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Tous les autres exemplaires originaux sont film6s en comm^^ngant par la premidre page qui comporte une empreinte d'impression ou d'illustration et en terminant par la dnrnidre page qui comporte une telle empreinte. Un des symboles suivants apparaitra sur la dernidre image de cheque microfiche, selon le cas: le symbole —^' signifie "A SUIVRE", le symbole V signifie "FIN ". Les cartes, planches, tableaux, etc., peuvent dtre filmds d des taux de reduction diffdrents. Lorsque le document est trop grand pour §tre reproduit en un seul ctich6, il est film6 d partir de Tangle supdrieur gauche, de gauche d droite, et de haut en bas, en prenant le nombre d'images n6cessaire. Les diagrammes suivants illustrent la mdthode. arrata to pelure, m d n 32X 1 2 3 1 2 3 4 5 6 a p ^ , C^t ^ " ON SOME GRANITES FROM BRITISH COLUMBIA AND THE ADJACENT PARTS OF ALASKA AND THE YUKON DISTRICT. By Frank D. Adams. V* 344 Canadian Record of Science. ^." Rtprivledfiom the Caiuulian Record of Science, SepUmber, 1891." On Some Granites from British Columbia and THE Adjacent Parts of Alaska and THE Yukon District. By Fkank I). Adams, Lecturer in Geology, McGiU University. Some three years ago, when on the ntaft'ofthe (Jeological Survey ofCanadn, the writer was requested by Dr. (J. M. Dawtson, to examine a nei-ies of rook specimens collected by that gentleman and his assistants, Messrs. McConnell and Ogilvy, during their explorations in the Yukon Districts and Northern British Columbia in 1887. The results of this examination were published as an appendix to Dr. Dawson's Report on the Yukon District.' The rocks examined were, for the most part granites, but included also, diabase por])hyrite8, diabase tuffs and other rocks, which, however, were normal in character, and posseshed of no features which here deserve especial mention or further desciiplion. Among the granites, however, there were three which were rather remarkable and seemed to be worthy of a moie extended study than it was at that time possible to make. I have accordingly, through the kindness of Dr. Dawson, re-examined the hand specimens, and with the aid (»f additional thin sections have made a more detailed studi* of the locks ill question. Granite fro7n Wrangell Island, Alaska.— The first of these I'ocks is a rather tine grained grey granite fi'om Wrangell Island, Alaska. Jn Di-. Dawson's Report it is referred to as follows : " The i-ocks aUmg the west shore of Wrangell Island, in the vicinity- of the town and harbor, are chief!}' black tlnggy ai-gilliios, i-emarkably uniform and regular in their bedding and with a westward dip. They are con- siderably indurated and contain small staurolite crystals in some layers, while on the surface of others crystals ' Appendix V. • Notes on the Lithologiciil Cliaracter of some rooks collected in the Yukon District and adjacent Northern parts of British Columbia, by Frank D. Adams. Annual Report of the Geological Survey ol Canada 1887. (i Granites from British Columbia, etc. 345 t of mica have been developed, Similai' rocks are found on other parts of the coast, both in the north and south, and from a lithological point of view, they inucli resem- ble the Triassic argiliites of the Queen (Jharlotte Ishmds, though no fossils are found at this place. The ridge behind the town of VV^rangell is chiefly comijosed of rather tine grained grey granite, which is probably intrusive and may have been the cause ol the incipient crystallization observed in the argiliites. The north part of the island is formed of a similar granite, probably a continuation of the same mass." Dr. Daw&on informs me Xliat the granites all through this district seem to be more i-ecent than the slates and that he regards the mass in question as almost certainly of eruptive origin. The hand specimen when examined seems to show a very indistinct tendency towards parallelism of mica individuals, and when thin sections are examined there is evidence in tiie somewhat uneven extinction of the quartz grains as well as in the twisting of the biotite, that the rock has been submitted to pressure. It is composed essen- tially of quartz, orthociase, plagioclase and biotite, with epidote, allanite, garnet, sphene, zircon and apatite, as accessory constituents. The essential constituents show nothing especially deserving of mention. The feldspars are generally fresh and frequently show a beautiful zonal structure due to growth-rings. Occasionally a distinct bor- der with well marked granophyre structure is seen about a portion of a feldspar individual. The garnet, of which a few grains are present in most of the sections, is light brown in