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 . R| ICROSCOPIC PETROGRAPHY 
 
 W. th •'»..», 
 
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 OF THE 
 
 0rift qf Çeàtral- Ontario. 
 
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 Tmm, K^. Sk., 
 
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 "^^ Section III, 1887. 
 
 i 43 
 
 Tbans. Roy. Soc. Canad.\. 
 
 VII. — Micro8copic Pétroijraphy of tJie Drift of Central Ontario. 
 
 L 
 By A. P, Coi^KMAN. 
 
 . '*• ' (Communicated by Dr. T. S. Hunt,^ay 25, 1887.) 
 
 Mioroscopic petrography is being so eagerly studied, aud affords such intoresting 
 results in ail lands at the présent day, that no apology is nedessary for the présent contri-^ 
 bution toward a subject hitherto but little cultivated in Canada. Where so much of the 
 région is petrographically terra incognila^ perhaps no better beginniug conld be madc than 
 withthe materials so profusely snpplied by the drift of Ontario, which oflfcrs spécimens 
 of an immense variety of rocks derived from Avarions distances to the north and east, and 
 especially represeuting the Laurentian région. ■ By way of foûndation, and for the sake of 
 comparison with the results brought out by the masterly works of Rosenbusth, Zirkel, 
 von Lasaulx, and a host of other enthusiastic students of this most récent of the sciences, 
 a somewhat compreheusive discussion of the microscopic characters of our rocks may be 
 permitted ; so that much that is well known will be briefly sketched, while spécial atten- 
 tion will be paid to features that appear to be new or^vinusual. It should be stated that 
 the spécimens examined hâve been collected at various points in Central Ontario, but 
 chiefly in the vicinity of Cobourg ; and it may be added that the mérely mechanical work 
 of prepmjing the 150 rock sections required has beea by no means inconsiderable. 
 
 I. — General Description of the Drift. 
 
 As exposed along water-courses and lake shores, the drift is seen to consist of clay, 
 sand, gravel and bould,er8, the finer materials often laminated, sometimes obliquely, 
 with a false bedding resulting from the action of shifting currents. In other cases 
 there is no stratification, and clay, sand and gravel, with intermixed boulders, lie 
 pell-mell where dropped by the melting of ice. The underlying SHurian limestone is 
 polished and striated, the striations near Cobourg running nearly east and west (S. 80° 
 or 86° E., magnetic), with the thrust from the east. " Soled '^ bouldei*s with one or 
 more flat striated surfaces shew the tools with which the work was done. 
 
 Sajids. — Examined with the microscope, the sands prove to contain, in addition 
 to sharp-edged particles of quartz, a large amount of calcareous matter and small 
 fragments of plagioclase, perhaps, also, orthoclase and green or brown hornblende — 
 shewing their origin in the massive and schistose rocks. 
 
 Oravel. — Imbedded in the sand and elay, or forming independent strata, are 
 Bubangular or ronnded pebbles, more than half of them limestone, the rest of varions 
 Laurentian rocks.^ The shape of the pebbleB ig détjftmydby th e clfiava ge of t hft jtatent^ 
 
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46 
 
 COLKMAN ON* THK MfCROSCOPIC 
 
 rock, iftassive rocks giving peBbles with their varions diameters net far from eqn^l, while \ 
 laminated or schistose rocks, afford flattâned ovoid forma. 
 
 Boulders. — The boulders are of ail kinds and sizes, fromlarger pebbles to masses of 
 several tons, which the farmer must blast or undermine and bnry to get rid of them from 
 hia fiëlds. They are usually more or less rounded, and dre very unequally distributed. 
 More than half of the smVUer boulders are ôf Lower Sifurian limestone, Avith the usual 
 fossils, and sometimes nodules of chert, which' is not found in, Silufîan outcrops near 
 Cobourg, " * 
 
 No further notice of the common limestones of. the drift, or of the other clastic rocks, 
 such as slate or sandstone, which are very rare, will be necessary in this paper, which 
 will be devoted to the crystalline rocks. The crystalline limestones will be referred to 
 briefly first, and afterward the massive and schistose rocks will be treated more ai 
 lengtn. \ , . ' ' 
 
 'IL— Crystalline Limestones anI) Dolomites. 
 
 Macroscopic. — ThesQ, rocks vary in grain from very coarsc to compact, and in color from 
 the pure white of saccharine marble to yellowish and bluish greys. They shew no traces 
 of fossils, but yet are more or less evidently stratified, and no doubt are metamorphosed 
 sédiments. 
 
 Microscopic.—JJuà&T the microscope they are found to consist, of course, of calcite or 
 dolomite, more or less pure, and présent the usual rhombohedral cleavage and duU 
 colors with polariéed light. As accessory minerais, quartz is the commonest, and may be 
 présent to the- extent even of one-third, while biotite sometimes occurs in so large an 
 amount as almost to form a calcite schist. In addition, pyrite, muscovite and hornblende 
 are found sparingly. Tremolite and actinolite, or intermediate varieties of hornblende, 
 make upan important part of the rock in a few cases, the tremolite in grey radiating 
 prisme, and the actinolite as handsome sea-green prisms. In one such specimein, there are 
 portions of quartz containing fluid cavities and cubes of sait. 
 
 It is pcrhaps worthy of mention that, in one spécimen, the outer layer of calcite proved 
 to be pierced by a network of the rhizoids of lichens. The boring power of thèse délicate i||k 
 thread-like cells is remarkable, and must dépend on the çresence of carbonic or some 
 organic acid dissolved in the cell sap. 
 
 III. — Chaloedony. 
 
 A few small masses of chalcedoiiy'are found in the drift, derived probably from veins. 
 One spécimen is of a pale turquoise bluè, fading on exposure, and cointains scales of talc 
 and small fragments of other mineraUf ; while a second spécimen is so impregnated with 
 yellow oxide of iron as to approach jasper. 
 
