Teen ck cuabch earns she am oe a 5s Dattu tter ia ceraeta ac en men =a enon aero er ee Se rt es = et teaver a senenerwaeeneree: or, A it Pe at PATO Cy DEPARTMENT OF THE INTERIOR MONOGRAPHS OF THE UNITED STATES GEOLOGICAL SURVEY VWiOGU ME. -V WASHINGTON GOVERNMENT PRINTING OFFICE 1583 + 4) *¥ ren “ ee Arar ehisscah, es UNITED STATES GEOLOGICAL SURVEY CLARENCE KING DIRECTOR COmr ine bwARENG ROCKS OF Mer, SUF GEOR By ROLAND DUBE IRV ING WeASS EET N GON GOVERNMENT PRINTING OFFICE 1883 PLS See a he a aa (91 VEL BIO tg ates ‘ Newport, R. I., October 23, 1881. Sir: I have the honor to transmit herewith the manuscript of the text and illustrations of Prof. Roland D, Irving’s memoir on the Copper-Bearing Rocks of Lake Superior. Very respectfully, your obedient servant, RAPHAEL PUMPELLY, In charge of Division of Mining Geology. Hon. Criarence Kina, Director of the United States Geological Survey. ek, iF lili Met or ELE on 5 4k ~h. ; - vik eres ys zy ak University or Wisconsin, DEPARTMENT OF GEOLOGY AND MINERALOGY, Madison, October 15, 1881. Str: I send you herewith the manuscript of my memoir on the Copper- Bearing or Keweenawan Rocks of Lake Superior. I an, sir, with great respect, your very obedient servant, ROLAND D. IRVING. RapHaEL PumPELty, In charge Division Mining Geology, United States Geological Survey, Newport, R. I. 4 * u“ é 5 Fy +e Ss. ~ part pris b Ay Pipen gh 9 <8 ry : ; - see ates Vth idl aera gps : tPA eB oaat he shar aie Lak yaa: ae el Fo 4 rT eee 4 PEE a ee ; | ge ee Pop! haste ae piace aa od (Uae rae . at x aqui Peo ROR: a) aban ata ; et lavas ate ene ree nee ees ae, tar se : ra - Mian eden 3 Ae Pines ; a ; Aas ny ai Re % i bts Sa “nh: ae ght 3 7 yay : fie Bae apf : ? ‘ ee s y + J y * . ‘ ve . - - @ as Fh a a) pall Les —_ COIN ES IN Ws. CUArICR lhl NORODTOLOR Siac tee a amas sien acenadae\som sins Gioae dsoemelcns Soaeideeelassar cence JIG UO RAMOINO) Saee SS a5s0 (Gecing Souso5 DeOOCO SSO aoa SS ScO Do OOCO OG060S CODCUIOODES too ssc once. 5 CHAPTER IJ.—EXTENT AND GENERAL NATURE OF THE KEWEENAW SERIES......-.-------- =55 CHAPTER Tl — Inn OLOGY; OMMEME ICH WEENAW, SERIES) ..<.cc0.cccss< wslceeeicc sc ceriecimesiccscncls SECIIONG le —-b ASIC ORIGINAM MR OCK Siar cece sariacce se cele teeieee Sem cemin oe eciceeaisteiecieesscee SECTION Ue-— ACID ORIGINATUMROCKS coc ccenerce. sneee ecm es ee eoce gece recess esses cies SrecTion III.—SumMMaRy VIEW OF THE ORIGINAL ROCKS OF THE KEWEENAW SERIES ..--- SECON Ve—DETRITAL ROOKS oe oa esas ees pein clnin wpe mioets memes eee = Cuapter [V.—STRUCTURAL FEATURES OF THE THREE CLASSES OF ROCKS OF TILE KEWEENAW SERIES CHAPTER V.—GENERAL STRATIGRAPHY OF THE KEWEENAW SERIES..-.- Cuapter VI.—Tur KEWEENAWAN ROCKS OF THE SOUTH SHORE OF LAKY INDRODUCIOR Nemes acess ee ieee sical eens civics rele stele ania eeinsictinet ome SECTIONG: — KEWEENAW? OIND saamaciseeee seeccas 16 cece sens as © eicinienceee oi acnn leeninisce se SEcTION II.—THE REGION BETWEEN PORTAGE LAKE AND THE ONTONAGON RIVER ..-.--- SHCHIONML Ue — RHE NS OUMH LANG Hite te senisen en eelasie acaicelcis ceieminiecin eins mista oeisins = toate SrcTIon 1V.—THE REGION BETWEEN THE ONTONAGON RIVER AND NUMAKAGON LAKE OF WISCONSIN, INCLUDING THE PORCUPINE MOUNTAINS. ...--- .----.---------- ---------- SrcTION V.—NORTHWESTERN WISCONSIN AND THE ADJOINING PART OF MINNESOTA ..---- Cuartrer VII.—THE KEWEENAWAN ROCKS OF THE NORTH AND East SHORES OF LAKE SUPE- NIOR sccoceem: Gaeta eee e Se ee nace eaeeee ee eat eases cea wess oh Sse cerebscon Sanit. INTRODUCTORY). <<.--1--="5- = eat a eae ei ncapesie So ee ere te ea esas somine aieieis ae eiet ase sts eels Section I.—THre MINNESOTA COAST Srecrion II.—Is_LE ROYALE TO NIPIGON Bay .-- < SEcTION III.—MICHIPICOTEN ISLAND AND THE East COAST OF LAKE SUPERIOR .-.- -.-.----- CHAPTER VIII.—RELATIONS OF THE KEWEENAW SERIES TO THE ASSOCIATED FORMATIONS.. - SrEcTION I.—To THE NEWER FORMATIONS..---. .---- SEcTION IIJ.—To THE OLDER FORMATIONS... CHAPTER IX.—STRUCTUKE OF THE LAKE SUPERIOR BASIN CHAPTER X.—THE COPPER DEPOSITS.....-.--..---.------------- - Rat ea Sar meee” bes i» hy c ek, an tae a nine See es cso are til coe ee ei sages = are Bhat ieee | ‘ St chong ae Ens ae A a he = Ar {= sobyth ee ini ae ges eal cee soe rate arte CBE UsSsT RATION S. PLaTE I.—General geological map of the Lake Superior Basin. Scale, spahony II.—Thin sections of olivine-free' gabbros - 2... ..---. 2 cec0 cenccs concee cn ccce once Fie. 1.—From half a mile southwest of south point of Beaver Bay, Minn. N. W. 4, Sec. 3, T. 55, R.8 W. Anorthite; non-diallagic augite. Scale, 21 diameters. Fig. 2.—The same in polarized light. Scale, 21 diameters. Fic. 3.—From the North Shore, near Duluth, Minn. N. W.4, Sec. 24, T. 50, R. 14 W. Anorthite; diallagic augite; titaniferous mag- netite; altered olivine. Scale, 30 diameters. Fic. 4.—The same in polarized light. Scale, 30 diameters. Tit:—Thini sections) of; olivine-pabbrosm.cns2s----sc-cesee «oo seecsoetieecsasscecee Fig. 1.—From bed of French River, Minn. N. line, N. E.4, Sec. 7. T. 51, R. 12W. Anorthite; diallage; olivine. Scale, 25 diameters. Fic. 2.—The same in polarized light. Scale, 25 diameters. Fie. 3.—From the north shore of Lake Superior, near the east point of Sucker River Bay, Minn. S. E. 3, Sec. 2, T. 51, R. 12 W. Anorthite ; diallage ; titaniferous magnetite ; olivine. Scale, 25 diameters. Fic. 4.—Large olivines from the same rock as represented in Figs. 1 and 2. Seale, 21 diameters. IV.—Thin section of coarse olivine-gabbro from Bladder Lake, Ashland County, Wis. Labradorite; augite; diallage; olivine, mostly fresh, but partly altered to biotite, viridite, tale and iron oxide; titaniferous magnetite. Scale, 10 diameters ...-......-..- V.— Dhin'sections of. orthoclase-gabbro!- «22-2. 222s ence one concen eee eens cses Fig. 1,.—From near Lester River, Minn. N. E. 4, Sec. 29, T. 51, R. 13 W. Labradorite; orthoclase; augite in twinned blades; dial- lage; titaniferous magnetite; brown alteration-product of angite; secondary quartz. Scale, 20 diameters. Fig. 2.—Another portion of the same section in polarized light, much enlarged. Orthoclase; labradorite; twinned augite; net- 3 work of secondary quartz. Scale, 37 diameters. Fig. 3.—From Bohemian Mountain, near Lac La Belle, Keweenaw Point. N. E. 4, Sec. 32, T. 58, R. 29 W. Red-stained oligoclase and orthoclase; diallage altered to uralite; titaniferous magnetite and gray substance from its alteration; large apatites. Scale, 20 diameters. Fig. 4.—From Brunschweiler’s River, Wis. S. E. 7, Sec. 16, T. 45, R.4 W. Labradorite; orthoclase; titaniferous magnetite; augite; secondary quartz; apatite. In polarized light. Scale, 25 diameters. xI Page. 40 5 50 Xxil ILLUSTRATIONS. Pratt VI.—Thin section of very coarse orthoclase-gabbro, from near Duluth, Minn. N. W. i, Sec. 28, T. 50, R. 14 W. (1800 N. 2000 W.). Oligo- clase; some orthoclase ; diallage, largely altered to uralite, which on cross-section shows the hornblende cleavage; titaniferous magnetite mostly surrounded by a border of brown oxide of iron, iu which are developed biotite blades; very large apatites; a little chlorite; rare pyrite particles surrounded by an ocherous alteration. Scale, 10 diameters. VII.—Thin sections of hornblende-gabbro and of anorthite rock... .-.. paccomesacao Fic, 1.—From Ashland County, Wis. N. W. cor. Sec. 35, T. 45, R. 4 W. Labradorite; orthoclase; augite partly altered to viridite and uralite; brown hornblende in and away from the augite; titaniferous magnetite; apatite. Scale, 36 diame- ters. Fic. 2—From Ashland County, Wis. N. line of N. W. 4, Sec. 17, T. 44, R.8W. Oligoclase; orthoclase; brown hornblende; dial- lage altered to green uralite; titaniferous magnetite; rare quartz; very abundant and large apatites. Scale, 26 diame- ters. Fic. 3.—From English Lake, at outlet, S. 4, See. 5, T. 44, R. 3 W., Wis. Brown hornblende grading iuto augite; labradorite; mag- netite. Scale, 23 diameters. Fic 4.—Anorthite-rock from north shore of Luke Superior. N. 4, 8. W. 3, Sec. 5, T. 54, R.8 W. Seale, 17 diameters. YVIII.—Thin sections of pseudamyydaloidal diabase and diabase -.-.---..--.----.--- Fig. 1.—From Union Mine “vein,” N. W. 4, Sec. 27, I. 51, R. 42 W. (1950 -N. 1750 W.), Poreupine Mountains, Mich. Oligoclase or labradorite; augite wholly altered to green and brown pseudomorphs; calcite; chlorite pseudamysdules. Scale, 26 diameters, Fic. 2.—From the Fond du Lae Mine, Douglas County, Wis. N. E. 4, Sec. 8, T. 47, R. 14 W. Oligoclase; augite altered to red- dish brown pseudomorph; magnetite; pseudamygdules of chlorite and epidote. Scale, 28 diameters. Fic. 3.—From near the Gogogashugun River, Wis. Sec. 16, T. 46, R. 2 E. Oligoclase, largely altered to chlorite; magnetite in rod-like forms; augite; chlorite pseudamygdules. Scale, 36 diameters. Fig. 4.—Diabase from north shore of Lake Superior below mouth of Split Rock River. . S..W. }, See.5, T. 54, R. 8 W. - Labrador- ite, in small tabular crystals arranged in a common direc- tion; augite, including many labradorites within each crys- tal; magnetite, very abundant in the interspaces of the augites. Seale, 42 diameters. IX.—Thin section of fine-grained olivine-diabase or melaphyr from the north shore of Lake Superior, Minn. S. E. }, Sec. 9, T. 51, R. 12 W. Augite in large areas, including many plagioclases; anor- thite; olivine and magnetite, chiefly in the interspaces of the augites; chlorite pseudamygdules. Scale, 20 diameters. X.—Thin sections of diabase-porphyrite and ashbed-diabase ...--.....------------ Fic. 1.—Diabase-porphyrite from the southeast shore of Michipicoten Island. Base of red and brown stained unindividualized material, minute plagioclases and black magnetite. Por- phyritic labradorite and altered augite. Scale,7 diameters. Fic. 2.—Part of the same section enlarged and as seen between the crossed nicols. Seale, 21 diameters. Page. an a G1 38 FO needle Tiel * = Po: Re. ILLUSTRATIONS. PLATE X—Continued. Fig. 3.—Diabase-porphyrite from Duluth, Minn., bed of Brewery Creek. S. E. 4, Sec. 22, T, 50, R. 14 W. Porphyritie orthoclase and oligoclase, in a base consisting of plagioclase, magnetite, augite, and unindividualized substance. Scale, 144 diam. Fic. 4.—Ashbed-diabase from Frog Creek, Douglas County, Wis. S. W. 3, Sec. 28, T. 42, R.11 W. Plagioclase; augite in grains; magnetite. Scale, 60 diameters. XJ.—Thin section of amygdaloid from the bay above the Great Palisades on the Minnesota coast. S. W.4, Sec. 22, T. 56, R.7 W. Unindi- vidualized ferritic base with plagioclases; gas cavities filled with fragmental material from above, and containing cal- cite deposited after the fragmental material. Scale, 24 diam. XII.—Thin sections of quartziferous porphyry ........-........------------------ Fic. 1.—From Yoreh Lake Railroad, Keweenaw Point. Sec. 36, T. 56, R. 33 W. Matrix with particles showing flowage; ortho- clase; rounded quartz crystals. Scale, 15 diameters. Fie. 2.—From a pebble of the Calumet conglomerate, Calumet Mine, Ke- weenaw Point, Mich. Matrix; porphyritic crystals of orthoclase and quartz. Scale, 12 diameters. Fic. 3.—From the Great Palisades of the north shore of Lake Superior, N. E. 3, Sec. 22, T.56, R.7 W., Minn. Matrix showing flow- age; porphyritic orthoclase and quartz. Seale, 9 diame- ters. Fig. 4.—Part of the same section enlarged, showing flowage lines. Scale, 32 diameters. XIII.—Thin sections of quartziferous porphyry ..........---------..-ses. ---------- Figs. 1,2,3,4,and 7 all represent quartzes in the quartziferous porphyry of Bead Island, at the mouth of Nipigon Straits on the north shore of Lake Superior, Ontario, Canada. Scale, 26 diameters. Fig. 5.—Quartz in quartziferous porphyry from cast shore of Michipicoten Island. Seale, 26 diameters. Fie. 6.—Quartz in quartziferous porphyry from Baptism River Point, north shore of Lake Superior, Minn. S. E. 4, See. 11, T. 56, R.7 W. Seale, 26 diameters. Fig. 8.—Glass inclusions in the quartz of Fig. 6 greatly enlarged, show- ing hair-like devitrification and black hexagonal crystals. Seale, 400 diameters. Fic. 9.—Banded quartz-porphyry from south side of Great Palisades. S. W. 4, See. 22, T. 56, R. 7 W. Drawn from the polished surface of a hand specimen. The quartses appear as black spots. Natural scale. Fic. 10.—Thin section of porphyry shown in Fig. 9, showing flowage banding. Scale, 11 diameters. Fic. 11.—Portion of the same section further enlarged. Scale, 33 diam. Fic. 12.—Portion of the same section enlarged. Scale, 33 diameters. Fig. 13.—Purple felsitic porphyry from the bed of Carp River, Porcupine Mountains, Mich. N. W.4, Sec. 20, T. 51, R. 42 W. Base of unindividualized ferrite-bearing substance charged with secoudary quartz; porphyritic orthoclase. Scale, 22 diam. Fic. 14.—The same section in polarized light. Scale, 22 diameters. Fig. 15.—Pink felsite from north shore of Lake Superior, 8. W. 4, Sec. 28, T. 56, R. 7 W., Minn. Cloudy base completely saturated with unusually coarse networked secondary quartz; ferrite particles and strings of particles. Secale, 2 diameters. Fig. 16.—Part of the same section further enlarged. Scale, 20 diameters. xiii Page. 95- 10k xiv ILLUSTRATIONS. PLATE X1IV.—Thin sections of granitic porphyry or granitell ......-.....-.-..-.-.-.------ Fig. 1.—From Eagle Mountain, T. 63, R.2 W., Minn. Orthoclase crys- tals saturated with corrosion quartz. Scale, 35 diameters. Fic. 2.—The same section in polarized light, showing how numbers of adjacent quartz particles polarize together. Scale, 35 diameters. Fic. 3.—From vein in gabbro of Rice Point Quarry, Duluth, Minn. Orthoclase decomposed, reddened by iron oxide, and filled with secondary quartz, which is largely in regularly out- lined forms like the quartz of “‘graphic granite.” Scale, 25 diameters. Fic. 4.—From area of red rock in the Duluth gabbro. Drawn with the polarized light to show the way in which the larger quartz areas and smaller adjoining ones polarize together. Scale, 25 diameters. XV.—Thin sections of augite-syenite, and granitell or granitic porphyry-.- ..---- Fic. 1.—Uralitic augite-syenite, from area of red rock within the coarse gabbro of Duluth, N. W. 4, Sec. 27, T. 50, R. 14 W., Minn. Orthoelase and oligoclase saturated with secondary quartz, which forms some large areas; greenish uralite; chlorite as an alteration of the feldspars; magnetite. Scale, 20 diameters. Fic. 2.—Angitic granitell from the north shore of Lake Superior, N. E. 4, ° Sec. 32, T. 56, R. 7 W., Minn. Oligoclase and orthoclase in large altered crystals; quartz in large areas, possibly primary; augite, mostly altered to a greenish substance, occurring in clusters between the large feldspars along with smaller feldspar particles. Fic. 3.—Red granitic porphyry from the old Ironton trail, Ashland County, Wis. Sec. 34, T. 46, R. 1 W. Reddened feldspar crystals saturated with graphically arranged secondary quartz; magnetite; greenish chloritic alteration-product. Scale, 27 diameters. Fic. 4.—Augite-syenite pebble from conglomerate at south foot of Mount Bohemia, north side Lac La Belle, Keweenaw Point, N. E. 4, Sec. 32, T. 58, R. 29 W., Mich. Orthoclase (twinned) and labradorite saturated with secondary quartz, both graph- ically arranged, and in exceedingly fine lines along the cleavage directions; augite altered to ferrite. Scale, 27 diameters. XVIi— Thin sections’ of Sand Stones ys ae ce aes ea Fig. 1.—The ‘‘ Nonesuch” copper-bearing sandstone, from the Nonesuch mine, S. E.4, See. 1, T. 51, R. 43 W., Mich. Diabasic detri- tus; porphyry detritus; abundant quartz fragments evi- dently -derived from the quartzes of quartz-porphyry ; magnetite; native copper indicated by the deep red color; one large pebble of a quartziferous porphyry with a char- acteristic quartz-saturated matrix. Scale, 16 diameters. Fic. 2.—Sandstone from the bed of Montreal River, N. E. 4, Sec. 20, T. 47, R. 1 E., Wis. Diabasic detritus; porphyry detritus; rare quartzes; calcite matrix. Scale, 27 diameters. Fic. 3.—Sandstone from near the Copper Falls Mine, Keweenaw Point, Mich. Fragments from the matrix and porphyritic feld- spars of a quartziferous porphyry and from an augite- syenite, with rarer quartz fragments, magnetite particles and fragments of amygdaloid matrix; calcite cement. Scale, 37 diameters. Page. 112 115 127 hes SO ae OE Mel ET NY, s sz » ILLUSTRATIONS. PLatE XVI.—Continued. Fic. 4.—Sandstone from the Calumet Conglomerate, Calumet and Hecla Mine, Keweenaw Point. Detritus of quartziferous por- phyry, consisting of feldspar and quartz fragments and fragments of matrices; magnetite particles; rather large particles of basic rocks; native copper. Scale, 28 diame- ters. XVII.—Geological map of Keweenaw Point, Mich.........-....---.--..------------ XVIII.—Geological sections of Keweenaw Point, Mich .......-.---..-----.----------- XIX.—Geological map of the Porenpine Mountains, Mich.-.-..-----..-------------- XX.—Geological section illustrating the structure of the Porcupine Mountains, Mi clientes eeeuis ean eyae een a son en teeter ae Ne onl idawieive XXI.—Geological sections illustrating the structure of the Porcupine ea agit XXII.—Geological map of the region Berween the Ontonagon River, Mich. 5 “one Nu- np aN AOE) Wee s ocaeageao coo soc ar scdnbe ston o8ee aes XXIII.—Generalized geological sections of the region between Portage Lake, Mich., and the Saint Croix River, Wis-.s------.------..-.-....--. XXIV.—Map showing the positions of the exposures of Keweenawan rocks and Pots- dam sandstone along the lower portions of Snake and Kettle Gays Ni TNS aah nese cen Qocone os adisEeSno BessEadete noeeeS XXV.—Map showing rock exposures in the vicinity of the Upper Saint Croix River, INVA seo tet eee ee ence, ceter i inte a sions nae stele ele XXVI.— Geological map of the moeth west! coast of Lake Sun one So epee cee Onaaeconoe XXVII.—Geological map of Isle Royale and the neighboring mainland -..------.------ ; XXVIII.—Map of the Lake Superior Basin, designed to show the structure and extent of the Keweenawan synclinal ...--........--.-.--...----- XXIX.—Generalized geological sections of the Lake Snperior Basin --.-..-.----------- Fic. 1.—Outlines of coast hills for 20 miles above Grand Marais-.-..--..--..-.----------------- Fic. 2.—Surface contour and arrangement of beds at Eagle Harbor. Represents a distance of PING Tea Aa Se encoce eco sacs coteeg es S016 OeL boo SBSse are SegoD So Se ssoCeacUmeoecp Fic. 3.—Map of exposures in the vicinity of west branch of Ontonagon River, T. 46, R. 41 W., MOTO Tin aps cote anon ESS SOBER IASI SOS5 BAS 50 BA05 HSC EE COC OoSE Oper EE ey caso sace ee EOS Fic. 4.—Map of exposures on upper Carp River, Porcupine Mountains. One inch= 90 paces. PIG) 5.—Cross-sectionon line GD) of Big, 42, 22-22 o ~~ oe cae eo = Ore owe ann =~ eee Fig. 6.—Section on line A B of Fig. 4 ......-. ---..<---- - << 23 1s ons 2-32 eos ee one Fig. 7.—Showing unconformable contact between Keweenawan diabase-porphyry and Pots- dam sandstone at Taylor’s Falls, Minn.; after Chamberlin -.-..--..---.---------- Fic. 8.—Map of exposures on Kettle River, Sec. 22, T. 41, R.20 W., Minn. Scale, 4 inches to LARGO MT )e, sone ecodSE BeOS Ae COS RSE Sa RS BOOsod CE SE oeOsSece clas pec cee EeSe DoS eso UbnooS Fic. 9.—Section on line AB of Fig. 8. Scale horizontal, 8 inches to the mile; vertical 300 feet to) the wnC Ws aete sama ae las ae ne eters oe wie lel eieeieininie [-limiaisinl oS iei> sie siemn=l =e mie Fie. 10.—Section on the gorge of Black River, Bowplas (Cotnings, Wit conecs sooesscseseedaoras Fic. 11.—Section in the gorge of Copper Creek, Douglas County, Wis.-..-.------------------- Fic. 12.—Sketch of a cliff-side near Agate Bay, Minn., illustrating the warped bedding of layers. The dip is toward the observer -.-.--. --------------++---++--+--+-------- Fic. 13.—Sandstone ‘‘ veins,” Minnesota coast—plan. ---.-- - “Sno caas sseocoseceensancdcccsbstes Fig. 14.—Sketch of cliff on Minnesota coast, showing penetration of fissures of amygdaloid by BANGStONG eee cee ees = ane = oo www veins aeelna nina welnienm oman ae wenninelmerwensecner Fig. 15.—Dike, two miles below Lester River, Minnesota coast ..-.------------------+-------- Fic. 16.—Generalized section of Portage Bay Island, Minnesota coast.-....------------------- Fig. 17.—Sketch-map of rock exposures near Split Rock River, Minnesota coast, T. 54, R.8 W- Fic. 18.—Sketch-map of rock exposures in the vicinity of Beaver Bay, Minnesota coast, T. 55, XV Page. XVl ILLUSTRATIONS. Hie. 19'—Sectionion! beaver River, Minn =~ -22o-. -2---c coon nsesenence as saeelanma eee neers Fic. 20.