DYKES ENCOUNTERED IN TUNNEL •*-»•>••»»••

DEPOSITED IB Y THE COMMITTEE OX (Srafcuate StuMes.

M^QILL UNIVERSITY LIBRARY

DYKES ENCOUNTERED; IN MOUNT ROYAI TUNNEL BETWEEN STATIONS 183+35 and 195+61, by Clara Muriel Aylard.

Submitted in part requirement for degree of Master of Science.

McGill University, April 30, 1924. Dykes Encountered in Mount Royal Tunnel between Stations 183+35 and 195+61.

This paper contains a description of the dykes encountered in a section of the Canadian National Railway tunnel through Mount Royal. The section is 1226 feet in length from station 188+35 in Trenton limestone, 3492 feet west of the eastern portal of the tunnel, to station 195+61 within the essexite, 91 feet beyond its contact with the limestone. The material studied consisted of specimens collected by Dr. J.A. Bancroft. In the table below is a comparison of the types of dykes found in this section with those previously des­ cribed by A.W. Carlyle in the limestone beyond the western contact of the essexite and limestone* Type of dyke Determined by Determined by A.W.Carlyle C.M.Aylard Gabbro-diorite 0 4 Diorite porphyry 7 0 Augitite 0 ...... 2 Tinguaite 4 0 Tinguaite porphyry ...... 3 2 Porphyritic plagioclase tinguaite 0 1 Monchi quite • 0 1 Fourchite 1 2 Maenaite 13 3 Nepheline syenite porphyry ... 5 2 Camptonite 38 27 Unclassified 1 1

1. Carlyle, A.W., "A Study of the Dyke Rocks of Mount Royal Tunnel from stations 260+00 to 283+00." 2.

As will be noted, of the 45 dykes examined, 27 are oamptonites, and a similar preponderance of these dykes over all others was observed by Carlyle-. Other students of dykes encountered in the vicinity of Mount Royal show that, throughout the whole area, oamptonites are by far the commonest dykes met with. The writer is deeply indebted to Dr. J. Austen Bancroft, Professor R.P.D. Graham and Dr. J.J. O'Neill for help during the preparation and writing of this paper.

1. Carlyle, A.W., WA Study of the Dyke Rocks of Mount Royal Tunnel from stations 260+00 to 283+00." 3.

Age Correlation.

By plotting all the dykes and sheets and carefully noting the different intersections, it has been possible, to some extent, to work out their relative ages. As might be expected, however, there are many gaps. In this section of the tunnel there are, according to dyke intersection, at least seven different ages. The following dykes and sheets have been found to intersect in such a manner that seven different ages are represented; they are in order of decreasing age, 186+04 (tinguaite porphyry), 187+21 (camptonite), 187+07 (fourchite), 186+45 (maenaite), 186+34 (camptonite), 186+41 (camptonite), and 186+82 (camptonite). 187+07 (fourchite) is also cut by 186+98 (camptonite) which is cut by 188+00 (devitrified pitchstone), 188+00 is out by 189+59 (camptonite). Another series, in order of decreasing age, is 183+70 (porphyritic plagioolase tinguaite), 183+35 (camptonite), 183+78 (camptonite), 185+07 (camptonite) and 184+82(camptonite). The fourth series is, as far as can be ascertained in this section, unrelated to any of the above. It is given below in order of decreasing age, 193+73 (gabbro*diorite), 193+77 (gabbro~diorite), 193+97 (camptonite) and 193+20 (nepheline syenite porphyry). In the following table, columns I and II give the sequence of the main intrusions, and of the dyke injection 4.

following each, as they have been determined by other observers from a study of Mount Royal, both An the surface and in sections of the Canadian National Railway tunnel. In column III an attempt is made to correlate in the same way the dykes and sheets occurring in the portions of the tunnel to which this paper is confined. The correlation is based partly on dyke intersections and partly on the petrographical similarity of the several rocks. Some of the oamptonites are definitely known to be younger than the maenaites, but on account of inadequate information it is impossible to state whether they are younger or older than the camptonite breccia. The same is true in the ease of the nepheline syenite dykes which may have attended either the first or second major injection of nepheline syenite. 5.

I. II. III. 1.1. Intrusion Intrusion of of 1. Intrusion of Essexite Essexite Essexite Bostonites(a) Tinguaite (a) Tinguaite porphyry Mica-tinguaites(b) Fourchite and (b) Camptonite allied dykes monchiquite Tinguaite-porphyry (o) Camptonite (c) Fourchite and Monchiquite Oamptonites(d) Further camp­ (d) Basic camptonite tonite Motiehiquites 2.2. Intrusion Intrusion of of 2. Intrusion of Nepheline-Syenite Nepheline-Sye nit e Nepheline-Syenite Nepheline syenite Nepheline syenite Nepheline Syenite ? porphyry porphyry Oamptonites Maenaite Maenaite Maenaites and Perhaps some other types. In­ oamptonites. cluded in this group are dykes of several dif­ ferent ages. 3. Intrusion of 3. Intrusion of 3. Intrusion of Camptonite Camptonite Breccia Camptonite that forms matrix Followed by dykes, that forms matrix of igneous breccia. some unrelated of igneous basic camptonites breccia. may belong to this Camptonites? period. 4. Dykes of more 4. Intrusion of later recent nepheline Nepheline Syenife syenite grading to segmatitic and Followed by aplitic phases (a) possibly some maenaites. Dykelets of two types of pj%matitic oamptonites. (b) Camptonites with resorbed hornblende. nepheline syenite. Camptonite with resorbed hornblende I. Essexites of Mount Royal, , P.Q., by J.Austen Bancroft and W.V. Howard. II. A Study of the Dyke Rocks of Mount Royal Tunnel between Stations 260+00 and 283+00 by A.W. Carlyle. 6.

