CANADA DEPARTMENT OF MINES Hon. Louis Coderre, Minister; A. P. Low, Deputy Minister GEOLOGICAL SURVEY R. W. Brock, Director. MEMOIR 43 No. 3G, Geological Series St. Hilaire (Beloeil) and Rougemont Mountains, Quebec BY J. J. O'Neill OTTAWA Government pRiNTiNa Bubbau 1914 No. 1311 Cornell University Library The original of tiiis book is in tine Cornell University Library. There are no known copyright restrictions in the United States on the use of the text. http://www.archive.org/details/cu31924101522054 3 1924 101 522 054 CANADA DEPARTMENT OF MINES Hon. Louis Codekre, Ministek; A. P. Low, Deputy Minister GEOLOGICAL SURVEY R. W. BnocK, Director. MEMOIR 43 No. 36, Geological Series St. Hilaire (Beloeil) and Rougemont Mountains, Quebec BT J J. O'Neill OTTAWA Government Printing Bureau 1914 No. 1311 OS 404. CONTENTS CHAPTER I. The Monteregian Hills 1 Introduction 1 Mount Royal 2 St. Bruno mountain 4 Mount Johnson 4 Chambly occurrence 5 Mount Yamaska 5 Shefford mountain 6 Brome mountain 7 Eastman 8 Tabulated summary 8 CHAPTER II. The Palaeozoic strata in the neighbourhood of St. Hilaire (Beloeil) and Rougemont mountains 10 General account 10 The Richmond age of the so-called Lorraine 10 Fossils from St. Hilaire station 11 Fossils from near Caroline station 13 Conclusions 15 CHAPTER III. Physiography 16 General features of the St. Lawrence lowlands 16 Erosional features 18 Suggestions of an older base-level 18 IV. CHAPTER IV. Page. Structural features of St. Hilaire (Beloeil) and Rougemont mountains.. 20 CHAPTER V. Petrology: St. Hilaire (Beloeil) mountain 28 Essexite: tj^e variety 28 Chemical analysis 30 Essexite: variety No. 1, rich in brown hornblende 32 Essexite: variety No. 2 33 Essexite: variety No. 3 , 34 Rouvillite 35 Chemical analysis 36 Nephelite-sodalite-syenite: type variety 38 Chemical analysis 40 Nephelite-sodalite-syenite: contact variety 41 Nephelite-sodalite-syenite: breccia variety 43 Tawite; feldspathic type 46 Chemical analysis 48 Variations in the tawite 49 Dyke rocks 50 Camptonite 50 Camptonite: variety No. 1 51 Camptonite: variety No. 2 52 Camptonite: variety No. 3 52 Camptonite: variety No. 4 53 Comparison of varieties of camptonite 53 Nephelite-syenite 54 Comparison of varieties of nephelite-syenite 57 Tinguaite 57 Comparison of varieties of tinguaite 59 Variety No. 1 59 Variety No. 5 59 Sheet rocks 60 Tinguaite 60 Chemical analysis 61 Tinguaite porphyry 62 Aplitic type 62 Hornfels 63 V. CHAPTER VI. Page. Petrology: Rougemont mountain 64 Yamaskite 65 Chemical analysis 67 Variety No. 1 of yamaskite 68 Variety No. 2 of yamaskite 68 Variety No. 3 of yamaskite 69 Variety No. 4 of yamaskite 69 Comparison of varieties of yamaskite 69 Essexite (Rougemont type) 70 Chemical analysis 71 Varieties of essexite 72 Rougemontite: the feldspathic type 74 Chemical analysis .' 76 Character of differentiation in Rougemont magma 78 Dyke rocks 78 Yamaskite 78 Essexite 79 Essexite porphyry 79 Chemical analysis 81 Camptonite 82 Aplitic dykes 83 Aplitic dykes: variety No. 1 83 Aplitic dykes: variety No. 2 84 CHAPTER VII. General petrology 86 Beloeil (St. Hilaire) rocks 86 Rougemont rocks 87 General discussion 88 Differentiation 90 Dykes 91 Age of the intrusions 91 CHAPTER VIII. Bibliography 93 Index 97 VI. ILLUSTRATIONS Map (100 A) of St. Hilaire and Rougemont mountains, Rouville and St. Hyacinths counties, Quebec in pocket ST. HILAIRE (BELOEIL) AND ROUGEMONT MOUNTAINS, QUEBEC CHAPTER I. THE MONTEREGIAN HILLS INTRODUCTION. From Mount Royal at Montreal, a series of eight, isolated hills stands out conspicuously upon the surrounding plain of the St. Lawrence lowlands and extends, with general trend a little south of east, across the Province of Quebec. Six of these hills are spaced at intervals of about 10 miles and occur in the following order from west to east : Mount Royal, Monterville or St. Bruno, St. Hilaire (Beloeil), Rougemont, Yamaska, and Shefford. Nine miles southeast of Rougemont is Mount Johnson, and Brome is situated 2| miles south of Shefford. These eight hills form the petrographical province named by Dr. F. D. Adams,' the Mon- teregian Hills. The investigation, of which this report is the result, was carried on during the summer of 1912 with the object of studying St. Hilaire (Beloeil) and Rougemont mountains and thus completing the detailed study of the petrographical province of the Mont- eregian Hills. A topographic map recently issued by the Depart- ment of Militia and Defence was used as a base for the geology, and field ,work was carried on alone, except for temporary assistance in surveying contacts, and in blasting to obtain fresh material. The pace and compass method of surveying was used in locating individual points and this was checked by aneroid determinations; a telemeter was used in surveying contacts. The author is greatly indebted to Professor L. V. Pirsson for assistance and criticism in preparing the petrographical section of this report, and to Professor Charles Schuchert for help in working out the stratigraphy; his thanks are also due to Professor Isiah Bowman for criticism of the physiography, and to Professor Joseph Barrell for suggestions bearing on structural geology. » The Monteregian Hills: A Canadian Petrographical Province Jour. Geol., Vol. XI, No. 4, April-May, 1903. The St. Lawrence lowlands in the Province of Quebec lie be- tween the Appalachian mountains on the southeast, and the Laur- entian plateau on the northwest. This intermediate lowland is the final product of Tertiary erosion upon soft strata of Palaeozoic age. The western portion of the plain of the lowlands is developed on nearly horizontal strata and is separated from the eastern part by a thrust-fault known as the "St. Lawrence-Champlain" fault, or the "Logan" fault-line of Schuchert.' This represents an overthrust from the southeast and the strata to the east are stand- ing on edge with steep dips to the southeast. Across this lowland, in a line a little south of east, extends a series of ten isolated hills which rise abruptly from the plain and are spaced at more or less regular intervals, making a bridge from the Laurentian plateau to the Appalachian mountains. The two most westerly of this series are outliers of the Pre-Cambrian and are not related to the other eight; the latter are closely related both in age and in the high sodic content of the intrusive igneous rocks forming the central portions of the hills, so that they have been called "The Monteregian Hills," and form a distinct petrographic province as pointed out by Dr. F. D. Adams. From west to east these mountains are: Mount Royal, St. Bruno, Johnson, St. Hilaire (Beloeil), Rougemont, Yamaska, Shefford, and Brome. Some of these have been described as typical volcanic necks, and others as of laccolithic origin; the present paper gives a de- tailed description of St. Hilaire (Beloeil) and Rougemont, and a summary of the other occurrences is here given for reference and comparison. MOUNT ROYAL. Mount Royal is the most westerly of the Monteregians; it has an area of about 2 square miles and an absolute altitude of 769 feet. It is made up of three principal hills, connected by ridges which have been more or less worn down, enclosing a broad, re- latively flat basin. The igneous mass of the mountain is the pro- duct of two main intrusions, the first one of essexite made up of "labradorite, reddish-violet augite, brown hornblende, and brown 1 Paleogeography of North America. Bull. Geol. Soc. Am., Vol. XX, 1910, pp. 427-606. 3 mica", while olivine, titanite, apatite, and other accessories are often present; "nephelite is present only in very small amount and hauyne can be occasionally detected". The second intrusion oc- curred on the north side of the essexite body, where a mass of ne- phelite-syenite cuts the essexite and sends off arms into it; the contact is well exposed at the Corporation quarries. This rock is "composed essentially of orthoclase, nephelite, and green horn- blende, with small quantities of plagioclase, pyroxene, garnet and nosean, and other accessory minerals"; Dr. Harrington has also found sodalite in it in some places.' These main intrusions were followed by the formation of great masses of breccia in sheets and dykes intruded into the sediments surrounding the igneous core of the mountain, and by a comple- mentary set of dykes of the bostonite-tinguaite-monchiquite series, cutting all the earlier rocks and one another. In the excavation for the Montreal reservoir on McTavish street. Dr. Harrington was able to determine five distinct sets of dykes, and to recognize their relative order of intrusion. There is also a dyke of alnoite' found at Ste. Anne de Bellevue, "which is probably also connected with the Mount Royal intrusion." The breccias of Mount Royal have been investigated by Robert Harvie,' who finds them to be of intrusive origin; they contain fragments of all the local formations from the Potsdam to the Oriskany, and are well exposed in many places, perhaps best on St. Helen island. The churning action which brought together in this breccia, fragments of rock of such widely different horizons (Oriskany to Potsdam) would suggest that the conduit of the magma extended right to the surface. In referring to the origin of Mount Royal, Dr. Adams says,' "In a recent paper by Buchan (Can. Rec. Sci., Vol. VIII, 1901, p. 321) the view was put forward that Mount Royal represents the remnant of a denuded laccolite — on the ground that on one side of the mountain, towards the summit, there is an isolated mass of flat-lying, altered Palaeozoic limestone, evidently a part of the sedi- ' Drs. Harrington and Adams as recorded in the Ann. Rept., Geol Surv. Can., Vol. VII, Pt. J, pp. 74-75. 2 Adams, F. D. Dr., Am. Jour. Sci. 3rd Ser., Vol. XLIII, pp. 269-279. ' Proc. Roy. Soc. Can., 3rd Ser., Vol. Ill, Sec. 4, pp. 249-299, 1910. * "The Monteregian Hills.— A Canadian Petrographical Province " Jour, of Geol., Vol. XI, No. 3, p. 253. mentary strata of the plain from which the mountain rises. This alone, however, is not sufficient to establish a laccolitic origin, and opposed to such an explanation is the fact that where the strata of the plain are seen along the immediate contact with the intrusion in many places, especially on the eastern and northern side of the mountain, they abut against the intrusive rock and are cut off by it instead of being uptilted, the igneous core of the moun- tain rising up precipitously like a wall across the trimcated edge of the beds." It appears that the origin of this mountain is yet in doubt, and further work is necessary for its determination. ST. BRUNO MOUNTAIN. This mountain has been described by John A. Dresser' as probably a laccolith, but the evidence was not such as would war- rant a definite decision. It has an area of 2"83 square miles above the 300-foot contour, with an igneous core of 2"16 square miles. The maximum elevation occurs in the northeast part of the moun- tain and is 715 feet absolute, or 620 feet above the surrounding plain. The surface is uneven, giving an imperfect drainage, and causing the formation of three small lakes which have beds of reworked glacial material, and a maximum depth of 17"5 feet. There was but one main intrusion, an essexite magma made up of abundant biotite, hornblende, and augite, with basic labradorite; olivine is occasionally present in considerable amount. This type seems to grade rather sharply into a rock termed umptekite, which occupies an area about 500 feet long and a Uttle less in width; it consists of "orthoclase, plagioclase, microperthite, biotite, and a colourless augite. It has a granitic structure and a medium texture." MOUNT JOHNSON. This is the smallest of the Monteregian hills and is described by Dr. F. D. Adams" as a typical volcanic neck or pipe. It is situated about 9 miles, a little west of south, from Rougemont 1 Geology of St. Bruno Mountain (Quebec): Can. Geol. Surv., Memoir No. 7, 1910. 2 The Monteregian Hills: A Canadian Petrographical Province. Jour. Geol., Vol. II, 1903, pp. 239-282. mountain; its area within the outer edge of the hornstone collar is approximately 077 square miles, and the area of the igneous core is 0'423 square miles. The mountain rises to an absolute elevation of 875 feet or about 720 feet above the plain; it is nearly circular in outline. There has been only one main intrusion in this case, and it shows an exceptionally perfect differentiation with more or less abrupt transition from pulaskite on the borders to an essexite core. The pulaskite, or soda-syenite, is made up of "biotite, horn- blende (pyroxene), soda-orthoclase, nephelite, sodalite, apatite, magnetite, and sphene." It has a decidedly porphyritic, but mas- sive structure, and has a marked preponderance of feldspar. The essexite contains the same minerals as the pulaskite, except that there is very little orthoclase present, and the plagioclase varies from an acid labradorite to oligoclase though most of it is andesine ; olivine is also present in small amount. The central portion is finer grained and is massive. Flow structure is well displayed in the essexite but more particularly in the transition zone to the pulaskite, where the large phenocrysts of feldspar are prominent. The banding follows the border contact, in strike, and in dip it is nearly vertical, showing an upward movement of the magma. CHAMBLY OCCURRENCE. "At Chambly a mass of porphyritic trachyte is in the form of a bed among the strata of the Hudson River formation (Richmond) ; and about midway on the Chambly canal, a similar trachyte is met with which contains in drusy cavities, crystals of quartz, calcite, analcine, and chabazite. The base of this rock is of a pale fawn colour, and appears at first sight to be micaceous, but on closer examination it is seen to be almost entirely feldspathic; minute portions of p5Tites and grains of magnetite iron are rarely met with, and small scales of a dark green, micaceous mineral are very abundant; they are sometimes an inch in length and one-fourth of an inch in thickness.'" MOUNT YAMASKA. This mountain is situated about one-half mile east of the St. Lawrence and Champlain fault line, and it has been said to be on the line of an inferred fault, parallel to the former, and forming the ' Geol. of Canada, Logan, 1863, p. 657. contact between two members of the Quebec group; the Sillery on the east is older than the Farnham on the west. It has been thor- oughly studied by G. A. Young, who is inclined to believe that the mountain is situated on the axis of an overturned anticline and not on a fault.' Yamaska is elliptical in outline with the long axis running northwest and southeast, and is bounded by two main outer ridges running lengthwise. The general elevation of these ridges is about 1400 feet, and the highest peak is 1470 feet above the sea. The divide in the interior basin is 950 feet above sea-level. The sedimentary collar is widest on the north and south faces where it reaches nearly to the summit; on the east and west faces, the contact is near the base of the mountain. The igneous core has an area of 3"1 square miles, and is very irregular in outline. It includes three main types of rock — akerite, essexite, and yamas- kite, with abrupt transitions, although there has been but one main intrusion. Owing to lack of exposures the complete relation- ships could not be established. The akerite is a medium to coarse-grained, light grey rock, in which labradorite and alkali feldspar greatly predominate over the diopside, biotite, and minor constituents among which there is a small amount of quartz. The akerite appears to be a border facies. Essexite is present in three varieties, divided on the basis of textural differences, and grades into the most highly ferromagnesian rock type present, which has been called yamaskite. This rock is characterized by the great preponderance of pyroxene, basaltic hornblende, and ilmenite, with about 2 per cent of anorthite (at 15 per cent of feldspar, the rock passes into essexite). The dyke rocks include bostonite, camptonite, syenite-aphte, nephelite-syenite, and yamas- kite, and are relatively abundant close to the margins of the main intrusive. The total weight of evidence points to the conclusion that this mountain is the remains of a volcanic neck. SHEFFORD MOUNTAIN. John A. Dresser^ describes Shefford mountain as a laccolithic intrusion, having an area of less than 8 square miles, and a maximum altitude of from 1,500 to 1,700 feet above the sea. 1 Geology and Petrography of Mount Yamaska: Ann. Rept., Geol. Surv. Can., Vol. XVI, Pt. H, 1906, p. 31. ^ Report on the Geology and Petrography of Sheflford Mountain Quebec): Ann. Rept., Can. Geol. Surv., Vol. XIII, 1902, Pt. L. It is the product of three separate intrusions; first, a normal essexite, without olivine, was intruded and this was followed by a nordmarkite magma composed principally of coarsely crystalline microperthite (albite-orthoclase) with a small amount of ferro- magnesian minerals, mostly augite. Lastly, a body of pulaskite was thrust in between the essexite and the nordmarkite. It differs from the nordmarkite in having a porphyritic structure and in having hornblende instead of augite as the characteristic bisilicate . Each of these three intrusions was accompanied by a set of dykes. The same foliated structure as described at Brome is here also in evidence. BROME MOUNTAIN. Brome mountain is a laccolith with an area of 30 square miles, and it is the largest of the Monteregians. It is rudely circular in form and the central portion is a nearly level basin 2 miles wide by 2'5 miles in extent, with an absolute altitude of 500 feet, or 50 feet above the country level. Surrounding this basin is a nearly continuous rim of hills which rise 600 to 1,000 feet higher; the high- est point on the mountain is thus 1,500 feet above the sea. In this case there were three igneous intrusions; the first was an essexite magma with about 90 per cent of plagioclase, varying from labra- dorite to bytownite, with a little nephelite; the second was com- posed of nordmarkite, which also contains about 90 per cent of feldspar, a kryptoperthic intergrowth of albite and orthoclase; the third intrusion was the smallest and proved to be a tinguaite, "a porphyritic rock having a green matrix and a few phenocrysts of light grey colour"; it contains nephelite, orthoclase, sodalite, and aegerite. There were relatively few dykes following these invasions. The rocks exhibit a foliated and incipient schistose structure parallel in direction with the foliation of the surrounding sediments, and this is thought to have formed during a late stage in the folding of the Appalachians. This mountain is only 2"5 miles south of Shefford and from the similarity in the order and composition of the intrusions. Dresser^ concludes that on the whole "it ^ Summary from Report on the Geology of Brome Mountain, Quebec Dresser, J. A., Can. Geol. Surv., Ann. Rept., Vol. XVI, Part G, 1906. seems probable that Brome and Shefford are merely parts of one great laccolith and that the connecting part is only lightly covered by Palaeozoic sediments." EASTMAN. A Monteregian in miniature was recognized by Mr. John A. Dresser during field work on the Serpentine Belt in the summer of 1910. This occurrence is only 200 feet in diameter, but it is dis- tinct, and represents the most easterly known member of the group. It is exposed in a cutting on the Canadian Pacific railway about If miles east of the village of Eastman, Que., and its distance from Mt. ShefTord, the nearest of the larger hills, is about 15 miles. The rock types of this locality have not yet been studied, but Dresser has stated that a dyke, presumably from this occurrence, is found cutting the serpentine a short distance away, proving it to be younger than the great peridotite-pyroxenite intrusion to the east. Tabulated Summary. Mountain. Area in sq. miles. Maximum absolute elevation. Maximum elevation above plain. Nature of intrusion. No. of main intrusions Brome 30 1,500 1,100 Laccolith . . 3 Shefford 90 1,500 1,300 Laccolith. . 3 Yamaska 5-5 1,500 1,300 Neck 1 Rougemont. . . * 95 1,260 1,140 Neck 1 Johnson t 0-771 876 720 Neck 1 St. Hilaire... * 6 -76 1,.375 1,230 Neck 2 St. Bruno. . . . t 2-83 715 620 ..? 1 Mount Royal. 20 769 650 Neck? 2 * Above the 200-foot contour. t Above the 300-foot contour, t Above a contour of 190 feet above the plain. Mountains in order from Main intrusions in each occurrence. in order of Nature of intrusion. Investi- gator. east to west. No. 1 No. 2. No. 3. Shefford Essexite .... Nordmarkite Pulaskite . . . Laccolith. Dresser. Brome Essexite to theralite. Nordmarkite to nephe- lite-syen- ite and dykes. Tinguaite. . . Laccolith. Dresser. Yamaska. . . Yamaskite to essexite to akerite. Neck Young. Rougemont. . . Yamaskite to essexite to rouge- montite. Neck O'Neill. Essexite to pulaskite. Neck Adams. St. Hilaire. . . Essexite to rouvillite . Nephelite- syenite. Neck O'Neill. St. Bruno. . . . Essexite to syenite (umptekite) Laccolith? Dresser. Mount Royal. Essexite .... Nephelite Neck? Laccolith? Adams. Buchan. 10 CHAPTER II. THE PALi^OZOIC STRATA IN THE NEIGHBOURHOOD OF ST. HILAIRE (BELOEIL) AND ROUGEMONT MOUNTAINS. GENERAL ACCOUNT. St. Hilaire (Beloeil) and Rougemont rise from the portion of the St. Lawrence lowlands underlain by gently dipping Palaeozoic strata which are here mainly Ordovician. The lowest member of the series is of late Cambrian or lowest Ordovician age, and over- laps the Pre-Cambrian about 30 miles to the northwest; south- eastward higher divisions successively outcrop culminating in the Richmond (Lorraine). The total thickness is estimated at about 4,000 feet of apparently conformable strata, but there are doubtless some disconformities. In the neighbourhood of St. Hilaire and Rougemont the strata consist of shale for the most part, with occasional thin interbedded limestone layers; the measures are comparatively undisturbed and are preserved as a hornstone mantle about the mountains to an elevation of over 1,000 feet above the plain. THE RICHMOND AGE OF THE SO-CALLED LORRAINE. The series of black shales conformably overlying the Utica shales in the Montreal district, varies in thickness reaching a maxi- mum of about 2,000 feet. It has been commonly classed as Lor- raine, and there is said to be a gradual transition from Utica to Lorraine. Collections of fossils have been made at various times from this formation: at Chambly, St. Lambert, Riviere des Hiu-ons, Rougemont, and St. Hilaire station. The fossils thus secured, except in the case of those from St. Hilaire, have been de- termined by Dr. Ami, and lists of them are published in the Annual Report of the Geological Survey of Canada, Volume VII, Part J, 1896. The collection from St. Hilaire station was described by Dr. E. O. Ulrich, in Memoir No. 7, Geological Survey of Canada, 11 "Geology of St. Bruno Mountain" by John A. Dresser. The strata at all of the places listed by Dr. Ami were placed in the Lorraine; it is now believed that there are no typical Lorraine fossils listed, and that the general character of the fauna, as well as the species, points to the Richmond. Concerning the collection made by R. Harvie, from St. Hilaire, Quebec, Dr. Ulrich says: "The St. Hilaire fauna, as represented in the small collection before me, is not decisively Richmond, but so far as it goes, it indicates lower Richmond rather than Lorraine. The matter is so important that it seems worth while to recom- mend the making of a full collection. The most significant fossil in the lot is the fragment provisionally referred to Whiteavesia pholadiformis. So far as we know, this type of shell occurs only in Richmond faunas. Pointing in the same direction is the pre- sence of two species of Whitella, a genus so far unknown in Lor- raine faunas. This evidence is further corroborated by the Palaeschare beani, but the specimen is small and not in sufficiently good preservation to permit positive identification. The "Oli- dophorus" I have found in both Lorraine and lower Richmond likewise Psiloconcha sinuata, Pholidops dncinnationsis and Cteno- bolbina ciliata. The remaining things being either new, or not definitely determinable, may be disregarded. I will say, how- ever, that I see nothing about them that might be used in rebuttal of the general trend of testimony afforded by the species men- tioned." FOSSILS FROM ST. HILAIRE STATION. On the strength of this determination, it was deemed advisable to make a full collection in connexion with the field work of the present report. The fossils thus secured have been examined by the writer, under supervision of Professor Charles Schuchert, and the following determinations arrived at: — Bryozoa. Stomatopora. Sp. undet. Rare. Palaeschare beani (James) . Nearly always growing over Cyrtolites ornatus. (B) 12 Brachiopoda. Pholidops subtruncata (Hall) or Pholidops dndnnationsis (Hall). Both forms appear to be present and may represent but one species. The individuals are not rare, and are larger than usual. Rafinesguina alternata (Emmons). Very rare. Zygospira modesta (Hall). Not common. Pelecypoda. Pterinea demissa (Conrad). Not common. Byssonychia subereda (Ulrich). A very common species in harmony with Ulrich's description and figures, but none attain the large size of the Ohio individuals. Psiloconcha sinuata (Ulrich). Common. Psiloconcha subovalis (Ulrich). Common. Psiloconcha inornata (Ulrich). Common. Modiolopsis concentrica (Hall and Whitfield). Rare. Whiteavesia pholadiformis (Hall)? Fragmentary and very rare. Whitella, species No. 1. Rare. Whitella, species No. 2. Rare. Whitella, species No. 3. Rare. Rhytimya radiata (Ulrich). Common. Cymatonota semistriata (Ulrich). Common. Cymatonota recta (Ulrich). Rare. Ctenodonta pectunculoides (Hall). Very common. Ctenodonta, sp. undet. Of the C. levata group. Clidophorus n. sp., near C. plenulatus (Conrad). Very common. Gastropoda. Cyrtolites ornatus (Conrad). Rare. Tubiculus annelida. Conchicolites richmondensis (Miller)? Smaller than is usual in this species. Ostracoda. Ctenobolbina ciliata (Emmons)? Common. 