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'fFsoM THX Ah. Jodrnal of Soiemcb and Abtb, You XLVIII, Nov. 1869.]

ON NORITE OR LABRADORITE ROCK,

By T. Sterry Hint. LL.D., F.R.S.

-♦-♦-^

[Read before the American As-sociation for tlie Advancement of Science, at Salem,

Auffust, 1869.]

• •» ■

The various rocks composed essentially of a triclinic or anor-
thic feldspar, with an admixture of hornblende, pyroxene,
hypersthene or diallage, have by lithologists been designated by
the names of diorite, dolerite, diabase, hypersthenite and gabbro,
among others. The latter name has by many been regarded as
synonymous with euphotide. I however pointed out many
years since that the true euphotide is not a feldspathic rock, but
consists of a mixture of diallage with saussurite, a white heavy
silicate apparently identical with zoisite. By an admixture of
labradorite or an allied feldspar, however, euphotide passes
into the so-called gabbro, which I have defined as a diallagic
diabase (this Journal, II, xxvii, 386V and which is closely related
to norite. The name of hypersthene rock or hypersthenite
(sometimes contracted into hyperite), was given by MacGulloch*
to a rock consisting of labradorite, or a related feldspar, and
hypersthene, found by him in the Western Islands of Scotland,
and subsequently recognized by Emmons in the Adirondack
Mounhtins of northern New York. By both of these obsorvers
it was regarded as an erupted rock. In 1861 I detected it
among the Laurentide hills of Canada, where, as in New York,
it tfxiends over considerable areas. Farther examinations of
this r6ck in place showed that though hypersthene, generally
in very small proportion, is a frequent element, it m often

* MecGulloch, Geology of the Western Islands, i, 386-390.

7! S. Ifurtt on Norite Rock.

repla«(!(l hy a green granular ityroxcnc, and still more often both
of these are wanting, so that we have a rock composed almost
entirely ol a trielinie feldspar, whose composition is generally
near that of labradorite, hut varies in different examples from
that of andesine to near that ol' anorthite. To these rocks I
provisionally applied the name of anorthosites, the pure feld-
Hpathic typ(! I'eing regarded as nornud anorthosite, associated
with wlii(!h, however, were to he found h.vpersthenic and pyrox-
enic varieties, lied garnet, epidote. a black mica, and more
rarely dichroite and cpiartz, are all occasionallv found sparingly
disseminated in these anorthosites of New Vork and Canada,
which cannot be distinguishefl from those first observed by
MacCulloch in the Isle of Skye, as F have convinced myself by
an examination of the s})ecimens then; collected by Inm, and
now ])reserved in tht; colUvtions of the (jcological Society of
London. Titaniferous inm ore (menaccanite') also frequently
occurs in grains and masses in these rocks, both in Skye, and in
North America, where it sometimes forms beds or masses of
considerable size. Details as to the ehemieal and mineralogical
character of these rocks will be fouml in the L. E. & 1). Philos.
Magazine for May, 1855, and also in the Geology of Canada,
18H3, pages 588-590.

The sub.sequent investigations of Sir William Logan have
shown that these anorthosites in Canada belmg to a great series
of stratified crystalline rocks which by the geological survey of
Canada have been designated the Labrador or Ui)per Laurentian
series, and which repose unconformably u})on the older or true
Laurentian gneiss and limestones. The area of the Labrador
formati<m most examined lies in the counties of Argenteuil and
Terrebonne, to the north and northwest of Montreal, and has a
breadth of more than forty miles. It is however met with on
the northeast shore of Lake Huron, according to Dr. Bigsby,*
and at several points below Quebec, notably in the parish of
Chateau-Richer, at Bay St. Paul, and around Lake St. John on
the Saguenay, where it occupies a large area. Proceeding north-
eastward along the left bank of the St. liawrence, Mr. Richard-
son has lately ol)served it at the mouth of Pentecost river,
about 160 miles below the entrance to the Saguenay, and I
have found it forming the shore of the Bay of Seven Islands
forty mil(,\s farther down. This area is probably connected
with the wide extent of this rock observed by Prof. Hind on
the river Moisie. In all of these regions it appears to be sur-
rounded and limited by the ordinary Laurentian gneiss. Bay-
field, moreover, describes a rock with a base of labradorite as
forming the coast for several miles near Mingan. Finally, it
is widely spread on the coast of Labrador, where its character-
istic mineral was first found, and from whence it takes its name.

* Geology of Canada, 1863, page 480.

