IMAGE EVALUATION 
 TEST TARGET (MT-3) 
 
 4 
 
 / 
 
 o 
 
 / 
 
 o 
 
 <" m. 
 
 ..^' .#/,^ 
 
 ^ 
 
 s 
 
 ^. 
 
 
 Q- 
 
 W.r 
 
 Ua 
 
 V. 
 
 1.0 
 
 I.I 
 
 1.25 
 
 ~ IIIM 
 - IIIIIM 
 
 IIM 
 
 14 
 
 M 
 M 
 
 III™ 
 1.4 11.6 
 
 7. 
 
 
 7 
 
 Photographic 
 
 Sciences 
 
 Corporation 
 
 « 
 
 V 
 
 \ 
 
 ^9> 
 
 V 
 
 4L>^ 
 
 \\ 
 
 <> 
 
 ^v^ 
 
 ^ 
 
 <'. 
 
 6^ 
 
 <^ 
 
 ^■i* 
 
 "<i> 
 
 ^^^N 
 
 23 WEST MAIN STREET 
 
 WEBSTER, NY. 14580 
 
 (716) 872-4503 
 
Cj?" 
 
 o^ 
 
 CIHM/ICMH 
 
 Microfiche 
 
 Series. 
 
 CIHM/ICMH 
 Collection de 
 microfiches. 
 
 Canadian Institute for Historical Microreproductions Institut canadien de microreproductions historiques 
 
 1980 
 
Technical and Bibliographic Notes/Notes techniques et bibliographiques 
 
 The Institute has attempted to obtain the best 
 original copy available for filming. Features of this 
 copy \A/hich may be bibliographically unique, 
 which may alter any of the images in the 
 reproduction, or which may significantly change 
 the usual method of filming, are checked below. 
 
 L'Institut a microfilm6 le meilleur exemplaire 
 qu'il lui a 6t6 possible de se procurer. Les details 
 de cet exemplaire qui sont peut-Stre uniques du 
 point de vue bibliographique, qui peuvent modifier 
 une image reproduite, ou qui peuvent exiger une 
 modification dans la mdthode normale de filmage 
 sont indiqu6s ci-dessous. 
 
 □ Coloured covers/ 
 Couverture de couleur 
 
 □ Covers damaged/ 
 Couverture endommagde 
 
 □ Covers restored and/or laminated/ 
 Couverture restaurde et/ou pelliculde 
 
 □ Cover title missing/ 
 Le titre de couverture manque 
 
 D 
 D 
 D 
 □ 
 
 r~7] Tight binding may cause shadows or distortion 
 
 Coloured maps/ 
 
 Cartes g6ographiques en couleur 
 
 Coloured ink (i.e. other than blue or black)/ 
 Encre de couleur (i.e. autre que bleue ou noire) 
 
 Coloured plates and/or illustrations/ 
 Planches et/ou illustrations en couleur 
 
 Bound with other material/ 
 Relid avec d'autres documents 
 
 D 
 
 along interior margin/ 
 
 La reliure serr6e peut causer de I'ombre ou de la 
 
 distortion le long de la marge intdrieure 
 
 Blank leaves added during restoration may 
 appear within the text. Whenever possible, these 
 have been omitted from filming/ 
 II se peut que certaines pages blenches ajout^es 
 lors dune restauration apparaissent dans le texte, 
 mais, lorsque cela 6tait possible, ces pages n'ont 
 pas 6t6 film^es. 
 
 I — I Coloured pages/ 
 
 D 
 
 Pages de couleur 
 
 Pages damaged/ 
 Pages endommag^es 
 
 I — I Pages restored and/or laminated/ 
 
 D 
 
 Pages restaur6es et/ou pellicul6es 
 
 Pages discoloured, stained or foxed/ 
 Pages d6color6es, tachetdes ou piqu^es 
 
 □ Pages detached/ 
 Pages d^tach^es 
 
 r~l^ Showthrough/ 
 I ^1 Transparence 
 
 □ Quality of print varies/ 
 Quality in^gale de I'impression 
 
 Includes supplementary material/ 
 
 I I Comprend du materiel supplementaire 
 
 adition available/ 
 Edition disponible 
 
 □ Only edition available/ 
 Seule 
 
 D 
 
 Pages wholly or partially obscured by errata 
 slips, tissues, etc., have been refilmed to 
 ensure the best possible image/ 
 Les pages totalement ou partiellement 
 obscurcies par un feuillet d'errata, une pelure, 
 etc.. ont 6t6 film6es d nouveau de fapon d 
 obtenir la meilleure image possible. 
 
 D 
 
 Additional comments:/ 
 Commentaires suppl6mentaires: 
 
 D 
 
 This item is filmed at the reduction ratio checked below/ 
 
 Ce document est film6 au taux de r6duction indiqud ci-dessous. 
 
 
 10X 
 
 
 
 
 14X 
 
 
 
 
 18X 
 
 
 
 
 22X 
 
 
 
 
 26X 
 
 
 
 
 30X 
 
 
 
 
 
 
 
 
 
 
 / 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 12X 16X 20X 24X 28X 
 
 ] 
 
 32X 
 
ils 
 
 lu 
 
 Jifier 
 
 me 
 
 age 
 
 The copy filmed here has been reproduced thanks 
 to the generosity of: 
 
 Thomas Fisher Rare Book Library, 
 University of Toronto Library 
 
 The images appearing here are the best quality 
 possible considering the condition and legibility 
 of the original copy and in keeping with the 
 filming contract specifications. 
 
 L'exemplaire film6 fut reproduit grSce d la 
 g6n6rosit6 de: 
 
 Thomas Fisher Rare Book Library, 
 University of Toronto Library 
 
 Les images suivantes ont 6t6 reproduites avec le 
 plus grand soin, compte tenu de la condition et 
 de la nettetd de l'exemplaire filmd, et en 
 conformity avec les conditions du contrat de 
 filmage. 
 
 Original copies in printed paper covers are filmed 
 beginning with the front cover and ending on 
 the last page with a printed or illustrated impres- 
 sion, or the back cover when appropriate. All 
 other original copies are filmed beginning on the 
 first page with a printed or illustrated impres- 
 sion, and ending on the last page with a printed 
 or illustrated impression. 
 
 Les exemplaires originaux dont la couverture en 
 papier est imprim^e sont film6s en commenpant 
 par le premier plat et en terminant soit par la 
 dernidre page qui comporte une empreinte 
 d'impression ou d'illustration, soit par le second 
 plat, selon le cas. Tous les autres exemplaires 
 originaux sont film^s en commengant par la 
 premiere page qui comporte Lne empreinte 
 d'impression ou d'illustration et en terminant par 
 la dernidre page qui comporte une telle 
 empreinte. 
 
 The last recorded frame on each microfiche 
 shall contain the symbol — ♦» (meaning "CON- 
 TINUED"), or the symbol V (meaning "END"), 
 whichever applies. 
 
 Un das symboles suivants apparaitra sur la 
 dernidre image de cheque microfiche, selon le 
 cas: le symbole — ♦► signifie 'A SUIVRE", le 
 symbole V signifie "FIN". 
 
 Maps, plates, charts, etc., may be filmed at 
 different reduction ratios. Those too large to be 
 entirely included in one exposure are filmed 
 beginning in the upper left hand corner, left to 
 right and top to bottom, as many frames as 
 required. The following diagrams illustrate the 
 method: 
 
 Les cartes, planches, tableaux, etc., peuvent dtre 
 film^s d des taux de reduction diffdrents. 
 Lorsque le document est trop grand pour dtre 
 reproduit en un seul cliche, il est filmd d partir 
 de Tangle sup^rieur gauche, de gauche d droite, 
 et de haut en bas, en prenant le nombre 
 d'images n6cessaire. Les diagrammes suivants 
 illustrent la m^thode. 
 
 rrata 
 :o 
 
 pelure. 
 
 □ 
 
 32X 
 
 1 
 
 2 
 
 3 
 
 1 
 
 2 
 
 3 
 
 4 
 
 5 
 
 6 
 
 d 
 

 -''if.iHjJu..^;..:'-' 
 
 msL^mmmmssOEidi 
 
 'S^'^£ -"(-.-J-'S^fi^'S 
 

 OSeoloQicnl 5<^^^i^»^t"^^^^t : ^U6ill 53;uibcrsiti). 
 
 Description of a Series of Thin 
 Sections of Typical Rocks. 
 
 BY • 
 
 FRANK D. ADAMS, Ph.D., F.G.S. 
 
 Logau Professor of Geology in McGill University. 
 
 *' 
 
 <^\ A H ] 
 
 MONTR KAL; 
 
 1896. 
 
m 
 
(Z^n I 
 
 * 
 
 (Ijcological ^i^P'ivlmciit ; ^HclOill (Lluibciciiln. 
 
 Desciiii'tion of a Seimi:s of Thin 
 Sections of Typical Ro(jks. 
 
 BY 
 
 FRANK 1). ADAMS, Ph.D., V.(i.^. 
 
 Loyaii Professor of lJt;(il()j;y in McGill University. 
 
 MONTREAL 
 
 1806. 
 
LIST OF MINEEALS DESCRIBED IN THE SECTIONS. 
 
 NaMK ok MlNKHAf,. 
 
 AndHlusite 
 
 Apatite , . 
 
 Biotite 
 
 Calcite 
 
 Chlorite 
 
 p]pidote . . 
 
