan's Geology of Canada, 1863, contains the first
reference to the rocks around St. Dominique and St. Pie. His
brief resume of the section includes all formations from the
Chazy to and including the Trenton. A small number of fossils
are listed from the Chazy rocks. The Trenton limestones, which
make up the bulk of the ridge, were evidently no better collecting
grounds at that time than they are to-day. Presumably the
identification of these few remains was made by Billings. Logan
considered the ridge to be anticlinal in structure and correlated
this with the Deschambault anticline which he traced from north of
the St. Lawrence to Lake Champlain. The economic resources and
possibilities of the district were also discussed.
In 1896, Ells1 report of the south-west sheet of the
Eastern Townships included a brief description of Trenton rocks at
St. Pie and of the Chazy, Black River and Trenton series, with
some mention of fossils at St. Dominique. In the appendix of this
same report Ami published four lists of Chazy fossils from the
St. Dominique area, three of which embodied the results of his
own work, and the fourth contained species previously identified by Billings.
Ten years later, Raymond published one of the first of a series of paleontological and stratigraphical papers on the Chazy formation and its fauna. This paper dealt with the formation in - 6 - its generally wide extent throughout the Ottawa-St. Lawrence
Lowlands and compared the faunas and lithology of various well known sections in Canada and north-east United States. In that
portion of his paper in which he described Chazy rocks in Canada,
Raymond included a revised list of the fossils from St. Dominique.
Raymondfs paper was the most valuable contribution to the geology
of the area since Logan's Geology of Canada. There still was,
however, no stratigraphic section or detailed measuring of the
rocks.
It was in 1914 that Parks1 "Report of the Building and
Ornamental Stones of Canada", Volume III, was published by the
Canadian Department of Mines. Excellent descriptions of the stone quarrying industry near St. Dominique with accompanying descriptions
of the lithology of the rocks were included in this work, but scarcely a word that would help in establishing a stratigraphic
section. Twenty-one years later, Goudge published Part III of his
"Limestones of Canada", and gave more detailed descriptions of the rocks than had his predecessor Parks. The lithologic descriptions given by Parks and by Goudge are splendid. The stratigraphic sequence and thickness of the formations are barely mentioned, they being frankly beyond the purpose of the reports.
The most recent reference to the rocks of the St. Dominique ridge is by G.M. Kay (1945) in an abstract of the geology of north-west
Vermont in the Bulletin of the Geological Society of America. Kay - 7 - measured and named a series of Middle and Upper Ordovician rocks
near Highgate Springs, Vermont, and correlated them with the
section at St. Dominique. In Vermont, the Beldens limestone
(500 feet thick) is overlain by the Carman sandstone
(135 feet thick) in turn followed by the Youngman limestone
(300 feet thick). These three are all of Chazy age, and in Kay's
article have been correlated respectively with the Beldens limestone,
and the St. Dominique sandstone and limestone at St. Dominique.
Unconformably above the Chazy in Vermont lie the Lower Trenton
limestone and Cryptolithus beds, the whole series being covered
by the Canajoharie dark shales. Kay's final report has not yet
appeared and when it does there will undoubtedly be faunal lists from
the Vermont occurences which will be invaluable in correlating the
Vermont rocks with those of the St. Dominique section.
In 1945 Dr. T.H. Clark made a thorough examination of the west half of the St. Hyacinthe map-area for the Quebec Department of
Mines. The greatest difficulty encountered in doing the geology was
the paucity of good outcrops and the presence of a deep soil cover, particularly on the plains areas to the east and to the west of the
St. Dominique ridge. On the ridge proper, soil and forest growth occupy 905K to 95% of the topography. Numerous quarries afford some of the best exposures but in one or two portions of the ridge comparatively excellent stratigraphic sections can be worked out. - 8 -
Because of this densely wooded cover over the ridge proper, traverses were run along lines 1000 feet apart and transverse to the general trend of the ridge, hence also transverse to the general strike of the formations. The paleontological collections made during the course of this work were relied upon for much of the stratigraphic correlation, but were not studied intensively.
Those same collections have been thoroughly reviewed by the present writer, and extensive faunal lists have been drawn up and are presented below.
In the fall of the same year, the author, in company with Dr. Clark, spent some time in the St. Hyacinthe area and was able to cover a considerable portion of it, particularly the portion called the St. Dominique ridge. At that time lithological samples and collections of fossils already collected were augmented, and as many field notes as possible were made to supplement the data already collected by Dr. Clark. The author has drawn freely from the field notebooks and the extensive collections of his thesis director and wishes to express his appreciation for this priviledge to both Dr. Clark and to the Department of Mines of Quebec. In the pages that follow, all of the identifications of fossils, the formational correlations, the structural explanations, the geologic history and conclusions are the products of the author's efforts and for which he alone is responsible. He acknowledges gratefully - 9 - the time and interest given throughout the work by his director together with the latterfs guidance, corroborations and technical advice which were freely forthcoming when requested.
Discussions with Dr. J. E. Gill concerning the structural aspect of the problem have been most helpful and enlightening. To Dr. W.M. Cady of the United States Geological
Survey and Dr. G.M. Kay of Columbia University, thanks are extended for their courtesy and encouraging suggestions. And finally, but not the least, the author is indebted to his wife for her patient and long hours spent in typing this manuscript. N
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GENERAL GEOLOGY
The western half of the St. Hyacinthe map sheet is
separated into three distinct units by two east dipping thrust
faults and the St. Dominique ridge is the central unit between
the two faults.
The easternmost thrust, which is probably a continuation
of the Granby thrust beginning farther south in the north-east
corner of the Sutton quadrangle, cuts across the south-east corner
of the sheet and separates the rocks of the St. Dominique thrust
slice from those of the Appalachian mountain-built province to
the east. It is in this eastern section of the map-area that the
red and green slates and quartz grits of the Sillery formation
occur. Except for this latter formation and the Recent alluvial
residual soils, all other sedimentary rocks in this part of the
St. Hyacinthe map-area are of Ordovician age. The rocks to the
west of the ridge are Lower Lorraine shales, and, in the extreme
north-west corner, Queenston shales and sandstones. Except for
local structural modifications, none of the rocks in this latter area were affected by the orogeny (or orogenies) which deformed
the rocks to the east.
The rocks of the St. Dominique slice range in age from
the Chazy through Black River and Trenton beds to include a - 11 - complex of shales which resemble the Utica and Lorraine formations exposed on the western foreland. This shale complex lies wholly within that part of the St. Dominique slice which is physiograph- ically distinct from the ridge proper and which forms a nearly featureless plain sloping down from the St. Dominique ridge towards the Granby thrust. Its width ranges from 3 miles in the southern part to nearly 6 miles in the northern part. Throughout this distance it falls only a few tens of feet. Although it is a major part of the St. Dominique slice, only occasional reference will be made to it; the prime concern of this paper being the
St. Dominique ridge, (Fig. 2).
The rocks of the ridge range in age from the Chazy to
Trenton and form not only one continuous stratigraphic unit but also a single structural unit. They are everywhere folded to a greater or lesser degree. Logan (1863, pp. 272, 273) credited this compact unit of rocks to the Deschambault anticline which
".....• brings to the surface, between St. Dominique and Faraham, strata of the Trenton, the Birds eye and Black River, and the
Chazy formations; the exposures being almost wholly confined to a comparatively narrow strip on the east side of the anticlinal axis. •••••. If continued in the same direction
/i.e. S. 15 W._y for eighteen miles farther, it would reach - 12 -
Missisquoi Bay on Lake Champlain, and run under the waters of this bay about three quarters of a mile west of Phillipsburg. From this, a gentle turn a little more southward, and would carry it, in four miles farther, to the shore of the same bay, near the
Franklin House, at Highgate Springs in Vermont. At this spot strata similar to those of St. Dominique, are brought to the surface by an anticlinal, which may not improbably be a con tinuation of that of St. Dominique and Farnham." Because the ridge is composed dominantly of competent limestones and dolomites, and to a lesser degree sandstones, the stricture is one of gentle open folds, whereas the less competent Utica-Lorraine shales to the east have been crumpled and badly distorted by the folding and overriding of the Sillery rocks along the Granby thrust. Subsequent weathering has added to the near obliteration of many of the original characteristics of these shales.