colour. The interest of the rock centres in the epidote with its associated allanite. The epidote is present in considerable amount and is generally associated with the biotite. It is colourless and has rather a high index of refraction, occurring in prisms elongated, parallel to the b axis with a perfect cleavage parallel to the length. Examined in convergent light between crossed nicols it is seen to be biaxial, the plane of the optic axes in all cases being at right angles to the 346 Canadian Record of Science. length of the prism. In some instances the double I'efraction is sufficiently strong to give I'ise to the greenish-yellow, yellow and pink colours usually seen in thin sections of this mineral, but in others, and almost invariably in very thin sections the mineral shows the deep blue interference colours chaiacteristic of Zoisite. It was thought at first that both minerals wore present, but a more careful study of the slides showed that the blue colour was given by thinner parts of individuals which elsewhere polai-ize in yellow tints, the blue colour appearing as border around the little bays or cavities, in the ci'vslals to be described further on, and where, therefore the epidote was thinner than else- where. Since, however, normal epidote has a sufficiently strong double refraction to give brilliant yellow interference colours even in the thinnest sections ordinarily attainable, it is probable that this is a variety poor in iron, and thus approaching Zoisite in composition, these two minerals being dimorphic, thoii- formula being identical, except that in epiuote a portion of the alumina is generally replaced by ferric oxide, The absence of the usual pleochroism in the mineral points to the same conclusion. Associated with some but by no means with all of those crystals of epidote are little individuals of allanite. These are sometimes very small and of a more or less irregular shape, but frequently have a good crystalline form consisting of a prism elongated in the direction of the b axis and j^en- erally having what are probably pyramidal terminations at one extremity. The plane of the optic axis is at right angles to the longer axis of these crystals. It has a high index of refraction, possesses a distinct zonal structure and is pleochroic, the colours being as follows : — jj — Light yellowish brown. U — Purplish brown. C — Pale yellowish brown. The light passing through the crystals parallel to a is of nearly the same colour as that passing through parallel to C. The colour is not so intense as is usual in allanite, al- t. Granites from British Columbia, etc. 84*7 t. though this may be duo in part to the fact that thewe crystals are very ismall. In two or three cases twin crystals of allanite were found, the twinning line probably being c»P.>j , in one ease extinc- tions of 23° and '11^ respectively on either side of the twinning line were observed, but nono of the crystals were cut quite pai-allel to the cliiiopinacoid. The epidote, when associated with these allanites, hut ci-ystallized around them, sometimes enveloping them completely, but at other times onlj' partially, foiming what is generally a very irieu:ular border. The allanite and epidote are probably intorgrown in parallel position, but no section was found 80 cut that this could bo actually proved. The mode of occurrence of these two-minerals is seen in the accompany- ing cut (Fig. 1) in the up[)er loft hand division, the epidote being represented in outline, while the allanite is black. This association of epidote and allanite has already been described from a number of localities.' The epidote is remarkable, not only as occurring in very considerable amount in the granite, but also from its mode of occuri'once. It is evident at the tirst glance thr.t it does not result from the decomposition of the plagioclase or other constituents of the rock, as is fre(|uently the case in much decomposed igneous rocks, since it occurs in lai-ge well defined crystals, these however seldom have a perfect form but possess a very peculiar eaten or corroded appearance, being traversed by little irregular canals and arms of another colourless mineral with much lower index of refraction. These arms are in many cases, too small to enable their character to bo determined, but on careful examina- ' Becker, Ewnld.— "Ueber das Mineralvorkommeii im Granit von Striegau, insbeaondere (iber den Orthorlas und dunkelt?ri'tien Epidote."— Breslau. Ilnbbs, W. H.— " Ueber die Verwachsung von Allanite (Orthit) und Epidote in (}estcinen."— Tschermak's Min. and Pot. Mitt., ISH'J, i., also Johns Hopkins Univei.si ty Circular, April , 1888. Lacroix, A.