The Rocks Of

a"Kaaa;--.aK::aa.L aaaa; THE ROCKS OF '•_: a 'i":aai •••*«>»••'>»>*»< DEPOSITED BY THE COMMITTEE OX (Braouate Stuoies.

11 11 r-~. ' W«-^-»* ..I...... *».*'"

ix1 . \p\A «\t)0^>

ACC NO. DATE

A P E T R 0 G R A P H I C ^ L STUDY

OF THE

E 0 G K S OF IS 0 U N T ROYAL.

1. INTRODUCTION.

11. LITERATURE ON THE SUBJECT.

111. PETROGRAPHY OF THE ESSEXITE.

IV. PETROGRAPHY OF THE NEPHELINP SYENITE.

V. A PETROGRAPHICAL STUDY OF THE DYKE ROOKS. 1. INTRODUCTION.

Mount Royal, situated as it is on the south-east border of the Island of Montreal, is surrounded for many miles by an almost flat plain; this plain is bounded on the north by the foothills of the Laurentian Plateau and extends southward to the Appalachian Mountains; this almost flat plain was once the bottom of an early Palaeozoic sea, and wfc**jk now constitutes the broad valley of the River St. Lawrence. Mount Royal is the most westerly of a group of hills which cut up thru these palaeozoic sediments - and which constitute the group known as the Monteregian Hills(? this group of hills gives us the best known example of a Petrographical Province in Canada. Standing alone, as Mount Royal does, on the westerly border of this ancient sea-bottom, it serves to break the monotony of the landscape and can be seen from many miles distant in any direction. This mountain represents the base or root of a once active volcano , but has been extinct for a long geological period of time; the top of this ancient volcano stood much higher than we see it today but owing to erosion and denudation it has been reduced

Dr.F.D.AdaraB -"Thejtfnteregian Hills "journal oc? Geol. jl. 1902 -2-

reduced to its present altitude which is about 750 feet above the St. Lawrence River,or 769.6 feet above sea level. The area occupied by Mount Royal (proper) is about one and a half square miles-r and is somewhat oval in shape, the narrower end pointing southwards. The mass of the mountain is composed of igneous rocks which together with the surrounding strata are much out up by a numerous and complicated series of dykes, and it is a petrographical study of thesevarious ig neous rooks and more especially of the dykes, with which this paper will deal. The rooks which compose the igneous mass of Mount Royal are Essexite, and Nepheline Syenite, and the dyke rocks which are varied in their mineralogical composition. As stated before Mount Royal is the remains of an ancient volcano in which three distinct periods of eruption are clearly recognized; the first of these eruptions gave rise to the Essexite, forming the eastern portion and occupying about seven-eights of the present mountain. A second disturbance tapped the reservoir and allowed the magma to flow up on the west side of the Essexite, this time as an acid magma, crystallizing out as Nepheline Syenite, now seen as a narrow band on the northwest flank of the mountain. Some time after this magma had become entirely solidified -3-

there occured a third disturbance, probably not so violent as either of the preceeding ones but cer tainly much prolonged, which cracked not only the former intruded igneous masses, but also shattered the surrounding strata for many miles and filled up many of these fissures with material which we now study as dyke rock. As has been stated these dykes are found cutting Syenite both the Essexite, the Nepheline^and the surrounding sediments, and as well traversing one another, which shows that the earlier intrusions had sufficient time to solidify before they were traversed by the later dykes. The majority of these dyke rooks are much more basic than either of the former intrusions, yet it seems quite probable that all three igneous masses have come from the same magma. The sequence of eruptions, which show a dif ferentiation of the magma, is interesting as well as worthy of notice; it affirms the hypothesis made by Ton Richthofen regarding the succession of acid and basic magmas; that is to say, a magma of medium ba$i|ity being intruded first, is succeeded by other intrusions at either extremes. Such is the succession in the oase of Mount

Royal, the medium basic Essexite constituting the -4-

the first intrusion, is followed by an acid variety, seen in the Nepheline Syenite, and constituting the second intrusion; this in turn is followed by dykes more trachytic in character at first and finally by the very basic dykes and sills. The dykes may be regarded as vertical or in clined walls of igneous rock, which are closely as sociated with the rocks of two preceeding eruptions. Besides these vertical dykes, there are several sheets or sills of the same rock material intercalated between the beds of limestone. These dykes and sheets represent the closing stage of volcanic activity in Mount Royal; many of these can be seen at various places about the moun tain, more especially in quarries, such as Mile End Quarries, Corporation Quarry - at Outremont, or Testmount Quarry, as well as on St. Helen's Island, Mount Royal Park, Fletcher's Field and Back River, The writer has made a careful microscopic study of several of these dyke rocks, from the following localities - the bed of the River St. Lawrence between St. Helen's Island and the Yictoria Bridge which dykes are at most timer covered by water; St. Helen's Island; the Reservoir Extension - also covered by water; Mile End Quarries; Maisonneuve; Back "River; and as well the slopes of the mountain. A description has been -5- written about each of these dyke rocks - and these have been catalogued. Specimens of a great many of these dyke rocks have been collected at various times and by several people-; these specimens have been stored in the Petrographical Labratory of McGill University, await ing detailed examination. As a great number of these dyke rocks are now covered up and unavailable, the material in the Petrographical Labratory is the only record which we have of many of these dyke rocks. Besides making a special study of the dyke rocks, the writer, in this paper, has noted the results that have been obtained by others, regarding the Essexite and Nepheline Syenite, and has verified many of these, by means of the microscope. A comparison has been made of these, with similar occurences. Finally, there has been considerable literature written on the rocks of Mount Royal, by various writers, at different times ; these papers have been reviewed and a resume made of the results obtained by the various writers. 11. LITERATURE ON THE SUBJECT.

The earliest literature on Mount Royal and vicinity was that written by Sir Wra. Logan and Dr. Sterry Hunt in the - Geology of Canada - and published in 1863 by the Geological Survey of Canada, in which is given a general description of the different sedimentary strata and the areas occupied by each, as well as a crude description of its igneous intrusives, dykes and inter calated sheets, vhich are classed as trachyte ,phonolite, diorite and dolerite; the last two represent the Essexite mass and certain dykes. This report also contains a considerable number of chemical analysis of certain rocks and more especial ly of certain constituent minerals in the various rocks,- these analyses being determined chiefly by Hunt. Many rocks, more especially the dyke rocks are described by these men, but most of these are so ^ne and often imperfectly described, that it is ver-y dif ficult sometines to recognize the specific rook describ ed; but this must necessarily be expected as the use of the microscope, and modern petrographic methods were unknown to them.

During the next thirty years after the publication of the Geology of Canada - onlyfpapers appeared, dealing in part with Mount Royal. The first of these was R -V-

reference made by Dr. B. J. Harrington on the oo- •f curence of sodalite.natrolite and analcite in cer- ''•> *• tain dyke rocks from the Reservoir on the slope of the mountain;- this appeared in -"Notes on a Few Canadian Minerals and Rocks" published in Annual Report of the Geological Survey of Canada 1874-75 Pg. 302. Another paper by the same writer appeared three years later in the Report 1877-78 pg. 42 G - which was called - On Some of the Diorites of Montreal - in which the writer described certain typical diorite dyke rooks, from the vicinity of Mount Royal, together with an analysis of one of these; he also refers to the age of the eruptive rocks. In 1888 M. A. Lacroix visited Montreal and after returning home to France he published his pamphlet - "Description des Syenites Nephdlinigues de Pouzao (Hautes - PyrSn^es et de Montreal (Canada) et de leurs phenomena de contact." - Bull. Soc. G6ol. de France, 3e s^rie, *ome X^lll, 1890. In this paper Lacroix discusses the rocks com posing Mount Royal and especially the Nepheline Syenite; T* he also describes a similar occurence of Nepheline Syenite at Pouzao - T^jxoneeB Mountains - which locality was later visited by Dr. F. D. Adams in connection with -8- the Eighth International Geological Congress - and which he vividly describes in the - Journal of Geology- Yol. IX pg. 28 - 1901. This paper by Lacroix, with the exception of his study of the Nepheline Syenites of Mount Royal, is largely a compilation of results of previous ^bors by other men. He describes the rooks under three groups - (1) Diabases and Teschenites, which cor respond to our Essexite. (2) porphyrites - largely the dyke rocks. (3) Nepheline Syenite. In the American Journal of Science - 1892, ap peared a paper by Dr. F. D. Adams entitled - " On Melilite Bearing Rook (Alnoite) from St. Anne de- Bellevue, near Montreal - Canada" - in which the writer gives a detailed description of this dyke rock previously unknown in Canada, and refers to Mount Royal as the probable source of the Melilite. In the years between 1893 and the present day several papers have been written in which references or are made to a particular rock of mineral about Mount Royal, but no detailed description of these rocks has been written.

Mention will be made to a few of these which h^ve a more or less direct bearing on the subject of this paper. "BS- ^ -—_

In the Canadian Record of Science, Vol. Till July 1899 appeared a paper by Dr. F. D# Adams on "Studies on the Geology of Montreal and Yioinity," in which he gives a clear and most pleasingly interesting ac count of the history and geology of Mount Royal. In the same volume for Jan. 1901 there appeared a short interesting paper on the question - "Tas Mount Royal an Active Volcanoe?" -by J. S. Buchan, K. C. of Montreal - in this brief essay he endeavours to prove that the evidences to be obtained about the mountain are such as point to the fact that Mount Royal is an uncovered laceelite rather than the remains of an active volcanoe. He states that an isolated patch of sedimentary rock is found near the summit of the mountain which would suggest that the mountain is of laccolitic origin- such evidences as these are easily disproven - since where noticeable the sedimentary strata are seemingly cut off abruptly -by the intrusives; and volcanic breccia is found on St. Helen's Island, while other deposits of breccia about the mountain are now being examined by Dr. Adams and Mr. R. Harvie of HcOill University.

A later paper by Buchan appeared in the July edition 1902 of Canadian Record of Science v0i. vill. entitled - "Some Notes on Mount Royal"-; this paper does not present any new features on the mountain and -10-

is rather a description of the area really included in the term -"Mount Royal." In the report of Dr. Adams and Mr. 0. E. Leroy on - "The Artesian and other Deep Wells on the Island of Montreal"- which appeared in the Annual Report of the Geological Survey of Canada Yol. XlY,- one part is devoted to - "A Sketch of the Geology of Montreal District" pg. 1*7 (o) in which the different geologic formations are discussed and then a general descrip tion and History of Mount Royal is given, and finally the writers show that between the Devonian and Pleist ocene, the geological records are lost and a broad gap exists; during this time the district was mantled by the Great Laurentian Glacier;- after the retreat .of this glacier a subsidence took place, evidence of which is seen in the terraces which surround Mount Royal; these terraces represent successive stages of emer gence of the land from the Pleistocene sea. In a paper on the "Monteregian Hills" which ap peared in the journal of Geology Yol. Y.1. No. 4. April - May 1903 - Dr. Adams refers to Mount Royal in his com parison of the group of hills which he called the- Monteregian Hills - and which represent the best example of a "petrographio province" known in Canada. In 1903 - American Journal of Science vol. XY. Dr. B. J. Harrington published a paper -"Notes on the -11-

Composition of some Canadian Amphiboles" - in which he compares the amphiboles found in Grenville, Ont., in the Essexite of Mount Royal and in the Essexite of Mount Johnson. This paper was soon followed by another - by the same writer - "On the Composition of some Montreal Minerals" - which appeared in the Transactions of the Royal Society of Canada, vol. XI 1905 - 06. In this paper the writer gives the resn?_ts of the Quantitative analysis of several Nepheline Syenite Minerals found in Mount Royal rocks - such minerals as - nepheline; acmite; lepidomelane; natrolite and analcite. A recent paper by F. Becke appeared in - Tschermaks Mineralogisohe und petrographische Mit- teilungen XXY. Band, 6 Heft, 1907 - entitled - H. Tertsoh, Optische Untersuchung von R>mblenden und Titanit ans Essexit von Montreal. In this paper the writer first describes the hornblende which is present in the Essexite of Mount Johnson, he then proceeds to describe fully two varieties of hornblende from the Essexite of Mount Royal. In his research he found that the hornblende individuals were frequently surrounded by a crystal of mica - the cleavage cracks of which, did not cor respond in direction to those in the hornblende. It is also interesting to note that ^rexir frequent ly did he ^ind crystals of apatite enclosed in the -12- hornblende grains - these were arranged - with their elongated.axis parallel to the face of the crystal, so they presented an appearance somewhat similar to a banded structure. Two varieties of hornblende were noted - a brown variety which he has called - Barke^Hs. ite Hornblendej and A green variety - with a lower index refraction - which he believes to belong to the group of riebeokite amphiboles - The latter p^rt of ptvper deals with the Titanite found in the Essexite of Mount Royal - and from the presence of a twinning face and a slight interference figure - the writer constructs the original crystal form. The following map is reproduced from one sur veyed by Mr. 0. E. Leroy.

Ill- PETROGRAPHY OF THE ESSEXITE.

I do not intend to give here or in the next part the results of personal research alone, but largely the results which have been obtained regarding these intrusive rock, by former writers, having verified many of the results for myself, by means of the microscope.

The Essexite or Thexalite represents the first outburst of volcanic activity on Mount Royal and oc cupies about seven-eights of the present mountain. Of the three eruptions represented here - the magma of the first is a medium between an acid and basic variety.

It varies widely in different parts of the in trusion - in some parts of it the iron-magnesian con stituents predominate largely and the result is a basic variety of rock - while in other parts the acid con stituents preponderate largely - giving rise to a rock dull grey in color.