13 Trilobita. Isotelus gigas (De Kay)? One large free cheek, with its genal spine. In summing up this collection, Professor Schuchert makes the following statement : — "Ulrich, in 1907, (see above quotation), pointed out that the St. Hilaire fauna is not decisively Richmond, but, so far as it goes, it indicates lower Richmond rather than Lorraine. While this fauna is now considerably enlarged, yet no marked addition has been made of decisive Richmond fossils. On the other hand most of the species have the time development of the Richmond, and the St. Hilaire fauna is for the present best referred to this time rather than to the Lorraine. The St. Hilaire fauna is derived entirely from shales and is, therefore, a mud-loving fauna, devoid almost entirely of brachiopods, bryozoa, and the other groups of inverte- brates usually met with in calcareous deposits. In general the Richmondian faunas are derived from limestones and calcareous shales." It is interesting to note that the fossils listed above were collected from nearly horizontal strata at an elevation of about 120 feet above sea-level, and that the same formation forms the hornstone collar of St. Hilaire mountain, which rises about one mile to the east, and it is foimd there at an elevation of over 1,000 feet above the sea; there is, therefore, a vertical exposure of about 900 feet with the top removed, so that the fauna is from the lower part of the formation, and not far above the Utica. No fossils were found in the hornstone near the mountain, although careful search was made at a number of points ; where they do occur they are prolific, in thin bands separated by many times their thickness of apparently barren layers. FOSSILS FROM NEAR CAROLINE STATION. In 1872, Thomas Curry made a collection of fossils from just south of Rougemont mountain; these are included in Ami's lists and also were regarded as indicating Lorraine, but now are thought to be distinctly Richmond. The writer was unable to 14 find this locality, but discovered fossils to the east of the moiintain near the Petite Caroline road, about one-fourth of a mile south of Caroline station on the Quebec, Montreal, and Southern railway. At this place the strata dip to the west at a low angle and only the edges of the beds are exposed so that the collecting of fossils is not easily accomplished; the beds containing the fossils are easily recognized by the fact that the abundant crinoidal colimmals have been dissolved out, leaving corrugated channels through the strata. Professor Schuchert examined this collection and determined the following: — Crinoidal colmnnals very abundant. Dalmanella testudinaria (Dalman). Plectambonites sericeus (Sowerby). Catazyga anticostiensis (Billings)? Cleidophorus, sp. undet. Calymene callicephala (Green). Trinucleus concentricus (Eaton). In discussing this fauna he says: "The fossils from this horizon are meagre and poor so that one cannot be certain of their time values. Catazyga anticostiensis appears to have the most reliable time value, and on this evidence the horizon is early Richmond. The other fossils do not help out one way or the other, excepting that Trinucleus is not known to be above the Utica. In north- western Europe, however, the genus is abundantly represented at the very top of the Ordovician, and, therefore, I see no reason why Trinucleus should not turn up in these northern Richmond faunas. Catazyga erratica is abundant in the Lorraine, and is closely related to C. anticostiensis. As the present material is poor, it may be that my identification is not correct. In this event the horizon would seemingly be Lorraine or even the lower Frankfort. With this view the association of Trinucleus concentricus is harmonious in making the age of these fossils Lorraine or Utica rather than Richmondian." It would seem, then, that this horizon may be lower than that from which Curry collected, which is only 2 miles distant, in a line nearly due west. The vertical distance between them is not very great. 15 CONCLUSIONS. In looking over the lists of fossils collected at (1) Chambly, Que.; (2) St. Hyacinthe, Que.; (3) Yamaska river near St. Hya- cinthe, Que.; (4) Rougemont, Que., (a) south of the mountain, (b) east of the mountain; and (5) the Riviere des Hurons, Que., it is seen that in cases (1) and (4a) the faunas contain Catazyga headi (Billings) which is typical of the Richmond, and that the latter fauna contains also Leptaena nitens (Billings), so that these tvsro places, at least, are in the Richmond. The fossils from (3) in- clude two characteristic Trenton fossils, i.e. Dinorthis pectinella (Conrad), and Plectorthis plicatella (Hall). The fossils from (2) and (4b) seem to resemble this group rather than the others; they have Trinucleus concentricus in common, which is not present, or at least has not been found, in the other occurrences. Geo- graphically these three points are situated on a line nearly north and south, about 4 to 5 miles west of the Champlain or Logan fault; the distance between (2) and (3), and (4b) is about 12 miles. All the other points are west of this line; (4a) is just 2 miles west of the line and is distinctly Richmond. In Mr. John A. Dresser's report on St. Bruno mountain, Que- bec,' a list of fossils collected about that mountain is given and is said to indicate "Utica rather than Lorraine". The determina- tions were made by Dr. J. F. Whiteaves, Dr. E. 0. Ulrich, and Dr. R. Ruedemann. This district is about 7 miles east of St. Hilaire station, and about 6 miles a little east of north of Chambly. It would appear then, that there is a tract of Richmond strata in a belt of from 10 to 12 miles in width, with a development of Utica on the western margin and perhaps some Trenton along the east, near the fault line. It is hard to see how any Lorraine can be present in the localities from which the fossils are said to come. It will require a thorough study, with the solution of this problem in view, to decide the matter, and it seems to be of sufficient im- portance to warrant such an investigation being made. I Memoir No. 7, Geol. Surv. Can., 1910. 16 CHAPTER III. PHYSIOGRAPHY GENERAL FEA T URES OF THE ST. LA WRENCE LOWLANDS. The lowlands of the St. Lawrence lie between the Laurentian plateau on the northwest, and the Appalachian mountains to the southeast; they are about 80 miles wide at Montreal, and extend from the city of Quebec westward to Lake Huron, a distance of over 600 miles. These lowlands are divided into two parts by a narrow spur of the Laurentians which extends southeastward across Ontario, crosses the St. LavsTence river at the Thousand Islands, and spreads out to form the Adirondack mountains of New York. The southwestern division has a diversified character; the slightly smaller, and less diversified portion, to the northeast of the dividing line, is the one with which this paper is concerned. It is a relatively flat plain, in which any irregularities have been largely hidden by a thick mantle of glacial drift. This drift is 100 feet thick in places, and has been reworked, in part, by later submergence so that the upper portion is sorted and stratified. The plain is traversed in a northeasterly direction by the St. Law- rence river and with comparatively low altitudes along the river, rises inland to maximum heights of about 400 feet above sea-level. A striking break in the general uniformity of the plain is made by the group of hills, the Monteregians, which rise abruptly from it at intervals of about 10 miles, along a hne nearly due east of Montreal. The Laurentian plateau to the northwest is an uplifted peneplain now in process of dissection. It represents the northern nucleus of the North American continent and forms a great horseshoe- shaped area about Hudson bay with an area of about 2,000,000 square miles. The plateau has a general altitude of about 1,500 feet above the"sea, but rises to a maximum of over 6,800 feet in the mountains infnorthem Labrador. 17 The Appalachian mountain system is represented in Quebec by the northern extension of the Green mountains in the form of three lines of hills rurming in a northeasterly direction, in a broad curve, and ending in the Shickshock mountains of Gaspe. For the most part, the summits are not more than 1,000 to 1,500 feet above the sea, though a few run up to a little over 2,600 feet. All have been subjected to glaciation which accentuated their subdued character acquired during an earlier cycle of erosion. The Monteregian hills are a series of eight so-called mountains which extend across the St. Lawrence lowlands in an easterly direction from Montreal. They are of igneous origin; some are described as laccoliths and the others as volcanic necks. Their altitudes above sea-level are: Mount Royal, 769 feet; St. Bruno, 715 feet; Johnson, 876 feet; St. Hilaire (Beloeil), 1,375 feet; Yamaska, 1,500 feet; Shefford, 1,600 feet; and Brome 1,500 feet. Each mountain is surrounded by a hornstone collar which in most cases is cut into benches, forming terraces at different elevations. Most of the moimtains have a steep northern face and a gentle slope to the south, which has been described as "crag and tail" structure; most of them present in plan the form of a horseshoe- shaped ridge, opening southward, surrounding an interior basin. The St. Lawrence river flows northeastward through the St. Lawrence lowlands, and, with its tributaries, drains the lowlands and the whole southern portion of the Province of Quebec. The principal tributaries to the main river in southwestern Quebec are the Richelieu, Yamaska, and St. Francis, all of which converge towards the St. Lawrence and discharge at no great distance from one another. The grade on all of these streams is very low, and they run, for a great part of their course, over drift; rock exposures are few and are usually due to the presence of some dyke or sheet cutting the sediments and offering a relatively greater resistance to erosion. Morainic material deposited upon the retreat of the great continental glaciers has greatly interfered with the drainage, damming some streams to form lakes, and altering the courses of others. 18 EROSIONAL FEATURES. The region of the St. Lawrence lowlands has been subjected to erosion presumably ever since late Palaeozoic time, and evidence of this is impressed on, and recorded in the present day topography. For instance, the plain is developed on horizontal strata and on steeply inclined beds without distinction. That erosive forces have swept away a great thickness of strata is evidenced by many of the Monteregian hills which are surrovmded by collars of metamor- phosed sediments reaching in some cases to over 800 feet above the plain, with bedding horizontal: and furthermore, since the igneous rock composing the tops of the hills is coarse-grained and clearly of a plutonic nature, it is reasonable to suppose that a thick cover must have been removed before the plutonics were exposed. The extent to which the region has been subjected to erosion is also in part indicated by the blocks of lower Devonian limestone entrapped in the breccia on St. Helen island near Montreal and which are now at the level of the Utica shales. This is the only occurrence of Devonian strata within 80 miles of Montreal, and, within 20 miles, there is a development of 2,000 feet of shale (Richmond) overlying the Utica, so it may be assumed that these have been stripped off the plain together with an unknovm thick- ness of the Silurian and Devonian formations. The superposed drainage gives a further proof of great denudation. To sum up, then, it would seem that much more than 2,000 feet of sediment has been eroded since late Palaeozoic time, and that the region at the present time is very near base level. SUGGESTIONS OF AN OLDER BASE-LEVEL. It was noted above, that the plain of the St. Lawrence is bordered on the northwest by the Laurentian peneplain, now at an altitude about 1,500 feet above the sea, and on the southeast by a northeast- ward extension of the Appalachian mountain system which may be regarded as a portion of the New England peneplain, which now varies in absolute elevation from 1,000 to 1,500 feet. If these two upland regions were planated at the same time it is to be expected that corresponding base-levels would be estabhshed. It is here 19 suggested that the gap between the two is bridged by the summits of some of the Monteregiaa hills; a glance at the altitudes shows that the five largest hills are over 1,250 feet in height, and that the highest (Shefford) is only 1,600 feet above the sea. Another feature bearing on this suggestion is that St. Hilaire (Beloeil) mountain has three of its four major portions at the same altitude, 1,375 feet, despite the fact that one of them is com- posed of a much denser rock than the others; these are all relatively flat on top although the sides in many places slope at an angle of over 30 °, or take the form of cliffs. The four parts of the mountain are separated by well-developed wind-gaps opening into the interior basin; the highest one of these is about 350 feet above the lake or 950 feet above the sea. They seem to be remnants of an old drainage system which had been superposed on the mountain, and which is being cut down and gradually destroyed by the present streams. It is interesting to note that the only one of the V-shaped gorges which is cut in rock (the others being cut in glacial debris) is floored with blocks of rock, of which many are erratics; hence it appears that this cut had been made before the advent of the glaciers and was protected from ice-action by its position. This shows that the topography of a preceding cycle of erosion' was in process of rejuvenation probably because of uplift, before the Pleistocene. 20 CHAPTER IV. STRUCTURAL FEATURES OF ST. HILAIRE (BELOEIL) AND ROUGEMONT MOUNTAINS As will be shown in the chapter on the petrology of St. Hilaire mountain, its igneous core is the product of two main intrusions — an essexite, followed by a porphyritic nephelite-sodalite-syenite. Upon approaching the centre of the essexite mass from any direc- tion, there is noticed a more or less gradual change from the medixma-grained, normal essexite at the border, into a variety which is very coarse-grained, and which is also characterized by a certain streaky or banded structure of the whole mass, due to the arrangement, in alternate layers, of the different mineral constitu- ents. The most conspicuous mineral in this banding is a light grey, plagioclase feldspar which occurs in large platy crystals averaging from 1 to IJ inches on the side, with a thickness of from tV to I of an inch; these are arranged with their two longer axes in approximately a vertical plane. In a few places a distinctly parallel arrangement of the flat faces of the feldspar is to be seen, but this is not by any means the general rule; rather, there is an eddying effect together with a diverging and converging of lines of crystals, and hence of the bands separating them, so that they appear to merge into one another; the effect produced resembles the lines of flow in a stream, where the channel alternately widens, narrows, and maintains a straight course. A closer study of the rock shows that the long feldspars are fre- quently slightly curved, often in two or more places in reversed directions, and that the bands between the feldspars are made up of pyroxene, hornblende, and black iron ore. It is further seen that there are many shorter laths of feldspar which are not oriented parallel to the larger ones, but which cut across the bands at an angle; this is also true for some of the crystals of pyroxene, but the general direction of the pyroxene crystals is roughly the same as that of the banding in which they occiu". 21 The detailed description of this rock, both megascopic and micro- scopic, is given in the chapter on petrography (variety No. 2 of the essexite). In a section across one of the flov? bands, the long feldspars are bent at intervals with increase of twinning lamellae, and have uneven extinction at these points. There is no evidence of slicing of crystals, and none of granulation except that pieces of feldspar crystals of an earlier generation are included poikilitically in the long individuals and in the ferromagnesian minerals. The augite and the hornblende crystals occur in stout prisms, irregularly bounded, and arranged at random between the long feldspars, and at times enclosed in them; they are clearly of earlier crystal- lization than the large feldspars, which were the last to form. It is clear that these minerals are all primary and not the pro- ducts of later recrystallization. The lack of definite parallelism in the banding, and the winding course of the lines of crystals, to- gether vrith the lack of deformation by slicing, granulation, gliding, etc., and the positive evidence of the primary nature of the minerals, seem to prove conclusively that the flow-like structures were pro- duced before final solidification of the magma, and not by later deformation. The strained character of the long feldspars shows the result of movement in a viscous magma, and their orientation, with flat surfaces nearest to the vertical, indicates that the direction of general movement was approximately vertical. In resum^, the central part of the essexite mass shows a flow structure from which it appears that the magma had an upward movement during the viscous stage, just before final solidification. Structures analogous to that just described have been noted by several observers. Professor Frank D. Adams' in 1893 de- scribed a flow banding developed in the anorthosite of the Morin district in the Province of Quebec, Canada. He notes not only this peculiar structure but also a decided change in texture from that of the normal rock type. He says: "Wir haben hier also einen Fall vor uns, wo ein zweifellos eruptives Gestein mit vollig massiger, wohl entwickelter ophitischer Structur allmahlich in ein gestreiftes iibergeht, dabei wird die gebandete Structur durch bedeutende Aenderungen, nicht nur in der Korngrosse, sondern auch in dem Mengenverhaltniss der Bestandtheile herbeigefuhrt." ' Adams, Frank D., "Ueber das Norian oder Ober-Laurentian vom Canada"; pp. 451, 452. 22 "An dem oben beschriebenen Ausschluss wurden durch wieder- holtes sorgfaltiges studium im Felde Thatsachen aufgefunden, die auf eine Bewegung wahrend des fleuerflussigen Zustandes hindeu- ten. Die Ungleiclimassigkeit in der Korngrosse ist primar und sicher nicht durch Druck hervorgerufen; die streifen oder unre- gelmassigen Bander neiimen nicht von vorne herein eine bestimmte Richtung an, sondern winden sich zuerst herum, weil wen die Masse im zahflussigon Zustanden sich bewegt hatte, undwerden erst dann mehr gleich gerichtet, wenn ein Grund dafur da ist, dass die StrSmung sich auf eine bestimmte Richtimg beschranken miisste." A more or less similar structure was noted by George H. Williams' in the gabbros of Maryland, in which he says: "In other cases a more or less pronounced banded structure is produced by an alter- nation of layers of different grain or by such as have one constitu- ent developed more abimdantly than the others. Such bands are not, however, parallel, but vary considerably in direction and show a tendency to merge into one another, as though they had been pro- duced by plastic flo^-" Some of the other Monteregian hills show this phenomenon, and it has been used as a proof that they are true necks. In the paper quoted above. Dr. Adams notes the occurrence of flow structure in the essexite of Mount Royal. In a later paper^ he describes in Mount Johnson a "banding or fluidal arrangement of the crystals in the essexite" well exposed in quarries on the mountain side. This arrangement is seen to be vertical, and the strike of the band- ing "curves around the mountain, following its marginal outline." Mount Johnson is described as "a neck in the most typical form." The essexite of Mount Yamaska shows banded structure in many places, and tabular feldspars one inch in breadth occur here as at St. Hilaire. John A. Dresser has also noted a banded structure in the essexite of St. Bruno mountain. ' Williams, C. H., "The Gabbros and Associated Hornblende Rocks occurring in the Neighborhood of Baltimore, Md": Bull. No. 28, U.S. Geol. Surv., p. 26. ^ The Monteregian Hills: A Canadian Petrographical Province Jour. Geol., Vol. XI, No. 4, p. 279, April-May, 1903. 23 C. K. Leith, in his "Rock Cleavage" (Bull. No. 239, U. S. Geol. Surv.), notes the parallel arrangement of tabular feldspars in the banded gabbros of the Adirondacks and northeastern Minnesota, the nepheline-syenite of central Wisconsin, the porphyritic gneiss from the main shaft of the Hoosac tunnel. Mass.. and certain other labradorite-porphyries from America and Europe (page 199). He notes (on page 47) , that such structures may be due to rotation of random particles during flowage of the magma, "although the parallel development of minerals in situ, due to differential stresses set up in the rock during the later stages of its cooling, may be more important than the rotation of random original particles." Brogger is strongly of the opinion that the forces in a cooling viscous magma are unequal in different directions; that at any point they may be resolved into three mutually perpendicular differential stresses.' In a paper on the "Banded Structures of some Tertiary Gabbros in the Isle of Skye" by Sir A. Geikie and J. J. H. Teall,' there is described a beautifully developed banding due mainly to segrega- tion of the light and dark minerals. The differentiation is thought to have taken place before reaching its present position and the banding produced by "deformation of the molten mass during intrusion." There is no particular difference in grain, and the crystals interlock uniformly throughout, showing the whole to be the product of one intrusion. There is no cataclastic structure as evidence of regional metamorphism, to account for the structure, and the crystals do not show alignment as a rule. It would seem, then, that a banded structure is not uncommon in deep-seated basic magmas. It is seen to be marked (1) by differ- ences in granularity, (2) by segregation of the light and dark con- stituents, (3) by alignment of prominent mineral constituents, or (4) combinations of these one with another, pointing to different conditions of formation. Again, the bands may be parallel to one another, parallel to the periphery of the mass, parallel to both or to neither of them. Leith, p. 150. Quart. Jour. Geol. Soc. Lon., V. 50, 1894, pp. 645-660. 24 Conditions numbers (1) and (2) frequently occur in combination with the banding roughly parallel to the periphery but not to one another, and condition number 2 is noted well developed where the bands are parallel to one another but not to the periphery; the former would be the result of flowage in a confined magma in some definite direction, with a rotation of the crystals showing much inequality in dimension, together with a certain segregation of constituents not so pronounced as in the second case, where the conditions seem to be more favourable. The nephelite-sodalite-syenite mass of St. Hilaire mountain has a strong development of breccia about its borders, in which most of the fragments are of essexite, hornstone, and marble. This breccia grades off into the normal syenite, but even in the interior of the mass there are some inclusions to be found. There are three large blocks of limestone and marble enclosed in this magma, two of which are over 500 feet in length and 150 feet in breadth. Dr. Ells has stated^ that a Devonian limestone containing Centronella hecate and Zaphrentis proUfica had been found on St. Hilaire mountain, and a sketch map indicating the location of this occurrence was kindly loaned the writer by Pro- fessor Adams. The exposures in this place show a few feet of shaly limestone, passing into purer limestone, and fine-grained, light grey marble; the beds are on edge with a strike and dip which closely corresponds with the cUff jointing of the hornstone 30 feet to the north. A large quantity of this material, mostly of the lime- stone, was shipped to New Haven and closely examined for fossils. Professor Schuchert has made the following determinations: — : "Crinoid columnals of a large, rounded, thick stem. Cyclospira bisulcata (Emmons). Rare. Cyclospira n. sp. Exceedingly abundant. As the specimens are uniformly small and occur by the thousands, it is probable that they are mature individuals. They are, however, very much like the larger Cyclospira bisulcata. Isochilina n. sp. Nearest to I. ampla, but the valves are some- what smaller, narrower, and relatively more elongate. ^ Communication to Professor Frank D. Adams. 