The main problem involved in the study of the St. Dominique ridge is whether the rocks comprising it are part of the Lowlands or whether they are part of the Appalachian province. The stratigraph- ically lowest rock exposed is a Chazy formation almost identical with the Beldens formation of central Vermont: the position of the latter is unequivocally within the folded province. Opposing this evidence is the fact that the higher beds of Black River, Trenton and Utica-
Lorraine ages are lithologically quite similar to those of the same ages in the Montreal region. Until the solution of this problem, - 13 - in which paleontology plays a strong part, is reached, we cannot satisfactorily reproduce the physiographic and sedimentation conditions as they were at the time of the deposition of the beds of the area as a whole. - 14 -
(D H H H CO •ri 0) 0) O o H .a o H 45 S3 •H H g s CD w a 0 o O § EH -P -P CO Q) -p CD Pi -p Q) Pi E-» s CD O H P« I CD o P» H EH g s 0) rO P* ft *d g o -P •H CD o » rl ft o Pi I •-5 O 5 1-5 W a) H •H s rA g CD o a> P* H CD •3 CD U H H PI Pi § CD CD CD CD CD p< no ft •p Pi •H O a) O ft O CQ PH 0 CD dj ei CD PI CD & s CD i -P O S O PI •H S M O •P Pi H o i-3 »3 EH PQ "A - 15 - FORMATIONS OF THE ST. DOMINIQUE RIDGE The two most advantageous localities where rocks of this unit may be seen are: 1. Along the main St. Dominique highway, in roadside cuts and nearly quarries and hills. 2. St. Pie hill - a small hill, not shown on the present topographic map, somewhat more than a mile north of St. Pie. The exposures here present in a very restricted area a compact section, showing all the formations of the ridge, though because of faults only the St. Dominique sandstone and limestone are completely displayed. The table of formations is shown on the preceding page. BELDENS FORMATION This is the lowest stratigraphic unit exposed in the St. Dominique ridge. For the most part, it occurs as the bordering formation along the western margin of the ridge. In a few places, where minor folding has disturbed the sequence of formations, the Beldens is also exposed as inliers within the area of the higher formations of the ridge. Logan mentioned the rock, though he did not name it, and also remarked on minor structural variations within it (1863, p. 206), thus:"A sandstone, , is supported by a very pure dove-grey limestone, without observed - 16 - fossils. Along the whole range of the exposures, the dip appears to be to the eastward; but in the neighborhood of St. Pie, some of the dove-grey limestone, a little removed to the westward of the range, has a westerly dip." The formation can be seen at several places along the ridge, but two localities surpass all others in presenting the most complete and unified exposure. One is in a disused quarry about one- third of a mile due north of La Carriere; the other is on the western flank of St. Pie hill. Of these two, that north of La Carriere is the better. Here the rock is well exposed in an anticlinal structure (axis 30 , plunging 10°N.E.). The predominant stratigraphic types, and these are typical of most of the Beldens exposures, are a pure light grey limestone, weathering white to dove grey, and a brown or orange brown weathering, fine grained dolomite, medium grey on a fresh surface. Measurement and examination of the rocks in the quarry and on the north-west flank of the anticline produced the following stratigraphic sequence: Tnp of Section Feet Inches A Brown weathering dolomite. 3 £ Solid grey limestone. 'Phytopsis' here and there. 2 6 Rubbly weathering impure grey limestone, rubbles formed by dolomitic streaks. Fossils; almost all ostracods. - 17 - Feet Inches 1 Brown weathering dolomite. 10 Unexposed. Probably dolomite. 2 Brown weathering dolomite. 6 Brown weathering dolomite with grey limestone in one inch fragmental layers. Intraformational (?) or structural. 2 6 Brown weathering dolomite. 4 Grey limestone. 6 Brown weathering dolomite. 5 6 Well-bedded grey limestone. Upper foot contains 'Phytopsis'. 1 Brown weathering dolomite. 8 Grey limestone. 2 Brown weathering dolomite. 6 Well-bedded limestone, in part streaked with brown. 2 Brown weathering limestone. 3 Pure grey limestone in beds about 2 inches thick. 3 Pure limestone below, grading upwards into a very pale buff weathering sandy limestone. 10 Finely banded pure light grey limestone. 1 6 Dense grained light grey weathering limestone. 4 Unexposed. 1 3 Dense grained, light grey weathering limestone, upper 2 feet well-bedded. 3 6 Dense grained, light grey weathering limestone, with 'Phytopsis' throughout. 53 feet 9 inches Total thickness, gaps included. In the quarry certain bedding planes are exposed over considerable areas. Many of these have slickensides whose striations strike at 115°, and the indications are that the upper beds moved towards the west over the lower beds. Such movement proved to have been general throughout the rocks of the ridge wherever this type of evidence could be found. - 18 - There is a remarkable resemblance between the grey limestones of the Beldens as here exposed and the dove grey limestones of the Lowville formation. Not only do both the fresh and weathered surfaces express this similarity but so also does the presence in the Beldens of those peculiar "fossils" (possibly worm tubes) which in the Black River are known as 'Phytopsis!. Were it not for the blebs, streaks and stringers of rusty dolomitic material in the Beldens, it would be exceedingly difficult to distinguish the latter formation from the Lowville where structural conditions were inconclusive. On a fresh surface both the orange weathering dolomite and the grey dolomitic limestone are medium grey colored, fine to medium grained and usually completely crystalline. The weathering is not confined to the exposed surface but penetrates for as much as half an inch, and can be seen developed on both sides of joint planes. A striking feature is the contrast between the almost white limestone and sometimes bright orange weathered dolomite. This criterion enables one to recognize the formation at a distance of several hundred yards. The limestone and the dolomite are inter- bedded in variable proportions, from laminations measured in hundredths of an inch to alternating beds each of which is several - 19 - feet thick. In another locality within a mile of the St. Dominique highway, the stone is traversed by a number of dolomitic stringers which in places tend to occupy the greater part if not all of the rock. The dolomite thus appears to be, in part at least, epigenetic in origin. Small scale cross-bedding is uncommon but can sometimes be seen where the dolomite and limestone are finely interbedded. Fossils found in limestone residuals in a partly dolomitized layer exposed 500 feet north of the quarry have not proved to be diagnostic of the age of the formation. Post-Beekmantown age is indicated by a variety of smooth-shelled ostracods, presumably of the genera Primitia and Leperditia. Fragmentary trilobites occur but nothing large or complete enough to be identified. Elsewhere, this formation can be seen at a number of places along the western margin of the St. Dominique Ridge. In fact, the most northerly exposure of the rocks is to be found in a small quarry 3^ miles north of La Carriere, where the light colored limestones and brown dolomites can be seen with an attitude of N.40°E., 65°E. About twelve feet are exposed. The St. Pie hill however is the best place for supplementing the information gained from the quarry previously described. Here the Beldens is the oldest in a remarkably well- exposed series of formations. Figure 4 is a detailed map showing Trenton £>/ack f?c ver Ch az y /mst. — Chaz.y Sdst. \3e/a/ens /mst showin9 Cf cr ion of exposures - 20 - the outcrop of this series. On the section line which passes from the summit of the hill towards the west, the succession of beds of the Beldens formation is as follows, in descending order: Top of Section Feet Inches White weathering sandstone of the St. Dominique sandstone member; Chazy age. 13 10 No exposure. 5 1 Buff weathering dolomite and dolomitic limestone. 10 Pale dove grey weathering limestone. 6 Missing. 3 5 Well-bedded dove grey weathering limestone. 1 9 Buff weathering limestone. 2 6 Missing. 1 9 Dove weathering limestone. 1 5 Pale buff weathering limestone. 1 5 Dove weathering limestone. 5 2 Missing. 3 U Well but irregularly banded pale buff weathering dolomite and dolomitic limestone. 6 8 Missing. 1 9 Grey limestone. 6 8 Pale buff weathering dolomite. 31 9 Missing. 3 10 Finely banded dove weathering limestone and buff weathering dolomite. 2 11 Solid, buff weathering dolomite. 1 9 Pale buff weathering dolomite. 6 10 Medium buff weathering dolomite. 30 11 Missing. Dove weathering dark grey limestones of the Trenton formation. Between these beds and the Beldens there intervenes a fault whose exact position is uncertain but which strikes approximately at 355°• 94 feet 10 inches Total thickness of Beldens beds, exclusive of stretches designated 'Missing' at top and bottom. 139 feet 7 inches Total thickness of Beldens beds, assuming that the stretches designated as 'Missing' at top and bottom belong to that formation. - 21 - Observation in the field shows that the overlying Chazy sandstone and adjacent Trenton limestone are relatively more resistant to weathering and erosion than the Beldens. It is, then, quite probable that the missing portions at the top and bottom of the section just recorded are occupied by rocks of the latter formation. Hence it seems justifiable to record its thickness as probably 140 feet. However a glance at the map will show that this cannot be the maximum thickness, for the section line does not cross the formation at its widest point. A further adjustment is thus in order. By suitable proportional allowances, the maximum thickness of the Beldens formation on St. Pie hill along the line Y-Y, can be determined to be, in relation to the section measured along the line X-X, as 166 is to 100. This results in a maximum thickness of 232 feet. Nowhere else along the St. Dominique ridge has such a thickness been observed. Elsewhere along the western margin of the ridge, the dis continuous outcrops add nothing to the characteristics of the Beldens formation already noted. North of the St. Dominique highway and visible from the road there are some exposures of dazzling white limestone. It may be that the limestone would always weather this brilliant white color under suitable conditions of exposure. It is in this same general vicinity that the previously described outcrops of limestone with dolomitic stringers occur. - 22 - FAUNA AND CORRELATION As previously mentioned the formation contains smooth ostracods and fragmentary trilobites. The following genera have been identified: Leperditia Leperditella Primitia Schmidtella Pterygometopus Bathyurus Of the four genera of ostracods, the last one presents some interesting variations. Several of our specimens have been tentatively referred to Schmidtella crassimarginata Ulrich. This suggests a Valcour age, although it has also been found in the Black River formation of Platteville, N.Y. Nevertheless, it has not been reported from rocks older than Valcour and for this reason may be of diagnostic value. Other species of Schmidtella in the Beldens will undoubtedly prove to be new. The fragmentary trilobites are not distinctive enough to be identified specifically. Like the ostracods the genus Pterygometopus is indicative of Chazy or later age. However, neither the ostracods or the trilobites have supplied anything d et ermina ble• Structurally the Beldens formation underlies the St. Dominique sandstones and limestones whose age has been ascertained by their contained fauna to be Upper Chazy. Help comes from another - 23 - source however. Cady, in his recently published work on the strat igraphy of parts of Vermont (1945, p. 550) described and named the Beldens formation for the first time. "Bright, orange-buff- weathering dolomite in beds 1 or 2 feet thick is interbedded with snow-white marbly limestone The sharp color contrast between these two lithologic types is distinctive. The dolomite has been described as "Chamois weathering" (Gordon, 1923, p. 258) and the peculiar sharply cut reticulations of the weathered surface make it look like "thread-scored beeswax" (Wing, letter to James Hall, 1867). Gleaming outcrops