—Sketch-map of exposures, Minnesota coast, Sec. 32, T. 56, R. 7 Ww. Bear O dane aeenadsto Fic. 21.—Section of wall DE of Fig. 20.-....-.--- BE BOO Sa iSO eo BEB Ben a OCSmed Cana nSe= Pie. 22,—Rlowagestracture in felsite/=.2. . css se= seer ee smal eee =e eee See eee Fie. 23.—Sketch-map of rock exposures in the vicinity of Great Palisades and Baptism River, Minnesota Coast). = olan eee epee ae eee aera eee Fic. 24.—Section on south cliff of the Great Palisades, Minnesota coast .--.-..----.---------- Fig. 25.—Dike in quartz-porphyry, Red Rock Bay. .-....-.-.---.---..--. ---------------------- Fic. 26.—Profile of island at mouth of Two Islands River. -......----.---------------------- EIG:27-—Sechion on LRemiperancey elven ese ese at ale eee ate eae alee ee Fic. 28.—Section on Minnesota coast, near empceance IREVien (sis sae s2 reo t een eee teeiaee Fic. 29.—Section on Minnesota coast, near Baptism River - ..-. --....-.-----.-.--------------- Fig. 30.—Showing relation of the Eastern Sandstone and Keweenawan melaphyr, Béte Grise Bay. Length of section, about 150 feet .....-.......-....---------.------------- K1G. 31.—Section on the Hungarian River, Keweenaw Point --...--.----.---..----.---------- Fic. 32.—Section showing relation of Eastern Sandstone to Keweenawan diabase, T. 50, R. 29 Nop GH AS BS oe oricod Spe oenoections HeSond GsEpseesbess costes seDeod Sead soase Fig. 33.—Bed of intrusive diabase in Seer slates, Pigeon Bay, Canada. -.....-.--.-....... Fic. 34.—Generalized section, showing hypothetical relation of the Animikie Group to the Vermillion Lake schiste=- <= 0- <2 -<-5-(- oe coe ae on clone eer eaenie ae Sesreneleee tea Fic. 35.—Outline geological map of the Nipigon Lake region, after a manuscript by R. Bell -. Fic. 36.—Hypothetical section of Lake Superior Basin ..--....---..----.---. ---------------- . 37.—Cross-sections of gorge of Black River, Douglas County, Wis .-....---..---- ------ THE COPPER-BEARING ROCKS OF LAKE SUPERIOR. BY R. D. IRVING. CoH. Az PT Halts I. INTRODUCTORY. Aim of this memoir.—Obstacles to the earlier accomplishment of this aim.—Investigations necessary to it.—Time allotted to these investigations.—Plan of field work.—Special areas studied by the sev- eral parties.—Acknowledgments of outside assistance.—Explanation of the irregularities in the amount of detail used in this memoir.—Previous examinations and accounts of the copper-bearing rocks of Lake Superior.—List of works from which facts have been drawn for this memoir.— General nature of the information drawn from each.—Account of different theoretical views as to the origin and geological relations of the copper-bearing rocks.—Different views as to the origin of the conglomerates; of the “traps” and amygdaloids; of the felsitic rocks.—Different views as to the geological relations of the copper-bearing rocks.— Use of the term ‘‘Keweenawan.”—These conflicting views have arisen in large measure from the small scope of the examinations of any one geologist.—Literature of the subject. This memoir aims at a general exposition of the nature, structure, and extent of the series of rocks in which occurs the well-known native copper of Lake Superior. This is a work which has never been attempted before, nor could it have been accomplished sooner. A number of geologists have written on different portions of the Lake Superior basin during the past fifty years, but until very recently any attempt to compile a general account of the copper-bearing rocks would have met with some insuperable obstacles. Not to speak of the difficulties to be encountered in trying to reconcile the con- flicting statements of different authors, any one making the attempt would have met the two serious obstacles of nearly complete ignorance as to the nature of the crystalline rocks which form so large a part of the series, and complete ignorance as to the distribution and structural relations of the (1) 2 COPPER-BEARING ROCKS OF LAKE SUPERIOR. formations of the western end of the Lake Superior Basin, both on the Minne- sota and Wisconsin sides. The first of these obstacles was in part removed by the microscopic studies of Professor Pumpelly, whose conclusions as to the nature of the Keweenaw Point rocks were published in 1878.1 The second was also in part removed by the investigations of the Wisconsin Geological Survey, whose results as to that portion of Wisconsin which bor- ders on Lake Superior were first published in 1880.° There still remained unknown, however, a wide extent of the series in Minnesota, a most import- ant omission, since in this region only is it possible to connect the rocks of the South and North Shores. The rocks of the southern range of Keweenaw Point were also still very vaguely known, and the structure of the Porcu- pine Mountains had never yet been made out. é It thus became necessary for any one attempting to present anything like a general account of the series to cover these gaps, and extend the micro- scopic investigations begun by Professor Pumpelly, so far as possible, over the whole extent of the series. It was also necessary that he should famil- iarize himself as much as possible with those districts which had already been more or less thoroughly worked up, by studying the descriptions of others on the ground. This work, including also the preparation of this memoir, I have undertaken to accomplish during the months between July, 1880, and March, 1882—short enough a time, especially when a large share of it has been given to other work. I was, however, already quite familiar with the series as developed in Wisconsin, with the microscopic characters of its rocks, so far as previously known, and with the literature of the sub- ject; so that, with the aid of several assistants, I have been enabled to accomplish the main objects aimed at. My chief regret in connection with the field work, which was of necessity confined to the season of 1880, has been my inability, on account of lack of time, to visit Isle Royale, the region about Lake Nipigon, and Michipicoten Island. The full descriptions of these places, given respectively by Foster and Whitney, Bell and Macfarlane, together with a type suite of specimens collected by the latter gentleman at 1““Metasomatic Development of the Copper-Bearing Rocks of Lake Superior.” Proc. Am. Acad., 1878, XIII, 253-309. 2R. D, Irving, R. Pumpelly, E. T. Sweet, T. C. Chamberlin, and M. Strong, in the Geology of Wisconsin, Vol. III. PLAN OF FIELD WORK. 3 Michipicoten, and kindly sent me by the Director of the Geological Survey of Canada, help to supply this deficiency in some measure. My plan of field work, as carried out, included: (1) a study of the north shore of the lake from Duluth to Nipigon Bay, including excur- sions up the principal streams for distances of from five to twenty niles ; (2) a trip from Grand Marais, on the North Shore, northward and westward to the headwaters of Cascade and Brulé Rivers, including an examination of the country about Brulé Lake and Eagle Mountain, a region never be- fore visited by any geologist; (8) a very rapid examination of the east coast from the Sault to Mamainse; (4) a study of the well-known mining region of Keweenaw Point, including the little-known district in the vicinity of Mount Houghton; (5) a comparatively thorough examination of the Porcupine Mountains, a knowledge of whose hitherto unknown structure was necessary to the understanding of that of the entire lake basin; (6) an examination of Silver Mountain, southwest from L’Anse; (7) a rapid exploration of the “‘South Copper Range,” eastward from Lake Agogebic; (8) an examination of the valleys of the Kettle and Snake rivers in Minnesota, with the view of determining the extent of the copper- bearing rocks in that direction, and the manner in which they terminate westward; (9) an examination of the valley of the Cloquet River to its junction with the Saint Louis, and of the latter stream from this junction to its mouth. Such extended investigations could not be all carried out in person in one season. My own immediate attention was given to the north shore of the lake from Duluth to Nipigon Bay, to the region of Portage Lake and Mount Houghton, and to the region south of Ontonagon. In the other work I was aided by Messrs. W. M. Chauvenet, A. C. Camp- bell, R. McKinlay, L. G. Emerson, and B. N. White. Messrs. McKinlay and Campbell made the river trips between Duluth and Grand Marais; Messrs. Chauvenet and McKinlay together examined the country from Grand Marais to Brulé Lake, and the valleys of the Cloquet and Saint Louis Rivers; Mr. McKinlay alone examined the valleys of the Snake and Kettle Rivers; Mr. A. C. Campbell made the trip from the Sault to Ma- mainse; Messrs. Chauvenet and White together studied the eastern half of 4 COPPER-BEARING ROCKS OF LAKE SUPERIOR. the Poreupine Mountains, while Messrs. Campbell and McKinlay took the western part. Besides the aid received from those directly connected with the work, I have to thank for assistance also a number of others, and especially the following gentlemen: Professor 'T. C. Chamberlin, for notes of observations on Snake River, Minnesota; Professor A. H. Chester, of Hamilton College, Clinton, N. Y., for a series of notes, accompanied by specimens, on the rocks of the Vermillion Lake region, and of the north shore of Nipigon Bay; A. R. C. Selwyn, Director of the Geological Survey of Canada, for informa- tion and for a suite of specimens illustrating Macfarlane’s reports on Michipi- coten Island; Professor N. H. Winchell, State Geologist of Minnesota, for loan of township plats of the Minnesota coast, and for information with regard to the back country between Pigeon River and the lake shore; Frank Klapetko, of the Delaware Mine, Keweenaw Point, for measurements made in the vicinity of Lac La Belle; Messrs. John Chassells and J. R. Devereux, of Houghton, for sundry favors; B.C. Chynoweth, agent of the Mass mine, Ontonagon, for assistance in that region; and B. N. White, of Ontonagon, for information as to the course of the slate belt of the Porcupine Moun- tains to the eastward. Mr. White had traced out this belt to some distance east of the Ontonagon, and kindly gave to me all the results of his labor. The combination of the results of previous work and of new original observations, by which this memoir must be made up, have compelled great irregularity in the amount of detail given in describing the different dis- tricts. So far as the statements are based upon older work, detail has been generally omitted, but whenever I have felt it necessary to differ from pre- vious writers, and in all new descriptions, I have used detail freely. The list of geologists who have during the last fifty years, from time to time, written on the group of rocks which forms the subject of this memoir isa long one. Omitting the names of those whose writings have not been based on personal examinations, or have been preceded only by very slight examination, or are obviously unworthy of notice from lack of geo- logical knowledge on the part of the authors, I may mention the fol- phere > EARLIER WRITERS. 5 lowing geologists as having written more or less copiously upon this subject, the dates of the first and last publications being added in each case: Bigsby, 1824-1852; Bayfield, 1829; Houghton, 1831-1844; Jackson, 1845-1869; Hubbard, 1846-1850; Logan, 1846-1866; D. D. Owen, 1847-1852; Foster and Whitney, 1849-1861; Louis Agassiz, 1850-1%59; Marcou, 1850-1859; Norwood, 1852; Whittlesey, 1852-1877; Rivot, 1855-1856; Hunt, 1861-1878; Macfarlane, 1866-1869; Alexander Agas- siz, 18677 Bell, 1869-1875; Pumpelly, 1872-1880; Marvine, 1873; Brooks, 1873-1876; Rominger, 1873-1876; Irving, 1874-1880; Sweet, 1875-1880; Chamberlin and Strong, 1880; N. H. Winchell, 1879-1881; and Wads- worth, 1880. The preparation of anything like a satisfactory account of the explorations upon which the numerous writings of these geologists have been based, or of the writings themselves, would have taken away more time than I could afford to lose from the original studies necessary to my own work, and I therefore have not attempted it. I have, of course, familiarized myself with these writings, but the pro- portion of them from which I have drawn facts for incorporation into this memoir is a small one. I name them here in order of time of publication: J. W. Foster’s and J. D. Whitney’s joint ‘“‘Report on the Geology and Topography of a Portion of the Lake Superior Land District in the State of Michigan, Part I, Copper Lands,” made to the Commissioner of the Gen- eral Land Office, 1850; Sir W. E. Logan’s ‘Geology of Canada,” 1863; Thomas Macfarlane’s, ‘Report on Lake Superior,” in the Report of Prog- ress of the Geological Survey of Canada for 186366; the same gentle- man’s paper “On the Geology and Silver Ore of Wood’s Location, ‘Thunder Cape, Lake Superior,” published in the Canadian Naturalist for 1869; Robert Bell’s reports on the regions north and east of Lake Superior, published in the Report of Progress of the Geological Survey of Canada for the years 186669, 187071, and 1872—73; the report of R. Pumpelly and A. R. Marvine on the copper-bearing rocks of Keweenaw Point, in the Geological Survey of Michigan, Vol. I, 1869-73, Part IT; R. Pum- pelly’s paper on the “‘Metasomatic Development of the Copper-Bearing Rocks of Lake Superior,” published in the Proceedings of the American Academy of Arts and Sciences, Vol. XIII, p. 268, 1878, and “Lithology 6 COPPER-BEARING ROCKS OF LAKE SUPERIOR. of the Keweenawan System,” published in Vol. III of the Geology of Wis- consin, 1880; my own reports on the ‘Geological Structure of Northern Wisconsin” and ‘‘Geology of the Eastern Lake Superior District” of Wis- consin, both in Vol. III, Geology of Wisconsin, 1880; E. T. Sweet’s report on the ‘Geology of the Western Lake Superior District,” in the same volume; T’. C. Chamberlin’s and M. Strong’s joint report on the ‘Geology of the Upper St. Croix District,” also in the same volume; and N. H. Winchell’s “Ninth Annual Report of the Geological and Natural History Survey of Minnesota,” 1880. In every case where I have taken information from these works I have indicated it by direct reference. It will, perhaps, be well to give a gen- eral statement here as to the extent of my indebtedness to each of them. Foster and Whitney’s work applies solely to that portion of the copper- bearing series which is included within the state of Michigan, 7. e., to the region lying between the eastern extremity of Keweenaw Point and the Montreal River, and to Isle Royale. For my statements as to Isle Royale I have had to depend almost exclusively upon this work, read in the light of my own experience. The former district I have myself examined, and have only used Foster and Whitney’s statements, chiefly to aid in mapping, as supplementary to my own observations. Logan, in his geology of Canada, describes briefly all of the rocks of the north and east shores of Lake Superior from the Minnesota boundary to the Sault. I have only drawn from him, however, for the east coast, Michipicoten, and the islands south of Nipigon Bay. Macfarlane’s “‘ Report on Lake Superior” includes a further description of Michipicoten Island and the east coast, having been based on more detailed observation than that of Logan. I have drawn somewhat from this report, but especially have used it for locating the series of Michipicoten rocks sent me by Mr. A. R. C. Selwyn, and which I de- scribe microscopically in Chapters III and VII. The same writer’s account of the Geology of Wood’s Location has aided me in reading rapidly the structure of the peninsula between Black and Thunder bays, though I differ from him in some of his most important conclusions. Dr. Bell’s sev- eral reports on the geology of that portion of Canada north and east of Lake Superior, including a manuscript map based on them, have been FORMER VIEWS AS TO ORIGIN OF CONGLOMERATES. 4 drawn upon liberally for accounts of those regions I have not myself seen, more especially of the Nipigon Lake basin, and for data for mapping away from the lake shore, although I have here again departed from the au- thor in some important points. The descriptions and maps of Messrs. Pumpelly and Marvine, in the first volume of the Geological Survey of Michigan, have furnished a large part of the material from which I have made up my account of the structure of Keweenaw Point. Pumpelly’s microscopic descriptions of the “trap” and amygdaloid of Keweenaw Point have formed the basis for my own microscopic studies, whose results I give especially in Chapter III, in which I have occasion to quote freely from his memoirs above mentioned. The general reports on the geology of Northern Wisconsin included in the third volume of the Geology of Wisconsin, by Messrs. Chamberlin, Strong, Sweet, and myself, have sup- plied all of the material for the description of that region which I shall give in Chapter VI. Upon N. H. Winchell’s reports I have depended for a few locations of rocks in the country back of the Minnesota coast and along the national boundary line. It is desirable that I should give here a brief account of the different views that have been held as to the origin and relations of the copper-bear- ing rocks, although this will involve reference to a number of points whose explanation must be deferred to subsequent pages. This series of rocks is described by all writers as made up of reddish sandstones, conglomerates, “traps,” and amygdaloids, while a few of the authorities recognize also the local development of reddish felsitic or ‘jasper”-like rocks. As to the ori- gin of these several kinds of rocks, however, as to their mutual structural relations, and as to their position in the geological scale, there has been the widest divergence of views. The sandstones of the series appear to have been taken by all as of the usual sedimentary origin, but the conglomerates into which they shade have been regarded both as eruptive and as sedimentary. Messrs. Foster and Whitney, whose work, having been for thirty years the most widely recog- nized authority upon Lake Superior geology, may appropriately be men- 8 COPPER-BEARING ROCKS OF LAKE SUPERIOR. tioned first, maintained the eruptive origin of the bowlder-conglomerates of Keweenaw Point in the following language: The conglomerate of Keweenaw Point and Isle Royale consists of rounded peb- bles of trap, almost invariably of the variety known as amygdaloid, derived probably from the contemporaneous lavas, and rounded fragments of a jaspery rock which may have been a metamorphosed sandstone, the whole cemented by a dark-red iron sand. This cement may be regarded as a mixture of volcanic ash and arenaceous particles, the latter having been derived from the sandstone then in the progress of accumula- tion. It is not unusual to meet with strata composed entirely of arenaceous particles associated with the conglomerate beds; and where these expand to a considerable thickness, the associated sandstone appears in alternating belts of white and red, and exhibits few traces of metamorphism; but where the belts of sedimentary rock are thin, and come in contact with the trappean rocks, the sandstone is converted into ajaspery rock, traversed by divisional planes, and breaking with a conchoidal fracture. The trappean pebbles often attain a magnitude of eighteen inches in diameter. Their surfaces do not present that smooth, polished appearance which results from the attrition of water; in fact, a close observer can readily distinguish between those which have been recently detached from the rock and those which have for a time been exposed to the recent action of the surf. The conglomerate appears to have been formed too rapidly to suppose that the masses were detached and rounded by the action of waves and currents, and depos- ited with silt and sand on the floor of the ancient ocean ; for, while the contemporane- ous sandstone remote from the line of volcanic foci does not exceed three hundred or four hundred feet in thickness, the united thickness of the conglomerate bands in the vicinity of the trappean range on Keweenaw Point exceeds five thousand feet. As we recede for a few miles from the line of the volcanic fissure, these amygdaloid pebbles disappear, and are replaced by arenaceous and argillaceous particles. We are, there- fore, disposed to adopt the theory, as to the origin of such masses, first suggested by Von Buch: “ When basaltic islands and trachytic rocks rise on fissures, friction of the elevated rock against the walls of the fissures causes the elevated rock to be inclosed by conglomerates composed of its own matter. The granules composing the sand- stones of many formations have been separated rather by friction against the erupted volcanic rock than destroyed by the erosive force of a neighboring sea. The existence of these friction conglomerates, which are met with in enormous masses in both hemi- spheres, testifies the intensity of the force with which the erupted rocks have been propelled from the interior through the earth’s crust. The detritus has suddenly been taken up by the waters, which have then deposited it in the strata which it still covers.” Those pebbles having a highly vesicular structure may have been ejected through the fissures, in the form of scoriz, while in a plastic state, and have received their rounded shape from having been projected through water—on the same principle as melted lead, when dropped from an elevation, assumes a globular form. In the jaspery fragments included in the conglomerate, we often observe a struct- ure analogous to the woody fibre of trees. These fragments are composed of lamina, more or less contorted, and furrowed longitudinally, like the markings in the extinct plants of the genus Sigillaria. A series of striz, as fine as the engraver’s lines, run parallel with the larger ones. These can be traced on some of the specimens, and gen- FORMER VIEWS AS TO ORIGIN OF THE TRAPS AND AMYGDALOIDS. 