The Essexite very frequently shows a distinct flow structure which is acquired when moving up thru

the neck of the volcanoe, while still in a Bem1-flnia condition - This flow structure is excellently seen ir. the Essexite of Mount Johnson/'15

(l)2)r.F.T). dwn» '^he Montere^ian PillsVournal of (* '. ^ A 0 1903. -14-

In the - Geology of Canada - the writers refer to the igneous rock of the first intrusion of Mount Royal as consiting of "Angitic dolerite,T, holding large crystals of augite in a fine grained, often black, gronndmass, holocrystalline in structure and sometimep passing into a pyroxenite. Then Hunt refers to the Essexite of Mount Johnson which is almost identical with that of Mount Royal, he calls it - diorite, because it contains some grains of olivine. It has been found from the examinations of thin sections under the microscope that the rooks from Rougemont, Montarville and part of Yaraaska Mountains are similar in composition and structure - to those already named. In the paper by Laoroix - mentioned above, the rocks of the first eruption are called Diabases and Teschenites which are the equivalents of our Essexite. Under the microscope the Essexite is holocrystal line and hypidioraorphic in structure, consisting essentially of plagioclase felspar pyroxene, hornblende and a little nepheline; the other minerals found in the Essexite are biotite, olivine,sodalite, apatite, zircon, sphene, magnetite, ilraenite, pyrite, limonite, peridotite and clinochlore as a secondary constituent - sometimes a small amount of orthoclase. Some of these minerals have a tendency to assume -15-

an idioraorphic development. The large hornblende and augite crystals and the elongated plagioclase felspar together form a sort of network about which the other constituents lie in a mingled mass; oftentimes with a tendency to fluxional arrangement. Similar properties are seen in the Essexite of Mount Johnson. PYROXEUE - This mineral is frequently intimately associated with the amphibole, more especially in the coarse-grained varieties of the rock. The pyroxene has been found to be of two varieties - the one is bright Qreen in color; the other has a somewhat violet color. Both these varieties frequently hold minute black inclusions arranged in lineB - and presenting a schiller structure in the interior of the crystal. Other globu lar inclusions are frequently seen in some of these crystals and may be regarded as negative crystals - i.e. an inclusion taking on the form of its host - these globules are sometimes filled with secondary products. Both varieties of pyroxene are slightly pleochroic - and a banded structure within the crystal is common. Lacroix says that the presence of inclusions, arranged in this banded structure is in part responsible for the pleochroism - these inclusions being localized - in bands - particularly in the violet ones. The crystals of ^l7^oxene are often twinned and an hour-glass struc ture is frequently present. -16-

The average extinction angle is about 39 degrees and similar to tho-&e of ahgite, although they frequently vary in different crystal forms. Some of the pyroxene grains polarize in such brilliant colors as to at first suggest olivine, but the straight lines of cleavage and the inclined extinction at once deter mine it to be the monoclinic pyroxene. This bright color is probably due to the high percentage of iron present in it.

AMPEIBOLE - In most varieties of the rock, this mineral is more abundant than the pyroxene, it sometimes shows hypidiomorphic structure but more commonly occurs in highly irregular grains or prisms, frequently accompanying a colorless diopside of which it seems to be a decomposition. It is strongly pleochroic - light brown, medium brown, reddish brown;- the absorption is C > b > L\. Pinacoidnl forms are common and the crystals are frequently twinned on face flOO) giving a maximum extinction angle of 23 degrees. Dark interpositions similar to those in the pyroxene individuals are sometimes found.

As before stated the pyroxene and hornblende are intimately associated and frequently the hornblende is present as a n£C/i about the pyroxene crystals; it would appear as though the hornblende was secondary and formed from the alteration of former - this -17-

association of the pyroxene and hornblende is called - / uralitization. The araphibole in the Essexite of Mount Royal is so pronounced in some of the rocks that a careful ^ macroscopic examination by Dr. B. J. Harringtono^ The specimen of araphibole was taken from the

•i;.A- coarse-grained Essexite in/Protestant Cemetery, about which he writes as follows, nBy reflected light the mineral is black, and brown by transmitter! light - it shows marked absorption* The }mrdness of the mineral is between 5 and 6 - having a specific gravity 3.159 at 17.5 C - and there is a well-defined pris matic cleavage." A similar Araphibole has been found in the Essexite of Mount Johnson, This mineral has been analysed from both localities by Prof. !!. }\ Evans - with the following results:-

0) Kotes on Composition of some Canadian Amphiboles. Amer. Jour. Sci. Vol Xy. 1903. -18-

Mount Royal Mount Johnson Silica 39.23 38.63 titanium dioxide 4.53 5.04 Alumina 14.38 11.97 Ferric oxide 2.92 3.90 Ferrous oxide 8.56 11.52 Manganous oxide 0.65 0.73 Lime 11.70 12.81 Magnesia 13.01 10.20 Soda 3.05 3.14 Potash 0.98 1.49 water 0.36 .33 99.37 99.76

The mineral was separated out by means of a heavy solution - Klein's solution was the one used - the

H20 was determined by direct method. The results obtained by chemical analysis of these two Canadian Amphiboles may be compared with similar ones from other localities - A few of these are as follows:- 1 Horatolende-frora tuffs of Hornblende Basalt- Hartlingen, Hassan. 11 Hornblende-from basaltic tuffs of vesuvine.

Ill " * « t, * Aetna

IV » * " Hoheberg, near Giessen. -19- y Hornblende- from basalt Laacher See. yi " " TTepheline Syenite of "Dungannon; Hastings Co. Ont.

11 "Ml IV v VI Silica 40.15 38.84 40.20 40.14 39.05 34.18 Titanium 5.21 3.34 4.26 4.68 1.53 dioxide Alumina 14.34 13.70 14.62 14.30 15.45 11.52 Ferric oxide 7.fi0 6.63 13.77 7.07 6.39 12.62 Ferrous oxide 4.53 10.90 6.27 7.03 21.98 Manganous 0.21 0.31 0.63 oxide Lime 11. 75 11.70 12.10 12.00 13.75 9.87 Magnesia 13.14 11.41 13.49 11.62 11.28 1.35 Soda 2.31 3.08 3.20 ? op 1.34 3.29 Potash 1.14 2.61 0.70 1 ^n 0.94 2.29 Tater 1.74 0.35 100.37-100.61-101.42 -99.44-100.22- 99.61

From these analyses it will be seen that the araphibole in the essexite of Mount Royal belongs to the class of basaltic hornblendes; it contains less ferric oxide than any of the others mentioned. -20-

FELSPAR - Most of the felspar present in the essexite of Mount Royal is triclinio and it occurs in well- developed forms - almost always excellently twinned according to the albite law but sometimes according to the Carlsbad and pericline laws. The twinning lamellae are often so clearly developed that they can be easily seen in parallel light. The extinction angles along these lamellae vary considerably - usually quite large - about 30 degrees - this would class it as labradorite according to Michel Levy's method. There is such a large amount of plagioclase felspar, twinned according to carlsbad and in *LSS eolation with those according to the albite law that it becomes easy to determine what variety is present; and following Tschermak the felspar ffills in the table under the Composition of Ab, An, - Ab, Ann . The plagioclase felspar grains vary widely in dimensions - the larger ones are usually associated with the ri-vroxer.e and hornblende,while about these and occupying some of the intervening spaces are smaller individuals but most of them equally well twinned. Poecilitic structure is ^rex^ common in the Essexite - such as when augite crystals enclose small individuals of plagioclase equally as well twinned as the larger grains; this frequently occurs - in which case the plagioclase felspar must have -21-

AK/iAA-i crystallized out earlier^or at the same time as the pyroxene. Plagioclase is very often penetrating / crystals of mica, hornblende, or augite - forming a diabase structure. In which case the felspar is in good crystal forms. There is not sufficient dif ference between the grains of different dimensions to say that the rook has a porphyritio structure for all gradations may be found. In some of the large crystals of plagioclase, a strain in the individual may be noticed - such as is common in quartz; this strain has been produced when the minerals were crystallizing out. A zonal structure is common among the felspar individuals which shows that the magma changed from one degree of acidity to another with a higher or lower percentage. In some specimens of Essexite a cross lamination is seen, caused by a twinning of the felspar accord ing to both the albite and pericline laws. Although the plagioclase is, as a rule quite fresh, yet kaolinization is sometimes present - the individual is replaced by minute flakes of musoovite and particles of grains of kaolin - while zeolitlzation is ooramoner among varieties of the rock which contain nepheline, 80dalite„hanyne. An analysis was made by Dr. Sterry Hunt of the felspar from the Mount Royal Essexite which he callsMolerite peridotite". - The result of -22-

this analysis is compared with those of other felspars from several of the Monteregian Fills.- These results are as follows.

I II III IV TT Silica 53.60 62.05 .^3.10 65.15 58.60 Alumina 25.40 £2.60 26.80 20.55 21.60

Ferric oxide 4.60 .75 1.35 - 2.88 Lime 8.62 3.96 11.48 .73 5.40

Magnesia 0.86 - 0.72 — 1.84

Soda - 7.95 4.^4 6.67 5.51

Potash - 1.80 9.71 6.39 3.08 T " ater 0.80 .80 0.60 .50 0.80 93.88 99.91 98.00 99.99 99.71 Specific Gravity 2.659 2.74 .651 2.563

I. Felspar from Essexite Mount Royal - Hunt says,- the silica contains 1.60 p.o. of an insoluble substance in a solution of carbonate of soda - it seems to be titanic acid. II. Felspar from Essexite (diorite) Mount Johnson. Ill " ?f " fdolerite peridotite) Montarville Mountain.

IV. Felspar from TTordraarkite - Shefford Mountain.

V. w n Granitoid trachyte (nordraarkite of Yamaska Mountain.) -23-

It will be seen from these analyses that the felspar in Land III. belongs to the labradorite class; while the other analyses vary - II has the composition of acid aiidesine; and in IVwthe f el spar has the com position of mioroperthite or an isomorphous mixture of albite and orthoclase molecules; while V. is an intermediate variety or an isomorphous mixture of andesine and labradorite.

BIOTITE - This mineral is deep brown in color and strongly pleochroic - C = yellowish, & = deep reddish brown; it frequently occurs as a fringe or border about individuals of iron ore, and is some times very difficult to distinguish from the horn blende, but in polarized light the biotite frequently shows the characteristic pitted surface. The biotite presents an analagons association with the pyroxene and araphibole - all of which tre very often found develop ed about the ilraenite and magnetite. Grains of biotite have been found enclosed in the plates of pyroxene - and this mineral as well as horn blende often possesses poikilitic structure - both frequently enclose individuals of plagioclase.

0^. Dresser J.A. Petrography of shefford Mountain - Araer. Geologist Vol. XXVIII 1901. -24-

OTJIVIBE - This mineral is present in the more acid varieties of^the essexite - which when present usually causes a diminution in the amount of the iron- magnesian constituents int he rook and an equal in crease of light colored constituents. The presence or absence of this mineral has led Lacroix to divide the Essexite into two classes - irhen Olivine is present in the rock he has found that hornblende is almost absent. The Olivine is granular - occuring usually in more or less rounded grains - traversed by cracks along the sides of which is developed the decomposi tion product - Qxeen serpentine. Logan and Hunt mention the occurence of olivine in certain parts of the dolerite (Essexite) mass of Mount Royal, which is developed especially on the north to east end. of the Mountain. This mineral oc curs in semi-transparent amber-colored grains, and the rook in which it occurs - consists of a greyish- white base of granular felspar - which frequently enclose^ crystals of bright black aujite and serai- transparent amber colored olivine. The olivine is frequently enclosed in the biotite and argite, which shows the priority of this mineral in the order of crystallization. -25-

ESPHELIItfE - occurs in a much smaller proportion than the felspar and is largely allotriomorphic in form - filling up the interstices after the felspar had crystallized out. This mineral has a low index of refraction and is feebly doubly refracting - it is sometimes enclosed within the felspar - very frequently the nepheline is highly altered to a fibrous mineral - which has a strong double refraction, with straight extinction, and is probably musoovite and kaolin - it is also found sometimes altered to certain zeolitio material and spherulites of clinochlore. The nepheline seldon shows cleavage,but when it does - it gives straight extinction.

SODALITE - is quite subordinate to the nepheline and fills up small spaces between the other mineral con stituents - being the latest mineral to crystallize out. It occurs in short rhombododecahedron and sometimes enclosed numerous ferruginous grains, by which it may be distinguished from nepheline - it is also isotropic. The presence or absence of nepheline or sodalite this rook, causes Lacroix to make a further two-fold division i. e. Diabases and Tesohenites, - the latter containing nepheline and sodalite and has two periods of crystallization represented ; tie first period —26 — represents the simultaneous crystallization of the araphibole and twinned felspar; - the second period includes the nepheline and sodalite, so that the word "teschenite" is applied by some writers - to rocks having a simultaneous occurence of a triclinic felspar with some nepheline and sodalite. Fouque and Le>y have thus employed this name, but by Prof. Rosenbusch such a rook is called a - Theralite. The word Teschenite was first applied to the rooks of Mount Royal by Dr. B. J. Harrington - to include a black dyke in the Reservoir Extension which contained crystals of hornblende and mica as well as some analoirae (?), pyroxene being absent and psendomorphous olivine present; he gave this dyke rook the nime -. Teschenite as the presence of analoite is characteristic of the Teschenites from Teschen.

APATITE - There is nn abundance of this mineral present, and as it was one of the first constituents to crystallize out, it is found in good crystal forms- oconring sometimes as good hexagonal prisms and not infrequently terminated by a double pyramid, it is found about the iron-magnesian constituents most frequently. The size of the Apatite crystals vary - but many of them attain a length of .5 ram.

Ferruginous inclusions are sometimes found within the -27-

apatite individuals.

SPHEJJE - This mineral is not always found in the Essexite - but in some parts of the rock it is abundant, sometimes as crystal individuals or as large plates frequently ocouring in well defined wedge- shaped crystals,- many of which are wholly or in part changed to ilmenite - which in turn may also be altered on the borders to a greyish-brown mineral transparent by reflected light - i.e. leixooxene. The ilmenite is sometimes associated with the pyrite, which is not abundant and which is sometimes in part changed to liraonite - when this alteration takes place the other minerals in the rook are usually more or less stained with it.

2IRC0H - this mineral is rare but when present it is usually euhedral - being one of the first minerals to crystallize out. It has a high index of refraction - polarizes in bright colors and generally occurs in Short stout prism-forms.

MAGNETITE - is abundant - usually allotrioraorphio sometimes in quite large irregular grains - occurs sometimes as cubes and is frequently enclosed in the iron-raagnesian constituents some of the larger masses being entirely surrounded by biotite or brown horn blende. -28-

It is difficult to distinguish the magnetite from ilmenite - probably due to the former being highly titaniferous. STRUCTURE AHD ORDER OF CRYSTALLIZATION - In structure the Essexite is hypidiomorphic, present ing the normal order of crystallization. Lacroix believes that there were two periods of consolidation, the former being "intratellnric"- to this one belongs those minerals which present ophitic structure - such as pyroxene - felspar and probably some of the hornblende - these minerals have crystallized out before the magma was poured out- but these minerals continued to grow after the other constituents crystallized out later. The basic accessories were the first to orvstal- lize, these were followed by the iron-raagnesian es sential constituents together with some felspar - the last stage in the consolidation being represented by the nepheline and sodalite minerals. Lacroix states that the appearance of araphibole represents the beginning of the second period of consolidation - which period may also be divided into two phases - the former includes the simul taneous crystallization of the felspar plates - the latter includes the crystallization of nepheline and sodalite. According to the method used by

Lacroix - the Essexite would have a formulae as follows. Tc» - (F 1.2.5. G.7) I 0. P4 A3 H ) T2 Si E. where fTtt) structure; f F )= basic accessories (magnetite; ilmenite; apatite; zircon; sphene) (0)

olivine; (P4) = augite; (A3) = araphibole; (M) = mica;-

fT2) = labrador felspar; (sA =, sodalite and (u) = nepheline.