 Microsœpic. — Thin sections display with polarised light the usual microcryatalline 
 structure, varied by radially fibrous parts in which a black cross may be seen. 
 
 / 
 
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 é. 
 
 PKTROGRAPHY OP ONTARIO. 
 IVi— Massive and Schistose Rocks. 
 
 47 
 
 In the rea mont of the^è roclcH. the line betweon massive and schistose oannot be 
 drawnso closely as m the/stndy of rocks in situ, ..hère the broad strnctural li nés are 
 easily se.n. Rocks wh,ch/on the small scale^f aboulder. show no trace of parallelism 
 m their constituents, wil ; be considered " massive " ; bnt in the case of the granités and 
 gneisses, where most of tf^e difficulty occurs, the distinction is perhaps not vital • since 
 m many places, as, for instance, in the Thousand Islands, the two seem to run into one 
 '^anotner. / 
 
 In gênerai, for the ^aasive rocks, the arrangement of Rosenbusch' will be folloWed 
 whiie, for the schistose, r^oks von Lasanlx^ will be taken as guide 
 
 Thèse rocks may bè divided broadly into an acid and a basic séries, and we shall com- 
 mence with the acid séries, which is characterised by the présence of one or more species 
 ^of potassium felspar^ It may be subdivided into a subsorios containing quartz as an 
 essential minerai, and a subseries devoid of quartz, or nearly so. -, 
 
 1 
 
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 ACID SERIES. 
 
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 MA'SSIVE. 
 (1.) Those coiitainiiiR Quartz. 
 
 TTie C ranites. 
 
 The aduç^rible description of the granité^ 
 Rosenbusch' hôlds for the most part when s^ppl 
 
 id their constituent minerais given by 
 'lo't^e granités of the drift of Ontario, 
 
 case of orthoclase, which Rosenbusch makes 
 granités it is almost wholljr replaced by a 
 
 though one ex<^éption should be made in the 
 an essential eleàlent, yhile in some of our 
 triclinic orthofilase felspar, microcline. j 
 
 We shall dofine granité as "a rock ' composed chiefly of quartz, orthoclase or 
 microcline, jnd some sodium-calcium-felspar, with more or less biotite, muscovite or 
 hornblende. Taking up the minerais in this order, we hâve :— 
 
 Quartz.^This never shews crybtalline faces, so far as my observations go, but alwavs 
 forms irregT^làt masses and fragments, consisting, as shewn by polarised light, sometipies 
 of but one individual. sometimes of a number clustered together. It is always fresh and 
 transparen^, unless rendered turbid by cavities and inclusions, which are often very 
 numerous. The ctfvities may contain a liquid (water or carbonic acid), à moving bubble 
 and often Jlso a cube of sait. Solid inclusions of varions kinds also occur..8lender and 
 hair-hke. 6r interrupted;like télégraphie charaeters, or eut ùp into rows of dot* or seat- 
 tered as dusty particles. Hexagonal plates of a drab color. partly covered with îed oxide 
 
 » MikrqèkopiBche Physiographie der maasigen Gesteine, 1878 ' 
 
 'Einfymng in die GeatetoBlehre. 1888. ^ .Mik^B. Phyi, der m«. Qe.t, pp. 7. etc; 
 
 / 
 
 * Sfêl^^i ^ 
 
 
 
48 
 
 COLRMAN ON THE MICROSCOPIC 
 
 S 
 
 of iron, are sometiraes numerous, and slender, trapsparent prisms of âpatite ; în fact, 
 almost ail of tho Bubstaiices meiitioned by Zirkel,' Hussak and others. 
 
 Orlhodase.—Oï tho ^felspars orthoclase may be described first, though in our rocks 
 microline is usuully more abundant. It is one of tho least satisfactory mineralp to diagnose, 
 since its crystalline form is rarely évident, and the cleavage angles of 90Vso distinetiVe^ 
 for maoro8(;opic déterminations, are seldora seen in microscopii; sections, and in gênerai thé 
 characters of the minerai are négative. When badly weathered, one iS often in doubt . 
 whether a given felspar is not a plagioclase, in which the atriations hâve been obliterated. 
 The orthoclase is generally flesh-colored or red, probably from the séparation of ferrie 
 oiide, though this is not al^ays evid^int under the microscope. Near fissures, where, 
 from the decay of plants, orgjinic matter is présent in solution, deoxidation sometimes 
 takes pla,ce, and the rock is bleached ^rey. Inclusions similar to thoso of quartz are 
 found, though in smaller .numbers as a Vule. Cavities containing a liquid hâve not been 
 certainly observcd by me in orthoclase from from the dyift. , . 9 
 
 Microperthife. — By far the most commun inclusions in orthoclase are thin lamelltc of a 
 transparent minerai, differing optically from orthoclase, and described by Hussak and 
 others as albite. Thèse lamellas are arranged in a roughly parallel way, and in cross- 
 section remind one of d shoal of slender fish. They do not swaim equally in ail parts of 
 the crystal, but vary much in numbers as well as in size.* This variety of orthoclase 
 (microperthite) is very common. In a few instances combinations of orthoclase and 
 plagioclase of a différent kind occur, in which an individual of each pénétrâtes the otl;ier, 
 80 that in polarised light an intermingling of cloudy patches, with twin striations and 
 without, may be seen. (Plate II, fig. 4.) 
 