T. S. Hun. on Norite Rock.

Prof. A. S. Packard, Jr., has given us valuable information
with regard to the occurrence of labradorite rocks at some

1)oint8 on the Labrador coast* One of its localities is at Square
sland, just north of Cape St. Michel, where the rock consists
chiefly of crysUilline labradorite smokv gray in color, trans-
lucent, and opalescent with greenish reflections. This feldspar
often shows cleavage planes two inches broad, and is associated
with a little vitreous quartz and with coarsely ciystalline
liypersthene, which appears in relief on the weathered surfaces.
This labradorite roclc, according to Prof. Packard, is sur-
rounded by and probably resti^ upon Laurentian gneiss. At
Domino Harbor he found domes or bosses of a similar labrador-
ite resting upon strata whi(;h consist in great part of a slightly
schistose quartzite, having for its base a granular vitreous quartz,
and enclosing grains of black hornblende, more rarely hypers-
thene, black mica, and red garnet Feldspar is generally want-
ing, but in some parts these quartzites oecome gneissic, and
they were nowhere seen in uncomformable contact with the
Laurentian gneiss of the vicinity. These quartzose strata Prof
Packard refers, with some doubt, to the Huronian system. The
minerals which they contain are not however met with, so far
as known, in the Huronian quartzites, and on the contrary, are
very characteristic of the quartzites of the Laurentian system,
which attain a great thickness in many parts of its distribution.
The overlying domes of labradorite rock, which Prof. Packard
was inclined to reganl, in this case, as erupted through Huronian
quartzites, are probably nothing more than outlying portions of
tne newer Labrador formation resting upon the Laurentian
strata, as already observed by him at Square Island. Along
the western coast of the island of Newfoundland Mr. Jukes
observed at Indian Head and at York JIarbor dark colored
rocks composed of labradorite and hypersthene, and others of
albite (?) and hypersthene, which may probably be found to
belong to the Laorador series.

R(x;ks composed chiefly of labradorite or a related feldspar
greatly predominate in the Labrador series, but these, at least
in the area near Montreal, which is the one best known, are
interstratified with beds of a kind of diabase in which dark
green pyroxene prevails, with crystalline limestone similar in
mineralogical characters to that of the Laurentian system, and
more rarely with quartzites and thin beds of orthoclase gneiss.
I have more than once insisted upon the rarity of free quartz
and the general basic character of the rocks in this series, an
observation with which I am credited in Dana's Manual of Geol-

* On the Oiacial phenomena of Labrador and Maine. Mem. Best. Acad. Nat
Hist., voL I, part ii, pp. 214-211.

7! *S' Hunt on XoriO- liuck.

o\i\ (p. 130), wlicn^ it socnis to l>t' aiipIuMl to tlic whole of tlie
rocks tlu'i-e classcfl as A/.oic, iiu'lu(|m<:- the Laiirciitiaii, J^abra-
(loriaii and Iliiroiiiaii syslcins. It is, in fact, rciiiarkabic that the
silicated rocks of the latter two consist chiellv ol' lahra<h)rites,
thorites and diahases; <ineissic an<l /granitic rocks hein<r exceed-
iiif/ly rare anion;^ tlieni, though (pnirtzites ahound in the Iluro-
nian. In tlie Laurentiaii system, on the contrary, thouj^h basic
silicated rocks are not wantinji', orthoehise fiiieisses, often grarii-
toid in structniv, and aboundiiiL'' in(|uart/, i)re(h)ininate.

'IMie anorthosite rocks ol' the Labra<h)i" series j»rest'nt great
variations in texture, being sometimes coarsely granitoid, and
at other times finely granular, ^riiey not nnfrequently assume
tlie bun(U'd structure of gneiss, lines of pyroxcine, hypersthene,
garnet, titanic iron ore or mica marking the planes of stratifi-
cation. Probably three-fourths of the unorthosites of tliis
series in Canada, whether examined in place or in the bouhUn's
which abound in the St. Jjawrence valley, consist oi })ure or
nearly pure feldspar rocks, in which the ])ro))ortion of foreign
minerals will not ex(^eed five hundredths. Hence we have come
to designate them by the name ol' labradorite rock. The coloi-s
of this rock are very generally some shade of blue, from bluish-
black or violet to bluish-gray, smoky gray or lavender, more
rarely purplish passing into llesh red, greenish-blue, and occa-
sionally greenish or bhiish-white. The weathered surfaces of
these labradorite rocks arc opaijue white. The anorthosites
which occu])y a considerable area in the Adirondack I'cgion, iis
described by p^mmons in his rei)ort on the Geology of the
Northern district ol' New Voi'k, and as seen by me in hand
sjx'cimens, closely resend)le the rocks of the Labrador series in
Canada.