 Garnet 
 
 Graphite. . 
 
 Hematite 
 
 Hornblende 
 
 Ilmenite 
 
 Leucite 
 
 Leucoxene 
 
 Magnetite 
 
 Microcline 
 
 Muscovite 
 
 Xepheline 
 
 Nosean 
 
 Olivine 
 
 Orthoclase 
 
 Plagioclase . , 
 
 Pyrite 
 
 Pyroxene (Khombic) 
 
 Pyroxene (Monoclinic). 
 
 Quartz 
 
 Kutile 
 
 Serpentine 
 
 Sillimanite , , 
 
 Ni;mbi'.u ok .Section. 
 IS 
 
 3, 5, 15 
 1, 7, 13 
 
 6, 14, 22, 23, 25 
 1, U 
 2 
 . 4, 5, 19 
 
 19 
 .13 
 
 3, 4, 10, 13 
 .5 
 16 
 .5 
 
 1, 17 
 ..2 
 
 2, 17, 22 
 
 ..4 .,..'.. 
 
 4 
 . . 7, 8, 16 
 1, 2, 3, 20 
 1, 5, 6, 13, 16, 21 
 4, 7, 19 
 .6 ■ • 
 4, 6, 7, 8, 13, 16 
 1, 2, 3, 20 
 19 
 . 6, 7, 14, 22 
 19 
 
IV 
 
 STItUCTirUKH KMIIItriKli IN rilK SK rioNS. 
 
 Spliciic 
 'I'oiii'iiuiliiiti 
 Zircon 
 Zoisite 
 
 (ilass . . 
 
 *i, 
 
 4, 
 
 "» 
 
 
 IS 
 
 
 
 
 1. 
 
 10, 
 
 •20 
 
 
 T) 
 
 
 
 
 !), 
 
 10, 
 
 14, 
 
 10 
 
 STRUCT QRES EXHIBITED IN THE SEOTIONS. 
 
 STKUCTIUK. 
 
 Allotiioniorphic 
 
 Ainygdaloidal . . 
 
 Calaclastio . . 
 
 Ci'yptoci'yftlalliiu; 
 
 Epic'lastio 
 
 Foliated . , 
 
 Fluidal 
 
 Holocrystalliue . . 
 
 Hypidionioiphic 
 
 Idioiiiorphic 
 
 Massive 
 
 Microcrystalliuo 
 
 Opliitic 
 
 Poikilitic 
 
 Porphyritio . . 
 
 Spherulitic 
 
 Semicrystalline 
 
 Vesicular 
 
 Vitreous 
 
 Number of Section 
 
 18 
 
 
 U 
 
 
 2 
 
 20, 21 
 
 II 
 
 
 '23, 
 
 24 
 
 19, 
 
 21 
 
 9, 
 
 II 
 
 1, 
 
 2, 3 
 
 t 
 
 
 13 
 
 
 1, 
 
 2, 3 
 
 13 
 
 
 15 
 
 
 8 
 
 
 11, 
 
 13, 16 
 
 11, 
 
 1'2 
 
 16 
 
 
 11 
 
 
 9, 
 
 10 
 
 ! 
 
 i 
 ■I 
 
IGXEOUS HOCKS (PLUTONIC DIVISION). 
 
 (1). BIOTITE GRANITE Bavcno, Italy. 
 
 A typical graiiitu, very extensively quarried, at Baveno, 
 on the S.W. shore of Lago Maggioro, Italy. 
 
 Essential constituents . . . Orthoclase, Quartz, Biotite. 
 Accessory " ... Plagioclase. Zircon. 
 
 Secondary " ... Chlorite. Magnetite. 
 
 Biotite. — This mineral can l)e at (.)iice distinguished from 
 the feldspar and (juartz l)y its hrown colour, these other con- 
 stituents heing colourless, or nearly so. It occurs in fairly 
 good crystalline forms. 
 
 Two classes of sections can be recognized : — 
 
 (a) Those ])arallel to the vertical axis. — These are oblon^' 
 m form, wiih one set of well-marked parallel cleavages run- 
 ning in the direction of the longer axis. Since the cleavage 
 of mica is parallel to the l^ase, it is evident that it is paral- 
 lel to this plane the crystals are elongated. Examined 
 l)et\veen crossed nicols they are anisotropic, and 1)ecome 
 alternately light and dark four times during a complete 
 revolution. Extinction (darkness) takes place Avhen the 
 cleavages marking the direction oi one of the elasticity 
 axes coincides with the vibration plane <jf one or other of 
 the nicols; that is, with the hair lines in the ocular. That 
 is to say, these sections show "parallel extinction." 
 
 Removing the upper nicol, thus employing the lower 
 nicol alone, and revolving the stage, the sections are found 
 
KJNEorS HOf'KS. 
 
 a > c 
 
 to b(i plcochroic — /.''., tlie li^'ht passinj:^ t]irnu.u,'h tliciu parallel 
 to one jixi.s of clasticily (liU'iTs in colour from that passing 
 through in the tlirection of the otlier. As this change is of 
 the nature of a darkening of the yellow colour of the sections, 
 owing to an absorption oi the light passing through in one 
 direction, this i»hase of pleochroisin is referred to simply as 
 absorption. The greatest al»sorption takes place when t!ie 
 cleavages coincide with the vibration plane of the lower 
 nicol. The character and intensity of the absorption is 
 represented as follows : — 
 
 il = deep l>rown, 
 
 C = pale yellowish brown, 
 
 (b) Sections parallel to the base. — These are, of course, 
 mucli less abundant, l)ut a section at least approximately 
 parallel to the base can usually be found. If parallel to the 
 base, these sections will not change in colour on revolving 
 the stage if the lower nicol alone be employed, but will 
 remain of a uniform dark brown colour. When, however, 
 they are examined between crossed nicols in convergent 
 light, they show the black cross of a uniaxial mineral, whicli, 
 when examined l^y means of a quarter undulation mica plate, 
 or gypsum plate showing red of the first order, will show a 
 negative sign. On revolving the stage when tins black cross 
 is visible, the latter will usually be found to separate into 
 two Ijlack hyperboles, which, however, always remain very 
 close to one another. This is due to the fact that biotite 
 is really biaxial, but the axial angle being very small the 
 optical properties of the mineral closely resemble those of a 
 uniaxial mineral' 
 
 These sections, being parallel to the base, show no cleavage. 
 They are also more or less irregular in outline, showing that 
 
BIOTITE GUANITE. 
 
 the mineral, while ocKturriiij^' in tabnhir individuuls, is not 
 bounded by well-d"Hned faces in the prismatic zone. 
 
 The biotite is frequently altenid to Chlorite, its most com- 
 mon (hicomposition product. This, like the biotite, is doubly 
 refracting, and has parallel extinction, but is distinguislied 
 from the latter Ijy its green colour and lower df)uble refraction. 
 This alteration may be observed in all its stages. 
 
 The chlorite is a typical exami)le of a secomhiry con- 
 stituent. Oxide of iron, in the form of Magnetite, is often 
 separated out during the alteration and lies embedded in 
 the chlorite. 
 
 Orthoclase. — P]asily distinguished from the quartz by its 
 turbidity, due to incipient alteration. Most sections are 
 anisotropic, but isotropic sections also occur, and these, being 
 at right angles to an optic axis, show the revolving bar of 
 a biaxial crystal. The mineral possesses good cleavages, 
 especially well seen at the edge of the section. Its crystal- 
 line form is less perfect than that of the biotite, which it 
 often encloses. Between crossed nicols, decomposition pro- 
 , ducts in the form of little flecks having a different orienta- 
 tion from their host are frequently seen. 
 
 Plagioclase. — Associated with the orthoclase in small 
 amount, distinguished by its polysynthetic twinning. 
 
 Quartz. — In clear fresh grains, without crystalline form, 
 occupying the space between the grains of biotite and feld- 
 spar. In [)laces, slightly turbid from the presence of little 
 inclusions, often arranged in little lines or bands, many of 
 which, when examined Avith a high power, are seen to con- 
 sist of little cavities, often containing a moving bubble. It 
 is distinguished from the orthoclase not only by its freedom 
 from decomposition products, but also l)y the absence of 
 
* IGNEOUS ROCKS. 
 
 cleavage, and l)y tlie fact that when isotropic sections are 
 cxanii' 'd bet\v(!en crossed nicols in convergent liglit the 
 mineral is seen to be uniaxial and negative. 
 
 Zircon. — A few little crystals or grains, colourless. Very 
 high index of refraction, giving an appearance of high relief, 
 and also very high double refraction, causing the mineral 
 to polarize in ])rilliant colours. Occurs as inclusions in all 
 the other constituents. 
 
 Note that the constituents have crystalliyxnl out in the 
 folio wiuL', order— Zircon, IJiotite, Feldspar, Quartz, as indi- 
 cated by tlie fact that each mineral contains inclusions of 
 those which precede it in this list, and that this is the order 
 in which the minerals stand in respect of perfection of their 
 crystalline form. 
 
 Note, also, that the texture of the rock is Hoiocrystaiiine, 
 Massive, and Granitoid. 
 
 (2|. BIOTITE MUSCOVtTE GRANITE -Stanstead, Province 
 of Quebec, Canada. 
 