can be seen in the fields southeast of Beldens and west of the highway north from Middlebury. In the lower part of the formation the white marble beds are less abundant and the rock is a duller buff or gray and less dolomitic". Cady (1945, p. 552) cites several localities where fossils have been taken from this formation. Prominent among these fossils are bryozoa. The latter are not known in beds older than the Chazy, hence the post-Beekmantown age of the Beldens may be taken for granted The Beldens is an interesting formation because it appears to be an eastern facies of the Upper Chazy. In west-central Vermont the formation overlies the Crown Point, a fossiliferous Middle Chazy formation. Also it is overlain in this same area by the Middlebury formation of Valcour or Upper Chazy age. Even this does not definitely place the Beldens in the Middle or Upper Chazy although a gradation upwards of the Beldens into the Middlebury may be taken, - 24 - as Cady suggests (1945, pp. 548, 552) as an indication of the Valcour age of the Beldens. Due to the westward "overlap" of the Champlain thrust plate (Cady, 1945, p. 565) much of this zone of gradation is cut out between west-central and north-west Vermont. No such gradation is to be seen at St. Dominique. Instead the contact, though nowhere precisely seen, indicates a sharp separation of the Beldens from the overlying St. Dominique sandstone. Kay reports (1945, p. 1171) three Chazyan formations from the Highgate Springs sequence of north-west Vermont, the oldest of which is the Beldens. This has been cor related on lithologic grounds with the Beldens farther south in the same state and dated as of Middlebury age. Another interesting speculation concerning the Beldens formation is how far north the Beldens originally continued as such east of the present limits of the Appalachian province. There is nothing between St. Dominique and Highgate Springs that resembles the Beldens; possibly it was cut out in the Philipsburg slice by pre-Middle Trenton erosion. Unfortunately preservation of the fossils is extremely poor in each locale of the Beldens, the Highgate Springs section being the most productive so far (Kay, personal communication). The fauna is as yet unpublished. ST. DOMINIQUE FORMATION Approaching the St. Dominique Ridge from the west, the observer is impressed by the abrupt change in topography where the ridge and foreland meet. It is the limestone member of the - 25 - St. Dominique formation which is most instrumental in maintaining this sharp declivity. Underlying the limestone, but not every where exposed, is a sandstone member. The latter grades upwards into the limestone and with unknown, but probably abrupt, relationship with the underlying Beldens formation. Splendid exposures are in view in the vicinity of La Carriere, where several quarries are being worked in the limestone member, and also at St. Pie hill. Of the two locations the latter is preferable with respect to measuring sections, chiefly because both members of the formation are completely exposed and outcrop in one continuous section. At La Carriere the sandstones are not exposed and the limestone is involved in an undulating structure which makes the elaboration of a single section difficult. Referring to the map of St. Pie hill (Fig. 4) it will be seen that the section was made along lines at 90° and 312 from the summit. The stratigraphic sequence and calculated thicknesses of each bed are given below: TOP of section - east side of St. Pie hill, going torcrd the summit along the 90° line. Feet Inches X 4 Dolomitic limestone. 5 4 Grey crystalline limestone. / Buff dolomite, not uniformly developed along strike, grades into limestone. 2 8 Massive limestone. 2 8 Fine to medium grained grey limestone with buff weathering dolomitic patches. 10 8 Pale buff to orange, very fine-grained dolomite. - 26 - Feet Inches 4 8 Missing. 7 4 Buff weathering, fine-grained, grey dolomite. Weathered surface is speckled. 1 4 Light grey to whitish grey or buff weathering, finely crystalline dolomite and limestone. 1 4 Light buff weathering dolomite. 8 Grey limestone. 8 Cream weathering dolomite. 8 Missing. 3 4 Solid, buff weathering dolomite, similar to above. 8 Very light grey to cream weathering fine grained dolomite. 2 Grey crystalline limestone. 6 Missing. 1 4 Light brownish grey crystalline limestone; buff weathering. Fossils. 3 4 Missing. 2 Solid dolomite. 1 4 Light brownish grey crystalline limestone. Weathers buff to grey. Fossils. 2 8 Missing. 6 8 Same as below grading upward into dolomitic limestone. Fossils. 2 Coarsely crystalline, streaky limestone, about half and half dove weathering limestone and siliceous streaky matter. Fossils. 1 4 Light brownish grey crystalline limestone, weathering buff and mottled (?)dolomitic. Well banded. Trilobite remains. 3 4 Light grey limestone; calcite veins. 2 Massive limestone. 4, 8 Limestone with dolomitic blebs up to one inch. Trilobite remains. 2 Missing. 4 Dark grey, finely crystalline limestone with large dolomitic blebs and calcite veins. 2 8 Missing. 2 Solid buff weathering dolomite. / 8 Massive limestone, no blebs of dolomite. 8 Missing. 2 8 Same as below with many dolomitic patches. Limestone darker with partial irregular shaly laminations. 3 4 Same as below but dolomitic patches larger. Bryozoans• - 27 - Feet Inches 8 Pinkish grey crystalline limestone with many patches of buff weathering dolomite. Fragmentary fossils. 6 Light grey, massive crystalline limestone. Calcite veins. 1 4 Missing. 1 4 Light grey, slightly brownish, massive crystalline limestone. Abundant calcite veins. 4 Missing. 6 8 Crystalline limestone not well stratified. Dolomitic patches shown on weathered surface. 2 Missing. 8 Buff weathering dolomite. 1 4 Streaky limestone with network of buff weathering dolomite. 8 Crystalline limestone with blebs of buff weathering dolomite. (?) Echinoderm remains. 8 Compact, buff weathering dolomite. 8 Missing. 3 4 Dark grey, finely-crystalline limestone with buff weathering blebs of dolomite weathering out on surface. Some calcite. 2 8 Limestone well streaked with network of buff weathering dolomite. 8 Crystalline limestone with buff weathering patches and beds. Well veined with calcite. Fossil fragments. SUMMIT - from here the section is measured along a line at 312° • 3 4 Mixture of crystalline limestone and buff weathering limestone and dolomite. 9 Missing. 4 9 Limestone with abundant siliceous material in streaks more or less parallel with bedding. 10 Sandy limestone. 7 9 Solid crystalline limestone, criss-crossed with calcite veins. 8 7 Same as above, but with many streaks of buff weathering dolomite parallel to bedding. 2 6 Same as above. 12 10 Missing. 10 Sandy limestone, brown weathering. - 28 - Feet Inches 10 Same as above, grey weathering. 8 7 Limestone with siliceous streaks parallel to bedding. 11 1 Missing. 6 Streaky siliceous limestone. 1 9 Missing. Probable boundary between St. Dominique limestone and [St. Dominique sandstone. 8 7 Sandstone, calcareous at base. 3 5 Same as above grading downwards into equal amounts of sandstone and limestone bands. 11 2 Sandstone• 8 7 Sandstone. Lower 5 feet white weathering, upper part brown weathering. 8 7 Sandstone, calcareous, pitted with weathering. 14 7 Missing. 5 2 Calcareous shale, streaky with siliceous material. 5 2 Missing. 10 White sandstone. 6 10 Sandstone. 1 9 Missing. 1 9 Sandstone• 1 9 Missing. 10 Sandstone. 2 7 Limestone, siliceous. 10 Missing. 10 White sandstone. 10 Missing. 16 4 White weathering sandstone. 8 8 Same as above, with fucoidal markings. Probable base of sandstone. Probable top of Beldens formation. 14 8 Missing. / Buff weathering dolomite of the Beldens formation. 406 feet 1 inches Total thickness of the St. Dominique formation neglecting the 14 feet 8 inches missing at the base. This thickness can be broken down as follows: 109 feet 1 inch St. Dominique sandstone. 297 feet st- Dominique limestone. 406 feet 1 inch Total thickness of the St. Dominique formation. - 29 - Another locality where the sandstone can be seen to advantage is at the north-west end of the woods road which transects the St. Dominique ridge about 3 miles north of St. Pie. At this point 260 feet of sandstone and arenaceous limestone can be measured across the surface, which with a 30° dip means that the strata concerned are 130 feet thick. In the light of the St. Pie hill section, however, it is possible that the thickness would be pared somewhat, for what were earlier called arenaceous beds might well now be included in the St. Dominique limestone. Close to the base there is a 6 inch layer rich in fucoidal markings, similar to that which characterizes the base of the St. Pie hill section. The lithology of the limestone of St. Pie hill is no different from that of the limestone in the quarries at La Carriere except that in the latter the beds are more massive. Goudge (1935, p. 183) reports "Bedding is exceptionally heavy, one bed being 15 feet thick without a distinct parting plane". Also in these quarries a few other details can be seen which have not been recorded elsewhere, for instance, the uppermost Chazy limestones are in places filled with a small Stromatoporoid fossil about a half inch across, and, again, in the woods to the north there is a great development of what appears to be a coarse - 30 - o&litic limestone, but the oftlites are composed of a black material and may be organic. A very characteristic weathering effect is produced in the middle and upper parts of the Chazy limestone. "The stone is all of the clacium and high-calcium types, but there is a considerable variation in appearance and in purity. That formerly quarried for building stone is very dark grey, fine grained, very heavily bedded and is striped parallel to the bedding with wavy seams of siliceous, ferruginous, magnesian material that weathers to a light brown in contrast to the light grey colour that the remainder of the stone assumes on exposure. This siliceous material is more resistant than the rest of the stone and on weathered surfaces it stands out in relief" (Goudge, 1935, PP» 181 - 1^3). Earlier in the same report (p. 93) Goudge described the Chazy limestones of Montreal Island. The same tendency to contain impurities is present but the manifestation of them is different. - "Nearly all the Chazy limestone in the Montreal area, however, is characterized by the presence of mottlings streaks, and, in some places, interbeds of fine grained, ferruginous, and siliceous magnesian material, which, though scarcely distinguishable from the remainder of the stone on fresh fracture, weathers rapidly to an unsightly yellow colour and finally disintegrates, leaving pits and scars in the stone". In describing the same limestone of the St. Dominique ridge, Parks (1914, P- 77) wrote "This is a very fine grained, - 31 - dark coloured limestone it is distinctly composed of two elements - a lighter very fine grained crystalline component and a darker, argillaceous portion in which crystalline structure is not observable with the hand lens. These two types of rock are mingled together throughout the beds in a very irregular manner, giving to the smoothed surface of the stone a characteristic mottled appearance by means of which the St. Dominique stone may be recognized very easily. " On corrosion the contrast between the two components is more pronounced. The dark part assumes a dirty brownish colour and the lighter portion shows the ordinary whitish grey colour with a fine "pepper and salt" effect, showing it to be composed of pulverized fossil fragments. In the dark part also are to be seen still darker lines which are probably due to bituminous matter." Of very common occurence in the Chazy limestone are calcite-filled gash veins. These are found for the most part on the low flanks of anticlines and accompany the minor faults which cut the limestone in places. The fact that such veins are practically restricted to the Chazy and occur only rarely in the overlying Black River and Trenton limestones is due probably to the ability of these latter formations to deform plastically and to accommodate themselves to the stresses involved in the folding. - 32 - One other important characteristic of all of the Chazy limestone of this area is its crystalline nature. In this it resembles the Chazy limestone of the Montreal area, where, however, the crystallinity