As has been seen the rock agrees with the characters of the Essexite group - having the closest resemblance to the essexite of the other Monteregian Hills - such as Mount Johnson yxi and Shefford Mountain {Z). The Essexite of Yamaska mountain (Z) also resembles this type - This rock is also analagons to the Essexite of Mr. j. F. Sears - at Salem, Mass. it was from this locality that the rock got its name. it occurs associated with the nepheline syenite in that locality and is an augite - olivine _ diorite allied to the theralites.

0) Adams Dr. F.D. - "Monteregian Hills" - Journal of

Geology v0l. VT 1903 pg. 258. (2,)Dresser J.A. - "Petrography of Shefford Mtn. Araer.

Geologist Vol. XXVTJT 1901, pg. 205.

0)Young O.A. _ summary Rep. 0eol. sur. Can. 1904. -30-

This rock is described by Washington in the Journal of Geology - 1890 pg. 57 - In Amer. Rep. U. S. G. S XVII. is described a similar essexite from Rosita Hills - Colorad^ by Cross. Prof. Rosenbusch describes similar rocks from Rangstock-Boheraia. A comparatively similar rock - rich in nepheline occurs in Crazy Tlountains- (Elbow C re ek) Mont ana. Brogger has found a rock of the Essexite group in the Christiana basin, which holds a titaniferous anjite - hornblende bring less abundant, and to which the Essexite of Mount RoyfO. is comparable. IV. PETROGRAPHY OF THE KEPHELINE SYEHITE.

The Hepheline Syenite represents the second eruption of Mount Royal - This eruption must have taken place sometime after the former magma had solidified, and was undoubtedly accompanied by violent earth move ments which shattered the essexite and adjoining Trenton limestone and it was up thru this shattered zone that the molten magma came. This intrusion was much less extensive than the first and as a result must have had a much shorter activity. It forms a narrow band on the northwest flank, of the mountain, nowhere exceeding 400 yards in width. This type of rock is a more acid phase of -the original magma and consists of a - nepheline-syenite, much lighter in color but which is closely related in origin to the first eruption* The normal type of nepheline syenite is a pale-grey rook with granite structure, frequently cut by pegraatitic veins - very coarsely crystalline, consisting of the following macroscopic minerals - white felspar; t)lue sodalite; rose colored nepheline; green aegerine, violet

^luorite; "honey yellow" sphalerite and galena. The nepheline syenite of Mount Royal has been studied carefully and Lacroix has reported to have found in it twenty-one different minerals - but this list is now supplemented by several other minerals - and the list has now grown to at least thirty-one minerals. The essential constituents of the Repheline Syenite are:- Orthoclase felspar, nepheline, hornblende, -pyroxene and mica - and as accessory constituents:- Albite, anorthoclase, raieroeline, aegirine (acmlte), nepheline. sodalite, apatite, sphene, zircon, garnet, steenstrupine (?) flnorite, nosean, astrophyllite, ' lepidomelane, (mosandrite, allanite, aenigmatite)? sphalerite, galena, native arsenic. TJ> [* As secondary constituents:- musoovite, cancranite, analoite, na+rollte, hydronephelite, calclte and other zeolitic material. All of these minerals will not be found in a single specimen - but are found throughout the mass. -FELSPAR- ORTHOCLASE - The felspar is largely a normal orthoclase occnring in crystals of various dimensions "4 frequently lath-shaped, and broad, often turbid in appearance and usually shows two good cleavages, parallel to M and P respectively. In the nepheline syenite the orthoclase is most frequently intimately associated with different lime- soda felspars- giving rise to mlcroperthite, which is and intergrowth of orthoclase and albite.

MICROCLINE - is found in small irregular grains but i 8 -33- seldom present; the same is true of the soda- mi crocline^ anorthoclase. The felspar is frequently more or less highly altered, so that it is 'sometimes difficult to deter mine whether orthoclase in independent crystals are present or whether it is mlcroperthite, but under a high lens in the microscope - the distinction can generally be made - as the several felspars have a slightly different birefringence. The orthoclase is frequently found thinned according to the Carlsbad law; many of the smaller crystals seem to be composed of an intergrowth of two varieties. ..L3ITE - is not abundant in the normal rock, but a mineral, having polysynthetic twinning can frequently be seen among the smaller grains. In the pegraatitic variety of thr nepheline syenite the lime-felspar is somewhat abundant - in narrow twinned crystals, sometimes the twinned lame! lae can only be recognized according to the albite law, under a high power; in some cases these lamellae are irregular and broken. The extinction angle was measured on several twinning lines and was found to be about 5 degrees on face (001); other maximum extinction angles were 20 degrees. The albite may occur as a single in dividual - or as a mixture of two varieties. w-L* jr

X(M^i O0y> » CJS$X. -34-

Microcline is sometimes enclosed within albite crystals. ANORTHOOLASE - (soda-mierooline or potash oligoclase) occurs in large grey plates and has an extinction angle from zero to .13 degrees; the twin lamellae can often be seen in these grains, raacros- copically - Another accessory felspar which is com mon in this rock near the contact zone is oligoclase, it occurs in very finely twinned crystals with paral- lei extinction. In order to find out the relative amounts of each felspar variety present, it would be necessary to make a series of careful separations of the rock powder, hy heavy solutions. F0RHBLEI5DE - This mineral predominates large ly in the rock - very frequently in hypidioraorphic forms - some of those forms which have been noted are (110), (100), (001) and 111). These crystals vary widely in dimensions - some elongated prisms being 5 rara in length. This mineral belongs to the brown varleth of hornblende - it is strongly pleochroio - dark brown - brown and yellowish brown-; the absorp tion is 1b > 0 > (X • Upon examining the rock un

the inner portion is brownish in color;- frequent ly the green color extends thru the whole crystal. This phemmifliwis also seen in some of the pyroxene grains and is supposed to be due to a change in the oxidation in the iron-contents of the mineral. It has been noticed that crystals of hornblende have been broken up and again cemented together, enclosing within themselves crystals of apatite, sphene, mag netite and frequently minute black interpositions, which gives it an appearance not unlike the dial- lage structure among the pyroxennes. The hornblende crystallized out early in the order of consolida tion.

PYROXENE - This mineral can not always be regarded as an essential constituent of the rock - and is found raOst abundant near the contact of the nepheline syenite with Trenton limestone. It occurs frequent ly in good crystals - the forms represented are (110) (010) (100). The mineral also occurs in flat grains or plates which are traversed by cracks, and in these cracks biotite r^nci hornblende are frequently found. The color of the mineral varies from pale violet

to grass Q^^^ - the former ve,riety being sometimes slightly pleochroic - Both shades of color may be found in the same crystal - the one grading into the other as was seen to be the case with the hornblende,- -36-

the green variety forming the outer rim. The maximum extinction angle in this mineral is between 40 and 45 degrees, so that it is largely an angite. In examining the nepheline syenite from Mount Royal, Prof. Rosenbusoh states that there is a remarkable variety of pzrroxene present in this rock - to which a new name might well be given if a portion of the mineral was separated and analysed; he has found it to be a variety rich in titanium dioxide as shown by the strong dispersion of the bisectrices as follows:- a= extinction; b= brown; C= blue.

AEGIRIHE - (ACIIITE). Another variety of pyroxene occurs in parts of the nepheline syenite and in varying amounts. They are usually present in needle-shaped fibres grouped in bunches; those oc- cubing thus are usually Qreen in color - and are pl'eochroic. Another variety is present which Is brownish yellow in color and very slightly pleochroic- this variety is known as aoraite; sometimes both varieties may be found within the same individual as was the case in the augite and hornblende. The extinction angle in both varieties is about 5 degrees and a cleavage is very good on the face (110). The larger grain; of this mineral -37-

sometimes contain inclusions of reddish brown biotite. This mineral, is found more frequently in the pegmatoid rook and in large crystals. A T very similar ooonrenoe of aegirine in the nepheline Syenite of Magnet Cove is described by J. F. Williams (1).

BIOTITE - This mineral is not very abundant in the rook and is one of the latest of the iron- raagnesian constituents to have crystallized out - the garnet being later.- It is even later than some of the felspar which it encloses frequently. The color of this mineral varies;- when it is in timately associated with the hornblende it is. green in color, and when associated with the aegirine, acraite and astrophyllite, it is yellowish. In both cases it is strongly pleoohroio. Zircon and apatite my be found as inclusions in the biotite. It has been noticed by Lacroix that •S the enclosed zircon often have a pleoohroio border about them - Muscovite occurs as a secondary pro duct, usually in thin small flakes.

(1) "The Igneous Rocks of Arkansas" - Araer. Rep. Geol. snr. Arkansas, Vol. II - 1890. -38-

1TEPHELINE - This mineral is very abundant in all parts of the rock and can be frequently recognized in the hand specimen. It usually occurs in large plates, some of which are 2 mm. in width and is some times found filling up intervening spaces between the felspar - Although it usually occurs in allotriomorphic individuals, yet the forms (1010) and (0001) have been noticed. A well developed cleav&ge is sometimes seen, but as this mineral is somewhat readily decomposed a very small portion of it will be found fresh, rfhen a basal section of nepheline can be found the mineral proves to be uniaxial and negative, and gives a black cross as an interference figure in convergent light. - The alteration products of nepheline are several- its decomposition to musoovite is probably the com monest; this alteration when complete is known as girseckite, but it has not yet been found in the Fepheline Syenite of Mount Royal. This decomposition is found in the Nepheline Syenite of Pouzao -Pyrenees Mountains. This mineral is found to be gradually altered to I Cancr^nite - this process of alteration can be traced in the rock; - the cancr.-nlte penetrates the finest fissures of the nepheline and continues to corrode thf '1x host until the whole is changed.K ' (1) Lacroix M.A .-Description of the Nepheline Syenites of Montreal-Canada. Bullae g<*ol.France ($\ XTTT 1890 !*o 7 PL* XI . fig. 1. ' -39-

The orientation of the decomposition may or may not be the same as that of the nepheline which it is replacing. When fresh this mineral is colorless - has a fair ly high double refraction and generally occurs free from inclusions. The nepheline is also found altered into zeolitic material, such as ranlte (hydronephelite); analoite and natrolite.These last two minerals are probably the com monest and occur as secondary product in cavities and veins. The analoite is found in white to Qrey trapezo id hedron - nearly a quarter of an inch in diameter. A portion of this alteration product (analoite) was examined by Dr. B. J. Harrington - he found it to be vitreous and sub-translucent - having a hardness of 5. and specific gravity 2.22. The following analysis was obtained from the analoite (1). Silica 54.83 Alumina 24.20 Lime 0.08 Soda* 12.01 Water 8.50 99.62

(1) Harrington B. J. - "Composition of some Montreal Minerals." Trans. Roy. Soc. Can. Vol. XI Sect Til. -40-

Th e natrolite oocnring in the nepheline syenite of Corporation Quarry was also examined and analysed hy Dr. B. J. Harrington,- a portion was freed from the rock. It occured in white, translucent and vitreous prisms,- had a hardness of 5 and specific gravity 2.234 - The results from a chemical analysis of the same are as follows :- Silica 47.09 Alumina 26.99 Ferric oxide trace Lime t rac e Soda 16.46 Potash 0.01 ^ater 9.80 100.35

Some fresh grai ns of nepheline were freed from the other admixed minerals of the nepheline syenite from the Corporation Quarry - and a quantitative analysis

i J. / was made of it by Dr. B. J. Harrington. With the analysis of this mineral from Montreal are given similar ones from other localities for comparison. These are as follows:- (2) (ibid) pg. 28.

(1) "Comp. of some Montreal Minerals"- Trans.Roy. Soc. Can. Vol. XI pg. 25. -41-

(2) I II III iy y Silica 44.98 43.51 45.10 43.39 41.87 Alumina 32.65 33.78 33.28 32.28 33.94

Ferric Oxide 0.72 0.15 - 0.92 0.70

Lime trace 0.16 - 0.70 0.47 Magnesia

Soda 16.08 16.94 16.36 16.52 15.03 Potash 4.54 5.40 5.05 5.62 6.68

Tater 0.97 0.40 0.70 _ 0.94 99.95 100.34 100.49 99.43 99.63

I. Nepheline - from Nepheline Syenite -(Forsyth) Corporation Quarry - Montreal- Canada. II. Nepheline - from Nepheline Syenite Dungannon, Ont Amer. Jour. Sci. July 1894.

III. Nepheline - from FredriksvTim, Norway - zE G.Ges 1876.

IV.| Nepheline - from Sodalite Syenite - Juliane - ) haab district, South Greenland. v. ) Same as IV.

(2) Lorenzen Joh. - Min. Mag No. 23 Nov. 1882 vol. V. -42-

SODALITE and NOSEAN - Both these minerals are present in the rock, but are rather difficult minerals to distinguish apart, as both are isotropic and there is a large proportion of isotropic material present in this rock, but-the nosean which is abundant may be dis tinguished by the crystal outline which it presents and also by the inclusions 'Ahich it contains. Lacroix believed that all this isotropic material was sodalite and described it as such. This isotropic material oc curs juite frequently in idiomorphie crystals - and. sometimes in broad flat individuals, some of these crystals are .F m.ra in diameter. The black inclusions are particularly abundant in those individuals of nosean which have the best crystal forms - and are frequently segregated towards the centre - leaving an almost colorless outer margin. The inclu sions which are abundant often seem to have Hrra.nQed themselves in lines parallel to the faces of the crystal while in other crystals - these inclusions appear in radial lines. The grains of nosean are found to some times enclose grains of aegirine and acmite. The al teration products are similar to those foiind in nepheline - the flakes of musoovite are sometimes ac companied by grains of calcite. Lacroix states that the fine plates of musoovite are sometimes nrranc;ed. parallel to the crystal faces - probably due to the de composition products following the oleavage of the -43-

isotropic mineral and as well the direction of crystallization of the calcite which accompanies the mica. LEPIDOMELANE - A lithia mica has been found, particularly in the pegraatitic segragations in the nepheline syenite. This mineral is found in large crystals or plates some of which measure a quarter of an inch in width. This is one of the minerals examined and analysed by Dr. Harrington (1) - The mineral is black in incident light, green in transmitted light - with a vitreous or adamantine lustre - It has a small optic axial angle - hardness is 3 and specific gravity 3. 269 - The result of the analyses is as follows:- Silica 32.96 Titanium Dioxide 2.80 Alumina 10.34 Ferric Oxide 8.85 u/ Ferrous " 27.19 Manganous oxide 2.79 Lirae 0.64 Magnesia 0.73 Soda 0.98 Potash 7.75 Bithia 0.03 Fl^lirine none Water 4.36

99.42

(I) " composition of Borae Montreal Minerals"- pg. 27. -44-

APATITE - is not very abundant but when present- it is in -slender, short prisms, often enclosed in the sphene and sometimes holding mobile bubbles.