 A granite occurring as a large intrusive mass cutting 
 strata of T.owor Pahp.ozoic age. It is extensively (piarried"^' 
 and used as paving stone in the City of Montreal and for 
 various other purj)oses elsewhere. 
 
 Essential constituents . . . Orthoclase. Quartz, Biotite. 
 
 Accessory " ... Microcline, Plagioolase. 
 
 Secondary " ... Muscovite, Epidot'^. 
 
 Orthoclase — like that in the Baveno granite. It is, how- 
 ever, fresher, and hence clearer, and more trans[)arent. Its 
 cleavages and biaxial character serve to distinguish it from 
 the quartz. Its place is taken to a certain extent by the 
 triclinic form of th:^ molecule, characterized by a very fine 
 
BIOTITE MUSCOVITE GRANITE. 
 
 5 
 
 cross-hatched structure, protkiced by a (loii])le set of pcly- 
 syiithetic twins, and which is known as Microoline. This 
 fehlspar is especially abundant in granites and similar rocks 
 which have been submitted to great pressure. Its presence 
 would suggest such pressure in the present case, a suggestion 
 strengthened ])y a study of some of the other constituents. 
 
 A considerable (juantity of ordinary Plagioclase is also 
 present as an accessory constituent. 
 
 Quartz — possesses the various properties described in JSTo. 1. 
 Almost every grain, however, shows an uneven extiHction ; 
 that is to say, a single individual, when revolved between 
 crossed nicols, does not extinguish simultaneously over its 
 whole surface. This is owing to the fact that the grain has, 
 subsequent to the consolidation of the rock, been twisted by 
 great pressure to which the rock has been subjected. In 
 some cases the movements have l)een so intense that an 
 individual can be o])served to have l)eeu broken into several 
 snudler giains, and an incipient Cataciastic structure thus 
 developed. This structure is especially well seen in gneisses 
 and similar rocks, many of which are merely crushed granites. 
 
 Biotite. — See No. 1. 
 
 Muscovite. — This mica dift^rs from the biotite in beinn^ 
 colourless. It is also ])iaxial, with a large axial angle, hence 
 an isotropic section ; i.e., one cut at right angles to an 
 optic axis will show the revolving bar of a Ijiaxial crystal. 
 Granites containing primary muscovite are extremely rare, 
 and there is good reason to believe that the muscovite in 
 this Stanstead rock is all secondary, having been derived 
 in part from the alteration of the biotite and in part from 
 the orthoclase. An ordinary decomposition product is not 
 taken into consideration in naming a rock, but the muscovite 
 
6 
 
 IGNEOUS ROCKS. 
 
 does not belong to this category, as it was probably prodiicetl 
 deep in the crust of the earth by the same forces which 
 turned the orthoclase to microcline and crushed the quartz ; 
 hence it has lieen considered in naming the rock. It occurs 
 in the feldspar as skeleton crystals, the various parts of 
 which, in the plane of the section, are often completely sepa- 
 rated from one another, but which were probably united 
 either above or below, the muscovite individual being in fact 
 in the form of a sponge growing in the feldspar. The sepa- 
 rated portions, often mere shreds, are reco<?nized as belou'dnc^ 
 to the same individual by the fact that they extinguish 
 simultaneously when revolved between crosseii nicols. The 
 muscovite is occasionally accompanied by other secondary 
 minerals as epidote, or i)y a feldspar having a slightly differ- 
 ent orientation from the rest of the orthoclase, but it is 
 usually embedded in })erfectly fresh and unaltered feldspar, 
 affording a remarkable example of the growth of a new 
 mineral in a soliil rock when this latter, in the crust of the 
 earth, has been submitted to conditions dilfering from those 
 under which the rock originated.* 
 
 Epidote. — Nearly colourless. High index of refraction, 
 and high double refraction. Occurs in small amount. Like 
 the muscovite, it is a secondary product. 
 
 * Adams, F. ]). : " On some Granites from British Columbia and the 
 adjacent parts of ^.laska and tlie Yukon District."— Canadian Record 
 of Science, September, 18U1. 
 
HOUNBLENDE SYENITE. 
 
 3. HORNBLENDE SYENITE Plaucnschc Grunde, near 
 Dresden, Germany. 
 
 A typical and very celebrated syenite occurring as a large 
 intrusive mass on the outskirts of the city of I^resden, where 
 it is extensively quarried. 
 
 Essential constituents . , . Orthoclase, Hornblende. 
 Accessory " ... Plagioclase, Quartz, Sphene, 
 
 Magnetite, Apatite. 
 
 Orthoclase. — SeeXos. 1 and 2. — Abundant. Oftentwinned, 
 Associated with it is a certain amount of Plagioclase, as in 
 the case of granites 
 
 Hornblende. — Abundant. Often with rude crystalline 
 form. Plcochroic. 
 
 Three classes of sections will be noted (see accompanying 
 cut), having approximately the following positions : — 
 
 e-C 
 
 a-CL 
 
 U 
 
 I I 
 
 (fe) 
 
 (c) 
 
 Sections of Hornblende. 
 
8 
 
 KiNEOUS ROCKS. 
 
 (a) Paralle. i () P.— These show two sets of cleavages 
 crossing one another at angles of about 124^. Strongly 
 pleochroic. a = pale yello , b = dark yellowish -green. 
 Absorption = b > a. 
 
 (h) Parallel to ,^Pcc. One set of parallel cleavages, 
 with parallel extinction I'leochroic, but not very strongly so. 
 b = (lark yellowish-green, c = deep green. Absorption 
 = C > b. 
 
 Sections possessing these characters are less abundant 
 than those of the two other classes. 
 
 {c) Parallel to go P co'.— One set of parallel cleavages, 
 as in the case of those parallel to co P x , but with inclined 
 extinction, the extinction angle l)eing about 18°. Strong 
 pleochroism. a = pale yellow, c = deep green. Absorp- 
 tion - c > a. 
 
 The absorption of the mineral, as determined from these 
 several sections, would therefore be c > b > a. 
 
 Plagioclase.^Distinguished l)y its polysynthetic twinning 
 (See Xo. 5). Present in considerable amount. 
 
 Quartz.— Few grains. By an increase in the amount of 
 quartz present, this Plauen syenite, in another part of the 
 area, changes into a granite. 
 
 Sphene. — In large individuals, usually presenting the 
 wedge-like forms, often very perfect, from which the name 
 is derived. Brown in colour. With high index of refrac- 
 tion, causing it to have the appearance of standing u]) from 
 the field ; also high double refraction. 
 
 The mineral, crystallizing in the triclinic system, is biaxial, 
 so that any section cut at right angles to an optic, axis, and 
 therefore isotropic, will show the revolving bar of a biaxial 
 crystal. It is very common in hornblende rocks. 
 
 xi 
 
 C 
 
ELAEOLITE SYENITE. 
 
 !N\ 
 
 Apatite.— fn colourless crystals, usually rather small. 
 These, when cut parallel to the vertical axis, give sections 
 which arc oblong in shape, Avliile sections parallel to the 
 base liavc a hexagonal outline. It has rather a high index 
 of refraction, which causes it to stand uj) from the field, 
 although the appearance of relief is not v(U'y pronounced. 
 
 The mineral is uniaxial, and has a very low double 
 refraction, which causes it to polarize in very dull tints. 
 The extinction is i)arallel in the case of the oblong sections, 
 while the hexagonal sections, 1)eing at right angles to the 
 optic axis are isotroi)i<;. Tlie revolving bar, however, is 
 not well seen except under the most favourable circum- 
 stances, on account of the very low double refraction which 
 the mineral ])ossesses. It occurs sometimes in the form of 
 
 littl 
 
 e irregular grains. 
 
 The structure is identical, in all respects, with that of 
 granite. 
 
 Magnetite. — A f(nv opaque black grains, often embedded 
 in the hornblende ; often partially altered to hematite, which 
 is transparent and red in colour. 
 
 (4). ELAEOLITE SYENITE-Cerporation Quarry. 
 Montreal, Canada. 
 
 A typical elaeolite, or nepheline syenite, forming a portion 
 of Mount Koyal, and extensively quarried for road metal. 
 Essential constituents . Orthoclase, Elaeolite, Hornblende. 
 Accessory " f Plagioclase, Pyroxene, Garnet, 
 
 I Sphene. 
 Secondary " . Noseau, Magnetite, Pyrite. 
 
 Orthoclase. — ^Colourless. Polarizes in dull blue tints. 
 Possesses same characters as in granites (See JS'os. 1, 2, 
 
10 
 
 lUNEOUS ROCKS. 
 
 'Jii 
 
 and 3). It is often intergrown with the Plagioclase, wliicli 
 is present as an accessory constituent, and can be recoi^nized 
 by its polysynthetic twinning. It lias ])een found to be, in 
 part at least, oligoclase. 
 
 Elaeolite. — This is also colourless, polari/x's in very dull 
 blue tints, and resembles the orthoclase so closely that it is 
 dillicult to distinguish the two minerals. It is, however, 
 uniaxial, and if a good basal (isotropic) section can be found, 
 will show a cross instead of a revolving l)ar, which cross will 
 when tested by a gypsum plate showing red of the first 
 order, prove to be negative. The most satisfactory method 
 of ascertaining how much of the colourless mineral is elaeo- 
 lite would be to remove the cover glass and etch the slide 
 with hydrochloric acid and then stain with fuchsine, when 
 all the elaeolite would ap[)ear red, while the feldspar would 
 remain unacted upon. 
 