has been shown to be due to the fossilization of echinoderm fragments (Parks 19H, p. 21). This is likely to be the case with the St. Dominique limestone though so far no direct evidence of the presence of cystids or of crinoids has been seen. FAUNA AND CORRELATION Very little work has previously been done on working out the fauna of the Chazy limestone of the St. Dominique region. Logan (1863, pp. 205-206) mentioned a small list of fossils which were taken from the Chazy rocks north-east of St. Dominique. The list follows: "Ptilodictya fenestrata Orthis borealis 0. platys Strophomena alternata Vanuxemia Montrealensis Pleurotomaria Crevieri Ampyx Halli " Ells (1896, pp. 115 - 117J) published four lists of fossils from St. Dominique, Quebec", incompletely identified by Ami. One of the lists is the one given above. Ten years later Raymond (1906, p. 555) compiled a composite list, appropriately revising the - 33 - nomenclature. The species included in the list are: Paleocystites tenuiradiatus Liospira americanum? Bolboporltes americanus Trochonema umbilicatum Solenopora compacta Pleurotomaria cf. P. laurentina Fletcheria inserta? Lonchodomas halli Hebertella borealis Bathyurus cf. B. angelinl Plaesiomys platys Isotelus canalis Hebertella accuminata Asaphus marginalis Rafinesquina alternata Illaenus globosus Clionychia montrealensis Qphileta cf. 0. compacta Raphistoma stamineum Raymond's comment on this list (1906, p. 557) was "While it is not possible to refer any of these faunas to any one of the three divisions of the Chazy recognized at Chazy and Valcour Island, yet they show that all these localities are in the region of the typical Chazy fauna." Since the latter publication there have been no further faunal lists from the St. Dominique rocks published. This fact is not suprising when the small number of workers and the insignificant size of the area are taken into consideration. Despite the fact that no systematic collecting was attempted in the present work, a fairly large collection has been assembled and examined. The examination has been preliminary in the sense that it went no further than to identify species already known. In addition to these there are numerous new species which will require further concentrated study before uitimate descriptions can be published. Among these new species the Orthids and Strophomenids of the brachioPods, the smooth- - 34 - shelled ostracods and the Asaphid trilobites are the most prominent and abundant. The following is the list of identifications and assignations of the fossils from the present collections: Bryozoans Camarella varians Billings Camarotoechia plena Hall Camarotoechia pristina Raymond Camarotoechia cf. C. pristina Raymond Camarotoechia cf. C. orientalis (Billings) Camarotoechia sp. Clitambonites aff. C. porcia (Billings) Clitambonites sp. Dinorthis platys (Billings) Dinorthis aff. D. platys (Billings) Dinorthis cf. D. platys (Billings) Dinorthis (Valcourea) strophomenoldes (Raymond) Hebertella sp. Hesperorthis sp. Leptaena incrassata Hall Plectorthis nov. sp. #1 Plectorthis nov. sp. #2 Rafinesquina cf. R. distans Raymond Rafinesquina champlainensis Raymond _?• Strophomena sp. Valcourea nov. sp. Pelecypod? T.ophospira rfictistriata Raymond Raphistoma stamineum (Hall) Raphistoma sp. - 35 - Leperditella sp. Eurychilina latimarginata Raymond Eurychilina cf. E. latimarqinata Raymond Numerous smooth types. Amphion sp. Ampyx (Lonchodomas) halli (Billings) Basilicus marginalis (Hall) Ceraurus sp. Cybeloides primus (Raymond) Eoharpes ottawaensis (Billings) Eoharpes sp. ? Glaphurus sp. Homotelus obtusus (Hall) Homotelus cf. H. obtusus (Hall) Homotelus aff. H. obtusus (Hall) Homotelus sp. Illaenus cf. I. punctatus Raymond Isoteloides angusticaudus Raymond Isotelus cf • I. gigas Raymond Isotelus platymarginatus Raymond Isotelus cf. I. platymarffinatus Raymond Isotelus nov. sp. Pseudosphaerexochus sp. Pterygometopus annulatus Raymond Pterygometopus sp. Remopleurides sp. Sphaerexochus sp. Thaleops vindex (Billings) Thaleops cf. T. vindex (Billings) Voffdesia bearsi Raymond Voeflesia cf. V. bear si Raymond The trilobites of the St. Dominique offer the greatest and most interesting variations within any of the phyla represented, with the brachiopods following a close second. In neither of these -36 - groups however, are there any perfect or near-perfect specimens. The trilobite remains, for the most part, are broken cranidia, pygidia and hypostomae. Since no complete specimen of any one species was found, most of the dissociated body fragments are meaningless. The brachiopods offer more complete preservation in so far as external form and ornamentation are concerned, but not a single interior view of any shell was found. Despite the drawbacks encountered in identifying the trilobites and brachiopods they did not present the ironical aspects of the ostracods. The latter group were particularly frustrating in that although they showed good preservation of form and were exceptionally abundant, they were almost entirely devoid of ornamentation. For this reason they are mostly unidentified, and it will require a tremendous amount of time and meticulous effort to work out not only the species but even the genera of these numerous smooth-shelled types. Several genera of bryozoans occur in the St. Dominique limestone but they remain at present unidentified. It is of interest at this point to note that such genera as Hebertella. Blastoidocrinus and Bolboporites, which are common in the Chazy around Montreal, are almost or completely missing from the St. Dominique rocks. Ells and Raymond include Bolboporites in their lists as occuring here but not a single specimen of it has been found so far in the present collections. - 37 - The Chazy age of the St. Dominique limestone is shown by the fauna it contains, but a definite correlation of this fauna with any of the known Chazy sections has not proved entirely successful. A comparison of this fauna with those from other areas is shown in the table on the following page. From this list it can be concluded that the fauna is Upper rather than Lower Chazy but there is nothing decisively indicative of either Crown Point or Valcour age. Although the species of Crown Point age outnumber either of those of Day Point and Valcour, this does not necessarily mean that the St. Dominique limestone was deposited in middle Chazy time. On the contrary there are several features which seem to out weigh all others and which point to an Upper Chazy age. First, a number of species show a relationship to the Chazy of the Quebec Lowlands. The relationship with the Caughnawaga formation of Montreal is not a close one, and is even more distant with the Chazy of the Ottawa region, but a number of brachiopod species indicates that the two areas were not completely dissociated in Chazy time. The absence of any trilobite species common to both the St. Dominique and Caughnawaga formations is of curious interest. Clark (1944, p. 259) writes " it can be seen that the Quebec exposures £ of Chazy_/ represent only - 38 - oO x x X S» !»X X X X X X X X X > MM u u E 0 X X XXX X X X X X O X X X XXX X Q to T3 CQ iH^*d (0 W)H to a o tuo dHbflO rA o cd A H s 3 •H CO PQ 0 o CO CO the upper part of the typical Chazy. Evidently this region was not inundated until toward the close of the Chazy time." Secondly, Bolboporites which has not been reported from rocks younger in age than Crown Point has not been recognized in the present study in any of the rocks of the St. Dominique ridge. Its absence then would seem significant in support of the other evidences which point to post-Crown Point (i.e. Tjpper Chazy) age. Finally, the abundant occurence of Camarotoechia plena is a fact which more than any other one impresses the author with the Valcour age of the St. Dominique limestone. Hall (1847, pp. 14 - 36) expanded the Chazy limestone, which at that time consisted of only the middle, or Maclurites ma gnus zone, to include a lower or Hebertella exfoliata zone and an upper or Camarotoechia plena zone. Since that time the presence of C. plena has been considered diagnostic of an Upper Chazy age. The stratigraphic position of the underlying Beldens, though not indicative in itself of a precise age, is stated by Cady (personal communication) to be an eastern facies of the Upper Chazy and that in west-central Vermont it grades laterally into strata that overlie the Crown Point and are much more like the Middlebury and typical Upper Chazy. The Middlebury contains - 40 - in its fauna (Cady, 1945, p. 553) such species as Raphistoma stamineum, Dinorthis platys. Ampyx halli and Camarotoechia plena. In the Highgate Springs area, the Middlebury is equivalent to a succession above the Beldens zone and beneath the Black River. Also the Middlebury is, according to Cady (ibid.) apparently equivalent in position to "Group C, 8 - 13" of the Chazy at Chazy, N.Y. (Brainerd and Seely, 1888, p. 325). This zone contains numerous brachiopods, particularly Camarotoechia plena. Although the St. Dominique formation in general differs lithologically from the "buff-streaked, dark blue-grey, somewhat nodular and granular, thin-bedded, incompetent, partially dolomitic limestone" (Cady, 1945, p. 552) of the Middlebury in having a sandstone member at its base and the more dolomitic and thick bedded limestone member at the top, the two formations are not irreconcilable. The occurence in the Highgate Springs section of two formations above the Beldens, a lower sandstone and an upper limestone, is in closer harmony with the Chazy stratigraphy at St. Dominique. Despite the not too compelling evidence it is almost certain that the St. Dominique formation is of Valcour age, and that while the lithology is more siliceous and argillaceous than equivalent strata to the south in Vermont and New York, the fauna has closer affiliation with the American Upper Chazy than with that of the Ottawa-St. Lawrence Lowlands. J A Trent o | \Leroy Imst. om/il/e /m: ? rbmc/ia J S I Ch a zy lm: / , i ath ' L .7 Ca< r riere andoned quarry - 41 - FORMATIONS OF THE BLACK RIVER GROUP Stratigraphically above the Chazy limestones are three formations which are provisionally assumed to represent the Pamelia, Lowville and Leray formations of the Black River group. There is an almost complete lack of fossils in them in this area besides the lack of good exposures and because of this, they are not positively correlated with the standard Black River of the Montreal area. A fair lithological similarity plus the added fact of being situated between the Chazy and Trenton formations are the criteria used in associating them with the Montreal Black River. Fresh rock exposures of the group are best seen in two places. First, in the quarries at La Carriere, some of which in 1946 were in operation, and second, on an old abandoned quarry I of a mile due south of La Carriere. Leray limestones, but not Lowville or Pamelia, have been identified in the woods north of the highway. South-west of the highway, the only rock identified as Black River other than in the localities listed above is to be seen along the woods road which cuts across the ridge about 3 miles north of St. Pie. Possibly some of the rocks involved in the faulting at St. Pie hill may belong to the Black River group. It is in and adjacent to the second locality cited above that the best outcrops are to be seen. The quarry (Fig. 5) is - 42 - 700 feet long and its walls range up to 15 feet in height. It measures 115 feet across at its widest point. The exposures are confined to the walls and nearby rims. The Chazy and Trenton are also exposed in this locality although no contacts between these limiting formations are known. The beds form the east limb of an anticline whose axis strikes almost exactly towards the quarries of Black River rock at La Carriere. The stratigraphic sequence, as measured in this quarry and immediate neighborhood, follows: East of the quarry wall Cryptolithus limestone Dark grey weathering, dark grey slabby, shaly and sandy limestone. Can be seen on a small knoll east of the farm road about opposite the middle of the quarry. Trenton Group- Gap of 66 feet Feet Lower Trenton 5 Fragmentary crystalline limestone containing bryozoa. Exposed continuously along eastern wall of the quarry. Leray limestone White weathering limestone, oolitic at the top, in part conglomeratic with pebbles of limestone up to one inch, in part fragmental with the grain 16 of a coarse sandstone. Dark, finely-crystalline limestone, medium grey weathering, with a few beds of limestone conglomerate. - 43 - Feet Dark conglomeratic limestone, weathering light grey, pebbles up to one inch. Fine-grained dark fragmental limestone, really a calcareous sandstone. Quartz grains up to one mm. present but uncommon. Thick and irregularly bedded; cross-bedded. Fragments of 18 unrecognizable trilobites. 