The principal constituents of these dykes are:- the feldspars, hornblende, augite and biotite.

The Feldspars. On account of the basic character of the majority of these dykes orthoclase is present less frequently than plagioolase. It occurs both in idiomorphic crystals and in grains. Twinning, according to the Carlsbad law, is fre­ quently exhibited. The plagioolase ranges in composition from oligo- clase to labradorite, the most common variety being andesine. The laths exhibit albite or Carlsbad twinning and many of the grains, although their index of refraction is higher than balsam, are untwinned. Calcite and sericite or saussurite are the most common alteration products of the feldspars.

The most abundant ferromagnesian mineral is a brown pleochroic (x>y>z) hornblende with a maximum extinction angle of 20°. It is present as a rule in two generations, forming idiomorphic phenocrysts and ragged flakes in the groundmass.

Two varieties of pyroxene occur:- augite. either colourless or violet (titaniferous) and aegirine-augite. The maximum extinction angle of the colourless and titaniferous augite ranges up to 47°. The titaniferous augite displays 7. pleoohroism (greenish pink to pale purple). Many of the grains and prisms are bordered with pleochroic (yellowish green to blue green) aegirine-augite with a maximum extinction angle of 28°.

The least abundant ferromagnesian mineral is biotite. The colour and character of the pleoohroism vary in the different types of dykes as follows: camptonites, pale yellow to dark brown; nepheline syenites, pale greenish yellow to olive green; and augitites, pale yellow to brownish red. The characteristic alteration products of the ferro­ magnesian minerals are:- of hornblende, chlorite, iron ore, carbonate and epidote; of augite, chlorite and calcite; and of biotite, chlorite.

The order in which these dykes are described is, as nearly as possible, the order of relative age, commencing with the essexite and ending with the resorbed camptonite.

This specimen of coarse-grained essexite was collected at station 194+70. the eastern contact of the main essexite plug with the Trenton limestone. The rock has granitoid structure and consists essentially of plagioolase and augite. Disseminated through the rock in minute irregular grains is a pale brownish-yellow mineral which is doubtless the wdhlerite referred to in detail below, in the description of the thin section. After powdering the rock 8. and boiling it with hydrochloric acid, it gelatinized. When examined under the microscope the thin section exhibits the same characteristics as the hand specimen. The augite, which comprises at least sixty to sixty-five per cent of the rock, is for the most part in ragged grains bordered with pleochroic (yellowish green to blue green) aegirine- augite. In addition to this the rock contains grains of feldspar, for the most part grains of untwinned basic plagio­ olase (considerably higher than Canada balsam) and lesser amounts of orthoclase and nepheline. There is a small percentage of a colourless mineral, in various sizes of irregular grains, occurring interstitially with properties very like those of wflhlerite. It has an extinction angle of 39°, distinct cleavage, the index of refraction is lower than aegirine-augite, and the birefringence comparatively high, and it is biaxial and optically negative. This mineral has been previously described in a sample of essexite taken at station 194+90. There is an exceptionally high per­ centage of accessories in this rock in the form of compara­ tively large idiomorphic and allotriomorphie crystals of apatite and sphene. The pyroxene is, for the most lpart, fresh but the feldspar is partially altered to saussurite.

1# "Essexite of Mount Royal, Montreal, P.Q.", by J.Austen Bancroft and W.V. Howard. 9.

The six rocks described below, in order of increas­ ing basicity, are all phases of the essexite and occur in dykes and sheets near the contact.

Gabbro-diorites. This sample obtained at station 195+61 is a dark, fine-grained porphyritic rock. Hornblende 4 mm in length and 0.5 mm in width, augite ranging up to 2.5 mm x 1.5 mm and feldspar in grains 1 mm in diameter are the phenoerysts. Embedded in a groundmass of twinned laths of labradorite (determined by extinction angle) which comprises about forty per cent of the rock, are idiomorphic and allo- triomorphic flakes of strongly pleochroic hornblende, biotite and pale green augite. The biotite is intergrown with both the hornblende and augite. The accessory minerals are pleochroio sphene and a great deal of iron ore (magnetite and pyrite) occurring in large and small patches as well as in tiny grains. The rook is comparatively fresh except for the fact that saussurite has practically replaced the feldspar.

194+30 In hand specimen this dyke is also fine-grained; the phenoerysts of augite while occurring in fairly large numbers are not as numerous or as large as in rock 195+61. There is an abundance of pyrite scattered through the rock. In contrast to 195+61, augite is the chief consti­ tuent and there is an absence of hornblende. This augite 10.

is titaniferous and pleochroic (green to brownish pink) occurring in prisms and also in little grains. Intergrown with the augite is biotite. This biotite exhibits strong pleoohroism (pale yellow to dark brown) and encloses small wedge-shaped crystals of sphene. There is a Jower percentage of feldspar in this rock than in 195+61. For the most part it is untwinned labradorite in grains but there is also some orthoclase, both partially altered. The calcite in the rock seems to be primary and not an alteration product. Scattered through the rook are irregular grains of brown garnet and crystals of sphene.

Although the dyke occurring at station 193+77 cuts the dyke at station 193+73 this does not necessarily signify that there is any marked difference in their relative ages, on account of their close proximity to the main essexite injection. The earlier dyke may have hardly finished solidifying when it was cut by the other.

