\
IMAGE EVALUATION
TEST TARGET (MT-3)
1.0
I.I
1.25
I- 1^
140
IM
M
1.8
U III] 1.6
V]
'c3
^
'■f
O
/,
^/
/
'/A
Photographic
Sciences
Corporation
23 WEST MAIN SfiiEET
WEBSTER, NY. MS80
(716) 872-4503
CIHM/ICMH
Microfiche
Series.
CIHM/ICMH
Collection de
microfiches.
Canadian Institute for Historical Microreproductions
Institut Canadian 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 which may be bibliographically unique,
which may altar any of the images in the
reproduction, or which may significantly change
the usual method of filming, are checked below.
D
Coloured covers/
Couverture de couleur
□ Covers damaged/
Couverture endommagde
□ Covers restored and/or laminated/
Couverture restaur6e et/ou pelliculde
□ Cover title missing/
Le titre de couverture manque
I I Coloured maps/
D
D
D
D
D
Cartes gdographiques 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/
Reli6 avec d'autres documents
Tight binding may cause shadows or distortion
along interior margin/
La reliure serr^e peut causer de I'ombre ou de la
distortion le long de la marge int6rieure
Blank leaves added during restoration may
appear within the text. Whenever possible, these
have been omitted from filming/
II se peut que certaines pages blanches ajoutdes
lors d'une restauration apparaissent dans le texte,
mais, lorsque cela 6tait possible, ces pages n'ont
pas 6X6 filmdes.
L'Institut a microfilm^ le meilleur exemplaire
qu'il lui a 6t6 possible de se procurer. Les details
de cet exemplaire qui sont peut-dtre 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 indiquds ci-dessous.
□ Coloured pages/
Pages de couleur
□ Pages damaged/
Pages endommagdes
□ Pages restored and/or laminated/
Pages restaur6es et/ou pellicul^es
I — I Pages discoloured, stained or foxed/
Pages d6color6es, tachet^es ou piqudes
Pages detached/
Pages d^tach^es
r~y Showthrough/
Transparence
□ Quality of print varies/
Qualit4 in^gale de I'impression
I — I Includes supplementary material/
D
D
Comprend du materiel supplementaire
Only edition available/
Seule Edition disponible
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 dt6 filmdns d nouveau de faqon d
obtenir la meilleure image possible.
D
Additional comments:/
Commentaires suppl6mentaires.
This item is filmed at the reduction ratio checked below/
Ce document est film6 au taux de r6duction indiqu6 ci-dessous
10X 14X 18X 22X
26X
30X
y
12X 16X
20X
24X
28X
32X
tails
du
sdifier
une
mage
The copy filmed here has been reproduced thanks
to the generosity of:
National Library of Canada
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.
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.
The last recorded frame on each microfiche
shall contain the symbol -^ (meaning "CON-
TINUED"), or the symbol V (meaning "END"),
whichever applies.
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:
L'exemplaire film^ fut reproduit grSce A la
gdn6ro8it6 de:
Bibliothdque nationale du Canada
Les images suivantes ont 6t6 reproduites avec le
plus grand soin, compte tenu de la condition et
de la nettet6 de l'exemplaire i\\m6. et en
conformity avec les conditions du contrat de
filmage.
Les exemplaires originaux dont la couverture en
papier est imprimde sont filmds 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 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<i.
The rock is a typi"al Aplite being composed of qunrtz,
orthochise, plagiodaso, and a largo amount of muscovite.
Tho muscovite is quite noi-mal in its mode of occuriencc,
and shows no signs of tho fretted or indented outline
possessed by muscovite in tho Pell}* Rivoi" granite to bo
described further on. It occasionally holds little bunches
of black rutile needles, sometimes geniculated twins, and
associated with these in the muscovite, a few stout little
crystals were observed having a very high index of lefiac-
tion and well dotined crystalline form — acute double ))yra-
■iids truncated by basal planes. These are probably an-
•tase. A few grains of topaz are also present.
Granite from Pelly River, Yukon District. — The second
rock, unlike that just described, was collected in the interior
of tho Yukon District, being found on the upper Pelly
River near to its confluence with the Lewes River. The
specimen is marked "61," the exact point from which
il was taken being indicated on Dr. G. M. Dawson's " Map
of tho YukoA pistrict and British Columbia," Sheet 3,
I
Oraniten from British Columbia, etc.