9 erally extend through the different folds; while others possess a structure like the cellular tissue of wood. We have no confidence in the vegetable origin of these mark- ings, nor have we any theory to offer in explanation. The same views are as strenuously maintained in other publications by the same authors,’ who were, however, preceded in them by Dr. Douglas Houghton. The latter speaks of the conglomerates under the name of “ trap tuff,” and states distinctly that they are made up almost exclusively of pebbles and bowlders of ‘greenstone and amygdaloidal trap.”* Even those conglom- erates in which there is evident more or less sandy material he speaks of as made up entirely of comminuted greenstone, while the sandstone and shale which with so great thickness form the upper part of the series on Kewee- naw Point, he considers to be of sedimentary origin, the material having been worn from pre-existing granitic rocks. So far as I have noticed, none of the other writers on Lake Superior geology have accepted these peculiar views as to the origin of these con- glomerates—-all regarding them as made up of water-worn pebbles detached from some pre-existing rock—and for the excellent reason that Dr. Hough- ton’s and Messrs. Foster and Whitney’s facts, as well as their theory, failed to stand closer study. The included pebbles are only in very subordinate quantity of “trap” or amygdaloid, being almost wholly of some sort of acid eruptive rock, i. e., felsite, quartziferous porphyry, quartzless porphyry, granitic porphyry, augite-syenite, or granite. The fundamental difference between such pebbles and the associated basic massive rocks is alone enough to overthrow the theory, even were there not other sufficient argu- ments against it. Further, the pebbles are just as plainly water-worn as those of any other conglomerates, though they may have in some cases had the polish removed by surface alteration. The “trap” and amygdaloid are by some writers considered as having had a common origin, but by others are separated. Under the generic term of “trap,” Messrs. Foster and Whitney included ‘‘greenstone, granular and amyedaloidal trap, basalt, etc.” and held to their origin in part as lava flows, contemporaneous with the deposition by ordinary sedimentation of 1 Op. cit., pp. 99, 100. 2Am. Jour. Sci. (2), XVII, 1854, pp. 11-38, 181-194. 3 Joint Documents, Mich., 1841, pp. 472-607. 10 COPPER-BEARING ROCKS OF LAKE SUPERIOR. the associated sandstones, and in part as protrusions ‘in vast irregular masses, forming conical or dome-shaped mountains,” or ‘‘ continuous lines of elevation.”' While they class the amygdaloids and traps together, they do not appear to have distinctly recognized that the former are the vesicular upper portions of the lava flows. Houghton regarded all the traps as intrusive, and the amygdaloids as semi-fused sedimentary matter or interfused eruptive and sedimentary matter,” in which view he was followed by Jackson.’ Similar views as to the intrusive origin of the traps were held by a few others at an early date, but the only one of these holding these views who had made any extensive field explorations was Norwood,‘ who in his account of the Minnesota coast represents a large proportion of the bedded crystalline rocks of that coast as intrusive; but even he does not regard all of the traps as having had this origin. The amygdaloids he appears to look on, for the most part, as sedi- ments altered by igneous action, his general term for them being “meta- morphic shales.” A few of these rocks he seems to regard as volcanic tufas, an origin which was somewhat doubtfully assigned by Hunt to all the amygdaloids.2 N. H. Winchell has recently revived the peculiar views of Norwood as to the origin of the amygdaloids of the Minnesota coast.® Of others who have written on Lake Superior geology the larger number have maintained the origin of the traps as lava flows. Among them may be mentioned Logan,’ Hunt,*® Macfarlane,’ Bell,” Pumpelly,” Marvine,” Irving,’* Chamberlin,“ and Sweet.’® Rivot’® only has maintained 1Qp. cit., p. 55. 2 Joint Documents, Mich., p. 490. 3Am. J. Sci. (1) XLIX, pp. 62-72. 4“Geology of the Western and Northwestern Portions of the Valley of Lake Superior,” in Owen’s Geological Survey of Wisconsin, Iowa, and Minnesota, pp. 333-424, 5 Geology of Canada, 1863, pp. 698, 699. 6Seventh and Ninth Annual Reports of the Geological and Natural History Survey of Minnesota. 7Geology of Canada, 1863, pp. 71,72. 8Second Geol. Survey of Penn., Azoic Rocks, Part I, p. 256. 2Report of Progress of Geol. Survey of Canada, 186366, pp. 115-164. 10Report of Progress of Geol. Survey of Canada, 1866—69, pp. 313-364, Proc. Amer. Acad. 1878, XIII, pp. 253, 254. 12 Geological Survey of Michigan, 1873, Part II, pp. 109-112. 18 Geology of Wisconsin, Vol. III, p. 7. 14Geology of Wisconsin, Vol. III, p. 391. 15Geology of Wisconsin, Vol. III, p. 336. 16 Annales des Mines (5), VIII, 173-328, and 364, 374. FORMER VIEWS AS TO NATURE OF THE FELSITIC ROCKS. 11 a metamorphic origin for them. Pumpelly and Marvine first recognized definitely that the amygdaloids are but the upper portions of the beds of “trap,” and the distinction between the true vesicular amygdaloids and the non-vesicular pseud-amygdaloids, which distinction the latter subse- quently made still plainer by his microscopic investigations, to which we are indebted for our first knowledge as to the nature of the so-called “traps.” Marvine’s conclusions from his examination of the beds of the Eagle River section of Keweenaw Point, made before the use of the micro- scope in the study of these rocks, deserve mention as containing the first plainly and thoroughly worked-out argument, from structural characters alone, in favor of the lava-flow origin of the “traps,” and of the connection with the trap beds of the amygdaloids. The results of the work of the Wisconsin Survey, as given in the third volume of the Geology of Wis- consin, by Chamberlin, Sweet, Strong, and myself, fully sustained the con- clusions of Pumpelly and Marvine. The most recent writers on the copper rocks of Lake Superior have been N. H. Winchell and Wadsworth. Winchell’s views as to the sedi- mentary and metamorphic origin of the amygdaloids of the Minnesota coast have already been mentioned. In the same category he appears to include a large part of the bedded traps, the more highly crystalline kinds only being regarded as of eruptive origin.” Wadsworth’s paper maintains the lava-flow origin of the traps, although no points are advanced in favor of this conclusion that had not already been fully covered by Pumpelly and Marvine. It is worthy of note that while maintaining that Foster and Whitney are the only authors who have written correctly on Lake Supe- rior geology, Wadsworth should yet depart from them in several very im- portant points—such as the origin of the conglomerates—and this without a word of comment. The reddish, acid, eruptive rocks, which I describe in subsequent chapters as constituting so important a feature of the copper-bearing series, have been almost wholly overlooked heretofore. A number of writers have 1Metasomatic Development of the Copper-Bearing Rocks of Lake Superior. Proc. Am. Acad. Sci., 1878, XIII, pp. 253-309. 2Ninth Annual Report of the Natural History and Geological Survey of Minnesota, 1880, Prelimi- nary list of rocks, pp. 10-114, 12 COPPER-BEARING ROCKS OF LAKE SUPERIOR. recognized such rocks among the pebbles of the conglomerates, but as massive rocks they have only been noticed by Foster and Whitney, Logan, N. H. Winchell, Macfarlane, and Bell. Foster and Whitney, who noticed them on Mount Houghton and in the Porcupine Mountains, looked on them as baked sandstones, the baking being regarded as due to the heat of the molten traps. Winchell has noticed them on the Minnesota coast, but re- gards them again as altered sedimentary rocks.” Logan* and Macfarlane* have observed them only on Michipicoten Island, where Macfarlane seems to regard them as eruptive and Logan as fused sedimentary material. Bell merely mentions the existence of quartziferous porphyry on Lake Nipigon.? The failure to recognize the importance and eruptive origin of these rocks is peculiarly strange in the face of the almost universal association in vol- canic regions of the two types of acid and basic eruptives. Widely divergent views have been held with regard to the geological relations of the series as a whole, as well as with regard to the origin and structural relations of its constituent rocks. In the earlier days of the study of Lake Superior geology the general lithological similarity between these rocks and the Triassic sandstones and eruptives of the eastern states led to the view that they were of the same age. This view was held by Houghton,® and at one time by Jackson,’ and latterly has been advo- cated by Bell.* Later, when the Cambrian age of the so-called ‘“EKastern Sandstone”, which forms the south shore of Lake Superior from the Sault westward to the east side of Keweenaw Point, came to be established, the copper-bearing rocks, being regarded as belonging to the same formation, were considered to be the equivalents of the Potsdam sandstone of New York. This is the position taken by Foster and Whitney,’ Owen,” Ro- 1Op. cit., pp. 64-65. 2Bighth Annual Report of the Geological Survey of Minnesota, pp. 23-26. Ninth Annual Report, pp. 12, 17, 31, 32, ete. 3Geology of Canada, 1863, pp. 81-82. 4Geological Survey of Canada, Report of Progress, 1863-66, p. 142. 5Report of Progress of the Geological Survey of Canada, 186669, p. 348. 6Am. J. Sci., 1843 (1), XLV, 160. 7Am. J. Sci. (1), XLIX, pp. 81-93. ®Report of Progress Geological Survey of Canada, 1866—69, p. 321. 9 Op. cit., p. 99. 10Geological Survey of Wisconsin, Iowa, and Minnesota, pp. 187-196. FORMER VIEWS ON GEOLOGICAL POSITION OF THE SERIES. 13 minger,! Winchell,? and Wadsworth,’ although these writers differ greatly among themselves as to the exact structural relations subsisting between the Eastern Sandstone and the trappean series. As early as 1846 Logan regarded the copper-bearing rocks of Kewee- naw Point as the equivalents of the Huronian of the north shore of Lake Huron,‘ and when, later, he abandoned this view, still regarding them as older than the Eastern Sandstone, he made them the equivalents of the so- called ‘“ Quebec Group” of Canada East.2 In 1872 Pumpelly and Brooks advanced excellent reasons for placing the Keweenaw Point rocks below the Eastern Sandstone, and as, on the whole, nearer to conformity with the Huronian.’ In 1876 Brooks changed his views so far as to abandon the conformity with the underlying Huronian, but he still maintained the unconformity with the Hastern Sandstone.’ In 1880 the third volume of the Geology of Wisconsin presented new and weighty evidence of the pre-Cambrian age of the copper-bearing rocks, which are in Northern Wis- consin found to be separated from the basal fossiliferous Cambrian sand- stones of the Mississippi Valley by a great intervening erosion, while from the underlying Huronian the separation did not appear to be so great. In that volume the copper-bearing rocks were described under the term of the Keweenaw or Keweenawan Series, following the previous suggestions of Hunt* and Brooks,’ and the same term will be used in this memoir. A few months later appeared the volume of Mr. M. E. Wads- worth, in which the copper-bearing rocks are placed as the upper part of a series of which the Eastern Sandstone is regarded as the basal member—a view which can, I think, be easily shown to be untenable. 1 Geological Survey of Michigan, Vol. I, Part IL, pp. 80-81. 2Eighth Annual Report Geological Survey of Minnesota, p. 25. 3 Op. cit., pp. 115-127. 4Am. J. Sci. (2), 1857, XXIII, 305-314. 5 Geology of Canada, 1863, pp. 67-86. 6Am. J. Sci. (3), III, 428-432. 7Am. J. Sci. (3), XI, 206-311. 8 Trans. Am. Inst. Min. Eng., I, 331-342. 9Am. J. Sci. (3), XI, 206-211. Op cit., p. 66. 14 COPPER-BEARING ROCKS OF LAKE SUPERIOR. LITERATURE. The following list of works includes all of any importance that embrace references to the Keweenawan rocks by geologists who have examined them in the field. The arrangement is a chronologic one, so that any one wish- ing to examine the history of the subject may do so conveniently.’ 1824. BIGsBY (JoHN J.). Notes on the Geography and Geology of Lake Superior. Quarterly Journal of Science and Arts, 182425, xviii, 1-34, 228-269. 1829. BAYFIELD (H. W.). Outlines of the Geology of Lake Superior. Transactions of the Literary and Historical Society of Quebec, 1829, i, 1-43. 1831. Hovucuron (Doveias). A Report on the Existence of Deposits of Copper in the Geological Basin of Lake Superior. November 14, 1831. In the Discovery of the Source of the Mississippi, by H. R. Schooleraft, 526-531. 1839. HovcuTon (DouGuas). First Annual Report on the Geology of Michigan, 1838. Lanman’s History of Michigan, 1839, 347-366. Second Annual Report of the State Geologist. Senate Docs., Michigan, 1839, 264-294, 1840. Hoveuron (DouGLAs). Third Annual Report of the State Geologist, 1840. Senate Does., Michigan, 1840, 66-157. 1841. HovuGuron (DouGLAS). Fourth Annual Report of the State Geologist. Joint Docs., Michigan, 1841, 472-607. 1842. Hovucuron (DouGias). Fifth Annual Report of the State Geologist. Joint Docs., Michigan, 1842, 436-441. Metalliferous Veins of the Northern Peninsula of Michigan. American Journal of Science and Arts, 1841 (1), xli., 183-186. 1For the names of some of the foreign works I am directly indebted to Wadsworth’s bibliography of Lake Superior geology, without which aid I might have overlooked them. Op. cit. pp. 133-157. LITERATURE. 15 1844, HovucGuton (DouGLAs). Copper on Lake Superior. Am. Jour. Sci., 1844 (1), xlvii., 107, 132. Locks (JoHN). Geology of Porter’s Island and Copper Harbor. Transactions of the American Philosophical Society, 1844, ix., 311, 312, with maps. 1845. JACKSON (CHARLES T.). On the Copper and Silver of Keweenaw Point, Lake Su- perior. Am. Jour. Sci., 1845 (1), xlix., 81-93. Sur le Gisement de Cuivre et d’Argent natifs des Bords du Lae Supérieur. Comptes Rendus, 1845, xx., 593-595; Bulletin de la Société Géologique de France, 184445 (2), ii., 317-319. SHEPARD (CHARLES U.). On the Copper and Silver of Keweenaw Point, Lake Su- perior. Proceedings of the Sixth Annual Meeting of the Association of American Geologists and Naturalists, New Haven, 1845, 60, 61. 1846. HovuGHTON (JACOB, JR.), and Bristou (T. W.). Mineral Region of Lake Superior. Detroit, 1846, 109 pp. and map. JACKSON (CHARLES T.). The Copper and Silver Mines of Lake Superior. Proceedings of the Boston Society of Natural History, 1846, ii., 110-114. Logan (WILLIAM #.). North Shore of Lake Superior. Geological Survey of Canada, Report of Progress, 184647, 5-46. RoeeErs (H. D.). Mineralogy and Geology of Lake Superior. Proc. Bost. Soc. Nat. Hist., 1846, ii., 124, 125. 1847. Dutton (T. R.). Observations on the Basaltic Formation on the Northern Shore of Lake Superior. Am. Jour. Sci. (2), 1847, iv., 118, 119. JACKSON (CHARLES T.). Report on the Mineral Lands of Lake Superior. Senate Does., 1st sess. 30th Cong., 184748, ii., No. 2, 175-230. Ores and Minerals from Lake Superior. Proc. Bost. Soc. Nat. Hist., 1847, ii., 256, 259, 260. LoGawn (WILLIAM B.). Remarks on the Mining Region of Lake Superior, and a Report on Mining Locations claimed on the Canadian Shores of the Lake. Montreal, 1847, 31 pp., with maps. MurRRAY (ALEXANDER). North Shore of Lake Superior. Geol. Sury. Canada, Rep. of Progress, 1846—47, 47-57. 1848. JACKSON (CHARLES T.). Age of the Lake Superior Sandstone. Proc. Bost. Soc. Nat. Hist., 1848, iii., 76, 77. ROGERS (WILLIAM B.). On the Origin of the Actual Outlines of Lake Superior. Pro- ceedings of the American Association for the Advancement of Science, 1848, First Meeting, 79, 80. 16 COPPER-BEARING ROCKS OF LAKE SUPERIOR. 1849. Burt (Wittr1AmM A.), and HUBBARD (BELA). Geology and Topography of the District South of Lake Superior. Senate Does., Ist sess. 3lst Cong., 1849~50, iii., 842-932. Hopes (JAmss T.). On the Mineral Region of Lake Superior. Proc. Am. Assoc. Ady. Sci., 1849, Second Meeting, 301-308. JACKSON (CHARLES T.). Mineral Lands of Lake Superior. Senate Does., 184849, 2d sess. 30th Cong., ii., No. 2, 153-163. Report on the Progress of the Geological Survey of the Mineral Lands of the United States in Michigan. Senate Does., 184849, 2d sess. 30th Cong., ii., No. 2, 185-191. Copper of the Lake Superior Region. Am. Jour. Sci., 1849 (2), vii., 286, 287. Remarks on the Geology, Mineralogy, and Mines of Lake Superior. Proc. Am. Assoc. Adv. Sci., 1849, Second Meeting, 283-288. On the Geological Structure of Keweenaw Point. Proc. Am. Assoc. Adv. Sci., 1849, Second Meeting, 288-301. LoGAN (WiLLIAM E.). Report on the North Shore of Lake Huron. Geol. Surv. of Canada, Rep. of Progress, Montreal, 1849, 51 pp. WHITNEY (J.D.). The Lake Superior Copper and Iron District. Proc. Bost. Soc. Nat. Hist., 1849, iii., 210-212. 1850. e Agassiz (Louts). Lake Superior; its Physical Characters, Vegetation, and Animals. Boston, 1850, 428 pp. Foster (J. W.) and Watney (J. D.). Synopsis of the Explorations of the Geological Corps in the Lake Superior Land District in the Northern Peninsula of Mich- igan. Senate Does., 1st sess. 31st Cong., 184950, iii., No. 5, 605-626. Report on the Geology and Topography of a Portion of the Lake Superior Land District in the State of Michigan. Part I., Copper Lands. Executive Docs., 1st sess. 31st Cong., 1849-50, ix., No. 69, 224 pp., with map. Apercu de ensemble des Terrains Siluriens du Lac Supérieur. Bull. Soc. Géol. France, 1850 (2), 89-100. JACKSON (CHARLES T.). Remarques sur la Géologie du District Métallifére du Lac Supérieur. Bull. Soc. Géol. France, 184950, vii., 667-673. Report on the Geological and Mineralogical Survey of the Mineral Lands of the United States in the State of Michigan. Senate Docs., 1st sess. 31st Cong., 184950, No. 5, iii., 371-503. Remarques sur la Géologie du District Métallifére du Lae Supérieur, suivies d’une courte Description de quelques-unes des Mines de Cuivre et d’Argent. HEx- trait par M. Delesse. Annales des Mines, 1850 (4), xvii., 103-115. Age of the Lake Superior Sandstone. Proce. Bost. Soc. Nat. Hist., 1850, iii., p. 228. On the Age of the Sandstones of the United States. Proc. Bost. Soc. Nat. Hist., 1850, iii., 335-339. Magcou (JULES). Réponse A la Lettre de MM. Foster et Whitney sur le Lac Supérieur. Bull. Soc. Géol. France, 1850 (2), viii., 101-105. LITERATURE. v7 1851. DESOR (EDWARD). Lake Superior. On the Silurian Rocks of the Lake Superior Land District. Proc. Am. Assoc. Adv. Sci., 1851, Fifth Meeting, 64, 65. FostiEr (J. W.) and WHITNEY (J. D.). On the Age of the Sandstone of Lake Supe- rior, with a Description of the Phenomena of the Association of Igneous Rocks. Proc. Am. Assoc. Adv. Sci., 1851, Fifth Meeting, 22-38. On the Different Systems of Elevation which have given Configuration to North America, with an Attempt to Identify them with those of Europe. Proc. Am. Assoc. Adv. Sci., 1851, Fifth Meeting, 136-151. JACKSON (CHARLES T.). Analyses of Pitchstone Porphyry from Isle Royale, ete. Am. Jour. Sci., 1851 (2), xi., 401, 402. Rain-drop and Air-bubble Impressions. Proc. Bost. Soc. Nat. Hist., 1853, Febru- ary 17, iv., 131, 132. 