a} E“
1““; v
THE PORCUPIN'E'
MOUNTAIN “RED ROCK"
Thesis Ior the Degree of M. S.
MICHIGAN STATE COLLEGE
Roberf Emerson Thaden
1950
|
|
I
4:? ‘~

‘ g, . :.
"iIIt

' I‘IIIIIIIIIII IIIII ' W ' I
I 10 77 5!48 I . ' ' -

I 3 1293

 

rHesns _ ,.~.,-~~- -_

I

I

This is to certify that the .'

I
thesis entitled . e

: "The Porcupine Mountain Bedrock" I ‘ if .5

presented by I I
3 Robert E. Thaden ~ I .
has been accepted towards fulfillment I:
5“ . of the requirements for '
Mdegree mm . i

 

L W I I, -‘

Major professor

H.

Date June 9, 1950 ' "

 

 

0-169 I ‘
‘ _L

 

1.4
I. -.

I

I . ,
l . , . a. ‘
.. . -‘ ' ' . -‘
ft,’. [3"], "l‘ 9. e
‘l‘.1'- “(P “I ;

 

 

 

 

SUPPLEMENTARY——
MATERIAL

IN BACK (BF BOW

 

 

gobert Emerson Thaden

A ?*SSIS

submitted to the School of Graduate Ltuaiee of Tichigax
Seate College of Agriculture and Applied i
in partial fulfillment oi the regu‘

for the deéree of

""ESIS

237085

.‘w-nnfir 1

A CRT. C" TIL n u 'i .gl' TI;

To Dr. B. T. Sandefur, the writer wishes to eXpress
his appreciation for critically editing the manuscript
and for suggestions as to style and wording which con-
_tributed greatly to its readability.

The writer wishes also to thank Dr. W. A. ?elly and
Dr. J. W. Trow for criticism of the maps and suggestions
for their improvement.

Tr. F. J. lonaghan and Tr. W. E. Grabau both loaned
photographic equipment, without which the photogr.phs
would have been impossible. Fr. arabau is also to be

(‘

thanked for drawing the physiographic diagram, plate z.
Acknowledgment is also made to Rudy Saari, Porcupine

Fountains State Park officer, and to Paul Fachamer of

Silver City. Their advice as to passible roads and

locations of trails and outcrops made the field work

much easier.

)
I;
(H

Acknowledgments . . . . . . . . . . . .
Introduction . . . . . . . . . . . . .
Geography . . . . . . . . . . . .
location and extent or area .

Culture . . . . . . . . . . .
Topography . . . . . . . . .

Drainage . . . . . . . . . .

GGOQOTQhOlcgy o o o o o o o o o 0

General geoloay and previous investija

5.4

Definition of the problem . . . . . . .
Field procedure . . . . . . . . . . . .

Termin010€y o o o o o o o o 0.. o o c o

Petrology, petrography, and mineralogical analy;

Eetrology of the "red rock" . . .
Petrography . . . . . . . . . . .
lineralogical analyses of the "red
Discussion . . . . . . . . . . . .
Structure . . . . . . . . . . . . . . .
Primary structures . . . . . . . .
Secondary structures . . . . . . .
Discussion . . . . . . . . . . . .
Conclusions . . . . . . . . . . . . . .

Eibliography o o o o o o o o o o o o o

O O O
o c O
o o o
o o o
0 O O
o a o
O O O
O O O
+4~
J-hw
o o o
O O O
o o o

. . .
. . .
rock"
. . .
. . .
. . .
. . .
. . .
. . .
. . .

o o o
o o o
. o o
o o o
o o o
o o o
a c o
o o 0
KS 0
o o o
o o o
o o 0
CSS
0 o o
o o o
o o o
o o o
o o o
o o o
o o o
o o o
o o o
o o o

0
1V)

. 22
. 22
. 27
. 75

~“late

l.

A“)
o

3.
4.

(31
o

6.

7.

8.

9.

13.

15.

14.

ILLUETdd?

Index map showing location of the Eorcu—

pine Nountains . .

Physiographic diagram and cross section

of the north central Porcupine Yountains

Photographs of hand
Photomicrographs of

Photonicrographs of

Id

-hotoricrographs cf

Photomicrographs of

Photomicrographs of

stylized camera lucida drawings of

an“ 1'?
us. J

specimens . .

thin
thin
thin

thin

sections
sections
sections

secti OILS

thin sections

microscopic textures .

Diagrams and stylized camera lucida

drawings of microscopic textures

drawings of microscopic textures

Photographs taken in the field .

Face poles of 95 fractures in the

"red TOOK" o o o o

Contoured diagram equivalent to plate

Topographic map of the north central

Porcupine Nountains

J.

OUDOIOP and structure map of a portion

of the Porcupine Fountains (Overlay to

plate 14) o o o o 0

iv -

and

diagrams and stylized camera lucida

in

in

pocket

Elate léo
“able 1.
2o

Compass traverse of a portion of the

upper Carp River . . . . . . . . . . . in pocket

Identification and correlation of

Veweenawan rocks . . . . . . . . . . . . . . . 15

v.-
I“

nineral percentages in various

1?

"red rook Specinens o o o o o o o o o o o o o 78

THE PORCUPIEE MOUETAIN "RED BECK”

IETRODUCTI?E

Geography

 

Location and Extent pg £332: The Porcupine Mountains
are located in northwestern Ontonagon County, Michigan (pl.
1). they comprise an arcuate ridge and highland topography
which is convex to the northwest and parallels the southern
shore of Lake Superior from a point a few kilometers west
of Silver City to the eastern edge of Gogebio County.

Culture: One good highway, Michigan State Highway
M-107, enters the area. Following the southern shore of
Lake Superior from the east, it extends up the northern
ridge of the mountains and terminates at a point Just north
of the western end of Carp Lake. This point is approxi-
mately 56.3 kilometers west of the city of Ontonagon.

Other than this one good road, the region is practically
devoid of permanent cultural features.

This does not imply, however, that the region has been
deserted. There are evidences of prehistoric mining oper-
ations for copper carried on by the Indians long before white
men entered the area, and since the United States government
acquired this part of the Northwest Territories from the
Mississippi and Lake Superior Chippewa Indians by treaty on
October 4, 1842 (A. G. Ruthven, 1906, p. 19), the natural
resources have been persistently exploited by white men.

After copper was discovered in extrusive basic flows

farther north on Teweenaw Peninsula, any such rocks were
considered indicative of the presence of valuable copper
lodes. Identification of this type of rock in the Porcu-
pine Mcuntains led to the organization of many companies
and to the sinking of many shafts in the northern part of
the region. However, the copper deposits were narrow and
lean, and by the end of 1848, according to Foster and
Whitney, most of the mines had closed down and the majority
of the miners had gone elsewhere (J. W. Foster and J. D.
Whitney, 1850, p. 80). Legging, trapping and deep sea
fishing have been the principal means of livelihood since
that time.- .

Because the region is heavily forested and contains few
settlements, there is an abundance of wild game. In an
effort to preserve for the future the primitive character
of the region, the virgin stands of maple and hemlock, and
the wide variety of floral and fennel representatives,
nearly one hundred square miles have been set aside by the
state of Michigan as a wilderness state park.

Topography; Elevated masses of pre-Cambrian rock

 

comprise the main topographic features of the region. In
the north is an elongate ridge which slopes with decreasing
steepness to the north until it finally disappears under
Lake Superior (pl. 2). The south side of this ridge is in
many places a precipitous cliff rising 100 to 150 meters
above the valley of the Carp River. Although the ridge

extends for many miles, it becomes lower to the east and to

. PLATE I
INDEX MAP SHOWING LOCATION OF THE
PORCUPINE MOUNTAINS

 

 

     
  
 
      

N
I
I O R
P E R
s I’ was .0

K E c I0 '

L A -cumet I
Ochcock
HoughtcnO

 

  

    

 

 

 

I 4—
00 t I '
\\\\\\\\\\‘ n coupon I Ifl—l
\\0 Silver City .
: I__I IBcrcgc
. \\ .‘\\ I '
3 1,-_. I
"I ' I I
'—--—‘ Berglcnd I I
«'\_ I . I .
L“ ‘ OBessemer “""' Lakgflraeb/c I I
' Ochefield | I
-Ironwood ' hmsrmunoi_ _flA8A§_A_9_Q.___
\ | mou cc.
L, IdnrmeushlI
\,_ cccselc cc. I
\“ a
/
“65455441 I
0N3 .
I/v \ I
.I \p I Crystal FcIIs
-~ -. -.\. LEGEND "\ 0 O
' ' mlrcn River
SCALE
IO IO 20 so
LE3; kg 3-7.5::1“ ““ ‘P*~‘L:‘EIMI
'E—E—tjgi Y:j__‘_’._.!o ‘ t: fiL—‘Jfiso__f: ‘43-”:2340 KM.
sermon: 1950-

 

 

 

 

,‘a at
->

r

J

’u—

 

 

\alt ‘

 

 

west of Carp Lake and is interrupted in many places by wind
gaps. Many gaps apparently deve10ped as a result of north-
south faulting in which there was very little vertical
movement. The highest points on the ridge are at elevations
as great as 275 meters above the level of Lake Superior,
which stands at an elevation of 183.5 meters.

Directly south of Carp Lake is another, and lower,
ridge which parallels the southern shore of the lake and
extends but a short distance beyond either end. To the
south of this ridge, in a valley between the ridge and
the main highlands, flows Scott's Creek.

The highland area is a plateau averaging approximately
500 meters in elevation and sloping gently to the south.
Lumerous knobs up to 110 meters in height rise from this
upland surface. The Kichigan Department of Conservation
records an elevation of 617 meters (2,023 feet) for
Government Peak, a knob in the northern part of the high-
lands. (On charts of the United States Lake Survey, this
elevation is given as 2,022.19 feet.) This is, allegedly,
the highest point in Michigan and, incidently, the highest
point in the Lakes States. However, recent field and
photogranmetric work by Dr. W. A. Kelly of the department
of geology at kichigan State College has established that
the elevation of Covernment Peak is but little over cos
meters (1,860 feet) and that a prominence approximately
1.5 kilometers south of Little Carp Lake, with an elevation

of nearly 600 meters (1,970 feet), is the highest point

in the Eorcupine Mountains and, probably, in Michigan (3.
A. Kelly, personal communication).

The highland area is abruptly terminated on the south
by a broad and concave valley in which flow the Little Iron
and Iron rivers.

Drainage: Draining the major portion of the Porcupine
Fountains are five streams. Union River on the east is a
rather small stream, although one of its sources is Union
Spring, one of the largest in richigan and, according to ?.
3. Wright (1935, p. 41), flowing at a rate greater than
759,003 gallons (2,750 kiloliters) per day.

Little Iron and Iron rivers occupy the lroad valley

CD

Th
south of the mountains and most of their tributaries head
on the dissected southern slopes of the highland area.

They are required to flow around the southern and eastern
sides of the highland in an annular drainage pattern before
entering Lake Superior east of the mountains.

Little Carp River and Carp River both originate in the
highlands, flow through the lakes of the same names, and by
circuitous routes drain northwestward into Lake Superior.
(Although the Urited States Board of Geographic lames still
lists these lakes as Carp Lake and little Carp Lake, the
Nichigan Departmert of Conservation, in deference to esthetic
tourists, no doubt, has unofficially renamed them Lake of
the Clouds and lirror Lake respectively.)

The highland surface is relatively impermeable and,

being rather flat, retains meteoric water as swamps. These

are breeding places for innumerable infamous "Yichigan
mosquitoes" and are the sources of the rivers. Springs,
which are numerous at low elevations in the region, and
which are thought to rise along fault planes (F. E. Wright,
1905, p. 39), are also probably fed by the swamp waters.
The proximity of the region to Lake Superior, the
prevalence of westerly winds, and the elevated nature of
the region combine to produce a positive precipitation
anomaly (A. d. Eichmeier, personal communication). host
of the precipitation falls on the western part of the

mountains; the eastern part is in the rain shadow.

Ceomcrpholcgy

 

The presently extant topographic features of the Por-
cupine Fountains are relatively permanent. The flat high-
land area is probably a peneplain developed during Cambrian
time after subsidence of the orogenic activity of the
Killarney Revolution. Van Hise (1896, pp. 57-59) even
considers base leveling taking place during a time extending
to the Cretaceous. Nonadnocks, such as Government Peak and
the unnamed eminent hill south of Little Carp Lake, were
preserved on this surface.

Geologists generally believe that fluctuating Paleozoic
seas alternately covered and uncovered the area. Sediments
were deposited, were removed, and were redeposited. Finally
Pleistocene glaciers advanced over the mountains, eroding,

sculpturing, and drOpping erratics as large as 4 x 7 x 10

meters on the upland surface. The ice occupied river
valleys which had been established, in many cases, parallel
to the strike of beds, widening, flattening, and probably
partially filling them with ghacial debris.

A strong shoreline of glacial Lake Duluth is devel-
oped at 355.1 meters on the northern slope of the northern
ridge, where highway M—lO? follows it for more than 4
kilometers. Although the position on the northern side of
the main highland mass to the south is not readily identi-
fiable in the field, it can be seen clearly on aerial photo-
graphs by a distinct change in flora. Careful observation
on the ground discloses a thin linear zone of maple occupying
the old beach, bounded on either side by hemlock forest.

Shore features of glacial Lake Algonquin at an eleva-
tion of 250 meters and glacial Lake Fipissing at an elevation
of 187.7 meters are well developed, marked by steep banks
as high as 10 meters. While the various lake stages were
evolving, the ridges in the northern part of the region
were, successively, offshore islands, points of land on the
seaward side of elongate bays, and, finally, ridges as
developed at present.

The rapid succession of glacial lakes at lower eleva-
tions was probably responsible for development of youthful
geomorphic characteristics in the lower reaches of the Carp
and Little Carp rivers. It was, in effect, a rejuvination
of the rivers, although incision of the streams has not

yet affected the mature upper parts of their courses.

I
LG
I

Other interesting geomorphic features are cirques.

Located along the southern edge of the highland area, they

were first identified by h. A. Kelly (personal communication).

Yhether the cirgues levelopeo at the advent, or at the

decline of Pleistocene glaciation is not kLown, and althovgh
they ale small the; are, nevertheless, present -- the first
known in iiohigan.

{tree m cap tul e and change in direction of flow o£ may;

‘ ‘0 r. - ".0_~ . Ii." .. "‘95‘ C’ I) - o 2- I 1 o o _ ‘ '
diver and the north Llancll ol :Inlon .AlVEL, it is hl lily

' -\ "- : I." ‘ !" t ‘L' ’ F "-0 ‘ \ 1— . " I ' ‘ '3- " ~ “ . ' "l. 'f. v‘ K r . 1
peselole b:du Carp alver once lloueu in one OQJObite alias-

+0 . ..w.,‘ . _‘ o L, -~.e. “h. .. J. ._| q}; .,"‘ .. Pf: L _ A ‘ o I
ulCD, ClCCllleflb 1.0:) £4.13CO‘3LU 02'.)th only sjlber I’CCE’S‘LIOf Di

("3
Q1
:75
(D
0')
1“
f i
H
0
<3
(I.
'3
O
S
p
m
C'

c
C)

4L9, ‘ —‘ . ,. , ’ ,. .' , ._ .
bub elECieEs enu Opeulut o_

- 'L ' “L. ' IL! -' ". . "I‘L a 1“ " r‘ ") '~ L, . ‘Fv: -. ’1": “N I '5
MGEuo In one BCQoUCln gale Ol one also, ollbulleEb {l

0 L L- _ _ o I, r‘ 1_ . c_ ,.‘ n . -. y,- .- Y- I“.‘ __'_o '_ _‘ q
led~3 II'Cf.‘ Diver 5...ch JCLliJust-u SEVELdL 'JJ.'J.LJL u.‘ 1.16:} C1.