25 This horizon is clearly in the Trenton, and probably in the lower part of this formation." All the limestones observed in this area have the same appear- ance and contain the Cyclospira in great abundance in certain layers. The other two occurrences are of coarse, impure marble and no fossils were to be found. To bring it to its present position this block of Trenton limestone must have been raised at least 1,000 feet. The limestone reported by Dr. Ells was not seen by the writer, but if the determination of the Devonian fossils was correctly made, and those cited are not easily mistaken, the block in which they occur must have dropped vertically over 300 feet. It would then appear that there had been a certain amount of churning in the magma, a feature which is characteristic of volcanic necks. An examination of the strata of the sedimentary collar about the igneous mass of the mountain shows that the beds have not been deformed, but that they have been indurated by thermal waters and heat from the magma, converting the shale into hornstone, and the sandy layers into quartzite. The more porous strata have been altered a greater distance from the mountain than the dense. The general covering of drift prevented extensive study of the contact phenomena. The plan of the contact of the igneous mass as a whole bears no relation to the topography, showing that the magma rose in a vertical channel. Both the essexite and syen- ite intrusions are elliptical (nearly circular) in outUne with the major axis running north and south. The circular form would give the maximum volume for least friction surface to the passing magma. In summary then, the evidence of undisturbed coimtry rock; the coarse texture of the igneous mass close to the outer contact; the vertical conduit through which the magma passed; the striking development of flow structure in the essexite; and finally, the churn- ing action shown in the syenite, all point to the conclusion that St. Hilaire mountain represents an eroded volcanic neck. The evidence at Rougemont mountain is not so positive, but is still suggestive. The texture of the igneous mass is coarse-grained close to the contact, and there is a strong development of breccia about the borders, but, so far as observed, the fragments are en- tirely of hornstone, so that no vertical mixing of strata can be 26 shown to have taken place in this case. The contact is, in plan, a wavy line, without regard to the topography, and this fact, together with the cliff development on the north and south sides, shows that the conduit of the magma was practically vertical. In the petrographical study of the igneous rocks of the mountain, it developed that while the mountain is the product of one main intrusion, there were two successive periods of injection, one fol- lowing almost immediately after the other. The olivine-yamaskite which occupies the eastern part of the mountain was followed, before it had become consolidated, by an injection of a great mass of rougemontite, which sent apophyses into the yamaskite, and developed fine flow-banding in many places. In r6sum6, then, the facts brought out are: (1) That the in- trusion has taken place forcibly, breaking off the strata and enclos- ing many fragments in a border breccia; (2) that the texture of the mass is coarse-grained close to the contact; (3) that the conduit through which the magma arose is vertical; (4) that there is evi- dence of flow within the magma. The suggestion is then very strong that Rougemont represents an eroded volcanic neck. The tables accompanying the chapter on the Monteregian Hills give a brief summary of the geological history of the Montere- gian province. It is seen that the four central mountains are volcanic necks and that the two to the east are laccoliths, while the evidence from the western occurrences is indefinite, although Mount Royal is very probably also a neck. The most violent volcanic activity apparently occurred in the central part of the Province, and towards its western end. The close grouping of such a number of volcanic necks goes to show that the parent magma could not have been at a great distance below the surface. The close association in origin of the several mountains, where more than one intrusion has occurred, is brought out by the order of these intrusions, and the correspondence in rock-type is striking; this is more fully discussed under general petrology. The rough linear arrangement of these mountains was noted by Logan and it was suggested that this probably indicated a line of disturbance, perhaps faulting. Suggestions appear in different reports that the location of the separate Monteregians was de- 27 termined by the loci of intersection points of a set of parallel fractures crossing the main line of disturbance in a north-south direction. No evidence of this faulting was observed at either St. Hilaire or Rougemont mountains, so, as no additional data are at hand, the evidence is summed up by two quotations from Dr. Ells' report' as follows: — "Of the two mountains just described, it may be remarked that the more easterly, viz., that of Brome, and ShefTord, occurs along the line of contact between the Cambro-Silurian and Cambrian rocks, while Yamaska Mountain is situated on the line of fault between the Sillery division of the Cambrian and the Lower Trenton formation. It is probable that the Shefford and Brome extrusion is also along a fault line, the presence of which is not so clearly indicated as that on which Yamaska Mountain lies, though the amount of dioritic matter is much greater at Brome." "Beloeil, or St. Hilaire Mountain is due north from Mount Johnson, and, on the hypothesis that these eruptive masses come up along north-south lines of fracture, would probably lie in the continuation of the fault which extends from near LacoUe to St. John." It does not seem clear that there is any positive evidence to show that there are lines of faulting related to these intrusions. On the contrary, it is usually found that volcanic necks, such as are found here, occur without any dependence upon fault systems, and that the magma, with its gases under high pressure, has drilled its way through the strata vnthout disturbing the bedding. Examples of occurrences of this kind are well described from the diamond- bearing craters of South Africa,* the volcanic necks of central Montana,' and the volcanoes of the Mount Taylor region. New Mexico * ' Report on the Southwest Sheet of the "Eastern Townships"map (Montreal sheet). Ann. Rept. Geol. Surv. Can., Vol. VII, Pt. J, p. 73. ' Hatch and Corstorphine, "Geology of South Africa," etc. ^ Pirsson, L.V., Bull. 237, U. S. Geol. Surv., 1905. ' Johnson, D. W., Bull. Geol. Soc. Am., Vol. XVIII, pp. 303-324. (c) 28 CHAPTER V. PETROLOGY : ST. HILAIRE (BELOEIL) MOUNTAIN. The igneous rocks composing St. Hilaire (Beloeil) mountains are of two main types: essexite, and nephelite-sodalite-syenite. Each of these types has a number of varieties, and there is a set of dykes representing the last stages of each of the main intrusions. The essexite was the first to be intruded and it is coarse-grained up to the contact with the sedimentary collar; the central portion shows a very distinct flow structure with the development of large platy feldspars standing on edge, giving an indication of movement in an upward direction. At various places in the essexite, brown hornblende becomes prominent; in one occurrence the ferromag- nesian minerals are very small in amount and labradorite and nephelite greatly predominant. It is proposed to call this variety rouvillite. The syenite at its borders forms a typical intrusion-breccia which occupies a zone of varying width, and foreign rock fragments are found widely scattered throughout the whole area of the syenite. The border variety of this type approaches a tinguaite in texture, and a nimiber of peculiar, unknown minerals are developed. The main mass has a porphyritic texture, and, in places, appears to have differentiated, forming a rock very high in sodalite, which is here called feldspathic tawite. ESSEXITE: TYPE VARIETY. As is the case in nearly all basic magmas, the essexite varies considerably both in texture and in mineral composition; at the same time one cannot, as a rule, point out any distinct phase as being confined to one or more particular areas. The central portion of the mass exhibits a flow structure with a parallel arrange- ment of platy feldspars, not seen about the borders. Owing to the great difficulty of obtaining fresh rock in some places, even by blasting, the selecting of type material was governed by this 29 condition. The type selected for detailed description and analysis represents the normal granitoid rock but is a little higher in feld- spar than the average rock. It was taken from the northwest face of the mountain where a perpendicular cliff overlooks the village of St. Hilaire and the huge blocks offer abundant fresh ma- terial. Departures from this type will be indicated later, and de- scribed as varieties of the type. The rock is holocrystalline, medium-grained, spotted black and white, and possesses an uneven but sharp fracture. The feldspar has a light grey colour and is a little more abundant than the dark minerals; it occurs as irregular crystals and in distinct laths up to 7 mm in length by 0'5 mm in width. Glittering biotite crystals, 2 to 4 millimeters by 2 mm, are easily distinguishable, and the horn- blende and augite can be readily determined. Minute crystals of titanite may also be observed, but the other mineral constitu- ents cannot be made out. The thin section shows the presence of apatite, pyrite, iron ore, titanite, zircon, olivine, augite, biotite, hornblende, labradorite, and nephelite, listed in the order of their crystallization, as well as small amounts of secondary minerals: chlorite, serpentine, and muscovite. Apatite, which seems to have crystallized first, occurs in short, rounded prisms, abundant in some slides. Pyrite is present in a few irregular grains. The iron ore has, in many cases, well-marked outlines and usually forms the nucleii of crystals of biotite. Titan- ite occurs in a few irregular grains. Zircon is present in two or three minute crystals. Olivine occurs in a few irregular grains, and shows a slight decomposition along cracks to a yellowish green serpentine. The augite has a very light grey colour, with a faint pleochroism to reddish violet, indicating the presence of titanium; the crystals have a maximum size of 2 mm with rounded, or subangular outhnes. Extinction takes place up to 43°, and twmning is common on (100). Biotite is fairly abundant, often surrounding iron ore, and usually as irregular crystals up to 1'5 mm in length by 1 mm in breadth. Pleochroism is from a pale yellow to a deep reddish brown, and the very deep absorption is striking. A few flakes show a radiating structure due to a break- ing down to chlorite and iron ore. 30 Hornblende is present in amount usually about equal to that of the biotite, but in some places it is more abundant. Crystals of a brown variety range up to 2 mm by 1 Tntn in size, some of the smaller crystals showing good outliaes. A green variety occurs usually as borders to either the augite or the brown hornblende, but seemingly not as a decomposition product; it is altogether subordinate to the brown in quantity. The brown variety will be more fully treated in the description of variety No. 1 of essexite. Plagioclase is in laths reaching 4 mm in length by 1 mm in breadth; the laths are irregularly bounded and often show zonary structme. It shows well-developed albite and carlsbad twinning and hence is easily determined by the method of Michel LeVy. It ranges between AbjAnj and AbjAuj. The variety is thus seen to vary between andesine and labradorite. Nephelite occiirs filling irre- gular openings about the feldspar laths; it is easily distinguished by an incipient alteration to muscovite. CHEMICAL ANALYSIS. The chemical analysis given below shows that the rock is a nor- mal variety of essexite. SiOj AlA FeA FeO MgO CaO Na^O K5O TiO, HjO PA Rest 49 96% 18 83 2 52 6 64 3 52 7 42 5 25 2 58 2 40 60 25 0-20 100 17 According to the Quantitative Classification of Igneous Rocks, the essexite belongs to class 2, dosalane; order 8, norgare; rang 3 salemase; subrang 4, salemose. 31 The mode was calculated from measurements made by the method of Rosiwald, and is as follows:— Labradorite Nephelite Augite Brown hornblende Biotite Iron ore Apatite Olivine Titanite % by vol. 55 4 5 19 6 5 5 5 3 1 5 5 100 Assumed sp. gravity. 2 -67 2-6 3-4 3-4 2-9 5-2 3-2 3 3 3-5 % by wgt. 48 3 21 6 5 8 3 1 •70 •87 •41 •76 30 •61 •18 •62 •60 100 05 This is, of course, only an approximate result, since the specific gravities had to be assumed for the different minerals; this error was minimized as much as possible by taking averages of several determined specific gravities for minerals exhibiting properties similar to those in this case. To determine roughly the specific gravity of the whole rock Labradorite 48 Nephelite 3 Augite 21 Hornblende 6 Biotite ... 5 Iron ore 8 Apatite 3 Olivine 1 Titanite . 72% X 87 X 41 76 30 61 18 62 X X X X X X 67 6 4 4 9 2 2 3 130 10 72 23 15 44 10 5 060 X 3^5 = 314-3 Specific gravity of rock as calculated 3 • 14 Specific gravity determined 2 • 92 Difference ' 22 32 ESSEXITE: VARIETY NO. 1, RICH IN BROWN HORN- BLENDE. This variety occurs in a few scattered places, mostly, however, within the central part of the essexite area; that is, in the more coarsely crystalline part exhibiting flow-structure. The specimen here described comes from the centre of the south face of the hill in the northwest part of the mountain; that is, from just north of the centre of the whole essexite mass. The appearance of this variety is intermediate between that of the normal granitoid essesfite described as the "type," and the por- phyritic variety with the large platy feldspars, described as variety No. 2. The dark minerals are only slightly in excess of the Ught ones; all are millimeter- to centimeter-grained, giving a mottled appearance to the rock; and the platy feldspars are subparaUel, giving the rock an uneven cleavage parallel to their long dimensions. Flashing prisms of pyroxene, averaging over 5 to 8 millimeters in length, are abundant, arranged with their long axes roughly in a plane parallel to the feldspars. Hornblende occurs more abund- antly than the pyroxene, in stout prisms which vary in size, and which tend to be bunched. The following minerals in their order of crystallization are seen in thin section: apatite, iron ore, ohvine, pyroxene, brown horn- blende, and plagioclase. It may be noticed that the minerals occurring in the "type" specimen which do not appear in this variety, are: zircon, biotite, green hornblende, and nephelite. Apatite is abundant in short, stout laths, and in hexagonal basal sections. Iron ore is in irregular grains, and small octahedra, not so abimdant as in the "type" variety. Olivine is in one or two small, roimded crystals, embedded in the hornblende. Pyroxene occurs in a few crystals sometimes intergrown with the hornblende; it is the same as that described as occurring in the "type" variety. Horn- blende is very abimdant in stout crystals averaging about 5 mm in length; they are irregular in outUne and are bunched so that they have interfered in one another's development. The mineral is also found intergrown with the augite. Pleochroism is pronounced, as follows: c = b, deep brown; a, pale brownish yellow. The absorption is c = b>a, and the extinction cAc = 14°. The horn- 33 blende is thus seen to be a barkevikite. The manner of intergrowth of hornblende and augite, which is so common in this essexite, is such as to very clearly show the primary origin of both minerals. Similar intergrowth has been noted by Iddings in the rocks of Electric Peak and Sepulchre mountain. Plagiodase occurs in laths over 8 mm in length, and in pieces of laths, or plates of varying width. There is a subparallel arrange- ment to the long crystals, but the broken ones appear often to be wedged cross-wise, often giving uneven and wavy extinction. The long individuals are frequently bent, producing the same phe- nomena as noted later in the tjrpical flow-variety. Measured by the method of Michel Levy, this plagiodase is found to be more basic than the average in the magma; it varies from AbjAn, to Ab, An, ; that is, from labradorite to bytownite. The texture of the rock is very similar to that of variety No. 2. ESSEXITE: VARIETY NO. 2. This phase forms an elliptical mass in the centre of the essexite body, shows distinct flow-structure, and grades into the normal granitoid rock on all sides. The exposure in the field shows a dark coloured rock, usually very coarse-grained, and characterized by large platy feldspars j inch to If inch on the side and yV inch to I inch in thickness, which are arranged in eddies or frequently in typical flow-structure with the flat sides of crystals parallel. The rock is high in iron and is frequently coated with brown iron oxide. The hand specimen shows a grey and black banded rock, in which the black constituents are pyroxene, hornblende, and iron ore; the white mineral is a plagiodase. The gneissic arrangement of the minerals is very well developed in some specimens and a sub- parallel arrangement is general in the whole phase. Under the microscope the minerals present are seen to be: apa- tite, iron ore, plagiodase, augite, and brown hornblende. OUvine and nephehte are absent. Apatite is abundant in large, irregular masses, usually enclosed by the ferromagnesian minerals. Augite occurs in stout prisms up to 2 mm in length, with irregular out- lines and, usually, intergrown with brown hornblende. It has a slight pleochroism from light grey to a reddish grey, and shows 34 distinct schiller structure. Brown hornblende is present in vsniahle amount, sometimes much less abundant than the augite, sometimes greatly preponderating. It is the same as described in the essexite, variety No. 1. It occurs usually intergrown with the augite, but also in distinct, irregularly bounded crystals, ranging up to 5 mm in length, and with well marked cleavage. Plagioclase is present in two generations, in roughly bounded laths, reaching in length to over 2'0 mm and to 2 mm in width. They are well twinned according to both the carlsbad and the albite laws, and measured by the method of Michel Levy, they prove to bejmostly labradorite AbjAn, to AbjAnjjWith some andesine, AbjAn,. Some of the crystals containing andesine have a tendency toward zonal structure. The crystals have a parallel arrangement; the smaller ones often penetrate, or are enclosed by, the ferromagnesian minerals, but the larger laths enclose crystals of all the other minerals and are grouped in bands, separated by bands of the dark minerals, producing a regular gneissoid arrangement. The long crystals frequently enclose fragments of smaller crystals of feldspar as well as masses of ferromagnesian minerals arranged poikilitically. The long individuals have been subjected to strain and show bend- ing of the lamellae in reversed curves with a discontinuity of twinning lamellae along the crystal and an increase in the number of lamellae about points of bending, together with a wavy extinc- tion from these places along the length of the section. In texture the rock is millimeter- to centimeter-grained, and inequigranular; the crystals are multiform, and irregular. The fabric is hiatal and poikilitic, in which the large feldspars form the oikocrysts, and the ferromagnesian minerals the xenocrysts. The oikocrysts are magnophyric, tabular, and equiform, and arranged in lines producing a linophyric texture. The relative proportion of crystals is xenoikic, and the xenocrysts are relatively medium- sized, multiform, and diverse. There is a tendency to ophitic structure where the smaller laths of feldspar penetrate the bisihcates. ^SSEXITE: VARIETY NO. 3. A medium to fine-grained rock, dark greenish grey in colour, occurs in an exposure about 700 feet south of the Pain de Sucre. It is about 3 feet X 2^ feet in area, and sticks cornerwise out of a 35 mass of coarse essexite which is highly weathered and crumbles easily for some distance around ; field observations do not give a clear idea as to whether the mass is a dyke, or an inclusion; it seems to be surrounded by essexite, however. The minerals seen in thin section are : orthoclase, olivine, brown hornblende, biotite, apatite, and iron ore, listed in the order of importance. Chemical test failed to reveal any feldspathoid present. Orthoclase makes up over 70 per cent of the rock. It occurs in stout laths 0*5 mm to 10 mm in length, and the un- certain birefringence shows it is not a pure variety. Carlsbad twinning occurs in a few crystals. It is very probably a soda- orthoclase. The other minerals are as described in the normal essexite. The rock is phanerocrystalline to microcrystalline, decimilli- meter-grained, and inequigranular. The crystals are irregular, multiform, and tend to form a seriate-intersertal aphyric fabric. The striking feature of this variety is the presence of abundant oUvine in a rock so high in orthoclase. ROUVI ELITE. This shows a peculiar phase of the differentiation; it is really an extreme variety of the essexite, but, for reasons given below, it is treated as a distinct rock type. Its description is as follows : — Holocrystalhne: medium- to coarse-grained; light grey colour, spotted with black. Highly feldspathic, the orthoclase in slender laths up to 15 mm in length by 4 mm in width, but mostly less in width, the nephelite not well outlined, but recognized by its dull, greasy lustre and a light greenish colour. Hornblende and augite crystals have well-developed cleavage and are 2 to 5 mm by 3 mm in size. The minerals seen in thin section are : apatite, iron ore, titanite hornblende, augite, plagioclase, and nephelite, given in their order of crystallization. Apatite is in short prisms up to 0'5 mm in length, quite abundant. Iron ore is not so abundant as in the "type" variety of essexite. Titanite is in a few irregular grains, in one case enclosing apatite. Hornblende is as described before, 36 but with a stronger absorption. It is much less abundant than in the "type" variety of essexite. Augite is about equally abundant with the hornblende; it shows a stronger pleochroism than in the "type" variety of essexite. It has the following pleochroism. a = light greyish purple: b = hght purpHsh red: c = colourless; absorption b>a>c; extinction, cAc = 41°. Plagioclase is the most abundant mineral in the slide, occurring in laths up to 11 mm by 2 mm in size. It shows well-developed albite and Carlsbad twinning, and varies between AbjAn, and Abj An,; that is, from labradorite to a medium by to wnite. A certain amount of intergrowth is also developed. Nephelite forms about one-fourth of the whole section; it occurs filling interstitial spaces, and as intergrowths with the plagioclase; partial decomposition to muscovite makes it easily recognizable. The rock is millimeter-grained for the most part, the small crystals of apatite and of some of the ferromagnesian individuals being decimillimeter-grained; it tends to be equigranular, and the crystals are multiform and irregular. The frequent intergrowths of plagioclase and nephelite give rather a graphic texture to the rock. CHEMICAL ANALYSIS. The chemical analysis of this rock type is given below, with a table of analyses of other rocks for comparison. Table of Analysis. SiO, AljO, FejO, FeO MgO CaO Na,0 K,0 H,0 HjO TiO, PjOs MnO Total Sp. g. 51 23 1 2 1 8 6 2 1 100 00 2-77 26 78 81 70 96 00 72 16 55 10 66 io 49 -96 18-83 2-52 6-64 3-52 7-42 5-26 2-58 07 053 2-40 25 0-20 47-67 18-22 3-65 3-85 6 35 8 03 4-93 3-82 2-97 0-28 51 15 1 4 4 8 7 4 100 18 2-92 100 15 99 2 38 88 48 39 43 62 57 20 42 12 45 88 37 1. Rouvillite, St. Hilaire mountain, M. F. Connor, analyst. (Analysis incomplete). 2. Essexite, St. Hilaire mountain. M. F. Connor, analyst. 3. Theralite, porphyritic, Elbow creek, Crazy mountains, Montana. (With 0"38% of hygroscopic water). 4. Shonkinite (Amphibole-malignite). North shore of Poobah lake. Rainy River district, Canada. Note. — Analyses Nos. 3 and 4 are taken from Rosenbusch, "Elements der Gesteinlehre," p. 176. A comparison of these analyses shows that the chemical com- position of rouvillite is very similar to the three types quoted. It is higher in alumina and soda, and lower in magnesia and potash than the normal theralite. According to the Quantitative Classification of Igneous Rocks, the rouvillite belongs to class 2, dosalane,; order 8 norgare; rang 3, salemose; subrang 4, salemase. The following is a calculation of the mode of rouvillite, based on microscopic measurement by the method of Rosiwald. % by vol. Assumed specific gravity. %bywgt. Nephelite . . . Plagioclase. . Pyroxene... . Hornblende . Pyrite Apatite 29 55 7 3 2 1 35 "2,- ■90 2- 50 s- 64 3 ■50 6- ■15 3' J 60 J 67 $4 5 4 50 5 '2 27 53 8 4 4 1 38 42 98 45 48 33 Total. 100 04 100 04 To determine the specific gravity of the rock; — ■ Ne 27-38% Flag 5342 Pyrox 898 Hb 445 Py , 4-48 Ap 133 X 2G = 711 X 2 67 = 1450 X 3 4 = 306 X 34 = 151 X 5 = 224 X 52 = 43 Calculated spec, gravity 2 885 Spec, gravity by weighing 2 ' 77 DifTerence . 