 Microcline. — A triclinic form of the potassium felspar, microline, is rarely absent from 
 the drift granités examined by me, and in many cases it surpasses orthoclase in amount. 
 The différence between the two is best brought ont by polarised light. Moderately thick 
 sections présent the most gorgeously colored tartan pattern imaginable, in which scarlet 
 and orange and blue are mixed in an extraordinary way. The imperfect twin lamellœ, 
 which are supposed to give this structure, cross nearly at right angles, and are sqmetimes 
 woven as warp and woof into a singular cloth-like texture, though generally more 
 loosely put together. Sometimes the structure described is distinct at the edges, but fades 
 out to a uniform color in the middle, reminding one of the effects of strain in modifying. 
 tl;ie optical properties of bodies. (Plate I, fig. 3.) Microline is very apt to contaiu the 
 inclusions previously mentioned as forming microperthite. Micropegmatite, a regular 
 intergrowth of orthoclase or microcline with quartz, is seen in a few of the sections. Ail 
 thèse varieties of felspar are very apt to weather, usually becoming turbid from the 
 formation of kaoUn, while in other cases a dirty, yellowish green substance of a fibrous 
 nature forms alonig the cleavage, lines and fiUs patches of the crystal. Epidote in pale 
 yellowish, faintly dichroic, grains or crystals is frequently found as a product of the 
 décomposition of orthoclase. 
 
 Plagioclase Proper. — The sodium-calcium felspars fire more variable in amount than the 
 the potassium felspars, and, when not too much weathered, are readily distinguished by 
 
 
 ' Zirkel, Mikr. Be^ch. der Mineralien und Gesteine, 1873, ppw 64, etc.; Rosenbusch, Mikr. Phys. der petro- 
 graphisch-wichtigen Mineralien, 1873, pp. 222, etc. ; Eugen Huasak, Gesteinbildenden Mineralien, 1885, pp. 106, etc. 
 
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 ►^ 
 
 PETROGRAPHY pF ONTARIO. 
 
 49 
 
 he.r polysynthetio structure, whi.h is well brpught ont by polari«ed OigM. The twin 
 lamellœ are often devdoped in two directions nearly perpendicular to one auother. form- 
 mg a cross-barred strmtturo qnite unlikc^jthat.of microclin/f The gênerai habit, inclusions 
 und décomposition procfucts of the plagiochvses are very much like those of the potassium 
 felspar. and need no spécial notice., No attempt has been mado in this iuvestigation to 
 dividp up the plugioclaM of tlie acid r(>ok8 into subspecies. ' 
 
 ^w/rtc-Of the ba^ic silicates biôtite «is the 'commonest. thôugh closely followed by 
 hornblende This mic« is usually browu, though sometimes green. and in sections not 
 paralWto ho chief basai oleavage is knqwn by its enormons absorption when its cleavago 
 18 parallel to the section of t^io lower ni<foI, the upper nicol having been removed. The 
 optical axes, which are eeen in basai sections, usually include so small an angle as to give 
 the idea of a hexagonal minerai, though sections of a hexagonal outline are rare in the 
 granités. Except small brown or black «cales wodged in betweenthe cleavage lamollœ 
 inclusions are uncommon. Biotite appéars to weather to a confused fibrous substance of 
 greenish or browni^ colt«-, with oxides of iron. In one case fragments appear to be 
 lucluded in epjdote, as though remuants of metamorphosed crystals. 
 
 Muscomte is much rar^r than biotite. and from its colorlessness or faint color. and 
 hence want of dichroism. is less obvions under tho microscope. A peculiar moiré lustr«4^ 
 polarised light is characteristic' In habit it is. much like biotite. with which it is fre- 
 que^tly found intergrown. In some instances tho muscovite seems to hâve originated 
 by the décomposition of potassium felspar. as shewn by its position within orthoclase 
 crvst&is. ., , 
 
 Homblende.-ThiB often âccompanies or replaces biotite, and is readily known by its 
 c eavage and optical properties. It is usually green, but sometimes brown. with strong - 
 pleochroism. It often weathers tb dirty greenish or brownishchloritic substances, with 
 the séparation of magnetite or other oxides of iron. In one spécimen it bas changed to 
 pale greenish epidote, which forma a perfect pseudomorph, with the exceptioa of an un- 
 changed remuait of hornblende in.the centre. In one section small fibre's of glaucophane 
 occur.having^insepleochroism (indigo blue.drab.coloHess).., « 
 
 Accessory^^erals are numerous, such as magnetite, which occurs with rectanirtilar 
 cross-sections or m irregulàr grains. In some cases thé magnetite is probably ù^Wmarv 
 ongin ; m others it is formed. often with brown or red oxides of iron as well. by the àl 
 composition of hornblende or other minerais rich in irJn. It is occasionally titaniferous 
 as shewii by an auréole of ^reyish leucoxene. Titanite also occurs in brown slightly 
 dichroïc cross-sections of the usual sharpened oval shape. Apatite. is vwy commob; but 
 in minute amounts. Its slender needles must hâve been the earliest crystallisations 
 since they transfix the other minerais impartially. Pyrite and other metallic sulphideJ 
 are «(^casionally found in dissemitfited grains or crystals. U products of décomposition 
 we tind secondary quartz, epidote, varions serpeïitinous and chloritic minerais, oxides of 
 iron and (rarely) calcite. 
 
 , The varieti'es of granité so lucidly described by Kosenbusch' are found in our drift - 
 » BiotUefhomblende-^^mUes exQ iiommonesi. ^— .-.- 
 
 Homblendê-gtmiies, mica being replaced by hWnblende, tome neit in freqnency. 
 
 Von Lasanlx, Einf. in die Gesteinslehr», p. 62. 
 
 'Mikr. PhyB.,pikl8,ete. 
 