44 Total thickness of Leray Black River Group Lowville limestone Sandy limestone, with abundant quartz grains up to one mm. rounded and frosted. Grading upward into exceedingly fine grained pure, pale dove grey lime stone with Tetradium. Other fossils rare; poor gastropods and pelecypods, neither collectible nor identi- 7 fiable. Pamelia dolomite Grey, yellow to brown weathering magnesian beds. Bedding obscure. No fossils. No contact with over lying or underlying beds. Might 15 to 20 belong to the Chazy Group. St. Dominique limestone Medium to coarse grained crystalline limestone, dolomitic streaks and Chazy Group- patches common. Small Stromatopora- like fossils up to one inch in 10 diameter. Other fossils scarce. - 44 - Thus in this quarry at least 51 feet of Black River rocks are exposed and possibly as much as 70 feet, depending on whether or not the lower dolomite is referable, as given above, to the Black River, or, as is possible, to the Chazy. Of the two localities previously cited as the best for exposures of Black River rocks, the one remaining is the group of quarries near the highway at La Carriere. The positions of the four quarries are shown on the accompanying map (Fig. 6A). The two most northerly of these were, in 1946, being worked for lime. The stratigraphic section in the northernmost quarry is as follows: Leray limestone Medium grey, light grey weathering, fragmental, even grained, crystalline limestone, some crystals pink. Cross- bedded in places. Probably an echinoderm detritus. Abundant quartz grains, rounded and frosted, up to 5 inm. Some thin layers are so full of these as 6 feet exposed to be almost a sandstone. Black River Group Lowville limestone Dense, light dove grey, white weathering limestone, abundant quartz grains up to 1 mm. 'Phytopsis1 tubes common, no Tetradium or other fossils seen. Evenly bedded layers from 2 inches to 12 inches thick, mostly 6 inches to 8 inches. Two zones of intra- 13 feet exposed formational conglomerate at top. Pamelia dolomite Brownish orange weathering, finely- crystalline dolomite. No fossils. Medium grey when fresh. Separated from Lowville by a vertical fault. 10 feet exposed No contacts with adjacent Chazy. X \ ' y 1 ^ x x' v y4 O IOO » • FIQU&EL 6r The most nort^er/y o / -^ / *v 23' " ~- / io- ^J N / >* ,5 c <* / \ X. N FIQU&E F/QURCZ 6A : Quarries at 6c: The most La Carr thr-e exposc n Leray Chazy \?Pame/ia Lowvi.l/e - 45 - The middle quarry of the three north of the road shows limestone which is essentially like the Lowville described above, save that it is somewhat lighter in color and it probably represents the lower part of the formation. About three quarters of the rock is "dense" and the remainder is made up of calcite crystals up to 5 mm. across. Rather than being crystallized echinoderm fragments these would seem to be the result of the crystallization of the "dense" calcareous material of the rock itself. It is of interest that the Lowville limestone in the southwest corner of the quarry nearest the road on the north side has a westerly dip, possibly related to the faulted contact visible on the road nearby, or possibly the reflection of a small anti clinal swell such as is seen in the quarry south of the road. This latter quarry is approximately in line of strike with the other three and the structure indicated above (see Fig. 6C) is shown in the north-east wall. The rock types here are the same as before with 10 feet of Lowville and 20 feet of Leray limestones exposed. Many of the beds are slickensided. The striations strike at 110° and indicate a westward movement of the upper bed. Both the slickensides and the drag fold are probably reflections of the deformation consequent upon the overthrusting of the Sillery slice. -46 - FORMATIONS OF THE TRENTON GROUP The bulk of the St. Dominique Ridge is composed of limestones and shales of Trenton ages. Although exposures are poor and few within the wooded portions of the ridge, the presence of these rocks is usually betrayed by abounding fracture cleavage slabs or blocks of pale dove grey weathering, dark grey to black limestone. In places where the woods have been cleared and the thin protective soil covering removed, the Trenton limestones and shaly limestones are exposed in prominent or in low ridges. Poorly developed flow cleavage and fracture cleavage, probably resulting from the abundance of argillaceous material within the limestone, have split the rock across the bedding in most of the outcrops. Consequently the search for fossils is difficult and disappointing. In the last mentioned quarry in the description of the Black River group, the lowest Trenton bed is found practically in contact with the Leray limestone, and forms the eastern wall of the quarry with not more than 5 or 6 feet exposed. Here the Trenton is a fragmental, partly crystalline limestone rich in comminuted shells and bryozoan colonies. In all cases, preservation was too poor to permit identification. It is suspected that this limestone is equivalent to the Mile End limestone of the Montreal - 47 - area. Although the evidence is inconclusive, the general lack of argillaceous material plus the high content of fragmentary fossils make such an assignment reasonable. Furthermore, it exhibits an appropriate stratigraphic position. THE CRYPTOLITHUS BEDS To the east of the quarry, 66 feet of sediments are hidden between the basal Trenton beds and a shaly limestone or limy shale exposed on a small knoll (Fig. 5). This rock contains Cryptolithus and strikes north-northeast towards the Cryptolithus beds extensively shown north of the St. Dominique highway. The latter beds occur in a long continuous ridge extending for more than half a mile until it merges into wooded topography to the north. The Cryptolithus beds are everywhere shaly limestones and contain Cryptolithus tesselatus in abundance. The fauna is meagre and consists of the following species: Prasopora Simulatrix Rafinesquina alteraata Sowerbyella punctostriata Cryptolithus tesselatus Calymene senaria None of these is of much value in placing the containing beds in a subdivision of the Trenton group, save Cryptolithus, which elsewhere is restricted to the lower middle part of the - 49 - Platystroohia amoena Zygospira recurvirostris Eotomaria sp. Calymene senaria Isotelus. large species Ceraurus sp. Despite the fact that all of the species are long- ranging ones, the assemblage as a whole is the same as that of the Middle Trenton of the Montreal area — i.e. Rosemount member of the Montreal formation. The absence of Cryptolithus separates it from those beds, and as far as the Montreal section is concerned the absence of Rafinesquina deltoidea. cystids and large cephalopods separates it from the overlying Tetreauville formation. THE HIGHER TRENTON BEDS Above the Rosemount beds there is a development of thin bedded, finely landed, shaly limestone, well exposed lj miles north-east of the road corner on the main highway between La Carriere and St. Dominique. The distinguishing feature of this rock is the remarkably fine and persistent banding. Bands ranging from 0.5mm. to 10mm. of light colored crystalline limestone alternate with relatively thinner bands of dark colored, apparently non-crystalline limestone or shaly limestone. No fossils were seen - 50 - anywhere in this rock but tiny gastropods occur in beds probably immediately underlying them. Only scattered exposures of rock occur to the east of these banded strata. Such exposures are to be seen in road cuts lj miles north of St. Pie and in nearby meadows. Similar rocks outcrop in road cuts towards the north-northeast. The rock is predominantly shaly, in places even slaty, throughout this belt. UTICA-LORRAINE SHALES To the east of and apparently overlying the higher Trenton beds just described is a group of predominantly shaly rocks; in fact, they are often slaty. These are the shales which occupy the nearly featureless St. Dominique plain forming the eastern portion of that structural slice between the Granby and St. Dominique thrusts. The plain slopes down very gently eastward from the St. Dominique ridge. Outcrops are not numerous, the soil cover of pasture and farm lands obscuring the greater part of the bed-rock. Road cuts afford most of the exposures but a smaller number are also seen in adjacent fields. Lithologically these shales have very little in common with the Trenton beds; they are, however, quite similar to the Utica and Lorraine groups of the Lowlands area, and they are shown as such on the accompanying map. The intensely broken and - 51 - disturbed character of this band of shales is akin to the structure of the so-called St. Germain complex in the Upton map-area farther north. The Trenton contact with these rocks was nowhere seen but the shortest distance between the two types is near the four corners a mile or so north of St. Pie. At this point in the roadside cuts, fine-grained micaceous slates and shaly limestone are exposed. Two brown and orange weathering lime stone beds, each about 6 inches thick (one slightly petroliferous) contain small black flakes which possibly might be organic fragments. It is in this respect that the rocks resemble the Utica brown and orange weathering limestones and sandstones where they are exposed at Lotbiniere shore. Utica-like rocks, almost the same as the ones just described, are to be found in the bed of the Black River which flows through St. Pie. At a point on the river where a 10 foot basic sill forms a rapid, a dam has been built. At and below the dam is a variety of grey and buff weathering limestones, calcareous sandstones, fissile micaceous shales and slates. Unidentifiable fragments of trilobites, brachiopods, bryozoans and crinoid stems were found in one of the limestone layers and feint carbonized traces of graptolites in shale members. Such obscure organic remains are typical of the Utica and basal - 52 - portions of the Lorraine. Ells (1896, p. 19J) remarks on the finding of graptolites in this vicinity and the ten fossils (1896, pp. 19J, 142J) listed as Trenton are undoubtedly from the bed of Black River. "At St. Pie, a short distance below the road bridge, ledges of black and bluish-grey limestone, with thin veins of calcite, cross the stream. These rocks are generally slaty and are cut by dykes or diorite In a band of slaty limestone, between the Canadian Pacific railwy-bridge and the road- bridge / a locality at present inaccessible^/ graptolites were found, with long, straight, single forms from a collection made in 1879 ...... ten species were determined by Dr. Ami which showed this horizon to be Trenton." Actually, the beds in the Black River below the dam site are of Utica age and it is possible that all of the exposures there are of the same age. To the north-east of these Utica shales and limestones, exposures of rock closely resembling Lower Lorraine rocks were found. At a locality l| miles north of St. Pie an outcrop of grey calcareous and slaty shales, shaly limestones and quartzites is exposed in a pasture. No fossils were found at this locality. At a distance of 7£ miles further north-east, and one mile south-east of St. Hector, shale and slate exposures contain fragments of bryozoan and brachiopod fragments of the same general kinds which characterize - 53 - the Lower Lorraine beds of the Nicolet River section. Except in very thin bands, Lower Lorraine shales are characteristically unfossiliferous even in those areas where they are practically undisturbed. In view of this, the absence of fossils in the numerous small exposures of relatively distorted shales is not surprising. Further north from the last locality, both at St. Liboire and about a mile south of the village, there are outcrops of shale and sandy shale and sandstones inter bedded with slate. The sandstone is well banded and weathers yellowish to orange; most of the shale is finely-bedded. This is typical of the upper