 Hornblende. — Deep green in colour, showing the same 
 cleavages and general characters as that in No. 3. It has, 
 however, a somewhat larger extinction angle and a remark- 
 ably small axial angle. It is very rich in iron, and in 
 composition probably resembles closely the remarkable horn- 
 blende which occurs in the nepheline syenite froniDunganuon, 
 Ontario.'*' It is in places intergrowii with some pyroxene, 
 rather paler in colour, and distinguished by the fact that the 
 two sets of cleavages cross at right angles, as well as by 
 its much larger extinction angle. (See No. 7). 
 
 G-arnet. — Occurs in occasional laige grains of a brown 
 colour and very irregular shape. It is transparent, and when 
 
 * Adams, F. 1). : "On a new Soda Hornblende from the Nephe- 
 line Syenite of Dunj^fannon, Ontario."— American Journal of Science, 
 March, 1895. 
 
 '¥ 
 
HORNBLENDE DIORITE. 
 
 11 
 
 
 examined between crossed iiicols is found to lie perfectly 
 isotropic. It also possesses a high index of refraction, which 
 causes it to stand up from the field. It contains many 
 inclusions of other minerals, especially of hornblende and 
 nosean, Avhich shows that it must have crystallized out after 
 these constituents, which is not usually the case, garnet 
 being, as a general rule, in rocks of this class, one of the 
 first V )nstituents to separate out. 
 
 Sphene. — In numerous little crystals of a pale yellow 
 colour, with the characteristic wedge-like form and high 
 index of refraction. (See Xo. 3). 
 
 Nosean. — This mineral is present in considerable quantity 
 in the form of colourless grains which at the first ^^lance 
 might be mistaken for the nepheline or orthoclase. An 
 examination lietween crossed nicols, however, shows that 
 they are quite isotropic. The grains possess good crystallin i 
 form, and towards the centre are usually filled with minute 
 opaque, black particles of magnetite, while the ])orders of 
 the grains are quite clear and free from inclusions. These 
 inclusions make it easy to recognize the nosean grains even 
 before polarized light is employed in the examination. This 
 mineral is rarely found in nepheline syenites, but is common 
 in certain other classes of nepheline rocks. 
 
 Magnetite.— A small amount, associated with a little 
 Pyrite. 
 
 (5). HORNBLENDE DIORITE-Halsbriicke, Kingdom of Saxony, 
 
 Essential constituents . . . Hornblende, Plagioclase, 
 
 Accessory " ... Garnet, Apatite, Iron Ore, 
 
 Secondary " ... Leucoxene, Zoisite, etc, 
 
 Hornblende.— As in syenite. (See Xo. 3). 
 
12 
 
 IGNEOUS ROC-S. 
 
 Plagioclase. — Colourless, clear and transparent, except 
 when tlcconiposed, it heint,' then grey and tiirUid, Its 
 cleavages can be; readily seen, (^'=![)ecially about the edge of 
 the section. It can be readily recognized by the polysyn- 
 thetic twinning, according to the albite law, wlii'^n results 
 in the development of a series of parallel bands of colour 
 crossing the grains. These, of course, can only be seen 
 when the section is (examined between crossed ni(!ols. These 
 bands are so arrangiMl that the alternate bands of the series 
 in any grain extinguish simultaneously as the stage is re- 
 volved. In this way the whole grain is never black at any 
 time during a complete revolution, for while one set of l)ands 
 are light the other set are dark. If the mineral is cut parallel 
 to the twinning plane, these twin lines will not, of course, be 
 seen; so that the absence of twinning is not a proof that the 
 mineral is not ])lagioclase. In some instances furthermore, 
 although these are rare, the })lagioclase occurs in untwinned 
 crystals, and therefore does not sho^.' the banding descil^od. 
 In this section there is a considerable amount of untwinned 
 felds[)ar, which in this way may really be plagioclase ; or 
 there may l)e a certain amount of orthoclase associated with 
 the plagioclase in the rock, as an accessory constituent. In 
 order to decide this, a separation by means of a heavy solu- 
 tion Avould have to be made. 
 
 The turbid, almost opaque, lath-shaped forms, now con- 
 sisting of an aggregate of minute grains of zoisite and other 
 minerals, are probably also decomposed plagioclase ; perhaps 
 more basic than the rest of the plagioclase, and hence more 
 readily decomposed. The Zoisite is colourless, and is recog- 
 nized by its high index of refraction and low double 
 refraction, polarizing in very dull l)lue colours. 
 
 ^4^ 
 
ANOllTHOSiTE. 
 
 13 
 
 Garnet. — In almost colourless grains, usually of irregular 
 sliape. High index of refra(;tion. Perfectly isotropic. 
 Traversed by numerous cracks. Sonietinies encloses grains 
 of liornl)lende as well as little grains of zoisite. (See No. 4). 
 
 Apatite. — .Some slides contain a consideraljle amount ; 
 in rather large, colourless grains of rounded outline. (See 
 No. ;?). 
 
 Titanic Iroa Ore. — < )[);ii)ue graitis, ])Iack by retlectiid light. 
 
 Leucoxene. — The iron ore is usually surrounded by a 
 narro\\^ zone of a transparent mineral, having a very high 
 index of refraction and also a very high double refraction. 
 This is a decomposition product of the iron ore, anil is a 
 silico-titanate of lime, called leucoxene, being in fact merely 
 a variety of sphene. Its presence here proves tliat the iron 
 ore is at least titaniferous, if not a true ilmenite. It is very 
 commonly found associated with the iron ore of gabbros, 
 especially when these rocks are much decomposed. 
 
 ( 
 
 .r > 
 
 (6). ANORTHOSITE Four Miles East of Ste. Agathe, 
 Trovlncc of Quebec, Canada. 
 
 This rock (Anorthosite) is a variety of gabbro in Avhich 
 the plagioclase preponderates almost to the exclusion of the 
 other constituents. 
 
 This specimen of anorthosite is ty[)ical of the rock as 
 developed in the great intrusions whicli cut through the 
 Laurentian in various parts of Canada, and often occupy 
 areas of several thousand square miles. The slide represents 
 the rock near the centre of what is known as the Morin 
 intrusion, which has an area of about one thousand square 
 miles, and shows the rock as it appears when it has not 
 been crushed or granulated by pressure. Section 16 shows 
 
14 
 
 IGNEOUS ROCKS. 
 
 the same rock from the margin of the area, wliere it has 
 been comi)letely granulated by tlie groat pressure to wliich 
 it has been submitted. 
 
 Essential constituents . Plagioclase, Augite, Hypersthene. 
 
 Accessory " . llmenite, Biotite, Pyrite. 
 
 Secondary " . Serpentine, Chlorite, Oaloite. 
 
 Plagioclase. — The polysyntlietic twinning, exphained in the 
 description of No. G is excellently seen. The rock is composed 
 almost exclusively of plagioclase, and almost every grain is 
 twinned. ( )ccasionally a second set of twin lines are seen 
 cutting the first, ap[)roximately at right angles. These are 
 due to the fact that the individual showing them is twinned 
 according to the Pericline as well as to the Albite law. The 
 feldspar is filled with minute dust-like inclusions, with some 
 larger rod-like inclusions which run in certain definite direc- 
 tions through the crystals. They are opaque, or nearly so. 
 They belong to the class of what Professor Judd* has called 
 " Schillerization Products " — for it is their presence that 
 gives to many feldspars as well as otiier minerals, the pecu- 
 liar " Schiller " or ]day of colours which they often exhibit. 
 They are found principally, if not exclusively, in rocks 
 which have been deeply buried, ami Professor Judd believes 
 that they are secondary and fill minute cavities which are 
 developed along certain planes ("solution planes") in a 
 mineral, when it is subjected to great pressure, without 
 being actually crushed, in the deeper portions of the earth's 
 crust. They sometimes have the appearance of partially 
 filling cavities, as can be seen in this section if it be exam- 
 ined under a high power. The inclusions in the case of tlie 
 
 *"Tlie Tertiary ami oldei Peridotites of Scotland."— (^. J. U. S., 
 Aup^ust, 189.5. 
 
 1 
 
ANOHTFIOSITE. 
 
 15 
 
 present rock probably consist for the most i)art of titanie 
 iron ore.* 
 
 Tiio plii<,'ioelase is either a basic ]abra(h)rite or bytownite. 
 
 Augite.— As this mineral occurs much more alnuidantly 
 in the olivine ,nabbro (Xo. 7), its optical properties will l)e 
 there (lescri])e(l in detail. 
 
 It is pale green in colour, not pleochroic, and has an 
 extinction angle of over 40°. It usually contains, more or 
 less abundantly, dark schilhjrization products sinular to those 
 descril)ed in the feldsi)ar, but is present in much snuiller 
 amount than the feldspar. 
 
 It is often much decomposed, the chief alteration product 
 being a rhombohedral carbonate, either caicitc or dolomite, 
 recognized by the peculiar silvery tints which it presents 
 between crossed nicols, and an almost isotropic pale green 
 
 Chlorite. 
 
 Hyperstheiie.— Intergrown with the augite is a rhombic 
 pyroxene, pro])ably bolonging to the s[)ecies hypersthene. 
 When fresh it is recognized by its lower double refraction, 
 its parallel extinction, and faint pleochroism in pale green 
 and pale reddish tints. It is, however, more easily decom- 
 posed than the augite, and is here seldom seen in a fresh 
 state, l)eing represented chielly by decomposition products 
 retaining the form of the original grains, and consisting 
 chieHy of Serpentine or bastite and a carbonate like tiiat 
 above described. 
 