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 00 , COLEMAN ON. TIIB MICÎROSCO^FO 
 
 . ^ ^ • ■ '..■-■■//■ 
 
 , Muscovite-graniles are tfucômmon. ,.. , / 
 
 Granité Proper, eousisthig of qu|-tz;'orth(xài8e,pla^iocIaiio, biotitjs and miucovite, 
 seems rurest of ail. ^^' - / . • ''* 
 
 Our granités vary in grdin from rocks with tL'individaal minerais an inch or ihore 
 in diamoter to very finè-grained ones ;^d in color from llesh-red. wliich is common. to 
 ligiit ot datk grey, or evàn light greenish grey, the prevailing felspar usually giving the 
 tond In relative amounts of their ingredityjts, also, tl^oy diller very much, sorao of the 
 muscovite granités, as observed by.Rosonbusch in Europe, being very rich in quartz, 
 whilo biotito-hornblende-granites, by tncrease pf thèse "two minUralsand diminutionN)f 
 quartz, fôrm a transition toward syenite. In a *few pcgmatitic spécimens mica is alraost 
 wanting. ' - -.■, 
 
 Felsite. 
 
 l 
 
 N 
 
 AfocrojovMf.— Quartz porphyries seem to be unreprèfeented in the drilf^f this région, 
 unless by a few felsites. Thèse are massive and, compact Ilesh-coloured rocks in which à 
 few quartz blebs and crystals of orthocllseand plfigioclaae may be recognised with a lens. 
 or the naked eye. ' 
 
 Microscopic.—Th^ b^lk of the rock is^coraposed of a microgranitic magma of quartz 
 and felspar, or else a microfelsitic one, giving a wândering play of lî^ht and shade between 
 crossed niçois without distinguish^ble minerais. The minerais found in thèse rocks are the 
 sameas those of the granités, but generally difFeVing in habitus. No cavities hâve beèn 
 observed iH the qtiartz of the magma, though thèse are common in the porphyritic blçbs, 
 and then conta^n a liquid with a moying bubble and often a cube of sait. In one section 
 a plagioclase crystal bas a portion broken out and shifte^d a little to one side, indicatinfe 
 motion after the formation of this crystal and before the solidification of the magma. îjTo 
 glass or oth,eT istropic substajice wafi observed. , 
 
 N 
 
 («.) MacMlre rooks ft-eo lyom Qaartz or nearly go. ' 
 
 Syenite. ' 
 
 This rock is comparatively rare in our drift, Jndthe spécimens e^amined ail belông to 
 the biotite-syenites of Rosenbusch. They are coarse or médium grained, reddish or reddish 
 Çreyin c^lor, and are composed of orthoclase, microcline &d ordinlugr.plagioclase, with 
 much biotite and a little hornblende. Apatite. magnetite and titanite occur as secondary 
 minerais. The descriptions of the constituents of the granités apply fully to those of 
 syenite. 
 
 . - ■ ■ f ",♦-■:, 
 
 ■ - o " ■ . ■ .B. 
 
 SCHISTOSE. 
 
 . _ „ • ,4 / 
 
 The dcid schistose rocks regularly contain quartz, so that the subdivision "free from' 
 q«artz,^« wlridi wTOld-correspond to th& syënîtës àmong the massive rocks, îs absent, fo 
 this rule a solitarjr exception bas been found in a single specimen»of felspar rock in which 
 quartz was wanting, ; 
 
 
 ■ I : 
 
 
 ^^^^^l^éS^IJ^i^.» Jii'iL"i *ii^.^j^^^ 
 
, 1 
 
 PliTRQORARUY OF ONTARIo", 
 
 01 
 
 Gnetsi 
 
 «ace it confina l.„e S\ ron^^T^ ÙT *, '*"'°" '" '"^ ""dently cImUc, 
 
 i^nite .he .»e w.yl .Cnd .iTl^» ° ""' '' ""•"" ""• "-^ «^J-'f—â-. ' 
 
 " - - Haileflinta. " ' < 
 
 . ■»iaer.l.c«,bedi°int^l(rMiût '^^ ?^ '«^'"'■'"', 
 
 ^ or hornblende mayoccur also bnt n«f «* -11.1: Tu "^ ^'***'*^' muscovite 
 
 ^ed .M.H. ^^^.^ m;^i=:'^^^ 
 
 _>^ 
 
 «,■ 
 
 
 »*. 
 
 '-? 
 
f^^^-^ 
 
 P^ifn^f-ctfe^-^--' 
 
 ■T-^^^'XQ:mr*^j 
 
 52 
 
 COLEMAN ON THE MICROSCOPIC 
 
 prismSi^nd pyrite. Exôèpt in porphyritic blebs of quartz,, no fluid cavities were observed 
 in the hâlleSinlaâ. Thèse obscure rocks vary much in composition, and transitional 
 forms Connecting them with gneiss and felsite are easily found. Some spécimens, con- 
 taining minute particles of hornblende in large numbers and but little felspar, are hard 
 to separate from the compact varieties of horublendic schist. 
 
 Felspar Rock. 
 
 A spécimen ^of pale flesh-colored rock, consisting of plagioclase and probably ortho- 
 clase, witn scarcely anything else, may be mentioned hère, as the rock seems, schîstose. 
 The felspar individuals are ill defined and badly weathered to a granular substance of 
 doubtful nature. . * 
 
 The other schistose rocks, such as mica.schist, quartzite, etc., bave not been observed 
 by me in the drift of this région. ) 
 
 BASIC SERIES. 
 
 - A. 
 
 MASSIVE. 
 
 The rocks are characterised by the présence of a plagioclase other than microcline 
 and hornblende or augite, almost invariably accompanied by magnetite or titanic iron ore. 
 
 The massive rocks of the séries may be divided into diorites, containing hornblende 
 or biotite as an essential minerai ; and diabases and gabbros, in which hornblende is 
 mainly or wholly replaced by some species of augite. 
 
 
 ^ 
 
 The Diorites. 
 
 Most of thèse rocks are badly weathered, so that their constituents are not easy to 
 détermine. Some spécimens coUected as diorites hâve proved to be diorite-schists on the 
 one hand, or diabases on the other, so that the group appears to be comparatively small. 
 