In all of these localities the coat'se or granitoid varieties often
hold large crystalline cleavable masses, generally ])olysynthetic
mades, and fre(pient1y exhibiting the peculiar opalescence which
belongs to labradorite. Although rocks coni])osed of labrado-
rite or similar feldspars, with hornblende or pyroxene, occur in
various other geological fornuitions, both as indigenous green-
stones aiul as eru])ted masses, they never, so far as my observa-
tion in North America goes, exhibit the peculiar character just
described; nanu'ly, that of a granular or granitoid rock com-
})Osed of nearly pure labradorite or some closely related
feldspar, frequently opalescent, and generally t)f a bluish color,
often violet, smoky blue or lavender l)lue. This type of rock
seems in North Anu>rica to characterize the Labrador series.

It may liere be remarked as an interesting fact bearing on
the distribution of the Labrador series, that two large boulders
of labradorite rock, one of the beautiful dark blue variety, are
found on Marblehead Neck on the coast of Massachusetts. It

T. S. Hunt on Noritc Rock.

does not seem probable that tlicsf inasses t;()iil<l have bcvii
derived Iroiii any ol' the far otV localities already inentiont'd.
and the liict that the ^meiss of eastern Massachusetts is. as I
iiavc recently ('()un<l, in jiart of Lanrcntian atrc. snj/ffcsts that
an outei'oj) of tiie Jial»rador scries may exist in some locality
not tar removed. In tiiis connection it may l)e adde<l tliat I
have lately found characteristic labradorite and hyperitc rocks
in southern Xt-w lirunswick, a few miles ciisl of St. .John,
occupyinjji- a position between tin* Lanrcntian and the Uuronian
or Cand)rian rocks, which there make their a|)pearance, aeeom-
panied l)y Lower Silurian strata, to the south ol' tin* ^Tcat
Carboniferous basin of the re;.non. This interesting^ hx-ality
was recently pointed out to me l)y Mr. (i. V. Matthew of St. John,
to wiiom we are indcbtctl for a ^.nvat part of our knowlcdjjrc of
the geolo<ry of .southern New Hriinswiek. Chester and liiieks
counties in Pcnn.sylvania, and the Wii-iiita Mountains in Arkan-
sas, are cited in Dana's Mineralogy iis localities of lal»ra«l<»ritc.
but as I liave never examine(l specimens from these places, I
am unable to say wlicther they resend)le the eharacteri.stie anor-
thosites of the Labrador series already describiid.

The name of norite, in allusicjii to Norway, was <riven V)y
Esmark to a rock eom[)Osed chielly ol' labradorite, which is
found in several localities in that country.* I had already
noticed the close resemblance bctwi-cn two .sj)ccimens of norite
obtained from Krantz of Berlin, and the labradorite rocks of
North America just noticed, when in 1807 I had the (»pportuinty
of examining at the Universal Exhibition at i*aris. a collection
of Norwegian rocks selected lor ornaiwental ]tur|»oses, exliibited
by the Royal University ol Christiania. Prominent among
these was a series oi' the nc^rites, which could not be distin-
guished Irom the labradorite rocks of the Upper Lanrcntian or
Labrador series of this continent. Lu a printed note accom-
panying this collection from the I'niversity it is said that the
numerous varieties of rocks consi.sting of labradorite with
iiypersthene, diallage and bronzite, have, in the geological maj)
of Southern Norway, published at Christiania in IbHfJ. l)een
designated by the common name of galibro. This note at the
same time suggests that "the name of norite should be pre-
served for certain varieties of gabbro rich in labradorite, which
varieties may in great part with justice be called labradorite
rock, since labrador feldspar is their predominent element."
With this excellent .suggestion I heartily concur, remarking,
however that the name of gabbro, as an ill-defined synonym
for certain anorthosite roek.s, including in part diorite, diaba.se.
hyperite, and even confounded with the non-feldspathic r<jek
euphotide, may very well be dispensed with in lithology.

* See fartlior ZirkeL Petrographie, II, 131.