SPHENE - This mineral is very abundant in these rocks, especially in those rich in iron-magnesian con stituents. The individuals vary widely in dimensions occuring usually in wedge-shaped forms - It sometimes encloses grains of magnetite and apatite as well as rutile in little long needles. The sphene is intimately associated with the amphibole - and is sometimes en closed in the latter. Prof. Rosenbusch in describing this mineral from Montreal writes - that it shows a remarkable decomposition into calcite - with little needles of rutile. The s^ae decomposition, with the addition of ferric oxide, occurs beautifully in some of the Brazilian elaeolite syenites. ™he altered material has a grey turbid appearance like leucoxene - which it cannot be - as this is sphene*

ZIRCON - This mineral is not so abundant as the sphene - some crystals have been found which were .25 ram.in diameter - and frequently occur In idiomorphic crystals as octagonal prisms, which in cross section (001) give good octagonal forms. A cleavage has been found in some of these crystals - parallel to the prism flOO) - It is frequently enclosed in the other minerals. -45-

FLUORITE - In this rock it is colorless to pale violet and purple - it has crystallized out later than the felspar and earlier than the nepheline - it some times shows cleavage planes and is not acted upon by polarized light - F3.uid pores still mobile have been seen in this mineral. ASTROPEYLLITE - This mineral has been found in the coarser varieties of the nepheline syenite; it oc curs in irregular grains and is strongly pleochroic - the absorption is pale yellow to deep yellow and is transverse to the elongated axis - as is the ease in tourmaline, This mineral is usually striated, and presents other properties characteristic of the mineral. Cubes of magnetite are frequently found embedded in the borders of the astrophyllite individuals. GARNET - There is frequently a large proportion of a reddish brown mineral present - but it is not equally distributed thru the rock. This mineral has a very high index of refraction and is quite isotropic between crossed nicols. The grains sometimes attain large dimensions and frequently assume fantastic formsT Laths of felspar are occasionally found penetrating an irregular mass of the mineral. It occurs more abundantly near the zone of contaot and may even be found to enclose crystals of perowskite;- a similar association has been found at Magnet Cove- Arkansas. -46-

This peculiar garnet-like mineral has been called Melanite-garnet by Lacroix - but Prof. Rosenbusch thinks that it is probably not a garnet but the rare mineral - Steenstrupine - which has been found - occurring in the Sodalite - syenite of Tunugdliarfik and Kangerdluarsuk in Juliane-haab district,- South Greenland. (1) This mineral is a mixture of several of the rare elements such as thorium, tantalum, cerium, didymium and. others. Prof. Rosenbusch states that all minerals containing thorium are isotropic whether the} belong to hexagonal, raonoclinic or triclinic systems.

Besides these minerals already mentioned - Lacroix was convinced that he had found other rare minerals in this rock - He found a allotriomorphic mineral in association with fluorlte and aegirite which is analagous to the mosandrite found in the sodalite-syenite of the Juliane-haab district - south Greenland. Another mineral occurs in small irregular grains brown in color - biaxial and slightly pleoohroio, which is similar in many respects to allanite.- He records a third rare mineral brown in color and strongly pleoohroio - which resembles the mineral - aenigmatite.

These rare minerals are commonly found in the con tact zone.-

(1) Described by Joh. Lorenzen - Min. Mag Vol.y. pg.49. -47-

Sphalerite, galena and Native Arsenic (1) have been recently found in this contact zone of the nepheline syenite.

STRUCTURE - The structure of the nepheline syenite is holocrystalline and hypidiomorphic - but varies widely in structure from a pegraatoid - to a finely crystalline variety. The normal rock is a medium type - granular in structure - some varieties being more coarsely crystal line than others - and which frequently contains mac roscopic crystals of hornblende, felspar and nepheline. In the pegmatitio veins - felspar is the principal constituent - occuring in large plates, round which and filling up the intervening spaces is the nepheline", sodalite, aegirite and fluorine minerals. A third type of structure is that seen in the con tact zone;- in some places the normal structure is re tained on the contact, while in others the alteration has gone on- ^or several feet - and in this zone all variations in the structure of the rook are ^ound,- frora the granitic or normal type to the trachytic or "micro-syenite" type of structure. From the main mass of nepheline syenite, branches are sent off into the surrounding rock - which are usually compact in structure.

'D Evans H. K. - ••native Ar8enl0 fron Montreal" Araer jour. soi. pels. 1903. -48-

Some of these branches present peculiar alternating bands of granitic and trftchytic rocks. The width of the zone of alteration in the lime stone varies greatly - the limestone is reorystallized and several new minerals added to it - such minerals as diopside, garnet, perowskite, wollastomite, sphene, zircon, cancranite etc. The igneous rock and the limestone are so thorough ly fused together that it is sometimes difficult and even impossible to define any sharp line of contact between these two masses of rook. A contact is frequently marked by a narrow band of cancranite or it may be a zone of felspar, where this mineral is present.

The order of crystallization seems to be the normal - the basic accessories have been the first to crystallize; these were followed by the hornblende, pyroxene and part of the felspar and nepheline. A later separation crystallized o\it the sodalite, nepheline, nosean and felspar,- the garnet-like mineral being one of the last to separate out - and as well probably some of the rarer minerals closed the process of crystallization. The name - phonolite - has been applied, by some writers to a variety of nepheline syenite which con sists essentially of orthoclase, nepheline, aegirite, -49-

sphene and garnet - and which really represents a dif ferentiation of the nepheline syenite magma with an increase in alkalies. The variety of rock is comparable with the-similar phonolites which accompany the nepheline syenite of Sierre de Tuigna, in Brazil and of Rio de Janiero - with but one exception - the orthoclase in the phonolite of Mount Royal occurs in broad plates whereas in the other localities it occurs in elongated prisms or microlites. Comp*irison with other similar localities ;- The nepheline syenite of Ponzao- Pyrenees Moun tains is probably the best comparative example - for in both localities the nepheline syenite has been preceeded and followed by more basic intrusives - The rock of Mount Royal,is of Silurian age whereas the nepheline syenite of Ponzao belongs to the Cretaceous period; anothe <* difference between these two localities may be seen in the extent of contact metamorphisra -, the contact zone Is much more extensive in the nepheline syenite of Pouzac than on Mount Royal - in some places it is seen for a distance of 400 metres. The nepheline syenite of sierra de Monohique (1) in Portugal is a typical rock and is of the foyaite

(1) Shelbner - Q. J. 0. S. Vol. VVYV. 1879 pg.42-47. -50- variety - consisting essentially of orthoclase and nepheline. The nepheline syenite of Sierra de Pocos de Caldas - Brazil is another similar ocetirence;- in this locality both foyaite and phonolite varieties are represented, the former never occurs in dykes and. it is believed that both masses are but different phases of the same magma. Several other similar localities may be cited -in the elaeolite syenite of Saline Co., Region (2) Arkansas - there are three varieties - a porphyritic, a granular and a pegraatitic variety. At magnet Cove (3) - Arkansas, the rook is an elaeolite-mica-syenite - v.hile at Potash Sulphur Springs (4), the rook is an elaeolite-sodalite-syenite. Another similar occurence may be noticed - which is probably the ne*trest approach to the nepheline syenite of Mount Royal,- i.e. the elaeolite syenite of Serra de Tingua (l)-3razil - In this locality as at Mount Royal the rocks vary in structure - some are

(2) Williams J. F. - Igneous Rocks of Arkansas - Rep. Geol. Sur. of Arkansas - Vol. n 1890. (3) ibid PQ. 208 (4) ibid pg. 349

(1) Graeff Franz F. - Untersuchung vol Elaeolithsyen.iten von der Serra de Tingua, Brasilien. Neus Jahrbuch 1887, Band II. -51-

holocrystalline - and finely or coarsely granular, while others are porphyritic in structure - resembling those rocks, called phonolites by some writers, which are found in certain parts of Mount Royal as stated above.

It must here be noted that the essexite and nepheline syenite of Mount Royal represent two con- sanguinous magmas closely associated with one another and both rich in alkalies. These two magmas are so related to one another, that wherever the one may be found - the other is accompanying it or in the close proximity of it. This has been found to be the case in all localities where such a magraa occurs; in all cases it may not be essexite ajid nepheline - of iden- tioal compositions, but it will always be some variety of this type - such is the case in Mount Johnson and Shefford Mountain - in both localities - the essexite is associated with pulaskite - which is a variety of nepheline syenite - in which the nepheline mineral occurs only as an accessory constituent. V. - A PSTROGRAPHIOAL STUDY OF THE DYXE ROOKS OF MOUNT ROYAL .

we have already seen the results of the first two periods of eruption on Mount Royal - &n& tlhere now remains to be noticed the result of the third and final disturbance of this ancient volcanoe. The final disturbance is marked by the numerous narrow dykes which traverse the main mass of the mountain as well as its slopes and the sedimentary strate surrounding it. These dykes radiate from the main mass in all directions and frequently intersect one another. There are also a number of sheets or sills, belong ing to the same magraa which are intercalated between the beds of limestone. The dykes and sills represent the closing stage of volcanic activity on Mount Royal. The disturbances may not have been so violent as in the two previous periods of eruption, but they must have had. a much longer duration, for there are such a great number of these vertical walls and horizontal floors- which were not all forced up at the same time - but which form several series of various ages;- this may be seen in the fact that these dykes intersect one another frequently - the former ones having become thoroughly cooled before the later ones cut thru them. -53-

From a careful study of these intersections, several series of dykes of different ages may be worked out. There have been specimens collected from over one hundred different dyke rocks about Mount Royal; these are stored in the Petrographical Laboratory to await A detailed examination. Doubtless these dykes of which we now have specimens may represent only a small number of those actually existing in this locality. The writer has made a careful microscopic study of about sixty-five different dyke rocks of which the locality and general description of the dyke had been noted by those who collected the specimens. A microscopic description of each of these rocks has been record in catalogue form; this catalogue is o to be found in the Petrographical Labratory of McGill A University. The structure an^ composition of these dyke rocks vary widely - ^rora a very fine-grained granular rock, to one coarse in grain and even pegmatitic; in com position they vary from an acid and almost white trachytic variety - seen in the bostonlte type -, to a black, very basic holocrystalline variety - seen in the pyroxenite (dolerite) type. In very few localities does Dne find such an ex tensive variety of dyke rooks; from those very rich in -54-

alkalies to those containing a low silica percentage - and very rich in ferro-magnesian silicates. These dykes vary in width, from a mere seam of a few inches to one of four or six feet in width. mhe narrow ones are usually very finely crystalline as they have cooled quickly; while others are banded - the ex terior being fine grained and the interior porphyritic in character;- as is seen in this figure.-

The dyke rocks of Mount Royal form a group of rocks ioh are consanguineous to the presence of proceeded Alkali - rich magmas such as essexite and nepheline syenite- The following types of dyke rocks have been found on and about Mount Royal:- bostonite, solvsbergite, tingualte, (nepheline-aplite), camptonlte, fourchite, raonohiqnite and /Incite. These types represent a peculiar group of rocks which are always found as sociated with Alkali-rich magmas, in all localities. -cording to Rosenbusch the dyke rocks in this vicinity may be divided into two distinct groups; the -55-

first of these he calls lemprophyres - these Include the more basic variety and those which contain a medium or low percentage of silica and which are rich in iron-magnesian constituents, and holding a con siderable quantity of alkalies. This group includes the camptonltes, fourchites, monchiquites and Alnoites. In the -Geology of Canada- these dyke rocks are call ed diabases, pyroxenites and dolerites. Lacroix (1) has called them - porphyrites and nephelinites, and Harrington has used the terms - diorites and dolerites to include these dyke rooks. The other group include the bostonites and tinguaites, which by previous writers were spoken of as- traohytes. Prof. Rosenbusch has defined these various types of dyke rocks as follows:- BOSTONITES (2) - belong to the foyaite group, and are always light in color, sometimes white, crey or greenish-grey. They are trachytic in character and frequently show a fluidal arrangement of the mineral constituents. The rock usually presents a panidio- raorphic structure and sometimes holds tabular felspar crystals which have a tendency to assume a porphyritic development. This type of rock consists essentiality

(1) Lacroix - Bull. Soo. G6ol. de France 3e s^rie Torae XVIII., 1890 (2) Massige Gesteine - 467. -56-

of crystals of a potash-felspar - with an entire absence of the ferro-magnesian silicates. The groundmass con sists of numerous felspar rods moulded together, which sometimes show trachytic character. The name Bostonite was first applied to dyke rock found near Boston at Marblehead, Mass. (3). Rosenbusch has given the name - Tinguaite- (1) to certain dyke rocks which are holocrystalline and panidiomorphio, consisting essentially of orthoclase, felspar sometimes in phenocrysts but often as fine lath- shaped crystals, and needle-like fibres of ^reen aegirine. These minerals are surrounded by a holo crystalline groundmass consisting of nepheline, ortho clase, aegirine, and occasionally quartz or lenoite. He divides his series into two groups,- orthoclase rocks with aegirine needles with quartz and those with out quartz,- the former group he calls quartz-tinguaites or grorudite which may hold arfedsonite crystals in place of aegirine needles. The latter group-without quartz- is further divided according to the presence or absence of nepheline. Then that mineral is present, the rock is called a nepheline-tinguaite- or with the addition of leucite it becomes a leucite-tinguaite.