11 38 The mode shows that the rock contains over 80 per cent of salie constituents, and that this is made up of 27 '38 per cent of nephelite, with 53'42 per cent of labradorite and bytownite. The rock is really a theraUte, but since the typical theralite contains predom- inant ferromagnesian minerals, it is thought advisable to distinguish this variety and the name "rouvillite" is suggested after the county in which the mountain occurs. NEPHELITE-SODALITE-SYENITE: TYPE VARIETY. The syenite mass shows numerous variations from the normal, depending largely upon its relations to inclusions, or to the contact with siirrounding rocks; these variations will be described as variet- ies of the type. The rock from the southeast face of the hill at the southeast end of the mountain, near the top, is fresh, free from inclusions, and represents the type porphyry as it appears where not changed by foreign causes. The hand specimen is phanerocrystalline with a porphyritic texture; large phenocrysts of feldspar and feldspathoid occur in a fine-grained groundmass of minute crystals of feldspar and greenish aSgerite : the whole mass is peppered with larger a^gerites of about 0'5 mm length. The rock thus presents a greyish green appear- ance, spotted with large, glassy feldspathoid, and light grey feldspars. Thin sections show the following minerals: a^erite, albite, nephelite, sodalite, eudialyte, and orthoclase, with a few small crystals of lavenite-like mineral. There has been crystallization in two generations of the a8gerite, and a continuous growth of feldspars. The albite and a6gerite started to crystallize and then the a€gerites stopped at a very small size. The nephelite and sodal- ite came next and attained large crystals, holding small aigerites and feldspars. About the same time eudialyte, and the second generation of a^gerite appeared, also holding inclusions of the earlier minerals; the orthoclase came after the eudialyte. The lavenite- like mineral contains inclusions of most of the other minerals and appears to have crystallized near the last. The groundmass is an aggregate of laths of feldspar and aSgerite with a trachytic struc- ture, and containing many fragments which were torn from the larger a^gerite crystals. Both the nephehte and eudialyte show indications of a certain amoimt of corrosion by the magma. 39 Aigerite-augite occurs in very minute laths and in large crystals up to 2 mm by 1 mm in size. It is very abundant, the small laths being included in all the other minerals, and the larger individuals penetrated by both orthoclase and albite crystals. A zonary banding is evident in the large crystals, in which the borders are lighter coloured. Frequently the minute aSgerites form a line par- allel to, and just within, the large nephelite borders. Absorption — a = pea green; b = brownish green; c = yellow green; a>b>c; aA c = 6°. Albite occurs in laths in all stages of growth up to I'S mm in length; it shows fine albite twinning but not many carlsbad twins. It is included, in small crystals, in all the other minerals, and forms intergrowths with nephelite and sodalite. Nephelite appears in phenocrysts up to 2 mm by 1 mm in size, although there are many smaller crystals in the groundmass. It is about equally abundant with the sodalite, together forming over 50 per cent of the section. Intergrowths with albite and orthoclase are seen in some crystals, and the border arrangement of the aegerite inclusions is quite noticeable. The crystals are relatively fresh, but show ragged edges as if corroded by the magma. Sodalite, like the nephelite, is seen in both large and small crystals about the same size as the nephelite. It often shows idiomorphic boundaries to the nephelite, and its edges are not corroded ; inter- growths with albite are rare. The sodalite is relatively free from inclusions and is completely isotropic. It is comparatively fresh, showing no decomposition product. Eudialyte is described more fully in connexion with the contact variety of this type; the mineral here is very light pink to colourless and occurs in rounded or sub- angular crystals about 0'5 mm in diameter. Orthoclase occurs in irregular laths about 0'3 mm in length. It is not so abundant as the plagioclase, and it often shows an uneven or patchy extinction. A lavenite-like mineral occurs in one or two small, ragged crystals; it will be described more fully in the case of the contact varieties where it is more abundant and in larger crystals. The type-specimen is decimillimeter- to millimeter-grained with some larger phenocrysts; it is inequigranular and has a hiatal, porphyritic fabric. The crystals are multiform and irregular; the ratio is dopatic, and the phenocrysts are usually mediophyric. 40 and arranged in clusters, forming a cumulophyric texture. The groundmass is holocrystalline, and, excepting the minute crystals and fragments of aSgerite, the rock may be said to be seriate- porphyritic; there is a break, however, between the largest pheno- crysts and the more seriate portion. The whole mass has a trachy- tic structure, with a roughly parallel arrangement of the long axes of crystals, and flow-structure around phenocrysts. CHEMICAL ANALYSIS. The analysis of this variety together with others, introduced for the sake of comparison, is given below. Table of Analysis. 1 2 3 4 5 6 SiOs 54-74 trace 54-20 1-04 53-28 5414 0-95 92 20 61 3-28 2 08 0-25 1-85 0-83 5-25 9-87 012 0-40 56-45 29 "26-68' 1 31 4-39 99 214 63 713 5-61 0-43 1-77 13 49-46 TiOj... . ZrOs 54 AljOj. 21-53 406 0-94 014 0-90 0-18 4-18 12-84 21-74 0-46 2-36 20-22 1-56 1-99 23-53 Fe,Oj 304 FeO 102 MnO 17 CaO 1-95 52 6-97 8-69 3-29 0-29 6-21 7-89 0-80 MgO 003 K,0 4 34 Na,0. . . 14-71 CI 2-25 H,0 P,0, 35 0-22 3-43 1-38 100 25 100-25 99-93 100-55 100-45 101-27 1. Nephelite-sodalite-syenite. St. Hilaire mountain, Que. M. F. Connor, analyst. 2. Nephelite-syenite, Serra de Monchique, P. Jannasch, N. Jahrb. f. Min., 1884, II, p. 11. 3. Nephelite-syenite, Magnet cove (Arkansas). J. F. Williams, Ann. Rept. Geol. Surv. Ark., 1890, II. 4. W. Ramsay and V. Hackman, "Der Nephelinsyenit des Umtek." Fennia II, 2, Helsingfors, 1894, p. 196. 5. Pulaskose (sodalite-syenite), Square Butte, Mont. W. H. Melville, analyst. L. V. Pirsson, Bull. 237, U. S. Geol. Surv., p. 68. 6. Sodalith-syenite, feldspathreich, mit eudialyte ebenda. Rosenbusch, Gesteinlehre, p. 126. 41 According to the Quautitative Classification of Igneous Rocks, the syenite belongs to class 2, dosalane; order 7, italare, rang 1, lujavrase; subrang 4, lujavrose. The mode of this rock calculated by the naethod of Rosiwald is as follows: — % by vol. Assumed sp. g. %bywgt. Sodalite 17 5 34-8 9-4 23 2 11 4 2 2 2 6 2 6 2 6 35 2-9 14 6 Nephelite Orthoclase Albite Aggerite Eudialyte 34 2 9 3 22-8 14-6 4-5 100 100 To determine the specific gravity of the rock : So., Ne.. Or.. Ab.. Agg.. Eu. . 14-6% X 2 2 = 321 34 2 X 2-6 = 889 9 3 X 2-6 = 242 22 8 X 2-6 = 593 14 6 X 3 5 = 510 4-5 X 2 9 = 130 Calculated sp. g Determined by weighing. Difference . . = 2 685 = 2 68 005 The abundance of sodalite is worthy of note, so the rock has been called, nephelite-sodalite-syenite. NEPHELITE-SODALITE-SYENITE: CONTACT VARIETY. This is characterized in many cases by finer grain in the ground- mass, but with phenocrysts about the same size as in the normal type. There is a tendency for the phenocrysts to collect in bunches and in the groundmass there is a massing of minute laths of plagio- clase, and of a6gerite, into mattes. There is a general trachytic structure which is very pronounced in some cases, not so strongly in others. 42 Accompanying the slight change in texture is a mineralogical difference in that the border varieties contain a much higher per- centage of eudialyte, and of the lavenite-Uke mineral mentioned before, together with an unknown, colourless mineral in some cases. These minerals may be described at this place. Lavenite-like Mineral. This occurs in stout crystals and attains a size of 1 '3 mm by 1 mm. Its properties are : bright yellow colour one good cleavage; biaxial; negative; index of refraction about l'? birefringence 0"035 prox.; extinction 0°-17°, usually less than 10° pleochroism:a = orange; b = yellowish brown; c = brownish yellow absorption a>b>c. This mineral differs from astrophyllite and lamprophyllite, both in pleochroism, and in having inclined extinction. It resembles the lavenite described by Hackman* as occurring in the nephelite- syenite of Umptek, in which the pleochroism is: c = orange yellow ; b = straw yellow ; a = bright wine yellow ; absorption c> b> a. Extinction cAa= 17°. If a and c were interchanged, the corre- spondence would be almost exact. An unknown colourless mineral occurs in irregular crystals; one measures 3 mm by 2 "5 mm but they are usually smaller. It was one of the last minerals to form, and is crowded with inclusions of the other minerals. It has the following properties: colourless; index about 1'65; biaxial; negative, birefringence about O'OIT; extinction parallel; plane of the optic axes parallel to cleavage. Eudialyte. The mineral described under this head occurs in subangular to rounded grains and sometimes stout laths. It is colourless, sometimes carmine, and in many cases the same crystal is part coloiu-ed and part colourless. It is probable that there is here some eudialyte and some eukolite, for some of the crystals appear to be positive, while others show a distinctly negative character. The coloured variety is only observed near the margin of the syenite mass, and the colour is usually confined to the borders or to the centre of the crystals; it is accompanied by a certain cloudiness as if from decomposition, while the rest of the crystal is quite clear. ' Ramsay and Hackman, Fennia II, 2, p. 146. Helsingfors, 1894. 43 No cleavage is visible, but in the elongated crystals, sometimes o is parallel to the long axis, sometime e, and in each case the ab- sorption is from carmine to colourless or yellowish, and the absorp- tion o^e. The birefringence is very low, and optical anomalies are not uncommon; there is a tendency to hour-glass structure in some cases. W. Ramsay^ found an isomorphous mixture of eudi- alyte and eukolite in eleolite-syenite from the peninsula of Kola. The double refraction was sometimes partly positive and partly negative ; extinction = 0. An hour-glass structure is very common in these occurrences. Biaxial anomalies occurring in eudialyte have been noted by N. V. Ussing* in nephelite-syenite from Green- land, and by J. F. Williams from Magnet cove, Arkansas. In these the axial angle changes in one and the same crystal, and can rise to 2 e = 50°; the absorption o>e. Lacroix observed a eukolite mineral in an aSgerite-foyaite dyke in Ampangarinara, in northwest Madagascar,' in which there was strong dispersion, and the centre was less coloured than the periphery of the mineral. In his work on "Les Syenites Nephe- liniques de L'Archipel des Los et Leurs Mineraux'V he describes eudialyte in which the pleochroism is as follows: — o = Ng or Np = rose carmine e = Np or Ng = colourless or yellowish. "On voit que la coleur est lies k une direction cristallographique et non aux indices." Lacroix also notes that, while the bire- fringence is sometimes uniform in section, it is more often variable in the same individual, not by concentric zones, but by irregular "alveoles"; frequently also it is seen to diminish along the fissures. NEPHELITE-SODALITE-SYENITE: BRECCIA VARIETY The nephelite-syenite mass is bordered in most cases by a devel- opment of breccia in which are enclosed fragments of many differ- ent rock varieties; theralite, essexite, nephelite-syenite, feldspathic 1 Fennia, III, No. 7, 42. Helsingfors, 1890. 2 Mineralogisk-petrografiska Undersogelser af Gronlandske Nefelin- syeniter og beslaegtede Bjaergarter. ' Extrait des Nouvelles Archives du Museum, 4 serie, Tome 1. * Extrait des Nouvelles Archives du Museum, 5 serie. Tome III. 44 tawite, tinguaite, camptonite, hornstone, limestone, and marble are all represented. In many examples the inclusions seem very slightly altered; in others, where flow structure is well developed, the smaller fragments have been drawn out into flat lenses, and are more intimately associated with the magma; in still other cases the frag- ments have been partially digested in the nepheUte-syenite, leaving parts of characteristic minerals to tell the tale. Close to the border the number of inclusions is great and the matrix is very fine-grained ; towards the centre of the mass they become widely scattered, but are not entirely absent. In size, the fragments range from a couple of inches in diameter to the great masses of limestone and marble which are hundreds of feet in length. Some of the interesting features of mineral change or development in this breccia will be described. In the inclusions of essexite, the augite and olivine are more or less altered to chlorite and to serpentine. Pyrite is developed along fissures and frequently occurs in thin lines between the min- erals, giving each a framed effect. In intergrowths of hornblende and augite, the augite is often completely decomposed, leaving the hornblende fresh, and in other cases, the latter also is changed to a bluish green chlorite: the feldspars are not greatly affected. Ex- cept in individuals showing good cleavage, decomposition begins at the periphery and works towards the centre of the mineral. Where essexite has been digested in syenite, there occur bunches of fragmentary crystals of ferromagnesian minerals, and skele- tons of iron ore, about which feldspar has crystallized, giving a hornfels appearance to the slide. The pyroxene is sometimes aggerite, or nearly so, and in other cases it has a centre of titanif erous augite, with distinct pleochroism, surroimded by a band of lighter violet tint, and an outside border of green pyroxene with a much smaller extinction; this border resembles a secondary growth. Intergrowths with brown hornblende are seen in some of the green crystals which are now an aSgerite-augite. There is also abundant biotite with strong pleochroism. Near the contact with the larger inclusions of marble, the syenite magma shows a development of new minerals, particularly near the northern inclusion^ here the magma has differentiated rather thoroughly in a few spots, developing a white rock made up 45 of minute laths of feldspar with an occasional crystal of aSgerite, and also a green variety, in which the aSgerite occurs in tufts and forms a regular matte. Scattered through both of these types, more or less abundantly, are prisms of a blue hornblende which have well-bounded outlines, and the terminal faces in some are clearly shown. This mineral is described as follows: — The mineral has a very strong dispersion of the optic axes, with no absolute extinction, but a sudden change of birefringent colour from brown to prussian blue ; a zonary structure becomes very marked during the change. Crystal faces are well developed, both prismatic and terminal, and the crystals range in size from 1 mm. downward. The pleochroism is as follows: a = greenish blue; b = brownish blue; c = hght grey-blue to light, yellowish green. The absorption is a>b>c and extinction a Ac seems to be in two phases, one commonly about 18°, and the other reaching a maxi- mum of 40°. The mineral is positive. The pleochroism agrees most closely with that of arfedsonite described by Ussing' from Greenland, in which he notes: a = greenish blue; b=blue to grey blue; c = greenish grey to yellow. Absorption a>b>c, and op- tically negative. It differs from this mineral in being positive. The positive character of an arfedsonite from Greenland is noted by Brogger in the "Mineralien der Syenite-Pegmatit Gange," Norwegen, 1890. Rosenbusch draws attention* to the usual association of arfedsonite with aSgerite, and notes its occurrence in lujavrite, pantellerite, and nephelite-syenite generally. There is another mineral, occurring in the feldspathic part of this rock, which is very pecuhar, and its properties do not corre- spond with any known mineral. Its characters are: colourless, or pahsh yellow; index of refraction =1"6 approx.; birefringence = 0'02 — 0"025; uniaxial; positive; probably tetragonal. The mineral suggests melinophanite, but differs from it in the direction of cleavage (parallel to (001) distinct in the former,) and in being optically positive. The variety of the rock containing this mineral has a peculiar groundmass made up of albite, orthoclase, and ne- ' Meddelelser om Gronland, Kopenlmgen, XIV, 1899, p. 191. 2 Mikroskopische Physiographie, Mineralien, p. 243. 46 phelite, of which the albite forms the longest laths, 1 ' 2 mm in length, and also some of the smallest; the albite crystals are fre- quently arranged in radiating tufts, and all have very irregular boundaries due to mutual interference in crystal growth. There is a general parallelism of crystals on the whole, producing a trachytic structure. TAWITE: FELDSPATHIC TYPE. This rock is really a variety of the nephelite-sodalite-syenite, and so is treated in this place. This variety of the main magma has been found at three different localities, on the borders of the syenite mass. Near the northeast contact just south of the in- cluded mass of limestone and marble, there are coarsely crystallized fragments of the rock included in the syenite. This was the only place observed where the field relations are definite. The other two localities are near the centre, on the east and west contacts of the syenite. The occurrence on the east is coarsely crystalline and appears to be in place, but the exposure is too limited to show its relations positively. The specimen from the west side was col- lected by Mr. LeRoy some years ago, but the writer did not find this particular occurrence. It is medium to fine-grained, and shows blue sodalite, together with streaky segregations of feldspar; it looks rather similar to the normal syenite, and might easily be overlooked in the field. It appears, then, that this variety is in part earlier than the main mass of syenite, and that part may be due to a differentiation in the magma during intrusion. It is quite likely that there are other localities where this rock occurs under the drift, for the very limited amount of total exposure makes it probable that only a small proportion of any one scattered type would be visible. The speci- men submitted for analysis is of the coarse grained variety, and was 'collected by Mr. LeRoy from near, or at the place, near the northeast contact, where fragments were found included in the syenite proper. The rock is phanerocrystalline, and has the appearance of a mo- saic of well-bounded crystals of feldspathoid, in a matrix of white feldspar together with a few small crystals of pyroxene and a little black iron ore ; the latter, however, is mostly in scattered masses. 47 It has a light grey colour and breaks with uneven fracture. The crystals of feldspathoid range from 2 to 7 millimeters across, and are in the form, usually, of hexagons or squares; they are rather closely packed and greatly exceed the finer groundmass in amount. The minerals seen in thin section are: aSgerite, plagioclase, or- thoclase, nephelite and sodalite, listed in their order of crystal- lization. A colourless zeolite is very abundant in minute needles in the sodalite. Aigerite is in two generations; in very small crystals included in all the other minerals, and in a few larger crystals, 1 mm. in length, which enclose small feldspars; its properties are similar to those of the algerite in the main type of syenite. Plagioclase occurs only in minute laths, with well-developed albite and carls- bad twinning; measurements prove it to be albite, nearly Ab, An,. Orthoclase occurs in laths and in irregular crystals ; it is more abund- ant than the albite and sometimes attains a length of 5 mm; the usual length, however, is about 1 mm. Nephelite is in subangular crystals ranging around 1 mm in length, and containing inclusions of all the earlier minerals, and some needles of a colourless zeolite. Sodalite is so abundant that crystal boundaries can be discerned only by noting the discoimected line of other minerals about its borders. The central part of the crystals is comparatively free from inclusions of a^gerite, feldspar, and nepheUte, but is crowded with minute needles of a colourless zeolite. The zeolite is a colourless mineral, occurring as needle- inclusions, and in long hair-like crystals in the nephelite and sodalite. It has the following properties: index of refraction is about 1"48; double refraction 0'012; parallel extinction; A is parallel to the axis of elongation. It is one of the natrolite group and differs from natrolite in the last property mentioned. The needles are too minute for further determination. The rock is millimeter-grained for the most part, and inequi- granular. The crystals are multiform and irregular, and form a hiatal, poikilitic fabric. The relative amount of the crystals is peroikic; the xenocrysts are relatively small, and are frequently arranged parallel, and near to the borders of the oikocrysts. The oikocrysts tend to form a seriate-intersertal fabric. 48 CHEMICAL ANALYSIS. A chemical analysis of this rock is given belo-w, with other analyses for comparison. 1 2 3 4 SiOs 41-84 000 45-28 49-29 54-74 TiOi ZrOa AI2O3 28-42 3-29 0-40 015 0-25 0-66 19-48 206 014 0-62 004 4-47 000 27-37 3-53 0-49 019 0-33 1-22 17-29 3-51 15-46 12-00 2-35 trace 1-32 1-61 14-74 1-23 21 53 FejOs 406 FeO 094 MnO 0*14 MgO. . . n-18 CaO 090 NaeO 12 84 KjO 4 18 H2O 035 HjO 0-40 PbOs CI COj T.nss on i^it.inn 1-85 * 0. CI 101-82 1-10 99-61 97-85 99-86 100-72 1. Feldspathic tawite. St. HilaireMt., Que., M. F. Connor, analyst. 2. Urtite, Lujaur-Urt. Halbinsel, Kola, Rosenbusch, Gesteinlehre, p. 126. 3. Tawite, Lujaur-Urt. Halbinsel, Kola. H. Blankett, analyst. Fennia 15, Helsingfors, 1899, p. 25. 4. Nephelite-sodalite-syemte,!St. Hilaire Mt., Que., M. F. Connor, analyst. The analyses -would seem to show that the St. Hilaire occmrence is more tjrpical ta-wite than the original described by Ramsay; the resemblance to the analyses of urtite is very striking. This type differs from the original tawite in being higher in alkalis and alum- ina, and lower in silica and ferric iron. According to the Quantitative Classification of Igneous Rocks, the ta-wite belongs to class 1, persalane, order 8, ontarare; rangl, peralkalic; subrang 5, persodic; section 4, dosonic. It is interesting to note that this is one of the few rock types which may be classified -with advantage, even to the section. There is no name corresponding to this variety, in the quantita- tive classification, so it is proposed to call it Beloeilose after the mountain on which it occurs. 49 Measured microscopically, the minerals are not present in con- stant proportions in the several varieties of this rock; the mode of the one for analysis will be here given. Assumed % by vol. specific gravity. %bywgt. Sodalite 70 2-2 65-2 Nephelite 8 2-6 8-6 Orthoclase 12 2-6 13-2 Albite 5 2-6 5-6 Aggerite 5 3-5 74 100 100 In the more commonly used system of classification of igneous rocks, the proportion of feldspar to sodalite in different main divisions of the syenite family and in the above described rock, is somewhat as follows : — syenite feldspar : sodalite : sodalite syenite feldspar : sodalite : f eldspathic tawite . . feldspar : sodalite : tawite feldspar : sodalite : 100 : 50 : 50 23 : 77 :100 It is at once seen that this rock comes between sodalite-syenite and typical tawite, on account of its abundant feldspar; the name most suited for this rock is thus feldspathic tawite. VARIATIONS IN THE TAWITE. (1) The finer grained variety from near the eastern contact resembles the one just described very closely in essential charac- teristics. It differs from the latter in that: — (a) The feldspar is nearly all microperthite, an intergrowth of orthoclase and albite. (6) Biotite is found intergrown with aSgerite, and the latter occurs in crystals about 1 mm in length; it is less in amount than in the former case. (c) There are a few crystals of titanite present. 50 (2) The western variety is coarse-grained, and differs from the type described in that it: — (o) Contains more feldspar and aSgerite. (6) Contains abundant eudialyte. (c) The feldspar tends to occur in bimches. This variety closely resembles the border type of sodalite, in that it is coarser, rather than finer, in grain than the main mass. (3) Many of the fragments of this rock, that are found embedded in the syenite proper, have the sodalite completely replaced by zeoUte for a distance of about 3 inches from the contact; the rest of the sodaUte is relatively unaltered. This zeohte is reddish coloured, fibrous and radiating; it has parallel extinction, low double refraction, and A parallel to the long axis; except for the latter quality it closely resembles natrolite. An interesting featiire is that Uttle specks of calcite occiir dotted through the zeolite, showing that the original mineral contained some lime. In places where the sodahte is hardly altered, the nephehte is completely decom- posed to cancrinite, and the unaltered sodalite in these fragments had frequently a bluish tinge. This variety is low in aegerite, and contains no eudialyte. DYKE ROCKS. CAMPTONITE. Occurs in dykes from a few inches up to 1'5 feet in width. It is found cutting the essexite, and one 16 inch dyke cuts the hom- stone in the Riviere des Hurons, about 1'5 miles below St. Jean Baptiste. These dykes vary in mineral composition, and in tex- ture, to a certain extent; so there are found all gradations into an essexite, of which camptonite itself is the representative hypabyssal type. The type camptonite will be described under this head- ing; it outcrops on the path to the Pain de Sucre, at an elevation of about 1000 feet. The rock is phanerocrystaUine, but very fine grained. It has a medium grey colour and a few small laths of feldspar hardly break the monotony in the even grain of the rock; the other minerals can not be readily distinguished. The minerals seen in thin section are : zircon, iron ore, apatite, hornblende, biotite, plagioclase. Zirconoccurs in manysmall grains 51 through the rock. Black iron ore and pyrite occur in irregular grains throughout the rock. Apatite is abundant in long, slender laths, and in rounded grains. Hornblende is found in irregular crystals varying from O'l to 0'5 mm in length. It is very abundant, forming about 35 per cent of the rock, and it has the following properties: pleochroism a = light brown; b = dark brown; c = brown; absorption is b>c>a with extinction cAc = 10°. It is a variety of the basaltic hornblendes, resembling the Rougemont variety, and that from Bohemia (Levy and Lacroix). The biotite is in irregular flakes reaching a length of 0'5 mm and is rather abundant. It has a strong pleochroism from a yellowish brown to deep reddish brown. The plagioclase occurs in laths with irreg^ilar boundaries and was determined as varying between andesine and labradorite. All the individuals show carlsbad twinning, but the albite lamellae are very faint in many cases and are hardly visible. Uneven ex- tinction is common, and there is a tendency to zonary structure. The greater part of the plagioclase crystallized after the ferro- magnesian minerals, but had begun to form at an earlier stage; this is shown by incliisions of feldspar in the hornblende and biotite. The structure shows a tendency to be ophitic; the crystals are decimillimeter in grain, and tend to be seriate. It is interesting to note that these rocks do not exhibit the "hampshiroid" habit of the tjrpical camptonite as described by Washington' from the Belnak mountains, N.H. CAMPTONITE: VARIETY NO. 1. The camptonite from the Riviere des Hiu-ons differs from the one just described in that the hornblende occurs in slender laths as much as 1 '5 mm in length, and also in short, well-bounded prisms with an average length of 0'2 mm. The plagioclase which occurs in narrow laths is frequently found in bunches or in nests about some mineral which has been replaced by calcite. There is a certain amount of light grey, non-pleochroic augite present which is partly decomposed, forming calcite. ' Am. Jour. Sci., Vols. XX and XXII, p. 502. 