1852. BiesBy (JOHN J.). On the Physical Geography, Geology, and Commercial Resources of Lake Superior. Edinburgh New Philosophical Journal, 1852, liii., 55-62. JACKSON (CHARLES T.). Geology, Mineralogy, and Topography of the Lands around Lake Superior. Senate Does., 185152, Ist sess. 32d Cong., xi., 232-244, LOGAN (WILLIAM E.). On the Age of the Copper-bearing Rocks of Lakes Superior and Huron. Am. Jour. Sci., 1852 (2), xiv., 224-229, Norwoop (Dr. J. G.). Geology of the Western and Northwestern Portion of the Val- ley of Lake Superior; in Owen’s Geological Survey of Wisconsin, Iowa, and Minnesota. Philadelphia, 1852, 333-418. OWEN (DAvipD D.). On the Age, Character, and True Geological Position of the Lake Superior Red Sandstone Formation, in the Report of a Geological Survey of Wisconsin, Iowa, and Minnesota. ~ Philadelphia, 1852, 187-193. SHumARD (B. F.). Local Details of Geological Sections on the Saint Peter’s, Wiscon- sin, Mississippi, Baraboo, Snake, and Kettle Rivers; in Owen’s Geological Survey of Wisconsin, Iowa, and Minnesota. Philadelphia, 1852, 481-522. WHITTLESEY (CHARLES). Description of Part of Wisconsin South of Lake Superior. With maps. In Owen’s Geological Survey of Wisconsin, Iowa, and Minne- sota. Philadelphia, 1852, 425-470. 1853. JACKSON (CHARLES T.). Igneous Origin of Calcite Veins. Proc. Bost. Soc. Nat. Hist., 1853, February 17, iv., 308, 509. Ueber den Metallfiihrenden Distrikt am Obern See im Staate Michigan. Karsten’s Archiv. 1853, xxv., 656-667. MARcOU (JULES). A Geological Map of the United States and the British Provinces of North America, with an Explanatory Text, Geological Sections, ete. Bos- ton, June, 1853, 92 pp. 2LS8 18 COPPER-BEARING ROCKS OF LAKE SUPERIOR. 1854. Foster (J. W.). Catalogue of Rocks, Minerals, ete., collected by J. W. Foster. Smith- sonian Report, 1854, 384-387. HA. (JAmzms). On the Silurian System of the Lake Superior Region. Am. Jour. Sci., 1854 (2), xvii., 181-194. JACKSON (CHARLES T.). Catalogue of Rocks, Minerals, and Ores Collected During the Years 1847 and 1848 on the Geological Survey of the United States Min- eral Lands of Michigan. Collected by Charles T. Jackson. Smithsonian Re- port, 1854, 338-367. Observations sur quelques Mines des Etats-Unis et sur le Grés Rouge du Lac Supérieur. Comptes Rendus, 1854, xxxix., 803-807. Locks (Joun). Catalogue of Rocks, Minerals, Ores, and Fossils Collected by John Locke. Smithsonian Report, 1854, 367-383. 1855. Dupre (J. A.). Ashbed of the Phoenix Mine. Proc. Bost. Soc. Nat. Hist., 1855, v., 279, 280. EMMONS (EBENEZER). Copper Mines of Lake Superior, American Geology, Albany, 1855, 171-173. JACKSON (CHARLES T.). On the Ashbed and the Origin of the Copper. Proc. Bost. Soc. Nat. Hist., 1855, v., 280, 281. Rrivor (L. E.) Mémoire sur le Gisement du Cuivre Natif au Lac Supérieur. Comptes Rendus, 1855, xl., 1306-1309. Voyage au Lac Supérieur. Annales des Mines, 1855 (5), vii., 173-328. WuHitney (J. D.). Remarks on Some Points Connected with the Geology of the North Shore of Lake Superior. Proc. Am. Assoc. Ady. Sci., 1855, Ninth Meeting, 204-209. 1856. BLAKE (WILLIAM P.). Review of a portion of the Geological Map of the United States and British Provinces, by Jules Marcou. Am. Jour. Sci., 1856 (2), xxii., 383- 388. JACKSON (CHARLES T.). Trap Dikes. Proc. Bost. Soc. Nat. Hist., 1856, vi., 23, 24. Rrvor (L. E.). Notice sur le Lac Supérieur. Annales des Mines, 1855 (5), x., 365-474. Uber die Kupfererz-Lagerstiitten am Obern See in den Nordamerikanischen Frei- staaten. Berg- und Hiittenminnische Zeitung, 1856, 261-265, 269-271, 293- 295, 277-279, 314, 315, 317, 318, 325-328, 333, 334, 341-343, 349-351, 357-359, 365-367, 381, 382, 1857. Dawson (JOHN W.). On the Geological Structure and Mineral Deposits of the Pro- montory of Mamainse, Lake Superior. Canadian Naturalist and Geologist, 1857, ii., 1-12. MULLER (ALF.). Ueber die Kupferminen am Obern See in Nordamerika. Neues Jahrbuch fiir Mineralogie, Geologie und Paleontologie, von G. Leonhard und H. B. Geinitz, 1857, 79-82, 589, 590. LITERATURE. 19 1858. DIEFFENBACH (OTTO). Bemerkungen iiber den Kupferbergbau in den Vereinigten Staaten von Nordamerika. Berg- u. Hiitten. Zeit., 1858, 47, 48, 66-68, 75, 76. 1859. AGassiz (Lous). On Marcow’s “Geology of North America.” Am. Jour. Sei., 1859 (2), xxvii., 134-137. JACKSON (CHARLES T.). On the Ashbed and the Origin of the Copper. Proc. Bost. Soe. Nat. Hist., 1859, vii., 31. LAPHAM (INCREASE A.). The Penokee Tron Range. Wisconsin State Agricultural Society Transactions, 185859, v., 391-400, with map. Marcovu (JULES). Dyas et Trias, ou le Nouveau Grés Rouge en Europe, dans l Amé- rique du Nord et dans V’Inde. Zurich, 1859, 63 pp. WHITTLESEY (CHARLES). On the Origin of the Azoic Rocks of Michigan and Wis- consin. Proc. Am. Assoc. Adv. Sci., 1859, Thirteenth Meeting, 301-308. 1860. JACKSON (CHARLES T.). Age of the Lake Superior Sandstone. Proc. Bost. Soe. Nat. Hist., 1860, vii., 396-398. RocErs (WiLi1AM B.). Age of the Sandstone. Proc. Bost. Soc. Nat. Hist., 1860, vii., 394, 395. Wuitney (J. D.). Note on the Geological Position of the Lake Superior Sandstone. Mining Mag., 1860 (2), i., 435-446. 1861. DEROUX (H.). Die Kupfergruben des Oberen See’s (Lake Superior). Berg. u. Hiitten. Zeit., 1861, 305-307, 829-331. Foster (J. W.) and WHITNEY (J. D.). On the Origin and Stratigraphical Relations of the Trappean Rocks of Lake Superior. Annual of Scientific Discovery, 1861, 285. Hunt (T. SrerRy). On some Points in American Geology. Am. Jour. Sci., 1861, Xxxi., 392-414, 1862. LOGAN (WILLIAM E.). Considerations relating to the Quebec Group and the Upper Copper-bearing Rocks of Lake Superior. Canadian Nat. and Geol., 1861, vi., 199-207. : 1863. LoGaN (WILLIAM E.). Geology of Canada. Montreal, 1863, 983 pp., with atlas. WHITTLESEY (CHARLES). The Penokee Mineral Range, Wisconsin. Proc. Bost. Soe. Nat. Hist., 1863, ix., 235-244. 20 COPPER-BEARING ROCKS OF LAKE SUPERIOR. 1864. LoGan (WiLL1AM £.). Kupfererzefiihrende Gesteine am Obern See. Leonhard’s Jahrbuch, 1864, p. 741. WINCHELL (ALEXANDER). Notice of a Small Collection of Fossils from the Potsdam Sandstone of Wisconsin and the Lake Superior Sandstone of Michigan. Am. Jour. Sci., 1864 (2), xxxvii., 226-232. 1866. EAMES (HENRY H.) Geological Reconnoissance of the Northern, Middle, and other Counties of Minnesota. St. Paul, 1866, 58 pp. Report of the State Geologist, Heury H. Eames, on the Metalliferous Region bor- dering on Lake Superior. St. Paul, 1866, 23 pp. MACFARLANE (THOMAS). Report on the Geology of Lake Superior. Rep. of Progress, Geol. Survey of Canada, 1866, 115-148. On the Rocks and Cupriferous Beds of Portage Lake, Michigan. Rep. of Progress, Geol. Survey of Canada, 1866, 149-164. 1867. AGASSIZ (ALEXANDER). On the Position of the Sandstone of the Southern Slope of a Portion of Keweenaw Point, Lake Superior. Proc. Bost. Soc. Nat. Hist., 1867, xi., 244-246. 1868. CREDNER (HERMANN). Die Gliederung der eozoischen (vorsilurischen) Formations gruppe Nord Amerikas. Zeitschrift fiir die Gesammten Naturwissenshaften, Giebel, 1868, xxxii., 353-405. MACFARLANE (THOMAS). On the Geological Formations of Lake Superior. Canadian Naturalist, 1866~68 (2), iii., 177-202, 241-257. WINCHELL (ALEXANDER). Geological Map of Michigan. Leonhard’s Jahrbuch, 1868, 99-101. 1869. BELL (ROBERT). Geology of Lakes Superior and Nipigon. Rept. of Progress, Geol. Survey of Canada, 1866-69, 313-364. OCREDNER (HERMANN). Beschreibung einiger charakteristischer Vorkommen des ge- diegenen Kupfers auf Keweenaw Point am Obern See Nord-Amerika’s. Leon- hard’s Jahrbuch, 1869, 1-14. Die vorsilurischen Gebilde der ‘‘ Obern Halbinsel von Michigan” in Nord-Amerika. Zeitschrift der Deutschen Geologischen Gesellschaft, 1869, xxi., 516-554. JACKSON (CHARLES T.). Sur les Mines de Cuivre du Lac Supérieur et sur un Nouveau Gisement @’étain dans l'état du Maine. Comptes Rendus, 1869, Lxix., 1082, 1083. Logan (WiLtiAmM E.). Notes on the Report of Mr. Robert Bell on the Nipigon Region. Geol. Survey of Canada, Rep. of Prog., 1866~69, 471-475. MACFARLANE (THOMAS). On the Geology and Silver Ore of Wood’s Location, Thun- der Cape, Lake Superior. Canadian Nat., 1869 (2), iv., 37-48, 459-463. LITERATURE. at 1870. CREDNER (HERMANN). Gewaltige Kupfermassen am Lake Superior. Leonhard’s Jahrbuch, 1870, 86. Ueber Nordamerikanische Schieferporphyroide. Leonhard’s Jahrbuch, 1870, 970- 984. 1871. BELL (ROBERT). Report on the Country North of Lake Superior, between the Nipigon and Michipicoten Rivers. Geol. Sury. of Canada, Rep. of Prog., Ottawa, 187071, 322-351 : PUMPELLY (RAPHAEL). The Paragenesis and Derivation of Copper and its Associ- ates on Lake Superior. Am. Jour. Sci., 1871, (3), ii., 188-198, 243-258, 347- 353. 1872. Brooks (T. B.) and PUMPELLY (R.). On the Age of the Copper-bearing Rocks of Lake Superior. Am. Jour. Sci., 1872 (3), iii, 428-432. 1873. BELL (ROBERT). Report on the Country between Lake Superior and Lake Winnipeg. Geol. Surv. of Canada, Rep. of Prog., Montreal, 187273, 87-111. Brooks (T. B). Geological Survey of Michigan, with maps, 186973, i., Part I., Iron- bearing Rocks, 319 pp. Hunt (T. STERRY). The Geognostical History of the Metals. Trans. Am. Inst. Min. Eng., 1873, i., 331-34 . The Origin of Metalliferous Deposits. Transactions of the American Institute of Mining Engineers, 1873, i., 415-426. MARVINE (A. R). Geology of Michigan, 18/3,i., Part I., Copper-bearing rocks. Chap- ters IV, VII, and VIII. NicHOLson (H. ALLEYNE). On the Geology of the Thunder Bay and Shebandowan Mining Districts on the North Shore of Lake Superior. Quarterly Journal of the Geological Society, 1873, xxix., 17-24. PUMPELLY (R). Geological Survey of Michigan, i., Part II., Copper-bearing Rocks, 1-96, and 62-95, with an atlas of maps. ROMINGER (CHARLES). Geological Survey of Michigan, 1873, i., Part III., Paleozoic Rocks, 105 pp. SELWYN (ALFRED R. C). Notes of a Geological Reconnoissance from Lake Superior to Fort Garry. Geol. Surv. Canada, Rep. of Prog. Montreal, 187273, 8-18. 1874. DovuGLas (JAMES). The Native Copper Mines of Lake Superior. Quarterly Journal ot Science, 1874, xi., 162-180. Hunt (T. StERRY). The Geology of the North Shore of Lake Superior. (Supplement- ary note). Trans. Am. Inst. Min. Eng., 1873, ii., 58, 59. IRVING (R. D.). On some Points in the Geology of Northern Wisconsin. Transactions Wisconsin Academy of Science, 1873~74, ii., LO7-119. 22 COPPER-BEARING ROCKS OF LAKE SUPERIOR. IRVING (R. D.). On the Age of the Copper-bearing Rocks of Lake Superior, and on the Westward Continuation of the Lake Superior Synelinal. Am. Jour. Sci., 1874 (3), viii., 46-56. 1875. BELL (RoBERT). The Mineral Region of Lake Superior. Canadian Nat., 1875 (2), vii., 49-51. NricHOLSon (H. ALLEYNE). On the Mining District of the North Shore of Lake Supe- rior. Trans. of the North of England Inst. of Mining and Mechanical Engi- neers, Neweastle-on-Tyne, 187475, xxiv., 237-249, with maps. WHITTLESEY (CHARLES). Physical Geology of Lake Superior. Proc. Am. Assoc. Adv. Sci., 1875, xxiv., 60-72. 1876. BELL (ROBERT). Report on an Exploration in 1875, between James Bay and Lakes Superior and Huron. Geol. Surv. of Canada, Rep. of Prog. 1875-1876, 294-342. Brooks (T. B). On the Youngest Huronian Rocks South of Lake Superior, and the Age of the Copper-bearing Series. Am. Jour. Sci., 1876 (3), xi., 206-211. Classified List of Rocks observed in the Huronian Series south of Lake Superior. Am. Jour. Sci., 1876 (3), xii., 194-204. ROMINGER (CHARLES). Observations on the Ontonagon Silver Mining District and the Slate Quarries of Huron Bay. Geol. Surv. Michigan, 1876, iii., 153-166. Sweet (E. T). Notes on the Geology of Northern Wisconsin. Trans. Wis. Acad. 187576, iii., 40-55. WHITTLESEY (CHARLES). On the Origin of Mineral Veins. Proc. Am. Assoc. Ady. Sci., 1876, xxv., 213-216. 1877. BELL (ROBERT). Report on Geological Researches North of Lake Huron and East of Lake Superior. Geol. Sury. of Canada, Rep. of. Prog., 1876~77, 193-220. EGLESTON (THOMAS). Copper Mining on Lake Superior. Trans. Am. Inst. Min. Eng., 1877, vi., 275-312. The Conglomerates of Lake Superior, and the Methods of Dressing Copper. Trans. Am. Inst. Min. Eng., 1877, v., 606-611. Irvine (R D.). Note on the Age of the Crystalline Rocks of Wisconsin. Am. Jour. Sci., 1877 (3), xiii., 807-309. SrRENG (A.) and Kioos (J. H.). Uber die Krystallinischen Gesteine von Minnesota in Nord-Amerika. Leonhard’s Jahrbuch, 1877, 31, 113, 225. WHITTLESEY (CHARLES). On the Iron River Silver District. Engineering and Min- ing Journal, April 21, 1877, xxiii., 254-255, 278-279. 1878. CREDNER (HERMANN). Elemente der Geologie, 4th ed., 1878, 726 pp. Hunt (T. SterRy). Azoic Rocks. Part I., 1878. Second Geological Survey of Penn- sylvania, E. 253 pp. PUMPELLY (RAPHAEL). Metasomatic Development of the Copper-bearing Rocks of Lake Superior. Proc. Am. Acad., 1878, xiii., 253-309. LITERATURE. 23 SPENCER (JOSEPH WILLIAM). On the Nipigon or Copper-bearing Rocks of Lake Superior, with Notes on Copper Mining in that Region. Canadian Nat., 1878 (2), vili., 55-81. 1879. HALL (C. W.). Field Report. In Seventh Annual Report of the Geological and Natu- ral History Survey of Minnesota for the year 1878, 26-29. Irvine (R. D.). Note on the Stratigraphy of the Huronian Series of Northern Wiscon- sin; and on the Equivalency of the Huronian of the Marquette and Penokee Districts. Am. Jour. Sci., 1879 (3), xvii., 393-398. MACFARLANE (THOMAS). Remarks on Canadian Stratigraphy. Canadian Nat., 1879 (2), ix., 91-102. Moser (CuR.). Der Kupferbergbau am Obern See in Nordamerika. Zeitschrift fiir das Berg- Hiitten- und Salinenwesen, 1877. Abhandlungen, xxy., 203-221; 1879, xxvii., 77-97. SELWYN (ALFRED R.C.). The Stratigraphy of the Quebec Group and the Older Crys- talline Rocks of Canada. Canadian Nat., 1879 (2), ix., 17-32. WINCHELL (N. H.). Sketch of the Work of the Season of 1878. In the Seventh An- nual Report of the Geol. and Nat. Hist. Survey of Minnesota for the year 1878, 9-26. 1880. CHAMBERLIN (T. C.) and StrronG (MossEs). Geology of the Upper Saint Croix District. Geology of Wisconsin, iii., 1880, 363-428. HALL (C. W.). Report of Professor C. W. Hall. In Eighth Annual Report of the Geol. and Nat. Hist., Survey of Minnesota for the year 1879, 126-138. Hunt (T. StERRY). The History of Some Pre-Cambrian Rocks in America and Europe. Am. Jour. Sci., 1880 (3), xix., 268-283. Irvine (R. D.). Geological Structure of Northern Wisconsin, with maps. Geol. of Wisconsin, iii., 1880, Part I., 1-25. Geology of the Eastern Lake Superior District, with atlas maps, and plates. Geol. of Wisconsin, Part IIT, 1880, iii., 51-238. JULIEN (ALEXIS A.). Microscopical Examination of Eleven Rocks from Ashland Co., Wisconsin. Geol. of Wisconsin, iii., 224-238. PUMPELLY (RAPHAEL). Lithology of the Keweenawan System. Geol. of Wisconsin, iii., Part I., 27-49. SWEET (EH. T.). Geology of the Western Lake Superior District, with maps. Geol. of Wisconsin, iii., 503-362. WaApbswortH (M. E.). Notes on the Iron and Copper Districts of Lake Superior. Bulletin of the Museum of Comparative Zoology at Harvard College. Whole series, vii., Geological series, i., No. I. 157 pp. WINCHELL (N. H.). The Cupriferous Series at Duluth. In the Highth Annual Report of the Geol. and Nat. Hist. Survey of Minnesota, for the year 1879, 22-26. 1881. WINCHELL (N. H.). Preliminary List of Rocks. In the Ninth Ann. Rep. of the Geol. and Nat. Hist. Surv. of Minnesota for the year 1880, 10-114. CHAPTERS EXTENT AND GENERAL NATURE OF THE KEWEENAW SERIES. General statement as to the scope of the term Keweenawan.—General statement as to the geographical extent of the series.—More detailed description of its extent.—Extent of the series underneath the waters of Lake Superior.—Its entire geographical extent in square miles.—Constancy of its general characteristics.—Basie crystalline rocks.—Detrital rocks. —Porphyry-conglomerates.— Other conglomerates.—Sandstones.—Source of the pebbles of the porphyry-conglomerates now found in the original acid rocks of the series itself.—General characteristics of these original acid rocks.—Recapitulation. That my statements as to the geographical extent of the Keweenawan rocks may be understood, it is necessary to say at the outset that I exclude from the Keweenaw Series the slaty rocks of the region of Thunder Bay and Pigeon River—the so-called ‘‘Lower Group” of Logan, and Animikie Group of Hunt. The nature and general relations of these slates are dis- cussed on a subsequent page. It should also be stated that I include in the Keweenaw Series the white and red dolomitic sandstones with accom- panying crystalline rocks, which are so largely developed in the peninsula between Black and Thunder bays, and stretch thence a long distance north- ward in the valleys of the Black-Sturgeon and Nipigon rivers, and occupy a large area about Lake Nipigon. Again, I exclude the horizontal sand- stones which form the South Shore east of Béte Grise Bay, on Keweenaw Point, and westward from Clinton Point, in Wisconsin, to Fond du Lae, in Minnesota. The Keweenaw or copper-bearing series, then, as considered in the following pages, is made to include only the succession of interbedded “traps,” amygdaloids, felsitic porphyries, porphyry-conglomerates, and sand- stones, and the conformably overlying thick sandstone, as typically devel- oped in the region of Keweenaw Point and Portage Lake on the south shore of Lake Superior. The series of rocks under consideration is almost entirely restricted to the Lake Superior basin, whose limits it passes only at the southwest, where 24) UNITED STATES GEOLOGICAL SURVEY ] 93 2 | DEVONIAN KEWEENAWAN at ||) BBB Pract state BEA y pper division ead Hamilton group BD Lower division SILURIAN HURONIAN | a ave Helderberg group F | The Original Canadian Huronan b Onondaga Se ____ Otherareas in Canada marke as Huronian byBell Most cal ondaga Salt: group | vithese areas undoubtedly comprise some true Anronian. |r i 5 but ithas not been satisfactorily shown that manyof the sc = “ } Niagara group here included do nut rather belong with the older gueisses yi | ‘ine ‘> NG] Anima kie or Thunder bay slates of the narth shore Vermillion} | | Cincinnati gr EP, (ar | Lake iron bearmg series, and tron bearmg rocks of the S.shore | y {zz Trenton group S : > Gneiss gramte and crystalline schists Some of the CAMBRIAN T | crystalline schists Here included belong with the Hurontan but have not been sufficiently separated as yet for {ar ] Lower Magnesian limestone mapping . a orCalciferous group £ (gl Potsdam sandstone of the _t. Dip and strike of inclined strata } |i Mississippi Valley {- Strata horzontal or nearly so The E pn or La S = > pad Peete ay AD fonyectiral positon of the hne between Ue upper and lower division of the Keweenaw series. VOI | The Western’ Sandstone P 2,000,000 or T inch = 31585 Miles _lepogmphy compiled tron charts of Survey of the Northern and Northwestern Lakes, Land Office | Lownsh tp lla Logical Reports: agan and Wisconsiy Maps of the Geological Survey of Canada~ Fumers Map higan and Nicodemus &lonovers Map of Wisconstr si : Geology based upon naps and reports. CD Jackson, Bela Hubbard, Wihister and J 7) Whitney omarige, i Hunpelly, AR. Marvine, TB Brooks, Me wrong, ETS TCthambertin DD Owen | nell, 6 Kowvod, ier W Loyan, dlaacuterMurray: omasHao Rurlane and Robert Bell, upon MSS notes or Maps by WM Chauvene, A.C Campbell, LAH Chester BN White ana BM hud upon miginal observations The correlation of the rocks madang up the older firm ations &s, often ortqinad, | Bay Leta ee gl \ ISLAND. pors Light le . nn ha i | \ fife 4 / Outer Id | re sgh LES Jyou = ————___ —-— : ae, (> Stockton 1a | t r oa omnia ith Channel La Pointe It House ° S | Lael elie tf 7 = a2 Bee se eas Sj bse - ap a L/ Le Ay me hy BAY NGA. 4 I KK =e Ber Hy ah ol. Ls es v4 ut = 3 a ein FANN ST, 3 GEOLOGICAL MAP Qi i: a : COPPER-BEARING ROCKS OF LAKE SUPERIOR PL. | Manitou Light House Peay Pore Point Abbaye sa fare Istana Let Fo que pers por Enea [sland Lt 7 = ri Detroit Id Pilot Light 1 §O IslandofMackanac ackinac — LAK i SUPERIOR BASIN i , A-Hoen & Co. Lit Baltimore UNITED STATES GEOLOGICAL SURVEY COPPER-BEARING ROCKS OF LAKE SUPERIOR PL. | —— =a —~ - - | DEVONIAN KEWEERNAWAN Zo a Tacielibate Upper division (7) Hamilton group ED hier division —- ry 02" ae i SILURIAN. TURONIAN BHA tadevers exp Te igs \Canatian Haren [es reketl sf byBell Most |) GBH) onondaga Sart group Oiierareas in Gala aromas oronan Hol et iEca| Dut ithas nol been sanstictoridy shownthat manyor the scl 5 I Niagara Group Here melured donot raQua belong with the older guesses AA ] Ciiteinnati group, (Gg Agere or under tay slates of Ove marth shore Veemill Lake iron bearing series, and tron bearmd: eal ‘Trenton group ; ] Gneess i idl crys tall schists Sor ft CAMBRIAN Doaeinn eel oun tate taedad belong eth Gan thea . Dal hare not been sufficiently separated ax yet for Lower Magnesia) Himestone i - : me Guciferous group mapping Pol iutone of the —t. Dip and strike of inclined strata é 4 Strata honxontal or nearly so. 7 1 é ‘ wrarsb sro Ags S058 VR oR novos cess nosvsquds oho k YoS+no2 seth oxddn yg so stndas& .c bsrp L2QTA uvsSasecnsh 1$ S9H90 SAQsS Hoxsxaloqg cash Ags) As\2Ssquss \AK\S SS yASsosct. ee a ’ sk Sg yrasshto LQ stxxSW. .Adss\s& +2955 nostoquG share Sirs09 scary ord dah) Seen t 29m ussdsrnIm op sin0d SAq3S Shossreadog We) gSsxo sows (UY SNasaecqors sorsS{SscOSSS (shsSsqaro ssqnSSosbo (Ww s¥sAdvarh 1 2 A : fi : Figszand2. Diabase or gahbhro from coast of Lake Supertor, near Beaver Bay, Minn. fie g.1. ordinary light. Frg2 polarzzer leght Scale 21 diameters Anorthi tet; augetel2 J, Figs.s andy. Gabbro from coast of Lake Supercor near Duluth, Minn Fug.8 orcdenary Light, Arg. 4 polarzzect leght. Scale so diameters Anorthitet/; deatlagze exugrte(2/, trlencferous magnetite (9); trom oxcale (4/ LITHOLOGY. 