 Macroscopic. — Thèse rocks are in gênerai médium grained, rarely coarse, and of a dark 
 green-grey color. 
 
 jSkrosœpic. — Quartz is found occasionally, but not in sufficient quantities toconsti- 
 tnte u au essential minerai. Secondary quartz is more common than primary. 
 
 Felspar. — It in doflbtful if orthoclase is présent, but if so, only in small quantities, 
 and microîcline hàs not been observed. On the other hand, the ordinary plagioclases 
 make up/fc considérable portion . of the rock. They are usually turbid and much 
 weathered. The variety seems to vary much, the angle of extinction from the twin plane 
 ranging from 8° to 20'. This w^uld indicate oligèclase and labradorite with intermed- 
 iate varieties. Two Systems of twin lamellsB are commonly found, inclined to one 
 another at an angle of about 86°. 
 
 Tu Honw of thft felapars {probably jglagioclase), the oentrejof the crystals jiflfers from 
 
iTj-j'w JT"<V î^T^^l:^^*^ 
 
 ^^. ' ^ , rt -'!^ ?^ ^^'* y 7' rTf ^ ..'™^. *f ^•* fy t, '*""î '^'^ .^.?".J.T ! 
 
 t . 4._ > <^'jH*^h \'*^' >; 7^1... 
 
 ^ 
 
 PETROGEAPHY OP ONTARtO. 
 
 88 
 
 the margin^n its angle of -«xtinction, the light or shade beginning in the centre and 
 flowing wave-like to the circumference on révolution between crossed niçois. This 
 probably results from a vague zonal structure, the centre differing chemically from the 
 exterior. 
 
 Hornblende. — In the spécimens examined, this minerai is generally in tolerably compact 
 crystalline masses. It is highly pleochroie, changing frçm blue-green or brownish-green 
 to yellow or yellowish-green. Occasional twins are seen, having the orthopinacoid as 
 twin plane. 
 
 Blottie. — A little biotite usually occurs, generally brown or dark green, sometimes 
 with parallel plates of light grass-green mica on the outside, perhaps a resuit of 
 weathering. . - 
 
 Magnetite is uniformly présent, unless replaced by titanic iron ore or ilmenite with 
 a wide rim of leucoxeim. Titanite is sometimes found, and in a few cases, augite is 
 suspected. Epidote a^|pther décomposition productsof the felspar and hornl^^^de, are 
 of course very often met. 
 
 With few exceptions, the drift rocks of this group belong to the diorites proper. In 
 one spécimen, however,- the biotite is important enough in amount to warrant us in 
 setting off the rock as biotite-diorite. Another may be named diorite-porphyrite, since 
 reddish and greenish plagioclase crystals are thickly d^seminated through a dark green 
 . magma, consieting of minute strips of plagioclase and hornblende, with grains of magne- 
 tite. This rock is decidedly handsome. é 
 
 Diabase. 
 
 ■\ 
 
 The rocks in which some species of augite is an essential ingrédient are not very 
 numerous iil the drift, but are interesting from the variety of minerais they contain. 
 
 Macroscopic. — Thèse are generally rather coarse-grained rocks,- differing from the 
 diorites in having a darker, often purplish, grey colour, and in wanting the light-colored 
 felspars, which are apt to give a spotted look to the latter whèn weathered. 
 
 Microicopic. — Quartz is rare in the drift diabases, having been found with certainty in 
 only twoof the sections examined. Orthoclase is found, more or less donbtfnlly, it is true, 
 in about half the sections studied, but>in small amonnts. 
 
 Plngiodases. — Thèse are found in considérable quantities in almost ail sections. 
 The twin structure is characteristic, and there are frequently two Systems of striations 
 Crossing at an angle of 86°. In addition to this Carlsbad twins are sometimes found. 
 
 In composition they appear to belong chiefly to the varieties rich in calcium. The 
 angle of extinction .on each side of the twin plane was found in a few cases to be about 7°, 
 corresponding to andesine. It was generally, however, in the neighborhood ôf 19°. In a 
 few crystals, where the angle coald be read for both sets of twins 24^° and 31° or 82° 
 were observed, indicating labradorite. 
 
 Most of the larger crystak are rendered more or less greyish by innumerable fine dots 
 and minute dashes, often arranged in ^ws, sometimes so as to look curioosly like the 
 short hair of an animal. Thèse inclusions maybe arranged in two or even three planes, 
 forming triangles in the latter case by their intersections. Oblong brown plates with 
 olean-cnt angles and othera pf ron nd or oval forma ar e alao Been. Apati te ory stal B ara. 
 
 t. 
 
 t 
 
 «k^^#t,^ 
 
 ,i* ïhjÀfk'"*','.. '!.$», 
 
 Vx-sd 
 
 -xHI 
 
 
■'ymf' 
 
 64 
 
 COLEltfAN OH THE MlCEOSCÔPlC 
 
 H, 
 
 common as inclusions, and also sharp-edged crystals of epidote gleaming like jewels in 
 polarised light. The latter may be secondary, but their complète odtline and the want of 
 other évidence of extensive change in the plagioclase, seem to suggest a primarjr origin. 
 
 Au^e.— Â.t least three species of augite appear in thesa rocks. în addition to the 
 common augito we hâve diallage and a rhombi,c species, probably hypersthene, 
 
 The first variety is colorless and transparent, or greyish or green, when pioderately 
 fresh. It is apt to take on irregular shapes, filling up the interstices betwcen the crystals 
 of plagioclase. It bas the usual rough surface, two jiot very perfect cleavages incliued 
 about 90° to one another, brilliant coloring with polarised light, and an angle of extinc- 
 tion of 35° or 40". It tends to weather into hornblende, uralite, or greenish chloritic 
 substances, slightly, if at ail, pleochroic and magnetite. 
 