193+73 In a medium grey, fine-grained groundmass are segre­ gations of augite, biotite and iron ore which reach the size of 4 mm x 3 mm and also large patches of feldspar. When the rock was powdered and boiled with hydrochloric acid, a little jelly formed. The thin section beautifully exhibits the segregations 11. of small flakes of pleochroic biotite, grains of titaniferous augite and small clumps of iron ore (pyrite and pyrrhotite). Between the segregations are some large crystals of augite, grains of untwinned basic plagioolase and a few of nepheline, the two last incipiently altered. A large number of tiny crystals of pleochroic sphene are scattered through the rock. The augite is partially filled with iron ore dust.

193+77 This rock is darker than the dyke 193+73. The phenoerysts are hornblende up to 1.5 mm in length and 0.5 mm in width, and feldspar ranging in size up to 4.5 mm x 2 mm. Pyrite in minute grains is diffused through the rock. When examined under the microscope the chief differ­ ences between this rock and 193+73 are that this one is more basic. Besides the above mentioned augite and biotite there has been an addition of hornblende. There has been no segregation of the ferromagnesian minerals into rounded clumps.

Augitites Two specimens taken at station 193+00 and 193+13.5 are samples from a blocky sheet, which is a grey, fine-grained rock containing very small ferromagnesian phenoerysts and minute grains of pyrite. This rock is the most basic encountered in this section, consisting essentially of small equidimensioned grains 12. of titaniferous augite and interstitial flakes of pleochroic (almost colourless to brick red) biotite. The feldspar is practically negligible, but there are patches of what appears to be devitrified glass. Calcite occurs interstitially and sphene is present in small crystals.

Nepheline-rich tinguaite-porphyry Slides 186+04, 185+86 and 185+57(a) are from a wide, irregular dyke which outcrops for eight feet along the floor of the tunnel. The normal rock is medium pinkish grey, but bleaching has taken place along cracks, and also at the margins, the zone in the latter case being very irregular and ranging up to twenty inches in width. The structure is porphyritic, with phenoerysts of white orthoclase measuring up to 5 by 3 mm, and small irregular blotches of sodalite. The groundmass is fine-grained but contains visible pyrite and is traversed by narrow white veinlets. The powdered rock gelatinizes when boiled with hydrochloric acid.

186+04 Although in the hand specimen this rock is porphy­ ritic the particular thin section studied is not. The minerals seen under the microscope are:- feldspar, sodalite, biotite, sphene, apatite amd iron which are primary, and cancrinite, sericite and calcate secondary. Two constituents, orthoclase and cancrinite in about 13.

equal amount, comprise approximately ninety per cent of the rock. The former occurs, for the most part, in lath shaped prisms displaying Carlsbad twinning, while the latter, doubt­ less an alteration product of nepheline, forms an abundance of equidimensioned grains, more or less segregated into clumps. In addition to feldspar and cancrinite, an abundance of sphene and iron ore (magnetite and pyrite), a fair amount of biotite in extremely minute idiomorphic and allotriomorphic flakes, partially altered to chlorite; and an occasional grain of apatite. A few small crystals of sodalite were also observed, but the section examined contained no large masses of the mineral such as may be seen in the hand specimen. In addition to the secondary minerals already mentioned, calcite and seri- cite occur as alteration products of the feldspar.

185+86 This is a three and a half inch wide branch of the dyke described above. The rock is non-porphyritic. Mineralogically it is similar but alteration has been more extensive. The sphene has gone over entireJLy to leucoxene. Cancrinite, however, is not so abundant, indicating that the rock contained less nepheline than the last.

185+57 (a) In this portion of the dyke the secondary nature of the cancrinite is very clearly shown, aggregates of small flakes of this mineral completely filling the space that was formerly occupied by sharply defined nepheline crystals. 14.

The percentage of biotite and iron ore is higher than in 186+04. The feldspar is in small grains as in 185*86 but

this slide on the whole is finer grained than either of the other two.

Porphyritic plagioolase-tinguaite 183+70 is a dyke eighteen inches wide, fine grained, greyish brown in colour containing phenoerysts of hornblende, and plagioolase feldspar, the former in prisms measuring up to 4 cms by 4r»5 mm and the latter in nearly square individuals which attain widths of 5 or 6 mm. When the powdered rock was boiled with hydrochloric acid it did not gelatinize. The dyke An thin section does not closely resemble 186+*04. It is strongly porphyritic, with phenoorysts of feldspar, both orthoclase and plagioolase and a few of com­ pletely altered hornblende. The plagioolase has a maximum extinction of 32° and exhibits the usual albite twinning. Some of the feldspar phenoerysts are fairly fresh, but others show incipient alteration to calcite and saussurite. The hornblende phenoerysts are all completely replaced by carbonate and iron ore dust, some having gone over entirely to the latter.

The groundmass is composed of feldspar laths with, as access­ ories, occasional grains of zircon and black iron ore. 15.