35 Section IL—BASIC ORIGINAL ROCKS. In his paper on “The Metasomatic Development of the Copper-bearing Rocks of Lake Superior,” published in 1878,’ Pumpelly first showed the true nature of the prevalent basic rocks of the copper region of Michigan. His work was chiefly on specimens from the section displayed on the lower Eagle River, Keweenaw Point. Subsequently (1880), the same geologist published? the results of an examination of a suite of specimens collected for the Wisconsin Geological Survey by Messrs. M. Strong, E. T. Sweet, and myself in the districts severally under our charge. These Wisconsin rocks he was able for the most part to throw into the same groups whose existence he had already determined in his Michigan work, the only im- portant addition being one or two varieties of true gabbro, now first proved to exist in the Lake Superior country. These gabbros were further de- scribed in the same volume by Mr. A. A. Julien, and in some detail by myself. At the close of the investigations of the Wisconsin Survey the list of the basic rocks of the Keweenaw Series stood as follows: gabbro, including gabbro proper, olivine-gabbro, uralitic gabbro, and an orthoclase-bearing gabbro; diabase, including the ordinary, prevalent, fine-grained type, one or two coarse-grained varieties, a type designated as “ashbed” diabase, a pseud-amygdaloidal diabase, and true diabase-amygdaloids; and melaphyr, including melaphyr proper, as also its pseud-amygdaloidal and true amyg- daloidal phases. The names gabbro, diabase, and melaphyr were given in accordance with the usage of H. Rosenbusch, who has classed the pre- tertiary plagioclase-augite rocks as indicated in the following scheme:* I. GRANULAR. a. Plagioclase-augite = diabase. b. Plagioclase-augite-olivine = olivine-diabase. II. PoRPHYRITIC, containing more less of an insoluble base. a. Plagioclase-augite = diabase-porphyrite. b. Plagioclase-augite-olivine = melaphyr. 1 Proceedings of the American Academy of Arts and Sciences, Vol. XIII, pp. 253-309. 2 Geology of Wisconsin, Vol. II, pp. 29-49. 3Microscopische Physiographie der Massigen Gesteine, von H. Rosenbusch. Stuttgart, 1877, pp. 317, 458. 36 COPPER-BEARING ROCKS OF LAKE SUPERIOR. III. GLASsy, known only as subordinate, vitreous modifications of diabase-porphyrite not deserving of a special name. TV. GRANULAR PLAGIOCLASE-DIALLAGE ROCKS. a. Plagioclase-diallage = gabbro. b. Plagioclase-diallage-olivine = olivine-gabbro. For the present work I have studied some eight hundred sections made from specimens collected from all parts of the entire extent of the Kewee- naw Series, including the typical localities of Pumpelly’s Michigan descrip- tions. I have also had in my hands the original sections made by Pumpelly for his study of the Wisconsin rocks. Although my microscopic work has been extended over so much wider a field than his—covering, as it has, not only the already partly studied districts of Keweenaw Point and northern Wisconsin, but also the hitherto wholly unstudied rocks of the north and east shores of the lake, of the Bohemian Range on Keweenaw Point, of the Ontonagon, Porcupine Mountain, and “South Range” districts of western Michigan, of the Snake and Kettle River region of Minnesota, and of Mi- chipicoten Island—its chief result, so far as the basic rocks are concerned, has been to extend the application of Pumpelly’s conclusions over the entire spread of the Keweenaw Series. I have been able to recognize a number of new varieties of his gabbro, melaphyr and diabase, and two new kinds— anorthite-rock and diabase-porphyrite—not to be included under any of these three, though closely related to them, and have found that there is a large class of rocks which are intermediate in point of acidity. The classification given below of the basic original rocks of the Ke- weenaw Series is based not only on microscopic differences and resem- blances, but also upon the characters and relations of the several kinds as seen in the mass, and on their prominence and persistence in the field. For instance, the first group given of the coarser grained rocks is made to in- clude orthoclase-free gabbro and diabase, olivine-diabase, and olivine-gab- bro,’ because all of these in the hand specimens bear the closest resemblance to each other, and in the field are seen to constitute parts of the same con- tinuous mass or bed, forming together one of the most prominently occur- ring types. 1The distinction between diallage and augite is a valueless one, since not only are both often found in the same section, but every gradation is found in the rocks of this class from augite to diallage. BASIC ORIGINAL ROCKS. 37 It will be seen at once that all of the kinds named are very closely related. Except one extreme phase—the anorthite-rock—they are all pla- gioclase-augite rocks (the diallage being but a phase of ordinary augite) and all carry magnetic or titanic iron, while olivine is a common ingre- dient. The differences consist only in variations in coarseness of grain, relative amounts of the several ingredients, presence or absence of olivine, presence or absence of unresolvable base, presence or absence of ortho- clase, variations produced by metasomatic changes, and variations in texture from granular to vesicular (amygdaloids). All of the kinds, though dis- tinct enough in the field, are in fact, lithologically considered, but phases of one kind of rock, for which usage has not established amy common name. The term “ basalt,” restricted by Rosenbusch to the younger equivalents of the pre-Tertiary olivine-diabase and melaphyr, has been much used with a more extended signification, and might, perhaps, be not improperly used as a general term for all plagioclase-augite rocks, young and old. BASIC ORIGINAL ROCKS OF THE KEWEENAW SERIES. I. COARSE-GRAINED. 1. Gabbro and diabase; olivine-gabbro and olivine-diabase; all free from ortho- clase. 2. Orthoclase-bearing gabbro. 3. Hornblende-gabbro. 4, Anorthite-rock. II. FINE-GRAINED. 5. Diabase of the ‘“‘ordinary type.” 6. Olivinitic fine-grained diabase and melaphyr. 7. “ Ashbed”-diabase and diabase-porphyrite. 8. Amygdaloids (vesicular diabase and melaphyr). COARSE-GRAINED BASIC ROCKS. Orthoclase-free diabase and gabbro, olivine-diabase and olivine-gabbro.—The rocks included here have a prevailing very dark-gray, often black, shade. More rarely they are light-gray, when the plagioclastic ingredient becomes greatly predominant, as is apt to be the case in the coarsest kinds. Not unfrequently a brownish film (ferrous oxide) over the shining black augite produces a resinous hue, and a somewhat similar effect is occasionally produced by a relatively large proportion of olivine. The texture is a 38 COPPER-BEARING ROCKS OF LAKE SUPERIOR. very highly crystalline one, causing a rough-surfaced fracture. The sev- eral primary ingredients, except olivine, can nearly always be recognized with a lense, and in the coarser kinds with the naked eye. The specific gravity ranges from 2.8 to 3.1. The olivine, which is a common, but not constant, ingredient of these rocks, is, when present, always the oldest of the chief ingredients, as is plainly enough shown by its relation to the others in the thin section. Occasionally in the fresher rocks it may be detected with the lens in char- acteristic glassy, green grains, and at times is even of so large a size as to attract the unaided eye; as, for instance, in a resinous-hued, rather coarse, and a good deal weathered rock, which forms a low cliff on the north shore of Lake Superior (Sec. 34, T. 57, R. 3 E., Minnesota), a short distance east of the mouth of the Brulé River. In this rock the olivine occurs in abundant, black, glassy particles, from one-sixteenth to one-third inch in diameter, with a scaly structure from commencing decomposition, and is evidently, from its high iron content, close to the variety hyalosiderite. In specimens from the vicinity of Bladder Lake, in Ashland County, Wisconsin, a light- green, glassy olivine is very noticeable to the unaided eye. As seen under the microscope, the olivine occurs nearly always in irregularly-outlined, rounded particles, from a fraction of a millimeter to two or three millimeters in length. Only very rarely does it present crys- talline outlines. Commonly, it is largely fresh, presenting a grayish or nearly colorless section, with the characteristic rough surface. It is, how- ever, very rarely so fresh as to be without some traversing rifts, edged with a greenish-brown or brownish-yellow alteration-product. In less fresh kinds this brown alteration has affected the whole area, and in such cases the rock has macroscopically a pronounced resinous appearance. Less fre- quently, but still often, the iron oxide, instead of heing deposited about and within the olivine, has been leached out, and then the mineral is more or less completely represented by a greenish material, supposed to be serpen- tine. In a number of sections in which this greenish alteration was observed magnetite was noticed in small particles, associated with the green in such a way as to suggest that it also was an alteration-result from the olivine. In some of the very coarse-grained gabbros of Bad River, Figs /and2z Coarse olirine-deabase or olivine-gabbro fram French River Ainnesota Pgs or @inary Zug ht Scale 25 @tameters Pug2z polarized leg ht. Olzrine (z/, wnaoréAzte (2/, Le allagec augele (3/ Sce POSESELAE/ fig ¥ Coarse olir2 ne-drabase or olivine-passro Srem north shore Lake Superzor, near Sucker Hrver, Alen Seale 26 deamelers. Ordinary aught. See 2p xiend7 Ole rexey/; arnorthile(2); diallagee augite(t), Lelan rferout magnetrle W/; Greex alteration prodrect oY odexe ne (S/ Pig 4. Zarge olivines from same rock as shown wn Figs andes Scale 28-@zamelers. Ordinary lrght. Jee ZR 7, 281 These oderznes ald appear as of cate x, or morn, only porleanrs are enteredy fresh (Wy they are traversed ay refts(2/; along whicek there te an alteraliow to serpentene(W, and ~ oxzde of zrow (4, both of whr~ek alleretzon products agro exten® aray rem the cracks. Vv ROCKS OF LAKH SUPHRIOF can nearly ls W ith the wns a low '! nesota), a YOGE the olivine oce: : ‘od re | 4 i: 1 LTTICLes rom ONG-sB1ixk : 1 Oone-thira SysSasrasS ESoshaahy Joyo /o ci dupSsovst yey, son with a 600] V\RRIERE UW ody RARGQIERENG Au lous OSORNO) SANOS Esse NRTA F ' “NGS SR Rag, sab hig SRqs3 Ssessesho SQsd = Wiskinan.: ask deren Ssgys5 SOSQDSs) CARY BYS RS ARN ax owsSO rv notice ® to the unaided eye eros vine occurs nearly always in mm a fraction of a millimeter to y very rarely does i eR ; ; ak ne Ly fresh, presepfing Las wfected the wholes which tus small irtic AT if mI V O; i LSrns LQ xr nwohy 19 hoors onor swore, taniesle ogiad SQth SHOT onEkog-owsxslo xo sinissbb-swserSostr909 bys Ms MX Kec Adgsd YrascsioxD LUsDascssHxs a8asB asso SSR AD xeKossk cass sWsTsgeb hol ovoky Axon TKOSIWOG WKS wcewco sestas Xp te sasegs Woe vernsiake ors hT XP Gus ik agosG -SAQS yrosxsh+O asssans s&S ~S aSoot Raval WS)tPE Se Ssursxoax aes Yes 8) Saad (Sorsdec3 os rouse s scadsd WY SSsqs5 SsqoSosb ‘WS\SSsASvosv9 ps0 yy Sara Wor sss 9a av oS grosNavsSfo ao Vs otsAS Losin Ne) r95¢sKa8e Vy Sonora scos sar ovin ss seb R, NH o¥sSorr gan WossS ong ucossoacs $a Losdw Ao Aso A) ucors Yo ohsrxo ; -TRoeano si esanh Vewa Basdxs ods «it ORTHOCLASE-FREE GABBRO. 39 Wisconsin, as first shown by Julien,’ the olivine shows a very interesting and unusual mode of change, namely, into biotite, viridite, and tale, the two former replacing the interior of the olivine grain, the latter forming a sort of shell of minute flakes around the outer part of the grain. Parti- cles may be seen in all stages of this change. Next to the olivine, in order of age, is the plagioclastic ingredient. Its crystals are usually in elongated forms, running from under a sixteenth of an inch in length to two or three inches in the coarsest kinds. The outlines of these crystals are commonly linear, or at least partly so, but in some sections the mutual interruptions have produced completely rounded con- tours. In composition—to judge from measurements of the angle contained between the maximum extinction positions of adjacent hemitropic bands, in sections cut at random in the zone OQ: 7%, as viewed between the crossed nicols—the plagioclase appears always to be near the basic end of the feld- spar series. The sections measured were known to be in this zone by their giving equal, or nearly equal, angles between the position of coincidence of a nicol plane and the lines of junction of the hemitropic bands, and the maximum extinction position of the one set of hemitropic bands on the one side of this position of coincidence and that of the other set on the other side. The method is Pumpelly’s modification of Des Cloizeaux’s method of distinguishing between the plagioclase feldspars.” According to it, those feldspars from which the largest angles obtainable, after measuring a number of individuals, are below 36°, are classed as oligoclase; those whose largest angles lie between 36° and 62°, as labradorite; and those giving angles above 62°, as anorthite—the size of the angles increasing with the basicity.’ 1Vol. III, Geology of Wisconsin, p. 235. 2 Metasomatic Development of the Copper- bearing Rocks of Lake Superior; Proc. Am. Acad. Sci., Vol. XIII, pp. 30, 31. (1878.) 3The method is, of course, open to the objection that it determines the presence of only the high- angled or basic feldspars. In a rock of which a number of sections refused always to give any but low angles this would not be any objection, but in those giving high angles it leaves room for doubt. Nev- ertheless, in the present case I have little doubt that there is only one feldspar concerned. This is indicated by the exact similarity in all respects in any one thin section between the high-angled and low-angled particles, the latter of which are, indeed, but few in number. So far as the Lake Superior rocks are concerned, I have always found those feldspars which refuse, through a number of sections, to give high angles to have strongly-marked peculiarities, among which greater tendency to decompo- sition, and relatively very narrow lineations between the nicols are most prominent. It is also my experience that these low-angled feldspars are always associated with orthoclase, or, if they occur with- out orthoclase, that they are only large-sized porphyritic ingredients in an aphanitic base. AO COPPER-BEARING ROCKS OF LAKE SUPERIOR. In the table given below the angular measurements always represent the largest angles that could be found. It will be noted at once that two- thirds of these measurements are high enough for anorthite—the most basic of the plagioclases—while in all the remaining sections entered as contain- ing labradorite, angles were obtained not far below the upper limit for that mineral. In some of these cases there was difficulty in finding enough plagioclase sections in the right zone, and other slices might have given higher angles. The plagioclastic ingredient of these rocks is commonly quite fresh, and always fresher than the olivine or augite. When alteration occurs, it is usually but a slight cloudiness. In the angular measurements made on over two hundred sections of the several kinds of basic rocks, it was ob- served that the freshness of the plagioclase bears a distinct relation to the size of the angle between the maximum-extinction positions of the adjacent hemitropic bands, the freshest feldspar always giving the largest angles, and vice versa. Pumpelly gives an instance (that of the rocks of bed 96 of the Eagle River section, Keweenaw Point) of a change of the plagioclase to prehnite in a rock of this class. This is an alteration commonly noted in the finer diabase, but in the rocks of the class now under description it is well-nigh unknown. In sections of the very coarse-grained gabbro of Bad River, Wisconsin, large areas are often seen which polarize monochromatically, and are hence parallel to the brachy-pinacoid. These areas are thickly crowded with minute black needles, arranged in several directions. The needles, whose nature is in doubt, are characteristic’ of the gabbros of many other regions. In the Bad River rock the set of the needles lying parallel to the vertical axis includes very much the larger number. Other needles, making an angle of 112° with the first, and evidently placed parallel to the strong basal cleavage, are fewer in number, but much longer. Still others, very numerous, lie oblique to the plane of the section, and are parallel to pyra- midal planes.? The occurrence of the large monochromatically polarizing 1Geology of New Hampshire, Vol. III, Part IV, pp. 94. 2Compare Geology of New Hampshire, Vol. Ill, Part IV, Plate V, Fig.5; also Fig.3, Plate XV D, Geology of Wisconsin, Vol. III; also Fig. 58, Plate X, Rosenbusch’s ‘‘Microscopische Physiographie der massigen Gesteine.” Coarse Olirne-Gabbro from Bladder Lake, 'Fes.; Ordinary legate. Scale zo diameLems Lebradoerite (1); argrte(2)/; deadlage(3/,; olivinel4/; tetanzferoue magnetrte (S$), Brotitels/ Secondary Zo éiivine,— brotete(z; c707-oxrdelay; Cale 9; rereaze [zo/, wrsdaseosh v1 SS.990 SAqsS rast sion O vty shad pyrite(t) ; pcher(P/ Surrounds ng the mag netrle anc pyrite and con- tarneng biotite seoazes ofa seooncdary reature [1a/. ORTHOCLASE-BEARING GABBRO. 5S the S. E. 4, Sec. 32, T. 48, R. 12 W., Douglas County, Wisconsin. Other instances are the coarse gray rock of the Saint Louis River bluffs at and near Duluth, Minn.; the exposures in the woods west of Lester River, Min- nesota, in Sec. 29, T.51, R.13 W.; the rock exposed in the bed of Cascade River, in the southern half of See. 10, T. 62, R. 2 W.; the rock of the south side of Eagle Mountain, about four miles north of the last-named place; and the rock forming the west wall of the gorge through which the trail passes from Eagle Mountain to Brulé Lake. Tabulation of observations on orthoclase-bearing gabbros. Angle between maximum ex- tinctions of adjacent hemi- “ tropic bands of o : the plagioclase a ince a Macroscopic char- | Constituents as determined by in sections cut 5 , 3 acters. microscope, in order of age. at random in a 3 - the zone O: 72. | a oa 2 E Fi rales Angles on | & 6 cs Bis E = opposite | og & Bae (Soul) wes sides of | Sg n Clalal wa eross-hair. | = ° ° ° 1902 | Bohemian Mount- | NE, | 32 | 58 |29W.