~- - 1., ’1 4- . r.—~..—. J, ‘ .r o :. ..1.'
Little Caro .lxel. ale. u~fl con ec nulel the rapid SCQJC'
9 A.

b

ward tilt ing of the whole region may no aiding stream

' .- - .0, 6.1. , .2 , 1.! .94, ,.... ,. : . 1. , 1:
piracy b; selea .'s llow na to the south, oze eredlents ol
- - T , t - , L‘ v. 1—.- ' r . ,2 ' v u. " (N .r : -- ',9
th ”e: and CQHCEiJEKle their clOulu; powers, increaslre
“." _ F+“1'l 'V "' FI?"I '-2
hip: Del {Pctflb ale ..'.'celu.Couo
ting can also 'e seen alOL; the shore

3' ':‘ '5" 7‘ 1'1 11.0"" . loo-1]" or '1 "n '- rm” f o “(‘0)" ~. T'C “36:04: ”f0 '1". ('3
OJ. .L'a.‘e 011;? J- Il. ‘1 15.»-..LC1. O'xlvlczD .J. J.» -8. ‘5... U v.1 J- . JU

shoreline and the pres nt shore ling is, in mast places, a

.nu-nnu. 3y these -lMl coler le-,nlres, a {graic ll; exhilar-
D l L- a ' r. a o a
gent consoling lh bVlLELto

General Geology and Previous Investigations

Stratigraphy: The rocks cropping out in the Porcupine
Mountain region belong to the Keweenawan series, upper Pro-
terozoic era. Lowest in the series is the "red rock", which
comprises the central highland region. Its origin, manner
of emplacement, and position within the geologic column have
been controversial issues for more than a hundred years.

‘Dr. Douglas Houghton (1841, pp. 487-490), observing
Keweenawan rocks as early as 1841, termed them "greenstone".
'He specifically included basic flows and sandstone conglom-
erates, but whether he also meant to include the acid rocks
does not appear. It is questionable whether Foughton ever
saw the "red rock".

Bela hubbard (1850, p. 837), reporting on his field
work in 1845, mentions an "imperfect sienitic granite" on
Keweenaw Peninsula, evidently referring to an acid porphyry.
Although he thoughLin 1845,that the basic flows were "dykes",
as did Foughton, he changed his mind the following year
while at work in the Porcupine Mountains. Fe mentions
(idem., pp. 886-887),

"...regularly disposed and alternating beds of

greenstone and amygdaloid... [which] ...give an

appearance of stratification to the mass."
With regard to the "red rock" he says,

"Associated, however, with the greenstone and

amygdaloid of that country, appears an argil-

laceous and silinous [siliciousfi] rock, which,

though we have classed it among the trap rocks,

is very distinguishable from all the other

varieties of trap, and is therefore entitled to
a separate description. This rock occurs in

-11-

belts, alternating with those which make up the
mass of the Porcupine ranges, and possibly may
be regarded as a volcanic mud, altered and
hardened by its vicinity‘to rocks of igneous
origin."

 

He thus hints at an igneous origin for the "red rock" and
goes on to describe it,

"It has been already mentioned, that, alternating

with the several rocks that compose the Porcupine

Mountains is a hard rock of red color, fine

grained, and sub-slaty in structure. It is

evidently trappose in character, but is at the

same time quite argillaceous, and sufficiently

siliceous to strike fire under the hammer. Its

color varies from a light to a dark brick red."
. Dre C. To JaCkSOn (1849, pp. 599, 400. 414). J. D.
Whitney (1849, p. 728; 1850, p. 64), and J. W. Foster
(1850, p. 64) were of the opinion that the acid rocks of
Keweenaw Peninsula were sandstones, indurated and grani-
tized by the associated basic traps. Dr. Jackson (1849,
p. 661) thought those in the Porcupine Mountains might be
volcanic in origin. Thomas MacFarlane (1866, p. 142) con-
sidered the acid rocks to be eruptive.

R. D. Irving, in "The Copper-Bearing Rocks of Lake
Superior", U. s. Geol. Survey Mon. 5, 1883, and with r. o.
Chamberlain in U. s. Geol. Survey Bull. 23, 1885, fails to
mention the bedded nature of the "red rock" but does con-
clude (1883, p. 150) that the Porcupine Fountains,

"...owe their existence in all probability to a fold,

the porphyry of the central portions being one

of the usual embedded masses laid bare by

subsequent denudation."

Later, however, Butler and Burbank (1929, p. 170),

I
’..J
(\J

I

"716 structure of the region is trebelly due to the
intrusion of an igneOus as: of l~ter age thar any of
the rocks in which deposits of cepper and silver
are [curd [Eonesuch shale ...All krown
11eou16 connected with this particular {art

of the region [Xhite Eine Eire] point to

file pron duction of the :1 Lotural features by

the intrusion of the he one core of the

S
d the doming up and
h

i
Eorcupine “ountair1e an
t e rocks that v.ere invaded ."

. ..., '1 o
outward tn1u111n 01
H ' r~ - ~. w

n. 3. lane, in Pne :eweena van nEElGS or ,iCnigan ,

he iich. Teol. Qurvey Ann. Len

but for the nest pert embraced the intrusive school

of thought. is late as 1936 the Tichigan 7eolegica1 Survey
(1936, centennial Lap) corsiJC1ec the "red rtcr" as intrusive,

but thought it was pre-Teweenawan in age. Vhe rock it was

supposed to have intruded 18 not known to the writer.

“‘\

The "red rock",1eirng of principal irter.st in this
paper, has been dwelt u;on at some length, and long quo-

tations £103 Bela Hubbard were introduced beca use he, as

one of the earliest workers in the region, held essential-

H-

ly the same views as are brought out in this thee s.

Gverlying the "red rock" are basic lava flows and
flow breccias, interbe dded with sanlstone breccias and con-

glomerates containing abundant "red rock" and basic flow

fragments. The base of this unit is primarily thin b sic

.4

fl 0? s which can the northern part of the "red rccc" area
and, weathering slowly, maintains a steep north-facing

$101.18 0

- 13 -

lext above these basic flows is a thick sedimentary
formation whose lower portion is predominantly sandstone
conglomerate; the upper portion is predominantly sandstone.
The well indurated upper portion forms the ridge south of
Carp Lake and extends up the precipitous southern face of
the northern ridge to a point Just below the crest.

Capping the northern ridge are the "Lake Shore traps."
They are a small number of basic amygdaloidal lava flows
with no interbedded conglomerate. Weathering less rapidly
than the underlying sandstone, these flows hold up the crest
of the ridge.

. The "Outer conglomerate" and the Nonesuch shale, respec-
tively, overlie the "Lake Shore traps" and represent the
youngest rocks in this area. The "Outer conglomerate" has
recently been renamed the Porcupine Mountain sandstone
(El Khalidi, 1950, p. 16) in the Porcupine Feuntain area.
Due to its relatively non-conglomeratic nature and to the
facts that, although lying directly above the "Lake Shore
traps" as does the "Outer conglomerate" in other areas, and
although similar in lithic character, it may not be a tem-
porally identical formation.

The lonesuch shale does not crop out in the northern
part of the region. It does, however, with steep dips to
the south, abut the "red rock" on the south. Other for-
mations were apparently faulted out.

. A good geologic section was made by Gordon (1906,

p1.XXKII) along the Black River west of the Porcupine

Nbuntains. Since the formations vary in thickness from
place to place, or are not continuous throughout the length
of the peninsula, other sections of Keweenawan rocks, many
of which are derived from inspection of drill cores, are
too distant, too general, or too limited in stratigraphic
extent to be of use here.

The writer has, therefore, constructed a section based
upon average dips observed in the field and upon photo-
grammetric measurements in the laboratory. An attempt is
made to correlate this section with that of Gordon and to
identify the various lithologic units with the several
groups generally recognized in the Keweenawan series. The
section (table 1), is normal to the strike and passes
through a point 100 meters west of Carp Lake.

Structure: Lake Superior fills a large synclinorium

 

formed, it is thought (W. 0. Fotchkiss, 1925, pp. 669-678),
by collapse of the earth; crust caused by the removal of
large quantities of magma. Keweenaw Peninsula and the
Porcupine Fountains are on the southeastern limb of this
synclinorium and the dipsof formations are, in general,
homoclinal to the north. 0n the northwestern limb, rocks simé
ilar in age and lithologic character to those cropping out
on Keweenaw Peninsula are exposed on Isle Royals and in
northeastern flinnesota.

The Porcupine mountains present a singular structure
in this region. As mentioned before, it is generally thought

to be a fold, truncated by erosion, and exposing older rocks

l;
0.;

 

 

 

 

 

 

 

 

 

 

TABLE 1
IDZLTIEICAPIOE ALB CORRELATIOE 3F KafsSlAfiAl ROCKS
GordonT Thaden
Porcupine
Black River Phick- Mountains rhick- Possible
section ness section nees correlation
Freda Ereda
sandstone ----- ----- sandstone
lonesuch lonesuch
shale 500 ----- shale
Sandstone and Duter
Outer conglomerate. conglomeratefi
conglomerate 5,020 Upper portion 2,000 (Porcupine
dips under hountain
Lake duperior. sandstone)*
Lake Shore fiasic flows. lake Shore
traps 500 10 sandstone 370 trapsg
or conglomerate.
Sandstone with
‘ conglomerate ) Great
conglomerate 550’ grading down to 1,885 conglomerateg
conglomerate
> with sandstone. L
mixed Conglomerate W
eruptives and 5,5TOJ gradiLg down 4BCJ
sediments to eruptives. L
total 5,850 total 2,375 Aehbed
——————————— 4——~—~—-——~————-—-—-—————-—~— group ?*
felsite 45o "ded rock" a )
--._ .1 _ .__.________ _____l_.______________________.______/____-___ '. ____
*FL FL 31 Ytalidi, 195?, p. 100

1’17. 0. Gordon, 1906

#Identified in the Porcupine mountains as such by G.

’ pl. Y.1‘1CXIIO

_I
LL.

Van Bias and 0. K. leith, 1911, p. 585.

fiidem., pl. KXVIII.

*According to A. C.
is exposed in he
89° 59' t.).

Pots

lane (1911, p. 624)

00 53, To 51 Fe, 0

, the Ashged group
42 7. (46 &" 1.,

It is highly probable that some duplication of beds

has taken place in both sections due to longitudinal

faulting.

at the surface, although quite a number of geologists hold
to a theory of igneous intrusion and subsequent uncovering
of the intrusive rock to explain the observed quaquavers-
ally dipping strata.

A complete chronologic bibliography of reports by the
men mentioned in this section, and of other works bearing
on the Keweenawan, may be found in "The Copper-Bearing
Rocks of Lake Superior", U. S. Geol. Survey Von. 5, 1883,
by R. D. Irving, on pages 14-23 inclusive.

Bibliographies of general works on the lake Superior

region are contained in "The Geology of the Lake Superior

1

Region", U.S. Geol. Survey Hon. '2, pp. 74-84, 1911, by
C. R. Van Rise and C. K. Leith, and in "The Copper Depos-
its of Kichigan", U. S. Geol. Survey Erof. Eaper,l44,

pp. 3-14, 1929, by B. S. Butler and W. S. Burbank.

Dad‘Ii-ITICL {"25“ ."iti PRC‘ELELI

The geology of the Porcupine Fountains is not well
known. The structure and stratigraphy have never been
satisfactorily solved, nor has careful identification of
several rock types been made. Fence, "red rock" and other
noncommittal and ambiguous, if descriptive, terms have some
into general, and almost exclusive use when reference is
made to the Porcupine Mountains.

The efforts of this investigation are directed toward
solving some unanswered problems and of elucidating several
poorly understood phenomena in the Porcupine Mountains.

Since the so-called "red rock" is almost unknown
geologically, and since additional information on the prob-
lems relating to t might be applied to other areas of
Keweenawan rocks resulting in, (1) a better understanding
of the structure there and, (2) the discovery of new ore
bodies of copper and silver, the "red rock" is the formation
treated in this thesis. ?he following major problems
are considered:

(1) An attempt is made to interpret the mode of origin
and manner of emplacement of the "red rock".

(2) An attempt is made to determine the percentages
of the various minerals present in the "red rock" and to
classify the "red rock" according to some standard system
which will allow a satisfactory identification using the

analytical data available.

(3) An attempt is made to determine the attitude
of the ”red rock", to correlate its various exposures, and
to define its relation to adjacent strata (i. 6., its
position within the geologic column).

(4) An attempt is made to determine the forces which
have acted upon the "red rock" and to interpret their

effect upon it and upon the surrounding region.

FIELD PRCCEDURE

The field work was done during June, July, and August
of 1949. A base camp was established along highway M5107
near the east entrance to the state park. From this lo-
cation the origins of several routes into the "red rock"
area could be reached by automobile.

It is possible to drive, for instance, to the end of
highway M—lO? and to enter the hinterland Just west of Carp
Lake. Likewise, the area can be entered approximately
4 kilometers east of Carp Lake by walking up the course
of the Carp River. On the east, the "red rock" area can
be entered from any point along ronesuch road or from
innumerable logging trails, impassable for automobiles,
which parallel the main highland mass on the southeast.

Vertical aerial photographs at a scale of approxi-
mately 1:20.000 were carried in the field. Outcrops,
swamps, faults, dikes, strikes and dips, and other infor-
mation was plotted on them. Localities of interest were
also plotted on them and numbered. Under corresponding
numbers in the field notebook, pertinent data were recorded.

Fo attempt was made to run straight line traverses
as the scarcity of outcrOps made this impractical. However,
all major streams were followed, all knobs and ridges were
visited, and swamps, where there was likelihood of out-
crepe, were traversed. It is believed that all of the

larger outcrops and most of the smaller ones were studied..

Attempts were made to obtain fresh rock specimens.
These were oriented and suitably marked before being re-
moved from the outcrop. Compass readings were taken on
foliation, lineation, and on fracturing wherever they were
identified. In addition, the bearings of linear elements,
such as stream courses and ridges with truncated sides,
were obtained.

Other features, such as changes in flora, orientation
of streams and roads, gecmorphic features, and attitude
of adjacent rocks were recorded. Compass traverses and
diagrams were made of particularly interesting or well
exposed areas and structures.

A resume of each days observations was made at night
and previously held theories aid partially solved problems

were appropriately revised.

TELVIYOLCGY

host terms of vague or ambiguous meaning ( e. g.,

melaphyre, felsite,

dolerite), and those of various

definition, are avoided in this paper. The contextual

definition of those which are used is given below;

Crystalline -
EntoBlitic

Eutaxitic

Exogenetic

Extoblitic

"Kainoblastic"

crystals visible to the naked eye

mineral matter projecting toward a
common point, line, or plane

banded; parallel arrangement of tex-
tures or minerals in extrusive rocks;
flow banding

apart from the main mass, as volcanic
dust

mineral matter projecting from a common
point, line, or plane

- Gr., kainos, new or recent, and
blastos, sprout or shoot. Introduced

as descriptive or metamorphic structures
and textures in general

Microcryptocrystalline - crystals which appear very

small under the microscope; in general,
less than three microns

"Planiolite" - L., planus, level, and Gr., lite,

Structure -

Texture -

equivalent to 11th, from lithos, of
stone. Introduced as descriptive of
spheriolitic structures oriented with
respect to a plane ( cf., spheriolite,
axiolite)

megascopic features of a hand Specimen;
also major features of, or in, a rock
body

microscopic features of, or in, a rock

P ‘5: more er, E 3 rec: 3A: HY, AITD 1:113; sauce: on r; AIYSE

U)

Preliminary to an attempt to interpret the mode of
origin, the manner of emplacement, and the attitude of the
"red rock", the criteria upon which such interpretation
is based must be defined and their value as criteria must
be demonstrated.