 Ilmenite. — A few grains, sometimes partly decomposed to 
 hematite and sometimes to leucoxene. 
 
 * Adams. F. 1).: '• Ueber das Norian oder Obei-Laurentian von 
 Canada."-X. J. fiir Min., etc., Beil. Bd., VIII. 1893, Translated in 
 Can. Riic. of Sc.,Vol. VI., 1895. See p. 1G9. 
 
16 
 
 ir.NKOUS HOCKS. 
 
 Biotite. — A few i^raiiis in soim; slides. I )(•('[) hiouii in 
 colour and slio\vin,L( tin; usual plijocliroisni and absorption. 
 Pyrite. — A very fmv t^'rains. 
 
 (7). OLIVINE QABBRO Mount Washing^ton River, 
 Now Hampshire, U.S.A. 
 
 Atyi)i(!al olivine ;4al)ltro,i»c(;urrin,^' in lar-^'e intrusive masses. 
 Essential constituents . . Plagioclase, Aiigite, Olivine. 
 Accessory *' . . Biotite, Iron Ore, Apatite, Pyrite. 
 
 Secondary " . . Serpentine. 
 
 Plagioclase. — See Nos. f) and (>. The pla^doclase in this 
 rock has hecii analyzed and found [n ])e lahradorit.'. 
 
 Augite. — I.arife amount. Pale hrownisli in colour. As 
 in hnrnhleiule (see No. .'5) there are thre(! classes of sections, 
 having- api)roximately the following' positions : — 
 
 t'b cC 
 
 u*^ 
 
 U 
 
 n- 
 
 i(r) (C\ 
 
 Si'XTIONS OF AuiilTK. 
 
 (a) ]*arallel to O P — These show two sets of cleavages, 
 intersecting nearly at right angles, and not so perfect as 
 those of liornhlende. The direction of extinction Ijisects 
 the angles made by the intersection of these cleavagc^s. l>y 
 determining the position of tlio plane of the optic axes, in 
 sections cut at right angles to an oi)tic axis, these cleavages 
 can 1)0 i)roved to he prismatic. 
 
 i 
 I 
 
ol.lVINK (iAIJllMo. 
 
 1 
 
 ( 
 
 i 
 
 {l>) rarallol to cc J' x . ( )\u' set of iiiir;illf>l clcaviif^'os, fuitl 
 extinction (ioincidin^' with tlicni. 
 
 ((•) Piirallel to c«j Vcc . One si-t of ])arallel cleavages, l.iit 
 with inclined (ixtinction, th(f angle of extinction heing verv 
 large, reaching 45°. 
 
 Sections in intermediates directions ami showing corres- 
 pondingly intermediates characters are also, of conrse, present. 
 
 The mineral has no iileochroisni. It is occasionally 
 twiniKMl. 
 
 Olivine. — Very pale green in coh.in-, almost colonrless, 
 with higher index of refraction than the augite, giving it 
 the apjuiarance of jmssessing a rough surface, like ground 
 glass, and also of standing out mon; prominently from the 
 field, rts cleavage is indistinct and imperf(!ct, hut, wliere 
 seen, the extinction is parallel to it. The mineral is, how- 
 ever, traversed l)y immy larg(> irn>gular cracks. It has a 
 high double refraction, and thus in this section, which is 
 thin, polarizes in brilliant colours. In some slides twin 
 crystals are .seen. It is usually more or less decomposed to 
 Serpentine, which is developenl along the cracks traversing 
 the olivine, and is recognized by its green colour, low doul>le 
 refraction, and aggregate polarization. 
 
 Biotite. — See No. I. — Occurs chiefly as borders about the 
 grains of iron ore, and is especially well developed when the 
 iron ore would otherwise come against the plagio ?lase. 
 
 Iron Ore. — Probably ilmenite or highly titaniferous maf^- 
 netitc. Considerable (piantity. Black and opaque. 
 
 Apatite. — A number of grains. — (See No. 3). 
 
 Pyrite. — A few little grains. Recognized l)y its yellow 
 metallic lustre; when examined by reflected light. 
 
 The order of crystallization lias been essentially as follows : 
 
i ' 
 
 18 
 
 IGNEOUS ROCKS. 
 
 Iron Oro and Apatite, Olivine, Biotite, Augite, Plagioclase. 
 
 Structure — Hypidiomorphic. 
 
 I 
 
 11 
 
 (8. PERIDOTiTE-llc de France, Matawin River, 
 Province of Quebec, Canada. 
 
 A large dyke-like mass, cutting Laurentian Gneiss, and 
 representing an extreme variation of the gabhro magma in 
 oni! direction a.s anorthosite (see No. Ct) does in another. 
 
 Kssential constituents . . Olivine, Aiigite. 
 
 Accessory " . . Biotite, Honiblende, Pyrite. 
 
 Secondary " . . Serpentine, Iron Ore. 
 
 Olivme. — See No. 7. — Often altered along cracks to a 
 mixture of serpentine and iron ore. 
 
 Angite. — See Xo. 7. — Nearly colourless. Resembles the 
 olivine somewhat, l)ut is distinguished by its cleavage and 
 other c' iracters already described. 
 
 Biotite. — See Xo. 1. — Strong pleochroism and good cleav- 
 age, with parallel (L\tinction. 
 
 Hornblende. — See Xo. 3. — lirown in colour, l)ut not so 
 intensely coloured as the biotite, imd much less abundant. 
 Distinguished by its cleavage as well as by its inclined 
 extinction and other optical proixirties. ( )ften intergrown 
 with the augite. This variety of IVi^idotite, conii)osed 
 essentially of olivine and augite, is called Pikrite. 
 
 In many sections of the rock a Poikilitic Structure is seen, 
 
 produced by the presence in a single large individual of one 
 
 mineral, e.i/., biotite, of a huge number of grains of other 
 
 constituents of the rock embedded quite without reference 
 
 to the crystallographic oi'ientation of their host or of one 
 
 iinother.* 
 
 * Williams, (1. H. : " (In the Use of the Terms Poikilitic and Mikro- 
 j)oikilitic in Pt'tiography." — Journa' of (Jeoloyy, February, 181)3. 
 
 i 
 
KJXEOrS KOCK.S (VOLCANIC DIVISION). 
 
 I 
 
 i 
 
 (9). OBSIDIAN Yellowstone National Park, Wyoming, U.S.A. 
 
 Occurs as a clit}", from 150 to 200 feci liigli, forming part 
 of a great surfa(!o flow of obsidian or volcanic glass.* 
 
 The rock consists of a nearly colourless isotropic Glass, 
 through which are distributed immense numbers of minute 
 Microlites and Trichites. The microlites are transparent, and 
 about -0002 inch in diameter, and occur either separately 
 or strung like beads on little opaque threads. They are 
 rudimentary crystals of Augite. The trichites are black hair- 
 like bodies, and a))out -000032 inch wideband maybe traced 
 through dillerent stages of growth into grains of magnetite, 
 which in larger form are recognized in the glass as intimately 
 associated with the augite, usually enclosed in a grain or crys- 
 tal of the latter mineral. These trichites give the obsidian 
 its black colour. Traces of Plow Structure can be seen in 
 most sections. In some sections, little crystals and irregular 
 spherulites are seen, which are composed of a micro-peg- 
 matitic intergrowth of quartz and feldspar. 
 
 (10). PITCHSTONE-Arran, Scotland. 
 
 Occurs in the form of dykes, pro])ably of Tertiary age. 
 A nearly colourless, isotropic Glass, filled with greenish, 
 acicular Microlites, sometimes so minute and so numerous as 
 
 IddinsH, J. P.: "Obsidian Cliff, Yellowstone National Park."- 
 Seventh Annual Report of the U. S. t;eo]. Survey, 188.-)..sr). 
 
20 
 
 IGNEOUS ROCKS. 
 
 to give merely a dusty aspect to tlie section when viewed 
 witli a low i)0\ver, sometimes large enough to show crystal- 
 lographic outlines. These are often aggregated together so 
 as to form exquisite arhorescent groups, resembling ferns or 
 fir trees, and sometimes have the shape of dumh-bells, etc. 
 Each group, having concentrated in itself tin; colouring 
 matter from the immediate vicinity, is surrounded by a zone 
 of clear glass. Tliese microlites consist of Hornblende — the 
 green colour and small extinction angle (about 15°) can 
 often be observed in the larger individuals. In almost 
 every section one or two rounded phenocrysts of Quartz, 
 Sanidine or Plagioclase are met with, holding inclusions of 
 the glassy base ; also a grain or two of Magnetite and of a 
 colourless transparent mineral, with high ind(;x of refrac- 
 tion and high double refraction, which is probably Zircon. 
 
 I 
 
 (11) RHYOLITE-Kremnicka, Hungary. 
 
 The product of one of a series of great eruptions of Ter- 
 tiary age. In this slide the Porphyritic Structure, with 
 well-marked distinction between phenocrysts and ground- 
 mass, which is the usual structure in volcanic rocks, is seen. 
 