52 CAMPTONITE: VARIETY NO. 2. This occurs in a dyke 30 inches wide cutting the essexite and also the dyke of type camptonite described above; it is exposed on the path leading to the Pain de Sucre. The rock is phanerocrystalline, with a medium to fine grain. It has a mediimi grey colour, and appears to be composed of dark coloitted hornblende, in slender crystals averaging 2 to 3 milhmeters in length, embedded in a groundmass of crystals of a white feld- spar. The amount of feldspar is slightly greater than that of the dark constituents. The minerals seen in thin section are the same as those noted in the type camptonite, with essentially the same properties and char- acteristics. The hornblende shows a stronger pleochroism than that in the former case, from a brownish yellow to a deep brown, and the extinction, cAc is as high as 13°; otherwise the properties of the minerals coincide very closely; the essential difference is one of texture. The rock is holocrystalline, decimillimeter to miUi- meter-grained, and inequigranular. The crystals are multiform, irregular, and seriate. A few long, narrow crystals of hornblende give a tendency to a porphyritic texture. CAMPTONITE: VARIETY NO. 3. This occurs as a 12 inch dyke cutting the essexite, and is ex- posed on the path to the Pain de Sucre about 800 feet before reach- ing the summit. It is a fine-grained, phanerocrystalline rock with a medium grey colour, and the only minerals distinguishable are hornblende and pyroxene in a few widely scattered phenocrysts. Under the microscope this variety differs from the normal type in containing abundant titanite and titaniferous augite. The titanite occurs in irregular grains and in characteristic wedge- shaped crystals, and it is idiomorphic to the other minerals except zircon, which is foimd enclosed in it in minute crystals. The pyroxene is in irregular grains and crystals and in well-bounded prisms averaging 0'2 and 0'3 mm in length; the cleavage is poorly developed. It is slightly pleochroic from a = greenish grey to c = yellow-grey, cAc = 38°. 53 CAMPTONITE: VARIETY NO. 4. A 24 inch dyke cuts the homstone near the south contact of the essexit*. It is dark grey in colour, and microcrystalline, but shows a few phenocrysts of augite about 1 mm in length; it is also dotted with small patches of pyrite. Under the microscope it is seen to be made up of phenocrysts of hght grey augite, and of plagioclafie, in a groundmass of feldspar and iron ore, together with products of decomposition. The augite is frequently highly decomposed and its borders show a sUght re- sorption. It is at times iatergrown with biotite. Chlorite and iron ore are products of the decomposition. The larger feldspars, 0'5 mm in length, show a zonary banding; they vary from labra- dorite to andesine in composition, the more basic forming the central bands. The crystals are gathered in bunches in the ground- mass. The small feldspars are frequently arranged parallel to the borders of the phenocrysts. COMPARISON OF VARIETIES OF CAMPTONITE. Tabular Statement. Variety ^ Hornblende i Pyroxene ! Titanite Texture. Type... Verj' abundant Some Ophitic : very fine-grained. No. 1. Very abundant Little Some Fine-grained. No. 2.. Very abundant 1 strongly pleo- 1 chroic. Some SliehtlvDorohvritifi: meHinm to fine-grained. No. 3.. Abundant Abundant. Abundant. Slightly porphyritic; fine- grained. No 4 Abundant Abundant. Pilotaxitic and slightly por- phyritic; fine-grained. The amount of feldspar in these types is fairly constant; the table simply summarizes the change iu mineral composition and in texture. 54 NEPHELITE-SYENITE. Nine dykes of this class are exposed in a narrow strip of hornstone about 300 feet in length, on the south side of the mountain within 100 feet of the essexite contact. They were not observed to cut the latter, and a covering of drift obscures the relationship. The dykes of this group vary in width from 4 inches up to 32 inches.. The nephelite syenite dyke rocks of St. Hilaire may be classed under three varieties, namely: — (o) Variety containing aSgerite-augite alone; (&) variety containing aegerite-augite and green hornblende; (c) variety containing aSgerite alone. These are phanerocrystalUne, medium- to fine- grained rocks having a little grey colour in the feldspathic variety, but becoming darker as the percentage of ferromagnesian minerals increases. There is some difference in granularity in the different dykes, and often in the same dyke. The minerals are not always evenly distributed throughout the rocks; the result is the appear- ance of a banded structure in which the bands merge, in places en- closing narrow lenses of coarse and fine material, or of light and dark colour, without definite arrangement, except that it is roughly parallel to the enclosing walls. A few of the dykes are breccias con- taining fragments of hornstone, essexite, and of very fine-grained camptonitic material. The majority of the dykes are of variety (6) and the pyroxene is easily distinguishable in small well-bounded crystals, and in laths, some of which show very irregular outlines. The nephelite is easily distinguished by its glassy appearance contrasted with the light grey colour of the feldspars; the former occurs in irregular crystals, and the latter in well-developed prisms. In variety (a) the aSgerite-augite and feldspar give rather a porphy- ritic tendency to the rock; no hornblende is visible. This variety cuts the former variety (&) showing it to be of later origin. Variety (6) will be described in detail. Thin sections show the rock of variety (6) to be made up of titan- ite, zircon, apatite, iron ore, pyrite, biotite, aSgerite-augite, horn- blende, plagioclase, orthoclase, nephelite, and sodalite. The feldspars and feldspathoids crystallized about the same time. Alteration products are cancrinite, fluorite, iron ore and biotite. 55 Titanite^ is abundant in many of the dykes, in characteristic wedge-shaped crystals, and in small irregular masses; zircon occurs in the feldspathic phases usually, in short, stout, subangular crystals; apatite in small amount is found in well-bounded laths, and basal sections, in the types high in bisihcates. Black iron ore and pyrite occur in small, irregular masses through- out the rock; they are not very abundant. Biotite in some of the dykes is abundant; in others it is altogether wanting; it occurs in scattered, ragged, crystals and has a pronoimced pleochroism from light yellow to a dirty, greenish brown. Pyroxene is very abundant in some of the dykes and resembles an arfvedsonite very closely, except for the cleavage, which is nearly at right angles, and often brighter polarization colours. It occurs in irregularly bounded prisms and in well-defined basal sections, some with eight sides, some with six. The colour varies in intensity; in different dykes, and even in the same dyke it changes from a deep green to an almost colourless variety. Many crystals have a deep green border about a lighter green interior. In some sections, where hornblende is prominent, there is seen an intergrowth of the green and colourless varieties of pyroxene. The deep green variety has a decided pleochroism as follows: a deep green; b green; c yellowish to brownish green. The absorption is a>b>c and the extinction c/\c is variable, frequently 3° or less; it goes up as high as 28°, and the colourless variety is still higher, reaching 38°. The pyroxene varies from a nearly pure a^erite to nearly pure augite, and is, therefore, an aegerite-augite. The green pyroxene resembles closely the a^erite-augite described by Hackman' as occurring in the ijolite from Kaljokthal, except that the pleochroism in the present case is more pronounced, a = b>c, grass green to yellowish green; extinction a Ac always less than 30°. He notes zonary structure, and attributes the changeable extinction in part to this. A very similar occurrence of aSgerite-augite is described by L. V. Pirsson' from the Bearpaw mountains, Montana, occurring in tinguaite- porphyry. » Fennia, II, 2, Helsingfors, 1894, p. 182. » Am. Jour. Sci., Vol. II, 1896, p. 190. 56 Hornblende occurs sparingly with the pryoxeae, but in some dykes is quite abundant. The hornblende prisms tend to become segregated into masses in the rock, surrounded by feldspar and feld- spathoids. In the dyke where it is most abundant, the crystals are not well bounded; they average less than 0'5 mm in size, and are roughly equi-dimensional. Cleavage on basal and prism sections is well developed. The pleochroism is as follows: a = yellow- brown; b = deep brownish green; c = brownish green; absorption b>c>a; and extinction cAc = 16°-18°. This variety of horn- blende has not received particular attention in standard text- books on petrography, but a variety which resembles it very closely is described by L. V. Pirsson' from the Highwood moun- tains, Montana, which has the following properties; pleochroism c = ochre-yellow; b = dark oUve; a = dark olive-green; "The ab- sorption is very strong and the arrangement rather peculiar b>c>a," and extinction cAc is as high as 30°. Pirsson states that it is imlike any hornblende he knows, and that "It is much like arfvedsonite in a general way, and is at aU events, considering its habitat and associates, one of the alkalic group of hornblendes." Closely associated with the green pyroxene and hornblende, fluorite is developed in the coarser parts of the dyke ; it appears to be a product of pneumatolysis. Orthoclase is not abundant usually; it occurs mostly in the f eld- spathic varieties, in laths which show carlsbad twins. Plagiodase, the most abundant mineral in some of the dykes, is a basic andesine, Ab, Ani, as determined by the method of Michel Levy. It occurs in stout laths, ranging from 0'3 mm up to 2 '5 mm in length, averag- ing 1 '5 mm. There is well-developed carlsbad and albite twinning, and intergrowths with orthoclase or nephelite are not uncommon. In most of the varieties the plagioclase is an intermediate andesine. Nephelite occurs most abundantly in the feldspathic variety of the rocks, and there it is found in crystals with nearly square shapes, 0"5 mm on the side. It is in larger crystals in some other of the dykes. It appears to have formed before the sodalite. It shows all stages of alteration to camorinote, and contains inclusions of all the earlier minerals. Sodalite is absent in most dykes, but abund- ant in others; the determining factor seems to be the relative ' Bull. U. S. Geol. Surv., No. 237, p. 95. 57 abundance or absence of the green ferromagnesian minerals. It occurs in irregular patches and is easily detected by its cloudy appearance, and isotropic character. It is seen to be filled with minute anisotropic inclusions, and also contains laths of orthoclase and albite. It appears that there are the following varieties among the dykes of this type: — COMPARISON OF VARIETIES OF NEPHELITE-SYENITE. Tabular Statement. Variety ASg-Aug. Agg. Hb. Ne+So Orth. Flag. No. 1... Very little Very little Little . . . . Little?.... Very abun- dant. Abs AnjAbjAnj. No. 2. Abundant. Little Little?.... Abundant AbsAni AbjAn, No. 3... Abundant. Abundant. Little No. 4... Much Abundant. Little Much. No. 5 . . . Abundant. Abundant. Abundant. Much. These dykes are all found within 1000 feet of the road to Lac Hertel about 100 feet south of the essexite contact. Nos. 4 and 5 are within 150 feet of the road, the others are grouped, about 800 feet farther. No. 1 is included in this group but appears to be a hypabyssal representative of the rouvillite described above. TINGUAITE. These dykes cut all the other dykes observed. They vary in width from 4 inches up to 3 feet, and are usually over 1 foot wide. None were found cutting the hornstone, and the majority were in the essexite. A few thin dykes of this type traverse the marble enclosed in the syenite. 58 This rock is microcrystalline, sparingly porphyritic, and in colour shows faint shades of grey, brown, and green, in different dykes; the rock as a whole has a greasy lustre. No minerals can be dis- tinguished except in the widest dykes where a few phenocrysts of white, porcelain-like feldspar can be perceived. With the use of the microscope on thin sections, this type is seen to contain the following minerals, in order of crystallization : zircon, aegerite, biotite, eudialjfte, plagioclase, orthoclase, nephehte, sodaUte, and a lavenite-like mineral. These do not all occur in the same dyke, however; for example, zircon and biotite are found in but one occurrence. The properties of all these minerals are very similar to those in the main mass of nephelite-syenite, so they will not be repeated. It is sufficient to add that the eudialyte has a bright carmine colour in this case, and that the extinction angle of the lavenite-like mineral is only a few degrees, usually, with a maximum observed of 7°. The rock is microcrystalline, micron-grained to decimillimeter- grained, and inequigranular. The crystals are hypidiomorphic and multiform, and tend to be hiatal and shghtly porphyritic. The phenocrysts are of orthoclase, aSgerite, or the lavenite-like mineral, and minophyric to mediophyric; they are scattered, producing a skedophyric texture. The groundmass is graniphyric, with a trachytic arrangement of the small laths of feldspar. The minute crystals of aSgerite are at times more or less segregated in bands running through the rock without apparent order, merging into one another, or spreading out again into the groundmass. A bunching into radial groups of aSgerite laths is characteristic of many of the dykes, but a typical trachytic structure, in which the minute prisms of feldspar and aegerite appear to "flow" around the phenocrysts, is usually well developed. 59 COMPARISON OF VARIETIES OF TINGUAITE. Tabular Statement. Var- iety. Zircon Lav- en ite. Eudia- lyte. Bio- tite. ASgerite Colour Texture. No. 1 Little Little Medium to light grey. 1 1 grained; ophitic. No. 2. ! ! Very abundant . Green- grey. Very fine-grained; trachytic. i 1 No. 3 . 1 . 1 Some. Abundant. Greenish- grey Fine-grained; pilotaxitic; slightly porphyritic. No. 4. Much. Abundant. Dark grey Fine-grained; trachytic. No. 5. Little Very Abundant. Grey- green Fine-grained; porphyritic. No. 6. Much. Much. Brown. Very fine-grained; trachytic. Nos. 1 and 5 occur within 150 feet east of the road to Lac Hertel, in the horn- stone exposure just south of the essexite contact. No. 2 is found at an elevation of about 1,100 feet, on the path to the Pain de Sucre. Nos. 3 and 6 cut exposures of essexite in the interior basin near the southwest side. No. 4 is found with the nephelite-syenite dykes about 1,000 feet west of the road to Lac Hertel, 100 feet south of the essexite contact. Variety No. 1. — A 4 inch dyke cutting the hornstone near the contact is composed principally of plagioclase, ranging from an- desine containing about 35 per cent anorthite to labradorite with 60 per cent anorthite. The laths average from 1 to 2 milHmeters in length, and have a subparallel arrangement. The other minerals present are nephelite, biotite, pyroxene, hornblende, titanite, apatite, and iron ore, in small amounts. Variety No. 6. — This differs from the type in that the only bisilicate present is a light yellowish green aigerite, with very slight, if any, pleochroism. It occurs in irregular crystals ranging from a fraction of a millimeter up to 2 "5 mm in length, sometimes in radiating bunches of smaller crystals. There are large crystals of orthoclase showing microperthitic intergrowth, and the plagio- clase in this case is andesine with about 30 per cent of anorthite. (E) 60 This variety occurs in a 4 inch dyke cutting two of the other varieties of this type. SHEET ROCKS. TINGUAITE. Two sheets of this rock are exposed in the sediments about the centre of the east face of the mountain at an elevation of about 110 feet above sea-level. One of them crosses the wood-road about one-fourth mile east of the main contact and its bluish-green ap- pearance serves to distinguish it from the hornstone. The thick- ness of this sheet could not be definitely determined since only the surface is exposed. About 300 feet to the west of the road, another sheet is exposed in a 25 foot cliff of hornstone. It is 5 to 6 feet in thickness and closely resembles the former one; they are separated by about 20 feet of hornstone. The lower sheet shows streaks and a few distinct layers of brown rock through it; the contact is sharp, so that the brown may be seen to wedge out horizontally. These layers are from one-half inch to 3 inches in thickness and are slightly coarser in grain; they appear to be due to a slightly later injection of the magma into the sheet. These sheets are very fine-grained, with a bluish-green colour, and are studded, more or less thickly, with phenocrysts of a pea-green mineral, with good crystal faces, and octagonal outline; these crystals have a tabular development, averaging 1"5 mm in diameter and 0'4 mm in thickness, have no good cleavage, and a hardness about 6. Blow-pipe analysis failed to determine what the mineral is, so it is described as an unknown mineral. Near the contact with the sediment, the tinguaite becomes even finer and darker in colour. Thin sections show the main masses of tinguaite to contain the following minerals: apatite, aSgerite, plagioclase, orthoclase, eudials^te, and an unknown coloiu-less mineral near the contact with the hornstone; quartz is also present in small amoimt. Chemical tests failed to reveal any feldspathoid. The apatite is in well-bounded laths and basal sections; it is fairly common. ASgerite is abundant in minute prisms, frequently forming matted masses; the pleochroism is from greenish blue to yellowish green. Blue hornblende in minute prisms forms a large percentage of the groundmass. Plagioclase is abundant in irre- gular laths. It is a basic oligoclase to acid andesine. It forms a 61 few phenocrysts about 0'2 mm in length. Orthoclase is common, usually in larger crystals than the plagioclase. Carlsbad twinning is common. Eudialyte, a colourless mineral, closely resembling that described under this heading in the main mass of nephelite- syenite, is present in a few crystals. Unknown Mineral. — The mineral is colourless; occurs in prisms; index about 1'8; birefringence 0'035; centre is filled with gas cavities; extinction is parallel; extension parallel to c; no cleavage showing; biaxial; negative, full of inclusions of the green granules, and of feldspar. There are ghosts of well-shaped crystals outlined by a brown iron-ore and fitting into the groundmass; none of the original mineral remains; but it was probably the unknown mineral just described. The rock is microcrystalline, inequigranular. The crystals are hiatal and porphjritic, with a perpatic to dopatic ratio. The phenocrysts are mediophyric and prismatic, with a skedophyric arrangement. The groundmass is graniphyric and has a trachytic structure. Chemical Analysis. The following is an analysis of the blue-green tinguaite which is exposed on the wood-road to the east of St. Hilaire mountain. SiO, 6000 A1,0, 15-33 FeA 602 FeO 067 MgO 0-61 CaO 112 Na,0 6-44 K,0 815 TiOj 0-40 HaO- 008 Hi,0-|- 032 MnO 0-63 CI 009 99-86 Less 0= CI 002 9984 62 According to the Quantitative Classification of Igneous Rocks, the tinguaite belongs to class 2, dosalane; order 5, germanare; rang 1, umptehase; subrang 3, ilmenose. TINGUAITE PORPHYRY. The brown variety differs in that there is more eudialyte, and some titanite present. The phenocrysts are larger and the trachy- tic texture more pronounced, especially around the large crystals. APLITIC TYPE. This occurs in a sheet extending into the sediments from the northeast end of the essexite mass, at an absolute elevation of 550 feet. The exposm-e on a small clifT is 4 feet thick, and it appears to thicken considerably towards the mountain. The rock is mediimi to fine-grained, phanerocrystalline, and has a medium grey colour. Feldspar is the chief constituent; black iron ore and biotite are the only other minerals that can be readily distinguished; they are in small amount. The minerals seen in thin section are : zircon, apatite, iron ore, biotite, tourmaline, feldspar, and quartz, stated in their order of crystallization. Zircon occurs in a few small, well-bounded prisms. Apatite in slender laths, not abundant. Iron ore in a few grains averaging about 0'2 mm in diameter. Biotite in scattered, irregular flakes, in some cases showing chloritization. Tourmaline occurs in one small bunch of crystals; it is the blue variety with decided pleo- chroism: o = deep blue, e = pale blue to violet; absorption o>e. Feldspar is the most abundant mineral present. It is in stout, irregular laths, reaching 2 mm in length, often showing carlsbad twinning. The extinction is rather patchy, but parallel, and the crystals show alteration to kaolin. It is probably a soda-ortho- clase. Quartz is rather abundant in irregular grains, filling interstices between the feldspars, and surroimding some of the small crystals. The rock is decimiUimeter to millimeter-grained, and inequigranular; the crystals are irregular, and multiform; the fabric tends to be seriate-intersertal and aphyritic. 63 HORNFELS. The sedimentary collar surrounding St. Hilaire mountain has been indurated to some extent by waters from the magma. The dark grey shale has been altered to a very typical hornstone, which closely resembles the one described by Rosenbusch' for the type of this rock. There are no idiomorphic minerals, but all are so pecuUarly interwoven and interlocked that there is no ap- parent order, and their relative ages cannot be determined. The minerals present are: quartz, feldspar, muscovite, and biotite, and, in one case, zircon. Biotite is abundant in small flakes, and gives the characteristic spotted appearance to the rock. The minerals do not contain the numerous specks of black material so often seen in rocks of this class, showing that the original shale was not highly carbonaceous. Gesteinlehre, 1901, pp. 101-102. 64 CHAPTER VI. PETROLOGY: ROUGEMONT MOUNTAIN There are three main rock types in the Rougemont igneous mass which grade into one another, and whose contacts may be defined only arbitrarily. These types are distinguished by the relative abundance of feldspathic and ferromagnesian constituents, and the gradation is seen to take place from a highly feldspathic variety on the west, to a nearly pure ferromagnesian rock on the east side of the mountain. The only feldspar present is anorthite, and, be- cause of this peculiarity, the western variety is here called rouge- montite, and the intermediate variety, or essexite, is called the Rougemont type of essexite. The ferromagnesian variety closely resembles yamaskite, a name given by G. A. Young^ to a rock characterized by the great abund- ance of pyroxene, basaltic hornblende, and ilmenite, with only a very small percentage of anorthite; on accoimt of the high content of oh vine, the present variety is called olivine-yamaskite. The in- trusions were brought to a close by sets of complementary dykes which are found cutting the country rock and also the magma itself. The contact in many places shows a development of breccia in which homstone forms the fragments. Yamaskite occupies, roughly speaking, the eastern half of the mountain. It is quite variable in mineralogical composition, showing all gradations from a nearly piu"e pyroxenite, but with some oUvine and feldspar, through several combinations of these minerals with brown hornblende and biotite, finally going over to an essexite in which the feldspar is present in amomit greater than 15 per cent. In texture also there is greater variation; it varies from very coarse to rather fine grain, and from porphyritic to even- granular. Essexite in general occurs about the border of the yamaskite, and they grade into one another. It is distinguished from the latter ' Geol. and Petrog. of Mount Yamaska, Que. G«ol. Surv. Can., Ann. Rept., Vol. XVI, Pt. H, 1906. 