T. S, Tfunt n)i Xori'tf' Rock.

Hy rclerriiifi to the p'olo^iwil niapjust niciitiont'd, it will bo
.seen that tiu'sc so-ciillcd i/sihhns ocHMipy considfniblc iircus in
tilt! Jiiiurciitiiiii gneiss rcji-ioii of Norway. Hy the authors of
till' ma|ts, Messrs. KJcniH' and Dahl, these jxahhros ari' rc/i-an led
as eruiitisc. thou/li they are deserihed at the same tiiiu' as often
assuniin'j' till' eharaeter of stratified rocks. It should however
))(• noticed that these ^'coloirists ifo so i'ar as t(t re;^anl the whole
(»l the ;xraiiitic gneiss of the rejiion as unstratilied and of plu-
tonie orijLnn.

The s|)eciniens of these norites (jxhibited in Paris were in
blocks polished on one side, and as was observed in the note
acconipanyinjr them, ])resented a curious resemblance to certain
varieties of marble. It is wortiiy of remark that Kmmons in
his report on the Geology of the Northern District of New
Y'ork. suggested the appiieatiim of the labradorite rocks of
Kssex coiniTy as a sul)stitute lor marble (pages 2i), -iib). An
ornamental vase of the same rock turned in a lathe with tiie
aid of a 1»lack diamond, has been in the Museum of the Geo-
logical Survey of Canada since 18o().

Of tli(! collection ol' norites from Norway the specimens irom
Sogndal and Egersund presented line varieties of grayisli or
brownish violet tints, wliile a dark violet norite came from
Krageroe and ahso from the islands of Langoe and Gomoe, and
a white granular variety from the gulf of Laerdal in the diocese
of Bergen.

It is only in rare eases that the cleavable feldspar of these
norites exhibits the ])eculiar oj)alescence which distinguishes
the liner labradorite found in some parts of the coast of Labra-
dor. Dpalescent varieties of this feltlspar are however occa-
sionally iiK't with in the area near to Montreal, and in northern
New York. In the Paris Exhibition of 1867 there wx're
exhi])ited from Jiussia, large polished tables of a beautiful
violet coh)red granitoid norite, portions of whicli exhibited a
tine o[)alescence. This rock, I was informed, comes from a
mountain mass in the Government of Kiew, but of its geognos-
tical relations 1 am ignorant.

Those peculiar labradorite rocks, presenting a great similarity
iti minoralogical and lithological character, have now been
observed in Essex county, New York, and through Canada at
intervals from the shore of Lake Huron to the coast pf Labra-
dor. They are again met with in southern New Brunswick,
in the Lsle of Skye, in Norway, and in southwestern Russia,
and in nearly all of these localities are known to occur in con-
tact with and apparently reposing like a newer formation upon
the ancient Laurentian gneiss. Giekie in his memoir on the
geology of a part of Skye,* appears to include the norites or

* Quar. Jour. Gteol. Soc., xiv., p. 1.

T. S. IhoitxH XoriU; Ii'ork. T

livpcrstluMiitcs of tliiit islaiKl with ccrtiiiii syiMiites and ^mvn-
stones, wliieli he tli'siTiht's its ni»t iiitrusivi', flioii^'li cniptive
all.T the iiiiinnrr ol-rnnitcs (loc. <Mt., p. 11-11). T\\r li.vprrs-
tiicniK's arc rcprcsciHt'il in liis inji|) as occniTiiii;- to tin- wvst nl
]jocli Shipin. Specimens in my possession from liocli Scaviir,
a little further west, ami others in Mac('iill<M'irs coll<'ction IVom
that vicinitv, -a^' however iilentieal with the North Ameriean
norites, whijse strutilied eharaett'r is lunloiilited. 1 ealle<l atten-
tion to these reseml)lanees in the Dnblin Quarterly .lonrnal for
July, 18H3,* and IIaii«:hton. who in istll visited Loeh Seavi<:.
lias" since described and aiialy/.ed the rock of that locality,
which consists of lal»radorite. often coarse nraine«l, with pyrox-
ene and inenaecanite, and is evidently, acc<»rdiii<i to him. a bedded
metamorphic rock (Dnblin Qnar. .lonr.. \xV}'k \k 'M). He. it may
i)e remarked, desi^niates it as a svenite. a term which most litho-
lo'i'i.sts ai)i)lv to rocks whose feldspar is orthoclase.

1 desire to call the attention of both Ameriean and Kuropeaii
litholonists to this remarkable class of rocks, of which the
norites may be rejjfarded as the normal and typical form, in the
liope that they may be indtu-ed to exannne stdl farther into the
question of the age and geognostical relations of these nx-ks in
varions reeions. and to (h^termine whether the niineralogical and
litholofrical character which I have pointed out are geological
constants.

-\A'-