| Medium - grained | Apatite, abundant, often quite | 14 17 31 ain, north side to coarse-grain- large crystals; oligoclase and | 11 13 24 Lac la Belle, Ke- ed; mixture of orthoclase, both reddened and 4 si 11 weenaw Point, red feldspars dulled; titaniferous magne- 2 4 6 Michigan. and shining dark tite; augite; diallage, mostly | 20 18 38 greenish - black altered to uralite; amorphous 4 5 9 mineral. green substance, secondary to | 15 12 27 augite; gray substance sec- ondary to titaniferous magne- tite; a little secondary quartz. Bed 94! Eaglo River sec- | SE. | 30 | 58 !31W. Medium - grained | Apatite ; oligoclase ; orthoclase ; 22 tion, Keweenaw to coarse; black, titaniferous magnetite; augite; 23 Point, Michigan. thickly studded a little altered magma ; sec- 31 with long red ondary ferrite, chlorite, quartz, 33 feldspars. Sp. from the feldspars ; secondary 33 gr., 2.94, yellowish-green mineral and 33 magnetite, from the augite. 36 6 W. | Old Ironton trail, | N. 4} 34 | 46 |1W.| Coarse-grained, | Plagioclase; orthoclase, highly Ashland County, red, black, and altered, much stained with Wisconsin. gray mottled; ferrite ; titaniferous magnetite, shows much coarse and abundant; diallage highly - magnet- largely altered to wralite ; chlo- ite. Sp. gr.,2.89. rite secondary to the feldspars ; magnetite, secondary to dial- lage; alittle secondary quartz. 1 Metasomatic Development of the Copper-bearing Rocks of Lake Superior, Proc, Am. Acad. Sci., Vol. XU, pp. 253-309, 54 COPPER-BEARING ROCKS OF LAKE SUPERIOR. Tabulation of observations on orthoclase-bearing gabbros—Continued. Angle between maximum ex- tinctions of adjacent hemi- tropic bands of 5 A : : a the plagioclase | Place. g Macroscopic char- Constituents as determined by in sections cut 5 3 acters. microscope, in order of age. at random in | S : the zone O: zi. g 4 | # ; Angles on | 2 4 = & é &p apiorite cet 2 Sie lboaleaal eas sides of | 43 a e l|alal| & crosshair.) © ° ° ° 61. | Cut on Wiscon- | SE. | 30 | 45 | 2W.| Coarse-grained; | Oligoclase, predominating in| 14 16 30 sin Central red - and - black large crystals, much clouded, 9 10 19 Railroad, Bad mottled ; rough- but still showing the banding | 14 14 28 River, Ashland textured. distinctly; orthoclase; very County, Wis- coarse titanic magnetite ; consia. greenish hornblende or uralite, showing strong dichroism, and in a marked degree the characteristic prismatic cleav- age, but evidently an altera- tion from diallage and augite, as proved by the existence of a few cores of the original substance. This hornblendio mineral fills in the spaces be- tween the oligoclases in the manner characteristic of the gabbros. 641. | Brunschweiler’s | SE. | 16 | 45|4 W.| Coarse-grain‘ed, | Apatite, in very large crystals; | 21 | 23 | 44 River, Ashland dark greenish- labradorite ; orthoclase; titan- | 16 22 38 County, Wis- gray, mottled iferous magnetite, very abun- consin, with dull red| dant and coarse; wralite; and white. quartz, ferrite, secondary feld- spars; chlorite, secondary to uralite. 1121. | Bayfield County, | NE.| 12 | 44 | 6 W.| Coarse-grained; | Oligoclase; orthoclase; highly | 10 14 24 Wisconsin. dark greenish-| altered titaniferous magnetite, gray, sparsely very coarse and abundant; di- mottled with] allage, almost wholly altered red; dull. to uralite ; chlorite secondary to feldspars ; ferrite. 2021. | Douglas County, | SE. | 32 | 48 |12 W.| Medium-grained; | Apatite in long crystals; oligo- | 10 il 21 Wisconsin. red- and - gray - clase, stained red; orthoclase; | 17 15 32 mottled. Sp. diallage, sparse, mostly al-| 10 ll 21 gr., 2.76. tered to a dark-green sub- stance; ferrite, chlorite, quartz, secondary to feldspars. 2051. | Aminicon River, | SE- | 32 | 48 |12W.| Coarse-grained. | Labradorite (in sections cut at Douglas County, Wisconsin. red-and black- mottled. random in the zone O: 72, the angle ranged from 37° to 509; a section cut independently and carefully parallel to O gave 12° to 14°); orthoclase ; augite; diallage in twinned plates. (Pumpelly, Geology of Wisconsin, Vol. III., p. 41.) iv? a ee ee oe ORTHOCLASE-BEARING GABBRO. 55 Tabulation of observations on orthoclase-bearing gabbros—Continued. Angle between maximum ex- tinctions of adjacent hemi- 4 tropic bands of 5B el, the plagioclase 2 Place. a Macroscopic char- | Constituents as determined by in sections cut g 3 acters. microscope, in order of age. at random in A S . the zone O: ii. g 4 | | ; Angles on| 2 : a ISlel § eppeste| 3 a B 2 | ° S 0 a n Clnla!] & cross-hair.| & @ ° ° ° 10. Near Duluth, | NE. | 33 | 50 |14W.| Very coarse-grain- | Apatite ; labradorite; orthoclase; | 23 22 45 Minn., 1,980 ed; light-gray;| titaniferous magnetite; diallage 9 10 19 north, 0 west. much pinkish | mostly changed to wralite. titanic iron; very rough-text- ured. 3...... Near Duluth, | N.4 | 28 | 50 |14W.| Coarse-grained; | Apatite in a few large crystals; | 22 21 43 Minn., 1,970 light-gray ; very labradorite; titanic iron, | 27 20 47 north, 680 west. rough-textured. abundant; diallage, highly | 27 23 50 fibrous and largely altered to uralite. | teen Near Duluth, | NW.| 28 | 50 }14W.| Very coarse-grain-| Oligoclase; orthoclase; little | 12 11 23 Minn., 2,000 ed; light- gray; titaniferous magnetite; dial- 8 13 21 north, 1,300 west. very rough-text- lage mostly altered to uralite. ' tured. | (Heeaas Near Duluth, |NW.| 28 | 50 |14W.| Very coarse-grain- | Apatite, in quite large crystals; | 13 16 | 29 Minn., 1,800 ed; light-gray; oligoclase ; orthoclase; titani- | 11 13 24 north, 2,000 west. very rough-| ferous magnetite; diallage,| 12 13 25 textured. partly fresh, partly altered to uralite; ochre; biotite. 509....| Top of bluff, Du- | SW. | 27 | 50 |14W.| Very coarse-grain-| Labradorite; titaniferous mag-| 20 24 44 luth, Minn. ed; dark-gray. netite; diallage, partly fresh, | 25 24 | 49 partly altered to wralite and | 21 25 46 chlorite. | BLL: soe| sees COs seeccccscse SW. | 27 | 50 | 14 W.| Very coarse-grain-| Apatite in large crystals; labra- | 20 19 | 39 ed; light-gray; dorite, much altered; titani- | 26 24 50 rough-textured. Jerous magnetite; diallage, | 23 23 46 much altered; chlorite. 508....| Near quarry, Du- | SW. | 27 | 50 |14 W.| Very coarse-grain-| Labradorite or anorthite, much | 31 31 62 loth, Minn, ed, the plagio- clouded; titaniferous magne- | 19 21 40 clases running| tite; diallage, mostly altered from ahalfinch| to uralite. to an inch in length. Sie => Lester River, Min-|NW.| 4 | 50 |13W.) Medium-grained;| Apatite abundant; oligoclase | 14 15 29 nesota, near red - black-and- much clouded; orthoclase; 8 10 18 northwest cor- green - mottled; titaniferous magnetite; non-| 13 13 26 ner. muchweathered.| diallagic augite; alteration- product of augite. At, os Near Lester River, | NE. | 29 | 51 |} 13W.| Clese to 39, less ; Labradorite, orthoclase, in the | 19 21 40 Minnesota. weathered. characteristic twins; titani-| 29 320 59 ferous magnetite; augite in| 16 14 30 long, twinned blades; dial- lage; a green alteration-pro- duct of augite; secondary quartz. 18 15 33 56 COPPER-BEARING ROCKS OF LAKE SUPERIOR. Tabulation of observations on orthoclase-bearing gabbros—Continued. Angle between maximum ex- tinctions of adjacent hemi- a tropic bands of g the plagioclase 2 Place a Macroscopic char- | Constituents as determined by in sections cut g . 3 acters. microscope, in order of age. at random in A 8 : the zone O: it. plaid ree & <] : ngles on| 2 .- i -i/2/a! & osite | oS 2 ER es Se) | sides of] 4¢ 1-2) oe \|aia Fy cross-hair.| & © ° ° ° heed boos: Gre coseecs SE. | 29 | 51 |13W.| Medium-grained| Apatite, large and abundant; | 20 25 45 to coarse-grain- labradorite; orthoclase; titani- | 16 21 37 ed; resinous;| ferous magnetite; augite in| 12 13 25 brownish; au-| long, twinned blades; dial-| 17 17 34 gite in long radi- lage; ochre ; much secondnry ating blades. Sp. quartz. gr., 2.82. 1057...| Bed of Cascade | S.4 | 10 | 62 | 2W.| Medium-grained;| Apatite; labradorite; ortho-| 21 18 39 River, Minne- black-and-gray - clase; titaniferous magnetite; | 30 28 58 sota; 12 miles mottled ; rough- diallagic augite,muchaltered; | 22 18 40 from mouth. textured. Sp. secondary quartz. gr., 2.82. 1062...) South side Eagle (abou|t)26 63 |2W.| Medium-grained| Apatite; labradorite; ortho-| 16 14 30 Mountain. | (Not surveyed.) tocoarse; nearly | clase; augite, sparse, highly | 22 26 48 black; rough. altered, and filled with dusty | 26 28 54 magnetite (alteration-pro- duct?); secondary quartz. Hornblende-gabbro.— Along a belt of country, some fourteen to twenty miles in length, running westward from Bad River, Wisconsin, through parts of townships 44 and 45, ranges 3, 4, 5, and 6 west, at a horizon not far above the Huronian slates, exposures of a peculiar hornblende-gabbro have been noticed. This rock differs from the uralitic gabbros previously described in containing, instead of the fibrous, greenish, comparatively weakly dichroic uralite, a deep-brown, intensely absorptive, so-called basaltic hornblende. Some of these rocks have been described briefly by Pumpelly in the third volume of the Geology of Wisconsin,’ under the name of ‘“‘augite-diorite.” He regarded the hornblende as primary, and the rocks as intermediate between diabase and diorite, whence the name.” In the same volume I suggested that the hornblende was secondary, and that the rocks were merely altered gabbros.’ This opinion I find sustained by a re-examination of Pumpelly’s sections, and a study of a number of 1Page 36. 2Page 170. 3Page 170. Figz Horn blencle-gabbro fiom Ashland County, Pris. Fig.2 Hornhblende gabbro from Ashland County, Mes. Ordinary laght. Scale diameters Ordinary lyht Scale 2¢ drametert Labradorite(1/; orthoclase(2); augrte (x) largely alleren O%goclase/z) | orthoclase/2), brown hornblende(s), ura live torerrdzle and uralrte, brown hornblende (4), tctancef- (#), altered from drallage ih se: leniferows magnetite (S) ; erous magnetile(s/, apatites), guartazlb/; apatrtelz), GZZ : oe ; Ar ‘ 4 ; Fe9.3 Hornhlende -gabhro from English Lake Hrs. Fig. 4 Anorthite rock from north shore of Lake Super- Ordinary leght. Scale 29 crameters tor, Sec.s, Li st, Re Minn. Polarizec LipAt, Hornbiendel1 mith cores of augrte(2),; labradorite (g/ Seale /7 diameters magnetite (as. Made up wholly of anorthite enderiduads si daca) foreasAak sory onhSng sbss A eo. spy as pyro) Sos oS Aw von as ddng-slosc 33d sexo xg avs¥ascsshb ds oVa0G SAG tastsGnO + i wrsSorc esha shart YAgsd wrascshrO SssV ora Leo esd Groh sow oth \( S\stsboaN sro 4 level 20gssO bers tis Msersd S¥sqssn. Adlsrarolss0 Avsywoboardok CUD OYsSoseQone naser Shs easy .2gsMinss sno} Sovsbds yy Assests As) Shcad&scrok pwovd Vo¥sSavas Sw odshosxo¥ oF A*heSsSaqa ,\d)\ sro NDISSOTG LY odsSongont vas09v9 : b fata a eee “Magul skal Yo sve Anos sovk Aon oF ehdworky. pgs ASK eXol Aidgxh meted onbdag abraldsra\ gs) SAV HasxsvaboN aesdhR WaK ba Nash oxo uvasescssh ts sinob SAqsS yronsbrO avabarsccssh sv sSa5b Xe) oYarnobbands) \s)oSsqsn Yo rer02 A¥rw Whobsrshdecrol\ Warsbbsshrs a¥sAross Xe Wor sas Seah Aw) a¥sdoscqart HORNBLENDE- GABBROS AND ANORTHITE-ROCK HORNBLENDE-GABBRO. 57 new sections from other outcrops. The rocks described in the table have been selected to illustrate the different phases of this hornblende-bearing rock. The first one is a rock in which the basaltic hornblende is in small quantity only. The next three contain more hornblende, and are peculiar macroscopically, being mottled black, white and pinkish. They also carry a good deal of original quartz. The last two are black rocks, in which the hornblende makes up most of the section. Abundance of coarse apatite, presence of a low-angled plagioclase, of orthoclase, and of original quartz seem to be prevailing characteristics. Tabulation of observations on hornblende-gabbro. Angle between maximum ex- tinctions of adjacent hemi- tropic bands of the plagioclase u oO * ¢ 2 a Macroscopic char- | Constituents as determined by | in sections cut g Place. 3 acters. microscope, in order of age. at random in A 3) 3 the zone O: 74. a 2 & — 3 Bg fa Angl on a ngles on| 2 B:| 2£/8/4a|¢ opposite | 3 3 SE /s|e& i My f| a2 EI Suliouliva sides 0: A a Se lala] cross-hair.| B © ° ° ° 137 W.| Ashland County, |N.W.| 35 | 45 |4 W.| Medium-grained; | Apatite, in large crystals, very | 12 17 29 Wisconsin. cor. dark greenish- abundant; labradorite, incrys- | 19 21 40 gray. tals often much rounded, quite | 24 21 45 fresh; orthoclase (?) ; magnetite or titanic iron, very large and abundant; augite, very abund- ant, in very large, rounded par- ticles between the feldspar grains, only rarely showing the diallage cleavage, partly fresh, partly altered by spots and streaks of a greenish fee- bly dichroic or non-dichroic substance; brown, intensely absorptive, and dichroic horn- blende, not very abundant, oc- curring partly away from the augite—but like it between the feldspar grains—and partly in patches within the areas of the altered augite, in such a manner as to suggest its sec- ondary origin; uralite, in little streaks within the altered - augite. ee 58 COPPER-BEARING ROCKS OF LAKE SUPERIOR. Tabulation of observations on hornblende-gabbro—Continued. | Angle between maximum eX- tinetions of adjacent hemi- tropic bands of a ; the plagioclase 4 Place. 8 ; Macroscopic char- Constituents as determined by ae aeougre cut =| 3 acters. microscope, in order of age. at random im EI SI ns the zone O: wt. g B a zl Angles on| & |; a £2 é E) opposite ice 2 5B |3|5|6é sides of| 4 8 nm Clalal & cross-hair. ' ——————— (asec ase ee ee SS ea ’ ° ° ° j 9022 I.| Ashland County, IS. W.| 53 | 45 | 3W. Medium-grained ; Apatite, very abundant, insmall | 20 19 39 f Wisconsin. mottled black crystals; labradorite and ortho- j | and white; clase, in much rounded parti- rough. Sp.gr., cles; diallage, often partly 2.83. altered to uralite; non-dial- lagic augite ; basaltic horn- blende; a few large scales of biotite; quartz, filling corners and apparently primary, abundant. 2020 I.|.---d0 ...------20-|--22°* 2 | 44 | 3W.| Medium-grained; | Apatite; oligoclase and ortho-| 7 | 5 | 12 5 d neatly black: clase in much-rounded grains; 5 3 8 rough-textured. magnetite, or titanic tron; 1 4 5 augite, very abundant, in large, rounded grains, attimes diallagic; basaltic hornblende, not very abandant, secondary, and grading into augite; quartz, filling corners, not abundant. 106 I..| Ashland County, |N.W.| 17 | 44 5W.| Medium-grained; | Apatite, very large and abun-| 7 P| abe Wisconsin, north mottled black, dant, just as in No.1 of this| 11 12 23 line of white, and yel- group—often in hexagonal sec- lowish-pink; | tions which reach .01™™ in rough-textured. diameter; oligoclase ; ortho- clase; magnetite, or titanic iron; diallage almost wholly changed to uralite; basaltic hornblende, occurring just as in 137 W., but very much more abundant; biotite, in ® few flakes; quartz, ina few spots, filling corners, apparently original; chlorite and ferrite, secondary. 187 W.| English Lake, at | S.4| 5 | 44 | 3W. Medium-grained; | Apatite, in afew large crystals; | 15 | 13 | 28 outlet, Ashland black; lustrous. labradorite; magnetite, small | 24 23°) 47 county, Wiscon- and sparse; augite, mostly | 13 14 | 27 - sin. quite fresh; basaltic horn- | blende, making up most of the section, in a few cases appear- | ing to shade into the augite; biotite. | 06 W..| Ashland County, | S.4 | 15 | 45 | 1 W- Medium-grained | Oligoclase ; orthoclase; magne-| 14 Ww 31 Wisconsin. 1 to fine-grained; | tite; augite; basaltic horn-| 13 | 16 | 29 nearly black. blende; biotite. Resembles | 11 13 24 Sp. gr., 3.08. No.5, but much finer grained. F e ANORTHITE-ROCK. 59 Anorthite-rock—At several points on the north or Minnesota shore of Lake Superior, between the mouth of Split Rock River and the Great Palisades, and again in the high point near the mouth of Temperance River, known as Carlton’s Peak, are to be seen exposures of a very coarse light-gray to colorless or white rock, occasionally with a faint greenish tinge. This is seen in the thin section to be composed exclusively, or nearly so, of anorthite feldspar. Often there is no other mineral present except in exceedingly minute inclusions, and these are very sparse. In one section a few grains of altered olivine were noticed within the anorthite, and in two or three a little augite between the feldspar grains. The feldspar appears in every case to be anorthite. In no section did it show the peculiar ar- rangement of needle-like inclusions met with in European gabbros, and so common in the coarse gabbros of Lake Superior, to which this rock is very nearly related. This anorthite-rock presents very interesting occurrences, as described in a subsequent chapter. It appears both as masses cutting black gabbro, and as included angular masses in the same rock. Tabulation of observations on anorthite-rock. Minnesota. light-gray. Angle between maximum ex- tinctions of adjacent hemi- 4 tropic bands of 5 the plagioclase a2 Pla FI Macroscopic char- | Constituents as determined by | 12 sections cut g cst 3 acters. microscope. at random in 5 8 : the zone O; it. 9 % & . oO a Pn es Z & £1814! 5} es |8/e a =} $|° g n CP ln|aA] & 729....| North shore Lake | SW.| 5 | 54|8W.| Very coarse-| Pure anorthite, without acces- | 28 30 58 Superior; 14 grained; the sory. 37 41 78 miles below crystals reach- 35 41 76 mouth of Split ing an inch in Rock River, lengthand Minnesota, near breadth; color- center of less to white; occasionally with a greenish | tinge. | 746....| North shore Lake | SW.| 5 | 54] 8W.| Very coarse-| Pure anorthite, without acces-| 34 40 74 Superior; 1} grained; the sory. 22 25 47 miles below single crystals : 29 24 53 mouth of Split often reaching Rock River, 4 inch across; 60 COPPER-BEARING ROCKS OF LAKE SUPERIOR. Tabulation of observations on anorthite-rock—Continued. Minnesota. g | | 2 Place. g | SESE char- 5 = ; FI | |S 5 By) SEH a 6 |a\|a] & 750....| North shore Lake | SW.| 5 | 54 | 8W.| Coarse-grained; Superior; 13 nearly white, miles below with faint green- mouth of Split ish tinge. Rock River. 759....| North shore Lake | NE.| 5 | 55] 8W.| Very coarse- Superior; 2 grained; nearly miles below colorless, with mouth of Split faint greenish Rock River. tinge. 792....| Falls of Beaver | SW.| 12 | 55| 8W.| Very coarse- River, Minne- grained; trans- sota. lucent; nearly colorless, but with faint green- ish tinge. 795..-.| Beaver River, | SW.| 12 | 55 | 8 W.! Coarse-grained. Anorthite, in large crystals, Constituents as determined by Angle between maximum ex- tinctions of adjacent hemi- tropic bands of the plagioclase in sections cut microscope. at random in the zone O: i. Angles on) 9 opposite| o S sides of|4¢ cross-hair.| B © | ° ° ° Pure anorthite .....-.----------- 39 34 73 42 40 82 35 33 68 Anorthite, in large crystals, makes up most of the section. The large crystals are often crushed into fragments at their extremities. Among the fragments are smaller an- orthite crystals, and numer- ous small rounded grains of augite. Pure anorthite, in very large, unbroken crystals. makes up most of the section. A few small grains of olivine, altered to a brown ocherous substance, occur in the feld- spars. A little augite lies be- tween the feldspar grains. Bands of viridite cross the feldspars. The anorthite car- ries long rows of minute, rounded inclusions, readily seen with a low power (70 to 80 diameters). These rows run for short distances paral- lel to the cleavage, but are mostly in rows crossing the cleavages. A higher power shows numerous bubbles in these inclusions. The bub- bles will not disappear or move at a temperature of 112° C. Black microliths also oc- cur in the particles. 3) PRS SE POY \ Oe Sw Kine : as (jor = ? S ) PSEUDAMYGDALOII DIABASE AND DIABASE -gsoQ cease selubhrol scot HsaisheyscahsseL ¢ yen vv aSssnSsH 38% shnod SKqs YT mead as rn) und ose sdsd \\spoSsqasa Yo booshoxs, sos ).a5 Wa seworxd . (sls aloogiO Save ww) s¥svoSho Yo. rahash gisanGrsaeg, Uc) eVssosgoss tssorway Xe) stolosqea SSH SL oO tyS& geo'ssel le se b-¢ $ s Wahaus xs bass gst wiayarvash os Snob YAqsagnste'sh pe HV, PEG Vis li tegen Ae a A IN | — { ee / : {i — \ \ fi NES ~ 2 \ | NI \ BOZGe*) 0 \ NG) bie WN ay fs RAE La 1 @s 1,4 eh is ‘ ak, NT LY 5, A ee /\ 4 Way. JN W\\ GTA “ne wy EZ / f vi / ” d y \ LO é SS / — AA ANG eae WZ wl AEX ; SS VA es From north coast of Lake Superzor, SEM Seco Ts Riz Minn Oreinery Lagat Scade-20 drametens Augrtep)inlarge areas including many plagroclases (anorthite /\2), olz rene(s) and magretrle (4, chrefly zn the enterslices of the augrtes, the olzvene altered to ferrite and veredite: chlorite/s) ana calerte(/pseudamygdrles ; zreterstetral virzeditlre substance|l7) which may ~npart Aealtlerecd glass mag 77 a my f i , hy Ln eae tld : > LA oes Me SA Dihwie-A\Wy, y IN } / a ps ) TW, : — c ‘ i \ ss > N ; f WINS / Nv By > Oy Tenet LINER AR a AN y ay i\ 2M) f Al ee -N S wAsdssnas os sh090 Shad wwrsss son KKK A SAK WT p05 SAG osnomsd sol Yo Sun 99 Adson oT, ws SNQONS Sr \s)ostsw No .