 In rhyolite. as a general rule, })henocrysts of quartz, feld- 
 spar, and l)iotite are }>resent. In this section the Biotite 
 and Feldspar alone are found, qu.artz phenocrysts not being 
 common in the rock. The biotite shows, in a more or less 
 well marked manner, the absorption phenomenon, known as 
 the Opacite Elm (See No. 13). Indications of Plow Structure 
 can generally be seen. The groundmass is in a much more 
 highly devitrified condition than in Xos. 9 or 10. It is for 
 the most part Oryptocrystalline, consisting, probably, of an 
 
 
APORHYOLITE. 
 
 21 
 
 exceedingly fine-irrained intergiowth of quartz and feldsi)ar 
 (See No. 9). ]\rnch of it lias a rudely Spherulitic arrange- 
 ment. The rock being somewhat Vesicular, a nnmber of 
 elongated irregular-sliaped holes are seen in the slide. 
 
 (12). APORHYOLITE-Raccoon Creek, Pennsylvania, U.S.A." 
 
 A rhyolite of i)re-Cambrian age, being a representative of 
 the great volcanic oiitl)ursts of this age which are found 
 along the line of the Appalachian mountain chain from 
 Gaspe to Georgia. The original glassy rock has in the lajise 
 of ages become thoroughly devitrified. The phenocrysts are 
 chieily Orthoclase ; some are of Plagioclase. These preserve 
 their perfect crystalline outlines, and in many instances 
 hold inclusions of the groundmass as in the case of modern 
 volcanic rocks. 
 
 The Groundmass is a very fine quartz-feldspar mosaic, 
 through which there is a certain amount of finely dis- 
 seminated sesquioxide of iron. Thi.^ mosaic is very hirgely 
 the result of devitrification and recrystallization, but a 
 portion of it may represent an original microgranitic ground- 
 mass. Numerous areas of a rounded or more or less irregular 
 shape, and coarsely crystalline in character, are seen. These 
 consist for the most psirt of quartz. Of these there are 
 two kinds, representing two dift\!rent structures in the origi- 
 nal rock. (Jne kind, usually irregular in shape, often long 
 and narrow as if drawn out by movements in the liqu, 
 
 * Willia,M.s, a. H. : "The Volcanic Rocks of South Mountain in 
 Pennsylvania and xMaryhmd/'-Anier. Jour, of Science, December, 
 18!)2. 
 
 liascom, v.: "The Structures, Origin, and Nonienchiture of the 
 Acid Volcanic Uocks of South Mountain."— Jour, of Go„loffv Nov 
 189;{. 
 
22 
 
 KiNEOUS HOCKS. 
 
 rock, with well-defined walls, were ori^iiiidly Vesicles, They 
 often show a banded arrangement ahout their borders, 
 fidlowing all the windings of the wall, rej)re8enting deposits 
 of seconthiry minerals in the vesicndar cavities. Little si)heru- 
 lites or gronps of crystals, originally of tridymite now 
 convert(Hl into (juartz, are often seen on the walls of the 
 original cavities, precisely as in the case of modern lavas. 
 The other kind are nsually more rounded in s\u\[)c and not 
 s) sharply defined against the groundniass ; faint concentric 
 markings can often be traced about them in the groundniass, 
 and areas of the groundmass— in the centre of each of 
 which one of these coarsely-crystalline mosaics occurs — are 
 marked off from one another by a line of iron oxide, which 
 lines form a species of network in the slide. These, it has 
 been found, from the study of a large; nund)er of s])ecimens, 
 were originally Spherulites, which have been more or less 
 comi)Ietely obliterated by devitrification, the centre of each 
 having been dissolved away and replaced by the mosaic in 
 (juestion. 
 
 The rock was therefore, originally, a vesicular spherulitic 
 glassy rhyolite. 
 
 The prefix apo is emi)loyed to indicate the specific altera- 
 tion known as devitrification : an aporhyolite is therefore a 
 de vitrified rhyolite. 
 
 (13). HORNBLENDE ANDESITE Stenzelberg, Siebengebirgc, 
 
 Germany. 
 
 Essential constituents (in form of Phenocrysts), 
 
 Hornblende, Plagioclase. 
 
 Accessory constituents (in form of Phenocrysts), 
 
 Augite, Biotite, Magnetite, Hematite. 
 (Ironndmass. 
 
 M 
 
MKLAl'HYRE. 
 
 23 
 
 Th" i)luMio('i;v«ts, being perfect crystals, are Idiomorphic 
 and show gooil crystalline outlines. Tliey'sliow the cleavas^es 
 and optical pro[)erties severally characteristic of them, as 
 already th^scrihed (See Xos. 1, 3, and 7). 
 
 The Hornblende and Biotite crystals are always surnnuKhMl 
 liyadark l)ord(!r, known as the " opacite xim," which consists 
 of a luixtui'e (jf Augite and Magnetite in veiy minute grains. 
 This is due to the corrosive action of the magma on these 
 tirst-mentioned minerals after they hail crystallized out. The 
 corrosive aijtion is sometimes seen to have gone so far that 
 the hornhlende or hiotite liave entirely disa[)peared, 
 leaving only an aggregate of little black grains. 
 
 As augite is one of the products of this action, the augite 
 grains themselves are not attacked, and have no l)()rder. 
 
 The Plagioclase usually shows growth rings, and is excel- 
 lently twinned, often according to both laws, while both the 
 horid)lende aud augite frequently show twinning also. 
 
 .Many small irregular-shaped grains of Magnetite are 
 scattei'ed through tin; rock. 
 
 The Groundmass is essentiallv microcrystalline, and is 
 made u[) chiefly of little lath-shai>ed crystals of plagioclase 
 with minute grains of augite and magnetite, often showing 
 distinct flow structure. A consideral)le amount of Hematite, 
 l)right red by reflected light, occurs linely disseminated 
 through i)ortions of the groundmass. 
 
 (14). MELAPHYRE Oberstcin, a.d. Nahc, Germany. 
 
 Occurs as sheets and flows, interstratified with rocks of 
 Permian age. 
 
 A melaphyre containing phenocrysts of Olivine and Augite 
 as well as phenocrysts of Plagioclase. 
 
L'4 
 
 KiNEOUS HOCKS. 
 
 '■ it 
 
 111 this piirticular s]K'(!iiiu'ii, liou'evcr, tlics ; iiiiiicrals are 
 less abundant tliaii ut^iial, olivino not lH'iii<i' p/csiuii- in every 
 slide and aiigite l)ein,i4' riivdy fonnd ; so that, jiid,ning from 
 some of the sections, the rock mi«>lit Ije cUissed as a lahra- 
 dorite porphyrite. 
 
 Tlie Olivine, where ori,^nnally ])i'eseiit, is now id ways en- 
 tirely altered to Serpentine, which still retains the form of 
 the olivine grains, and is reco'^ni/.ed l)y its j)ale j^reen eolour, 
 librous structure, and ag;u,'rcgate ])olarization. 
 
 The transparent reddish-l)rown lines and hands which 
 traverse the Plagioclase pheiuxa'ysts are due to Oxide 
 of iron inliltrated into cracks in tlui crystals, and derived 
 from *,he alteration of various fcu'ru^inous minerals in th" 
 rock. The same material, l)y its [)resence all through the 
 groundinass, gives the rock its dark opatpie charai'ter. 
 
 The Groiindmass consists chieHy of luiuute lath-shaped 
 crystals of plagioclase, hut hetween them a certain amount 
 of Glass filled Avith dark inclusions still remains, and can lie 
 recognized l)y its is(.)tropic character. 
 
 The Amygdaloidal Structure of th(> rock is remarkably m'cII 
 seen. The smooth outline of the cavities will I)e noted, as 
 well as the concentric arrangement of tin; mimu-als fillinu' 
 them. Some of these have a beautiful Spherulitio arrange- 
 ment. They are Oalcite, Chlorite, Quartz, oftiui in tli(i form 
 of Chalcedony, and occasionally Zeolites. 
 
 Quartz is not found in all sections, and when it does occur 
 is present only in very small amount. 
 
 The Apatite needles are often very long and slender. A 
 few grains of Pyrite are usually jiresent. 
 
11 
 
 
 
 LEUCITE BASANITE. 
 
 (15). OLIVINE DIABASE-Ncar Sudbury, Ontario, Canada. 
 
 Occurs in the form of ii lar^e dyke cutting rocks of 
 Huronian age. 
 
 Essential constituents . . Plagioclase, Augite, Olivine, 
 Accessory " .. Iron Ore, Biotite, Apatite, Quartz, 
 
 Pyrite. 
 Secondary " . . Serpentine, Chlorite. 
 
 A fresh and ty[)ical rock of tliis class, ditl'ers from No. 7 
 only in structure, the same minerals being present in both 
 rocks. 
 
 Tliis rock sliows tlie "Diabase" or "Ophitic" Structure, the 
 Plagioclase occurring in hjng lath-shaped crystals, running 
 into th(! Augite, which crystallized later than the plagioclase. 
 
 (16). LEUCITE BASANITE Mount Vesuvius, Italy. 
 
 A A^esuvian lava of the erui)tion of 1873. 
 
 Essential constituents (in the form of Phenocrysts), 
 
 Leucite, Plagioclase, Augite, Olivine. 
 Accessory " Magnetite. 
 