The criteria are, obviously, the megascOpic and micro-
scopic structures and textures developed in the rock, both
contemporaneous with, and after, its deposition. ”herefore,
a complete examination and description of the rock in the
field, in hand specimen, and under the micrOSCOpe is
necessary.

Since the genesis of the described rock was not ob-
served, only on the basis of comparison with published
works, written by eXperts, and describing rocks of sivilar

‘

character but of known origins, can interpretation of it

(P

formation 5nd structure be wade,

Petrology of the "Red Rock"

 

 

Hand specimens, oriented with respect to north, to the
horizontal, and to the foliation if megaSCOpically evident,
were collected in the field. An attempt to group these
according to megascopic physical characteristics was made.
Unfortunately, each specimen was so different from the
others that grouping for descriptive purposes was impos-
sible. Therefore, only a general definition of structures

and textures is given.

"fl

Flow Rock: The "red rock" of the forcupine Fountains,

 

while exhibiting wide ranges in physical characteristics,

is striking in its chemical and mineralogical uniformity
(table 2). The color of freshly broken surfaces, depending
upon the locality in which they are observed, ranges through
various shades of pink, purple-pink, yellow, orange, red,
and red-brown.

Weathered zones are shades of pink or yellow, and
may extend so deeply into the rock that fresh samples
cannot be obtained. This deep penetration of weathering
processes may be due, not only to the original high porosity
and permeability of certain portions of the "red rock"
mass, but also to the great length of time during which
weathering was able to progress.

In addition, fractures related to original flow and to
shrinkage upon consolidation, and conninuted zones related
to later defornational forces, present avenues of access
to weathering agencies even in those portions of the "red
rock" which are hard and dense. Such open fractures are
universally covered with drusy quartz.

The rock possesses a clayey odor even on fresh sur-
faces, indicating considerable kaolinization by infinitely
penetrating solutions.

In general, the rock exposed in the northern and
northwestern parts of the area is dense and compact. It
is aphanitic and looks like dull red jasper, or is

aphanitic-spherulitic, in which case the accretion of more

- 24 -

highly quartziferous material in the spherules imparts to
the rock a spotted appearance and a somewhat more vitreous
luster. In either case, the rock breaks with conchoidal
fracture.

Vesicles are uncommon in the "red rock" but miarclitic
cavities are prevalent. Large cavities, distorted and
drawn out into the plane of foliation are occasionally
developed in the rock eXposed on the upper part of the
Carp River near locality 74 (pl. 15, in pocket). These
cavities range up to 12 inches in length and are partially
or wholly filled with euhedral quartz (pl. 3, A). Similar
rock is exposed at the top of the cliff on the west side
of Government Peak near locality l, but here the cavities
are subspherical and average 5 millimeters in diameter.

A well developed, finely laminar, eutaxitic structure
is common in the rock of the northern part of the area.
The separate bands constitute layers of varying compo-
sition. The dark bands are composed of magnetite, glass,
and partially crystallized feldspathic material and light
ones are composed of quartz and quartz-feldspar inter-
growth. The distance between successive dark or light
bands is usually a millimeter or two (pl. 3, D), but
occasionally, as at localities 8 and 58, single layers,
generally those of the quartziferous material, may be
25 millimeters wide (pl. 3, E).

Weathering is relatively easier along those planes

in which magnetite and feldspathic material is predominant

due to chemical instability of these minerals in the
presence of oxidizing and hydrolizing solutions. Therefore,
the deeply weathered, foliate phases of the rock possess

the appearance of old lumber, the light bands protruding
while the dark bands are recessed.

The texture of the "red rock" in the southern part of
the area is generally granitic or aphanitic-porphyritic.

The phenocrysts of the porphyritic varieties are euhedral
or subhedral quartz averaging l millimeter in diameter,
or potash feldspar averaging 1.5 millimeters in diameter.

The feldspar phenocrysts are zoned. This zoning is
made evident by differential alteration or by differential
inclusion of foreign material, probably hematite or other
ferrite, or by both, resulting in abrupt changes in color
oriented concentrically with reapect to the center of the
phenocryst. This coloration, various shades of red, is
usually more intense in the outer zones of the crystals.
Carlsbad twins can occasionally be identified by the
darker shade of one twin.

Other megascopic structures are cracks which formed
during the final consolidation of the rock. As the more
completely crystallized portions of the rock were carried
forward by still fluid portions, tension fractures developed.
Whose were, in some cases, completely filled by the re-
maining liquid which, as the end product of crystallization,
was considerably more acidic (quartziferous) than the

earlier crystallized portions and hence a lighter color.

In other instances, the cracks were left cpen or were only
partially filled. Many of these open fractures persist
in the rock at the present time.

Pyroclastic Rock: Pyroclastic "red rock" was seen at

 

many localities. The best outcrops are near locality 11
on the upper Carp River, and at locality 22. The rock
exposed at locality 22 is composed of angular blocks of
typically foliate "red rock" cemented by a hard, dense,
aphanitic material of the same composition. Foliation

in the cementing material conforms to the outlines of the
included fragments, wrapping around them in smoothly curv-
ing layers and breaking up into disorganized eddy-like
bands on the lee sides of the larger fragments.

“he included angular blocks, usually flat sided, are
rhombohedral or rectangular. They range from 1 millimeter
to more than 40 centimeters in diameter (pl. 3, C; pl.

11, o). _

The agglomerated zone at locality 22, although not
exposed in its entirety, has a minimum thickness of 5 meters.
This type of brecciated material is typical of the t0ps of
those flows in which a crust of solidified lava was formed
and subsequently fractured and envelOped by the remaining
fluid lava. The writer believes that rending of the crust
may have been accomplished by bulging and bursting due to
an increase in hydrostatic pressure in the fluid lava;
by collapse due to a decrease in hydrostatic pressure and

consequent failure of support, or by an extension of the

crust beyond its elastic limit through differential trans-
location during continued flow by magma below. Formally,
several of these processes act in conjunction.

The pyroclastic rock on the upper Carp River near
locality 11 is composed in part of included angular blocks
as described on page Ed. The fragments here, however, are
much smaller, usually averaging about 1 centimeter in
diameter. In addition, a very small portion of the rock
is composed of compressed and indurated volcanic dust, and
of fragments less than 4 millimeters in length. This is
interbedded with the fine breccia.

The tuffaceous material shows an indistinct bedding
(pl. 5, B). The bedding is sinuous and discontinuous and
consists of fine dark bands weaving around small, light
colored, ellipsoidal clots. Induration, accompanied by
alteration, has obscured the original character, so an
accurate description of structures is impossible. Uowever,
the small clots are similar in many reapects to structures
described in many papers on pyroclastic rocks as mud balls
or as muddy rain drops. An abundance of cryptoclastic
devitrified glass shards is also indicative of its exo-

genetic origin.

Petrography

 

Thin sections were made from hand specimens. They
were oriented, in cases of megascopically foliate rocks,

normal to the plane of foliation and were ground to 50

A.

U
C

Explanation of flats 3

pecimen collected near locality 74 on the Upper Carp
River. liar olitic cavities are well developed, one to

t he bottom being com-

Cf‘

the left of the large cavity

fil’a

pletely filled. Saintly visible is flow banding trend-

ing from lower right to upper left. x 0.35.

Specimen from the upper Carp River near locality ll

showingd dis placement of a thin pyroclastic zone by a
small fault trending from the bottom to the top of the

’ PQ ' r' ')."\‘-.‘
photograph and Glyplu-

m
d'

o the right. x 3.40.

Volcanic agglomerate from locality 22 north of lirror

I4

lake showing subangular fragments cemented by a foliated

matrix. x 0.75.

fpecimen from locality 54. Two feces polished at right
angles show the complex form that flow banding may
assume. Tote the occas1onal large magnetite pheno-

crysts tithin the L,uartziferous (light colored) layers.

>4
0
O
q
()1

Specimen from loos li ty 3 illustrating the pronounced
plat narity that most of the "red rock" ext ioits, and also

showing the extremely variable thickness of flow layers

noted in some specimens. lots the penctiat io f
Weathering agencies (light streaks ) along ihe do;

l\‘\

m

magnetitiferois layers and ;l o the large number of

spherulites (da rk clots). x ~[.75.

PLATE 3

 

- 30 -

microns thickness. When discovered that in some cases the
direction of flow could be determined, other sections were
cut normal to the foliation but parallel to the direction
of flow, in order more clearly to observe the structures
develOped as a result of movement.

The micros00pic petrography of the "red rock" is not
difficult in so far as the number of minerals present is
concerned. It is extremely difficult, however, in that the
minerals are exceptionally small and are not only incom-
pletely crystallized in some cases, but are to a great
extent altered to, and masked by, secondary minerals.

The minerals were identified by physical and Optical
characteristics using a standard leitz petrographic micro-
s00pe and heterochromatic light. As criteria for micro-
scOpic identification of minerals can be found in such
works as Rogers and Kerr (1942) and Wahlstrom (1947), only
in those cases where abnormal or variable features are
observed, is reference made to them.

The "red rock", although of manifold megascogic
character, shows a relatively large but limited number of
crystalline types. To obviate the description of each thin
section, an attempt was made to group the specimens accord-
ing to microscopic characters. It was found that each thin
section would conform to one of eight types. These types
are described in detail.

An ocular micrometer, calibrated to several lens

systems, was used to measure mineral diameters. The diameters

of minerals in thin section, are not true size. Where,

in a broken rock, full sized minerals may be exposed on
the surface (if fracturing occurs between minerals rather
than through them), the minerals are transected in a

thin section. Whey are, consequently, somewhat smaller.
Krumbein (1935, pp. 494-496), using averages of many
observations, indicated that the full size minerals are
approximately 4/fi larger than those exposed in thin sec-
tion. Later, Chayes (1950, p. 159) brought out the fact
that this ratio holds regardless of the mineral shapes.
Therefore, to obtain true sizes for the described minerals,
the measurements given must be multiplied by approximately
1.25, except in cases of sections cut parallel tola line-
ation of minerals or of minerals less than the thickness
of the sections (36 microns).

"Red Rock", Type 1: Good examples of specimens of

 

type 1 are exposed at localities 3, 34, and 5e. lhese
represent a phase of the "red rock" in which eutaxitic

structure is well developed (pl. 4, E).

I

Vhe purple bands, which range from 'O to 5C0 microns

L

in width, resolve themselves into aggregates of closely
disposed, strictly parallel, and relatively continuous

layers of magnetite grains. The rrains of magnetite are

(m

equidimentional and average 3 microns in diameter, or are
elongated crystallites and small asymretrically developed
crystals with columnar appearance. (See pl. 9, A for

the various types of crystalline development of ma petite).

~
9.4

U
C )J
I“

I

These crystallites and assymmetrically developed crystals
may be as long as 40 microns. long axes of the crystals,
and the long directions of margarites and elongated cum-
ulites into which the small grains are often gathered,
are oriented normal or subnormal to the trend of the
layers.

Hagnetite as phenocrysts, ranging up to 500 microns
in diameter is distributed throughout the rock irrespect-
ful of foliation, and situated as likely in the light
colored bands as in the magnetiferous ones. host magnetite
phenocrysts are euhedral and equidementional but a few are
skeleton crystals with one, and sometimes two faces incom-
pletely developed.

Directly on either side of any dark band and con-
stituting interstitial material between magnetite grains
within the dark band, is a zone of partially crystalline
and incompletely individualized substance which appears to
be an aggregate.of devitrified ferritic glass and quartz-
feldspar mixture’%4, C). Originating at the edges of, and
extending away from the dark bands for a distance of ap-
proximately 350 microns, this material is arranged in
groups of fibrous tufts. Each radiating tuft subtends
two to five degrees and each group of tufts approximately
forty degrees in the plane of the section. The fibres are
submicroscopic in width near their origin but individuals,
or small groups of individuals, can be seen due to dif-

ferences in composition and consequent differences in color.

- 33 -

The tufts are slightly flamboyant and grade from dark
brown isotropic material near their bases to more or less
anisotrOpic material near their termini. They distort or
even split the arms of the anomalous pseudo-uniaxial cross
which is present when radial aggregates of acicular crys-
tals or partially crystalline material is viewed under
crossed nicols. The tufts are mutually interfering and
margarites of magnetite grains are often insinuated be-
tween them (pl. 9, E).

In those portions of the tufts where the Optical
characteristics are not obscured by ferritic material
(pl. 4, B), their relief is low and their indices are
split by Canada Balsam. It is believed, therefore, that
the composition of the feldspar constituting these clear
areas is oligoclase, with a composition somewhere between

AbBDAnzo and AbQOAn If this mineral is oligoclase,

10'
it is normal and expected that the composition will become
more sodic with continued crystallization, and it is likely
that the unidentifiable feldspar near the origins of the
radiating fibrous tufts is the more calcic.

At an indefinite and gradational boundary at the terminal
ends of the planiolitically arranged radial tufts, olig-
oclase gives way to small but identifiable orthoclase
crystals which, in turn, give way to large orthoclase
euhedrons. These large crystals project from the spherules

in a manner well described by Iddings (1899, p. 412),

"The spherulites bordering more crystalline areas

in lithoidal rhyolite have sometimes continued

their crystallization a short distance into these

areas, when they exhibit distinct prismatic rays

that project beyond the apparent periphery of

the spherule and resemble the teeth of a

cogwheel."

The only well developed terminal crystal faces are 901,
parallel to the basal cleavage. The large orthoclase
crystals range from 15 x 50 microns to approximately 150

x 600 microns. Commonly, several will develOp parallel and
adjacent to each other with their prismatic faces close or
even touching. Carlsbad twinning is common, one twin
usually more highly altered and ferritic than the other.

Interestingly, sanidine, which might have been ex-
pected in a rock such as this, is entirely lacking.

Filling the interstices between orthoclase crystals,
and occupying the remaining space in the area between
adjacent dark bands, is anhedral to euhedral quartz. “he
grains are quite uniform in size, averaging 170 to 203
microns in diameter. Contacts between them are usually
sutured, but occasiona1.well developed pyramids or even
bipyramids can be found.

Strained quartz is present within unstrained quartz.
Occasional wavy extinction in one crystal, and occasional
extinction progressing from one to another of elongated
individuals arranged in fascicular groups, indicates
crystallization while there was still a tendency for flow

within the mass.

A peculiar micrographic quartz-feldSpar intergrowth

is present in small areas of the specimen from locality 3.
This intergrowth is an intertongueing of thin projections
of quartz and orthoclase in the manner of a rabbeted joint.
Each projection is about 5 microns in length (pl. 9, C).

Tany large orthoclase crystals have been broken off
and included in the quartz. these fragments are often
oriented with their long axes inclined toward the plane
of flow as illustrated in plate 9, D.

The Specimen from locality do has many microspheru-
lites . These nicrospherulites, less than 80 microns in
diameter, originate at any point in the rock and radiate
outward from a group of magnetite granules.

In the specimens from localities 3 and 54, large
epherules up to 5 millimeters in diameter occur everywhere
in the rock (pl. 4, A, D). When in the dark bands, these
large spherules radiate from a core of magnetite grains
but do not affect the disposition of the layers of mag-
netite grains, radiating through and including them without
distortion (pl. 8, A).