Monchlquite dykes 185+63. This dyke is irregular in width reaching its maximum at twenty-three inches. In the hand specimen it is porphyritic, with numerous small pseudoamygdales filled with a white opaque substance and ranging up to 1.5 mm x 1 mm in cross section, long slender needles of hornblende up to 4 mm x 0.5 mm, and a few flakes of biotite, the largest about 2 mm in diameter, scattered through a dark, fine-grained groundmass. Examination in thin section shows the following minerals to be present:- hornblende, olivine, analcite, iron ore, chlorite, calcite and serpentine. Basaltic hornblende, the most abundant ferromagnesian mineral, is present as numerous Idiomorphic crystals, many incipiently altered to chlorite, and a myriad of tiny gfrafcsi pale green microlites forming part of the groundmass and growing into the pseudoainygdaloidal cavities. Olivine occurs only as phenoerysts, some of which are comparatively fresh, while others are partially altered to serpentine. As is almost invariably the case in basic dykes of this area, pyrite and black iron ore are prominent accessory constituents. Analcite is not only the most important constituent of the groundmass, but also, with crystalline calcite, forms the filling of the pseudoamygdales. Other minerals in the groundmass, besides analcite and the hornblende microlites already mentioned, are minute flakes of chlorite and calcite. 16. Analyses of Monchiquites A B C by by by M.F.Conner B. J.Harrington M.F.Conner sio2 37.56 36.69 37.34 ^z°z 14.58 11.96 11.84 fe203 6.15 5.45 5.37 F.O 8.20 8.90 6.40 MgO 7.47 7.85 9.66 CaO 10.08 10,28 11.92

HagO 4.24 3.88 2.91 EE° 1.94 2.07 2.05

Ti02 3.72 D.4c4 3.93 0.23 0.62 0.04 P2°5 so3 0.07 0.92 - CI 0.05 0.04 0.04

FeS2 0.41 - 0.47 MnOg 0.23 0.38 0.18

BaO - - 0.04

3r20 - - 0.04 co2 1.80 3.78 5.08

H20 3.11 1.95 2.80

99.84 100.21 100.09 17.

Norms. by C.M. Aylard A B C Or? 11.12 12.23 12.23 Ab 3.66 13.10 13.62 An 15.29 8.90 13.34 He 17.73 10.78 5.68

Halite - - .12 Dt 18.31 11.61 10.43 01 10.16 11.99 14.33 Mt 9.05 7.89 7.89 11 6.99 10.49 7.45 py 0.41 0.72 0.47 Ap 0.34 1.34 0.34 CaCOg 4.10 8.60 11.60

H20 3.11 1.95 2.80 99,87 99.60 100.80

Name and Symbol Locality Classification A. Monchiquite Mt.Royal Tunnel tflass III Salfemane III .6(7).(2)3.4 Station 185*63 Order 6 Andofelic Portu­ gal Rang 3 alkalicakic Limburgase Subrang 4 dosodic Limburgase B. Monchiquite Reservoir End Class III Salfemane. III .7.2.4 Montreal Order 7 Cufellc Earnerunojre £.£.&.<3« Rang 2 domalkalic Kamerunojse Subrang 4 dosodic Kamerunose C. Monchiquite Mile End quarry Class III Salfemane III.(5)6."3."4 Montreal Order 6 Cudofelic Portugal 3.3.2.2. Rang 3 alkalicakic Limbur- fOfie mburgase B and C Guide Book No.3. XII International Geological Congress 1913. Monchiquite. I85| 53. 18.

Fourchite dykes At station 18?M)7 is a sheet of fourchite which is dark, fine-grained and porphyritic, varying in width from sixteen to thirty-two inches. Within it are amygdaloidal cavities drawn oat at right angles to the contact and also arranged perpendicular to the bottom of the sheet, are numerous needle-like hornblende crystals up to two inches in length. The porphyritic structure of the rock is clearly seen under the microscope. Augite, hornblende and feldspar form the phenoerysts, while the groundmass consists of small flakes of chlorite, resorbed prisms of hornblende, calcite, and grains of pyrrhotite. Though not as numerous as the prisms of basaltic hornblende, the augite phenoerysts are larger. A poikilitic structure is exhibited where these include small blades of the hornblende. Both minerals show partial alteration to chlorite and fine grains of iron ore. The augite only occurs in one generation while the hornblende is present in two. The resorbed hornblende in the groundmass retains the otiginal outline but alteration has been complete to chlorite and iron ore dust. Aggregates of plagioolase crystals, some in tiny laths and the majority apparently untwinned, have been replaced by calcite, sericite and chlorite. The more precise Identification of the feldspar is impossible owing to its highly altered condition. The fine-grained groundmass is, in part, the result of devitrification of some isotropic mineral or glass, but, it is also in part composed of very small flakes of secondary chlorite and calcite. 19.

There is also a dyke of fourchite at station 188+01. This dyke is younger than the sheet 187*07 just described. It has a fine even-grained appearance with phenoerysts of hornblende 2.5mm x .5 mm and augite 3.5mm x 2»5 mm. Petrographically the two have much in common but in dyke 188+01 the phenoerysts of augite are smaller and more numerous, and those of augite less plentiful than in 187+07. In the former the amount of iron ore has increased which makes the groundmass darker.

Nepheline-Syenite dykes The dykelets, each three inches wide, at stations 193+20 and 194+14 are medium grey with a feldspar rich band near the contact. Rock 194*14 is slightly darker than the other because it contains a higher percentage of augite crystals, many of which form phenoerysts, which range in size up to 4 mm x 2 mm. Both of these rocks gelatinize when powdered and boiled with hydrochloric acid.

193+20. This rock is about forty-five per cent aegirine-augite and accessories. The feldspar includes both orthoclase and oligoclase and occurs in laths exhibiting albite-twinning and in untwinned grains, while nepheline in prismatic form is present in fair amount. The aegirine- augite is present in the form of prisms and rugged grains, and here and there flakes of hornblende may be seen intergrown 20. with it. The accessory minerals are pleochroic sphene and irregular grains of iron ore (pyrrhotite and magnetite).

The sample from station 194*14, as already mentioned, contains a higher percentage of augite than the dyke described above. Besides this difference there are two others:- the aegirine-augite is often just the border of a titaniferous augite crystal, and the feldspar is wholly in untwinned grains.