 ( Iroundmass or base. 
 The rock has a typical porphyritic structure. 
 The Leucite occurs in clear colourless crystals with poly- 
 gonal outlines, of approximately cirt.'ular shape. These are 
 sections through tetragonal trisoctahedra or other allied 
 forms of the isometric system. Between crossed nicols they 
 appear isotro})ic, or show sets of parallel and very faint 
 bands of colour crossing one another. These are probably 
 due to a complicated system of twinning, and are seen more 
 particularly in the large individuals — smaller ones being 
 usually ([uite isotropic. 
 
•JG 
 
 IGNEOUS UOCKS. 
 
 TlicPlagioclase ofcurs in well dctiiKHl colourless lath sliai»eil 
 iiuli 'idiials liavinj,' the usual polysynthetic twinuinif. 
 
 Tl'o Augite is pule green in colour, and o(;curs with j^ood 
 (Crystal outlines. It may Ije reco,^nized by its cleax'ages and 
 its optical properties. 
 
 The Olivine is also in good crystals, l)ut is colourless, and 
 possesses its distinctive optical properties. See No. 7. 
 
 Magnetite. — A few small grains. 
 
 The Base or G-roundmass, in which these phenocrysts are 
 embedded, is a brown isotro[)ic glass. 
 
MKTAAIOIJPHIC HOCKS. 
 
 (17). SPOTTED CLAY SLATE Andlau Valley, Vosgrcs 
 Mountains, Germany. 
 
 This rock, a well as Xo. 18, aro taken from the celel)rate(l 
 Barr-Andlaii (Jrauite Contact Zone, made classical Ity the 
 investigations of Prof. Ilosenbusch.* 
 
 This .section, which really represents a transition between 
 what are known as the Spotted Clay Slate and the Spotted 
 Mica Schist Zone's, shows the clay .slate in an incipient stage 
 of alteration, while Xo. 18 shows it in its most altere<l 
 condition. 
 
 The s(;ction presents a lighter coloured portion with 
 nnmerous dark spots disseminated through it. 
 
 The darker spots represent portions of the original slate in 
 an almost unaltered condition. Their presence is very char- 
 acteristic of the outer and less altered portions of contact 
 zones, in cases where the altered rock was originally a shale 
 or slate. They are composed for the most part of the same 
 minerals as the lighter coloured portion, but in much smaller 
 individuals and with more carbonaceous pigment and much 
 less muscovite. 
 
 The lighter coloured portion is the metamorphosed portion 
 of the rock. When examined under a very high power it is 
 
 * " Die Stsiger Schiefer und ihre Contactzone an den Graniten von 
 Barr- Andlau iind Hochvvald." Abh. zur Geol. Specialkarte von Elaass. 
 — Lothringen, Strassburg, 1877. 
 
^ 
 
 28 
 
 Ml'n'A.MOKl'JlIC U(X'lvS. 
 
 seen tolx' composed of initiuto slireds of Muscovite ;uul Kaolin 
 (which ro.senil)](^ one anoLhor very closely), iiiiiiute ^niins of 
 Quartz, some Mack Carbonaceous Pigment, with a few^'raijis of 
 Tourmaline iind possibly a litth; chlorite. Crystals of Magnetite 
 have also heen diivcloped all throuj;h the altered portion. 
 
 (18). ANDALUSITE HORN8TONE Noar Andlau, Vosgcs 
 Mountains, Germany. 
 
 From same contact zone as No. 17 (which sec), ))ut nearer 
 tlie fri-aiiite, heing })rodu(;ed hy the re(;rystallization of the 
 slate into a comparatively coarse grained aggregate of several 
 mineralH. Of tliese, Quartz, Biotite, Muscovite and Magnetite 
 are abundant, and will be readily recognized. A portion of 
 tlu! opacpie black mineral which looks like iron ore is 
 graphite. 
 
 Andalusite is present in large amount. It is colourless 
 and possesses a high index of refraction, but a low double 
 refraction. The extinction is parallel. It also shoM's a faint 
 but very characteristic pleochroism — i>ale red and pale green, 
 the former in the direction of the vertical axis, the latter at 
 right angles to it. 
 
 Tourmaline. — A few little grains,with high index of refrac- 
 tion, strong ])leochroisni, and deep greenish-black colour. 
 
 The minerals are perfectly Allotriomorphic, and grow through 
 one another in an irregular manner, quite different from the 
 orderly succession of crystallization found in igneous rocks. 
 
 (19). SILLIMANITE GNEISS St. Jean de Matha, Province 
 of Quebec, Canada. 
 
 Occurs in thick bands, interstratitied with a white gar- 
 netiferous quartzite, the whole lying nearly flat, and forming 
 part of the (irenville Series (Laurentian). 
 
.'frac- 
 
 SILMMAN'ITE GNEISS. 
 
 29 
 
 This gneiss has the elieinical composition of an ordinary 
 ehiy shito, and in all i)rol)al)ility rej)resents an extremely 
 altered form of an ordinary sedimentary rock.* 
 
 Essential constituents . . Ortlioclase, Quartz, Sillimanite, 
 
 Garnet, 
 Accessory " . . Pyrite, Graphite, Eutile, Biotite. 
 
 Orthoclase, — See Xo. 1. 
 
 Quartz. — See No. 1. — This, as well as the orthoclase, 
 usually shows some evidences of pressure in a slightly un- 
 even extinction. Frequently in long and narrow grains, 
 their long axes being arranged parallel to the foliation of 
 the rock. 
 
 Sillimanite. — Abundant, and usually occurs in large indi- 
 viduals. It is colourless, and has both a high index of 
 refraction and a high double refraction, which enables it to 
 be readily distinguished from the quartz or orthoclase. It 
 crystallizes in long, nearly square, })risms, with a single good 
 cleavage parallel to a pinacoid. There are thus two sorts 
 of sections to be observed : — 
 
 (a) Elongated sections, parallel to the vertical axis, which 
 may or may not show a cleavage parallel to tlieir length, 
 according to the plane in which they lie. They show paral- 
 lel extinction, and high polarization colours. 
 
 (h) IJasal sections, nearly square in cross section, and 
 showing a good cleavage bisecting two of the angles. These 
 are nearly isotropic. In convergent light the mineral is 
 seen to possess a very small axial angle and to l)e positive. 
 
 * Adams, F. I). : "A Further Contribution to our Knowledge of the 
 Laurentian.''— American .Journal of Science, July, 1895. 
 
w 
 
 30 
 
 MKTAMOlll'llir UDCKS. 
 
 Garnet. -Sec Nus. 4 mid ').— In hir^^r irrcguliii' shaiu'il 
 cdloiirh'ss iiidivitliuils. Pcrtcclly isotropic (>ftt'ii holds 
 iiii'lusions of silliiuaiiitc, riiLilc, litc, iis if il had ^rowii 
 ai'oiiiid ihi'iii. 
 
 Pyrite. Sec Nos. I and 7.— XCry ronsiih'ral>h' ainouiit. 
 In irri'L^ruhir shapccl little strin.t^'s and i^rains. l*rol)iil)ly 
 ii)»p(!iii't'il after tln' (l('V('lo])ni('ni of the other constituents, 
 as it, is frecjuently seen to occupy little cracks in the rock. 
 It is associated, in some slides, with a little ])yrrhotite. 
 Ilydrated ses(|uio\ide of ii'oii, reddish hro.wn hy I'clleeted 
 li,L,dit, occurs as a decomposition product, runninif,MhroUL;h tlie 
 rock in cnicks and alomj,- the cleavaiyros of the various nnnorals. 
 
 Graphite. In ion- and narrow opa(]ue hlack strings or • 
 in scales. 
 
 Rutite. -In sniidl, in(',L!,ular shaped, dee[) hrown grains; 
 nearly opacpie. High index of I'efract-ion. 
 
 Biotite. A few grains, deep hiown in coloui'. 
 
 (20 . HORNBLENDE GNEISS Trembling Mountain, 
 Province of Quebec, Canada. 
 
 Tremhhng .Mountain, whose summit is the highest point 
 in the Laureiitian j)lateau in this ])art of the Dominion, was 
 was referi'eil to i)y Sir W'illiam Logan as a t;y|)ical oci'Ui'reiico 
 of tiie l''undaniental ( Jneiss. The rock posscssi's a distinct 
 altliough not a very p(M'f(M;t foliated structure, and forms 
 almost the entire mass of the mountain. 
 
 It has the chemical com|)ositioii of a, granite, and is 
 nothing moro than a hornhlcnde granite of igneous origin, 
 which hy great earth movements has hoen stjuoezed into the 
 form of a gneiss.* 
 
 
 * Aflanis, V. D. : " A I'mther Coiiti'ibiitioii to our Kiioulcilgc of the 
 Laurentiiin.' ^ — .American .lomnal of .Science, -July, ISiC). 
 
llOHNltl.F-lMtK (iNKISS. 
 
 31 
 
 h..l(ls 
 
 
 Kssciitiiil ('()nstitiioiit.s . . Ortliodase, Quartz, Hornblende. 
 Accessory " . . Biotite, Magnetite, Zircon, Apatite. 
 
 Ortlioclase. — Tlic rock c insists ])rincij)iilly of rutlicr larnc 
 aiitl vci-y irrcgiiliir sliapcd orthocliisc f^'rains iinhcddod in ii 
 mass of liiicly <,M'aiudat('d rice like material, also ortlioclase 
 for the. most part,. 'J'lie large indi\idiials show " sti'ain 
 shadows,'" and often a somewhat lii)r(ins appearance, due to a 
 very thie microperthitic interj^jrowth. The linely j^rannlated 
 iiiiiterial is formed hy the peripheral ,i,M'annlation of the lareer 
 individuals. 
 