 Diallage occurs chiefly as irregulJtly terminated prisms, with longitutinal fibres or 
 striations. It is usually dull greenish or brownish grey, only faintly pleochroic, and 
 faintly colored in polarised light. It very commonly encloses regularly oriented scales of 
 a brownish color, sometimes two sets at right angles to one another. Edgewise, thèse 
 scales look like délicate dashes (Plate II, fig 3). The diallage weathers to the same 
 products as common augite. 
 
 Hypersthene, or possibly sometimes bronzite, resembles diallage, but is rhombic, as 
 shewn by the extinction when the striations are parallel to the chief section of either 
 nicol. It should be mentioned, however, that extinction is only faintly marked as a rule, 
 and that some fibres seem to bo always light. 
 
 Inclusions similar to those of diallage are found in hypersthene, but generally in 
 much greater numbers, so as even to détermine the color. The hypersthene is quite pleo- 
 chroic, yellow and blue in crystals eut so as to show the edges of the inclusions ; red- 
 brown and drab where the flat sides are presented. Patches of hypersthene are often 
 encloeed in diallage crystals. (Plate II, fig. 8). The glints of bronze or copper reflection 
 caught from rocks of this group come from crystals of hypersthene or diallage. 
 
 Hornblende is sometimes to ail appearance primary, but generally secoriflary and 
 uralitic in look. The irregular masses of hornblende hâve at times a spattered appear- 
 ance, spreading from a centre, and greatly mixed with other minerais. Their color is gen- 
 erally green, but sometimes brown and almost red. Hornblende often forms a margin 
 around the augites, the twp minerais having their chief axis in common. (Plate II, figs. 
 1 and 2). 
 
 Biotite occurs in small amounts, and, as a rule, apatite is found in the same spéci- 
 mens, Magnetite seems universal, but titanite is rare. Scapolite is found in one or two 
 sections. 
 
 FoUowing Rosenbusch, thèse rocks may be divided into : — 
 
 Proterobase, containing primary hornblende. 
 
 Diabase Proper, containing only secondary hornblende. 
 
 Gabbro, in a fe>Hr spécimens where diallage replaces common augite entirely. 
 
 tlypersthene Diabase, where much rhombic augite accompanies the monoclinic species. 
 
 It should be stated, however, that the gênerai habitas is very constant, and the varie- 
 ties are united by transitional forms. . ' 
 
 One spécimen of diabase proper is worthy of separate mention for its remarkable 
 mode of weathering. Thé plagioclase, which is in long prisms, has a comparatively clear 
 
 \ 
 
 \ .J-fe'Ai.» 
 
 \, 
 
 r ^ 
 
 **W. ÊJa t ..^ ilA-ili* lUh,*'.V • *<.'"«■»! 
 
 r^ 
 
•^■y *■ ' ! - 
 
 •' -■♦»" ;; 
 
 PETBpGKAPHY OF ONTARIO 
 
 86 
 
 margin, but in the centre is so Â;|owded with brownish or greenish particles arraneed 
 in rows parallel to the Idngest A^ of tho crystals as to be almost opaque even in the 
 thinnest sections. , / | . 
 
 . The augite is surrounded by a! double zone of décomposition products, the outer ono 
 dujl grey the inner one traflspareùt and made up largely of fibres^perhaps of quartz and 
 hornblende) arranged radially aroiind the kernel of sound augite (Plate I fig 2) Similar 
 zones surround almost ail the other minerais, such as biotite, apatite, and even pla- 
 gioclase. Some cryatals which appear to be augite are crossed by irregular bands of 
 magnetite m a way suggestive of olivine, and even the optical characteristics sometiraes 
 resemble those of a rhombic minerai. Unless thèse are really olivine. that minerai seems 
 to be wantin^ m our diabases. 
 
 f . * 
 
 B. 
 
 SCHISTOSE. 
 
 Turning now to the schistose basic rocks, we fihd very few spécimens belongin- to 
 the augitic group. 1 , " 
 
 I Diabase Schist. 
 
 But one example was studiéd under the microscope. This is very fine grained li<rht 
 green-grey, and cotoposed of minute grains of quartz, probably some felspar, a little'green 
 hornblende, and much badly IVeathered augite in dirty grey fragments or prisms Its 
 cleavage and optical characters make its nature certain. A little titanite is found as an 
 accessory. 
 
 Scapolite-Diorite-Schist. 
 
 Before considering the hornblendic schists proper, an interesting group of rather 
 doubtfu position may be described. Ab they présent an unusual combination of minerais 
 they wiU be treated somewhat in détail. * 
 
 Several handsome coarse-grained rocks of green-black hornblende, intermingled with 
 violet-grey portions, shewing hère and there the striations of plagioclase, were collected 
 as diorites. They are massive in appearance. but often shew traces of a rough parallelism 
 of their constituents. so that tKey should probably be referred to the schists 
 
 Muroscoptc-JJnder the microscope, the hornblende proves to be of the usual dark 
 green, non-fibrous kmd, and needs pao particular mention. 
 