(3) Washington H. S. Journal of Geology 1899, VTT. pg. 293. (1) Massige Gesteine - p. 477. -57-

When nepheline is absent he calls the rock a -Solvsbergite- (2) which is characterized by the presence of tabular felspar. Then the rock has orhtoclase and nepheline with out aegirine needles it is called a - nepheline-aplite. The following table shows the division of the Tinguaite series, according to Rosenbusch:-

TINGUAITE SERIES

ORT:-:CCLA3E - POCKS WITH AEGI?.I:;E I 1 With Quartz Without Quartz i r i 1 Without nepheline with nep- Quartz-tinguarite i helene or ' leucite or Solvsbergite i Grorudite ' Nepheline-tingua! I leucite tinguaite

This n*me was first given to certain dyke rocks from Serra de Tingua - Brazil which are intimately as sociated with the Nepheline Syenite in that locality.

(2) Washington F. S. - Solvsbergite and Tinguaite from Essex Co. Mass. U. S. Geol. ?>nr. 1898., vi - 176. -58«

CAMPTONITE - is the name given by Rosenbusch to certain dyke rocks which are rather low in percentage of silica and high in Iron raagnesian silicates. All these rocks have either a panidiomorphic or porphyritic struc ture,- they frequently enclose macroscopic black cry stals of hornblende and augite. This type consists essentic-.lly of hornblende, pyroxene, biotite, and a small quantity of plagioclase felspar;- these minerals are held together by a finely crystalline groundmass which may also contain varying proportions of nepheline and olivine. This rock type is intimately associated with the nepheline syenite or foyaite find theral ite magmas. 1' Rosenbusch based the name of this rock type on a dyke rock from Carapton IT. H. which has been (2) described by Hawes. The name -Monohiquite-* has been applied by Rosenbusch to a group of dyke rock, of the foyaite type, from Serra de Monohiqne - Portugal - which are basaltic in character and always intimately associated with elaeolite-syenite' ' - It is hypocrystalline in

(1) Rosenbusch H. - Massige Gesteine - 1896 - pQ. 535 (2) Hawes G. W. - Araer. Jour. Soi. Feb. 1879 ryu 147-151. (3) Van Werveke - N. J. 1880 n 177-186.

(4) Rosenbusch H. - Ueber Monchiqnite eln Camptonitisches Ganggesteine aus der Gefolgschaft der Elaeolith Syenite,- Mineral, und petrog^.phie. Mittheil, Band XI 1890 pg. 446. -59- structure and frequently consists of a porphyritic combination of rounded grains of olivine, pyroxene, biotite - rich in titanite and a brown variety of araphibole - barkevite. The minerals are frequently found in idioraorphic crystals - and o,re embedded in a x •/ glassy base which may enclose irregular grains of any of these minerals and as well minute laths of plagio clase felsnar and even nepheline; some of the cavities may be filled with natrolite and analoite. Rosenbusch applies the name -Fourchite- to an oliv?ne- free amphlbole, rich in angit. it was first used by Williams in describing a rock from Fourche Mountain, .Arkansas.

It has been found that the dyke rocks of Mount Royal corae under this group which has Just been defined. In.the following pages of this paper will be given a description of the various rock types which have been examined from the various localities about the mountain. Certain dy^e rocks have been examined microscopical ly from the following local1ties:- (a) The bed of the River St. Lawrence - opposite Point St. Charles - on approach to victoria Bridge. (b) The south slope of Mount ^oval.

(1) '"illiams J. F, - Igneous Rocks of .'rkansas - Am.

Hep. Geol. sur. Ark. 1890. v0l. II PC- 107. 0r Rosenbusch H. Massige Gesteine - 543. -60-

(a) Bed of River St. Lawrence, on Approach to victoria Bridge, Opposite Point St.Charles

Specimens of ten dyke rooks were collected by Dr. Adams on Nov. 6th, 1895 from this locality. On this date the water was sufficiently low to expose a por tion of the river bed; being one foot lower than previous ly recorded. The area extended a few hundred yards from the west end of Victoria Bridge and eastward as far as the Guard Pier was then built. Dr Adams found that within this area the river is floored with Utica Shale which is cut up by a number of dykes - numerous in some parts of the area - some times intersecting one another; while in other parts - dykes are almost absent. Several blocks of breccia were found lying on this floor- and were similar in ap pearance to that found on St. Helen's Island.

These dykes v^TlT in width from two inches to at least eight feet and have an average strike of w 50° **r with the exception of No. 6. which runs w and s.

They are all basic rocks and are greenish-grey to -61-

black in color, when examined under the microscope they represent four types of dyke rocks- the campto nltes, fourchites, alnoites and peridotites. The Camptonites present a holocrystalline, panidio morphic structure, some of which are porphyritic in character while others are finely crystalline. A few of these have a banded structure and frequently araygdaloidal; the araygdules are filled with calcite - which is sometimes enclosed by a rim of yellowish green chlorite. These rocks consist essentially of brown hornblende, augite and varying amounts of plagioclase. The spaces between these crystals are filled with a second genera tion of hornblende and augite - as well as plagioolase- hauyne minerals, apatite, iron ores and sometimes - allotriomorphic grains of nepheline which is very feebly refracting. The augite phenocrysts are usually pale purplish-grey, and non-pleoohroio. The hornblende is brown in color and stongly pleoohroio, usually occuring in smaller panidiomornhic crystals than the augite, the extinction angle of the hornblende varies from 15 to 25 degrees. Several crystals of both minerals have idiomorphio outlines. In one of these rocks the hornblende is so well developed and so abundant that it has been classed as 62- a hornblende camptonite. Biotite is almost entirely absent from these rocks - or in small irregular grains. The felspar is seldom found well developed, and twinned individuals are rare. The'nepheline occurs in small allotriomorphic grains usually filling np small interstices, being one of the latest minerals to crystallize out. It is some times distinguished from fflspar by its feeble double refraction, but oftener has to be determined by etching and staining. In the groundmass of some of these rocks will be seen a colorless mineral, Isotropic, and which frequently encloses dark segregations; this mineral is hauyne. In dyke 6, a considerable number of ex cellent forms, characteristic of hauyne may be noticed; the interior of some of these is often highly corroded.^) All of these dyke rocks are rich in phosphoric and titanic acid, as they all contain numerous crystals of apatite and are also rich in magnetite and ilmenite; the latter mineral is sometimes altered to its silico-lime-titanite,- leucoxene. On account of the advanced state of decomposition of these rooks, there is an abundance of oaloite, chlo rite, musoovite, epidote, etc., which render them dif ficult to study microscopically.

One of these dykes - No. 5, is more highly decompose -63-

than the others, but nevertheless it is holocrystal line. Large phenocrysts of pale-purplish augite, some times showing zonal structure, and brown hornblende individuals lie in a dark browninsh red groundmass which is also more or less highly altered - This base is now holocrystalline - but when fresh may have been glassy. For these reasons the rock has been called a fourchite, which agree with definition given it by Williams. This dyke rock is cut by another dyke which is Important as it belongs to the group of a*3.- noites and which will be described later. Dyke 10 represents one of the most basic rocks found in the vicinity - it is a peridotite and.may be most interestingly contrasted with the most acid variety, seen in the bostonites. This rock is made up almost entirely of grains of hornblende, pyroxene.bio tite andolivine. The rock is black and weathers with a rough pitted surface; it is holocrystalline and hy~ pidioraorphic in structure. The pyroxene preponderates largely, is pale-purplish and occurs in small ir regular grains as well as in well developed pheno crysts. In both cases the pyroxene polarizes in very brilliant colors.

(1) Williams J. F. Igneous Rocks of Arkansas - 1890, vol. II. -64-

Th e hornblende is not abundant but occurs in brown slightly pleochroic, panidiomorphic crystals, similar to the pyroxene. The biotite is well crystallized and is more abun dant than the hornblende, it is strongly pleochroic XX- deep brown, C= yellowish brown. Cubes of mag netite and ilmenite are often enclosed within the biotite. These three minerals, together with olivine, make up almost the entire rock, the latter occurs in irregular rounded grains deeply traversed by cracks, which are filled up with green serpentine, sometimes showing aggregate polarization. The intervening spaces between the grains are filled with alteration pro ducts including feebly polarizing natrolite and color less isotropic analcite. One of the most important and interesting dyke rock occurs in this locality, which according to the classification by Rosenbusch - belongs to the Alnoite (1) -type. It is important because it has been found in but few localities, and is, so far as I can find out, the third occurence of a melilite-bearing rock found on this continent. The first melilite- bearing rock in America was one from St. Anne de Bellevue, (2) situated on the south end of the Island of Montreal.

(1) Rosenbusch H. fc'assige Gesteine.

(2) Adams F. D. - On Melilite-Bearing Rock (Alnoite) from st. Anne de Bellevue- Amer.Jour.Sci. 1892 p. 269. -65-

A few years later an Alnoite dyke was reported at Manheim N. Y. (1);but in neither of these localities does the mineral melilite occur so abundantly as in this one from the bed of the River St. Lawrence. An "Alnoite-like rock (2) has been reported at Ashcroft, British Columbia - but so far as I am aware - melilite has not actually been found in it. The first melilite-bearing rock was discovered by Tornebohm on the Island of Alno, Sweden in 1682 and which he has described as melilite-basalt. (3) This dyke rock (No. 6) may prove after more thorough study to be of the best examples of a true Alnoite, or melilite-bearing rock yet discovered. It is unfortunate that more of this rock had not been collected when available, as it is now under several feet of water and cannot be obtained until the water shall fall extremely low as it was in 1895 -, \ > when this single small specimen was collected - but A this does not seldom occur.

(1) Smyth C. E. Jr. - Notes on recently discovered dykes of Alnoite at Kanheim, N.Y. - Amer. Jour. Sci, Vol.11 1896, p. 290.

(2) Ferrier V;. F. - Ann Rep. Geol. Sur. of Can. 1894. (3) Tornebohm A. E. - Melilitbasalt fran Alno .. Geol. Foren. i. Stockholm Forhdl., 1682 VI p. 240. -66-

Dyke - 6 forms a well defined dyke, cutting thru the Utica Shale; it is two and a quarter feet wide and is running IS — S and dipping at a high angle to the West. This rock is described fully in the catalogue of these rocks - to be found in the Petrographical Labratory and is slide No. 1720. This alnoite dyke represents one of the later dykes as it cuts across dyke-5. which has been described as belonging to the fourchite type. The following diagram shows the relation of these two dykes.

CO 1 4~. 1 •M1 2' i II

2 7 inches This dyke rock is dull greenish on fresh surface and weathers to a dull greyish color, which is usually pitted or rough. It has a peculiar lustre and on a fresh surface shows several small shiny flakes. The rock shows advanced alteration so there are no good phenocrysts present. It consists of augite and biotite much corroded, surrounded by a greyish groundmass made up of melilite, apatite, olivine, perowskite and magnetite grains.

The augite and biotite are not abundant and are large ly changed to chlorite and oalcite. -67-

Small irregular grains of the former are sometimes found fresh - but the latter is usually in shreddy fragments - some of which are slightly pleochroic. The biotite is yellowish-brown and frequently encloses cubes of magnetite and octahedra of perowskit. Only a very few grains of olivine have been found - these are traversed by cracks which are lined with green serpentine; the olivine grains also sometimes alter to a colorless greyish mineral - with high double refrac tion and which seems to be magnesium carbonate- magnesite. The groundmass of this rock is very dark - almost isotropic at times, in which are embedded the small in dividuals of pyroxene, needle-like prisms of apatite and numerous tabular and lath-shaped crystals of mslilite- also numerous cubes of magnetite and isometric 'grains of perowskite. MELILITE - This mineral,which is characteristic of the Alnoite group, predominates largely thru the rock. After several measurements had been icade of this mineral in various thin sections it was found that about 20 percent of this rock is mede up of the mineral melilite. It occurs in colorless, narrow, elongated, tabular plates, which give straight extinction, and which are lengthened in the direction cf their horizontal axis - Basal sections are isotropic and sometimes have an -68-

octagonal form. From the sides of these elongated crystals, curious peg-shaped rods extend inwards towards the centre - This "peg structure" is at right angles to the basal cleavage and parallel to the vertical axis, in a basal section the pegs appear as dots or little holes. From the direction of the cleavage was determined the orientation of the in dividual of melilite,- by inserting a gypsum plate of red of the first order, at right angles to the cleav age of a good crystal of melilite, a faint bluish tinge is added to the crystal, parallel to the direction of the gypsum plate, thus giving a negative sign; this shows that the vertical axis in melilite is the axis of- greatest elasticity, so that the melilite is negative. The individuals of melilite vary in dimensions, in thickness they range from .01 mm. to .12 mm. and in length from .20 mm. to 1.02 mm. This mineral is easily attacked by dilute hydrochloric acid and re tains the stain when fuchsine has been added to an etched portion of a thin section-, the apatite needles are not effected by the acid - thus the two minerals may be distinguished. Accompanying the melilite is its frequent as sociate - perowskite - v/hich is abundant thru this rock in the form of cubes and small octahedra, brown or brownish yellow intransmitted light - and yellowish brown in incident light - it is weakly doubly -69

refracting and has a light index of refraction - a dark border is formed round the crystal due to the total reflection, A separation of the minerals of this rook - ac cording to their specific gravities, was made by means of Thoulet's heavy solution process. As many of the constituent minerals in the rock are extremely minute - the rock was powdered so fine as to all pass thru a 160mesh sieve; the magnetic particles were removed by means of a bar magnet, about four-fifths of the powder was attracted by the magnet. The non-magnet powder was added to Thoulet's solution - and the usual process followed. When the separation was completed, the powders with different sp. gr. were examined under the microscope respective ly - Many composite grains still remained as the - 160 mesh sieve was not fine enough. Those grains which were precipitated when the solution had a specific gravity oi 3.052 - consisted of perowskite, unseparated magnetite - apatite, olivine and augite. Lost of the augite and biotite were separated out at 2.937 - As the melilite was largely in com posite grains - a good separation could not be carried out- some of the melilite grains were included in the powder which fell at specific gravity 2.855. but the greater part of it was separated out at sp. gr. 2.699 - The secondary constituents and decomposition products had a -70-

sp. gr. lower than 2.699. If fresher material of this rock could be ob tained it would be well to have an analysis made of it. A further study of this mineral, as well ae the whole rock might give valuable information regarding its occurence in this locality - Melilite has not been found in any of the other dyke rocks which the writer has examined from this vicinity.