part of the Lower Lorraine series. From the foregoing observations it may be generalized that there is a progression from older to younger rocks eastward across the St. Dominique plain. This same generalization may be applied to the rocks of the St. Dominique ridge. However there is no justification in assuming that the thickness of these Upper Ordovician sediments can be estimated with any degree of accuracy, for they have doubtless been folded and fractured by the overriding Sillery slice and the subsequent distortion of the argillaceous beds, which may well have lubricated the thrusting mechanism, has made impossible any evaluation of the present complicated structure. - 54 - STRUCTURE FOLDS AND FAULTS The St. Dominique slice is bounded on the west by the St. Dominique thrust and on the east by the overriding Sillery rocks along the Granty thrust. There is no direct evidence that the western boundary is marked by a thrust fault, or a fault of any kind, for none has actually been seen. It is possible that the rocks just described are part of the eastern limb of a nearly recumbent anticline which has been overturned towards the west by a force acting from the east. Inasmuch as the western edge of the ridge marks the boundary between the St. Lawrence Lowlands and the Appalachian mountain-built province and also contains appropriate competent formations, it is not impossible that the mountain-building movement could have died out in an overturned fold rather than the thrust fault type which dominates the structure to the east. This would imply that the overturned anticline is superimposed on an adjacent, underlying syncline which in turn must be thought of as being continuous with the strata under- !ying the immediate Lowlands. Such continuity would not oppose the thesis that the rocks of the St. Dominique slice, though showing affinities - 55 - with the Lower-Middle Ordovician rocks in the Appalachian province, are more probably allied with those of the St. Lawrence Lowlands and are nothing more than a fragment of the periphery of the latter sedimentation area which has been caught and crumpled by the Appalachian orogeny. There is no real evidence of such a continuity. The hypothesis would require the subjacent syncline to be forced some distance below the present surface which in turn requires extraordinary plasticity of beds and a strong deforming pressure. It would be more feasible to consider the St. Dominique slice as originally having been an uninterrupted part of the rocks to the west which was caught in the Appalachian orogeny, folded and thrust-faulted westward. In this process it would have overriden rocks of its own sedimentation province and in turn would have been covered by a successive thrust slice from the east. In the absence of conclusive evidence, the boundary is mapped as a thrust fault which, following subsequent erosion, is expressed partly ty its sinuous character. Along the west side of St. Pie hill, Upper Trenton limestones (N.6°E., 50°E.) are in contact with both the Beldens and the St. Dominique formations (N.10°E., 70°E.), and possibly the Black River sediments, along a straight line striking 355°. This is one of the few instances where faulting - 56 - has been mapped with confidence. The fault has been traced for 2000 feet in a straight line from the southernmost tip of the hill northward where it is lost in the soil cover of a pasture. The actual fault plane was never seen but the outcrops of dove grey weathering, dark blue grey Trenton rocks on the west and sub-Trenton series on the east are in such a juxtaposition as to place the fault trace within a zone not more than several feet wide. The fault, cutting the general strike of the beds o o at an angle of 10 to 15 is a steep-dipping to vertical, trans verse slip fault with a minimum horizontal displacement of 844 feet. This figure is arrived at from the following computations. Using the figure 400 feet for the St. Dominique formation and 60 feet for the Black River and estimating the Lower Trenton and Cryptolithus zone to be 150 feet thick, the minimum displacement where the top of the Beldens and the dove grey Trenton come together in 610 feet. The Beldens dolomite is estimated (p. 13) to be 232 feet thick at the north end of the hill where the fault is last shown. This is aminimum and would be increased by such stratigraphic thicknesses as might have been present above the exposed base of the upper dove grey Trenton. Hence the Tfclue of 844 feet. Within the limits of the St. Dominique slice the ridge - 57 - area is dominated by a series of competent, often thick bedded strata which are gently undulating and in general dip toward the east. Rarely do the dips exceed 20°. Locally as much as 75° to the east has been recorded but for the most part a range of 5° to 20° is the case. In some places a reversal is noted with a low dip to the west. These beds of the ridge are followed over the plains area by stratigraphically higher and higher beds. The latter have more shaly facies with a tendency to slaty cleavage and steep dips, until at the eastern margin of the map they are intensely folded. The distribution of the formations in the area is shown in Fig. 3« Except where irregularities are shown, the beds strike north-northeast with a uniform dip to the east. However at those points where a deviation from the general rule is encountered, there are undulations down the dip with horizontal attitudes and even western dips. Such is not a common occurence but then again it is not unusual. The varying outcrops widths undoubtedly are due in part to these irregularities of dip. One mile north of La Carriere, two low synclinal folds with a plunge N.10°E. have been mapped. These account for the greater outcrop width of the Chazy between the lines A-A and B-B (^g* 3). Immediately to the north the much lessened outcrop ^dth of the same formation is difficult to explain on the single -58- hasis of folding. There is a small south-plunging syncline of Chazy sandstone at the point Z, but this alone would hardly account for the sudden narrowing of the outcrops north of line B-B. A more probable explanation is advanced below. In each of these cases of folding the fold axes trend about N.30°E. and do not exceed 10° in plunge. Splendid examples of slickensides are also shown. North of La Carriere the bedding planes in the low folds have slickensides at 295° and showing the upper beds to have moved west. Halfway between this locality and La Carriere in a small quarry slickensides (at 295°) again show a westward movement of the upper beds. In the quarry immediately south of the road at the same town, the observation is repeated: slickensides at 110°, upper beds moved west. As indicated in the introduction, the geological mapping of the ridge was accomplished by traverses at right angles to its trend and spaced 1000 feet apart. The results showed not only irregularities in the outcrop width but also discontinuity of the formations along their strike. In those instances where an offset of the formations reaches a large value there is difficulty in interpreting the cause In the northern half of the areawhere the undulatory nature of the toe is definitely established, the minor irregularities along the - 59 - strike are probably best explained as an expression of flexures or shallow folding. Such a solution however does not lend itself to the interpretation of the major discontinuities. For instance, between lines A-A and B-B the outcrop width of the Chazy limestone is almost three times as great as that between B-B and C-C. In itself this difference could probably be explained as due to undulations of the limestone betvreen A-A and B-B, whereas between B-B and C-C, the normal outcrop width is maintained by the uniform east dip of the beds. But this does not satisfy the problem of such a sudden structural change. Moreover it demands that the widely separated, equally thin outcrops of Black River be connected nearly along the line B-B and shown as a severally folded bed. There is no evidence at this particular locality of such folding. The only other reasonable hypothesis is that during the time of thrust-faulting, the area was divided into a number of transverse fault blocks by a series of vertical faults. Unequal tilting of these blocks has resulted in varying widths of outcrop as well as displacements along the strike. The same embarrassment as for that of folding arises with this explanation — lack of field evidence other than irregularity of outcrop. The dips of the beds involved do not wholly corroborate this view of block tilting. - 60 - South of the St. Dominique road the Chazy limestone preserves a nearly uniform width of half a mile for some distance. There is no evidence of plunging folds from either the map or the field. Along the lines D-D and E-E however there is considerable narrowing of the limestone. This particular case could have resulted from the tilting of a narrow block between two cross-faults- or it might be the result of a combination of folding and faulting. However, it is noteworthy that towards the southern tip of the ridge, there is a general tapering of the beds with a persistent narrowing of the outcrops in that direction. Accompanying, and presumably causing, this there is a general increase in the easterly dip. It is more than probable that the irregularity of the strike of the outcrops in this particular sector is due to nothing more than a minor fold in an area of increasingly steeper dip. In the absence then of complete structural data it has been necessary to introduce cross faults wherever nothing else serves to explain the phenomena. None has been seen, and generally there is no direct field evidence of them, merely irregular distribution of the strata. In view of the fact that gentle flexures have been mapped in portions of the area it is not unlikely that such structures account for many of the variabilities. In other places the combination of cross-faulting and plunging folds aPPears to be the most likely interpretation. - 61 - The cross-faults have been placed half way between the surveyed lines, consequently it is quite possible that they may be a few hundred feet out in either direction. In the northern part of the map the faults have been drawn to strike nearly 315°. No presumptions are made as to the precise accuracy of this direction. It is however best adjusted to the mapped outcrop pattern. Minor faults occur in many places. In the northernmost of the three quarries exposing Black River rocks at La Carriere, a strike fault and a dip fault are shown (Fig. 6B). Again north of La Carriere, small faults are seen in the Beldens formation, while south of the highway at the same town others may be seen in the Chazy limestone. CLEAVAGE In the rocks of the St. Dominique ridge, very little cleavage of any kind is found. In the plain to the east of La Carriere the Trenton limestones and calcareous shales show marked fracture cleavage with an attitude of N.20°E., 60 E. In the Trenton limestones north of the highway it is very evident striking N.15°E. with dips of 60° to 80°E. In this general area it is impossible to break the rock along bedding - 62 - planes, this feature contributing largely to the difficulty in collecting fossils. Along the highway between St. Dominique and La Carriere, fracture cleavage is very well shown in the road cuts. A persistent attitude here is N.20°E., 60°E. In the Utica-Lorraine terraine farther east, folding is so complicated as to make bedding almost indistinguishable from cleavage. Recordings of attitude show a variation in strike from N.20°E. to N. 70°E. with all the dips from 70°E to nearly vertical. GASH VEINING The Chazy limestones appear to be exceptionally susceptible to gash veining while the other formations show very little, if any, of it. For the most part the veins occur on the flanks of low anticlines and accompany minor faults which cut the limestone in places. Generally they approach a vertical attitude in the horizontal beds but assume a radiate pattern in the dipping strata, always cutting the bedding at right angles. Some of them are remarkably Persistent, coursing through 20 feet of heavy bedded limestone. On the average they are 3 to 7 feet long and pass from one bed to another without any respect for slight lithologic changes. In the quarry south of the road at La Carriere, they are