65 by a higher percentage of feldspar, together with a more even, and, usually, finer grain. Rougemontite. This is found in the western part of the mountain and is characterized by much finer grain and higher percentage of feldspar than the other types. It is more homogeneous than the others, and formed a later injection, but before the earlier part had fully sohdified. This is brought out by the relations of apophyses of this type extending into the yamaskite and essexite. The greater part of the contact is hidden by the mantle of drift and vegetation which covers nearly the whole mountain, and could not be studied closely. YAMASKITE. This occupies the eastern half of the mountain. Since it was necessary to choose the specimens for analysis before detailed study of the thin sections could be carried out, those chosen were such as appeared in the field to best represent the various rock varieties as there noted, and to be of the freshest and best material. Thus the specimen selected to represent this type proves to be an olivine-yamaskite. The rock has a very dark, green-black colour; it is coarsely crystalline, and breaks with an uneven fracture. Well-bounded pyroxene crystals up to 2 cm in length are the chief constituents, but there is an abundance of a reddish olivine in irregular crystals ranging from 1"5 cm in length downwards. Small flakes of biotite occur at intervals, and small, white patches of feldspar give the only relief to the prevailing dark colour. A study of the thin sections shows the presence of the following minerals arranged in the order of their formation : olivine, augite, brown hornblende, biotite, anorthite, black iron ore, and serpen- tine. No apatite is present. Titaniferous augite in stout crystals averaging V2 cm in length is the most abimdant mineral present; it has irregular or rounded boundaries, but well developed cleavage and slight pleochroism as follows: a = purplish grey, b = grey to yellowish grey, c = pale brown. The absorption is a>b>c and the extinction cAc reaches 37°. It occurs frequently intergrown with brown hornblende and biotite, and contains poikilitically small, rounded crystals of olivine. The purplish tinge is character- istic of the titaniferous variety of augite, and the optical orienta- tion corresponds also with that mineral. 66 Olivine occurs in large, colourless crystals with an average length of about 1 cm, and in small individuals with a diameter of 1 mm. All the crystals are rounded and are traversed by irregular cracks along which a greenish serpentine and iron ore have begun to form. A Schiller structure is developed by the parallel arrangement of some brownish lath-shaped inclusions which occur in bunches and are too minute for determination. Basaltic hornblende frequently forms a narrow border to the augite individuals, and is often inter- grown with the latter, shown by numbers of flakes of hornblende through the augite, which extinguish simultaneously. It is small in amount but is seen to have the same properties as the hornblende described in a subphase of this essexite. Biotite occurs in rather large individuals, and in small flakes. The larger crystals are usually found intergrown vnth the augite. The very strong pleochroism is as follows: a = light brownish yellow, b = c = dark reddish brown, the absorption is c = b>a. Anorthite. The crystals of feldspar fill interspaces between the other minerals; the amount of the mineral is very small. Albite twinning is well developed, and some carlsbad twinning also, but many of the individuals show the result of strain in the bending of lamellae and in uneven extinction. Zonary growth is visible in a few crystals. Measured by the method of Michel Levy, these feldspars prove to be anorthite; their character is more fully treated under Type No. 3. Black iron ore is seen to occur in irregular grains scattered through the rock; part, at least, is the result of the alteration of olivine. The rock is holocrystalline, centimeter-grained, and equigranular for the most part. The crystals are multiform and irregular. The minerals in this rock tj^e were determined microscopically by the method of Rosiwald, to be present in the following relative proportions. % by vol. Sp. gr. %bywgt. Anorthite 6 06 2-8 503 Augite 70 -75 3-4 71-60 Olivine 13 38 3 3 13 15 Hornblende 8-82 3-4 902 Biotite 50 2-9 045 Iron ore 050 5-2 77 100 01 100 02 67 From these calculated percentages of the various minerals, the specific gravity of the rock was calculated. Calculated specific gravity 3 '37 Spec. grav. determined by weighing. . 3 ' 35 Difference 002 It is seen from the mode that the rock falls in the class of yamaskites; the high percentage of ohvine must be noted, hence the name olivine-yamaskite. With increase of anorthite up to about 15 per cent we have the essexite type coming into prominence. This yamaskite differs from the original one described by G. A. Young,' from Mt. Yamaska, Que., in that in this case, augite preponderates over the brown hornblende, and there is abundant olivine present. CHEMICAL ANALYSIS. A chemical analysis of this rock was made by Mr. M. F. Connor of the Department of Mines, Ottawa, Canada. The following table gives this analysis contrasted with other similar t}rpes as noted. SiOs... AljOs. . FejOs.. FeO. . . MgO... CaO... Na,0.. KjO. . . H,0+. H,0— .. TiO,... P^C.... MnO... BaO... OOj.... Soa.... FeSs... S.G. 45 5 2 6 16 18 1 1 1 44 85 84 49 24 16 03 38 15 10 50 24 99 3 42 35 39 97 8 68 8 63 7 99 10 32 15 18 1 19 74 57 4 05 10 19 1 15 1 01 99 77 } '■''{ 44 62 7 90 4 22 6 67 14 00 19 44 1 20 31 75 07 1 87 10 61 100 75 1. Olivine-yamaskite, Rougemont. M. F. Connor, analyst. 2. Yamaskite, Mt. Yamaska, G. A. Young, analyst. 3. Essexite (Rougemont type), Rougemont, M. F. Connor, analyst. 1 Op. Cit., p. 16. 68 According to the Quantitative Classification of Igneous Rocks, the yamaskite belongs to class 4, dofemane; order 1, hungarare, section 2, dopyric; rang 1, permirlic, section 3, calcinitic; subrang 3, magnesiferrous. This rock fills a gap in the tables of the classi- fication and the name carolose is proposed; this name is derived from the Petite Caroline road which skirts the east base of the mountain in vi'hich the olivine-yamaskite is found. VARIETY NO. 1 OF YAMASKITE. This type is found in patches showing a gradation from yamas- kite to an essexite-porphyry in which medium to large crystals of augite, and a few of olivine, occur as phenocrysts in a fine-grained groundmass made up of small laths of anorthite and small, irre- gular pieces of augite and olivine which have been broken ofT and separatedjfrom the larger crystals, and mixed with the feldspars. This occurs in many places throughout the yamaskite and essexite, near the southeast end of the mountain, but in too small amount in any case observed, to permit of separate mapping; a hand speci- men of average size shows the change quite well. Under the microscope the larger augite and olivine crystals show very irregular boundaries; pieces have evidently been split off and some may|be seen just opposite the place from which they were removed; the rest are mixed with the feldspar laths. The augites often show schiller structure. Iron ore occurs through the slide in irregular grains, together with a few flakes of biotite and brown hornblende. Thejanorthite occupies most of the groundmass in short, stout prisms with irregular boundaries, and seldom exceed- ing 1 mm in length. A few of the larger crystals show bent lamel- lae, the result of strain. Many small laths are enclosed by the augite. VARIETY NO. 2. OF YAMASKITE. This variety occurs near the southeast border of the igneous core, and is exposed on the clifT which forms the terminus of the igneous part of the mountain in this direction. It is associated with the variety just described, and occurs as coarse, pegmatitic nodules in a medium to coarse-grained matrix. The nodules range up to one foot in diameter and are composed chiefly of stout crystals of pyroxene 1^ to 2 centimeters in length, with some oli- vine and anorthite. It appears to differ from the normal type mostly in coarseness of texture; the constituents are the same. 69 VARIETY NO. S OF YAMASKITE. This variety is found in a ridge 200 feet long, 50 feet wide, and 10 feet high, surrounded by normal yamaskite. There is no exposure within a few feet, so that the field relations could not be definitely determined. The rock has a dark grey to black colour; it is even and fine grained, and is phanerocrystaUine. Crystals of pryoxene and a few of olivine make up the rock; no feldspar is visible in the hand specimen. Under the microscope this variety closely resembles the type described as oUvine-yamaskite. The minerals present are the same, except that there is less hornblende, the real difference being in the texture, which is holocrystalline, and decimillimeter- grained, with a few larger crystals of augite and olivine. It is inequigranular, with multiform, irregular crystals which are con- sertal in arrangement, and seriate in size. VARIETY NO. 4 OF YAMASKITE. Occurs on the northeast face of the hill forming the highest part of the mountain, about 150 feet below the summit. This is within the borders of the main feldspathic type, and is the freshest part of an exposure which shows several varieties of the rock. It appears, then, to be a segregation. The difference from the oli- vine-yamaskite described above is merely one of texture; this sub- phase is millimeter-grained and inequigranular, with a multiform, seriate fabric. Olivine is abundant but subordinate to the augite; they together form about 90 per cent of the whole rock. The rest is made up of a small amount of anorthite and broken hornblende, and the products of decomposition — serpentine and iron ore from the olivine, and calcite from the pyroxene. COMPARISON OF VARIETIES OF YAMASKITE. Tabular Statement. Olivine. Augite. Anorthite. Brown horn- blende. Grain. Type Abundant. Much Very little Abundant. Medium to coarse. No. 1 Abundant. Abundant. Much Little Fine and porphyritic. No. 2 Abundant. Much Very little Little Very coarse. No. 3 Abundant. Much Very little Very little Very fine. No. 4 Abundant. Much Very little Little Medium to fine. 70 ESSEXITE {ROUGEMONT TYPE). This rock, which is intermediate between yamaskite and rouge- montite, is found as a border facies of the yamaskite, and perhaps of the whole igneous mass, so far as it was possible to judge from the limited exposures. There is also a band running nearly north and south through the centre of the mountain, of uncertain width , separating the yamaskite from the feldspathic type. This appears to grade imperceptibly into essexite to the east, but the change to rougemontite on the west is more pronounced because of the de- cided difference in granularity, as well as in mineral composition. The detailed description of the type chosen for analysis is as fol- lows : — The rock has a dark grey colour; it is phanerocrystalline, medium- grained, with a few larger crystals of pyroxene. The minerals present are seen to be the following: augite in stout, well-formed crystals, a few of which reach 1'5 cm in length, but for the most part, it is in smaller individuals averaging about 3 mm. Olivine is next abundant of the dark constituents; it has a reddish brown colour, and the crystals are rather small, but evenly disseminated throughout the rock. Black iron ore is visible in a few grains. The white component is wholly feldspar in small crystals, and it is rather evenly distributed as a groimdmass for the dark coloured minerals. Under the microscope the minerals present are seen to be: black iron ore, anorthite, oUvine, augite, and brown hornblende, stated in their order of crystaUization. Calcite and serpentine are secondary products. The iron ore occurs in irregular masses and in small grains; the latter, at least, are the result of decomposition of the oh vine. It is developed in fine hues in the pyroxene, form- ing a very dense schiUer structure, in some instances. Anorthite crystaUized before the ohvine, at least in part, as large crystals of the latter contain laths of the feldspar. The mineral occurs in stout laths averaging about 1 Tnm in length, but of irreg- ular outline. It is bunched in the interspaces between the large crystals of augite and olivine, and penetrates their borders, or is completely enveloped poikihtically by them. It is altered in some cases to calcite and kaolin, but is mostly fresh. The properties are more fully described under Type No. 3. 71 Olivine occurs in large and small rounded crystals, traversed by irregular cracks, showing a slight alteration to serpentine and iron ore. A schiller structure is developed by bands of iron ore in den- dritic forms, but with sharp outlines. Titaniferous augite is seen to be present in stout, irregularly bounded prisms averaging 3 to 4 millimeters in length, and con- taining poikilitically, small laths of anorthite and rounded olivines. Cleavage is well developed and a slight pleochroism is apparent, as already described. Needle-like inclusions of iron ore in parallel arrangement give a schiller structure which becomes so dense in places as to considerably darken the mineral. Intergrowths with brown hornblende occur in some crystals. Calcite is scattered through some of the augites, and is arranged along cleavage lines. Brown hornblende occurs in a few cases intergrown with augite in mixed crystals. Biotite is very small in amount in this type, bordering the iron ore, and as minute flakes in the augite. The texture of the rock is intermediate between the fine texture of type No. 3 and the coarse texture of No. 2 of the yamaskite. The mode is also intermediate, and there are all gradations from the one to the other. The presence of such a basic feldspar as anorthite, as the only representative of that class of minerals, is very unusual in essexites and for this reason the rock is here termed the rougemont type of essexite. CHEMICAL ANALYSIS. 1 2 3 4 SiOj. . 44-62 7-90 4-22 5-67 14 00 19-44 1-20 0-31 0-75 0-07 1-87 "6- 10 60 49-96 43 91 43 66 Al,Os 18 2 6 3 7 5 2 2 83 52 64 52 42 26 58 07 53 40 25 20 19 4 5 5 9 4 63 16 55 20 49 49 51 53 80 32 07 51 17 7 5 4 9 5 2 35 FeaOa 88 FeO 40 MgO. 27 CaO . . 39 NajO 12 KjO 07 HsO+ HjO— . 1 1 TiOi 21 P.O. 32 MaO COs FeSj 0-64 100-75 100 IS 99 81 99 66 1. Essexite (Rougemont type) Rougemont mountain, M. F. Connor, an- alyst. 2. Essexite, St. Hilaire mountain. M. F. Connor, analyst. 3. Essexite, Yamaska mountain. G. A. Young, analyst. 4. Essexite, H. Rosenbusch, "Elemente der Gesteinlehre," p. 172, M. Dithrich, analyst. 72 According to the Quantitative Classification of Igneous Rocks, the essexite belongs to class 4, dofemane, order 1, hungarare, rang 1, pennirlic, subrang 3. Magnesiferrous. This rock fills a gap in the scheme of classification. It is seen from a comparison of the above analyses that the rouge- mont type differs from normal essexite in its high content of hme and magnesia, its low percentage of the alkahes, and of alimaina. The mode of this rock type is variable; it is intermediate between that of the olivine-yamaskite already described and that of the rougemontite, which will be explained later. No. 1. No. 2. Anorthite 503 71-60 13 15 902 0-45 0-77 45-75 Augite . 3454: Olivine 8-64 0-48 Biotite. . Iron ore 10-58 100 02 99-99 No. 1. Mode of olivine-yamaskite. No. 2. Mode of rougemontite. It is ob-vdous from the mode that the rock falls into the class of essexites but is rather abnormal, as explained above in discussing the chemical composition. VARIETIES OF ESSEXITE. It will not be attempted to describe specimens showing the gradation from yamaskite through essexite to rouvilhte, but imder this heading will be treated certain variations in texture or in miner- al composition, which include the presence in abundance of some mineral other than those normal to the type. One variety is high in brown hornblende. It occurs in three or four places in the igneous exposure; most of the specimens came from the southeastern part of the mountain, but one is noted from the centre-top of the western face. This latter occurrence is finer grained and probably represents a border phase. The rock varies in texture, often showing a mixture of coarse and fine material in the same specimen; otherwise it does not differ markedly in appearance from the type of essexite and it would not be especi- ally noted in the field. 73 Under the microscope the abundance of brown hornblende, biotite, and black iron ore, with the absence of olivine, are the prominent differences from the main type; the order of crystal- lization is the same, and the description of the minerals appHes for both types, except that the feldspars show bent lamellae as the result of strain. It will be only necessary then to describe the nature of the hornblende as follows: — The hornblende occurs in large, irregular crystals 15 mm to 9 mm long, and in smaller individuals. It is frequently inter- grown with augite and biotite, and encloses small laths of anorthite and numerous grains of black iron ore. The iron ore occurs in hues of small grains traversing the hornblende in different direc- tions, and also in needles arranged parallel to one another to form a fine schiller structure similar to that noted in the augite. Pleo- chroism is strong, and as follows: b = dark reddish brown, a = pale yellowish brown to brownish yellow; c = orange brown. The absorption is b>c>a, and the extinction cAc varies up to a maximum of 28°; many sections show 17° or less. It would appear then to be a variety of the basaltic hornblende with exceptionally high extinction angle. The pleochroism distinctly places it in this group, as shown by the accompanying table, but the variety which is recorded there with high angle of extinction does not re- semble this mineral in pleochroism. The minerals for comparison were taken from Iddings' "Rock Minerals", page 351. Comparison of Hornblende. Variety. X = A Y = B Z = C ZaC=CaC Author. Basaltic hornblende (Rougemont) yellowish brown to brownish yellow dark reddish brown orange brown 28 Basaltic hornblende (Bohemia) pale brown brown dark brown 0-14 Levy and Lacroix Kaersutite (Kaersut) light brown dark red- dish brown. darker reddish brown. 10 Ussing Barkevikite (Norway) light brownish yellow. reddish brown. deep brown. 0-14 Brogger Basaltic hornblende (Aranyer Berg) olive green yellowish brown greenish bro?m 37 Franzenan 74 ROUGEMONTITE: THE FELDSPATHIC TYPE. This t3T)e of the Rougemont magma occupies the western half of the mountain; it is characterized by predominant anorthite, with pyroxene as the only important ferromagnesian mineral; its detailed description is as follows: — The rock is phanerocrystaUine, medium to fine grained, and has a medium grey colour. A slight fluidal arrangement of the con- stituents is usually apparent, giving a suggestion of gneissoid structure. A white feldspar is the predominant mineral and the dark constituents are: dark coloured augite, reddish brown oUvine, and black iron ore; these are evenly distributed throughout the rock, and give it a mottled appearance when viewed at a short distance. The rock is very tough and breaks with uneven frac- ture. Under the microscope the minerals present are seen to be : iron ore, olivine, anorthite, augite, biotite and brown hornblende and secondary serpentine, in their order of crystallization. The iron ore is black and occurs in irregular masses and in small grains, often surrounded by a narrow border of biotite. Most of it is primary but part of it is formed from the olivine. Olivine is present in small rounded crystals which are traversed by irregular cracks, along which a yellowish green serpentine has begun to develop. The olivine is quite subordinate in amount to the augite and is frequently found embedded in it. Anorthite. The feldspar crystallized later than the oUvine but before the pyroxene, since small laths are found contained in the latter; it is the predominant mineral in the rock. The crystals vary in size, reaching 1 mm in length, and are not well bounded, because of mutual interference during crystalHzation, and of the effect of the previously formed minerals. Both albite and carlsbad twinning are well developed; the broad lamellae and the stronger birefringence indicate a very basic plagioclase, and, measured by Michel Levy's method, it proves to be anorthite. An interesting verification is shown in some of those sections cut normal to (010) ; when the albite twins in one carlsbad half show equal illumination, the twinned albite lamellae in the other carlsbad are both totally extinguished; this is a peculiarity of anorthite. 75 Titaniferous augite. Augite, nejrt to feldspar, is the most abundant mineral in the rock; it occurs in irregular crystals up to 2 mm in length, and shows well-developed cleavage. A schiller structure is developed, at about 45° to the cleavage, by minute needles of some dark mineral; these are too small to identify. The augite has the purplish tinge characteristic of the titaniferous variety, and a slight pleochroism as noted in the oUvine-yamaskite type; it is closely associated with the small amount of brown hornblende present, and contains crystals of iron ore, olivine, and anorthite. Brown hornblende is very small in amount, and appears closely associated with the augite in such a way as to suggest that con- ditions were nearly right for its formation instead of the augite. It occurs in small, irregular patches and does not appear to be the result of alteration. The pleochroism has been noted in the ferro- magnesian type. Biotite is present in a few individuals, mostly as isolated patches between the other minerals, but these are arranged in groups with the same optical orientation showing them to be parts of the same crystals. It also occurs as a narrow border about some of the mag- netite grains. The pleochroism is from a faint brownish yellow to a dark brown. The rouviUite is holocrystalline, millimeter-grained, and in- equigranular. It has a multiform, seriate, aphyric fabric, and the larger tabular feldspars have a subparallel arrangement. (F) 76 CHEMICAL ANALYSIS. The chemical composition of this rock is given in the first column of the following table. 1 2 3 4 SiOj 40-68 19-83 4-68 6-49 7-67 17-64 1-10 0-27 0-27 008 204 46-24 29-85 1-30 212 2-41 16-24 1-98 0-18 1 0-91 54-45 28 05 0-45 "9-68 6-25 1-06 0-55 43-65 AUOs 11 -48 FesOs 6-32 FeO 8 00 MgO 7-92 CaO 14 00 NajO 2 -28 K2O 151 HaOH- h'o- :::::::::::: 100 TiOa 400 PA MnO 010 trace BaO 100 85 S.G.314 100-35 S.G.2-85 100-49 S.G.2-69 100-16 1. Rougemontite, Rougemont mountain, Quebec. 2. Anorthosite, mouth of Seine river, western Ontario. 3. Anorthosite, fine-grained, almost white, Rawdon, Morin district, Quebec. 4. Essexite, Brandberg, Kirchspiel Crau, Norway. According to th^ Quantitative Classification of Igneous Rocks, the rougemontite belongs to class 3, salfemane; order 5, gallare; rang 5, kedabekase. The rock suggests a basic anorthosite in which the plagioclase is all anorthite; the content of ferromagnesian minerals is, how- ever, too high to make the resemblance very close. On the other hand, an essexite is much lower in alumina, and higher in iron and magnesia than the rougemontite; the analysis cited is the one most closely resembhng the latter. Rougemontite appears, then, to occupy an intermediate position but with alkalic re- lationships. 77 The following are the results of a calculation of the mode of rougemontite. %hjwgt. Anorthite. . Augite Olivine Iron ore Hornblende 52 25 2-8 45- 32 51 3-4 34- 8 35 i 3-3 8- 6 52 ; 5-2 10- 043 1 3-4 0- 100 04 ■75 ■5i &4 •58 ■48 99^99 From the mineral composition, the specific gra'vity of the rock was calculated as follows: — Anorthite 45 Augite 34 Olivine Iron ore . . . . Hornblende . 8 10 ■75^ 7oX 2 ■54 X 3^ ■64 X 3- •58 X 5^ ■48 X 3- 99^99 128 117 2S 55 1 1 •3 6 ■6 330-0 Calculated spec, grav .... Determined by weighing. Difference . = 331 = 314 017 The specific gra-vities for the different minerals were assumed, hence there is some error there. The iron ore was all calculated as magnetite, which is probably not the case. The mode shows the peculiar character of this rock; no rock t\-pe has been noted before in which there is such a high percentage of anorthite as the only feldspar present, associated -with such a high percentage of pyroxene ■with abundant oh\-ine and iron ore; it is, therefore, proposed to call this rock type rougemontite, after the mountain in which it is found so abundantly. 78 CHARACTER OF DIFFERENTIATION IN ROUGEMONT MAGMA. The differentiation in the Rougemont magma is very well shown by a comparison of the analyses of the three main t3^es. SiO.., AljOs FesOj FeO.. MgO. CaO.. Na,0. KjO.. H,0.. H,0.. TiO,. P.O5.. MnO. CO,... 45 44 5 85 2 84 6 49 16 24 18 16 1 03 38 1 15 10 1 50 24 99 42 44 62 7 90 4 22 5 67 14 00 19 44 1 20 31 75 07 1 87 60 10075 40 68 19 83 4 68 6 49 7 67 17 64 1 10 27 27 08 2 04 10 100 85 1. Olivine-yamaskite. 2. Essexite (Rougemont tyi)e). 3. Rougemontite. The striking fact, seen at once, is that there is a decrease in silica with increase of feldspar. The high percentage of lime throughout is a notable feature. DYKE ROCKS. Among the dykes of Rougemont moimtain are f oxmd the follow- ing tjrpes : yamaskite, yamaskite-porphyry, essexite, camptonite, and rocks showing a tendency towards aplitic forms. YAMASKITE. The yamaskite is essentially the same as that described for the main intrusion. It forms a 6 foot dyke in the essexite on the northeast face of the mountain. 