351
I
In hiH ropoi't, Dr. DawHon referb to this granite uh tbllows :
(p. 132).
"Nine miles above the confluence, by the eourHo of the
river, a great mass of impuie serpentine comes out on the
bank, and six miles and a half above the same place, grey
granite of the usual character is again met with and appears
to constitute the hills to the east of the river for the
remaining few miles of its course." It is a grey muecovite
biotite granite of miduum grain. There is a barely percop
tible parallelism visible in the arrangement of the constit-
uents, so that it might possibly be termed a giTi'^ic
gneiss. It consists of the following minerals, (juartz, ortl.')
clase, microcline, plagioclase, muscovito, biotito, cpid )to,
garnet, calcite, spbene and pyrite. The quartz ar 1 )rtho-
elase constitute a 'arge proportion of the ruck, while iho
plagioclase, micu,» and other constituents are less abunr^nn.
The q\ :' -tz and feldspar are sometimes broken ;ijid
show uneven extinction, in fact the rock seems to havo
been considerably crushed, but I can see no evidence of
anything like complete re-crystallization. The biotite it
not very abundant and is sometimes partly altered to
chlorite. The garnet, which like the sphene and pyrite is
present in small amount, occur.sin irregular shaped isotropic
grains which are much cracked. The epidote, muscovite,
and calcite, however, oi'e of especial interest.
The epidote is the normal variety with one good cleavege
at right angles to the plane of the optic axes and generally
possesses a faint pleochroism, colourless and greenish
yellow. It occurs occasionally in fairly pei-fect crystals,
but is frequently found in the tame curiously imperfect
forms which it assumes in Wrangell Island rook. The little
arms and bays which run into these epidote individuals
are sometimes quartz. In very many ca8e8,bovvever, they are
feldspar (plagioclase) as indicated by the biaxial tigureand
polyoynthetic twinning, the included poi-ions being con-
tinuous and having the same optical orientation as the
feldspar surrounding the epidote, being in fact, a portion
of the same iodividual. The muscovite is rather more
352
Canadian Record of Science.
plentiful than the biotite, being present in rather largo
amount. It has the same curiously irregular outlines as
the epidote, being sometimes in very slender forms and
delicate skeleton crystals and at other times in tolerably
stout individuals. The little indentations which frequently
form a very delicate and complicated lace work about the
edge of the crystals are occupied by whatever mineral the
mica happens to be embedded in, sometimes quartz, but at
other times orthoclase or plagioclase, and in the great
majority of cases when the little arms are so cut that they
can be accurately tudied, the mineral occupying them is seen
to have the same extinction and to be continuous with that
surrounding the mica, forming in fact, as in the case of the
epidote, pait of one and the same individual. Sometimes a
number of little muscovite crystals situated near each othei"
will be found to have the same orientation, although in the
plane of the section there is no connection between them,
in fact in one grain of feldspar, probably plagioclase, two
well defined sets of small slender muscovite individuals
were seen crossing one another at an angle of 55°, the mem-
bers of each set extinguishing simultaneously, while a third
set formed of fewer individuals also similarly oriented was
arranged in a third direction cutting aeross these. In Fig.
1, (Nos. iv, V, vi), three occurrences of this muscovite are
represented, the separated parts in each case having a
common orientation.
The muscovite showing this peculiar structure is fre-
quently found immediately in contact with biotite which
shows no signs of it, nor is the muscovite a bleached biotite,
for no transition stages are ever observed, though both are
seen in contact along a sharp line in several cases. The
biotite, however, is as above mentioned, sometimes altered
to chlorite. The calcito occurs in large individuals, some-
times alone and sometimes associated in groups of two or
three. They are generally irregulai- in shape and show
the usual twinning. Like the muscovite and epidote it is
frequently developed as skeleton crystals, and has been
found enclosed in muscovite, ii\ plagioclase, and .in un-
Granites from British Columbia, etc.
353
I
twinned feldspar, presumably orthoclase. It haw also been
found partly surrounded by quartz, but never completely
embedded in that mineral. All three minci-als, muscovite,
epidote, and calcite, frequently occur associated and inter-
grown, all having apparently a similar origin, the calcite,
like the other two, apparently growing into the other
constituents of the rock.