The epherules are compound, that is, made up of several
concentric layers of tufts of radiating fibres, and are,
often separated to some extent by zones of magnetite or
quartz granules. Occasionally these zones are entirely
devoid of mineral matter. Bifurcation of the pseudo-
uniaxial cross under crossed nicols is common in the
compound spherules and double, or even triple splitting is

not infrequent. Kargarites and micro-phenocrysts of

magnetite occur along the sides of the tufts of fibres,
separating them into distinct units (pl. 8, A).

Other spherulites, entoblitic, and cored by aggregates
of small quartz grains, or even enclaves of quartz grains
without surrounding fibres, occur between or near the layers
of magnetite and impart a mottled appearance to the dark
bands. These spherulites average about 5931 n1i arena in
diameter (pl. 6, B). fh mineral coring these spherulites
may be the high temperature quartz, tridynite, since
identical textures described by Whitman Cross (1392 , p. 441)
contained this mineral.

Other minerals occur in minor agmbunt. Very small,

but perfectly developed zircon is seen occasionally in the
dark bends. ch asional biotite flakes, not larger than 50
microns, are found in the planiolitic zores. A dark red,
transparent mineral With parallel extirc tion, aid so»3times
as la‘ge is 73 microns, is found in quartz. This mineral,
although not positively identifiable, is probably sphene

L
1

PU

or sta llite

r‘ fl.
C L- L.

$33

(titanite). Yiridite, as aggreg gpt WI:

green scales, is present near several large ragnetite
phenocrvsts. Vhis unidentifiable mineral say be either
an alteration product, or microlites of a ferromagneeian
mineral.

.0

Fematite and leucoxene are alteration products 01

1.

magnetite, the presence of leucoxene indicating that tne
nagnetite is titahiierous. In addition, feldspars have

ered to kaolin, and small scaly masses of yellow

I
( \1
x]

D

calcite have been secondarily introduced. The above n>med
alteration products, together with the secondfry calcite
and microcryptocrystalline Opacite grains, so thoroughly
permeate the rock that it has a dirty, dusty-brown appear-
ance, and the optical characteristics of minerals are
obscured to the point that smaller individuals can rarely
be identified.

Layers of Opacite grains occupy cleavage planes in
orthoclase and fill curved fractures in quartz. Small
magnetite granules occupy interstices between quartz
crystals, and occasionally occur as long strings lying
in, or nearly in, the plane of foliation.

Elongated fluid inclusions are found in quartz and
orthoclase. the clear, colorless liquid of the inclusions
infrequently contains small immoveable gas bubbles. The
inclusions are oriented in strings or layers in the plane
of foliation and transect quartz boundaries, although
those in orthoclase do not transect boundaries. Ortho-
clase may, thus, have a reticulate appearance, due to
planes of cpacite grains in the cleavage surfaces and to
fluid inclusions in the plane of foliation (pl. 10, A).
Quartz may be filled with opacite grains and then be
included in a larger “ass of clear quartz (pl. 1?, E).

"Red Roakfi, Type 3: Specimens from localities l4

 

P

and 89 are representative of type c. regaecopically,
type 2 is dense, white, and homogeneous, with scattered,

black, pepper-like spots. The thin sections appear

brown under the microscope due to the universal distri-
bution of small fluid inclusions and grains of dark minerals.

hagnetite, in the section from locality 14, is rep-
resented only as crystallites of cargaritic, spiculitic,
and skeleton crystal form. These are evenly disseminated
throughout the rock. The section from locality has evenly
distributed magnetite granules 2 to 5 microns in diameter,
and scattered euhedrons and skeleton crystals of magnetite
approximately 50 x 179 microns. The larger crystals range
from perfectly developed, although asymmetrically formed
crystals, to loose spongy aggregates of granules which
tend to conform in shape to typical magnetite crystal
outlines.

The groundmass consists of a finely crystallized
aggregate of quartz and orthoclase averaging 30 microns
in diameter, associated with tufts of radial fibres of
hemi-orystallinq material. The tufts are probably de-
vitrified glass and partially crystalline acidic plagio-
class, and are about the same size as the quartz and
orthoclase.

Quartz, with occasional crystals which show the
typical wedge-shaped twinning of tridymite, forms enclaves
in the rock about 1 millimeter in diameter. The individual
grains are sutured and range in size from 100 to 209 mi-
crons.

The Specimen from locality 89 has, in addition to the

above structures, orthoclase phenocrysts up to 150 x 500

microns. Extinction on 010 faces at 5 or 6 degrees im-
plies that the orthoclase is very low in soda content.

A curious and unusual primary constituent in the
Specimen is calcite. It is perfectly clear, colorless,
fractured, and is associated with quartz in enclaves.
Boundaries between calcite and quartz are sutured, and
calcite occasionally occurs in small grains completely
surrounded by clear quartz. The calcite exhibit. vari-
able relief according to the orientation of the section,
has indices both higher and lower than quartz, and is
highly twinned, the 8 or 9 color bands produced by refrac-
tion being visible on the inclined twinning surfaces.
These are the only primary constituents; biotite, zircon,
apatite, and other minerals are absent in specimens of
type 2.

Spherulization is absent but the groundmass has areas
of more, and less, coarsely crystalline substance, the finer
grained and more felt-like material forming an indistinct
and partially developed layering in the plane of flow.
However, megascopic eutaxitic structure is not present.

Nagnetite, of three distinct generations (pl. 4, a),
has been partially altered to hematite and leucoxene, and
feldspars have been altered to scaly and fibrous secondary
micas. large quantities of secondary yellow calcite re-
places feldspars and devitrified glass, destroying the
mineralogical identity of large portions of the sections.

Elongate fluid-filled inclusions l to 60 microns in

- 4g -

length (pl. 13, C), and large quantities of small Opaque
grains, cinder-like, and averaging 1 micron in diameter
but ranging from 530 millimicrons to 9 microns, are orien-
ted in discontinuous crenulate layers in the plane of
flow. They may transect mineral grain boundaries or may
stop abruptly.

"Red Rock", Type E; Rock of type 3 is similar in

 

many respects to type 1. It lacks, however, planar flow
structure (pl. 5, F). Rather, it has ellipsoidal spheru-
lites oriented in rude planes and often connected and to
end. An individual spherule may be extended in this manner
to 20 times its width.

EntoBlitic spherules are well developed in specimens
from localities 110 and turning point 8 on the traverse of
the upper Carp River (pl. 16, in pocket). Individual
spherules may be 3 millimeters in short dimention and, in
the case of connected strings of spherules, as much as 60
millimeters in length.

The centers of the spherules are usually aggregates
of anhedral quartz surrounded by older euhedral quartz and
sometimes bounded by layers of magnetite granules (pl. 5,
C). In addition to quartz, small tridymite crystals are
occasionally identified in this zone in the specimen fnam
locality l. Quartz individuals range from 250 microns to
4 millimeters in size.

Extending entoBlitically into the spherules from the

periphery are small quartz grains or euhedral orthoclase

crystals or both (pl. 5, B). Occasionally there will be
an alternation of layers; a layer of orthoclase, one of
quartz granules, another of orthoclase, and culminating at
a center composed again of quartz. The crystals in these
peripheral zones average approximately 155 microns in
diameter.

Bounding the spherules, in some cases, are dark brown
bands of altered devitrified glass and magnetite grains.

The bands, conforming to the outlines of the epherules, are

U:

contorted and discontinuous (pl. , 3). In other cases,
tufts of fibrous feldspar-devitrified glass mixture is
interposed between the margins of the ssherules and the

.'

arm magnititiferous bands. In these, the layers of mag-

pl

netite occupy a position between Opposing sets of tufts

radiating from adjacent spherules.

\‘H

\

The situ t

IJ

on in the interspherulitic areas is often
confused. Innumerable microspherulites are sosetimes
present. They are either composed of radiating fibres, in
which case good pseudo-uniaxial crosses are developed urder
crossed nicols, or are composed of an interesting, a_parently
homogeneous, brown substarce thich will neither become

bright nor go extinct upon rotation under crossed nicols.

U

Although unidentifiable, it is inferred that the materi l

b

is brown glass, devitrified only to the point where it is
not isotropic and yet not anisotroyic.
Tagnetite is present as phenocrysts 5?? milliricrors

in diameter and as granules 5 microns in size. The pheno-

crysts are evenly distributed throughout the rock and the
granules are linear crystallites of varicus types in the
felty and semi-amorphous groundnass. fine crystallites are
often insinuated between crystal interfaces of other minerals.
This is well exemplified in the specimen from locality l.
?he specimen from turning point 8 has small quantities
of primary calcite associated with quartz. I is, as
described before, small, clear, colorless, fractured grains,
with sutured contacts.
Orthoclase euhedrons in all Specimens go extinct on
910 faces at positive 5 degrees. Small tabular orthoclase
euhedrcns 10 to 15 microns in dianeter occur in the specimen
from locality 79. These are included in areas of quartz;
the quartz individuals range from 65 to 15; microns in
diameter. “h. small orthoclase crysta s are arranged in
lines, the lines bifurcating and sometimes branching in
one plane and at a high angle from a central axial line of
crystals. This arrangement is best described as dendritic
(pl. 5, A). What the paragenesis of such quartz-feldspar
intergromths might be is not Known to the writer. It can
only be hypothesized that the crystallization of the nin-
erals was contemporaneous and that the inti ate presence
of quartz affected in sore manner the habital preference
of the orthoclase. ”he peculiar dendritic structure of
the orthoclase is tell described by J. P. Ideings (1699,
p. 415) v.-ho says,

"These crystals branch out in two different

ways. In some cases they appear to split, the

parts being slightly inclined to one another at

first, and becoming more divergent f rther on.

... In other cases the branching of the long,

twinned prisms is seen to obey a crystallo-

graphic law. :hort prisms project from

Opposite sides of the ?anebac h twin at an angle

corresponding to that between the ver tical axis

and clino axis, about 64°

The quartz crystals which bear the dendritic ortho-
class are oriented with their elongated c axes parallel to
the trend of the orthoclase dendrites. Clear quartz tends
to become euhedral, and perfect hexagonal prisms with
si ple pyrani Md 1 tern r;a tions extend into partially filled
miarclitic cavities.

Planes of oriented fluid inclusions, filamentel mag-
netite crystallites (pl. 5, D), and linear aggregates of
Opacite grains are present in the feldspar and quartz.
“hose are oriented in the sane direction as the quartz-
feldspw rintergrowths, the elongation of spheruliizes, and
the la; ers of magnetite grains. Also included in the
quartz are zircon euhedrons up to 10C microns in length.

Again hematite, leucoxene, and various other alter-
ation products cloud the rock. secondary calcite is
abundant in the felt; fibrous areas and interstitially
between quartz grains in the centers of spherules. Its
color is yellow and its form is radiating "books" of
scales, no "book" more than 20 microns in length.

3- 6

"Red Rock", Tree 4; Examples of type 4 crop out at

 

 

localities 39, 6O , and 62. A specimen from locality 75

was obtained from a sandstone conglomerate overlying the

—44-

"red rock". Whether tie conglomerate is in the Ashbed
group or in the "Great conglomerate" is not known.

Specimens of type 4 appear mottled megascogically
(pl. 6, A, B). TicroscOpically, the light colored spots
are aggregates of quartz crystals and the dark areas are
masses of radially fibrated felty material and minute
quartz granules. Actually, the basis of the rock is quartz,
the dark material sca tered through it in Jagged patches.
This imparts to the rock a brecciated or stippled aspect.

Although alike texturally, the degree of crystalli-
zation of the several samples is different. fihe average
diameter of quartz grains in light colored areas of the
rock from locality 62 is 4? microns, and those in specinens
from localities 59 and 75 average 80 microns. quartz in
the specimen from locality 60 is intermediate between these
in size. Cther minerals vary proportionally. glartz in
the light colored areas may, however, be as large as 2??
microns. It is generally sutured and includes strings
and layers of submicroscopic opaque grains and small fluid
inclusions oriented in the plane of flow.

The dark areas of less Well crystallized specimens
are composed entirely of fibrous and tufted devitrified
glass-feldSpar nixture in random orientation, and mag-
netite granules. The magnetite averages 2 microns, and
the fibrous tufts 4? microns, in dianet r. In the more
completely crystallized specimens, equant anhedral quartz

grains are associated with the fibrous tufts, both

averaging 40 microns in diameter. shall unidentifiable
feldsgar crystals were noted. the feldsptrs are somewhat
larger in specimens from localities 59 and 75 than in the
specimen from lOCflllt' 60, but they very little from an
average diameter of approxinetely lO nicrons. Since there
are no enclaves of single minerals, the dark areas are
homogeneous throughout.

Spherulites of fibrous material and small orthoclase

crystals become better developed with increasing crystal-

(0

linity of the rocks. In the samples from localities 5
and 70, splerulites become compound, concentric layers
of feldspar-devitrified glass mixture alternating with
quartz (pl. e, C). "any of these compound epherules have

dinneters greater ttan 4 millineters. chneeted crystal-

4-
'4

[Jo

lites ol nagne te grinules radiate frcr the centers of
J-L‘ ' ~'-- -' ~ ’ ‘ '. . 4? "r ,2 r . .- ‘ r
ole sp:erulos, but elsewqere in one VdIK areas, are

heterogeneously Lriet590'

0"
t—J
(Y!
3
n
F.)
(7‘
2
, '\
{D
U)
Q
r...
:5
YD
{\
(D
_L.
H
\ I
(P
m?
*‘1
p
H
"w
u)
(l1
'1
Q

uh Cherie

u A " ‘
b -7 x. v

r“

(U

sheleton crystals of nagnetite, COtJ as l rge as ch. microns,

V .3"! 1" ’ N‘ L. ‘- \..A ~ , . ' -.
Eulofl one “EgKEblbe phenocr..

An unusual structure prestrt in one sample lroi

a :zeoture, :vident"; it: so during consoli-

'JJ

- I I -.- ’1 ‘ :
loofl;ty o: l

dat on of the roon, and filled sith a more iirely crystalline

material of the same composition and texture. 7he hand
Specinen exhibits portions of this crack which were never
filled. It may be assumed that at this s
was too viscous to enter the crack (pl. 0, C).

Cther than the above, tyne 4 specimens are similar
to other "red rock". Planes of fluid inclusions with small
gas bubbles, and pl nes of magnetite, are pr sent in quartz

J.

and feldspar. Secondary calcite and dusty hematite, leu-
coxene, end kaolin minerals cover all portions of the rock.
also, unidentifiable viriditic material associated with

magnetite, and appearing in interstitial spaces between

hoclase, is present in shall Quantities.

"Red dock", Type 5; type R rocks ere apnanitic-

 

 

porphyritic to aplitic-porphyritic in texture. A specimen

“A

from locality its consists principally of sutured guertz

A

individuals about 1?. mibrcns in disaster, orthoclase

.

rains. a specimen from

\Q

I'

phenocrysts, and magnetite
locality lld, occuring as an included pebble in a con-
glometate lens in the Ashbed group, has a basis not so
completely quartziferous, but composed of microsc0pic
unoriented orthoclase laths.

Nagnetite phenocrysts in this specimen reach dimen-
tions greater than 1 millimeter end are often nearly
destroyed by the growth of a light green, scaly, unidenti-
fiable secondary mineral. Tagnetite phenocrysts in the
specimen from locality 125 are smaller, avaraging about

20 microns in diameter. 1"bees are usually euhedrons or

semi-euhedral skeleton crystals, many of which have columnar
outlines, or are aggregates of small grains. Both specinens
are filled with globulites, longulites, and trichites of
magnetite, occurinp anywhere in the rock, and assuming
random orientation except in a few partial spherulites

in the specimen from locality llb. In these, they are

arranged radially with respect to a central point.

C?