Maenaite dykes 5wo specimens, taken at stations 186*82 and 186*45 from the same dyke, were found on examination to be maenaites. ^his dyke is a medium grey, dense, fine-grained, non-porphyritic rock, with sete of more or less rectangular joint planes covered with a coating of pyrrhotite and calcite. The minerals observed in thin section are:- hornblende, augite and plagioclase as primary, meIanite and iron ore as accessory and biotite, calcite and sericite as secondary minerals• Although not apparent in the hand specimen the rock in thin section is seen to have a porphyritic structure, due to the development of relatively large hornblende crystals. 3?hey are almost entirely altered to small flakes of biotite and carbonate. In addition to being present as phenoerysts, hornblende occurs as colourless microlites in the groundmass. Laths of plagioclase, determined as dligoclase by the extinction 21. angle, twinned according to both albite and Carlsbad laws, constitute about eighty per cent of the groundmass. The remainder is mainly minute flakes of biotite and small grains of black iron ore, minor amounts of allotriomorphio a&g&te grains, microlites of hornblende and a few irregular grains of melanite. In addition to the secondary biotite there is abundant calcifce and sericite, alteration products of the feld­ spar, diffused through the slide. Notwithstanding the fact that 186+45 is a section from the same dyke as 186+-82, it has a distinct peculiarity in the presence of secondary quartz. This quartz is not only in more or less rounded grains showing strain shadows but is also interstitial.

188»12 is a narrow dyke two and one-half inches wide, which is darker than 186*82 and shows porphyritic structure in the hand specimen. The phenoerysts are 3.5 mm x 0.5 mm. As in 186+82 the few hornblende phenoerysts are replaced by minute flakes of biotite and iron ore. The rock is so altered to calcite and sericite that it is almost impossible to determine the character of the feldspar compris­ ing the groundmass. Garnet and augite are absent, but there are, besides an abundance of iron ore (pyrite and magnetite), a good many comparatively large idiomorphic crystals of dusty 22. apatite. On being powdered and boiled with hydrochloric acid, this rock did not gelatinize.

Unclassified sheet A sample of a very curious fine-grained sheet, 9-10 inches thick, resembling hornstone in texture, was taken at station 188+00. Within the sheet, two and one-half inches from the bottom, was a zone, one and one-half inches wide, consisting of braided yellow streaks. The limestone on both sides of the sheet has been marmorized below for two or three inches and above for two feet, except where heated vapours must have been rising where the marmorization extends for six feet. The only minerals that can be recognized under the microscope are colourless microlites of hornblende, and feld­ spars and some crystals of zircon. Samples of the contact rock between limestone and a sheet and a dyke were taken at stations 187*07 and 187+22 respectively. Both specimens are light coloured fine­ grained rocks. When powdered, sample 187+07(a) did not effervesce very strongly in hydrochloric acid until it was heated, and when the powder was tested with ferric chloride the colour remained unchanged. It is a dolomitic limestone. When examined in thin section, both rocks seem to be composed almost wholly of fine-grained carbonate. Rock 187+07(a) contains irregular patches of iron ore (pyrite and pyrrhotite) 23. and little veinlets of more coarsely crystalline calcite, while traversing the section of specimen 187*22 there is a veinlet composed of small grains of colourless pyroxene, unstriated feldspar and grains of black iron ore.

The Camptonites The greatest variation is seen in the types of camptonites. They range from an extremely basic phase, hardly distinguishable from fourchites, to an acidic phase resembling maenaites. The following method is used in differentiating them for the purpose of description.- Variety I - ultrabasic. Variety II - more acidic. Each variety is again subdivided into types according to texture and proportionate amounts of constituents. As in the case of the other dykes, these are described below as nearly as possible in the order of their relative ages. Even though the more acidic camptonites are the oldest, they are, at the same time, found among the youngest. For this reason the basic camptonites are described first.

Variety I. Ultrabasic. Type 1 This type includes four dykes ranging in width from four to six inches. All are dark, dense and fine-grained, but microscopically most of them exhibit a porphyritic structure and contain small phenoerysts of hornblende 4 mm x 3 mm, and in some cases also of augite 3 mm x 2 mm. The rock is fractured 24. by numerous joint planes covered with a thin film of pyrite and a little calcite. None of these rocks gelatinized when powdered and boiled with hydrochloric acid.

187*51. Under the microscope there are small pheno­ erysts of brown hornblende distributed through a groun&mass composed essentially of minute laths of plagioclase feldspar, much diffused caloite and chlorite, and an abundance of dust­ like particles and irregular grains of black iron ore and pyrite. The groundmass includes numerous small prismatic outlines, now occupied by chlorite and dusty black iron ore, which represent an early generation of hornblende crystals that have been resorbed. In addition there are some irregu­ larly rounded aggregates of plagioclase feldspar, which show every stage from incipient to complete alteration to calcite and sericite. Some of the feldspar is untwinned. One more or less rounded grain of brown garnet (melanite) was noted in this slide examined.

Specimens of dykes occurring at stations 187*72, 187+79 (branch of 187+72), 186*98 and 192*59 are essentially like 187+51 at least in so far as the groundmass and the ratio . of ferromagnesian to feldspathic constituents are concerned, but they exhibit differences in structure and in %ht proportion­ ate amounts of the several ferromagnesian minerals, as indicated in the following table. 2g.