79 The hand specimen shows a phanerocrystalline to cryptocrya- talline rock with a dark grey colour. There are a few small pheno- crysts of olivine and pyroxene visible, but the great mass of the crystals are too fine-grained to be easily distinguished. Under the microscope the minerals present are seen to be: black iron ore, pyrite, olivine, augite, and anorthite. The iron and pyrite occur in small irregular masses and grains scattered through the rock; olivine in rounded crystals much subordinate in amount to the augite; the augite has a light grey colour and is not distinctly pleochroic; it has extinction cAc about 43°. The anorthite crystaUized last, in stout laths, often enclosing small augites. It is very small in amount. The texture is inequigranular and the crystals are multiform, with averaging size of grain a little less than 1 mm, hence decimil- limeter grained: they are seriate. ESSEXITE. This type occurs in a number of places in the coarse material in such a way that it could not be definitely decided whether it was merely a fine-grained phase of the latter or a true dykj; in a few places, however, it was possible to determine a definite rela- tionship as that of dyke to country rock. The specimen to be described is from an 8 inch dyke cutting coarse yamaskite, near the southeast end of the mountain. The rock is phanerocrystalline to cryptocrystalline with a dark brownish grey colour. A few crystals of augite with a length of 2 mm are visible and white feldspar can be distinguished in the dark groundmass. Under the microscope the rock is seen to have an ophitic texture, and differs mineralogically from the type essexite in that there is more brown hornblende present, with less olivine and less iron ore included in the pyroxene; otherwise the former description applies equally well here. ESSEXITE PORPHYRY. These dykes were found cutting coarse and fine essexite and also in the sedimentary collar. The largest found measured 2 feet 6 inches in width, and cut the hornstone about 1,000 feet from the southwest contact. 80 The smaller dykes and the contact fades of the larger ones show scattered phenocrysts of augite and olivine in an aphanitic ground- mass ; the texture is dopatic. The central part of the dyke becomes coarser and more abundant in phenocrysts, until in the centre of the large dyke cited above, the groundmass is holocrystalline, with a millimeter grain, containing phenocrysts of augite ranging from 1 to 2 centimeters in length. The rock has a dark grey colour and is given a greenish tinge by the amber-green, glassy olivines and the darker green pyroxene phenocrysts. The weathered portions show roughened surfaces where the pyroxene crystals are in relief; a newly broken svu-face of this portion shows spots of brown iron rust, where the olivine crystals have been decomposed, and also little nests of calcite crystals replacing some mineral, or filling cavities in the rock. Since the coarse variety approaches the normal essexite, only the finest porphyry will be described. Under the microscope the minerals observed are : black iron ore, pyrite, olivine, augite, calcite, and decomposition products; no feldspar is visible, even with high power objectives, in the fine- grained portion. Black iron ore is abundant in small grains evenly distributed through the groundmass, and in phenocrysts 0'5 mm in length. Pyrite is in irregular grains about O'l mm in length, and included in all the phenocrysts, frequently surroimded by calcite in the replaced minerals. Olivine is found in small round- ed crystals enclosed in augite, and in phenocrysts 2 mm in length by 1 mm in width, which show six-sided outlines, with rounded angles; it is highly decomposed. The products of decomposition of the olivine are: serpentine, black iron ore, talc, and chalcedony. The serpentine is greenish yellow and is found on either side of the cracks in the olivine. The iron ore is in little bimches, but usually in minute grains arranged in short, wavy lines throughout the crys- tals. Talc occurs in flakes and in radial growths within the crystal, and also forms a narrow margin about the whole crystal. It is colourless and has its usual high double refraction. Augite occurs in well-bounded crystals up to 2 mm in length. Cleavage is well developed, and many of the individuals are twinned ; some show zonary banding, and also an hom:-glass structure. They contain a few crystals of olivine, but are relatively free from in- clusions of iron ore. It has a light grey colour, but no apparent 81 pleochroism, and its extinction c A c is up to 40°. Calcite is present, filling many small, irregular cavities throughout the rock, into many of which extend minute prisms of brown hornblende. It also forms part of the fine groundmass. Brown hornblende is recognizable only in the minute laths which extend into the cavities filled with calcite. The groimdmass contains abundant brownish crystals which are too small to be determined, but are very probably horn- blende also. The groundmass is very fine-grained, for the most part, an intimate mixture of brown hornblende, calcite, and black iron ore. The rock is holocrystalline, porphyritic, and microcryptocryst- alUne in grain of groundmass, with millimeter-grained pheno- crysts. It is dopatic (that is, the groundmass predominates), and the phenocrysts vary in size from minophyric to mediophyric and are prismoid in shape, with a skedophyric arrangement (scattered uniformly). Chemical Analysis. The following is the result of an analysis of an essexite porphyry dyke 1,000 feet southwest of the border of the essexite body. SiO, 44 AlA 8 Fe^O, 2 FeO 8 MgO 16 CaO 12 Na^O 1 KjO 1 Ti02 1 H2O - H,0 + 2 MnO 39 36 18 25 70 90 28 28 98 02 08 15 99 -57 According to the Quantitative Classification of Igneous Rocks, the essexite porphyry belongs to class 4, dofemane, order 1, hungarare, section 5, pyreniare; rang 1, permirlic, section 2, domiric; subrang 2, domagnesic. This rock fills a gap in the classification tables. 82 CAMPTONITE. Only a few true camptonites were found, and these with a width measured in inches rather than in feet. They occurred cutting the yamaskite and essexite. The description of this type is as follows :— The rock has a dark grey colour; it is phanerocrystalline, but very fine-grained, with only a few small phenocrysts of augite and hornblende. Inclusions of the coarse country rock are seen in some places, in small fragments. Besides the scattered pheno- crysts, small laths of feldspar and grains of pyrite can be readily distinguished, but not the dark minerals. In weathering, the rock takes on a brown spotted appearance, with cavities where some ferromagnesian phenocrysts have been dissolved out. Under the microscope the following minerals are seen to be present, given in the order of their crystaUization; garnet, iron ore, plagioclase, and hornblende. Garnet is a colourless mineral with high index of refraction, occurring in irregular to rounded grains about the hornblende crystals. It is traversed by irregular cracks and is isotropic. Iron ore is abundant in small grains throughout the rock and enclosed in all the other minerals. Most of it is pyrite, but some black iron ore is also present. Plagioclase is the most abundant mineral present. It occurs in laths with an average length of less than 1 mm but a few are 2 mm long. Most of the crystals show well-developed twinning, both albite and carlsbad, and many of them exhibit a zonary structure. Measured by the method of Michel Levy, most of the feldspar proves to be labradorite Ab, Auj to Ab, An,; many of those crystals showing zonary structure have a core of bytownite, Abi An^ sur- rounded by a border of labradorite; but a few show a basic labra- dorite Abs An, surrounded by the more acid Ab, An,. Apatite is very abundant in some of the dykes, in long, slender prisms and in roimded grains. Hornblende is, next to the feldspar, the most abundant mineral, occurring in irregular crystals, few exceeding 1 mm in length. Many individuals are crowded with iron ore inclusions which often form reed-like masses arranged parallel to the cleavage, and also across it, giving a schiller structure. Where augite is present, the two are always intergrown. The pleochroism 83 is very pronounced and shows a = very light brown, b = brown, c = brown. The absorption is b = c>a and its extinction cAc is observed to be 10° in the maximum seen, usually 9°. APLITIC DYKES. These dykes show some very peculiar features; they were only found on the southeast end of the mountain and were not observed in relation to the other types except where one is cut by a 2 inch dyke of camptonite. Two varieties of this type occur, one where pyroxene is the only ferromagnesian mineral present, the other where there is considerable hornblende and biotite. Aplitic Dykes: Variety No. 1. Variety No. 1 occurs in a 12 inch dyke cutting essexite near the southeast edge of the mass. It is highly brecciated with fragments of the essexite in places, and is cut by a 2 inch camp- tonite dyke which also cuts the essexite. The rock has a medium grey colour with a greenish tinge; it is phanerocrystaUine, but very fine-grained, except for phenocrysts of pyroxene which are about 3 mm in length on the average, and have good crystal outUne. The minerals seen in thin section are: iron ore, apatite, pyroxene, plagioclase, and quartz, in their order of crystallization. Black iron ore and pyrite occur in irregular grains scattered through the rock. Pyrite is the more abundant. Apatite is not abundant; it is found in a few slender laths and in basal sections. Pyroxene occurs scattered uniformly throughout the rock in small, irregular pieces averaging O'l mm in length, torn from larger crystals; a few well-bounded crystals are present up to 1 mm in length, also fragments of larger ones; but none of the larger pheno- crysts are seen in the section examined. The larger pieces con- tain many gas cavities. The pyroxene has a Ught grey colour with no apparent pleochroism and an extinction angle cAc from 0° to 12°, frequently parallel, and maximum usually 6° — 8°; the bire- fringence is about 0'013; it forms about 35 per cent of the whole rock. The low extinction angle is very unusual in a pyroxene of this class and the low birefringence points toward the ortho- rhombic varieties. 84 The plagiodase is present in stout laths about 1 mm in length or less, \dth a few reaching as high as 2 mm; the outlines are not at all regular. Carlsbad twinning is very common and albite lamellae are well developed, especially on the larger crystals. Measured by the method of Michel Levy, the feldspar is seen to vary from Xb^ An, to Ab, An,, with a preponderance of the latter; so that it is mostly bytownite, going over in cases toward labrad- orite. This mineral occupies about 40 per cent of the rock. Quartz was the last mineral to crystallize out and so occurs in the interspaces between the other minerals. It occupies about 10 per cent of the rock. The rock is holocrystalline, inequigranular, with a hiatal, porphyritic fabric. It is perpatic and the phenocrysts are media- phyric in size and prismoidal in shape; they are scattered, giving the rock a skedophyric texture. Aplitic Dykes: Variety No. 2. This occurs on the face of the hill at the southeast end of the mountain at the contact with the homstone and its relations could not be made out, as to width and strike, but it cuts into coarse essexite. The hand specimen is aphanitic, dark grey in colour, and shows abxmdant scales of biotite, and some quartz; the other minerals cannot, as a rule, be distinguished. The minerals present in thin section are seen to be: zircon, apatite, iron ore, plagiodase, augite, biotite, and quartz, listed in their order of crystallization. Zircon occurs in a few fine needles ; apatite in a few slender laths; black iron ore in small, irregular grains scattered through the slide. Plagiodase occurs in short, stubby laths, for the most part, often enclosed poikilitically in the augite and biotite. It is also found in longer laths, about 0"3 mm in length, gathered in bunches in different parts of the rock. Carlsbad and albite twinning is common; and some crystals show microperthite intergrowth, with a tendency in cases to zonary banding. The feldspar is found to be mostly Abj An, bytownite, but going up toward a labradorite. The augite is the same as that described in sub-variety No. 1 of the aphtic dykes. It occurs in irregular grains through the rock, seldom reaching 0'5 mm in length. Biotite occurs in large flakes 2 mm side, with irregular 85 boundaries and often filled with minute feldspars, iron ore, and augite. It has a strong pleochroism from pale yellow to deep reddish brown. Quartz varies in amount; at times it forms the whole groundmass; it is probably derived, in part at least, from the nearby homstone which is digested in it. 86 CHAPTER VII. GENERAL PETROLOGY In discussing this subject, St. Hilaire (Beloeil), and Rougemont mountains will be treated separately, and their relationship to the general Monteregian province shown as far as possible. ST. HILAIRE (BELOEIL) ROCKS. The igneous rocks of St. Hilaire mountain are characterized by a high content of soda, very high in some varieties. The main types represented are: essexite, rouvillite, nephelite-sodalite-syenite, and tawite. The following analyses of these types were made by M. F. Connor: — SiO,. . . AljO,. . FejOs. . FeO... MgO. . . CaO... NasO.. K,0... Hs,0+. HjO— . TiOs... P.Os. . . CI MnO... 1 2 3 4 49 96 51 26 54 74 41- 18 83 23 78 21 53 28- 2 52 1 81 4 06 3- 6 64 2 70 94 3 52 1 96 18 0- 7 42 8 00 90 5 26 6 72 12 84 19- 2 58 2 16 4 18 2- 07 55 0-35 53 10 trace 2 40 1-66 trace 0-25 trace trace trace 020 4- 10 6 14 0- L-84 ?-42 5-29 )-40 )-25 )-66 )-48 206 )14 )-62 )00 )04 1-47 )15 1. Essexite. 2. Rouvillite. 3. Nephelite-sodalite-syenite. 4. Tawite. Since these rocks represent two separate intrusions, they will be first compared as such, and then treated as a whole. The rouvillite is a differentiate from the essexite, and analysis No. 2 shows that there is an increase of iron and magnesia; the mode of the rock shows that it is very feldspathic, and the chemical analysis resembles that of an anorthosite. The high content of Ume and soda, and low percentage of iron and magnesia are more closely related to an alkaUc anorthosite than to a theralite. The 87 amount of rouvillite is relatively so small that the composition of the original essexite magma must have been approximately the same as that shown in analysis No. 1. Similariy the tawite represented by analysis No. 4 is a product of differentiation from the nephelite-sodalite-syenite. The most noticeable points of difference are the increased percentages of alumina, soda, and chlorine, with a decrease in the silica and potash. The very high content of soda is unusual, and the abundant chlorine points to the presence of a large amount of sodalite. The original syenite-magma had a chemical composition very similar to that in analysis No. 3, since the amount of tawite is not sufficiently large to make much change in it. The whole of these rocks from St. Hilaire mountain are related in their high content of soda. The syenitic types are characteristically different from those of the essexite, in their low percentage of lime, iron, and magnesia, with a higher content of alkalies. The in- trusions here closely resemble those at Mount Royal, for in that area also an essexite mass was later intruded by nephelite-syenite. ROUGEMONT ROCKS. These rocks will be treated together since they are differentiates from one main intrusion. The rock-types represented are : yamas- kite, essexite, and rougemontite; a comparison of the chemical composition of these types is given in the accompanying table: — SiO... A1,0,. FesOs. FeO... MgO.. CaO... NajO.. K,0. . . H,0-|-. HjO— TiO... CO,... MnO.. 45 44 5 85 2 84 6 49 16 24 18 16 1 03 38 1 15 13 1 50 24 99 -42 44 7 4 5 14 19 1 1 ■62 90 •22 ■67 00 ■44 ■20 31 •75 07 ■87 ■60 10 100 75 40 68 19 83 4 68 6 49 7 67 17 64 1 10 27 27 08 2 04 10 100 85 1. Olivine-yamaskite, M. F. Connor, analyst. 2. Essexite (Rougemont type). M. F. Connor, analyst. 3. Rougemontite. M. F. Connor, analyst. 88 These rocks are marked by their high content of lime and mag- nesia. There is a decrease of (iron plus magnesia) with decrease of silica, from the yamaskite, through the essexite, to rouvillite. A comparison of the mineral composition of the two extremes of the differentiation shows: — 1 3 Anorthite 5 03 71-60 9-20 13 -15 0-45 0-75 45 -75 Augite 34 -54 Hornblende 49 Olivine 864 Biotite Iron ore 10-58 100 00 100 00 No. 1. Olivine-yamaskite. No. 3. Rougemontite. Note. — The essexite is intermediate between No. 1 and No. 2. The change shown by this table is from a ferromagnesian rock to a feldspathic one, and the absence of brown hornblende in No. 3 is accompanied by a high content of iron ore. Rougemont is more closely related to Mount Yamaska than to any of the other Monteregians. At Yamaska, however, the feld- spathic differentiate of the magma is an akerite, and is much more acidic than the yamaskite, while at Rougemont the rougemontite is less acidic than the ferromagnesian rock. GENERAL DISCUSSION. It seems to be a general rule, that, in regions of alkalic rocks, the feldspathic varieties greatly preponderate over the ferromagnesian ones. An exception is found in the rocks of Gran, as described by Brogger\ in which case the feldspathic varieties are very small in amount. As instances of those localities which follow the general Quart. Jour. Geol. Soc. London, Vol. 1, Feb., 1894. 89 rule, may be cited the Highwood mountains of Montana, as des- cribed by Pirsson,' the Province of Kola,' the Greenland occurrence,' and the Red Hill district of New Hampshire.* In the Monteregian provinces, the amount of rock high in bisili- cates is in all the mountains fully equal to, and in some of them greatly preponderant over, the quantity of syenitic material. With this fact in mind, then, the suggestion arises to study the region surrounding the Monteregian province, with a view to ascertaining whether there are any facts which serve to explain the phenomenon. To the northwest there lies an enormous area of nephelite-syenites, and of anorthosites, of Pre-Cambrian age; and to the southwest, anorthosites occur over a large area in the Adirondacks. To the southeast and east there are the great masses of diabase and serpentine, known as the Serpentine Belt, which are of post-lower Devonian age and were intruded probably not long before the Monteregian magma, as will be shown later. As Dr. F. D. Adams pointed out,' the more easterly mountains contain proportionately more syenite and the western ones, a greater proportion of essexite. The syenitic types at Shefford and Brome mountains, which are the largest and most easterly of the series, are highly acidic, and the nordmarkite (of Dresser) even contain a little quartz. This general gradation from east to west would suggest a chemical relationship to the larger intrusions to the east which are so closely related to these in point of age. It has already been pointed out that the rouvillite of St. Hilaire, and the rougemontite of Rougemont mountain, are very strikingly suggestive of a relationship to anorthosites in chemical composition, and both these rock types are differentiates from the typical essexite, as foimd at those places. The inference from these facts is, then, that the intrusive rocks of this whole region may have some relationship with one another and that the Monteregian provinces may form but one part of a much greater one. ' Bull. 237, U. S. Geol. Surv., 1905, etc. ^ Ramsay and Hackman, op. cit. ' Ussing, op. cit. ' Bayley, W. S., Bull. Geol. Soc. Am., Vol. 3, pp. 231-252. ' Jour. Geol., Vol. XI, No. 4, April-May, 1903, p. 251. 90 To cite analagous occurrences : Brewer has shown that the dis- trict of Gran is but a local demonstration of a much larger province, known as the Christiana province, which, taken as a whole, is highly feldspathic. Similarly, Pirsson has pointed out that the laccoliths and volcanic necks of central Montana form but the centre of a much larger province, in which the acidic representatives occur on the borders. So that it may well be that an exhaustive study of the region of western Quebec and the adjacent country will establish a similar major province in which the Monteregians are included. DIFFERENTIA TION. It will not be attempted to discuss here the different hypotheses that have been advanced to explain differentiation, but the phenomena seen at St. Hilaire and Rougemont will be treated in relation to the conditions under which the process has operated in these instances. At St. Hilaire mountain, the feldspathic rock was intruded later than the ferromagnesian one, so that this differ- entiation must have been completed before the first intrusion took place. The rouvillit* and tawite occurrences are, however, probably partly due to the local segregation of minerals contem- poraneous with the intrusion of the differentiated magmas; their isolated occurrences and relatively small area would indicate that local conditions were operative in their formation, rather than a general cause. At Rougemont the conditions show that there has been but one main intrusion, but that the feldspathic portion represents a slightly later phase in this intrusion than does the ferroms^neaian rock. The latter is not at all homogeneous, but varies from a feld- spathic essexite to a yamaskite which is made up almost entirely of bisilicates. No general separation of the two can be made in the field; the geological map shows, however, that exposures of the yamaskite occur irregularly throughout the mass, but the boimdar- ies of each type are very indefinite. In this case, as at St. Hilaire, there was a differentiation before the intrusion took place, and a segregation contemporaneous vrith the intrusion served to accen- tuate the contrast between the two main products of differentia- tion, and to produce a third type intermediate to the extremes. 91 DYKES. Each of the main intrusions at St. Hilaire mountain is repre- sented in the dyke rocks; the intrusion of essexite was followed by dykes of camptonite, whose fine grain indicates that the wall-rock (essexite, in most cases) was cold at this time, or that there was a lack of mineralizers in the magma, or that both conditions were effective. There is also an aplitic sheet, in connexion with the essexite, which represents the extreme acid phase of differentiation in the residual magma. Accompanying, or following, the syenitic intrusion was a development of dykes of nephelite-syenite and tin- guaite, together with a number of sheets of the latter. A small dyke of tinguaite cuts one of nephelite-syenite, showing that the former, at least, was later than the main syenite magma. At Rougemont mountain there are representatives of both acid and basic phases of differentiation in the residual magma from which the dykes were produced; they range from yamaskites to acidic varieties containing some quartz which are described as aplitic types; the relative ages of these dykes were not definitely deter- mined, since they were not observed in the same exposure. It would seem, then, that the dykes represent a more complete differentiation in the original reservoir than is shown in the main in- trusions ; this would be expected because the differentiation in the residual magma would go on after the main intrusion occurred, and before the dykes were injected. AGE OF THE INTRUSIONS. There are a few facts which furnish a clue as to the general age of the Monteregian intrusions. At Montreal there is a development of igneous breccia, in con- nexion with Mount Royal, in which there are entrapped blocks of limestone containing fossils of Oriskany age, so that the in- trusion must have been post-lower Devonian. This is borne out by the fact that a dyke of a camptonite, from a small outlier of the Monteregian province, near Eastman, Quebec, cuts the ser- pentine of that region. The age of the serpentine is also con- sidered to be post-lower Devonian. (G) 92 Following a different line of evidence Dresser found that the igneous masses of both Sheflord and Brome mountains show the effects of the regional disturbance which occurred at the close of the Appalachian revolution in Pennsylvanian-Permian time. It appears then that the Monteregian iatrusions occurred some time between the lower Devonian and early Permian. It is very probable, however, that they took place in the upper Devonian which was a period of great volcanic activity in eastern North America. 93 CHAPTER VIII. BIBLIOGRAPHY Adams, Frank D. — "On a melilite-bearing rock (alnoite) from St. Anne de Bellevue, near Montreal (Quebec)." Am. Jour. Sci., 3d. ser., Vol. 43, 1892, pp. 269-279. "Notes on the Geology of Montreal and Vicinity." Abstract: Science, new ser.. Vol. 7, 1898, pp. 51-52, (J p.) "Accounts of Explorations in the Eastern Townships of Que- bec." Geol. Surv. of Can., Kept., Vol. 3, new ser., pt. 1, Rept. A, pp. 84-85. Montreal, 1888. "The Monteregian Hills: a Canadian Petrographical Pro- vince." Jour. Geol., Vol. 2, 1903, pp. 239-282. McGiU Univ. Dept. Geol. Papers, No. 14, 1903. Can. Record Sci., Vol. 9, 1905, pp. 198-245. Bigsby, John I. — "Sketches of the Geology of the Island of Mon- treal." New York Lyceum Nat. Hist., Annals, Vol. I, 1824, pp. 198-219. Buchan, J. S. — "Was Mount Royal an Active Volcano?" Can. Rec. Sci., Vol. 8, 1901, pp. 321-328. Abstract: Am. Geol., Vol. 27, 1901, p. 313. "Some Notes on Mount Royal (Quebec)." Can. Rec. Sci., Vol. 8, 1902, pp. 517-525. Davis, W. M. — Physical Geography. Cinn. & Co., Boston, 1898. Dawson, J. W. — "Remarks on the Geology of Beloeil Mountain and Vicinity." Can. Nat., new ser., Vol. 8, 1878, pp. 286-288. "Canadian Ice Age." Montreal, 1893. Decks, Wm. — "The Lower Helderberg Formation of St. Helen's Island." Can. Rec. Sci., Vol. 4, 1890, pp. 105-109. 94 Donald, D. T.