well displayed and here seem to be due to tension accompanying the drag of the beds on the -63 - side of the fault. A splendid example of gash veining is on the north face of the new quarry at La Carriere. It is rather remarkable that they are rarely seen in the overlying Black River and never in the Trenton limestones. Probably it is because these formations were more easily deformed plastically to accommodate themselves to stresses involved in the folding. -64- GEOLOGIC HISTOBJ OF THE ST. DOMINIQUE RIDGE The absence of Cambrian and Lower Ordovician sediments in the St. Dominique slice leaves an important gap in the early history of the area. That Cambrian and Lower Ordovician beds were continuous below the Beldens prior to faulting is most likely true, for they are present below the Middle Ordovician to the west and south. There is no evidence of them however, and consequently no speculations as to their nature can be made. The sediments forming the St. Dominique ridge were laid down in a part of the Ordovician settling basin which at one time or another was open to the south and to the west. Undoubtedly the present position of the St. Dominique rocks is not their original position, for the rocks have been folded and thrust westward. In comparison with those to the east this slice is almost insignificant in size. Its present position together with the relation of its rocks to those of both American and Canadian known sections, leads to the conclusion that the original site of deposition was not far to the east of its immediate locale; probably not more than several miles. Since the exact location of this deposition area is unknown, the following history of the region is written with respect to where it now stands. It should be kept - 65 - in mind however that the place names are used for the sake of explaining the relations of the rocks and are not to be con sidered as indicating the localities where the original deposition took place. The Beldens formation is lithologically similar to and is here correlated with a formation of the same name in north-west and west-central Vermont. It is quite certain that there was, during Beldens time, an open basin of sedimentation connecting St. Dominique and west-central Vermont (Fig. 7B). The lowest dove grey weathering, light grey dolomitic bed of Beldens limestone is the first record of the Ordovician rocks in the St. Dominique ridge. The maximum possible thickness of this formation is somewhat less than 240 feet. Compared to the Highgate Springs and west-central Vermont areas where maximum thicknesses of the Beldens are recorded as 500 feet and n600 or 700" feet (Cady, 1945, p. 551) respectively, this thickness is remarkably small. The base of the Beldens in the St. Dominique area has never been seen and it is possible, in fact probable, that only an upper minor portion of the formation became involved in the immediate thrust. Previous writers have described the Chazyan sediments of the Ottawa-St. Lawrence Lowlands as having been laid down in an embayment of a more widespread Chazy sea in - 66 - the eastern part of the Appalachian geosyncline. The embay- ment, which would be part of the so-called St. Lawrence sea or St. Lawrence geosyncline (Schuchert, 1923, pp. 172, 177), probably spread westward to some point north of the Lake Champlain area and thence southward, for there is a progressive overlap of younger Chazy sediments to the south along the west side of Lake Champlain. That the sea did not come directly from northern Atlantic or Arctic areas is evidenced by the complete lack of Lower and Middle Chazy rocks in the regions of Ottawa, Montreal and St. Dominique and also by the thinning of Upper Chazy rocks north of these localities. From some point south of St. Dominique, and probably near west-central Vermont, the Chazy embayment began to spread north and west towards, and finally beyond, Montreal. It was in this first advance of the Chazy sea over the St. Dominique region that the Beldens dolomite was deposited. The lithology of the Beldens at St. Dominique compares favorably with the white, dense limestone and buff weathering dolomite at Highgate Springs but lacks the sandy- streaked limestone member of the Beldens formation (the Weybridge member) found in west-central Vermont. At Isle La Motte, Brainerd and Seely (I896, p. 312,- Brainerd, 1891, P- 298) reported a - 67 - "dove limestone with bands of magnesian limestone" in the Upper Chazy which is similar to that in the Highgate Springs slice and resembles the "dove" limestone described in the Upper Chazy at Chazy, New York, west of Isle La Motte. At the latter point the particular facies is referred to as "Group C, 1-7" (Brainerd and Seely, 1888, p. 325) and recorded as 23 feet thick. There is some evidence of shallow water conditions in part of the Beldens exposed at La Carriere. This is shown in a 6 inch bed of brown weathering dolomite in one inch fragmental layers about 25 feet from the top of the formation. There is doubt as to whether this thin bed represents an intraformational conglomerate or some precon- solidation disturbance. In the same quarry at both the top and bottom of the section, the peculiar markings known as 'Phytopsis1 may be fossil worm tubes, and if so it is a possible indication of shallow water conditions. On the whole, the hard, fine, compact nature of the formation indicates that the sea was well established over the areas and that sedimentation in fairly clear waters some distance offshore had been in progress for some time (Fig. 7B). Because the contact has never been seen, there is no evidence of the nature of the change from the Beldens type of sedimentation to that of the St. Dominique sandstone. It is probably abrupt because at one locality where the two formations are within 13 feet of each other there is no promise in the Beldens of impending transformations. - 68 - The St. Dominique sandstone is a hard, grey to white, fine-grained quartzitic rock, for the most part quite pure but having calcareous and shaly layers throughout. The lowest beds have fucoidal markings. Following the Beldens time there was probably a sudden change in sedimentation conditions. There is not evidence that the top of the Beldens was subjected to subaerial erosion, rather the evidence suggests a persistent marine environ ment with a change in sedimentation. Either the sea withdrew until near-shore conditions existed where formerly Beldens limestone was deposited or else renewed river activity began to bring in clastic sediments: or the invading sea had found plenty of detritus in its advance westward towards Montreal and Ottawa and this sediment was reworked and deposited far and wide by the waves and currents. These hypotheses require changing geographic conditions at the end of Beldens time, and that it was not merely a local change is shown by the presence of Upper Chazy sandstone beds to the south in north-west Vermont as well as to the west in the Ottawa-Montreal region. With the exception of the Montreal area where about 80 feet of sandstone and interbedded shales and limestones are reported at the base of the Chazy, the thickness is remarkably uniform. The uniformity is more apparent in the St. Dominique and Highgate Springs areas with 125 feet and 135 feet respectively measured. In the Ottawa region an average - 69 - 165 feet of sandstone was deposited. There is no assurance however that these sandstone beds were deposited in a freely connected sea. The absence of fossils, save of the fucoids, in the St. Dominique sandstone, makes correlation almost impossible. Apparently there was some faunal barrier between the Ottawa and Montreal regions, and obviously conditions were not the same in the Montreal and the St. Dominique-Highgate Springs areas during part of the Chazy time, for the Beldens is unknown in the former. It is concluded then that the St. Dominique sandstone and the Carman sandstone at Highgate Springs are contemporaneous deposits which were laid down in close-adjoining, probably continuous, portions of the same sea (Fig. 7C) • Possibly these two freely connected areas were part of a larger sea which spread beyond Montreal and Ottawa and that although rivers were bringing in vast new quantities of sand throughout the entire region, the sources were different and the sedimentation conditions varied with respect to location. At any rate, a thick, fairly homogeneous series of sands was laid down at St. Dominique: a series which gradually changed to calcareous sands, thence to sandy limestones and finally to the arenaceous and somewhat argillaceous lower calcareous beds of the St. Dominique limestone. With this fresh deepening of the sea and withdrawal of the sea shore (Fig. 7D), a large and - 70 - varied fauna appeared. If there had been an extensive fauna previous to this time it left few clues, for the St. Dominique sandstone is barren of fossils except for obscure markings, and the Beldens limestone is only slightly more productive. The presence of considerable quantities of argillaceous material not only throughout the greater portion of the limestone itself but also as thin and irregular inter beds is testimony favoring the assumption of shallow water conditions during upper most Chazy time. Two other criteria support this evidence; first, the occurence, often in quantities large enough to mask the limestone characteristics, of small (1 to 2 mm.), rounded, frosted, translucent, quartz sand grains. There is no certainty that these are wind blown sand grains but their wind-abraded appearance and their haphazard, unbedded scattering throughout various layers of the lime are almost positive indications that they represent aerial sands which from time to time were blown by strong winds out to sea, dropped and allowed to settle into the argillaceous limy sediments on the sea floor. The second piece of evidence supporting the shallow water environment of the St. Dominique limestone is the abundance of ostracods. These tiny marine organisms are to-day dominantly benthonic inhabitants of shallow water where they feed on dead remains of other animals. There is - 71 - nothing in their phylogeny to indicate that their habitat has changed since their first appearance. They are abundant in some layers of the St. Dominique limestone. With the change from sandstone to limestone-depositing environs, the St. Dominique region had marine conditions continuous with, and similar to if not identical with, the Valcour sea along the west side of Lake Champlain. During the time of sandstone deposition to the east, the Lake Champlain district was one of continuous limestone deposition, as one would expect in an area farther seaward from the near shore conditions between St. Dominique and St. Albans. Now the two areas merged into one open sea-way. There were few if any barriers to prevent the inter-migration of the faunas along this north-south trough, for some Middle as well as Upper Chazy species moved northward into the St. Dominique area. Probably the migration began in Middle Chazy time and it may well be that by the time some of them had reached the latter place, their progenitors had been displaced farther south by the new Valcour elements. An alternative explanation is that the few Middle Chazy forms that are found in the Upper Chazy of the St. Dominique region are nothing more than "hangovers" from the Middle Chazy of Lake Champlain region and not necessarily the hardy forms that were able to weather the vicissitudes of their northern migration. Nevertheless it was during this time that - 72 - the Chazy sea reached its maximum expansion. Minor barriers existed in places, discouraging but not entirely preventing the intermingling of faunas between such places as St. Dominique and Montreal, and Montreal and Ottawa. At the initiation of Black River time there was little change in marine conditions. With the contact between the two formations missing it is impossible to determine what happened at the end of Chazy time in the St. Dominique region. According to Wilson (1937, p.54) the Chazy stage ended with a complete withdrawal of the sea in southern Quebec and probably its retreat was in the same direction as that from which it came. It is possible that this hypothesis includes the St. Dominique region. The almost complete lack of fossil evidence in this thin (not more than 70 feet) sequence of rocks makes