Number of Structure Hornblende Augite Biotite Slide

187*51 porphyrit ic two genera­ none none tions; few phenoerysts; mainly resort­ ed in ground- mass 187*72 non-porphy­ all resorbed small very ritic amount in little groundmass 187*79 porphyritic fewer and none none smaller pheno­ erysts than in 187-51 186*98 porphyritic phenoerysts large abundant but phenoerysts none small quite abun­ dant 192*59 porphyritic none in pheno­ some pheno­ erysts all in erysts little groundmass

Type 2 In the hand specimen it is impossible to distinguish type 2 from type 1. They are dark, with the same fine-grained texture and with phenoerysts of hornblende and augite scattered through them. They, too, do not gelatinize when powdered and boiled with hydrochloric acid. The widths of the dykes vary from seven to twelve inches. The dissimilarity between these two types is clearly seen in the thin section. The most outstanding differences are the presence of allotrlomorphic prisms of basaltic horn- 26. blende instead of resorbed prisms in the groundmass, the occur­ rence of augite in two generations, and the comparatively fresh appearance of the minerals. There are three dykes of this type in the sections of the tunnel dealt with in this paper. All are composed of hornblende, augite, biotite, and feldspar with secondary chlorite and iron ore.

191*38. Basaltic hornblende in two generations makes up about seventy per cent of the rock, another twenty per cent being augite and biotite. The hornblende is present both as numerous, small, idiomorphic prisms, and also in allotrlo­ morphic flakes in the groundmass. Many of the phenoerysts of this mineral contain iron ore dust. In addition to form­ ing phenoerysts, augite occurs in small equidimensioned grains in the groundmass. Small flakes of strongly pleochroic brick-red and brownish-yellow biotite were observed associated with large patches of pyrite and intergrown with some of the augite phenoerysts. There are in the groundmass more or less rounded patches which seem to be devltrified and now are filled with fine-grained feldspar, granular augite, and small flakes of bright green chlorite.

There is a similar dyke at station 191*82, and a third,at station 192+-19, differs from them only in having a higher percentage of feldspar. 27.

Type 3 Megaseopically these dykes are lighter in colour than either of the two previously described types. The majority are porphyritic, the phenoorysts being hornblende 6.5 mm x 1 mm and feldspar in grains about 0.5 mm in diameter. Four dykes of this type were encountered varying in width from two to nine inches. Two out of the four gelatinized slightly on being powdered and boiled with hydrochloric acid. As inspection of the hand specimen but suggested, the rocks when examined in thin section contain a higher per­ centage of feldspar than either types 1 or 2. On the whole they resemble type 2 more closely than type 1.

193»97. Examined in thin section this rock is seen to be holocrystalline and porphyritic. The minerals present are:- hornblende, biotite, augite, feldspar, cancrinite, chlorite, calcite, sphene and black iron ore. Hornblende occurs in minute flakes intergrown with biotite, as well as in a few small prismatic phenoerysts. These two minerals comprise over sixty per cent of the rock, the former being the more abundant. A few large phenoerysts of colourless augite are present, but, for the most part, this mineral occurs in allotrlomorphic grains in the groundmass. Colourless microlites, possibly of augite, are enclosed in small laths and irregular grains of feldspar which make up the bulk of the groundmass. Some of the feldspar is untwinned, 28. but most of it exhibits Carlsbad twinning. It is slightly turbid owing to the presence of inclusions already referred to as well as to partial alteration. The former presence of nepheline is suggested by a few flakes of cancrinite which form small aggregates. Irregular grains of pyrite and black iron ore are associated with sphene. The rocks are relative­ ly fresh but some chlorite has been developed from the horn­ blende, and the calcite has replaced some of the feldspars and augite in the groundmass. ^he other dykes of this type occur at stations 191*94. 191*57, 192*07 and 192*05. They have the same characteristics as 193*97, which has been described as the type specimen. The main difference is in the amount of augite, which is abundant in 191*94 and 191*57 but lacking in 192*05 and 192*07. The texture of 191*94 is coarser than that of the other members of the series.

Type 4 This sample (183*35) represents the basic phase of the sheet 182+15, which is eighteen inches thick. Pheno­ erysts of hornblende (2.5 mm x 1.5 mm) and grains of calcite ranging up to 3.5 mm x £ mm are embedded in a dark, fine­ grained groundmass. The rock is predominately composed of narrow prismatic crystals of hornblende, altered grains of augite and flakes of biotite in a groundmass consisting almost entirely 29. of chlorite, saussurite and irregular grains of iron ore

(pyrite and magnetite). Feldspar is practically lacking. The augite grains are broken up and partially altered to dusty iron ore and chlorite has begun to replace the hornblende and biotite. At station 152*15 the sheet is somewhat more acidic with feldspar constituting about forty per cent of the rock and hornblende absent.

Acidic Variety Type 1 189+92, 189*94, 190*33, 190*83 and 190*92. are The first three/specimens taken at different points along the sheet while the last two are from a dyke nearby. These rocks represent a transitional stage between the ultra- basic oamptonites and the more acidic ones. They are extremely dense, fine-grained, dark rocks containing no pheno­ erysts visible to the eye. Even under the microscope it is difficult to identify with certainty the several minerals present, especially in 190+83 and 190*92. Allotriomorphic grains of hornblende, augite and biotite, in the order named, are the most abundant constituents of the groundmass. There is a scarcity of feldspar but cancrinite occurs which suggests the former existence of nepheline. The presence of a few hornblende individuals rather larger than the average gives to the rock 30. a minutely porphyritic aspect. Pyrite and iron ore are the only accessories . The usual alteration products, calcite, sericite and chlorite in minute flakes are disseminated through the groundmass. The above description applies to the three thin sections of the sheet. Those of dyke 190*83 and 190*92 differ in containing no augite, making the percentage of ferro­ magnesian minerals lower.