Figure 2 shows the mode of occurrence of these minerals
in this Pelly River granite and their relation to the other
constituents of the rock. All the little inclusions and arms
in the central portion of the large muscovite crystal have
precisely the same orientation as the large plagioclase
individual which here bounds the muscovite on one side,
having formed apparently at one time portions of the same
individual.
Fig I HE 2.
Section of the Granite from Pelly River x 42 diameters.
M — Muscovite- B— Biotite.
E — fipidote- P — Plagioclase.
C— Calcite.
Muscovite occurring in skeleton crystals in plagioclase in
364
Canadian Record of Science.
precisely the manner described above was also observed in
thin sections of a granite collected by Mr. J. B. Tyrrell of
the Canadian Geological Survey at Eock Point, Lake St.
Martin, Manitoba. Mr. Tyrr«.'! states that it is, without
doubt, an eruptive granite. It occurs penetiating a dark
green hornblende schist through which arms of the granite
run in all directions while the schist contains imperfectly
developed staurolitic minerals, the result of contact
raetamorphism. In other simila^r rocks from the Lake
Winnipeg district, epidote occurring in these peculiar forms
was observed.
Granite from Coast Ranges, British Columbia. — The third
rock is from the Coast Banges of British Columbia, where
it forms large exposures on the Stikine liiver not very
far from its mouth. It is of medium grain, grey and
porphyriie with numerous small plagiociase crystals.
It is composed of quartz, plagiociase, orthoclase, biotite
and hornblende, and should be classed either as a quartz
diorite or a biotite hornblende granite, accoi-ding to the
relative amounts of plagiociase and orthoclase present
in the rock, amounts which can only be determined by
a separation of the constituents by means of heavy
solutioiis or by chemical analysis. The rock is interesting
from the occurrence in it of allanite in rather large brown
pleochroic crystals with well marked zonal structure which
must be rather abundant, as they were 'found in three of
the six thin sections of this rock which were prepared.
Conclusions. — The origin of the epidote and muscovite, as
well as of the calcite above described, is a question of con-
siderable interest. We may supjDOse these minerals to have
been produced in one of three ways. They might be: —
1. Origiiuil minerals which were crystallized from a
granitic magna and subsequently corroded, eaten away and
partially reabsoi-bed as in the case of the quartz phen-
ocrysts in quartz porphyries, or the biotite and horn-
blende in many volcanic rocUs.
2. Minerals which have been developed during a complete
re-crystallization of the original rock, owing to pressure or
Granites from British Columbia, etc. 356
some other motamorphic agency, but which did not com-
plete their t;rowth.
3. Minerals which have grown in the rock after its
Holiditication, but without re-crystallization of the other
constituents.
The first hypothesis does not seem to be tenable in the
present case, for not only is epidote a mineral which occuis
but very rarely in granites, except as a decomposition
product, but a careful examination under the microscope
would seem to show that, as above mentioned, the apparent
corrosion of the crystals, whether epidote, muscovite or
calcite, is quite ditferent in character from that produced
by the corrosion and partial resolution of a caustic magma.
If the muscovite were so corroded, the biotite should also
have been attacked with the removal of the muscovite
molecule at least.
Further, if a crystal of muscovite weie eaten away until
the merest skeleton alone remained, or until the crystal bad
actually been separated into several pieces, it would be im-
possible for the entire skeleton and even the several dis-
connected portions to preserve exactly the same orientation
had there been the slightest motion in the molten magma,
and we cannot but suppose that there would be a certain
amount of motion when such extensive resolution was
taking place.
Moreover, as above mentioned, there is reason to believe
from their similarity in mode of occuri-ence and close associa-
tion, that the epidote, muscovite and calcite, have had a
similar origin, but we would hardly expect calcite as an
original mineral in so acid a rock, much less crystallized
in large individuals in actual contact with quartz.
Neither does there seem to be reason to believe, after a
careful study of the thin sections of the rock, that anything
like an entire crystallization of the granite has taken place
as supposed in the second hypothesis. Were it not for the
epidote, muscovite and calcite, the rocks would be considered
normal granites probably somewhat crushed. Their
character is that of eruptive rocks, not of crystalline schists.
r
35$
Canadian Record of Science.