Between this locality and St. Helenfs Island - when dredging the river - a white or light greyish dyke rock was brought up by the dredge - specimens of which were collected - The rock shows several mac roscopic white phenocrysts and a complete absence of ferro-magnesian silicates. It belongs to the b'ostonite (reihe) group. When examined under the microscope the rock presents a porphyritic structure; consisting of phenocrysts of orthoclase felspar, largely replaced by flakes of musoovite and kaolin; some of these phenocrysts occur as Carlsbad twins, while others show an intergrowth of a potash-soda felspar. These phenocrysts are surrounded by a greyish groundmass partly composed of small felspar laths which frequently show trachytic structure. The remain ing interstices are filled with colorless isotropic material, which is largely glass, but some of this isotropic material encloses minute black grains and -71-

alters to calcite - this strongly suggests the presence of hauyne.

On St. Helen's Island few dykes are exposed;- a small one may been seen on the East side of the Island and a few hundred yards above the two masses of Lower Helderberg limestone. It is a vertical wall between eight and ten inches thick and cuts thru the volcanic breccia - running N. 15 W. This rock is sometimes porphyritic and holds large black crystals of hornblende and mica. Further up the slope and nearly opposite the block-house a similar porphyritic dyke is exposed cutt ing the breccia at I 15 W and may be a continuation of the previous one described. In -Geology of Canada- pg. 356 it is stated that "two parallel doleritic dykes running I 75 W cut both the limestone and conglomerate". One of these dykes, according to Dr. Harrington's notes, is about 4 feet thick and dips to the North at angle of 70 degrees. This dyke cuts thru the Lower Helderberg limestone and encloses masses of it; the same dyke cuts thru the breccia and contains fragments of this volcanic tuff which over lies the Lower Helderberg, and is therefore later. This evidence shows that some of the dyke rooks were forced up after the deposition of the Upper Silurian -78-

sediments and after the volcanoe had ceased being such. The other dyke which cuts the Lower Helderberg is running N 75° W and is two feet six inches wide. In color it is greenish grey - and appears spotted with amygdules which are filled with rhombohedral carbonates. This rock is a hornblende camptonite - containing the usual constituents; plagioclase felspar is somewhat abundant, and was found to be an acid variety ranging between oligoclase and andesine - and which on a twinned face, gave an extinction angle between 12 and 16 degrees. It is impossible to work out the age of these dykes other than what has already been stated -as only por tions of them are exposed - and intersections are wanting. (b) South Slope of the Mountain - Three dyke rocks were examined from the junction of Pine Ave. and Cote des Neiges Road and all are of the camptonite type, rich in titaniferous hornblende, T.hich have the common typical structure. Magnetite sphene and ilmenite are abundant, the latter is frequently altered to leucoxene. The hornblende is worthy of notice as it frequently encloses numerous minute needle-shaped crystals, deep brown in color, which have a high index of refraction and are feebly transparent - these are rutile needles and are probably due to alteration of the highly titaniferous character of the hornblende. These slender crystals of rutile may be well seen in -slide 1718 and -73-

are frequently arranged in parallel lines. A dyke rock from St. Antoine Reservoir, presents another type of rock - rich in alkalies - It belongs to the type Nepheline-aplite - rich in orthoclase felspar. This mineral forms about 25 p.c. of the rock, occuring sometimes in well developed crystals. The rock is porphyritic and holocrystalline. The small phenocrysts of pyroxene are frequently altered to green hornblende which sometimes has a fibrous appearance. The groundmass is a finely crystalline mixture. Nepheline was deter mined by etching and then staining a thin section and prov ed to be less abundant than the felspar. Hauyne minerals are abundant, and the rock is rich in titanic ores. (c) Reservoir Extension - This locality is one of the best in which to study the relationship between the various dyke rocks. The "Reservoir Extension" is the newer or northern end of the City Reservoir on McTavish Street. A complicated group of dyke rocks are exposed in the bottom of this ex cavation. When the extension was being constructed, about thirty-five years ago, the opportunity was taken and the various dyke were surveyed by Dr. a. J. Harrington, and at a later date made a map of this portion of the Reservoir on which he showed the various dykes ano the complicated manner in which they intersected one -74-

another. A reproduction of this map on a small scale accompanies this paper, on which the angle of dip is given and the various dykes are numbered for convenience- and to which references wi]i be made in the description of the several dyke rocks. When making the survey of these dykes, specimens were taken and notes were made on the general character of these dyke rock$, but he did not publish any detailed account of his research. As the notes on these dyke rocks were not available until a very late date - they have been of little advantage in preparing the work covered by this paper, but these notes may now be found o in the Petrographical Labratory. In this small area, known as the heservoir Extension which is about 200 yards in length and 100 yards in breadth, over forty dyke' exposures were found which belong to at least thirty different dykes. As specimens of all these dykes have not been collected only the more important ones have been examined. In working out the relationship and order of these various dykes - Dr. Harrington found that there were probably seven series cf dykes representing at least three or four different ages of intrusion; each series cutting those which preceeded it. All the intersections have not been noted by Dr. B. J. Harrington, but from a hasty review of his notes -

-75- the complicated manner in which these dykes intersect one another is interesting and worthy of consideration, as these intersections show that dykes of several ages are here represented. In order to avoid c*onfusion, and for clearness, a list of the various dykes which intersect others and are likewise intersected by later ones, has been drawn up separately and is as follows:-

dumber of dykes Dyke or dykes which it cuts -

Ho. 3 cuts 12 5 "4 which is continuation of Ho. 3 " IE and is same age or younger than 6 6 " 12, 5. 7 " 5i. 7i, 9(f), 10, 10s, 12, same age as Ko. 11 or younger. 7i « 5i 8 » 7i, 9, 12. 9 w 13 (apparently) 14 " 15, (14iHapparently) 18 " 15, 24, 25,(26\ (apparently) 21 " 20, 28. 22 n 20 23 "18 -76-

Th e following list gives the dyke rocks which have been examined in the Reservoir Extension - and the group to which it belongs. Dyke lo. 1 Hornblende Camptonite 1a Nepheline tinguaite - vidth 6 inches 2 hornblende camptonite 8 inches

jW n

5 r? 10 inches 6 camptonite 2 feet 7 hornblende camptonite 2 feet

9 u n 12 bostonite 15 i> I to 6I feet 18 nepheline tinguaite 27 inches 20 monchiquite 20 inches 21 it 18 n

23 »i 12 n

24 « n

25 hornblende camptonite 20 Tt

26 monchiquite 12 II

Analoite dyke (similar to 21) monchiquite.Dyke north of E'o. 15 - nepheline aplite. -77-

From the list of the rocks examined it will be seen that the various rock types represented - are those which are frequently associated - with alkali-rich magmas, such as essexite and nepheline syenite;- these are camptonites- monchiquites - tinguites and bostonites. A description will be given of each of these types of rock as found in this locality - commencing with those belonging to the camptonite type - CAMFTOITITES To this group nine of these dyke rock belong as indicated in the table - They vary considerably in struc ture - some of which are porphyritic and holocrystalline - while others are granular and both frequently contain panidiomorphic crystals. All are highly altered s-o that there is always an abundance of alteration products present in these rock - Many of these rock,if fresh - could be considered as typical camptonites - as theycon- sist essentially of brown hornblende - which in some cases is the only ferro-magnesian silicate present in the rock. The hornblende is sometimes in idiomorphic crystals - but oftener is it found partly or entirely changed over to chlorite and epidote as is the case of No. 9. in which the elongated prisms of hornblende are replaced by iron inclusions and chlorite, while in other rock, the horn blende has an outer rim of green chlorite about it. The hornblende is very often of two generations - the -78-

phenocryst representing the first, while the smaller irregular grains in the groundmass represents the second. Augite is seldom found in any of these rocks, but when present it frequently shows a banded structure. The plagioclase felspar and nepheline - vary con siderably in the proportion present in the different rock, and the former is seldom found in well developed crystals, but oftener in allotriomorphic forms and some times lath-shaped individuals - frequently showing twinning. The amount of iron ore varies widely - and may be magnetite, ilmenite, pyrite or pyrrhotite - and in dyke lo. 2, this last iron mineral is co abundant that it has been called the pyrrhotite dyke. Apatite crystals are present in all these rocks - but the proportion varies. The rocks sometimes show amygdaloidal forms which are usually filled with rhombohedral carbonates - and in dyke 1, many of them are filled with - highly doubly refracting epidote. Dyke 6 is much more highly decomposed than No. 5, and is very probably the older of the two as is suggested in the tabje of intersections - it contains minute isometric crystals of Perowskite. A chemical analysis was made of dyke 2. W. by Dr. Harrington, this it compared with a similar "diorite" dyke from the same locality which he analysed some years ago. With these two camptonltes from Montreal may be -79-

compared - two others from different localities I II III IV Silica 45.51 40.95 . 41.94 44.87 Titanium dioxide3 3.84 3.39 4.15 6.74 Alumina 15.84 16.45 15.36 17.28 Ferric Oxide 1.90 13.47 3.27 11.04

Ferrous " 7.59 - 9.89 -

Manganors Oxide .40 0.33 0.25 - Lime 8.35 10.53 9.47 7.54 Magnesia 3.85 6.10 5.01 4.95

Barium Oxide .12 - - - Soda 5.09 4.00 5,15 1.61 Potash 1.88 1.28 0.19 2.62 Phosphorus pentoxide .61 0.29 - 0.45

Sulphur trioxidei .60 - - -

Carbonic acid ' 2.23 2.47 - Water at 110 C .16 ) 3.8

99.69 100.63 100.44 99.59

I. Camptonite-Dyke 2W. Reservoir Extension -Montreal, Can. II. Diorite-dyke - n " Geol. Sur of Canada, 1877-78 p. 4&ft* L(L{ Q -80-

III. Camptonite by G. 7. Hawes, Campton Falls U.ir.-- Amer. Jour. Sci. XVII p. 14. IV. Camptonite by L. M. Dennis - Hudson River Highlands • Amer. Nat. August 1808 p. 694. These analysis show a considerable variation in composition, but all are about the same in the amount of silica and all under 45 p.o. The -Norm- of No. I has been calculated out - in order to fix the position of this rook in the classifica tion (1) drawn up by Messrs. Cross, Iddings, Pirsson and Tashington - and also in order to determine the correct name for thte rock according to this system - The norm was found to be as follows (2) :- Albite - 23.63 p.o. Anorthite - 16.96 " Orthoclcise - 11.12 " Nepheline - 8.21 " Noselite - 1.14 " Diopside - 1^.19 " Olivine - 5.86 " Magnetite - 2.78 " Ilmenite - 7.30 " Apatite - 1.39 " (1) Quantative Classification of Igneous Rocks - by Cross, Iddings,Pirsson and Tashington,University of Chicago Press. 1903, p. 14? (2) The -norm has been calculated ont without calcite,as the calcite is all secondary. -81-

Garbonic Acid - 2.23 p.c. Tater - 1.83 " 99.64

The position of this rock in +he Quantative Classifica tion would be as follows. Class II, - dosalane

i Order 6, - norgare Rang 3, - Salemase Subran^ 4, - Salemose.

Rocks having a similar name have been found at the following localities - according to the classification of chenical analyses by Washington;- at Salem Neck, Essex Co. Mass. the rock has been called a hornblende- gabbro - cind is closely associated with the essexite magma - Another rock with a similar name and with a somewhat similar norm has been analysed; it occurs at Portland Head, Portland, Maine, and the rock belongs to the camptonite group, a dolerite from Dyer's Pass, Canterbury, New Zealand, has also a similar name to this

one • A |—s. Dykes of a camptonite rock occur about some of the Monteregian Hills, - small ones are found at Mount Johnson. These dykes are very probably connected with those found about Mouit Royal, similar dykes are also -82-

found in many of the localities mentioned - in con nection with essexite and nepheline syenite magmas. Dyke rocks similar to the American camptonltes have been found in the Black Forest - and are described by Goller (1). MONO17!SUITES - This type of dyke rock - is represented by six dykes in the Reservoir Extension - They are all very highly decomposed, but a distinction can bf: made between them - according to their stage of decomposition. Nos. 20, 24, 26 are more highly altered - so are probably the oldest of the monchiquites - whereas dyke 21 is much fresher than the rest and Is probably the youngest - This division seems to hold good in the table of intersections, for dykes PA and 26 are both cut by No. 18 - and dyke 21 cuts No. 20. These rocks differ from the typical ones, in that these consist essentially of hornblende - with much smaller amount of pyroxene present, and biotite is almost absent. Small crystals of plagioclase sometimes occur and nepheline in varying amounts which can only be determined by etching and. staining a thin section of the rock. The groundmass is very dark - and usually consists of ^lass - or as in dyke 20 - Is de^ltriped in part to a mass of feebly doubly refracting microlites.

(1) S. Goller - Die Laraprophyrgange des su'dliohen vorspessart. Neus Jahrbueh - Vol VI. Beil. Band 1888 p. 485. -83-

Dyke 21 is the freshest of these rooks - and con sists essentially of panidiomorphic crystals of deep brown hornblende - in a finer crystalline and glassy gronndmass. The rook itself is porphyritic - the dyke is 18 inches wide - The outer portion of the dyke is finely crystalline - while the centre is porphyritic and holds many macroscopic black needles of hornblende - which are arranged cit right angles to the walls of the dyke - this is.characteristic of several other dyke rocks found about Mount Royal, sometimes a sharp line na^ be seen between the outer and central band. The hornblende in No. 21 - frequently occurs in idiomorphic crystals - some of the forms represented are pinacoidal faces (010) (001) also the form'OOp. (110). It is strongly pleochroic & - light brownish yellow; fo ^rlight reddish brown; C ^ deep brown - \\>' The absorption is C ? 3> y CL %£ ^ T3ae maximum extinction angle is less than 15 .^ A -3 degrees. This amphibole is analagons to the variety - A •& "*5 ^4 hornblende barke^ikite - Banded crystals are common ' 4A V <^ ^ ^ among the hornblende, very little augite can be found . 6 ^ ^ in the rock and olivine is almost absent. Iron ores a-) ^5 are abundant. In the gronndmass which is largely glass - plagioclase laths and a small quantity of nepheline may be found. This dyke rock has been analysed by Dr. B. J. Harrington and Is given below - -84-

It may be compared with other monchiquites from other localities. These analyses are as follows:-

T II III. Silica 36.69 46.48 43.50 Titanium dioxide 5.44 .99 2.10 Alumina 11.96 16.16 18.06 Ferric Oxide 5.45 6.17 7.52 Ferrous oxide 8.90 6.09 7.64

Manganons oxide .38 - Lime 10.28 7.35 13.39 Magnesia 7.85 4.02 3.47

Barium oxide trace - -

Soda 3.88 5.85 2.00

Potash 2.07 3.08 1.30 Phosphorus pent- oxlde .62 Sulphur trioxide .92 Carbonic acid 3.7R Tater at 110° .25 ) 4.72 1 90 ) Tater above 110° C) 1.70 ) Chlorine .04

100.21 100.91 100.20 i -85-

I. Monchiquite - Dr. B. J. Harrington - Reservoir Extension - Montreal. II. Monchiquite - from Brazil - Hunter and Rosenbusch, Tscher. Mitt. XI, 454. III. Araphibole Monohijuite - Magnet Cove, Arkansas - Ark. Geol. Survey 1890, vol. II p. 295.