The dykes at statione 187+21, 186+34 and 189*59 are somewhat alike petrographically, although the dykes from which they were cut are not all of the same age. In the hand specimen, while both 186+34 and 187*21 are medium grey, dense, fine-grained porphyritic rocks, the latter is very much the denser. In it also phenoerysts are rare and consist of feldspar only, whereas in 186-*34 there are hornblende phenoerysts as well.

186*34. In thin section this type of dyke is entirely different from those previously described. The groundmass is medium grained and consists of approximately equal amounts of hornblende and feldspar; the former in small ragged flakes and pale green microlites, the latter in allo­ triomorphic grains, the majority untwinned. Some of the feldspar is quite fresh while some is turbid, due to the presence of minute flakes of sericite. Both the feldspar 31. and the hornblende occur as phenoerysts. Sphene and iron ore are abundant. Besides the usual calcite and sericite formed from the alteration of the feldspar and chlorite from the ferromagnesian constituent, there is epidote in small grains replacing prisms of hornblende.

187+21 and 189+59. In these two dykes the proportionate amount of ferromagnesian and feldspathie constituents is about the same as in 186+34, but instead of the major part of the hornblende occurring in ragged individuals it is present in prisms. Idiomorphic augite and flakes of biotite are additional con­ stituents of 187+21. Dyke 189+59 is peculiar in that it contains abundant, fresh inclusions of different varieties:- essexite types, nepheline syenite and limestone rich in vesuvianite. The limestone inclusions are thought to be fragments of the major contact aureole with the essexite plug. Some of the inclu­ sions are four inches in length and three inches in width. Five different types of inclusions are described below.

189+59(a) Inclusion of Potsdam Sandstone. This is a three sided inclusion, with rounded corners, composed almost entirely of quartz grains and siliceous cement. Dotted here and there through the quartz are opaque grains, flakes of a green ferromagnesian mineral and an occasional cube of pyrite. When broken, the inclusion 32.

split through the grains. About seventy-five to eighty percent of the slide is composed of irregular grains of quartz pierced by myriads of tiny needles of rutile. Besides the quartz there are turbid ragged fragments of feldspar, allotriomorphic grains and prisms of green pyroxene enclosing small flakes of brown hornblende and biotite, a few cubes of pyrite and several grains of sphene. The rook has been altered to a quartzite. In one place on the edge of the inclusion there is graphic intergrowth of quartz and feldspar which suggests that some of the quartz was absorbed by the magma.

189+59(b) Inclusion of Essexite. The rock is coarse grained with a granitoid struct­ ure, containing numerous erystals of hornblende up to 20 mm x 5 mm,rectangular prisms of augite, 5 mm x 5 mm, and laths of feldspar. In the thin section the same characteristics are portrayed as in the hand specimen. Pale purple augite and strongly pleochroic, yellow to very deep brown,hornblende occur in large grains. In addition to these two minerals there are twinned and untwinned laths of plagioclase, a fairly large number of idiomorphic apatite crystals and large patches of magnetite. Calcite and sericite are the secondary minerals formed by alteration of the primary ores. 3 3.

189+59(o) Pyroxenite. This is a small inclusion composed of pale greenish pyroxene crystals. In thin section, too, the rock is almost entirely composed of colourless diopsite, but contains minor amounts of plagioclase, light coloured pleochroic (pale yellow to deep brown) mica, sphene, apatite and pyrite. The inclusion may be a fragment of altered Grenville or Trenton limestone.

189+59(d) Pyroxenite. In the hand specimen it is fine-grained and medium grey. This inclusion, in thin section, resembles 189+59(c) very closely except for the fact that it laoks the apatite and sphene and contains less mica.

189+59(e) Gneiss. This inclusion is a light coloured holocrystalline rock possessing gneissic structure due to the alteration of the pyroxene and feldspar crystals into rude bands. Under the microscope this structure is not as pro­ nounced. This rock is entirely composed of large grains of e aegiring-augite and twinned oligoclase, with the exception of patches of sphene and pyrrhotite associated with the pyroxene. 34.

Type 3. Dykes 183+78 and 184+67, each ranging in width from thirteen to sixteen inches, are almost identical both in the hand specimen and in thin section. They are dark, dense and fine-grained. Dyke 183+78 contains only a very few small phenoerysts of hornblende while dyke 184+67 has in addition nearly rectangular crystals (1 x 0.75 mm) of feld­ spar. The rock is fractured by rectangular joint peanes covered with oalcite and pyrrhotite.

183+78 Under the microscope, embedded on a groundmass of twinned laths of plagioclase and numerous resorbed prisms of hornblende, are several comparatively large phenoerysts of hornblende, partially altered to iron ore dust, and irregular aggregates made up of laths of twinned plagioclase. Other minerals on the groundmass are small grains of augite, colourless microlites of hornblende, small grains and crystals of sphene, and the decomposition product of the plagioclase, saussurite.

186+41 The main differences,between this dyke and the last dyke 183+78. are that the plagioolase laths are slightly larger and have a more or less parallel orientation; and instead of aggregates of plagioclase laths, there is an occa­ sional large twinned phenocryst. The phenoerysts of horn­ blende are also smaller. 35.

Specimens 190+43 and 190+51 are samples taken from different parts of a four inch dyke. The dyke is light grey, dense and fine-grained with phenoerysts of a ferromagne­ sian mineral up to 0.75 mm x 0.5 mm. Under the microscope, these rocks are finer grained than 183+78 and the aggregates of andesine laths are larger. The ferromagnesian constituent has been replaced by minute flakes of biotite. In addition to sphene there is pale grey apatite, the colour probably being due to inclusions of fine iron ore dust.