 Pl^lase.-The lighter portions ar« found to consist partly of plagioclase of a type 
 resemblmg that of the diabases. It is slightly dusty in appearance, and of varying com- 
 position, as suggested by the angle pf extinction from the twin planes. A variety ranginir 
 ri!".^.«';«''°*r'^?^'°"^''^= anotherwith about 21° is the most fréquent, thougha 
 tJurd ot 81 . perha^om twin plagies according to another law, is uot Visual. This ■ 
 indicates albite oijpsine and labtadorite. The plane.of the twin striations. as in the 
 diabases, , s often bent, and there is a tendency for a crack to appear at the apex of the 
 
 4 -m 
 
 \'': 
 
 
86 
 
 COliEMAN ON THB MICROSCOPIC 
 
 Scapolite. — In addition tcrthè plagioclase, and ofteû laygfeïy replacing it, is a minerai 
 which appears to be one of the sqapolit'es. It forms irregularly shaped masses, wedged in 
 between the hornblende and plagioclase ; or olse oval portions are massed together, with 
 their longer axes nearly in the same direction. Sections not at right angles to the chief 
 axis, nor nearly so, shew a decided longitudinal cleavage, sometimes with hints of an- 
 other cleavage perpendicular to it. Those sections shew bright red and green hues in 
 polarised light, and are bordered with strips of rainbow coIots. Extinction is very perfect 
 parallel to the cleavage." jr 
 
 Other sections nearly at right angles to the chief axis hâve a rather imperfect rect- 
 angular cleavage or no deiiuite cleavage at ail. Suoh sections give faint coloration or 
 none between crossed niçois, and observed thus with the eyepiece reraoved, display a 
 black cross which does not separate into hyperbolas on révolution. The minerai is qiiad- 
 ratic and optically négative. The only spécimens thât could be examined macroscop- 
 ically were from a veihlike portion of rather weat^ered rock. They haye a yellowish 
 col or, waxy lustre, and hardness of about three. A portion examined by blowpipe 
 méthode by Dr. Haanel was pronounced " wilsonite ", a modified scapolite. A less 
 weathered portion obtained with difllculty gave hardly a trace oCjnoisture in the matrass ; 
 so that probably the clear sections observed under the microsc&i)e may be considered 
 scaiwlite (Plate J, fig. 4). *.„ ^i * 
 
 lu most sections, the rainerai appears quite fresh and free from inclusions. The plagio- 
 clase beside it is of the ordinary type and but little weathered, so that the scapolite must 
 be considered an original constituent of the rock. Since it makes up in most cases at 
 least a quarter of the whole (as estimated under the microscope), it cannot be looked on 
 as an accessory minerai. 
 
 Magnetite is common in the rock, while ilmenite and titanite are much less so. A 
 little quartz occurs in perhaps half the sections, and orthoclase is suspected in a few. 
 Biotite is seen now and then, but in very small quantities. The rock, which is not un- 
 common in the drift, may be named : — 
 
 Scapolite-diorite-schist, or posfiiblyl since the schistose character is rather undecided, it 
 may prove to be scapolite-diofîte. 
 
 One spécimen proved on examination to contain beside much hornblende and scapolite, 
 a considérable amount of microcline and quartz, the latter with fluid inclusions and 
 moving bnbbles. In addition to the minerais mentioned, a large quantity of sea-green 
 angite was fouud, often bordered with hornblende, the two minerais having their chief 
 axis in common. This rock seems to connect scapolite-diorite-schist with gneiss on the 
 one hand, and diabase on the other, certainly a wide range of affinities. 
 
 X>iorite and Homblendic Schists. 
 
 Coming now to the undoubtedly schistose homblendic rocks we find a most extensive 
 and varied, but not specially interesting, group of rocks. They fill the same position in 
 référence to the diorites as the gneisses occupy toward the granités. They range from 
 compact to coarse grained. In color they are chiefly dark grey, verging on green. In 
 structure they are usually distinctly schistose, sometimes exceedingly so, the cleavage 
 being determined by the parallelism of the hornblende individuals. In some cases where 
 

 K'-t" 
 
 P'ETBGGEAPHY OP OîiTARIO. 
 
 87 
 
 {his minerai forms élencler parallel prisms, the rock has two very perfect cleavages and 
 splits into long, roughly prismatic slabs. ' 
 
 Microscopk.—în the composition of thèse rocks, hornblende almost invariably plays 
 the chief part, regularly accompanied, however, by a considérable amount of jjuartz and 
 magnetite in small grains. In most cases also more or less plagioclase is found/ Accessory 
 minerais are tolerably common, such as biotite, ilmenite &n^ pyrite or some other sulphide. 
 As products of décomposition, chloritic minerais, oxides ofliron, calcite and epidote are of 
 fréquent occurrence. Thèse rocks may be classified as : — I 
 
 Gneissoid-diorite-schisfs, when there is comparatively little hornblende. 
 
 Quartz-diorile-schisls, which are by ail means the most common. 
 , Quarlz-diorile-porphyroides, OT perh&pa better, plagioclase porphyroides. The third 
 group is quite common and embràces rocks with a microgranitic or microfelsitic magma, 
 formed, so far as the constituents canj be detejmined, of fine fibres- or grains of horn- 
 blende, with particles of quartz and mignetite. This magma encloses crystals of plagio- 
 clase, lesB frequently hornblende, and Jbw and then clusters of epidote or chloritic masses 
 with calcite and magnetite, representint some completely metamorphosed minerai. 
 
 Homblendic Halleflintas. 
 
 There is a not insignificant group of compact rocks much resembling halleflintas, bût 
 v^ith darker, greenish tones. They may be, joined almost as appropriately to the halle- 
 flintas as to the homblendic porphyroides. The name " hornblendic h'âlleflinta " may be 
 Iffoposed for them. They are microgranitic or microfelsitic, but scarcely porphyrltic, and 
 t^ey differ from the halleflintas simply in the large number of particles of hornblende and 
 magnetite mingled with the quartz and felspar. 
 
 V. — CONOIiUSlON. 
 
 We hâve passed in brief review the varions rocks of the drift of Central Ontario, 
 éspecially as found near Cobourg, and as we may suppose that farther investigation over 
 ia wider range of country would add largely to the list of varieties, it is. évident that our 
 j drift présents a very interesting and extensive lithological collection. With the excep- 
 iion, however, of Iqose aggregations, such as clay, sand and gravel, and the very numerons 
 jfossiliferous limestones of Lower Silurian origin, ail the rocks examined are crystalline and 
 apparently of Archœan âge. The almost complète absence of rocks of the later Archœan, 
 such as quartzites, slate's and mie» schists, may be uoticed as a négative characteristic of 
 our drift. 
 