It will be seen that No. I is much more complete than either of the other two analyses, Md. is also low in silica. In order to place this rook in the Quantitative Classification - and in order to determine the name of this rock, its -Norm- has been calculated ont, and is as follows (1):- Orthoclase 9.01 Anorthite 12.51 Leucite. 2.53 Noselite 1.56 Nepheline 14.48 Diopside 27.42 Olivine 7. 26 Hagnex ix e...... r.o.7 Ilmenite 10.34 Apatite 1.39 Carbon dioxide 3.78 Tater 1.95 100.12 fl) As this rock is rich in decomposition products,the norm BeSon&nm?*1™1"**'1 °,7t.™u+'*nc the oaloite.whiol is always -86-

No. I has, therefore, the following position in the quantitative classification (1) :- Glass III - salfemane Order 7 - kamerunare Rang 4 x fdocaloic) Subrang 3 - x (prfesodie)

It may be noted that as yet it has no name in the classification of chemical analvses, as no exact equivalent has yet been recorded. If this is correct - it would be necessary to give this rock a new name - but in order to make certain that its position is correct - it would be necessary to have other analyses made of the same rock. This rock was also calculated out including calcite - and was found to have the following position.- Glass III seilfemane Subclass I salfemone Order 6 portugare Rang 2 monohiqucise (doraalkalio) Subrang 4 monchiquose (dosodic). fl) Chemical analyses of Igneous Rocks - H. S. Washington Prof. Paper No. 14 U. S. G. S. -87-

There is one more dyke rock which belongs to this tvpe - it has been called the-analoite dyke- as it contains a colorless isotropic mineral which is probably analoite. On examining this rock microscopically it is found to be identical with dyke 21 just described which also contains an occasional grain of a similar mineral. The analoite occuring in this rock was examined and analysed by Dr. B. J. Harrington (1). It is a glassy white mineral- has a specific gravity 2.255 and ooovrs as white spots thru the rock - The chemical analysis are as follows:- Silica 53.29 Alumina 23.29 Ferrous oxide Lime 0.64 Magnesia trace Soda 14.54 Potash 8.47 100.27

ii (1) L. V. Terweke : Uber de Nepheline-syeniten der Serra de Monlchique im Sndlichen Portugal und die denselben durohsetzenden Gesteine. Neus Jahrbuch 1880 - vol. I pp.141 - 186. -88-

Sinilar rocks of the monchiquite type have been found associated with nepheline syenite magmas in several localities, the f-*rst was discovered in Serra de Monohique - Portugal - while others have been found in Brazil (2) - as well as in Monteregian Hills. The type of rook which Rosenbusch has called nepheline tingualte is represented by three dykes in this locality - but none of these are strikingly interesting - consisting essentially of orthoclase nepheline, hornblende, biotite &nd sometimes augite, in a dark holocrystalline base - in which the con stituents frequently show a trachytic structure - and in which is found the aegirine, in slender needle- shaped crystals. Apatite is abundant In some of these - and has developed extremely long slender un broken needle-shaped crystals, which shows that the rock must have cooled very slowly. One of these rocks is porphyritic - the phenocrysts being brown- hornblende slightly pleochroic - in which the ab sorption is C ? i) > t\ - Augite is scarce in these rocks. a Dyke 1 presents a peculiar kugel-structure - rounded areas are abundant - which are free of iron- magnesian silicates and is apparently composed of the

(2) O.A. Derby - On Nepheline Rocks in Brazil,- Q. J. G. S. London 1887, p. 457. -89-

sarae material as is found inthe gronndmass, so that they cannot be called amygdules - a further examination of these is required. I21 some of these spherulitlc growths - are found numerous slender crystals of a highly doubly refaoting mineral - and which has the appearance of zircon. These needles are sometimes quite long and are frequently arranged parallel to one another. A narrow dyke on the north side of No. 15, and at the east end of it, proves to be a nepheline-aplite - and differs only from those just described by the absence of aegirine - these dykes seem to represent a stage in the consolidation of the magma, when it was changing from an acid variety to one quite basic in character. The dyke rocks which are richest in alkalies are nos. 12 and 15. On the map they are seen to be the largest - and are marked as trachytic in character. These are intersected in many places by later dykes so they represent the earliest s"» a^e of intrusion of dykes - which from a study of the intersections has continued to become more basic in character - Dr. Harrington thought that probably these trachytic dyke were formed even before the previous eruptions of Mount Royal - but nothing definite can be stated on this T>olnt. -90-

Both of these dykes belong to the bostonites - and are almost free from ferro-magnesian silicates - consisting essentially of orthoclase - no nepheline is present in this rock. The gronndmass frequently shows a tendency towards a trachytic structure. Dyke 15 is bluish Qrey when fresh and almost ^ '\ -A .white when decomposed - it has been called the sodalite ^%\W dyke by Dr. Harrington, as it contains several maC- \ AA ^ \ \,\ VJ> *H>V' v roscopic crystals of azure blue to white sodalite to ..• ., which was found to have a specific rravitv of 2.152. \X X" fphiR roc]!: was analysed by Hunt (1) - which is recognized by the presence of pyrite cubes - and to which ^ reference is made when he is describing the rock. The analyses are as follows:- Silica - 63.25 ACM^I Alumina - 22.12

Lime - .56 |A * Potash - 5.92 Soda 6.29

7ater . 9v^ 99.07

The other bostonite dyke No. 12 is also spoken of in the -Geology of Canada- and a crude analyses was made - which is as follows:-

O.) Geology of Canada 1863 r>. 658. -91-

Silica - 62.90 do Alumina - 23.10 Ala 4.-H Lime - .45 Potash - 2.43 Soda - 8.69 l^y^'^ ^ater - 1.40 98.S7

This dyke has been called - Dawsonite dyke by Dr. Harrington as the outer edge of this dyke is covered with a mineral in thin white flakes with shinin surfaces - This mineral has just been carefully examined by Mr. R. "p. Graham of McGill University - he hae just completed this examination, and the following are some of the results which he obtained. The mineral is Dawsonite - having the composi tion Na 01 (OH)c.CO- . It belongs to the orthorhombic system in which a : 1 : c 0.64755 : 1 : o.5^395 and 110 : 110 = 65° 5l' ; - Oil : 010 = 61 54f ;

110 : 011= 75° 10* . it occurs in thin bladed or needle shaped crystals, striated vertically - which are white to colorless and transparent - with a vitreous lustre and white streak. Cleavage perfect // jlio) - brittle-, H = 3 Sp. gr. 2.44. It is optically negative, and the dis persion is (J* < £/] not marked. It has a strong -92-

birefringence y -*-0.085 i.e c< - 1.511; o i JS = 1.542; y ^ 1.596 ^ 2V^ - 76 45 .

m?hv e mineral is infusible, but exfoliates, and is easily soluble in acids with effervescence. Both carbon dioxide and water are driven off at a red heat o but neither at 140 c. He found that the percentage composition of the mineral is as follows - Carbon dioxide -30.6 Alumina 35.4 Soda 21.5 • = r ter 12.5 100.0

similar mineral is found on the sides of some other dykes in this vicinity, A short distance above the Reservoir Extension fro/a the Park a dyke rock has been examined - and is fully described in the catalogue referred to above. It is called the furrowed dyke on account of the peculiar manner in which it weathers- which is the chief point of interest, It is porphyritic in structure twoards the centre, but finely crystal line on outer edge.

• uuf TOW ed. D^ltc Mj rMu.rji -*»u.A\ -93-

Frora the study of intersections of the dykes in the Reservoir Extension - it is found that the trachytic dykes were intruded first - especially the bostonites, these were followed by the nepheline tinguaites, nepheline aplites and some of the mon chiquites - and at least one camptonite, dyke No. 25 the -remaining d vices are very much complicated - but at two different ages of both camptonltes and mon chiquites are represented - but unless fresher specimens can be obtained -> e.nd a careful examination made of all the intersections no further definite in formation can be given regarding the various ages of these dykes. (d) Maisonneuve and Back River. A careful survey was made by Mr. 0. E. Leroy of all the outcrops, both igneous and sedimentary, within a radius of about ten miles of Montreal. He found that most of the igneous rock exposed was in the form of intercalated sheets or sills, between the lime stone strata, specimens of these various sheets or dykes were collected and are in the Petrographical Labratory with the specimens of other dyke rocks. A large intercalated mass of igneous trap- similar to and probably continuous with the one which is mentioned in the -Geology of Canada- 1863, p. 144, is exposed at Petite Cote or (Oote de la -94-

Visitation). This sheet is divided into two layers,- the upper one is 6 feet 8 inches thick - and the lower one is 4 feet thick. The breadth of the sheet which is ex posed is 128 feet - and has a maximum dip of 16 degrees to N. W. The rock belongs to the nepheline-tingaaite type; it is sometimes porphyritic, but often granular in character. When the rock is porphyritic, the phenocrysts consist of pyroxene, nepheline, hauyne and orthoclase; the nepheline usually occurs in idiomorphic macroscopic crystals, whereas the ferro-magnesian silicates are not abundant at any time. Large individuals frequently occur impregnated with inclusions, and in some of these grains the black inclusions are arranged in bands which correspond to the outline of the crystals - the'se individuals are the mineral hauyne. The groundmass is holocrystalline, consiting of numerous green aegirine needles and lath- shaped crystals of felspar which sometimes present a trachy tic structure. Slender crystals of apatite are abundant in most of these rocks, whereas iron ores are almost absent. In some of these rocks - a colorless allotriomorphic material frequently fills up cavities between the larger crystals and has the appearance of analcite, while in other places it resembles natrolite. Small irregular grains, are some times seen intimately associated with other larger crystals; it has the appearance of apatite but polarizes in yellowish- -95-

white color, with these and other properties it seems analagous to rinkite - but as such a small amount of * this material is present it was impossible to determine fully what this mineral may be. At St. Vincent de Paul, just below the Peniten tiary, a cliff rises from the edge of the water, composed of interstratified beds of limestone with sills or sheets of trap rock. These igneous sheets vary in width from 2 inches to 2 feet. When a thin section of one of these sills was examined under the microscope, the rock is found to belong to the camptonite type - in which the larger phenocrysts are pale purplish augite, while the smaller ones are hornblende which frequently-show a tendency to form idiomorphic crystals. These crystals are free from inclusions and are sometimes found with a mould of pyroxene about them. The hornblende is strongly pleochroic, C ^ dark reddish brown; (b ^ reddish brown; - (X- yellowish brown. The absorption is C /> fo > & , The groundmass is the same as that un similar rock types previously described. A,trap sill was examined from Back River, (R. des Prairies Village) - which is similar to the last one described. It is about 6 feet thick where exposed and varies in composition from porphyritic -96-

to finely crystalline. Thin sections of both varieties were examined and were found to belong to the camp tonite type in which pyroxene predominates. The rock is rich in titaniferous minerals and apatite - which seem to be characteristic of all the more typical camptonites which I have examined. Olivine is present in small amount, but hauyne minerals are somewhat abundant in all these trap sheets about the mountain. In some parts of the sheet, the rock is amygdaloidal; the amygdules are filled with calcite. Another intercalated sheet was examined from Longue Point - it is exposed near Cote St. Leonard on Lot 435 - and is 5 feet thick. Like those- from Petite Cote it belongs to the nepheline tinguaite type of rocks and is greenish grey in color. The upper portion of this sheet is porphyritic in character - whereas the lower portion is granular. Phenocrysts of green monoclinic pyroxene are some times abundant; which belong to the variety - aegirine - augite, having slight pleochroism, C = yellowish green, &* bluish green; the extinction angle of these phenocrysts is always less than 35 degrees. There are also a few phenocrysts of augite present - which have an extinction angle of 40 degrees. The other constituents are similar to those -97- previously described in this type of rock. Specimens have also been collected from a trap sheet at Rockfield which is exposed between the Park and Island Railway and the Grand Trunk Railway and about 450 feet east of the Upper Lachine Road; this exposure is about 250 feet long and from three to five feet thick. In places the rock is amygdaloidal - and also holds angular fragments of the limestone thru which it cuts. A porphyritic band is distinctly noticed thru the centre of the sheet. It is a basic rock in iron ores and ferro-magnesian silicates, belonging to the augite-camptonite type ol rocks. In structure it is holocrystalline, porphyritic and panidiomorphic. It contains large rounded grains of olivine which are deeply traversed by cracks in which is crystallized green serpentine and chlorite. Apatite is numerous in colorless elongated prisms, frequently corroded, giving it the appearance of melilite. Colorless irregular grains of isotropic material, filling the small corners between the larger crystals, have the appearance of analoite. After a study of the intercalated sheets from various localities - one can clearly see a close resemblance between the various rocks; that is to say all those which belong to the camptonite type have marks of similarity; the same is true of the nepheline tinguaites. -98-

This would suggest that they all came from one magma and were intruded at or about the same time. Thus far it has been impossible to work out the age of these sheets. Other thin sections of these various sheets should be examined for the presence of melilite and other rare minerals such as rinkite and lavenite etc. (e) Mile End Quarries - These quarries are situated at the North end of the City and about one mile and a half north of ^ount Royal. The rock flooring this area is Trenton limestone which is being worked ex tensively for building material; - as a result of these excavations the geology of the district can be profit ably studied. The Trenton limestone is cut by numerous dykes; some of these have been left standing up in the excavations as unsupported walls. A careful survey was made of this district about five years ago by lir. George Shanks B.A.*04 who after wards made a map of the area covered, on which is shown the various excavations, as they then were, to gether with the various outcrops of dykes which cut thru limestone. This map is now in the Petrographical Labrat ory. At the same time as the survey was made, specimens were collected from several of these dykes, and are to be found among the collection of dyke rock^ from this vicinity. -99-

When making this survey it was found that there were at that time about sixty outcrops of dyke rocks which actually represented about thirty-four different dykes, which had an average dip of 80 degrees, varying o o in strike from I 30 W to S 30 W; the width of these dykes varying from one to eleven feet. These dykes are genetically connected with igneous mass of &ount Loyal - sc that the dyke rock belong to the same groups as those already examined - with but one exception - i.e. certain rocks which have a pitchy or glassy appearance - and which have been called Pitchstone dykes. The types represented in this locality are camptonites, monchiquites, tinguaites and pitchstone dykes. With the exception of this last group all are highly decomposed which makes it very difficult to study them microscopically. When making this survey, I-r. Shanks noted several intersections which seemed to show that the pitchstone dykes were the youngest, whereas those, too highly decomposed to determine were probably the oldest, then between these come the remaining camptonites, mon chiquites and tinguaites - regarding whose relative age - he was unable to obtain any evidence. Those recks whioh belong to the monchiquite type offer nothing extraordinary - but differ from those of the Reservoir Extension, in that augite of two -100-

generations predominates in most of them, with few exceptions. The augite usually occurs in panidiomor phic crystals - it frequently shows good cleavage as well as a banded structure, which is common among the similar dyke rocks from Lake Champlain. The pheno crysts are pale violet in color - and give extinction angles between 40 and 45 degrees. In outcrop .50 the phenocrysts consist of pale brown hornblende frequently well developed, slightly pleochroic and remarkably free from inclusions. These phenocrysts are surrounded by an undeterminable grounds mass, in part feebly doubly refracting - but oftener perfectly isotropic. Those rock which belong to the camptonites a're also highly altered - No. 49— and 15 are so far alter ed that only lath-shaped crystals of plagioclase can be determined - but the forms which the iron grains and chlorite appear in, strongly suggest that horn blende was present when the rock was fresh. No. 25 is among the freshest and is coarsely amygdaloidal - the amygdules are filled with rhombohedral carbonates of calcium and magnesian - in some of these amygdules ankerite - the magnesium dolomite rich in iron is reported to have been found.