Orthoclase was the only feldspar iden if ied. It is

located in the areas of gxar tial spherulitic growth and is

-'

associated there with fibrous devitrified glass-fel dspar

material. It is develOped as laths in those portions of the

groundnass which are completely crystalline, it is found

as interm owths with quartz, and it occurs as phenocrysts.
In the areas of partial spherulitic growth, the

orthoclase crystals are elongated, twinned according to

the Carlsbad law, and average about 10 x 4? microns.

As laths in the groundmass, it is gra da tional in size,

but a tendency to group into three sizes is apparent.

A

These are approximately 10 x 4G microns, 5M x 120 microns,
and 183 x 556 microns. Carlsbad twinning is common in

the lathe and is alnost universal in the phenocrysts.

The phenocrysts, highly altered to kaolin, and filled with
layers of magnetite, ferritic grains, and fluid inclusions,
range up to l x 3 nillimeters in size. Clinodomes and
various oblique faces are present on some crystals.

Yicrographic intergrowth of quartz and feldspar is

common, but the orthoclase, rather than crystallizing in

- 48 -

dendritic forms as Fanebach twins as described earlier,
exists as separate, more or less equant, euhedral, and
untwinned crystals arranged in lines parallel to a micro-
SOOpically well defined, but megasCOpically unobservable,
foliation.

Quartz is often twinned in the section from locality
116. The twinning is especially noticeable in quartz
occurring in a primary fracture which was filled by more
acidic later magma (pl. 6, E). The c axes of the twins
are parallel, and the twins, if oriented parallel to the
proper prism face, will become extinct as a unit. Usually,
however, extinction is progressive, and looks much like
the albite twinning of plagioclases. Associated with
quartz is subhedral zircon up to 5?0 microns in length.

"Red Rock", Type 6: Rocks of this type vary in

 

megascopic appearance in that some, like the specimen from
locality 74, are uniformly dark brown and appear completely
aphanitic, while others, including a sample of the suppos-
edly intrusive rock from the hill upon which stands the
Eergland fire tower (46° 43' f., 89° 38' W.),'possesses
numerous small light colored Spots and feldspar phenocrysts.
This rock appears in the literature as the "Chippewa"

felsite.

Kicroscopically, the basis of all specimens of this
type is a micrographic intergrowth of quartz and orthoclase.
The quartz individuals average 213 microns in diameter,

have sutured contacts, and are equantly subpolygonal to

-49-

subcircular in outline. Upon insertion of the upper nicol,
the Specimen assumes the appearance of a "buttermilk sky"
(the intergrowth), superimposed upon a larger "patchwork
quilt" (the sutured equant quartz crystals) (91. 7, A, E).

The intergrown subhedral to euhedral feldspar is high
potassium orthoclase. the crystals are slightly elongate
and average 7 microns in diameter. Post are thinner than
the section and, therefore, go extinct with the enveloping
quartz. These are oriented, long axes parallel, in lines
and in bifurcating and branching linear groups like similar
structures described in specimens of type 3. The linear
groups transect boundaries of the quartz grains without
changing direction.

light colored areas in the specimens from the Eergland
Fire @ower hill are merely zones of relatively clear quartz
which have no intergrown orthoclase. These areas average
35? microns in diameter and usually contain several quartz
individuals. Cccasionally, however, a single crystal, as
large as 633 microns, will constitute a light area. A
progressive tendency to euhedrality is apparent in quartz
cr‘stals in a traverse of the section from an area of
intergrowth to an area of pure quartz.

Bounding and projecting into the quartz enclaves are
elongated euhedrons of orthoclase approximately 10 x no
,micrcns in size. These are apparently untwinred, althcugh
the presence of ferritic material might obscure such

structures. Also in the quartz are curved and inter-

secting perlite-liie cracks filled with magnetite
granules.

The rock from locality 74 also has areas of quartz
more or less free of orthoclase, although they are not
megascopically apparent. Vhis is due to the continued
presence of intergrown orthoclase. It is, however, in
leaser amount and more widely dispersed than elsewhere.
“he feldspar crystfls, averaging approximately 8 x 25
microns in these areas,are unoriented and harger than
those in the rest of the rock. The quartz here, as in
similar areas of other specimens, tends to become euhedral
and to possess curved cracks filled with ~asnetite
granules.

Buhedrons cf zircon u; to lffi vicrons in length, and
grains of sphene less than 13 microns in length, are pres-
ent in small quantities as inclusions in the quartz of all

‘ h
v

r

specimens. Biotite in ver; small and thin flakes is al

present, but usually occurs associated with, or relatively

near, groups of magnetite grains or hematitic zones.
Tagnetite in all specimens v:ries from 1 to 1?”

microns in diameter, but a large percentage of the grains
fall into one of three distinct sizes, 2 microns, 1?
microns, an 53 microns. It is much altered to hematite;
leucoxene is rare.

7he only real difference betneen the other specimens
of type c and the Specimens from Eergland Tire “ower hill

is the developnent in the latter of orthoclase phenocryst,.

These are elongate, up to 1.1 millimeters in length, and,
if those exposed in the thin sections are representative,
untwinned.

Yaolinization is far advanced and ferritic material,
mostly hematite secondfry after magnetite, has so thor-
oughly clouded the rock that mineralogical identification
is often impossible. The feldspars, especially pheno-
crysts in the specimen from the fire tower hill, are masked
with these alteration products, staining them dark brown
and rendering them incapable of reacting anisotropically
under crossed nicols.

"aed Rock", type 7; Cnly one thin section of this

 

 

type of rock was made. The specimen came from locality
75 and occured, as did one of the specimens described in
type 3, as an included pebble in a san stone conglomera‘e.

This thin section is similar in microscopic charac-

...Jo

ter stics to those of type 6, but is approximately twice
as coarsely crystalline, with quartz crystals averaging
450 microns in diameter as opposed to a diameter of El?
microns in type e specimens. “he size ratio of other
minerals is similar.

Orthoclase is again intergrown with quartz. ”he
separate euhedrons average 15 x 25 microns and are thinner
than the section, going extinct with the quartz in which
they are included. Only an occasional crystal shows
Specific mineralogical characteristics, and Optical measure-

ments of these were the basis upon which they were identified.

As described before, clear areas are produced by the
failure of intergrown orthoclase to oonpletely fill the
quartz. fhe clear areas thus left usually have polygonal
outlines, not in the shape of quartz crystals, but square
or rhomboid. The cause for this habit of parallelogramme-
tricity of clear areas is unknown to the writer. Slightly
larger orthoclase crystals project into these clear quartz
enclaves, nhich, in this Specimen, average 250 microns in
diameter and are usually a single individual.

Crthoclase phenocrysts are considerably altered,
untwinned, and similar in every respect to those of type s
except they are larger, averaging 2 x 3 millimeters.

lagnetite aggregates as large as 1.5 millimeters, and
made up of loosely grouped, 6 micron grains, are scattered
through the rock (pl. 6, F). Sons of these aggregates
have been oxidized to hematite, the henatite spreading
through the rock and enlarging the area covered by ferritic
material to 5 or 4 times its original size. ”agnetite
euhedrons averaging 5¢O microns in diameter are also
abundant.

Other primary minerals are biotite, calcite, and
euhedral zircon. The biotite occupies cracks in quartz,
and calcite is found as clear, fractured grains, sutured
to quartz and surrounded by it (pl. 7, 0).

Secondary calcite is abundant. It replaces both
feldspar and quartz and, further, tends toward selective

replacement of individual quartz crystals, assuming the

original sutured quartz boundaries, rarely transecting them.
The replacement progresses by precipitation of spell ca.cite
crystals which eventually coalesce by continued growth.

All calcite crystals replacing one quartz individual will
assume the same orientation and, when the quartz is con-
pletely replaced, will go extinct as a unit as the quartz
originally did. A "ghost" of the original micrograohic
intergrowth texture is preserved. Thus, one not acquainted
with the specimen, and viewing it for the first time, not
knowing otherwise, would be inclined to believe it a

prinary mineral.

res

"Red Rock", TV

t
—-

e g: Specimens classified in type 8

 

are the pyroclastics. Since such fragmental rocks occur
under a variety of environments, both endogenetic and
exogenetic, they can be expected to possess wide ranges in
physical and mineralogical characteristics. 7hey are
extremely difficult to describe sufficiently accurately
that one not having seen the specimen can picture its
appearance. In cases like this, one photograph is, indeed,
worth ten thousand words. 1‘he specimen to be described is
from locality 2?, the only outcrop of pyroclastic rocks
of which a satisfactory photograph is available (pl. 11, C).
This rock is type 5. 1‘wo large included fragments,
approximately 30 millimeters in diameter, have all the
characters described in the section on type 3 rocks. In

addition to large fragments are small angular pieces,

variable in composition, and evidently the result of

brecciation or exfoliation of larger fragments. These
range in size from 53 microns to about 5 nillineters.
Although not shown in the section, a full range of fragment
sizes, from very small ones to blocks several decimeters
in diameter, is probably present.

7he fragments have come from previously consolidated
and differentiated material and therefore include those
which have discontinuous, closely spaced strings of mag-
netite granules, and those which are coaposed of brown,
semi-anisotropic, felty .aterial filled with microcrypto-
crystalline ferritic grains. Eroken pieces of zircon
crystals up to £0 microns in diameter, and angular rock
fragments which include numerous sutured quartz grains
with strings of fluid inclusions, are also present.
Eieces of rock with well deveiOped and relatively coarse
foliation like those of type 1, and fragments of spherulites
with attached dark bands, mineralogically and texturally
identical with portions of the foliation of type 1 rock,
are abundant (pl. 7, D). This is to be expected since
Specimens of types 1 and 5 are separable only in degree
of planarity of foliation; the degree of crystallization,
and the number and behavior of minerals in the two types
is identical.

7he presence of numerous fragments of perfectly clear,
colorless, vitreous glass filled with fagnetite granules
and with elongated fluid inclusions, a few of which have

very snail gas bubbles, is unusual.

The fragmental material has been inundated and cemented

9

by still fluid portions of the same Jaama. Differentiation

k,

between the inclusions and the cementing material is diffi-

cult due to continued fracturing through both the cementing

B
m

q

terial and the fragments, both of vhich were la ate er cemented.

As this cycle progresses, the reaaini re magma became sore

acidic, until the latssc fractures were filled with quartz

The cenenting magma COhfLTHS to t
graphic intererovth of crthocl las and ouartz is com on

oua-tz is sutured; euhedral zircon up to 11? microns in

i"
r‘
C

"K’

in anal

.Cl.

evident everywhere, and 1ar§e areas of pa rtiall_. crystal

devitrified glass-feldspar mixture occuning as fractured

fl 7

11', .
gm' lie... ULxc if

in
0)

fr
through the rock. These fractured brhdrh'luLC growths
are, ir this specimen, nearly isotroyic and range from

lEI'LLlJ. JCBS

H"

dark brown to black. In rost places these Sp

are surrounded by sinuous and discontinuous bands of me:

netite grains, typical of type 5.

0
«rates of a brown ;- teiial LECCme

w
~
«\J H

extinct progressively and at a slight positive angle.

faint granular tex ure in these aggregates at, or just

5-,».

*oe 3 rock. Ticro-

ctures filled with Quartz, are scattered

the limit of resolution of the eye-microsCOpe combination,

is ini erred to be ainut e orthocla se crystals a few milli-

microns in diameter and arrerged in parallel orientation.

This mineral could, by the single criterium of slight

positive extinction, be inferred to be plagiociase.

vowever, after consideration of he facts that plagioclase

was found exclusively in fibrous radiati1' tufts that the

'1
(K!

texture in question is, like the usual quartz-or

C?
D-
O
O
'1 _J
uh
I
(D

intergrowths, in lines or granules --although sneller than

usual, and that the

D"
01
(D
i» i‘
y...
D
C
:5
DJ
,9
(1'
...
F"
"\
t—a
$10
"O
1.
(1‘
CL
*3
no
:4.
O
O‘
(D

f.

homogeneous like guar

,2, its identification as orthoclase
is felt to be correct. .

The banding in the cementing material conforms to,
,and wraps around, the included fragments. The fragments
have been attacked, corroded, and embayed by the cementing
material, and as a result their crystallinity has been
considerably reduced for distances as great as 5 nilli-
meters into their interiors. In rany places, the outer
edges of the fragments have become colorless to brown glass,
filled with nagnetite granules (pl. 7, 3).

Secondary calcite as yellow, radiating packets of
scales, has replaced large quantities of glass, feldspar,
and quartz.

Basic Rock within the "Red Rock" Area: Although not

 

 

 

 

properly a part of this paper, several basic rocks asso-
ciated with the "red rock" are described.

Two dike-like bodies of dark rock are found within the
"red rock" at localities 13 and 15 on the upper Carp River.
The specimen from locality 15 exhibits a faint megescopic
lineation which is reproduced micros00pically by sub-parallel
orientation of elongated plagioclase laths. These range

in composition from Ab72An to Ab7oAn24. They are often

bent into simple or sigmoid curves, and are approximately

25 x 125 microns in size. Between these laths are 19 to
40 micron grains, globulites, and spiculites of magnetite.
Being interstitial to the feldSpar, they are also in
linear orientation.

Unoriented plagioclase phenocrysts averaging l x 2
millimeters are scattered through the rock. Their compo-
sition is approximately Ab40An54 and twinning in them is
uncommon or is obscured by ferritic material and fluid
inclusions.

The specinen from locality 15 is exceedingly fine
grained, but has occasional phenocrysts of feldspar. This
rock fractures ccnchoidally to knife-lite edges. The
groundmass consists of plagioclase laths of composition

Ab76An and averaging 13 x 80 microns, although they may

24
range from 1/4 to 4 times this large. Associated with the
groundmass feldSpar is euhedral, equant to prismatic
magnetite crystals 5 to 15 microns in diameter. There are
also patches of magnetite and quartz, the quartz strained
and going extingt in an extremely wavy and discontinuous
manner.

Feldspar phenocrysts, averaging AbeeAndé' and zoned,
are scattered through the rock. They are never more than 1
millimeter in diameter and are highly twinned according
to the Carlsbad and albite laws.

Evenly dispersed through the rock are dark patches,

up to 6 millimeters in diameter, and consisting of concen-

trations of dagnetite and pennine. Eennine, an alteration
product of basic silicates, is a member of the chlorite
group. The iron for this nineral was probably derived
from magnetite. Whe dark mineral concentrations, although
containing many small crystillites, tend to have rectangular
outlines, and the tendency for magnetite granules in them
to gather into linear strings oriented parallel to the
long axes of the darn concentrations is evident (pl. 7, F).
Other secondary products are kaolin and spell Quanti-
ties cf epidote from feldspar phenocrysts, and hematite
from magnetite. Vhe hematite is in dust-like particles
and clouds all ninerels. A small anount of secondary

calcite is also present.

Basic Rock Superincumbent upon the "Red ROCK": Basic

 

 

 

 

flows overlying the "red rock" are usually quite vesicular
near their tops and their bottoms, although the vesicles
are generally small. They are elongated and oriented in
the direction of flow. They are filled with secondary
epidote, quartz, and microlites of calcite and epidote.
The microlites are intergrown with the quartz.

In a Specimen from an outcrop 40 meters downst eam
(north) from locality 11, the intervesicular material is
small plagioclase lathe oriented in the direction of flow
and ranging in albite milecule from 70 to 80 percent.
Unoriented plagioclase phenocrysts which are, curiously,
unzoned, range in albite molecule from so to 70 percent.

Cleavage planes in these are often filled with biotite.