— "The Helderberg Eocks of St. Helen's Island." Can. Nat., Vol. 9, new ser., 1881, pp. 302-304. Dresser, J. A. — "On the Petrography of Shefford Mountain (Que- bec)." Am. Geol., Vol. 28, 1901, pp. 204-213. "Report on the Geology and Petrology of Shefford Mountain (Quebec)." Can. Geol. Surv., Ann. Rept., new ser.. Vol. 13, 1903. Also separate, 1902. "Report on the Geology of Brome Mountain, Quebec." Can. Geol. Surv., Ann. Report, Vol. 16, Pt. G, 1906. "The Monteregian Hills: a Series of Volcanic Buttes." Jour. Geol., Vol. 5, 1906, No. 2, pp. 74-77. "On a Rare Rock Type from the Monteregian Hills, Canada." Am. Jour. Sci., 4th ser., Vol. 28, July 1909, pp. 71-73. "Report on the Geology of St. Bruno Mountain (Quebec)." Can. Geol. Surv., Memoir No. 7, 1910. Ells, R. W. — "Report on the south-west Sheet of the Eastern Town- ships iSIap (Quebec)." Can. Geol. Surv., Ann. Rept., Vol. 7, Pt. J, 1896, p. 6. Harrington, B. J. — "On some of the Diorites of Montreal." Can. Geol. Surv., Ann. Rept., 1877-78, 42 G. Harvie, Robert.— "On the Origin and Relations of the Paleozoic Breccia of the Vicinity of ^Montreal." Can. Roy. Soc, Proc. and Trans., 3rd. ser., Vol. 3, sec. 4, 1910, pp. 249-299. Hunt, T. S.— Geological Survey of Canada, 1858, pp. 171-187. "Geological Features in the Vicinity of Beloeil Mountain." Can. Nat., new ser., Vol. 4, 1869, pp. 218-224. "Notes on the Mountain of Montarville and its Geological History." Can. Nat., new ser.. Vol. 6, 1S72, pp. 224-226. LacroLx. — "Description des syenites nepheliniques de Ponsac et de Montreal (Canada) et leurs phenomenes de contact." Bull. Soc. Geol. de France, 3d. series, tome XYIII, 1896. 95 Lampart, Henry. — "A few Notes on the Extinct Volcano at Mon- treal, Canada." Abstract: Am. Ass. Adv. Sci., Proc, Vol. 40, 1891, p. 260. Logan, Sir Wm.— Geol. of Canada, 1863, pp. 656-659. Nolan, A. W., and Dixon, J. D. — "Geology of St. Helen's Island (Quebec)." Can. Rec. Sci., Vol. 9, 1903, pp. 53-66. Osann, A. — "Ueber ein Mineral der Nosean-Hauyn-Gruppe im Elaolith-Syenit von Montreal." Neues Jahrb. f. Min., etc., Band i, Heft 1, 1892, pp. 222-224. Schuchert, Charles. — "On the Helderbergian Fossils near Montreal (Canada)." Am. Jour. Sci., Vol. 27, 1901, pp. 245-253. Yoimg, Geo. A. — "The Geology and Petrography of Mount Yamaska (Quebec)." Can. Geol. Surv., Ann. Rept., Vol. 16, pt. H, 1906. 97 INDEX. A. FAOG Adams, F. D., cited 1, 4, 5,21, 22,89 Afegerite 44, 45, 47, 49, 50, 55, 58, 59, 60 Afgerite-augite 39, 44. 55 Age of the Monteregian intrusives 91 Akerite of Mount Yamaska 6 Albite 39, 45, 47 Ami, H. M., cited 10 Analysis, see chemical analysis. Andesine 30, 34, 51, 53, 56, 59, 60 Anorthite 65, 68, 69, 70, 73, 74, 79 Anorthosite, resemblance of rougemontite to 76, 89 " resemblance of rouvillite to 89 Apatite 29, 32, 33, 35, 51, 55, 59, 60, 62, 82, S3, 84 Aplitic dykes, Rougemont mountain, petrology of S3 " " variety Xo. 1, Rougemont mountain, petrology of S3 * " variety No. 2. Rougemont moimtain, petrology of S4 Aplitic type, sheet rock, St. Hilaire mountain, petrology of 62 Appalachian mountains 2 Areal distribution of rock types, Rougemont mountain 64 Arivedsonite 45, 55 Augite 29, 33, 36, 44, 51, 53, 55, 68, 69, 79, 80, 84 ' titaniferous 65, 71, 75 B Banded structure in basic plutonics, character of 23 " " in essexite, of St. Hilaire 20 " "in nepheline syenite dykes 54 « " of Isle of Skye gabbro 23 " "of Maryland gabbros 22 " "of Morin anorthosite 21 « "of Mount Johnson essexite 22 " "of Mount Yamaska essexite 22 " " of St . Bnmo essexite 22 " " origin of, according to Leith 23 Barkevikite "" Basaltic hornblende 51, 66, 73 Beloeil mountain, see St. Hilaire mountain. Biotite 29, 35, 44, 49, 51, 53, 55, 58, 59, 62, 63, 66, 6S, 71, 73, 75, 84 98 B — Con. PAGE Blue hornblende 60 Breccia 25, 28, 64, 91 " at borders of St. Hilaire syenite 24 " in nepheline-sodalite-syenite 43 " in syenite 50 " Mount Royal 3 " Rougemont mountain 64 Brogger, W. C.,cited 23, 88, 90 Brome mountain, origin of 7 " " rocks of 7 Brown hornblende 68, 71, 72, 75, 81 Byssonychia suberecta (TJlrich) 12 Bytownite 33, 36, 82, 84 C Calcite 50, 51, 69, 70, 80 Calymene callicephala (Green) 14 Camptonite, comparison of varieties 53 " Rougemont mountain, petrology of 82 " St. Hilaire mountain, petrology of 50 " variety No. 1, St. Hilaire mountain, petrology of 51 " variety No. 2, St. Hilaire mountain, petrology of 52 " variety No. 3, St. Hilaire mountain, petrology of 52 " variety No. 4, St. Hilaire mountain, petrology of 53 Cancrinite 50 Caroline station, fossils from near 13 Catazyga anticostiensis (Billings)? 14 Centronella hecate 24 Chalcedony 80 Chambly occurrence, rocks of 5 Character of banded structure, in basic plutonics 23 Chemical analysis of essexite, Rougemont type 71 " " of essexite, type variety, St. Hilaire mountain 30 " " of essexite porphyry, Rougemont mountain 81 " " of nephelite-sodalite-syenite, St. Hilaire mountain 40 " " of rougemontite, feldspathic variety, Rougemont mountain 76 " " of rouvillite, St. Hilaire mountain 36 " "of tawite, St. Hilaire mountain 48 " " of tinguaite, St. Hilaire mountain 61 " " of yamaskite, Rougemont mountain 67 Chemical relations of rouvillite to essexite, St. Hilaire mountain 86 " " of tawite to nepheline-sodalite-syenite, St. Hilaire mountain 87 C—Con. PAGE Chlorite 29 Churning action in St. Hilaire magma 25 Classification of nepheline syenite dykes, St. Hilaire mountain 54 Cleidophorus 14 Cleidophorus, n. sp 12 Comparison of varieties of camptonite 53 " " of nephelite-syenite 57 " "of tinguaite 59 ' " of yamaskite 69 Conchicolites richmondensis (Miller)? 12 Crag and tail structure, Monteregian hills 17 Ctenobolbina ciliata (Emmons) 11, 12 Ctenodonta 12 Ctenodonta pectunculoides (Hall) 12 Cyclospira bisulcata 24 Cymatonota recta (Ulrich) 12 Cymatonota semistriata (Ulrich) 12 Cyrtolites ornatus (Conrad) 12 D Dalmanella testudinaria (Dalman) 14 Devonian limestone block in St. Hilaire syenite 24 DifTerentiation, as indicated by dyke rocks 91 " character of 90 * in Rougemont magma 78, 87 " in rocks of St. Hilaire mountain 87 Drainage of St. Lawrence lowlands 17 Dresser, John A 4, 5, 6, 7, 8, 11, 15 Dyke rocks, Mount Yamaska 6 " Rougemont mountain, petrology of 78 " St. Hilaire mountain, petrology of 50 Dykes at Mount Royal 3 " inferences relating to differentiation to be drawn from 91 E Eastman, rocks of 8 Ells, R. W., cited 24, 27 Erosional features of St. Lawrence lowlands 18 Essexite, chemical relations to rouviUite, St. Hilaire mountain 86 " of Brome mountain 7 * of Mount Johnson 5 " of Mount Royal 2 100 E—Con. PAOB Essexjte, of Mount Yamaska 6 ■ of St. Bruno 4 " of St. Hilaire, banded structure in 20 " of St. Hilaire, flow structure in 21 " of St. Hilaire, variations in 28 " of Sheflord mountain 7 " included in nepheline-sodalite-syenite breccia 44 " Rougemont mountain 64 " Rougemont mountain, petrology of varieties of 72 " Rougemont type, chemical analysis of 71 " " " mineral composition of 72 " " " mode of occurrence of 70 " " " petrology of 70 " type variety, St. Hilaire moimtain, chemical analysis of . . . . 30 " type variety, St. Hilaire mountain, mineral composition of. 31 " type variety, St. Hilaire mountain, petrology of 28 " variety No. 1, St. Hilaire mountain, petrology of 32 " variety No. 2, St. Hilaire mountain, petrology of 33 " variety No. 3, St. Hilaire mountain, petrology of 34 " dykes, Rougemont mountain, petrology of 79 " porphyry, Rougemont mountain, chemical analysis of 81 " porphyry dykes, Rougemont mountain, petrology of 79 Eudialyte 39, 42, 50, 58, 61, 62 Eukolite 42 Feldspar 62, 63 Flow structure in essexite of St. Hilaire 21 Fluorite 56 Fossils from near Caroline station 13 " from St. Hilaire Station 11 " from St. Hilaire, Ulrich's opinion on 11 " from Trenton limestone block in St. Hilaire syenite 24 Garnet 82 Geikie, Sir A., and Teall, J. J., cited 23 General petrology 86 Glacial drift of St. Lawrence lowland 16 Green mountains 17 101 H PAGE Hackman, cited 42, 55 Harrington, B. J., cited 3 Hornblende 30, 32, 35, 44, 51, 52, 53, 56, 59, 69, 73, 82 " basaltic 66, 73 " blue 45, 60 " brown 34, 68, 71, 72, 75, 81 Hornblendes, tabular comparison of 73 Homfels, St. Hilaire mountain, petrology of 63 I Igneous core of Mount St. Hilaire, shape of 25 " "of Rougemont mountain, shape of 25, 26 Intrusion, St. Hilaire mountain, order of 28 Iron ore. .29, 32, 35, 51, S3, 55, 59, 62, 65, 66, 68, 69, 70, 73, 74, 79, 80, 82, 83, 84 Isle of Skye gabbro, banded structure of 23 Isochilina 24 Isotelus gigas (De Kay) 7 13 J Johnson mountain — see Mount Johnson. Labradorite 30, 33, 34, 36, 51, 53, 59, 82, 84 Lacroix, cited 43 Laurentian plateau 2, 16 Lavenite-like mineral 39, 42, 58 Leith, C. K., cited 23 Limestone blocks in St. Hilaire syenite 24 Linear arrangement of the Monteregian hills, its cause 26, 27 Lorraine(?) age of strata at St. Hilaire 11 " "of strata at St. Hilaire station 13 " "of strata near Caroline station 14 Lorraine, Richmond age of the so-called 10 M Maryland gabbros, banded structure of 22 Melinophanite 45 Metamorphism of sedimentary collar, St. Hilaire mountain 25, 63 Microperthite 49 102 M—Con. PAGE Mineral composition of essexite, Rougemont type 72 " " of essexite, type variety, St. Hilaire mountain. . 31 " " of nephelite-sodalite-syenite, St. Hilaire moun- tain 41 * "of rougemontite, Rougemont mountain 77 " " of rouvillite, St. Hilaire mountain 37 " "of tawite, St. Hilaire mountain 49 " "of yamaskite, Rougemont mountain 67 Modiolopsia concentrica (Hall and Whitfield) 12 Monteregian hills 1 " " origin of their linear arrangement 26, 27 " " physical features of 17 " Intrusives, age of 91 Monteregians possibly part of a larger province 89 Morin anorthosite, banded structure of 21 Mount Johnson, origin of 4 " " essexite, banded structure of 22 " " rocks composing 4 Mount Royal, origin of 3 " " rocks composing 2 Mount St. Hilaire, see St. Hilaire mountain. Moimt Yamaska, akerite of 6 " " essexite, banded structure of 22 " " origin of 6 " " rocks of 5 Muscovite 63 N Natrolite 50 Natrolite group 47 Nephelite 30, 36, 39, 45, 47, SO, 56, 58, 59 " alteration of 50 Nephelite-sodalite-syenite, Breccia variety, St. Hilaire mountain, petrology of 43 " " " contact variety, St. Hilaire mountain, pet- rology of 41 " " " field relations to tawite 46 " " " St. Hilaire mountain, chemical analysis of 40 " " " St. Hilaire mountain, chemical relations of to tawite 87 " " " St. Hilaire mountain, mineral composition of 41 103 'S—Con. PAGE Nephelite-sodalite-syenite, type variety, St. Hilaire mountain, pet- rology of 38 " variety of 46 Nephelite-syenite, comparison of varieties 57 of Mount Royal 3 " " dykes, banded structure in 54 " " " St. Hilaire mountain, classification of 54 " " " St. Hilaire mountain, petrology of 54 Nordmarkite of Brome mountain 7 " of Shefford mountain 7 O Older base level of St. Lawrence lowlands 18 Oligoclase 61 Olivine 29, 32, 35, 44, 66, 68, 69, 71, 74, 79, 80 Olivine-yamaskite, Rougemont mountain 64 " " Rougemont mountain, petrology of 65 Order of intrusion, St. Hilaire mountain 28 Origin of banded structure according to Leith 23 " " " " in essexite of St. Hilaire 21 " of Brome mountain 7 " of Mount Johnson 4 " of Mount Royal 3 « of Mount St. Hilaire 25 " of Mount Yamaska 6 " of Rougemont mountain 25 " of St. Bruno 4 " of Shefford mountain 6 Orthoclase 35, 39, 45, 47, 56, 68, 59, 61 Palseozoic strata near Beloeil and Rougemont mountains 10 Palaeschare beani (James) 11 Petrology, general 86 " of Rougemont mountain 64 " of St. Hilaire mountain 28 Pholidops cincinnationsis (Hall) 11, 12 Pholidops subtruncata (Hall) 12 Physical features of Monteregian hills 17 Pirsson, L. V 55, 56, 90 Plagioclase 30, 33, 34, 36, 47, 51, 53, 56, 58, 60 Plectambonites sericeus (Sowerby) 14 104 V—Con. PAGE Psiloconcha inornata (Ulrich) 12 Psiloconcha sinuata (Ulrich) 11, 12 Psiloconcha subovalis (Ulrich) 12 Pterinea demissa (Conrad.) 12 Pulaskite of Mount Johnson 5 " of Shefford mountain 7 Pyrite 29, 44, 51, 55, 79, 80, 82, 83 Pyroxene 32, 52, 53, 55, 59, 68, 83 Q Quartz 62, 63, 85 R Rafinesquina alternata (Emmons) 12 Ramsay, W., cited 43 Relation of rock types, Rougemont mountain 64 Rhytimya radiata (Ulrich) 12 Richmond age of the so-called Lorraine 10 Richniond(?) age of strata at St. Hilaire 11 " " of strata at St. Hilaire station 13 " "of strata near Caroline station 14 " "of strata near Rougemont mountain 13 Richmond strata, areal extent of 15 Rosenbusch, H., cited 45, 63 Rougemont magma, character of differentiation in 78 Rougemont mountain, areal distribution of rock types 64 " " differentiation in rocks of 87 " " essexite 65 " " mode of occurrence of varieties of yamaskite. . 68, 69 " " olivine-yamaskite 64 " " origin of 25 " " Palaeozoic strata near 10 " « petrology 64 " " petrology of aplitic dykes 83 " " petrology of aplitic dykes, variety No. 1 83 " " petrology of aplitic dykes, variety No. 2 84 ' " petrology of camptonite 82 " " petrology of dyke rocks 78 " " petrology of essexite dykes 79 " " petrology of essexite porphyry dykes 79 " " petrology of olivine-yamaskite 65 " " petrology of rougemontite, feldspathic type. . . 74 " " petrology of varieties of essexite 72 105 R— Com. PAOB Rougemont mountain, petrology of yamaskite 65 " " petrology of yamaskite, variety No. 1 68 " " petrology of yamaskite, variety No. 2 68 " " petrology of yamaskite, variety No. 3 69 " " petrology of yamaskite, variety No. 4 69 " " petrology of yamaskite dyke 78 " " relation of rock types 64 ' " shape of igneous core 26 " " structural features of 20 " " yamaskite 64 Rougemont type of essexite, mode of occurrence of 70 " " " petrology of 70 Rougemontite, feldspathic type, Rougemont mountain, petrology of.. 74 " feldspathic type, Rougemont mountain, chemical analysis of 76 " name proposed 64 " resemblance to anorthosite 76, 89 " Rougemont mountain, mineral composition of 77 Rouvillite, chemical relations to essexite, St. Hilaire mountain 86 " hjTJabyssal representative 57 " name proposed 28 " resemblance to anorthosite 89 " St. Hilaire mountain, chemical analysis of 36 " St. Hilaire mountain, mineral composition of 37 " St. Hilaire mountain, petrology of 35 St. Bruno essexite, banded structure of 22 " mountain, rocks composing 4 " " origin of 4 St. Hilaire, fossils from 11 " mountain, breccia at borders of syenite 24 " " classification of nepheline syenite dykes 54 " " differentiation in rocks of 86 * " limestone blocks in syenite 24 * " metamorphism of sedimentary collar 63 * " mineral composition of rouvillite 37 « " mode of occurrence of tinguaite sheets 60 " " order of intrusion 28 « " origin of 25 " * Palffiozoic strata near 10 « " petrology of 28 " " petrology of aplitic type, sheet rock 62 106 S — Con. PAGE St. Hilaire mountain, petrology of camptonite 50 " " petrology of camptonite, variety No. 1 51 " " petrology of camptonite, variety No. 2 52 " * petrology of camptonite, variety No. 3 52 " " petrology of camptonite, variety No. 4 53 " " petrology of dyke rocks 50 " " petrology of essexite, tjrpe variety 28 " " petrology of essexite, variety No. 1 32 " " petrology of essexite, variety No. 2 33 " " petrology of essexite, variety No. 3 34 " " petrology of hornfels 63 " ' petrology of nepheline-sodalite-syenite, breccia variety 43 " * petrology of nephelite-sodalite-syenite, con- tact variety 41 " " petrology of nephelite-sodalite-syenite, type variety 38 " " petrology of nephelite-syenite dykes 54 " " petrology of rouvillite 35 " " petrology of sheet rocks 60 " * petrology of tawite, feldspathic type 46 " * petrology of tinguaite dykes 67 " " petrology of tinguaite sheets 60 " " petrology of tinguaite porphyry 62 " * shape of igneous core 25 " * structural features of 20 " " variations in essexite 28 St. Lawrence lowlands 2 * " drainage of 17 * " erosional features of 18 " " general features of 16 " " older base level of 18 Schuchert's determination of Trenton fossils from Mount St. Hilaire 24 " opinion on fossils from near Caroline station 14 " "on fossils from St. Hilaire 13 Sedimentary collar, St. Hilaire mountain, metamorphism of 25, 63 Serpentine 44, 66, 69, 70, 80 Shape of igneous core of Mount St. Hilaire 25 " " "of Rougemont mountain 26 Sheet rocks, St. Hilaire mountain, petrology of 60 Shefford mountain, origin of 6 " " rocks of 6 Sodalite 39, 46, 47, 50, 56, 58 " alteration of 50 Soda-orthoclase 35, 62 107 S — Con- PAGE Stomatopora 11 Structural features of St. Hilaire and Rougemont 20 Superposed drainage of St. Lawrence lowlands 18 Syenite at contact with included marble 44 Talc. 80 Tawite, chemical relations to nepheline-sodalite-syenite, St. Hilaire mountain 87 " feldspathic tj^je, St. Hilaire mountain, petrology of 46 " field relations to nepheline-sodalite-syenite 46 " St. Hilaire mountain, chemical analysis of 48 " " " mineral composition of 49 " variations in 49 Teall, J. J., and Geikie, Sir A., cited 23 Tinguaite, Brome mountain 7 " comparison of varieties 59 " dykes, St. Hilaire mountain, petrology of 57 " St. Hilaire mountain, chemical analysis of 61 " variety No. 1, petrology of 59 " variety No. 5, petrology of 59 " porphyry, St. Hilaire mountain, petrology of 62 " sheets, St. Hilaire mountain, mode of occurrence 60 " " St. Hilaire mountain, petrology of 60 Titaniferous augite 52, 65, 71, 75 Titanite 29, 35, 49, 52, 53, 55, 59, 62 Tourmaline 62 Trachyte at Chambly 5 Trenton limestone block in St. Hilaire syenite, fossils from 24 Trinucleus concentricus (Eaton) 14 Tubiculus annelida 12 U Ulrich's opinion on fossils from St. Hilaire 11 Umptekite of St. Bruno 4 Unknown colourless mineral 42 Unknown mineral 61 Ussing, N. v., cited 43, 45 Utica(?) age of strata near Caroline station 14 108 PAGE Variations in essexite of St. Hilaire mountain 28 " in tawite 49 Varieties of camptonite, comparison of 53 " of essexite, Rougemont mountain, petrology of 72 " of nephelite-syenite, comparison of 57 " of tinguaite, comparison of 59 " of yamaskite, comparison of 69 W Washington, cited 51 Whiteavesia pholadiformis (Hall) 11, 12 Whitella 12 Williams, G. H., cited 22 Yamaska mountain — see Mount Yamaska. Yamaskite, Mount Yamaska 6 " Rougemont mountain 64 " Rougemont mountain, chemical analysis of 67 " Rougemont mountain, mineral composition of 67 " Rougemont mountain, mode of ocurrence of varieties of 68 " Rougemont moimtain, petrology of 65 " variety No. 1, Rougemont mountain, petrology of 68 " variety No. 2, Rougemont mountain, petrology of 68 " variety No. 3, Rougemont mountain, petrology of 69 " variety No. 4, Rougemont mountain, petrology of 69 " dyke, Rougemont mountain, petrology of 78 Young, G. A., cited 6, 64, 67 Zaphrentis prolifica 24 Zeolite 47, 50 Zircon 29, 50, 55, 58, 62, 63, 84 Zygospira modesta (Hall) 12 CLASSIFIED LIST OF RECENT REPORTS OF GEOLOGICAL SURVEY. Since 1910, reports issued by the Geological Survey have been called memoirs and have been numbered Memoir 1, Memoir 2, etc. Owing to delays incidental to the publishing of reports and their accompanying maps, not all of the reports have been called memoirs, and the memoirs have not been issued in the order of their assigned numbers, and, therefore, the following list has been prepared to prevent any misconceptions arising on this account. Memoirs and Reports Published During 1910. REPORTS. Report on a geological reconnaissance of the region traversed by the National Transcontinental railway between Lake Nipigon and Clay lake, Ont. — by W. H. Collins, No. 1059. Report on the geological position and characteristics of the oil-shale deposits of Canada— by R. W. Ellis, No. 1107. A reconnaissance across the Mackenzie mountains on the Pelly, Ross, and Gravel rivers, Yukon and North West Territories — by Joseph Keele, No. 1097. MEMOIRS— GEOLOGICAL SERIES. Memoir l.—No. i, Geological Series. Geology of the Nipigon basin, Ontario — by Alfred W. G. Wilson. Memoir 2. — No. 2, Geological Series. Geology and ore deposits of Hedley Mining district, British Columbia — by Charles Camsell. Memoir 3. — No. 3, Geological Series. Palaeoniscid fishes from the Albert shales of New Brunswick — by Lawrence M. Lambe. Memoir 5. — -No. 4, Geological Series. Preliminary memoir on the Lewes and Nordenskiold Rivers coal district, Yukon Territory — by D. D. Caimes. Memoir 6. — No. 5, Geological Series. Geology of the Haliburton and Bancroft areas, Province of Ontario — by Frank D. Adams and Alfred E. Barlow. Memoir 7. — No. 6, Geological Series. Geology of St. Bruno mountain. Province of Quebec — by John A. Dresser. MEMOIRS— TOPOGRAPHICAL SERIES. Memoir 11. — No. i, Topographical Series. Triangulation and spirit levelling of Vancouver island, B.C., 1909 — by R. H. Chapman. Memoirs and Reports Published During 1911. REPORTS. Report on a traverse through the southern part of the North West Terri- tories, from Lac Seul to Cat lake, in 1902 — by Alfred W. G. Wilson. No. 1006. Report on a part of the North West Territories drained by the Winisk and Upper Attawapiskat rivers — by W. Mclrmes. No. 1080. Report on the geology of an area adjoining the east side of Lake Timis- kaming — by Morley E. Wilson. No. 1064. MEMOIRS— GEOLOGICAL SERIES. Memoir 4. — No. 7, Geological Series. Geological reconnaissance along the line of the National Transcontinental railway in western Quebec — by W. J. Wilson. The Edmonton coal field, Alberta — Bighorn coal basin, Alberta — by Memoir 8. — No. 8, Geological Series. by D. B. Dowling. Memoir 9. — No. p, Geological Series. G. S. Malloch. Memoir 10. — No. 10, Geological Series. An instrumental survey of the shore-lines of the extinct lakes Algonquin and Nipissing in southwestern Ontario— by J. W. Goldthwait. Memoir 12. — No. 11, Geological Series. Insects from the Tertiary lake deposits of the southern interior of British Columbia, collected by Mr. Lawrence M. Lambe, in 1906 — by Anton Handlirsch. Memoir 15. — No. 12, Geological Series. On a Trenton Echinoderm fauna at Kirkfield, Ontario — by Frank Springer. Memoir 16. — No. 13, Geological Series. The clay and shale deposits of Nova Scotia and portions of New Brunswick — by Heinrich Ries assisted by Joseph Keele. MEMOIRS- BIOLOGICAL SERIES. Memoir 14. — No. i, Biological Senes. New species of shells collected by Mr. John Macoun at Barkley sound, Vancouver island, British Columbia — by William H. Dall and Paul Bartsch. Memoirs Published During 1912. MEMOIRS— GEOLOGICAL SERIES. Memoir 13. — No. 14, Geological Series. Southern Vancouver island — by Charles H. Clapp. Memoir 21. — No. is, Geological Series. The geology and ore deposits of Phoenix, Boundary district, British Columbia — by O. E. LeRoy. Memoir 24. — No. 16, Geological Series. Preimlinary report on the clay and shale deposits of the western provinces — by Heinrich Ries and Joseph Keele. Memoir 27. — No. 17, Geological Series. Report of the Conmiission appoint- ed to investigate Turtle moimtain, Frank, Alberta, 1911. Memoir 2S.— No. 18, Geological Series. The geology of Steeprock lake, Ontario — by Andrew C. Lawson. Notes on fossils from limestone of Steeprock lake, Ontario — by Charles D. Walcott. Memoirs Published During 1913. MEMOIRS— GEOLOGICAL SERIES. Memoir 17. — No. 28, Geological Series. Geology and economic resources of the Larder Lake district, Ont., and adjoining portions of Pontiac county, Que. — by Morley E. Wilson. Memoir 18. — No. ig. Geological Series. Bathurst district, New Brunswick , by G. A. Young. Memoir 26. — No. 34, Geological Series. Tulameen Mining district, B.C. — by C. Camsell. Memoir 29. — No. 32, Geological Series. Oil and gas prospects of the north- west provinces of Canada — by W. Malcolm. Memoir 31. — No. 20, Geological Series. Wheaton district, Yukon Terri- tory — by D. D. Cairnes. Memoir 33. — No. 30, Geological Series. The geology of Gowganda Mining division — by W. H. Collins. Memoir 35. — No. 2q, Geological Series. Reconnaissance along the National Transcontinental railway in southern Quebec — by John A. Dresser. Memoir 37.— No. 22, Geological Series. Portions of Atlin district, B.C. — by D. D. Cairnes. Memoir 38. — No. 31, Geological Series. Geology of the North American Cordillera at the forty-ninth parallel, Parts I and II — by Reginald Aldworth Daly. Memoirs Published During 1914. MEMOIRS— GEOLOGICAL SERIES. Memoir 23. — No. 23, Geological Series. Geology of the coast and islands between the Strait of Georgia and Queen Charlotte soimd, B.C. — by J. Austen Bancroft. Memoir 25. — No. 21, Geological Series. Report on the clay and shale de- posits of the western provinces (Part II) — by Heinrich Ries and Joseph Keele. Memoirs in Press, January 31, 1914. Memoir 40. — No. 24, Geological Series. The Archaean geology of Rainy lake — by Andrew C. Lawson. Memoir 32. — No. 25, Geological Series. Portions of Portland Canal and Skeena Mining divisions, Skeena district, B.C. — by R. G. McConnell. Memoir 19. — No. 26, Geological Series. Geology of Mother Lode and Sun- set mines, Boundary district, B.C. — by O. E. LeRoy. Memoir 22. — No. 27, Geological Series. Preliminary report on the serpen- tines and associated rocks in southern Quebec — by John A. Dresser. Memoir 36. — No. 33, Geological Series. Geology of the Victoria and Saan- ich map-areas, B.C. — by C. H. Clapp. Memoir 39. — No. 3s, Geological Series. Kewagama Lake map-area, Quebec —by M. E. Wilson. Memoir 43. — No. 36, Geological Series. St. Hilaire (Beloeil) and Rouge- mont mountains, Quebec — by J. J. O'Neill. Memoir 44. — No. 37, Geological Series. Clay and shale deposits of New Brunswick — by J. Keele. Memoir ^.—Geological Series. Gold fields of Nova Scotia— by W. Mal- colm. Memoir 30. — Geological Series. Basin of Nelson and Churchill rivers — by W. Mclnnes. Memoir 41. — No. 38, Geological Series. The "Fern Ledges" Carboniferous flora of St. John, New Brunswick — by Marie C. Stopes. Memoir 47. — Geological Series. Clay and shale deposits of the western provinces — by Heinrich Ries. Memoir 42. — No. i, Anthropological Series. The double-curve motive in northeastern Algonkian art— by Frank G. Speck. Memoir 48. — No. 2, Anthropological Series. Some myths and tales of the Ojibwa of southeastern Ontario — collected by Paul Radin. Memoir 45. — No. 3, Anthropological Series. The inviting-in ieast of the Alaska Eskimo — by E. W. Hawkes. Memoir 49. — Anthropological Series. Malecite tales — by W. H. Mechling .