The hornblende is abundant in this rock in stout panidiomorphic crystals - slightly pleochroic; the -101- absorption is £ > h & and those showing cleavage lines - give a maximum extinction of 20 degrees. In No. 48 pyroxene phenocrysts replace the horn blende which is present only in small grains - The pyroxene is a pale violet variety - polarizing very brilliantly - which is probably due to its richness in titanic iron ores. The rock is amygdaioidal - these amygdules are frequently filled with rounded grains of clear colorless quartz - which are often in with calcite which cements the grains together. Perfect interference figures were obtained from some of these grains. Other large rounded grains of quartz are found in the groundmass and which appears primary - giving the rock a porphyritic structure. Several highly decomposed rocks were examined but they are too highly decomposed to classify them. Some of these, however, are porphyritic - holding phenocrysts of brown mica and hornblende and all are rich in well developed crystals of apatite - elongated and frequently terminated by blunt pyramids. Iron ores are abundant in all of these rocks and sometimes occasional grains of olivine may be found.

These rocks belong to the camptonite and mon chiquite types - but it is important to make a divi sion between these highly altered rocks. The rocks from outcrops 40 and 41 belong to a -102- more acid type of rock and may be classed ss nepheline-aplite rich in felspar. Some large pheno crysts of both orthoclase and twinned plagioclase occur,largely altered - Nepheline phenocrysts are also present, sometimes changed to hydronephelite. The groundmass is very turbid, and holds several well developed crystals of apatite. Other rounded grains occur, deep brown in color, grey by reflected light, and sometimes show cleavage; it is very slightly pleochroic at times and almost isotropic. This mineral v/as probably biotite but owing to the infiltration of iron, it has become brown; and frag ments of the original biotite may sometimes be found enclosed within the brown individuals. This mineral is analagous to the reddish or rust- brown biotites - called rubellan, which is found in the tuffs of Laccher See and Bohemia. The rock from outcrop 44 - is somewhat similar to these but also contains small fibrous crystal forms - most of which are now altered but, which suggest the presence of aegirine - thus the rock would be called a nepheline-aplite. The "pitchstone" dykes are interesting and not by any means common. These rocks are found in a fresh condition - are bluish grey in color and have a peculiar -103- pitchy lustre. Macroscopic crystals can be seen thru all these rocks - white in color - and which prove to be nepheline - having a very low index of refraction. There is sometimes a border found round the nepheline crystals but which has the same orientation. Prof. Iddings thinks that this may be due to nepheline having two different compositions, one more potassic than the other. There are also phenocrysts of some alkali-felspar which is sometimes unstriated, but well cleaved, having an extinction angle of 10 degrees - which is probably a soda- orthoclase. The structure of the orthoclase is sometimes such as to suggest cryptoperthite. The ferro-magnesian silicates are almost absent in these roekfy- some of them contain slen der crystals or fibres of a greenish-brown mineral, with very low extinction angle which has the appearance of acmite. The groundmass is made up of acicular prisms of untwinned felspar and nepheline - usually allotriomorphic. The remainder of the groundmass consists of a glassy isotropic material - which is probably analoite as has been suggested by Dr, Adams and Prof. Iddings. In some rocks- the proportion of this isotropic material is very large - while in others it has a peculiar streaky appearance - this may be seen in slide 795. , The sp. gravity of the rock was found to be 2.43. -104-

An analysis has been made of this "Pitchstone dyke" rock from Mile End Quarry - by M. F. Connor, of the Can. Geol. Survey - at Ottawa, with the following proportions:- Silica 53.99 Alumina 22.89 Ferric Oxide 1.04 Ferrous Oxide 0.44 Magnesia 0.07 Lime 0.38 Soda 10.79

P0tash., 4.87 Titanium dioxide 0.25 Manganous oxide 0.23 Sulphur trioxide 0.06 Chlorine 0.15 Carbon dioxide none Water (Hygroscopic) 0.18 Water (Combined ) 4.70 99.98

The -norm- of this rock has been calculated out by Dr. Adams - who has carefully examined this rock. The normative proportions are as follows.- -105-

Orthoclase - 24.19

Nepheline - 11.87

Nosean - .71

Sodalite — 2.43

Analcite - 57.47

Diopside - 1.18

Magnetite •m .7

Ilmenite M .46 99.21 + (Water .18)

This gives the rock the name -laugenose; in which division, according to I/ir. H. S. Washington, there are only two similar analyses in his list - this is of a foyaite and of a nepheline -porphyry" from the Laugendal, Norway (l)

In the -Geology of Canada- 1863 p. 144 - the writers state that "an intercalated mass of trap, some importance, crosses the Papineau road about a mile and a half from the St. Lawrence."

(1) Zeit Erys. 2V1, 1890 - p. 41. -106-

This huge sheet - intercalated between the limestone can be traced - within half a mile of the north end of Mount Royal, where it is covered over v/ith drift and beach deposits - but it has been traced for a dis tance of over five miles to the northward. According to the Geology of Canada - it is between 200 and 300 yards in width at the Papineau road, an dips at an angle of about 5 degrees - which would give it a total thickness at that point of about seventy-five feet. This sheet forms two distant parallel escarpments - which can easily be traced for a few nlles to the north. This rock is being quarried for road metal in ^»— several places at Mile End, so that that fresh rock is J . . - , L |Vw> in K* iu easny available. In one of these excavations several * inches of limestone is found cemented on to the upper surface of the sheet - this evidence shows that it is truly a sheet and not an overflow. Several specimens of the fresh rock were col lected by Mr. J. Austen Bancroft of McGill University and the writer, from one of these excavations at the corner of Delormier Ave., and Jerome Street. This rock is a typical nepheline-tinguaite - it is greenish-grey in color - very brittle - and frequently contains macroscopic crystals of white nepheline; black crystals of pyroxene and hornblende; greyish areas which prove to be hauyne minerals; and sometimes -107- yellowish crystals of a garnet-like mineral - When examined under the microscope - the rock is holo crystalline - orthoclase felspar is abundant sometimes in large flat plates, but oftener in lath shaped crystals - which frequently show Carlsbad twinning. In some parts of the rock the felspar is largely altered. The nepheline is abundant and apparently of two generations - small idiomorphic crystals are sometimes found enclosed in the orthoclase. Many crystals show perfect development - well cleaved, and with parallel extinction - Several of these idiomorphic crystals were measured - and 7/ere found to vary from .12 mm. to .17 mm. whereas the macroscopic ones reached a diameter of 3.5 mm. The nepheline is found enclosing numerous crystals of hauyne and apatite - and in the mere decomposed rocks is changed to hydronepbelite. Neither hornblende or pyroxene are abundant among the phenocryst - but a green variety of the latter is sometimes present - which is slightly pleochroic - and may be aegirine - augite. Some pyroxenes shew zonal structure as well as hour-glass structure - which shows a change in its iron contents when crystallizing out. The groundmass is holocrystalline and consists of numerous needle-shaped crystals of green aegirine, with a small extinction angle, about 5°. This mineral is younger than nepheline or hauyne as it is found grouped -J08- grouped about these crystals. Sphene is abundant in wedge-shaped forms - some of which are partly altered to ilmenite and leucoxene. Large crystals of hauyne are abundant - some of which are 1.2 m.nr. in diameter - and frequently have good crystal outline - especially among the smaller ones. It frequently encloses - black grains - which are sometimes arranged in zones parallel to the face of the crystal. Alliotriomorphic forms of this mineral are also abundant - some of this material resembles nosean and sodalite - but when tested did not contain any chlorine or sulphates. A separation was made of this mineral - by Thoulet's heavy solution method - the details of which may be found in the catalogue on these rock. The pow der which was precipitated - having a Sp. Gr. below 2.497 was tested; it contained no chlorine, a trace of sulphate and much lime - which shows that hauyne is present. In some specimens of this rock, rinkite is abundant in elongated prisms frequently terminating in a bunch of thin fibres, and in stout irregular colorless grains, having low double refraction - and polarizing into yellow ish white color. Lavenite is also present but not so abundant as rinkite - it occurs in irregular shaped grains yellowish -110-

and slightly pleochroic to darker colors. These rarer minerals are to be expected in this rock as it is high in the amount of radium which it contains. A successful experiment was carried out by Messrs. Eve and Mcintosh (1) at McGill University - on several of the Montreal rocks - the following results were obtained - Tinguaite - 4.3 grams of radium per gram of rock Tinguaite (different lo IT n IT n rt IT w cality) - 3.0 Essexite .26 IT IT IT H 1\ TT W Nepheline Syenite 1.1 if n n n n it n

From this analysis it can be seen that these rarer minerals are to be expected in the rocks about Mount Royal. The yellowish-brown macroscopic grains seen in this rock is the same garnet-like mineral - found in the Nepheline Syenite and which Rosenbusch has called Steenstrupine (2).

(l)"The amount of Radium present in typical Rocks in the immediate Neighborhood of Montreal":- A. S.Eve,ft.A. and D. Mcintosh L,Sc.-Phil. Mag - Aug. 1907. (2) Min. Mag. and Journal of Min. Soc. of Gt.Britain - lo. 23, Nov. 1882 p. 67. -111-

A sample of this tinguaite is being analysed by Mr. Connor - in Ottawa, but it was not completed in time to be incorporated in this paper. A dyke rock from Fletcher's Field has been examin ed - it is light greyish-green in color and weathers white. As it is very highly decomposed it is difficult to determine to which type it belongs, but it apparent ly belongs to the Solvsbergite group - It consists of an intermingled mass of lath-shaped crystals of untwinned felspar; many dark segregations in slender form in the rock suggests that aegirine was once present - and if this is the case then it is truly solvsbergite - otherwise it would be a bostonite. The felspars are highly kaolinized - and zeolitic material - frequently arranged in spherulitic forms, is abundant. It is nec^Fsary to examine fresher material of this rock - and as well other dyke which occur about the same locality. -112-

SUMKARY- A short summary might here be made of the work covered in this paper. It was noted that the present Mount Royal is the remains of an ancient volcano> longsince extinct ^but which was active in early Palaeozoic period - probably about the close of Silurian times. Signs of volcanic action is seen in the volcanic breccia found on St. Helen's Island and at various other localities about the mountain. Three periods of violent disturbances are represent ed by the Igneous rocks comprising the mountain^present ing widely differing rocks but all of which are genetical ly connected with one and the same magma basin. The Essexite represents the first intrusion and oc cupies the greater part of the mountain; this was fol lowed by the nepheline syenite magma, richer in al kalies,- while the closing stage of disturbance is seen in the numerous and vastly varying dyke rocks, which cut thru, not only the surrounding strata but also the previously intruded masses; these also intersect one another in a complicate "d manner. The first two intrusions give us an example of two consanguinuous magmas - which are intimately associated wherever found - and wherever the one occurs the other may be found in the same neighborhood. Several examples have been cited both on the continent and abroad; one of -113- the best being the monteregian Hills, where one or both of these magmas have been found in several of these hills. The practical work accomplished for the prepara tion of this paper, was largely a careful microscopic examination of over 65 different dyke rocks from various localities about the mountain. Many of these dykes are now unavailable, such as those in the bed of the Fiver St. Lawrence, in the Reservoir Extension and certain ones in the xrile End Quarries, which are be ing continually covered up. From this examination it was found that the types of dyke rocks found here are such as are usually associated with essexite and nepheline-syenite centres - such as camptonites, monchiquites, alnoites, tinguaites and bostonites. In very few localities does one find so many different types occuring together and providing such a variety,- from those rich in alkalies as seen in the bostonites, to those low in silica and very rich in ferro-magnesian silicates as seen in the pyroxenites. These series of dykes have been seen to represent various ages of intrusion, this is especially seen in the Reservoir Extension - where several intersections have been noted, but owing to the lack of detailed knowledge, nothing definite could be accomplished regarding their relative ages. Decomposition is so advanced in these rocks that it renders them difficult to be studied microscopically. One remarkable rock was determined -114-

that of the alnoite dyke from the bed of the River St. Lawrence; which is very rich in melilite and perowskite; while as equally an interesting one is seen in the tinguaite sheet at Mile End, which is rich in radium and in which was found a considerable quantity of rinkite and lavenite. Although melilite and these last two minerals was not detected in any of the other rocks examined - yet it is probably present -and might be found if fresh specimens of many of these rocks could be obtained. It is necessary that several more of these dyke rocks occuring about the slopes of the mountain should be examined before anything definite can be published on the relationship of these various rocks. The writer desires to acknowledge the valuable advice and assistance received from Dr. Frank D. Adams,

(ULH'IMII** VV\ while preparing this investigation - and also to Mr. J. Austen Bancroft, and Mr. J. A. Dresser for their aid in the practical work.

Petrographical Labratory HfU A)- X/JAICZAAL,. McGill University - 1908. "~