Ferritic material, mostly hematite surrounding mag-
.etite grains, is abundant to the point of making large
sections of the rock completely black. “hese large opaque
sections are nore or less spheroidal and are evenly distrib-

uted throughout the specimen.

d"
”<1

Q)

("5

Another Specimen, from a loca'i proximrtely 1??

meters downstream from locality ll, is highly vesicular,
even scoriaceous. fihe vesicl.s, arranged in rude lines,
average approximately 60 nicrons in dianeter. fhe original
vesicular structure has been preserved but most inter-
vesicular areas have become Opaque with secordsry hematite.
Epidotization of the groundnass is nearly complete, and

Y

quartz and calcite constitute the rest of tne secondary
mineralization. To original feldspars are left, nor are
pseudomorphic outlines of then retained.

A specimen from locality 18 is also highly vesicular,

D

the vesicles 500 microns to 1? millimeters in di meter.

(

"-
W

The specimen comes freq the extreme bottom oi a flow, and

(0

{DJ
(D:

the vesicles, which are elongated an crush , decrease
progressively in size and number toward the center, and
disappear entirely within 4 meters.

The poorly oriented feldSpars of the groundmass are

approximately Ab Ana . Opaque ferritic areas are present

7C co
in the groundrass of this Specimen, but the vesicles are
filled with beautiful, clear, suonedral quartz wtioh

often surrounds and suspends the broken walls of the

vesicles. Small uuantities of secord‘ry epidote are

also found associated with the quartz within the vesicles

Easic Econ within Sandstone: Year the lonesuch road,

 

and an roximately 045 meters south of the point vhere th

road crosses Ynion River, is a basic dike intruding a sand-
.I In! I. A I. ‘01, _‘ ‘ro -3-~.~ 4FO . - 1L1
scone. _ne sandstone Sbilneb so and o_ps so ool.i.
7he has ic rock is aplitic and nearly tlack. -lt hos"

lb is not entirely exposed, it is thought to be a dike rather

'1‘.» fr . W ’ ~" ‘- 1", “ '\ ‘ . "‘ ‘ .W ‘ ’11 Y"
than a slow, bCCaubU l nan the riots

u.

and l-ac {s vesicles. I trends 1?; and dips 430 north.
Zlagioclase lathe in "log jat" orientation and averaging
239 x 550 microns are ,le oasis of ,ne rook. "heir com-
position ranges fron AbQDAn50 to AboOAnég. :luid inclusions
lying in cleavage planes rare noted. Interstitial between
the plagioclase lathe is pigeonite, but unusual pigeonite
in having an extr enely snail axial angle.
Tagnetite euhedrons and sneleton crystals, “any with
wilqflntlc outline and ave r'~irj 1?? icrons in diameter,
are scat red through the rock. A few, however, are as
large as 6¢C microns and a few are as small as 49 microns..
Eiotite, in small thin fla 356s, is also present.
A secondary nineral, pennine, is relatively abundant.
It replaces bot h pyroxene and feldspar, and rystcllizes
as fibrous, "Berlin blue", agg egates thich show the negative
axial figure under crossed nicols (pl. 8, D, d). It is
a member of the chlorite group, occuring in metamorphic

and altered roczs.

-."r_’\..l .~‘ + o ‘ .D --- ,.¥_
migrate-tion cl :la.e 4

r:‘- . '_ O '_= a x) -;.', 1 I, .o L ‘1‘ I - _' ‘L. ‘_ . L ._ ‘ I‘: . , _, l' . "f w.
coe01men lion lOLcllJQ7eJ rllustratinc dark and ll

TV .‘.} \-- ' , -I: . ;;- a a ‘H ,— r - _ 7 . -r .- .— -_ ., ‘-..' ~, . ’ .—
lEJELS, euneuicl th10c1:r0 UL‘SLJLC’ and machetlte
-.- ' ‘ 'a'” . ~ ' 4", ~.~r.‘v -~-: ~-' ‘1 >--~ . ~»- . ‘
yuchOClgStL in one ,leitaiieious layers. It ~iao

shows sphcrnlitas Elan Lifurcatin; neaative axial

crosses. Iicols crossed. x 1%.

i ‘ 6"

““ .~'~'n - .— 3 v '/ .n\~' w‘A.‘ - 1 0 "L 1.0
DJGClntu from loco it‘ o Suthlug leiritic hauellal

“2.: ° -, ~\ 4. 'I‘ 4--.). 1....-. r. 9 or v. -.- .:~-.
v ion uCnQ: to oe {Lab dense near toe earl L nus.

J-v?

Specimen from localiu; showing tfiiitire in Ortho‘

(f!
$\

J
*3

~. m ~~ . J- J- , «ex-n, « ~ . .~ . ° --r..
i la. ne tits ranules COIIJLJOSII;5

('1'
...)
;L
(D
J
(P
"L
m
0

one Jar; b hd, and orientation of elon'ited crystals
hornel to the trend of flow bands. Yicols crossed. x 14.

f’,‘

Sgecimen from locality 54. .ane iield as 3. lots

spherule in the quartziferous bard. Elain light. X lo.

:pecimen Irom locality 50 showing contorted foliation,
t

multip"e der? lagers separated by partially cr;stalline

-
I

material, and penetration of veaJhering along the dark

1...)

o X 14-.

L!

avers. llCOLS CESSSG

(a

k
H
(J
C?"
( '0
(D
b
*‘3
m
c+
H‘
(‘1
5
(D

Speciien iron locality as showing 5 dis

f meanetite crystals. Elain light. x lo.

0

PLATE 4

 

I‘J‘J

nglanation of Ilate o

Tgecimen from locality 79. Intergronn Quartz and
l

'a ’ ‘5- (.0- ~" L. 7" ~~Lw 1- . - 'r' r. -~'~ -
orthoclase Slob outceirllr sly" dEJECto r

X :50
‘peciren iron looslity 79 showing spherulitic ground-

nass and euhedral orthoclase in uuartz enclaves. Crossed

nicols. x 14.

Specimen from localitv 119 illustrating sinuous flow

banding and quartz clots. Elain light. x 16.

Speciheh from locality 79.’ Elongated nagnetite crys-

tallitESo Plain light. X 2500

Cpecimen from locality 8 on the upger Carp River
traverse (91. 16, in pocket). guartziferous scheru-
lites connected end to end and surrounded by radio-

0
litic felt; :aterial. Crossed nicols. x 14.

Specimen 1"rot locality 1 showing torturous flow
ending. Dark bands are levers of magnetite grains.

ba
llain light. X lo.

PLATE 5

 

Do

r‘J

Explanation of Elate d

pecinen from locality 62 showing patchy apgearance.

V”?

‘ 1* --~ n ' . r't "1(- ‘1 r ' 2 ‘r' ‘ — , ~
Tue light areas are ;uaitz and tn” oael areas are

microcryst lline feldspar. Zlain light. x lo.

' 62. Care field as A. 110018

1

Specimen from locality 53 showing compound spherule

and a primary fracture (right side of photograph)

filled with a more acidic later magma and broken rock
fragments. Plain light. x 16.

Specimen from locality 73 showing euhedral zircon in
magnetite phenocrysts. Tote the shell elongate mag-

netite crystallites. Elain light. x 55.

Specioen from locality lld. Chis is a prirary fracture
filled with a magra of Quartz and zircon. tote small
twinned quartz near the bottom. Che twinning is parallel

to the c axis. Crossed nicols. x 5C.

Specimen from locality 75. This is typical of large

J.
U

‘eti

I)

e granules in ohenocrystoid

L

CD
(D
O
F a
.31;

(1?)

masses. lots the "buttermilk sky" quartz-feldspar

intergronth. Plain light. x 55.

PLATE 6

 

o7-

A.

U)
.

Specimen from Eergland Fire Tower hill showing euhedral

zircon in duartz enclaves. Elain light. x 55.

Sane field as A showing the "patchwork quilt" with

superimnosed "buttermilk sky". Crossed nicols. x 59.

Specimen from locality 75 showing primary calcite (high
relief) in quartz. Tote spongy magnetite aggregates.

Elain 113 t. x 55.

specimen from locality 22 showing the microbrecciation
of the "red rock" in pyroclastic zones. Plain light.

at

X 160

Specimen from locality 22. “his is the contact between
enveloping magma (upper right) and an included fragment.
The outside of the fragment has become glassy. rote

how the fragment has become darr brown with oxidized

ferritic material. llain light. x 55.

J.

Specimen from the basic dike-like body at locality 15.
the rock is aphanitic and c3ntains straight sided

aggregates of dark minerals (bottom). ?lain light.

PLATE 7

 

A.

EU
0

dxplanation of Elate 8

Stylized camera lucida drawing of a spherule, cored in I
magnetite, and penetra in: layers of magnetite without
distortion to the layers or to the Spherule. Iota

bifurcation of the negative axial cross and the several

~netite granules or by

layers of fibres, bounded by na

:-
‘.’
Ha

I

open spaces (right).

Stylized camera lucida drawing of an entohlitic epherule.

Bounded by magnetite, it is cored by quartz.

pecimen from locality 18. This is a basic flow direct-

(I)

1y overlying the "red rock". lots the broken vesicle
Walls, surrounded and suspended by secondary quartz.

Crissed nicols. x 14.

S;eciren from basic dike along lonesuch road showing

q

nd secondary pennine. Ilain light.

m

rl-gioclase laths

5

Q)
C"

0'1

X50

Sane field as D. Crossed nicols. x 5D.

PLATE 8

 

-71...

(3
o

explanation of Ilate 9

orrs that incipient

(D
Fig

Dia3ram ill ustratin; variou

a
r
4

as "red rock".

3
L1)
,4.
'3
C f'

U...

m
(D
m

stagnetite cr;‘7stals may

2tylized camera lucida drawing of the planiolitically

r

arranged radial tufts. Phey originate at a layer of
magnetite granules and radiate subnormal to it. lots

9 granules between adjacent

'5
LD
C?-
H
c f'

the strings of re

Canera lucida drawing of a peculiar intertongueing

intergronth of qu:rtz and orthoclase.

Stylized camera lucida drawing of a quartziferous
layer in the "red rock" showing how orthoclase crystals

are broaen off by differential movement.

PLATE 9

 

ixplanation of Plate 10

Diagram illustrating the attitude of fluid inclusions,
strings and layers of magnetite, and ferritic material
in quartz and orthoclase. Note especially that ferritic
material occupies cleavage planes in orthoclase and

that magnetite and fluid inclusions lie in the plane

of flow. lots also that fluid inclusions transect
quartz boundaries but do not transect orthoclase

boundaries.

Liaeram illustrating the attitude of layers and areas

V

of magnetite in quartz.

ged canera lucida drawing of one series of fluid

C A
{3
*4
(Y)
H

inclusions. lots the occasional gas bubble.

 

 

lineralogical Analyses of the "fled sock"

 

 

 

 

Vineral Percentages; Tineral percentages were obtained

 

by counting units occupied by the various minerals in
linear traverses across the thin sections, a method first
used by Rosiwal (1598). This method is considerably easier
and probably more accurate than areal estimation by use of
a grid.

Finerals in well crystallized Specinens were counted
through the microscope using an ocular micrometer and a
magnification which :ade short di entions of the smallest
minerals approximately equal in length to the finest
divisions on the licroneter. the rinerals in poorly
crystallized or exceptionally fine,grained specimens were
counted by passing light through the micros00pe and, by
using a prism, projecting the image onto a table. If
appropriately lined graph paper was used, the added mag-
nification by projection allowed linear units intercepted
by the smallest crystals to be easily counted.

Obviously, determinations of mineral percentages by
counting linear units would be erroneous if traverses were
made parallel to eutaxitic structure, since such structure
is develOped by differentiation of minerals. Traverses

were, therefore, nade at high angles to any linear or

{A
H
U
)
"7
l 3
O
'1
'(4
U)
,.+
H'!
H

foliate structures present. Approximatel?
diameters nere counted on each slide. This is more than
is necessary, and since the method is not of extreme

accuracy, especially in rock as fine grained as the "red

rock", decimal percentages were rounded off to the nearest
percent, except in those slides where it was felt that
greater accuracy was obtained (table 2).

Yineral Determinations: Since plagioclases occur in

 

small amount, and only as microcryptocrystalline aggregates
with other minerals, they could not be counted. likewise,
ferritic dust, biotite, and Sphene were not counted.
?erritic dust, although in large volume, is submicrosc0pic,
and biotite and sphene occur only in traces, their combined
volumes not significant to proper classification of the
rock.

Specinens with uuartz-orthoclase intergrowths presented
an unusual problem. The distances across orthoclase crys-
tals averaged approximately 3 microns, and interfeldspar
areas of cuartz, approximately 2 microns. In view of the
fact that counting through this raterial in each traverse

the sections would involve an unnecessary amount of work,

H.

c
an average composition for this material was obtained.
Traverses of 5 millimeters were made across this material
on each of ten slides. Thus, approxinetely ,C?? crystal
units per slide were counted. In every case, the ratio
of quartz to orthoclase was 43 to 57. From these measure-
ments it was assumed that similar areas in other thin sec-
tions would have similar composition.

Unidentifiable groundmass feldspar was counted as such,

and assumed to be 13: percent feldSpar. This assumption

may not be valid since such areas may include considerable

quantities of glass. Clouding by ferritic material, however,
makes identification of the minerals impossible, and since
the grounduass appears anisotrOpic, the assumption that it
is feldspar is probably not far from the truth.
Spherulitic growths contain a variety of mineral
matter in such small particles that differentiation cannot
be nade. Iddings (1899, pp. 412-41e) considers spherules
from Yellowstone Park to be composed entirely of orthoclase.
The writer, unable to determine the ninerels, with the
exception of a highly uncertain identification of oligo-
class in one thin section, was faced with the necessity
of assuming a composition not based on experimental data.
Interestingly, and possibly significantly, if the
material in spherulitic growths is assumed to contain
quartz and orthoclase in the same prOportion as was deter-
mined for the micrographic intergrowths, the quartz-feldspar
ratio of a large percentage of the specimens will be
nearly the same (table 2).

Classification: Unfortunately, the determination of

 

mineral percentages was so uncertain that synthetic chemical
analyses derived from mineralogical determinations for
purposes of comparison with analyses of acid extrusive
rocks from other areas, was impossible. Vowever, they

’3

were sufficiently accurate that classiiication could be
made. A classification by Johannsen (1952, pp. 141-161)
was used since it is based upon the percentoge by volume

of minerals present. It has the ad itional advantage

 

 

 

that rocks can be identified by number as well as by name
and, thus, do not suffer from the frailities of language.

According to this classification, the "red rock" is
1153. “he first number indicates that there are less than
5 percent dark minerals; tne second number indicates that
the plagioclase is more acidic than Ab9CAnlj; the third
number indicates that the orthoclase is in larger quantity
than Quartz and that there is less than 5 percent plagio-
clcse; E denotes that the rock is extrusive.

By name, this rock is halitordrillite, a rock similar
to the extrusive alaskites of the Tordrille fountains,

Alaska, but containing less plagioclrse.

Discussion

 

Origin; The possibility that the "red rock" is elastic
or metamorphic must be considered. The evidence presented
in the descriptions is overwhelmingly againse the "red rock"
being elastic and no more need be.added here. However,
structures and textures similar to those in the "red rock”

are sometites develOped in metamorphic ro he, espeCi lly

{11

those which have been derived from clastics by graniti-
zation due to lit-par-lit injection or allied process.
?herefore, a camparison and czntrast between the
structures and textures of the "red rock“ ?Ld those 0.
metamorphics .ieht be gade as follows:
(1) Several generations of niherel growth are eVi-

dent in th "red rock". Lagnetite, for instance, is

Often present in three, or even four, distinct Sizes,

.ile metamorphic min rals teri to be of one

.-
~

(2) A normal pregiessive erys s‘li"ficn, t“;ieai

I
be!»

is

21.

a

(*9 i~ .,-. ...I‘ ‘11. 1." g. 1.“ ,— .-
., .1. E;KLCOLLC' J. (:6 -S ’ Lay.) .o'j. .’~ 6“

Eh

; ee in the "red roe t", older,
basic, minerals included in younger, more acidic, ones.