Type 4 Of the three samples of this type, two were taken from a sheet at stations 185+07 and 184+97. The third is a dyke 185+37. They are dense, dark, fine-grained rocks with rectangular joint planes coated with fine pyrite and calcite dust. This type is fine-grained, more basic and more highly altered than type 3. Mineralogically they are similar to the latter with the exception that augite is absent.

Type 5 184+82. This dyke, a camptonite with resorbeft hornblende individuals,represents what is believed to be the youngest type of dyke in the Mount Royal area. In the hand specimen it is dark, dense and fine-grained, containing numerous small 36. needle-like phenoerysts under 1 mm in length. It resembles type 3 more closely than any other type but it is coarser grained and peaetieally all the hornblende has been replaced by iron ore (magnetite). The feldspar has suffered partial alteration to calcite. 37.

Tabulation of the dykes Number Name Width Field Remarks Relations 183+35 Porphyritic 18" Cut by 183+78 sheet Augite Camp­ tonite 183+70 Plagioclase 18" Cut by 183+78 straw Tinguaite coloured Porphyrite dyke 183+78 Camptonite 16" Cuts 183+70 dyke and 183+35 184+08 Bostonite 28" to 3" Cut by 183+35 dyke, com­ pletely bleaohed |oint planes 184+32 4n dyke 184+51 Bostonite dyke to 184+74 184+82 resorbed 13" Cuts Bostonite dyke Camptonite 184+70 sheet 185+18 Bostonite 16"-20" Cut by 185+21 dyke 185+22 Bostonite 14" Cut by 185+21 dyke 185+57 Tinguaite 4-1/2* Cut by 185+57 dyke Porphyry (b) 185+63 Monchiquite ~23" Cuts 186+04 dyke 185+86 Tinguaite 3-1/2" dykelet Porphyry 185+33 sheet 186+04 Tinguai te Cut by 185+63 dyke Porphyry 186+34 Camptonite 9" dyke 38.

Number Name Width Field Remarks Relations 186+41 Camptonite 9" Cuts 186+34 186+45 Quartz 6" Cut by 186+34 dyke Maenaite and 186+41 Cuts 187+07 186+98 Camptonite 6" Cuts 187+07 dyke 187+21 Camptonite 11" Cut by 187+07 dyke 187+25 3" dyke 186+82 Cuts sheet 18' dyke 187+51 Camptonite 4" dyke 187+72 Camptonite *6" dyke 187+79 Camptonite 3-4" probably a branch of 187+72 187+97 4" 187+78 Devitrified 9-10" Cuts 188+24 sheet (188+00) Pitchstone 188+24 2-1/2" Cut by 188+00 dyke 189+09 Camptonite 4-4 1/2" dyke 189+59 Camptonite 3-3 1/2" Cuts sheet at dyke 189+49 189+92 Camptonite 6-8" sheet south ? contact with marmorized edges somewhat brown in colour 189+94 Camptonite right hand contact of sheet 189+92 190+16 Nepheline 1/3 - dykelet Syenite 1/2" 39.

Number Name Width Field Remarks Relations 190+43 Camptonite 4" dyke 190+53 7-8" dyke which is blocky 190+70 12" Cut by 190+90 dyke 190+85 Nepheline 1" Syenite 191+33 Camptonite 5" Cut by Nephe­ line Syenite dyke which is inside it 191+41 12" sheet that is somewhat irregular and wavy with mar- morixed contacts 191+57 Camptonite 7" dyke braided and wavy-marmori z ed contacts 191+67 3" dyke which 6-l/2ft above floor feeds into sheet which forms two dykes 191+72 Camptonite 1-1/2" Cut by Nephe­ dykelet line Syenite Pegmati te 191+73 2" dyke parallel to 191+72 191+76 3n dykelet 191+90 1" tiger skin seam 191+94 Camptonite 8-9" Cuts 191+90 dyke and sheet of 191+41 192+05 Camptonite 22n spray of three dykes 192+14 3" sheet blocky and disconnected 40.

Number Name Width Field Remarks Relati ons 192+17 7" sheet blocky with marmorized contacts. 192+14 and 192+17 probably originated from last dyke of 192+05 192+33 Nepheline 2" Cuts 192+14 dykelet Syenite and 192+17 Pegmati te 192+44 3-6" dyke 192+59 Camptonite 18" dyke 192+52 Nepheline 1-3" Cuts 192+59 dyke Syenite Pegmatite 192+82 4-8" Seems to cut dyke 192+17 and 192+05 193+20 Nepheline 3" Cuts 192+05 dyke Syenite cut by nepheline syenite pegmatite 193+35 Nepheline 2" dyke Syenite . 193+29 Nepheline 2" dyke Syenite 193+44 Cut by 193+29 sheet irregular blocky and wavy 193+62 Nepheline 11" Syenite 193+73 Gabbro- 3-6" Cut by 193+77 disjointed diorite sheet like dyke broken and blocky 41.

Number Name Width Field Remarks Relations 193+77 Gabbro- dyke diorite 193+87 Nepheline 2-4" Cuts 193+77 dyke Syenite Pegmatite 194+03 disconnected dyke some of the bite cks separated one foot from each other 194+10 Nepheline 3-4" wide dark borders Syenite 1/4 to 1/2" Pegmatite 194+14 Nepheline Cut by pegma­ dyke Syenite tite, cuts 194+03 194+24 spray of stubby dykes 194+30 Gabbro- diorite 3" similar to 194+24 194+40 Nepheline 1-1/2" three little Syenite stringers 194+50 Nepheline 14" dyke braided with Syenite pegmatite stringers 194+52 Camptonite small irregular blocks 195+21 Nepheline 15 dyke Syenite