correlation with known sections difficult. Lithologically the rocks resemble the Black River of the Montreal region and it is possible that the two areas were directly connected during Black River time. There is no direct evidence of an erosional unconformity between Chazy and Black River time at St. Dominique. On the other hand pronounced changes must have occured to obliterate all traces of the Chazy fauna. None of the Chazy species is present in the succeeding formations, either Black River or younger. That this was a time of shallow water limestone deposition not dissimilar to the Chazy - 73 - is shown by occasional limestone bands with wind-blown quartz gand grains, intraformational limestone conglomerates and cross- bedding in the coarsely crystalline layers. Despite being formed under somewhat similar marine conditions the two formations are lithologically distinct. Upper Middle Ordovician or Trenton time in the St. Hyacinthe map-area was a period during which marine aspects persisted* Crystalline limestones, for the most part argillaceous, were laid down in wide shallow seas into which river-carried silt was brought and intermingled with the pervading carbonate sediments. The faunas of these beds varied little, with the occasional introduction or disappearance of certain species that mark the boundaries between the three different members of the formation. Toiard the end of Middle Trenton time, the shale facies began to dominate and the fine interbanding of shaly limestone and crystal line limestone, looking almost like annular deposits, gave way at the end of the Trenton to the shales and fine sands of the over lying mca-Lorraine beds. It was a time of land stability; the sea having spread far and the land having been planed down by sufeerial erosion. Gradoally tae rivers which had been pouring into the north-south sea tailt their vast deltas westward and * Upper *•*• and Utica ti*e, the last of the great Ordovician lim«stoo* - 74- stages had disappeared. With it went the large invertebrate assemblages: those animals which remained changed to adapt themselves to the new muddy environment, their remnants being sparsely preserved in the less favorable habitat. Those which could not change were wiped out at the end of the Trenton or moved to less exacting latitudes. The fossils and the lithology of the Trenton here have much in common with the Trenton of Montreal; there is little doubt but that the two developments took place in adjacent parts of the same sea. All through Utica, and possibly part of Lorraine time, extremely shallow seas covered the seaward portions of the muddy river deltas. The basin which had received the great thicknesses of Lower and Middle Ordovician sediments continued to sink under the load of the shales and sandy shales which had been deposited. How great a thickness they attained and to what subsequent Paleozoic processes they were subjected are questions for which we have no complete answers. At the end of the Ordovician period the rocks of the St. Dominique region were unquestionably caught in the peripheral zone of the mountain-building movement which thrust up the first generation of the Appalachian mountains. The absence of post- Ordovician sediments in the region makes any definite verification of this statement impossible but it is highly unlikely that the - 75 - disturbance did not affect tho Q+ n • • nox, anect the St. Dominique region. Schuchert (1923, p. 178) stated " that th* **<=+ Tinat the eastern side of the whole of the Saint Lawrence trough / which would include the St. Dominique region^/ was folded toward the close of the Ordovician." The second major disturbance, and probably the most important in the sense that it terminated all further sedimentation in the St. Lawrence sea, occured at the close of the Devonian when "It has been stated that the Saint Lawrence trough was blotted out by the late Devonian orogeny." (ibid). These diastrophitic movements were undoubtedly the forces that contributed to the major part of the St. Dominique folding and faulting, but more than likely the area was again involved to a lesser degree in the final Paleozoic orogeny which thrust up the main development of the Appalachian mountains and drained away the Paleozoic seas from the Appalachian geosyncline. It is assumed then that the main structures of the St. Dominique ridge resulted from the terminal-Ordovician thrusting and folding. Low and high-angled faults broke the tight, often overturned north-south folds; vertical cross-faults cut the area in a series of blocks which were unequally tilted. The St. Dominique slice, once part of the relatively undisturbed foreland became part of this orogeny, was folded and thrust westward only to be almost - 76 - completely covered by successive overriding slices from the east. At the end of the Devonian period further crustal disturb ances perhaps exaggerated the structure. Henceforth throughout most of the remainder of geologic time, the area was above sea. Subsequent Paleozoic and Mesozoic erosion has cut away the mountains of the lower Paleozoic diastrophism, leaving only the cores of what once was presumably an extensive mountain range. Glaciation and other subaerial forces have smoothed off the irregularities and the St. Dominique ridge now stands a low, long, sinuous hill, covered by soil and forest growth, at the same time a physical boundary and a link between two distinct types of topography whose differing geological histories are intimately bound together. - 77 - SUMMARY AND CONCLUSIONS The St. Dominique ridge is part of the peripheral zone of the major physiographic division known as the Appalachian mountain- built province. Stratigraphically it is a continuous series of Ordovician rocks ranging in age from Upper Chazy to Utica and possible Lorraine; structurally it is the east limb of a nearly recumbent anticline which has been overturned and thrust-faulted westward over the adjacent, nearly undeformed rocks of the St. Lawrence Lowlands. Prior to the deformations which occured at the close of the Ordovician and Devonian periods, the rocks now forming this particular slice probably occupied an original site several miles to the east. This conclusion is reached from three separate lines of evidences: first, the bordering position of the slice lying unconformably on rocks of its own province, covered by slices of more distant origin and marking the initial rise of the land above the Lowlands; second, the close correlation of the lithology of the rocks with those to the west in the Lowlands and to the south near Highgate Springs, another bordering structural slice; third, the correlation of the fossils, partic ularly those in the lower middle part of the section, with the ,. T+ i another coextensive with rocks of similar age and derivation to the west around the Montreal region and also to the south around the Lake Champlain region. The Ordovician sea in which they were deposited came in from the east as an embayment of the Appalachian geosyncline and at first had its western edge somewhere between St. Dominique and Montreal and its northern shore some distance south of St. Dominique. It spread south in Lower Chazy time to the present position of Lake Champlain, a position which it main tained and expanded even farther south during Middle Chazy time. Then it began spreading northward, reaching to, and probably somewhat beyond St. Dominique, and during this advance the Beldens limestone was deposited in the clear shallow seas. With continued crustal sinkings the Upper Chazy seas increased in size westward. The advancing waves reworked the regolith and deposited large quantities of the sand that now forms the base of the Upper Chazy in the western parts of the St. Lawrence Lowlands. These sand deposits were possibly augmented by increased river- borne deposits. The sand beds are persistent throughout the entire region from Amprior and Ottawa to Montreal, St. Dominique and south to Highgate Springs and St. Albans on the east side of x. it -i«,++or reeion. deeper off-shore facies Lake Champlain. west of the latter region, a P of limestone continuex- d/. t+«o be developeaevej.op«d« in the Valcour and Chazy areas 4. „» +h«re is little indication of its extent. Northward and eastward there is nv - 79 - The overlying Middle and Upper Ordovician sediments were dominantly argillaceous limestone containing a large and varied fauna. The Ordovician sea reached its maximum extent during these latter stages. Finally, towards the end of Ordovician time, the basin was gradually filled in by the westward advancing mud flats built out from deltas of rivers flowing into the sea from the east. Utica-Lorraine deposits originating as shallow water and delta mud-flats deposits took possession of the one-time extensive marine basin and the Ordovician period neared its close. Following the Ordovician and Devonian disturbances which folded and faulted the area, subaerial erosion and glaciation have left their marks. To-day a long low hill of Ordovician sediments, covered almost completely with soil accumulations, is the only evidence remaining of the tremendous processes which went on in the past. The area leaves much to be desired in the completeness of its structural and stratigraphic data. The Chazy limestone is the only formation that has supplied good fossil collections, consequent ly a major part of the correlation has been concerned with this formation. Succeeding formations, though apparent stratigraphic entities, have been disappointing faunally. Nevertheless, with the evidence at hand, the author has gone as far as he has been able. Many of the conclusions reached are acknowledge only tentative. - 80 - In those cases where a particular problem can be explained by more than one hypothesis, the alternative explanations have been set down, and wherever possible the author has indicated his preference. Undoubtedly in the light of new evidence, some of the prefered hypotheses will need modification, if not complete revision. Throughout the entire length of the St. Dominique ridge work has been hampered by forest growth and soil accumulation. The plains areas to the east gave even fewer exposures: a great deal more field data is required concerning these Upper Ordovician rocks before their complete history can be unravelled. The forest growth throughout the length of the ridge is fast disappearing and with it will go most of the protecting soil. It may well be that in several decades much of the soil cover will have disappeared, and new, more conclusive evidence unearthed. Until then many of the problems will be without adequate solutions. - 81 - BIBLIOGRAPHY OF REFERENCES CITED Brainerd, Ezra - (1891) - The Chazy Formation in the Champlain Valley, Bull. Geol. Soc. Am., Vol. 2, pp.293-300 - and Seely, H.M. (1888) - The Original Chazy Rocks. Am. Geol. Vol. 2, pp. 323-330 Cady, W.M. - (194-5) - Stratigraphy and Structure of West-Central Vermont. Bull. Geol. Soc. Am., Vol. 56, pp. 515-588 Clark, T.H. - (1944.) - The Unfolded Rocks of the St. Lawrence Lowlands. Geol. Que., Vol. II, Geol. Rept. 20, pp. 250-291 Ells, R.W. - (1896) - Report on the South-West Sheet of the "Eastern Townships" map (Montreal Sheet). Geol. Surv. Can., Ann Rept., 1894, Vol.VII, Part J Goudge, M.F. - (1935) - Limestones of Canada, Their Occurence and Characteristics, Part III, Quebec. Canada, Mines Branch, No. 755 Hall, James - (1847) - Containing descriptions of the organic remains of the lower division of the New York System, equivalent of the Lower Silurian rocks of Europe. Nat. Hist. N.Y., Pt. 6, Paleont., Vol. I - (194-5) - Highgate Springs Sequence, Northwestern Vermont Kay, G.j and Southeastern Quebec, (abstract) Bull. Geol. Soc. Am., Vol. 56, pp. 1171-1172 Logan, W.E. - (1863) - Geology of Canada. Geol. Surv. Can., Rept. Prog, to 1863 Report on the Building and Ornamental Stones - (1914) - Parks, W.A. of Canada Vol. Ill, Quebec. Canada, Mines Branch, No. 755 The Chazy Formation and its Fauna. Raymond, P.E. - (1906) - Annals Carnegie Us., Vol. Ill, No. 4, pp. 498-596 - 82 - Schuchert, C. - (1923) - Sites and Nature of the North American Geosynclines. Bull. Geol. Soc. Am., Vol. 34, pp. 151-230. Wilson, A.E. - (1937) - Erosional Intervals Indicated by Contacts in the Vicinity of Ottawa, Ontario. Trans. Roy. Soc. Can., 3rd ser., Vol. XXXI, Sec. IV, pp. 45-60. McGILL UNIVERSITY LIBRARY A" v UNACC.