(s)\ 93 sMrore) YANIDGS YANG \sseosse QS SbasSos Srsen * ies oSah qQuecaipes seq ooVagesa oF viorqess onsttbasr sMieSovs ed «8 Figs Jands. diabaserporphyrite from Miohrpsecten Tsland ordinary crpht. Fig.2 seate t/ diameters. polarized Zepht. Fig. 7 Seale 7 @zamcters, Jee pages. rt, 78 Fb, 244, Parphy rite labradorite tiara augzte(2/, reth the latter is assoceated mmagnelete(s/ and & Greenrsh akleratconpro duct (¥/ / 7e@ Starne@ insoluble groundmas($/, Carrying enru- merable mioroliths of plagroclase Lhe latter are. very rnadeguatety Shomuzn the engraring, their representatcon dering. Beyond the engravers art. Fey S ‘drahaseporphyrile Jrou Duluth, Meni. Scale vg deameters, Ordcnary leght Jee pages XU PZ TT Porphy rete urthoclare(1/ and olrgocdase(2/ often mth an eprd@otec alteration(s/; bace (4) Conse sle? lageocdare, magnets te, auge €e, pre wudamyg dalovd ancl an trresolrasle rudvtance Ys». l, = Hg. 4 ashbed-diabase from Lotoyatrg Rrver, Mek. Scaletodrameery Lelarized Ceght See pages ati, P9 Plagroclareyjaugrte in prarns(2/; magnretile (7. DIABASE-PORPHYRITE. ii Tabulation of the results of a microscopic study of fine-grained olivinitic diabases (includ- ing melaphyrs)—Continued. | | Angle between | maximum ex- | tinctions of adjacent hemi- | tropic bandsof | 8 | the plagioclase | 2 ives a Macroscopic char- Constitutents as determined by in sections cut g : a acters. microscope, in order of age. at random in 5 S “| | the zone O: 77. A a A= | ® eB :\a f | Angles on| © . =| & eat E 2 i/sia|] gs opposite | os = € 3S E g aden of| Ha E ejin'ial & cross-hair.| i | } } | | °o ° °o 958....| North shore Lake | SW. | 11 | 60 | 2W. Fine-grained; | Olivine, abundant, in small | 34 | 32 66 Superior, Cari- | dark reddish- grains, wholly altered to a red 32 35 67 «| bou or Black brown. substance and crowded into 25 | 30 55 Point, Minne- | theaugiteinterspaces; anorth- | 35 | 34 69 sota, from a) | ite; magnetite; augite, in the | layer overlying | | usual fresh areas; an exces- red sandy shale. | sively fine-grained rock. | | Diabase-porphyrite and ashbed-diabase-—The olivine-free, fine-grained diabases of the ordinary type pass into still finer-grained kinds, in which there is a black or brown color and a more or less perfectly developed con- choidal fracture. The finest of these rocks are completely aphanitic, and all kinds tend to a porphyritic development, carrying, as porphyritic ingre- dients, oligoclase and orthoclase, and, more rarely, labradorite and augite. The augite is always a subordinate ingredient, and appears at times to be almost wholly absent, at least as an individualized substance. These rocks play a very prominent réle in the Keweenaw Series, and are always very strongly characterized in the field. Some of the more distinctly crystalline of these rocks, as already stated, Pumpelly has described under the name of ashbed-diabase, the name being given from the fact that such a diabase forms the base of a flow, whose upper vesicular portion is the well-known and so-called ashbed of Keweenaw Point. As the external characteristics of this class of rocks, Pumpelly gives a light or dark gray or black color, a very compact texture, and a conchoidal fracture, and, as the accompanying microscopic characters, the subordinate position of the augite, and more especially its occurrence in rounded grains, whose contours are not determined by the feldspars.’ 1Geology of Wisconsin, Vol. III, p. 32. 78 COPPER-BEARING ROCKS OF LAKE SUPERIOR. My own study has shown that the typical ashbed-diabases of Pum- pelly are but phases of a large class of rocks; that between these typical kinds and the fine-grained, olivine-free diabase of the ordinary type there are various gradation-forms, in which the rounded grains of augite are mingled with more and more of the augite whose contours are determined by the feldspars; and also that, in the other direction, there are gradation- forms into aphanitic kinds, in which there is much non-polarizing, unindi- vidualized material. In extreme cases, as in a rock from Michipicoten, fig- ured at Plate IX., Figs. 1 and 2, the unindividualized base makes up the greater part of the rock. The presence of unindividualized base and the absence of recognizable olivine place these rocks among the diabase-por- phyrites, according to Rosenbusch’s nomenclature. But the ashbed- diabases are so plainly linked with these, both through intermediate kinds and through similarity of occurrence in the field, that all are considered here together. They all indicate rapidity of solidification, not only by the presence of unindividualized matter, but by the mode of occurrence of the augite. The groundmass of these rocks externally varies from light-gray to dark-gray in color, in more distinctly crystalline kinds; and is from light- gray to jet-black, and in one phase deep reddish-brown, in the less crystal- line kinds. With the former kinds the fracture is sub-conchoidal, with the latter very highly conchoidal and even glass-like, as in the case of some black semi-vitreous rocks that have a large development on Michipicoten Island. Under the microscope the tabular oligoclases usually make up most of the section in the more distinctly crystalline kinds, the more acid phases containing also orthoclase with the oligoclase. The augite is in irregularly- outlined particles, commonly very subordinate in quantity, though occa- sionally, as in some dense black rocks from Portage Bay Island, at the east end of the Minnesota coast, it makes up most of the section. The augite particles lie in the little spaces between the feldspars, which, how- ever, no individual particle ever completely fills. Several augite particles will occur together in such a space, or fill it along with the magnetite, or— and on the whole this is much more common—there is present more or less DIABASE-PORPHYRITE. 719 of a non-polarizing, cloudy, grayish, or red-stained substance, which repre- sents the original magma. This substance, when present in small quan- tities, fills the sharper angles between the feldspars. From these smaller quantities it increases in amount until it becomes a preponderating ingre- dient in the denser and more highly conchoidally fracturing kinds, when the feldspars are seen floating about in it in wholly separate particles. The red ferrite, which is an important ingredient in all of the browner kinds, has evidently come from the alteration both of the original magma and the augite. Among the porphyritic ingredients of these rocks the feldspars are much the most prominent. Commonly they are red, though occasionally white or colorless. The size usually is one-eighth to one-sixteenth inch in length or less. Orthoclase occurs among these feldspars, but they are more commonly oligoclase and rarely Jabradorite. Augite occurs as a porphy- ritic ingredient, but much more rarely than the feldspars. It is commonly much altered to chlorite. As adventitious ingredients may be mentioned epidote, quartz, calcite in pseud-amygdules and true amygdules, and apa- tite in the usual crystals. These diabase-porphyrites frequently assume an amygdaloidal char- acter in the upper portions of the flows, when they are commonly extraor- dinarily vesicular, very often with the vesicles elongated in a common direction. Frequently these extraordinarily vesicular amygdaloids have mingled with them, and often filling the vesicles, a red, shaly matter. The rocks here included vary considerably in silica content, ranging from 48 to 60 per cent. It is possible that some of the more basic, blackish kinds may represent the half-glassy forms of the olivinitic diabases, but this has not been proved by analysis or recognition of olivine as an ingre- dient. On the other hand, there is evidently in some kinds, especially in some of the redder varieties nearly free from augite, a greater amount than usual of orthoclase material, and with this often is a little secondary quartz. These kinds make up much of the so-called quartzless por- phyries, and are plainly the half-glassy form of the more acid orthoclase- gabbros. These kinds have about 55 to 60 per cent. of silica, and stand 80 COPPER-BEARING ROCKS OF LAKE SUPERIOR. between the acidic and basic half-glassy rocks, just as the orthoclase gab- bros do between the basic and acid granular rocks. As typical localities for the rocks of this class may be mentioned, for the more distinctly crystalline kinds, Beds 45, 65 and 66 of Marvine’s Eagle River section, Keweenaw Point;* for the kinds highly porphyritic with red feldspars, but without much non-polarizing matter in the base, the porphyry at the Duluth elevator, Duluth, Minn.; for the black and dark-gray kinds, with much non-polarizing matrix, the south shore of Michipicoten Island; and for the red aphanitic and brown aphanitic kinds, the north shore of Lake Superior, one mile below the mouth of Silver creek, N. E. 4, Sec. 22, T. 53, R. 10 W., and the bay above the Great Palisades, on the same coast. 1Geological Survey of Michigan, Vol. I, Part II, Chapter VIII. DIABASE-PORPHYRITE. 81 Tabulation of the results of a microscopic study of diabase-porphyrite and ashbed-diabase. Specimen number. 1963... Place. a Macroscopic char- | Composition as determined by in sections cut | 3 acters. the microscope. at random in 3 : the zone O: ti. 2 A & ;|4 : Angles on| 2 . £ g 8 & op osite| oS 8 io 8 sides of| 42 I S eq p |] Ce lala] «a cross-hair.| E ° ° ° 1900...| Bohemian Range, 30 | 58 |}29W.| Aphanitic; dark | Oligoclase predominates; augite, Keweenaw brownish-gray ; in minute grains; magnetite ; Point, Michigan. of a conchoidal chlorite pseud -amygdules. fracture. Old Suffolk min- | SW. | 10 | 57 |31W.) Matrix aphanitic; | This rock presents a deeply- 5 8 ing location, | cor, mottled dark stained groundmass, in which | 12 12 24 Praysville, Ke- reddish-brown} are scattered very large and | 13 | 14 | 27 weenaw Point, and black. Very abundant porphyritic oligo- 7 11 18 Michigan. abundant red clases and orthoclases, the 5 6 ll porphyriticfeld-| former much the more abun- 6 7 13 spars, which at dant of the two. In some sec- 0 6 6 | Angle between maximum ex- tinctions of adjacent hemi- tropic bands of the plagioclase times carry na- tive copper and native silver as replacements. SiO2, 59.52 per cent. 6LS tions the groundmass pre- sents much the appearance seen in 1799 (infra), except that the minute tabular feld- spars are more often recog- nizable. In these sections also are found the same al- tered porphyritic angites that are characteristic of 1799. In other sections the ground- mass presents a peculiar in- tertwisting of colorless and deeply brown-stained por- tions, often so arranged as to indicate flowage, and in some of these sections there are abundant, minute, elongated gas vesicles, now filled with quartz or a greenish chlorite. These vesicular sections are of specimens taken from nearer the upper surface of the bed. The proportion of unindivid- ualized matter is large in the more vesicular sections and in those indicating flowage; the deep-brown portions represent- ing the unindividualized mate- rial, the lighter portions being made up of completely indi- vidualized quartz and feld- spar. The rock verges close on the limit between the more acid diabase-porphyrites and the quartzless porphyries. 82 COPPER-BEARING ROCKS OF LAKE SUPERIOR. Tabulation of the results of a microscopic study of diabase-porphyrite and ashbed-diabase —Continued. 5 E Place. g es char- lige 2 | |s z |e /s]e] 3 n CC |n)|aA!] & | ee 2560.... Porcupine Mount- | NW. 23 | 51 43 W.| Aphanitic; dark ains, Michigan. | purplish-brown; conchoidal frac- ture; carries minute porphy- ritic feldspars. SiOz, 59.38 per cent. 1245...| Falls, Little Carp | SE. | 17 | 50 |44.w.| Nearly aphanitic; River, Poreu- | dark-brown; pine Mount- conchoidal frae- ains, Michigan. ture; numerous porphyritic feld- spars. 2568... Porcupine Mount- | NE. | 23 | 51 |43W.| Aphanitic; dark ains, Michigan. | chocolate- | brown; holds minute porphy- ritic feldspars. 2062 's.|.c sen G0esceseeeens NW.) 24 | 51 43 W.) Aphanitic; dark- brownish to black. Composition as determined by the microscope. Angle between maximum ex- tinctions of adjacent hemi- tropic bands of the plagioclase in sections cut at random in the zone O: ii. Groundmuss:—plagioclase, in very minute tabular crystals; unindividualized substance ; magnetite; much red and brown ferrite; rare and bril- liantly polarizing particles be- longing to augite; secondary quartz. Porphyritic ingredi- ents:—rather rare orthoclases and oligoclases; much rarer augites ; pseud-amygdules of calcite. i Groundmass :—in ordinary light, much stained with ferrite; consists of unindividualized substance, oligoclase, magnet- ite, and ferrite recognizable; augite particles very rare. Porphyritic ingredients :—or- thoclase and oligoclase very abundant; augites rarer, of good size, almost wholly al- tered to ferrite and green sub- stance. Groundmass as in 2560. Porphy- ritic feldspars larger and more abundant; the augite com- monly much altered to green- ish substance with bands of red and brown ferrite. Groundmass :—plagioclase ; un- individualized substance; mag- netite ; ferrite ; augite, in mi- nute, not abundant grains, often altered to a green sub- stance; secondary quartz. Porphyritic ingredients:—not very abundant, good-sized or- Angles on| < ; opposite om sides of rs cross-hair.| © ° ° ° 8 9 17 2 5 7 5 6 ll thoclases and oligoclases, much |_ altered to chlorite; augite, much altered to green sub- stance with bands of ferrite. 83 Tabulation of the results of a microscopic study of diabase-porphyrite and ashbed-diabase— Composition as determined by the microscope. Angle between maximum ex- tinctions of adjacent hemi- tropic bands of the plagioclase in sections cut at random in the zone O: ii. Labradorite, in small strips; augite, in small grains; green substance in clouds of granu- lar masses. Oligoclase ; augite, inaggregated grains; magnetite or titanifer- ous tron. Oligoclase; augite, in rounded |; grains; magnetite ; chloriteand quartz pseud-amygdules. Plagioclase, predominant; augite, in grains; magnetite. Oligoclase; augite, in grains; magnetite. Groundmass: — much stained with red ferrite; consists of plagioclase in minute tabular crystals; unindividualized sub- stance; magnetite; ferrite; augite, in very minute grains. Porphyriticingredients:—rare JSeldspars; altered augites. Oligoclase, both in the ground- mass and in rare porphyritic crystals; augite, abundant in grains; wnindividualized sub- stance; magnetite; ferrite; chlorite pseud-amygdules. Oligoclase, predominates ; augite, in grains; magnetite. DIABASE-PORPHYRITE. Continued, 8 : E Place, g Dee eT char- A 8 . 3 eee 3 # /2\e] & 8 a |/3/6| 8 n So |n]|A!] & 2 W!..| Potato River, Ash- 24) 46 |1W.| Nearly aphanitic; land County, compact; black; Wisconsin. conchoidal frac- ture. 9W}..| Old Ironton trail, 34 | 46/1 W.| Fine-grained; com- Ashland County, pact; black; sub- Wisconsin. conchoidal frac- ture. Sp. gr., 2.98. 386 S1.| Clam Falls district,| NW.| 24 | 37 |17 W.| Aphanitic; black; Polk County, conchoidal frac- Wisconsin. ture. 393 S!.| Totogatig district, | SW. | 28 | 42 |11 W. Aphanitie; black. Douglas County, Wisconsin. 426 S!.| Upper Saint Croix | SE. | 6 | 43 |aa-w. Fine-grained; district, Douglas black; conchoi- County, Wis. dal fracture. 1......| Mouth of Brewery | SW. | 23 | 50 |14 W.) Aphanitic; choco- Creek, Duluth, late brown; Minn. 75 north, highly conchoi- 1,850 west. dal fracture; carries very mi- nute porphyritic feldspars. ik yee Bed of Brewery | SE. | 22 | 50 |14 W.) Matrix black; aph- Creek, Duluth, anitic; thickly Minn. crowded with small red feld- spars one-six- teenth to one- fourth inch long; alsopseud-amyg- dules of epidote and calcite. 45.....| Bed of French |NW.| 6 | 51 |12 W.) Very fine grained; River, Minne- dark-gray; con- sota. choidal fracture. Soe aiar Bed of Beaver| N. 2|55|8 W.! Nearly aphanitic; River, Minne- | line. black; conchoi- Bota. dal fracture. Angles on opposite | Stites of cross-hair. ° ° 4 8| 10 3)0 4 Aa Ey 8 4 $ QD B ° A BS B e - Ss Al4 5 £ 5 4 = a3 6 2 7 13 17 8 8 1R. Pumpelly, Geology of Wisconsin, Vol. III, pp. 37-38. 18 12 30 16 84 COPPER-BEARING ROCKS OF LAKE SUPERIOR. Tabulation of the results of a microscopic study of diabase-porphyrite and ashbed-diabase— Continued. 3 : z Place. E Mecracoric char. a = : a = | & E 2/8/38! ¢ 3 a 1Si/E| a a 6 jalale on eine 533....| Near mouth of |Sw.| 4 50 |13 W.| Very fine grained, Lester River, | but plainly erys- Minnesota. | talline; dark \ brownish gray; conchoidal frac- | / ture. 547....| North shore of Sw. 34) 51/13 W.| Aphanitic; very Lake Superior, dense; dark) two miles below brown; rare mi- the mouth of nute porphyritic | Lester River, | feldspars. } Minnesota. | 589....| North shore of | SW.| 31 | 51 | 11W.| Very fine-grained; Lake Superior, | light gray ; sub- one mile above | conchoidal frac- | themouthofthe ture. Knife River, Minnesota. 655....| North shore of | NE. | 22 | 53 |10W.| Aphanitic; red- Lake Superior, dish brown; one mile below highly conchoid- the mouth of alfracture; car- Silver Creek, ries elongated foot of Encamp- amygdules of ment Bluff, Min- calcite. SiOz, nesota. } 60.03 per cent. 712....| North shore of | West) 7| 54|8W.| Nearly aphanitic; | Lake Superior, | side. | indefinitely mot- | one-half mile) | tled red and north of Split | black, weathers Rock River, | bright red; very Minnesota. highly conchoid- | al fracture. 797....| North shore of | SW.| 12 | 55|8W.| Veryfine-grained; Lake Superior, ; nearly black; | | Beaver Bay, conchoidal frac- | Minnesota. ture. 884....| North shore of | SW.| 22 | 56 | 7W.| Nearly aphanitic; | Lake Superior, chocolate brown, bay above Great | conchoidal frac- Palisades, Min- ture. nesota, under- | lies the palisade | Tock. Constituents as determined by the microscope. . Oligoclase. predominates ; augite, grains not abundant; magne- tite; ferrite, abundant. Plagioclase; unindividualized substance; qaugite, in grains, not abundant; very abundant red and brown ferrite. Labradorite predominant, longer axes of crystals often incommon directions; magne- tite; augite in grains, abund- ant; afresh rovk. Groundmass :—oligoclase; much unindividualized substance, saturated with red ferrite; magnetite. Porphyritic in- gredients :—oligoclase; much altered augite. Oligoclase ; augite, abundant in grains; magnetite; ochre- stained, unindividualized sub- stance abundant, filling sharp- ly the spaces between the feldspars. Oligoclase ; augite in rounded particles very abundant, un- usually coarse for this class of rocks; magnetite. Plagioclase, predominant; unin- dividualized substance; rare minute grains of augite; mag- netite ; red ferrite completely saturating the entire section. Angle between maximum ex- tinctions of adjacent hemi- tropic bands of the plagioclase in sections cut at random in the zone O: it. 14 i 25 14 u 25 9 6 15 5 4 9 2 13 23 DIABASE-PORPHYRITE. 85 Tabulation of the results of a microscopic study of diabase-porphyrite and ashbed-diabase —Continued. | Angle between maximum ex- tinctions of adjacent hemi- z tropic bands of g = the plagioclase 4 Place: 8 Macroscopic char- | Composition as determined by | in sections cut | 3 acters. the microscope. at random in a 3 ies the zone O: i. a a & : 2 | 3/3 | ¢ aseee cal 3 3 g 3 E FI sides ‘of =e n Cln|AH]| & cross-hair. ° ° ° 907....| North shore of | SE. | 11 | 56|7W.| Minutely crystal- | Plagioclase; magnetite ; augite Lake Superior, 2 line; dark- in grains; unindividualized miles below the brown;semti-con- substance; very abundant red mouth of Bap- choidal fracture.| ferrite. tism River, Min- | nesota. | 1051...! Bed of Cascade 23 | 62 | 2W.| Aphanitic; dark | Unindividualized substance; River, Minne- brown; conch- plagioclase needles; magnetite sota. oidal fracture; patches. an excessively | dense rock. 1551...) North shore of 63 | 5E.| Aphanitic; dark- | Plagioclase; wunindividualized Lake Superior, reddish-brown; | substance; magnetite; augite, below Red Rock highly conch-| particles rare; much red fer- | Bay, Indian oidal fracture ; rite. reservation, comes out in Minnesota (not thin slabs. surveyed). 