The thii-d hypothesis, namely that the niineials in question
have been developed in the rock after its solidification, ,
perhaps by dynamic action, and indicate a first stage of
metamorphism but without complete re-ci-ystallization, is
not nearly so startling as it might seem at the first glance.
Wo have examples of such a development in a number of
cases, and it may be that the growth of minoials in this
way is a much more common factor in development of
crystalline schists than is generally supposed. It is what
takes place in almost every case of pseudomojphism by
alteration.
"All the rocks situated at considerable depths in the earth's
crust must be subject to great pressure resulting from the
weight of the superincumbent masses. Under these pressures,
liquids and gases may be made to penetrate between the
molecules of the solid crystals. The evidence that such
permeation of solid crystals by liquids and gases has
taken place is overwhelming. In the words of Van der
Waals, ' All bodies can mix with one another when the
pressure exceeds a certain value.' " ' That by the action of
such solutions secondary minerals may be developed is a
very reasonable supposition, and that they have been so
developed in the rocks at present under consideration seems
to be the explanation which best accords with facts observed.
As a good example of the growth of one mineral in and
through another after the solidification of the rock of which
it is a component part, the development of woUastonite in
the plagioclase, of a plagioclase-pyroxene rock from Brittany
described by Dr. Whitman Cross may be cited.*
Another example is the alteration of quartz into steatite
described by Dr. Weinschenk.'' In this case the steatite was
found to grow in the crystals of quartz which were tiaversed
by very fine capillary cracks, thus forming a net work
' Chemical changes in rocks under Mochanioal Stresses " by Prof. J. W- .Tudd)
Journal of Chemical Society. May, 1890. (p. 410).
^ " Studien uber bretonische Gesteine Tschermach's Min. u. Pef. Mittheil,
1880, iii.. 369."
'■* " Ueber die Umwandlung des Quarzes in Speokstein." /eit. fur Kryst, 1888.
(p. 306).
r
Granites from Bnlish Columbia, etc.
357
enclosing angular bits of quartz which were tinally com-
plecwiy altered to soapstone. It was found, moreover, that
the process could be repealed artificially. By boiling
finely powdered rock crystal in a solution of carbonite of
potass and sulphate of magnesia, the quartz giains were
found to become coi'roded and converted along their outei-
portions into a scaly aggregate, lich in magnesia, undocom-
posed by aqua regia, and having the optical properties of
talc.
The development of andalusite and slaurolite in contact
zones might in many cases also serve as an excellent example
of this mode of giowth, since in many cases such slates
have not undeigone complete re-crystallization.
Lastly, there are the double zones of pyioxene and horn-
blende, which have been described as surrounding the
olivine where it would come in contact with the plagioclase
in so many gabbron from various parts of the world. If
these "rims " are really the result of dynamic action as has
frequently been asserted, they afford one of the best
instances of the growth of one mineral in another in a solid
rock, for here we have the hornblende in many cases
occurring in the most delicate acicular crystals, distinctly
growing out into the large unfractured plagioclase crystals
on all sides. In the norite from Lake St. John,' however,
where these zones are especially well developed and which
is the occurrence that I have been able to study most care-
fully, there is practically no evidence of great dynamic
action, and the zones seem to bo due to the caustic action of
the molten magma before the solidification of the rock.
There is, however, one difference between occurrences
described in this paper and those described by Cross and
Weinschenk, namely, that in these Yukon rocks the mineral-*
in question penetrate and apparently grow into, not one
mineral but several mineral;*.
This third hypothesis seems, therefore, to be the one
which best accounts for the very peculiar mode of occur-
'"On the presence of zones of certain Hilicates about the Olivin occurring in
Anorthusitu rocks from the River SaKuenay." American Naturalist, Nov., 1885.
358
Canadian Record of Science.
rence of these minerals in the rocks described in this paper.
It is hoped that similar occurrences may present them-
selves in more accessible localities so that a more thorough
study of them may be made, since, if it could be shown
that secondary minerals are commonly developed in this
way much light would be thrown on the natu e of the com-
plicated processes at work during the metamorphosis of
rocks. . .. ,
. t
I ; ".-.i