 Among positive features may be remarked the laage number of transitional forms, 
 jintermediate varieties being found between the majority of the main groupa of rock. 
 This is the less surprising, however, when we remember that rocks, nnless composed of a 
 single substance, hâve in no sensé the individuality of minerais*;* for, by graduai additions 
 and subtractions, one oflen passés into another. This carries with it the disadvantage of 
 making clean-out définitions d^fficult or impossible ; but also the advantage of bringingto 
 -Ti ftw t h ftffl aaàttaity4hi^4tBd erIi e aY a ri e ty. ■- - - 
 
 Sec. iii, 1887. 8. 
 
 \ 
 
 =if= 
 
 
 
 
 
 f"(- T .'.»i»^.tWA Ïf^ixii-Ji A^i^-M, 
 

 88 
 
 COLEMAN ON ÏHE MICfiOSCOPIC 
 
 \ ■''i 
 
 ^■— ^ 
 
 ««1 
 I 
 
 O 
 
 
 1^ 
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 I 
 
 •i 
 
 •§ 
 
 i 
 
 e 
 
 es 
 
 O 
 
 •o 
 
 ■a 
 o 
 
 g 
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 s 
 
 
 •c 
 
 i.l 
 
 â 
 
 
 S. 
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 1 
 
 f 
 
 •g 
 
 '■*3 
 
 
 
 O 
 
 
 ■• o 
 
 cq 
 
 S 
 
 rH 
 
 ci 
 
 oi 
 
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 F 
 F 
 F 
 F 
 
 -' siiiÀsfci^ayj-iaJï» t i ' ,, , 
 
 
 V 
 
 \.i ^ « t- .-^ Sr i^i -Mj' 
 
 
 
'^.' 
 
 PETBOGE^PHY OP ONTARFO. 
 
 39 
 
 l,n..W« I "" '^ constxtnents are concerned. it is noticeable how prévalent the minerai 
 hornblende is m our rocks, forming an essential ingrédient in the great majority of basic 
 
 2^». 1 /''''°'*''"''""^^- ^""^ ^^^' '- wSichitisra'eis'the sJu 
 oneofthehmestonesanddolpmites. 
 
 of nfh?.' ^^f ^P;^'^^^^""-^^^^ of niicrolAe is also worthy of remark. That this is true 
 
 fro^ th?r t t ^Tu"'' '' '^'^^ ^y ««^^''^^^ °^ ^*">*« «»d ^«^«i^^ i^ -^y collection 
 ôTJÏ .? , '^^n*"'' ^''""^'" TWgh differing mnch in habitue from thoee of 
 Ontario, they almost ail contain large qua^tities of the minerai. 
 
 r^in^rT^'"''''''!* considérable irro«p of rocks containing scapolite as an essential 
 
 i .MH T^ ^ Mjchael-Levy. Br5gger and others ; and that Mr. F. D. Adams contri- 
 ltl\ t^e Mont 1 Meeting of the British Association a paper on Canadian rocks of the 
 fn« ; ? !ï îf . ""^ P"^"'^'^ '"^ '^' Proceedings of the Associatipn. Unfor- 
 
 IZnM r. ""^ *^' '"'^J'*^* ^' "'^^ ** "^y «°°^«^*'^'i' «o th-t it is impossible at 
 
 présent to compare the scapolite rocks of out drift with those described by th«.di8ting- 
 uwhed petrographers mentioned. ^ . y ^ ë 
 
 _ For the convenience of référence there wiU be found on the opposite page a tabular 
 hst of the massive and schistose rocks described in this paper. 
 
 • I EXPLANATION OF PLATES. 
 
 i 
 
 I Plate I. 
 
 (AU betwaen orosaed nieola and magnified 85 diameters.) 
 Fia. 1.— Augite with tonea of décomposition prodncta. , 
 Fio. 2.— Epidote in weathered plagioclaso. - - 
 
 FiG. 3.— Transition from orthoclase to microline. » 
 
 Fia. 4.-Scapolite, longitudinal eecUon red and green, cross section dark grey. 
 
 \ 
 
 Plate IL 
 
 ♦ (Rir., 1, 2 «,d 3 with the lower nieol only , fl,. 4 between.o««ed niools. AU m^mifled 85 diamoten,.) 
 
 Sn 2"~^,'^"î"L"lïï"'''^ *^° *°'^'*^ ""'* hornblende with chief axis in common; also brown Utanite 
 FiQ, 2,^AuK.te and h^niblende sa in flg. 1, but longitudinal secUon. < 
 
 FK}.^3.-Diallage (yellow) enclosing bluish bypemthene and brown hornblenda ^ 
 *1o. 4.-Intergrowth of orthoclase and plagioclase (microperthite?) 
 
 y^l 
 
 ;w. 
 
I 
 
 ^ • 
 
 / 
 
 i 
 
 /' 
 
 ■r -^ \ "^ 
 
 ir?^!<. 
 
'■' r 
 
 t.* 
 
 Trans. R. S. C, 1887. 
 
 Fig. 3 
 
 rat^r 
 
 S«c. lïl. Plate I. 
 
 Fig. 4. 
 
 To iUustratnVof. Coleman's PapTupon Microscopic Petrology. 
 
 z' 
 
 ^-ï_ V '4 iSjiXt,_. <| 
 
 \ 
 
X 
 
 ^:- 
 
 rV-liVl? " 
 
 
 Iv^ 
 
 V ^ I 
 
 
 feiAdi^-"*» y •lî- 
 
 .f • 
 
/ 
 
 T»»n«RS.C.. 1887, 
 
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