In lht‘.0FwLiu roots, CfoJL. lliz ati on of all mirczals is
often contemporary, ard produces a crystalloblastic texture,
all minerals included in tne others. Cther metamorphic
rocks, sepecialiy contact as amorohies, stow a reverse

"\

order of i'ys t l_lization, acidic minerals iorming first,
followed b? basic hirerals.

L

S

"7

7531'

L
.L

9:

el

t“;

20 red , indie :tin; progressive crystal-

he
(:1
V

»n and progressive charge in composition, are present

F)
H.
N
m
t'T'
l—’°
F)

n every specimen of the "red rock" studied. In dtSt t ;es

Ho

of metamorphic rocks, feldspars are unzoned, due to simul-
taneous developnent of all ninera s.

(4) Sta rp bourda ried phenocrysts of guar,z and ortho-

elas e, as found in the "red rock", are seldom develoged in
metamorphic rocks. Ihenoerysts in metamorphics are usually

high temperature arhydrous tinerals more or less t
size, and in the eese of porphvro“ias
and rounded.

(5) Cry,s tellitic growth such as globulites, mar-

01

gar ites, trichite s, cumulites, nd skeleton crystals,
abundant in the "red rock", are rare in metamorphic

I‘OOCS.

(d) Spherulitic and radiolitic textures are almost
universal in the "red rock" but are rare in metamorphies.

(7) jutaxitic structure is present in the "red rock".
The foliation is relatively continuous, with rinerals
crystallizing subnornal to them in most cases. In meta-
morphic rocks, true eutaxitic structure is absent. In these,
only a lineation or foliation of minerals is develOped and,
depending upon the type of metamorphism, is either strictly
normal to compression or strictly parallel to planes of
weakness in the original elastic rock (H. F. Read, 1959,
pp. 772, 773).

(8) Although some crystals in the "red rock" are
strained, they are surrounded by later crystals which are
not. Crystals in metamorphic rocks are generally strained
or deformed.

(a) Typical metamorphic winerals, such as staurolite,
garnet, serieite, actinolite, cyanite, and tourmaline, are
universally absent in the "red rock".

(13) Tridymite, glass, end other primary igneous min-
erals and mineraloids, comhon in flow rocks, and found in
the "red rock", are rarely, if ever, developed in metamorphic
rocks.

Kanner of Emplacement; The evidence indicating an

 

 

igneous origin for the "red rock" likewise indicates that
it is extrusive, although textures and structures in a few
specimens might suggest an intrusive manner of emplacement.

Fest "red rock" specinens can be recognized as extrusive

I
O )
IN)

I

rather than intrusive from the following comparisons and
contrasts;

(l) Puff, agglomerate, volcanic dust, and other
pyroelastie materials are found at the tops of some "red
rock" flows or interbedded with them. Pyroclastic
materials of this type are absent in intrusive rocks.

(2) Sutaxitic flow structure is well develOped in
most of the "red rock". Such structure is, according to
Balk (1957, p. 91), weakly developed in laccolithic and
other near-surface intrusions; nor is eutaxitie structure,
with minerals oriented subnormal to the foliation, developed
in dikes or sills. Such rock bodies possess only a
foliation or lineation of oriented minerals.

(3) Eutaxitic structure, as finely banded as that in
the "red rock", is rare in intrusives.

(4) Glassy textures, including spherulitic and crys-
tallitic forms and glass, abundant in the "red rock", are
seldom developed in intrusive rocks, and if present, occur
only at chilled contacts.

(5) Although foliation of the "red rock" is usually
well developed at, and subparallel to, contacts with ad-
jacent rocks, these contact zones are not gneissic, or
obviously chilled, as is often the case in intrusive rocks.

(6) Although miarolitization is not by any means
prevalent in the "red rock", it is, nevertheless, much

more common than in intrusives.

(7) Voids in the "red rock" are often large, elon-

gate, and sinuous. Voids in intrusive rocks, if present at
all, tend toward sphericity and small size because of
greater pressure and less movement.

(8) The "red rock" lacks pegmatitic zones --with the
exception of miarolitic cavities; intrusive bodies often
have them.

(9) The "red rock" is aphanitic; intrusive rocks are
usually pheneritic.

(10) The "red rock" has abundant phenocrysts in a
microerystalline to microcryptocrystalline groundeass.
Intrusives seldom crystallize as a fine grained grourdmass
with phenocrysts.

(ll) Phenocrysts, although common in th "red rock",
are larger and more abundant in intrusive, especially
hypabyssal, rocks.

(12) Tridymite, high temperature 3132, observed in the
"red rock", is seldom if ever developed in intrusives.

(15) The length-width ratio of netanorphic minerals is
usually greater than that of the minerals in the "red rock".

(14) Tension fractures, formed in the "red rock"
during consolidation and immediately filled with the same
magma, are not developed in intrusives. Pressure at greater
depths prevents fissures from forming.

.J

Fineral Iaragenesis: Interpretation of the mineral
paragenesis of the "red rock", based upon inferences de-
rived from observation of mineral associations and textures,

and upon results of previous investigations of extrusive

rocks, especially those of Yellowstone Eark, is as
follows:

(1) “he agma rises in its corduit while scattered
phenocrysts of feldspar and small crystals zircon are
forming. lossibly some small grains of magnetite are l
forming. Vhese grains may group into bundles because of
viscosity differences or because of turbulent flow of the
maéma past 0 struc' tions in the conduit walls. Probably a
linear or planar fluid compositional eterogeneity is pres-
ent. ?his may have been developed by near-surface stoping
of a previously consoli eted heterogeneous rock and flow of
the ifferenti ally viscous material in tte corduit.

(2) Tear the surface, the eagna picks up large guan-

tities of ground water, possibly initiating a new generation

I'D

of crystallization of .agnetite or elds ar or both. The
meter is heterogeneously dispersed uithin the magma, taking

a position within the more viscous, asic, ‘ortions or the

‘

magna, adjacent to the nagnetite.

s.“

(a) jxtr va- tion of the segue tanes place, resulting

rr;
CL}-

. V

1n a change of pa sical enV1ion.en ( a temperature or

(‘7‘,

pressure change, or both). another generation cf magnetite
begins.

(a) .he rag ra beccr s greatl; extended tnrtuet an,
"...evenly distributed, very penetrative, differential,
viscous glow" (J. E. Kayo, 1944, p. 696). Segregacion of
magnetite crvs;"ls irto li"?r s, along nit? the spell

rcon phenocrysts, is accomplished. “hese are segerated

Ho

2.

by ltgéfs of still fluid, and more acidic materiel. At this
time tridymite, which forms betneen 14750 C. and 57? 3.,

Leg1ns to crrs H11 26 ‘lons vit

:I
(

r1
.1
(D

magnetite in the dark

’ \ 1‘ o o n r, o
(a) :artially crust lline material iorms as fibrous
tufts nearly normal to the lagers of “egnetite erains. It

originates at the ea; ne tit e layers and extends

\1
>1
\‘1
0 4
r
*‘5
n
i

them in either direction. 3016 tu.1ts originate at groups
of na¢netite gr;nules \lile ot'ers originate at tridymite

cr"stals. Sore .argerites of

('13

ghetite and small flakes of
biotite develop interstitially in the tufts of radiating
sat erulitic naterial. “he rate of movement of the maria

-

becomes very slow during this period.

(c) Large crgm tals of sub Wedr _ feldsLars form at
the termini of the spherulitic ;rov. th. As consolidation

of the magma progresses, the remaining fluid beco es more

eldew<r crgstCls are

0-

F7.)

acidic. Therefore, these euh dral

J-
I

ortnoclase, and ex remsly high pote ssium orthocl as e at that.
Layers and strings of fluid inclusions occur in great number

H

Waral el to the

l
.—

in the orthoclase. mhe; are oriented, not
cleavage, but to the lev—rs of teenstite grains (the
foliation).

(7) Quartz, along Witfl svall ciantities of ephene and
biotite, are the last minerals to crystillize. “te ouertz
fills the space between Opposing sets of orthoclase crystals
and occupies interstices between tiem. ividence that the

magna is still moving at this

1..
b

izne is shown by orthoclase

- 36 -

crystals bro‘ren off at their bases and inclined toward the

planes of differential movenent. “hose in less reriily
movi 5 layers are inclined toward the direction of greater

noVement, nhile th_se in mrre rapidly moving layers are
snept stay from the direction of greatest movenont (fl. 9,

q

). ”:118 first ferns ed quartz, nhich encloses abundant lines

t‘}

of fluid inclusions oriented in the plane of flow, is

strained. his indicates that some move:nert of the lava
is still ta ring place. The last formed quartz, completing

"“\

the consolidation :f the rock, is usually unstrained, and
fluid inclusions, although fewer in number than in earlier
formed minerals, show little tendency to orient. This

s ceased to move. At the completion

0‘

indicates the lava t

of consolid

SE)

tion, the feldspar phenocr r3s st are Well zoned,
"ith nearly puie TAlSi ?. in the outer zone and more sodic
toward the center.

(8) Subsequent to consolidation, alteration and de-

hes lace Secondary hematite,

Q)

‘0

vitrification of glass t

n, in dust-like particles, cover end

{—10

leucoxene, and heel
obscure all minerals. Secondary calcite Les also, in nany
Specimens obscured the original minerals.

Evidence Indicating a "Tet" Tagna; “hat a large

 

 

H

quantity of water was present in the "red rec: as assumed

in number 2 (9- 34). is indicated by the following obser-
vations;
!

(l) Decrease in tne luantity of water and othe

liquids in a magma increases the vapor pressure. then

sufficient uuantities of liquids have been removed by

crystallization, vapor should form. Yet, quartz and ortho-

. L
U

clase the 1 two minerals to crystallize, and after most

0
Q?
(P

of the liquids have been removed by crystallization, contain
abundant fluid inclusions. in the other hand, the fluid
inclusions rarely contain gas bubbles.

(2} With decrease in liquids and formation of vapor,
vesicles should develop, but vesiculation in the "red rock"
is very low.

(5) For ation of vapor because of inadeuuacy of
liquids results in explosive eruptions with consequent
forretion of large quantities of pumice, scoria, ash, and
other exogenetic pyroclastic material. mhe "red rock"
has little of this material.

(4) large uuantities of water Iesult in the ability
of a magma to remain fluid to much lower temperatures.
Formation of large ouantities of quartz and small uuantities
of tridymite are indicative of low temperatures of con-
solidation in the "red rock".

(5) Likewise, development of orthoclase, rather than
its hig- temperature dimorph, sanidine, indicates a low

consolidation temperature.

15

(e) The presence of large ou ntities of water results

(

in the magma naintainirg low viscosity at low temperatures.
?his is shown by the extreme thinness of the eutaxitic
structure.

(7) Since minerals in the "red rock" have little

tendency to orient With their long axes in the pl're of
flow, the magma must have flov.ed ra:id ly --notWiths ending
its extremely acidic and, therefore, sunp os edly viscous

Jr

nature, and come to rest tefore much crystallization took

(8) As will be brought out in the section on structure,
the flows are relatively thin, also indicative of the
extreme fluidity of the flows.

(9) the ninerels for ed are dependent ufon the
presence of v ter.

(13) is indicated by Iddin s (1899, n. 424),

(m

ization of vater causes forqation cf spherules in areas

Where crys allizat ion would not otherWise tale place.
Spherules are prominent in the "red rock", While glass

“I '3

The assumption that the Water was derived Irot near-

3

surface sourCes was based, in part, ugon the fac.
nas can hold only a small Quantity of water in solution
+2 I"!

o. 38). Since it is evident

“ftér Were available than can be

(0

O

H.)

5'
\

larger euantitie
dissolved in a magma, Water must have been present in an
undissolved state, and its only source could be around Water.

In addition, Water orig inall y in the ma

(D
p;
0
d
H
U)
D
O
m
U)
{‘i
O
C
m
‘L
1‘
CT
(D
cf-
[1‘
4")
O
(5“
’0
(I)
o

Eeteously diSpers
AS Idiinas save (1399, o. 425).
"The heterog enei Ht; of the acid lavas, so far

as is known, is confined to the distribution
of vapors, :res umably of Water, and Suggests

that the water thus irregularly disseminated
has not existed Within the magma long enough
to become uniformly diffused. It must there-
fore be looked upon as water absorbed near
the earths surface."

7

(D

Q)

Classificetion; As indicated on paaes 77 en
V !

 

the "red rock" is a Lalitordrillite, or 1153, by
Johannsen's classification (1932, pp. lel-lol). It is a

rock high in quartz and orthoclase, and has less than 5

percent each of dark minerals and acid plagioclase.

I
15)
O

I

ST'IUCFCLQ
T) 1‘ A;- f-~ ‘
-ll'PaJy oorU.C,uleS

 

Flowa:e Fold The "red rock" is highly flow folded

(D

 

in many places. It is thought that these structures develop
because of viscosity differences in adjacent portions of

a flow (5. B. Vnopf, and Earl Ingerson, 1958, p. 132) and
that less plastic portions were dragged forenard by more
fluid adjacent portions (pl. 11, A). In the "red rock”,
folds as large as 5 meters from trough to apex, Were seen.

-.

s similar to

...-
Q4

Tayo (1944, 9. one) describes flowag fo

’15

those in the "red rock", in a erClite 468 :15 line,

California. Sardberg (1948, pp. 814, 315} describes siviler

'7
E. '-
(T-
O
O
D."
u.
Cf‘
’7
to

ic Ieneerawan flows along

Ho
p:

structures in ac

oa—

Tinnesota;‘Umae floWs are ossioly correlative kiCu tLe

tc i

1

"red rocl'.
She direction in Which the iloW moved cannot be
determined, as fluid portions may occur above, as Well as
belov, more viscous portions. The; file adiainostic, liie

current ripple dares.
7he eutaxitic structure “sually reteirs its

1

co-planarity (pl. ll, 3) even When involve; in flow

edfirg; Lediing is not clearly evident in the field,

 

- _ - ' I-.. ,._ .~ L ,1_', A. ‘L‘ _._ ,-:: ‘ ' .1
but at a fee lOOEllules, as an the southern slut ti

overnnent Zeal, one is repuiied to ascend a series of

step-lite rises over several flows

"...I. . . '7‘ f'1.,“ "' i "N _ , - c . -..’ ._ . 1 . ‘I _ J YT, ‘ _ —
\ Ll ‘..",‘l'l a :1") , d. ..\.;-_I..alr.c.1\vl.an .10)- ‘.,.‘;c.:L.....L.-,- Cit-EL", 1:21?
,-._. . p 'n. Lu . -. 1.. - . - ,. - . - ., . - .. - ..i
lll‘bt 0:3ch Ug’ then 10 ub‘ LtOl-C:lUr 1. art): 6 to USCG-’48 tht

4-D ‘\ «I . Lfif lf‘ \' " r " ’ . ‘ ‘1 ‘5 . rr~ . 7 3' ' x ' '

SUV -...l.(e uL. 10“l::rl;’ JCT-7.41.1. 1th.: LL 0'1] I 1C3 ulLlCiEhtlEL

v “4-,, ‘ r. ’ G \ ‘- 'L ~ r 'r " ‘ ‘ ’- v ~ ~'— -

M€<u19flLv 01 ‘J99rlLCdjskLu qua llomao) Ponever, tLe
, —«. a ‘4. h 1! w- J. a nu __ , \

COKt’ICut L6 (1 .C‘CU alike *LOWD 51C} (04 6"\L.C"’Jw O L‘ die,

“-2 -- vo ~ \ .L'- ., ‘ ., , ~ - - .L‘ 1 r
cvluct-o 9', [11. .ll,‘ . Jumble“, recest'eu, 91-1, o'tlclOl'e,

v . 3. 4—? -‘ 'J- .- ‘ ‘ n ‘ ‘ ' ‘ ' ‘- ‘ —~' « 1.-
COVeieu V1 b.) tQLu-Uo -1; :1 .L‘c.’ 1 .LO ';'_..Lul‘:»:‘ 9&9 UxCOUl.;-. 16.2

v‘ r .- | ' 'J -- , v - W ,~‘ ' ~‘ I 1 s "
MLJ_‘CL C'IU'L uJ-KL-U \J- LLO‘ub 31-6 ("X_.O.:Ed '\;‘.L. 1.1, v) . di J:-COJ"Ll
L. c: r‘ 2' ‘ r L! d c C .- ' ."