 Quartz, — A few lari^c individuals, also irreeidar in shape 
 and with uneven extinction, often much Ki'oken. Also, a 
 numher of smaller erains inteiauixed with linely .granulated 
 ortlioclase. 
 
 Hornblende. — Set; No. 4. — Strings of small grains, green in 
 colour. 
 
 Biotite. A few grains. 
 
 Magnetite.— An o[) .(pie black iron ore, in irregiilai' shaped 
 grains, usually associated with the li(trnbh,'nde. There is 
 also a hydrated o\id(i of iron, ndiicli occurs in small amount 
 as a secondary jiroduct, and has found its way betwtM'ii the 
 grains of the .several minerals or int(j their cleavages, thus 
 straining the rock. 
 
 Zircon. -Sec No. 1. — A number of minut<^ lu'ismatic crys- 
 tals, witJi high index of refraction, high double refraction 
 and paralhd extinction. 
 
 Apatite, — S(mi No. 3. — \ few small grains. 
 
 The rock shows a Oataclastic Structure, the foliation bavins 
 b(MMi ])r()(liH'(Ml l»y pressure. 
 
32 MET AMORPHIC ROCKS. 
 
 (21.) FOLIATED ANORTHOSITE-Near Chertsey, Province 
 of Quebec, Canada. 
 
 Tliis is ii finely foliated variety of Xo. G, taken from the 
 margin of the same area, the Morin anorthosite. Here, 
 however, the roek has moved like a plastic mass under tlie 
 influence of the great pressure to which it has heen subjected, 
 and the manner in which the movement has taken jjlace is 
 clearly seen in the slide, l^otli the Plagioclase and the 
 Pyroxene individuals, while remaining unaltered in composi- 
 tion, liave, under the influence of the pressure, been granu. 
 lated, and the broken grains have moved in a direction at 
 right angles to the pressure, and are often seen to be arranged 
 in l(^ng strings or trails on either side of a remnant of the 
 large original individual from which they were derived, 
 which shows well-marked Strain Shadows, and can often be 
 seen to be in the very act of shearing into two smaller indi- 
 viduals, very long and narrow, or to be gradually breaking 
 down by peripheral granulation. 
 
 Whenever this granulation sets in tlie Schillerization 
 products disappear. This slide show excellently one way in 
 which a foliated rock is developed from a massive rock It 
 should be studied in connection with No. 6. 
 
 (22). SERPENTINE LIMESTONE Near Rawdon, Province 
 of Quebec, Canada. 
 
 A tyj)ical Laurentian crystalline limestone, occurring as a 
 thick l)and interstratified with gneiss. 
 
 Essential Constituents . . . Oalcite, Serpentine. 
 Accessory " ... Muscovite. 
 
 Oalcite.— High index of refraction and very high double 
 refraction, causing the mineral to polarize in silvery tints. 
 
rince 
 
 0111 the 
 Here, 
 (lor the 
 l)jected, 
 |)l;K'e is 
 iiul the 
 ;oinposi- 
 i granii- 
 ction at 
 irraiiged 
 t of the 
 derived, 
 often be 
 Her iudi- 
 breaking 
 
 SEUrENTINE LIMESTONE. 
 
 33 
 
 The rliomboliedral cleavage is very distinct. The mineral 
 is in some places clear and transj)arent, while in oilier 
 places it is turbid from the presence of numerons dust like 
 inclusions. The same grain will sometimes b(^ clcai' in one 
 part and turbid in another. These turbid spaces are 
 highly suggestive of ol)literated fossil fragments. (See 
 Section No. 25.) 
 
 Serpentine. — In rounded grains of a very pale green colour, 
 end)edded in the calcite. Has a very low double} refraction 
 and shows aggregate polarization. 
 
 Muscovite. — A numl)er of rather large grains, usually 
 S(miewhat bent or tAvisted. (See No. 2.) 
 
 leri/.ation 
 le way in 
 rock. It 
 
 rovince 
 
 rring as a 
 
 atme. 
 
 i^h double 
 ^rery tints. 
 
AQUKors IJOCXS. 
 
 (23). ARKOSE— Campbellton, Prince Edward Island, Canada. 
 
 A highly fclilspathic redsancl stone of Penno-Cail)oiiifc'i'ous 
 
 Jln-O. 
 
 Quartz. — Abundant. Often sliows strain slmdows, indi- 
 cating that it luis been originally derived, in part at least, 
 from gneiss or some other (jnartzosi^ rock wliich has been 
 submitted to great pressure. 
 
 Ortlioclase. — Much kaolinized. 
 
 Plagioclase. — A fcnv grains. 
 
 Muscovite. — A few grain.s. 
 
 Oalcite. — Cliielly in the form of large individuals serving 
 as a cement. 
 
 A few comitosite fragments consisting of line grained 
 sandstoiu', etc., are i)resent. A good deal of reddish hydrate 
 oxide (tf iron also occurs coating the grains or scattered 
 through the rock, giving to it its red colar. 
 
 'I'hc rock has a ty[)ical Clastic Structure, licing made \\\> of 
 broken grains of \arious minerals with some comi)osite 
 rock fragments. 
 
 (24) SANDSTONE Lachute, Province of Quebec, Canada. 
 
 A typical <]uart/o.se sandstone of Potsdam age. Made up 
 almost exclusively of clear transjiarent ([uartz grains, more 
 or less perfectly rounded in sha|>e. The original outlines of 
 the grains are marked by the lines of impurities which 
 
FOSSILIFEUOUS LIMESTONE. 
 
 nn 
 
 coated tlio surface of tlie original grains. The most interest- 
 ing and important [)oint to note in the section is tliat the 
 original grains have in many cases become enlarged by the 
 deposition of Secondary Silica in the little interspaces betwetm 
 the grains, the silica so dei)0site(l having the optical orienta- 
 tion of the adjacent ({Uartz grain. A little space l)etween, 
 say, three grains, can often be ol)served Avhich has thus 
 become lilled uj) with quartz, portions of Avhich are orien- 
 tated partdlel to each of the three quartz grains, as can 
 be ascertained by an examination between crossed nicols. 
 
 This process results in the formation of a qiiartzite from a 
 sandstone.* •• , ■ 
 
 The rock process is a typical Clastic Structure. - 
 
 (25). FOSSiLIFEROUS LIMESTONE Montreal, Province 
 of Quebec, Canada. 
 
 A dark gray stratihed limestone of Trenton age. 
 
 Composed exclusively of calcite, containing in places as an 
 impurity a certain amount of a d;irk carbonaceous materia} 
 in minute disseminated grains, which give to the limestone 
 its dark colour. 
 
 A large [)art of this calcite, comprising almost all that 
 darkened by the ])reseiice of the imi)urities above referred to, 
 consists of the fragments of broken up fossils of several 
 kinds. The forms can be readily recognized as of or<fanic 
 origin, an<l are (piite dillerent from anything .seen in other 
 sections of this collection. Among these fragments those of 
 Monticulipora and Ptilodictya are most abundant, both made 
 up of cells usually oval in section, the latter having the cells 
 
 * Irving and Van Hise : "On Secondary Enlargements of Mineral 
 Fragments in Certain Rocks. "--Bull. H.S. (Jenl. Smvev, No. 8, 1884. 
 
% 
 
 AQUEOUH IlOfKS. 
 
 in two TOWS, arranged eith(>r side of a central canal. Next 
 in abundaiKM; are fragments of Orinoids, some of them annular 
 cross se<?tions of elements of the stalk; (»thers of various 
 shapes', acconling to the forms of the plates and the direction 
 of the sections. A few long, narrow forms, shoAving little or 
 no stn-uf turo, are cross sections of Brachiopod Shells, 
 
 llctwecn these fossil fragments and lilling u|) their cells 
 is i\ (;emenl consisting of large clear calcite individuals, 
 which show the [)erfect rhomholunlral cleavage and various 
 ojjtical properties of the mineral (see No. 22). These can 
 often he observed to form a clear border about a fossil frag- 
 ment, while the latter can be recognized only by its darker 
 color, due to the inclusions of carbonaceous matter. This 
 is especially noticeable in the case of the crinoid fragments, 
 for eveii in a living state each crinoid element is a skeleton 
 crystid of calcite, and hence the secondary calcite is deposited 
 in optical continuity with original calcite of the fragment, 
 and the whole polarizes as a single individual. In such 
 a compo.site grain the original fragment is seen as a more or 
 less shari)ly defined dark inclusion, the 1)()undaries in some 
 instanees,. however' being indistinct, the original fragnuMit 
 being rei)resented merely by a turbid area in tlu^ interior of 
 the grain, like that seen in some cases in Section No. 22, 
 and in the description of that Section stated to be suggestive 
 of an organic origin of the limestone. 
 
 Bef(.)re consolidation this limestone must have been a 
 niaterial closely rtisembling the "coral sands" found abtnit 
 the coral reefs of the modern seas.''^ 
 
 1 
 li 
 
 *Se.' Sir Will i:nn 1)m\vs( 
 
 >n 
 
 On the Microscopic Striicturt' of soin 
 
 (Janjwlian liiniestonos." Can. Nat., .iiiiie, iSo!). 
 
 I 
 
•w^-