—" Contributions a I'etude des (JneLss k Pyroxefle et des roches 4 Wernerite." Bull. Soe. Min., France, April, 188!». Tornebohm, A. E.— " Mikroskopiska Berg.irtstudier XIL.Epidot gneiss," (led. For. i., Stock Forb, No, 75, 1882. 348 Canadian Rrrord of Science. tion it is found that they aio tor the must part (jUiii'tz, in fact arms of quartz oaii in many places be seeti running into the epidote crystals fr-om adjacent (piartz grains, the arm and the oxtornal jtnrtion of the grain belonging to the Hame individual. In othei- |)lacos, howevoi', these little arms were found to consist of plagioclase and to be continuouH with the plagioclase associated with the epidote in the same manner as in the case of the ([uai'tz described above, prob- ably some of them mtiy also be orlhoclaso. Three of these epidote ciyslals are lepresentod in outline in Fig. 1, (Nos. i, ii, iii). They were drawn with theaid ofa camera lucida from epidote crystals occurring in the sections of the Wrangell Island granite. In the second one (No. ii), how- ever, it was found lo be impossible to show all the inclusions and little ai-ms, only th<3 largest and best defined being lepresented, while a number of smaller ones are omitted. Figure 1. i. — Epidote, enclosing AUanite in Granite from Wrangell Island, ii, iii. — Epidote in Granite from Wrangell Island, iv, V, yi, — jingle individuals of Muscovite in Granite from Pelly Jliver. I Granites from British Columbia, etc. 849 The mode of occuiTonco in oxactly tlio Hiiine a» that des- cribed by Dr. (loo. H. Williutns in tlio case of the epidoto oc- I'UiTing in the Mica Dioiito from Stony Point on the Uwi- Hon Rivcv {American Journal of Science, .June, 18H8). The nearest analoi^y to il observed in other rocks, is the struc- ture of tlic ^ai'iicts in many garnetifoi-ous gneisses. In the garnetiferous gneisses of ihc Laurentian System which I have had an opportunit}- of examining in thin sections, the garnets, although sometimes lorming comi)act ind' viduals, in other specimens have a structure closely resembling, and often apparently identical with that above described. This structure in gneisses and in the granite under consideration, does not seem to be due to the eattng away or partial solution of crystals which oi-iginally had a perfect foi-m. as in the (|uartK phenocrysts of (juni'tz porphyries, where fiagments of what were evidently once quartz crystals which have been eaten apart, can ol'ten bo found lying near each other having lost their common orientation, nor are the bays which run into the ej)idote always or generally large and well doHned like the arms of the groundmuss in the (juartz phenocrysts in <|Uostion, but on the contj-ary, they are geneially long, slender curving arras and little irregular canals, and are frequently found closed at the outer end, forming cavities which then appar- ently become filled up, leaving tinally one or more minute inclusions or little points of the quartz or feldspar com- pletely isolated in the epidote individual. In other grains these have apparently also disappeared, and a crystal free from all inclusions is the result. The epidote, like the garnets in the gneiss, presents the appearance rather of having grown into the surrounding minerals by first send- ing out little ai-m like extensions of its substance which subsequently meet one another, in this way including some of the foreign mineral which may or may not finally dis- appear. The few grains ot garnet which as above men- tioned, occur in sections of the Wi-angell Island granite have this same sti-ucture. Where an ftll^nite crystal is enclosed in the epidote this ^^ 350 Cnnntlian Record of Science. irregularity in structuro docH not extend lo the allunite. The latter haH the appoariinee of a primary minerul, around which the opidoto would naturally tend to ci'ystalize, if any vrevv developed in tho rock, the two minerals bein^ isomorphous. Ah it wan noceHsary to carry aw little weight as possible over the long stretches of country traversed by the Yukon expedition, only single hand specimens of each rock wore collected, and the description given above is that of the single specimen of this VVrangell granite collected by tho party. The only other specimen which I could obtain from Fort Wrangell was one kindly given to me by Mr. R. Ct. McConnell ofthctJeological Suivoy of Canada, which was collected by him from the slopes of the hill behind Fort Wrangell some years jneviously, and which proves to be a tine grained .MuHcovite(iraniteor Aplite. It occurs associated with the argillites, piobaldy in tho form of a dyke. The occurrence of this rock in the vicinity would also point to a probable eruptive origin for the granite above do8Cribe