LL... ('6 Ll'lL VCK J’sbhs ~'V LC) (lav.
:“ 0 ‘fl 0 _ '1‘. ‘- .¢-- V ’1‘! ." 'H I

leuuir: 1s \ELL later On aeri-l pn UQ;1'_LDO lot all
,.- up _ L, -‘ n~ l- g. L‘\"‘Pr"‘c. 1..., , L-J. . ,. - - _. L;
U--L U" b‘JD bLl‘; LI» .11 C LLJO'J‘VE'L’ :‘14L ’ U'JLLI L'r‘x l IIK’ELJ lU't‘I- 4.1.-
’1. 1"- n ‘ ’1 I :4 L ‘ . \ a " J‘. ‘ I ”v
liable Ohm” :1: ,lotieu 0n ,l-ue la (1r 'CCxtb)o IYL‘lE“+‘
- -~, '.. "11L-,.l.-. H .‘3,- 'J..-, For. J.’ _-,.. ,.. ~9., ,_-
IKSLJ, the chippeta lclsite b tne lel»lu<d .116 over
‘i_ . " (‘- '1’ H '3. 8"” J“. r‘ I :v" \ ’j b ". C L
Li .L.L la CLbO LaC‘kUE--, d". (blueliil 45K“: {JEuLC 4.:4” Lexiev'c 'Lu

, 4* -—-.. u'. . JL' - ,7. W .F «2‘ -. -. 2’.”
The llons are txlu. a bfllCi iloW would QlCLdult have

:econuer; StruCtures

 

Fractures: Practuies in the ”red rocr" include both

 

(I)

' ' - '* ' a . " a J“ ’1 f? a" a n .. -.
JOints and lasté (pl. ll, b). slat l- snot: tn late

.3 er.— ..n.,,_ .L. . . _- r“ .o . .1. m - '4. i, ' , - "
poles 01 9o llactures, and plate 1 is its coxtoureu
,.-...-v,.‘ ,2“... . a..,.-. . 0,, J.” , a. .‘ -._, '._J_.2..
salivalcnt. “he nulber oi pwlnts lo too all to be e abLS‘
O " -— A ~ '.-‘ J— -' A -\ L" ‘ ‘ 3 O l ‘ l- y‘ L. r ‘ I. ~ ~ . .
tloally accurate, and t1; COULLU'Ed 41a;ld., Jeerelore, is

merely an indicat'on, and not a true picture of the streSses

fluldb have acted on the "red rocx". However, it is felt

(Ii
0

C)

Explanation of Elate ll

Contorted flow banding by flow folding in the "red rock"
ex;osed in an outcrop at locality 2. 1 inch eguals

1 foot.

Extremely oarse foliation of "red rocz" at locality

63. ,cte the resistance of more guartziferous layers

to Leatheritg. 1 inch canals 1 foot.

Coarse volcanic agglomerate at locality £2. iota
diversely oriented foliate blocis. 1 inch equals 1.1

fGEto

Pear locality llo on the upper Carp River. Intersection

Pb

o the bedding of basic flows with a major set of
joints controls the course of the stream. The Ledding
dips gently to the left ard the Joints dip steeply

to the right.

 

 

 

 

      
      
  

' RT‘s EQUAL AREA PROJECTION POLAR CASE
- PLe eweo on Low-R newSPHERE

Pumas ARE. MAGNETIC

       

..V fié‘

JGINTs AND uNRecoanzeo FAULTs
. :7; W FAULTS - -

 

L

 

PLATE l3

CONTOURED DIAGRAM EQUIVALENT TO PLATE l2

 

CONTOURS

[W712 .‘T—TMVO
[_ T3270 -5,57.

-j 3‘7» -7,87'

R ET ‘50

that the addition of more readings would only ccnfirm
that is indicated on the contoured diagram.
The first faulting Was shallow and steep angle strike

he rajor reverent along these fau Us was Verticsl,

it's
(1
.5
H
Cl"
(1)
0
*4

but a small amount of lateral movement accompanied the
vertical; the south blocks moved east. Whe shallow faults
dip either north, or scuth, and probably represent shear
surfaces developed as a result of subhorizontal north-

scuth ccmpression. These faults are inferred to be
correlative in age with the main Porcupine Fountain fault --
Which probably digs northward, and with the great Feweenaw
fault to the south near lergland.

Dip faults, u ually vertical, develoyed later. These

(0

are not parallel, as are the strike faults. Skis may be
because they trend near the strike of a set of major joints
and, in some cases, develooed alont the joints rather than
at an angle to them. The nest blocks, in general, moved

down with resyect to the east blocks.

discussion

 

Eeddina: Structural observations lendirr more evidence
“—é 5'

to the extrusive character of the "red rock" are the

(l) Yhe "red rock" is bedded in the form of a series
of lava flows.
(2) Flowege folds, present in the "red rock", do not

generally occur in intrusives.

I
1.0
Q

I

q

(") The overlyir:gs ec1imerts and tra s are not meta-

'0

morphosec at their bases.
(4) The "red rock" apparently maintains one horizon,

remaining just below the mixed basic extrusives and sedi-

U)

mentaries of the A hbed group.

(5) The over lyirg sediments and traps contain fragments
o the "red rock".

(6) lo overlying rocks were seen as xenoliths in
the "red rock".

(7) F0 apophyses or stringers of the "red rock", so
far as is k1o Wh, project intc the cverlyitg roc .cs.

Since the " “h ewa" felsite is mineralogically and
texturally line the "red rock", and since they are both
bedded (extrusive) and apparently occupy the same horizon,
the "red rock" of the Porcupine Teurtains is inferred to
be the same formation as the "Chippewa" felsite. 11
is so, the "red rock" has a maximum thickness of approx-
imately 2,?CC feet, the approximate maximum thickness of
the "Chippewa" felsite as det r ined by diamond drill
holes.

Attitude: It is thtught that subhorizontal, north-
south, compressive forces were responsible for the develop-

he Eorcupire “curtains, the ”old

.—

ment of a large fold in
subsequently denuded, exposing the "red rock" ("Chippewa"
felsite). Yhis fold trends ap roximately east and test.

During this compression, the southern limb of the fold

was thrust above the adjacent rocks to the south. The

upthrown beds were bent down in the vicinity of the fault

I

later, north-south faulting, the nest blocks down-
thrown, displaced the east-west faul s. This later

faulting may have been due to the developnent of tension

fractures in a north-south direction during the first

J

(east-nest) faulting, and nornal faults were the result of

relaxation of compression.

Other forces have acted on the "red rock". Lvidence

from foliation readings indicates numerous seall folds,

west and north-south, superimposed on

trending both east-
the larger anticline. this minor folding may be a northward

extension of the situation described by Allen and Earrett

(1914, o. dd) in he region of lake Cogebic.

b

I
(p )
10

|

fiAr n- vTry-fifi'w -
Vv‘JuUJ—cUL/J.~ 1.x)

fin the basis of the evidence acquired in the prosecution

of this investigation, it is felt that the following major

conclusions are justified:

F0

(1) The "red rock" is igneou
(
(

indeterminable.

ed as lava flows.

0

) The "red rock" was empla

1‘0

()1

) fhe direction from which the lavas care is

(4) The magma was an extremely "net" magma, and the

lows were, consequently, very thin, averagirg less than

to

l

(‘J

feet in thiCKLeS‘

U

()1

(5) The "red rock" is a leucocratic rock, a kali-
tordrillite (1153) by Johannsen's classification (1952,

pp. 141-101) .

(0) fhe "red rock" is the "Chippewa" felsite brought

to the surface by denudation of a large anticline which is

(D

Q]

thrust to tLe south OVer younger rocks. It is the b s.l

meaber cf the Ashbed group in this region.
(7) Its total thickness is less than 2,?30 feet.
(3) fhe folding was probably correlative in time with

development of the great Veweenaw fault.

EIELITCHA ""

Ebu,:hton,Dou:1as, Third annual report of the deals mi 31

U

Survey of lichisan: Iish. point Locs., pp. 487-490, 1841.

Jackson, 3. T., Resort on the geolo :ic cal and minarelogical

survey of the mineral lands of the United States in the

State of Iichigan: 51st Con§., lst Sess., iich . Joint 3005.,
pp. 571- 502, maps, 1819.

to!

Jackson, C. T., idem., pp. 649-696, by J. D. unitney.

Whitney, J. 3., Field notes for 1847; 51st Cong., lst Sess.,

Tich. Joint Docs., 96. 713-758, 1849.

A:

Foster, J. W., and Whitney, J. D., Report on the geology
and topography of a portion of the Lake Superior land district
in the State of ichigan, pt. 1, Copper lands: Slst Cong.,

lst Sess., n. Ex. Doc. ca, 224 pp., maps, 1850.
Vlhitney. JO 1:... i‘emo

Hutbard, Bela, Geological regort of field work in the Lake
Superior Land Dis trict: dist Cong., 2nd Sess., Nich. Joint

Docs., pp. 853-842, 832-952, 1850.

HacFarlane, Thomas, Report on the geology of Lake Suterior;
Canada Geol. Survey nept. Progress for lacs-1506, pp. 115-

145, ldcb.

Irvin-, R. D., The copper-bearing rocks of Lake Zujerior;

- lTl -

U. S. Geol. Survey Ion. 5, 464 pp., maps, 1885.

Irving, 8. 3., and Chamberlain, 9. 0., Observations on the
junction between the Eastern sandstone and Teweenaw series
on fieneenaw Ioint, Lake Superior: U. S. Geol. Survey Bull.

2a, 124 pp., 1835.

Cross, C. 9., Constitution and origin of spherulites in
acid eruptive rocks; Ehil. Soc. Wash. Bull..ll, pp. 411-

445, 1892.

Van hiss, C. 3., A central Wisconsin base-level; Science,

Ye! Ser., Vol. 4, op. 57-59, 1396.

b

Rosiwal, August, Ueber Geometrische Gesteinanalysen,

Verhandle. K. K. Geol. Reichsanstalt, Vien, 1598.

0

=, J. 2., GeoloSy 01

n

Idding the Yellowstone Fational Iarh:

f

U. S. Geol. Survey Yon. 32, pt. 2, ch. 19, The rhyolites,

pp. sap-439, 1899.

Wright, F. 3., Report of the progress made by the Porcupine
Fountain party during the summer of 19C5; Tich. Geol. Survey

Ann. Eept., 1933, pp. 35-44, 1935.

Gordon, W. C., assisted by Lane, A. C., A geological section
from Bessemer down Black River: rich. Geol. Survey Ann. Rept.,

1930, pp. 405-507, maps, 1930.

fiuthven, A. 3., Ln ecological survey in the Porcupine

Jountains and Isle Royale, Tichigan: Tich. Geol. Survey

- 1C2 -

Ann. Lgepto’ 19b5, pp. 17‘55, lgf‘o.

Wright, E. 3., and Lane, A. 3., Preliminary geologic map
of the Porcupine Tountains; rich. feel. Survey Ann, Rept.,

Lane, A. C., The feweenawan series of fiichigan; Tich.

Gaol. Survey Ann. fiept., 19T9, 2 vols., 985 pp., 1911.

Van Hise, C. 3., and Leith, C. Y., The geology of the Lake
Superior region: U. S. 9801. Survey Ton. 52, 641 pp., maps,

1911.

Allen, R. 3., and Larrett, L. 2., Contributions to the pre-
Cambrian geology of northern Fichigan and Wisconsin: Tich.

Ceol. Survey Puhl. 18, Ceol. Ser. 15, pp. 13-104, maps, 1914.

Hotchkiss, W. 0., The Lake Superior geosyncline; Geol. Soc.

America Eu11., Vol 34, Yo. 4, pp. c69-d78, 1923.

'\

Butler, E. 3., and Lurbank, J. 3., The copper deposits of

lichigan: U. 5. Ceol. Survey Irof. Eaper 144, 258 pp., 1929.

tohannsen, Albert, A descriptive petrogranhv of the igneous

rocks, Vol. 1, 318 pp., Vniversity of Chicago Press, Chicago,

Illinois, 1952.

Yrumbein, W. C., Thin-section mechanical analyses of

,—

induratcd sediments: Jour. 9601., Vol. 45, IO. 0, pp. 492-

La

49c, 1935.

fichigan Geological Survey, Centennial map: iich. Geol.

- 1C5 -

REEto, 1956, 19360

Survey Ann.
balk, Lobert, Structural behavior
em. 5, 177 pp., 1937.

fl.

America
Structural petrologv

SOC.

Ynopf, 5. 3., and Itgerson, Earl,

Geol. Soc. America Fem. 6, 27? pp., 1958.

Sandberg, A. E., Section across Veneenawan lavas at Duluth,
'- ' o

'O

ota: Geol. Soc. America Bu11., Vol. 49, 10. o, p

Tinnes.
tion: Iature, Vol.

‘q
a
U.

Ketamorphism and igneous

Optical mineralogy, 2nd
94

3‘7)

Rogers, A. 3., and Ierr, I. 3.,
ed., 393 pp., TcGrew-Eill hook Co., Inc., Iew York, 1 .

Rhyolite near Big Fine, California; ”eel

Yayo, J. 3.,
Aaerica Eu11., V01. 55, Yo. 5, pp. 599-619, 1944.

Soc.
Igneous minerals and rocks, 307 pp.,

v P
u. 130,

Wahlstrom,
Sons, Inc., Lew York, 1947.

John Tiley

John Wiley &
\hand, 3. J., Eruptive rocks, 5rd ed., 488 pp.,

cur,

a Sons, Inc., Ken York, 1949.
grain-size measurements made

the bias of
VClo 58’ 1:0. 2’ pp. 15U-1DO'

Chayes, 3., 3n
in thin section; Jour. 7e01,
195?.
fi, H. H., A field and petrographic study of the

,_ -1o4-

1.,

sandstones and conglomerates of the Porcupine Truntains,

Entonaron County, fiichigan, Unpublished Iaster's Thesis,

‘

iichigan State College of Agriculture and Applied Science,

“aSt lensing, Fichigan 11? ms. 99.. 1959.
Sichmeier, A. H., t. G

. Weather Iureau, East lensing
Station, personal communication.

Kelly, 7

. A., Department 02 Geology and deggrapby’

State College of Agriculture and Applied Science,
communication.

~N-\\ \ \

x e 4.24:

 

 

- 3:3...

I. l . ...
I’L‘FMIOI 1b\\.

43?.

/
J
:‘r

 

9

W912?

 

"TIE 1111:1917 @lflITMleflflllllllill

 

it

754