1568...) Portage Bay Isl- Black; aphanitic; | Plagioclase, in matrix and in|3 (4 6 10 and, north shore rough fracture. porphyritic crystals; magne- | il} 10 | 21 of Lake Superior, tite; green and brown altera- | (24) 26 | 50 | Minnesota. tion-products. (o) South side of Nearly aphanitic; | Minute tabular oligoclases pre- Michipicoten dark gray; con- dominant; magnetite; augite Island. choidalfracture;| in grains; some residuary no porphyritic magma. ingredients. (@) | Southwest side of Completely apha- | With a medium power this rock Michipicoten nitic; very dark- presents merely a pinkish- Island. gray; highly] tinted background, minutely conchoidal frac- dotted with gray, and no re- ture; no por- cognizable ingredients; with phyriticingredi- a higher power, in polarized ents. light, there are recognized ex- ceasively minute tabular plag- ioclases ; larger but still mi- nute magnetite particles; rare and excessively minute brightly polarizing particles which may belong to augite ; residuary magma predominat- ing, producing no effect what- ever between the crossed nicols. 1 Macfarlane’s Michipicoten Collection, No. 2, ‘‘Compact Melaphyr.”” 2Macfarlane’s Michipicoten Collection, No. 4, ‘Compact Melaphyr.” 86 COPPER-BEARING ROCKS OF LAKE SUPERIOR. Tabulation of the results of a microscopic study of diabase-porphyrite and ashbed-diabase —Continued. Place. Macroscopic char- Composition as determined by Angle between maximum ex- tinctions of adjacent hemi- tropic bands of the plagioclase in sections cut at random in 7 3 Fi 3 2 acters. the microscope. thezonetOeen a @ & penne cal ° a 5s | a oO 5 \glal¢ “opposits| 38 a 5s |8/6| 4 sides of | 43 & @lelale cross-hair.| & © 7 ° ° ° () South side of Aphanitic; dark | Tabular plagioclase for the most Michipicoten chocolate-brown ; part, with the longer axes in Island. conchoidal frac-| a common direction, the crys- ture; no por- tals minute, but still several phyritic ingredi-| times largerthan in No. 4, pre- ents. dominating ; magnetite in not abundant small particles; qugite inminute grains; some residuary magma. ?) | Copper mine, Like No. 4of Mich- | The base of this rock is much Michipicoten ipicoten collec-| like that of No.4 of this col- Island. tion. lection. In it are rare but quite large (#; to } inch across) erystals of augite, largely changed to a greenish ma- terial, but with cores of fresh augite remaining. (8) | Southeast corner Matrix aphanitic; | Base:—light and dark brown, | 10 14 | 24 Michipicoten greenish - gray; unindividualized material, Island. very abundant producing little or no effect porphyritic between the crossed nicols; white feldspars, this is thickly studded with ysto finch long; minute plagioclases and holds also, rarer and rarer and more minute black much more mi- particles of magnetite. Por- 25 24 49 nute black por- phyritic ingredients :—very |.4 [32 o7 59 phyritie parti- abundant, large-sized, and E 29° 30 59 cles. very fresh labradorite, several fF Gi 21 42 crystals often clustered in an interesting way; also augite, much smaller and rarer, com- monly much altered to green- ish material and asseciated with magnetite. aT eeesas OO reaaciactaae Matrixaphanitic; | Close to preceding, differing |4 (46! 99 36 dark brownish- only in having much red ma- E}i0 19 35 gray; very terial in the base and the feld- abundant pink spars somewhat decomposed porphyritic and dulled. Figs. 1 and 2 of | feldspars, aver- Plate IX. represent this sec- | aging yy inch in tion. | length. SiOz, | 60.89 per cent. 1 Macfarlane’s Michipicoten Collection, No.5, ‘‘Melaphyr.”’ 3Macfarlane’s Michipicoten Collection, No. 16, ‘‘Porphyrite.” ?Macfarlane’s Michipicoten Collection, No.9, ‘‘Melaphyr.”’ 4Macfarlane’s Michipicoten Collection, No. 17, ‘‘Porphyrite.” i y'} ‘ ¥ Vry ~ Ps Wa AAS yy SK y { (fy Waxes (% iy % i ( e YOR WN { WY m AVR io bia) a BN | FS, ve. PAWN AN lu Lith. Baltimore A. Hoen & Co. AMYGDALOID -stsohnd ea mwar= Asis yrasbiO -Senoo stozsnm\ zehaz3si tad secon, bsalsbypyent LansSaormcnib ss aSn3t Amygdaloid from Great Falisades Minnesota coast. Ordinary light. Scale 24 diameters. Tabulation of the results of a microse DIABASE-PORPHYRITE—AMYGDALOIDS. 87 opie study of diabase-porphyrite and ashbed-diabase —Continued. Angle between maximum ex- tinctions of | adjacent hemi- | : tropic bands of 8 : the plagioclase | E Place. 8 Macroscopic char-| Composition as determined by | ft peer out = s ie acters. the microscope. the zone O: it. | a a = SS q aI ;|4 5 Angles on| © . | = 2\3 So opposite | 6 3 S |/s|E| 8 sides of | 42 a oe lala! & cross-hair.| © ° ° ° @) South side of Aphanitic; nearly | An excessively dense rock, in| 10 il 21 Michipicoten black; highly which are recognizable, with Island. conchoidal frac- a high power in the polarized ture; no por- light, very numerous minute phyritic ingre- augile grains embedded in a dients. non-polarizing matrix, along with much rarer plagioclase | and magnetite. The rock is remarkable for its relatively large content of augite. (i a |eaoccs oecese-eab es Completely apha- | Has a base which in ordinary nitic; jet-black ; light looks much like that of greasy- vitreous No. 4 of this series; but there luster; glass- is more non-polarizing mate- like fracture. rial, large areas remainirg Si Oz, 57.92 per completely dark between the cent. erossed nicols, and the pla- gioclases are still more mi- nute. Occasional minute bril- liant points belonging to au- gite are seen, as also some | magnetite particles. 1 Macfarlane’s Michipicoten Collection, No. 18, ‘‘Basaltic melaphyr.” 2Macfarlane’s Michipicoten Collection, No. 19, ‘‘ Pitchstone.” Amygdaloids—The flows of the finer-grained rocks are all commonly provided with upper vesicular portions, by the subsequent filling of whose vesicles, and the various degrees of alteration of whose matrices have been produced the manifold types of amygdaloid known in the Lake Superior region. The coarse rocks—olivinitic and orthoclastic gabbros—are not furnished with amygdaloids save when tending to a distinctly finer grain than usual. Externally, the matrix of the amygdaloid is commonly quite different ! Pumpelly has spoken of the olivinitic fine-grained kinds, his melaphyrs, as less commonly pro- vided with amygdaloids than are the olivine-free diabases of the ordinary type, but in my observations this is only true when the melaphyrs have a distinct tendency to become coarse-grained, as in “The Greenstone” of Keweenaw Point. When they are fine-grained they appear to have amygdaloids quite as frequently as the olivine-free kinds. 88 COPPER-BEARING ROCKS OF LAKE SUPERIOR. from that of the rest of the bed. This difference consists principally in greater denseness of grain, from solidification while much of the matter was not developed into distinct minerals. The difference is least, then, in the case of those beds whose lower portions are composed of some phase of the diabase-porphyrites, in which there is also a greater or less proportion of unindividualized matter. In some of these beds, especially when the rock is of the dense brownish kind with highly conchoidal fracture, above described, there is no perceptible difference between the matrices of the vesicular and non-vesicular portions of the bed; but more usually there is a great difference in this respect between the lower and vesicular portions of a flow. The internal changes to which such an open vesicular substance, composed largely of a molecularly unstable material like glass, must always be liable, have greatly increased the difference, and have given rise, by the variation in the decomposition-products, to a great variety of amygdaloids, which it would seem at first sight hard to place together. Under the microscope the matrix of the unaltered, or relatively little altered, amygdaloid shows nearly always much non-polarizing matter, commonly deeply stained with red ferrite. In this are developed needles of plagioclase to a greater or less extent, and often these needles seem to be but microliths arrested in the process of aggregation into crystals.’ Augite particles occur, but are usually relatively sparse, and frequently fail entirely. Very often there is a fluidal structure brought out in the arrangement of the plagioclase microliths and other particles, and in many cases the flowage direction is found to coincide with the longer axes of the elongated vesicles. The vesicles themselves, filled or empty, as the case may be, are always sharply outlined in the thin section, and there is im- mediately about them a crowding of the plagioclases and ferrite particles, as if by pressure in the cavity. Moreover, the individualized minerals, as Pumpelly has shown,” are often more minute in the vicinity of the vesicles than away from them. Porphyritic feldspars, macroscopically visible, are frequently developed in the matrix of the amygdaloids—so far as my observation has gone they are at least as often present as not—and in this 1R. Pumpelly, ‘‘Metasomatic Development,” p. 282. 2Tbid., p. 283. AMYGDALOIDS. 89 respect we have yet another affinity between the amygdaloids and the non- vesicular diabase-porphyrites. Macroscopically, the vesicles are seen to be commonly filled with secondary minerals—one or more of “calcite, chlorite, epidote, quartz, prehnite, laumontite, copper, orthoclase, or their products of alteration.”* Often, however, I have observed the vesicles empty, either from the removal of the amygdules or from their having always remained empty. The walls of these empty cavities are commonly found to be smooth and dense, apparently from the pressure of the confined vapor. Although a large number of sections of amygdaloids were cut with this object in view, I have not been able to find the time to extend the studies, so ably begun by Professor Pumpelly, of the changes which have brought about the fillings of the vesicles and the various stages of altera- tion of the matrix. He sums up the results of his studies on the alterations of both pseud-amygdaloids and the true vesicular amygdaloids in the fol- lowing table, which is designed to show the course and final results of the most common process of alteration: I. Hydration of chrysolite, when present. Il. Change of augite, loss of lime, and partial loss of ; iron and magnesia. Pseud-amygdaloid stage. < III. Change of feldspar to prehnite, and formation of prehnite pseud-amygdules. IV. Change of prehnite to chlorite. IVa. Change of prehnite to orthoclase. ( I. Filling gas vesicles with prehnite, or other minerals. Change of matrix to ferruginous prehnite. II. Change of the prehnite, in places, to chlorite; in Amygdaloid stage..---.- others, to calcite and green-earth; in others, to epidote and calcite. Ill. Entrance of quartz, filling all the interstices, and re. placing the calcite. The following are Pumpelly’s comments on this table: This is the broader history. Orthoclase is here, as in the pseudo-amygdaloid, of sporadic occurrence, and a product of the prehnite. The changes under II. may affect only the amygdules, or, if the matrix was preh- nitized, it applies to the whole mass of the amygdaloid. It does this in such a manner 1R, Pumpelly, Geology of Wisconsin, Vol. III, p. 31. 90 COPPER-BEARING ROCKS OF LAKE SUPERIOR. that, where carried to its extremes, considerable portions of the bed have lost every semblance of an amygdaloid, and consist now of chlorite, epidote, calcite, and quartz, more or less intimately associated, or forming larger masses, of the most indefinite shapes, and merging into each other. Sometimes portions of partially altered preh- nite occur. In places, considerable masses of rich brown, and green fresh prehnite filled with copper occur; but, as a rule, this mineral has given way to its products. To this process, the copper-bearing beds of Portage Lake—wrongly called lodes— owe their origin. Considerable portions of these beds are but partially altered amyg- daloids, containing amygdules of prehnite, chlorite, calcite, or quartz, with more or less copper; other portions are in the condition described above. This, too, (I. and III.), appears to have been the principal period of concentra- tion of the copper. In the still amygdaloidal portions, this metal was deposited in the cavities and-in cleavage-planes of some minerals, and replaced calcite amygdules, ete. But in the confused and highly altered parts of the bed it crystallized free, where it had a chance: more generally it replaced other minerals on a considerable scale. It formed, in calcite bodies, those irregular, solid, branching forms, that are locally known as horn-copper, often many hundred pounds in weight; in the epidote, quartz, and prehnite bodies, it occurs as thread and flake-like impregnations; in the foliaceous lenticular chloritie bodies, it formed flakes between the cleavage-planes and oblique joints, or in places—and this is more particularly true of the fissure-veins, which we are not now considering—it replaces the chloritic, selvage-like substance till it forms literally pseudomorphs, sometimes several hundred tons in weight. When the amygdaloid has arrived at the condition we have been describing, it assumes some of the characters of a vein, in that, although it presents no open fissure, it contains greater or smaller masses of calcite and other minerals that are easily re- placed by an intruder. To this period, probably, belongs the replacement of calcite by datolite; and here, also, the rather rare occurrence of analcite crystals, and the pseudomorphs of orthoclase after these. As I have already remarked, the pseudo-amygdaloids are merely altered forms of the same rock as the lower zone. There seems to be a definite limit at which this progressive change stops, and that is when all augite is changed to its green pseudo- morph, and a large percentage of the rest of the rock consists of pseudo-amygdules of delessite, and partial pseudomorphs of this after plagioclase. The occurrence of epi- dote and quartz is not general, and is then confined to scattering pseudo-amygdules, — in which these minerals have succeeded prehnite, perhaps in the local absence of the conditions necessary to produce the usual delessite. Thus I conceive that the extent of the change to the pseudo-amygdaloidal form is conditioned essentially by the amount of augite present, to supply first the lime necessary to aid in changing the plagioclase to prehnite, and next the iron and mag- nesia to form the delessite, whether by acting directly on the feldspar substance or on the prehnite. The amygdaloids proper were, probably, both structurally and chemically, some- what different from the lower zone, in that it is reasonable to suppose that, in addition to being more or less porous, they contained a greater or less amount of amorphous base, which is more easily altered than a crystalline aggregate. But, from whatever cause, the amygdaloids have, as we have seen, been capable of much greater changes - e ACID ORIGINAL ROCKS. 91 than the lower zone: in them the tendency is undoubtedly towards the formation of quartz, chlorite, and epidote rocks as a more stable limit, through the mediation of prehnite and calcite. There are other forms of alteration which Pumpelly’s investigation does not cover, but none of so great importance as those above deseribed. SEcTIon IIl.—ACID ORIGINAL ROCKS. As indicated in a previous chapter, I have been able to show that the several kinds of felsite and acid porphyry, which make the pebbles of the conglomerates and the material of most of the sandstones of the Keweenaw Series, exist in the same series in the original condition; and that while sub- ordinated to the basic rocks in total amount they yet form a very important element in the make-up of the series, throughout its entire circuit about the Lake Superior Basin. These acid rocks may be conveniently described under the following heads: 1. Quartzless porphyry. 2. Quartziferous porphyry and felsite. 3. Augite-syenite, and granitell or granitic porphyry. 4, Granite. Quartaless porphyry.—There are several phases of porphyritic rocks in the Lake Superior region, occurring both as pebbles in the conglomerates of the Keweenaw Series and as flows in the same series, which would form- erly have been classed together as “quartzless porphyries,” that name applying to felsitic rocks in which quartz is present neither in the base nor as a porphyritic ingredient." These several phases have in common an aphanitic, dark-brown base, frequent abundance of porphyritic feldspars— although kinds occur in which the feldspars sink out of sight—and freedom from visible porphyritic quartz. They are also distinctly softer than the true acid quartziferous porphyries. A study of the thin sections, however, aided by silica determinations, has shown that in such a grouping we should really be placing together kinds which are but the half crystalline or cryptocrystalline phase of the less basic diabases, others which verge on ‘Conf. R. Pumpelly in Geological Survey of Michigan, Vol. I, Part II, p. 16. 92 COPPER-BEARING ROCKS OF LAKE SUPERIOR. the true acid felsites in acidity (70 per cent. silica or over), and kinds again which are intermediate between these. There exist in the Lake Superior region, in fact, porphyritic rocks which range from the true basic kinds, with less than 50 per cent. of silica, to the very acid felsites and quartziferous porphyries with over 70 per cent., thus forming a continu- ous series. It thus becomes necessary to adopt some rather arbitrary divisions between the different phases. The kinds with from 50 to 60 per cent. of silica have already been considered under the heads of ashbed-diabase and diabase-porphyrite, while those reaching 70 per cent. are taken up below with the true felsites. There yet remain the kinds intermediate between these, both as to silica content (60 to 70 per cent.) and as to their microscopic characters. These are the kinds which are here considered under the head of quartzless porphyry. They are, in fact, the semi-crystalline phases which correspond to the completely crys- talline augite-syenites described below. Macroscopically these rocks show an aphanitiec matrix of a dark red- dish-brown or brown color, and more or less strongly developed conchoidal fracture. The porphyritic feldspars vary considerably in size and abund- ance, but are usually minute. They show habitually a red color, and in- clude often striated as well as unstriated kinds. The thin sections generally show a reddish background, with abundant brown ferrite particles and needles scattered through it. In most sections more or less of this base is isotropic, being either cryptocrystalline or truly glassy in its nature. There are in some slices darker and lighter bands, plainly due to flowage. The darker bands are always the least crystalline. Minute tabular feldspars are nearly always rather abundant; far less so, however, than in the sec- tions of the diabase-porphyrites; but always much more so than in sec- tions of the acid felsites, from which they are often completely absent. The individualized particles are, however, for the most part irregular in outline, and appear to belong to both orthoclase and quartz, which latter mineral seems to be nearly always of a secondary origin, since it com- monly occurs in the characteristic ramifying forms. It is, however, far less abundant in the rocks here included than in the felsites and the bases of the quartziferous porphyries. In a few places these quartzless porphyries pe QUARTZLESS PORPHYRY. 93 were found with a tendency to a vesicular structure, and then the thin sec- tion shows flowage lines and isotropic material at the maximum. The porphyritic feldspars are orthoclase and oligoclase, the latter the prevailing one. Both are always reddened and clouded by alteration. Many sections show also porphyritic augites, with crystalline outlines often remaining, and always with the peculiar red and brown, opaque, ferritic alteration-product, which characterizes the augites of all of the acid rocks here described. As instances of the occurrence of these porphyries—which are less com- mon than any of the other original rocks of the Keweenaw Series—may be mentioned the rock of the Stannard’s Rock reef; the prevailing pebbles of the Eagle River conglomerate, Keweenaw Point; the massive to vesicular rock of the old Suffolk mining location (Praysville), Keweenaw Point; many of the pebbles of the Portage Lake conglomerates ; the rock exposed in the bed of the Gogogashugun River in the northern part of Sec. 8, T. 46, R. 2 E., Wisconsin; the rock at the falls of the Brunschweiler River, NW. 4, See. 22, T. 45, R. 4 W., Wisconsin; and a rock showing on the southwest shore of Michipicoten Island.1 Called by T. Macfarlane ‘‘porphyritic melaphyr,” p. 138, Report of Progress of the Geological Survey of Canada for 1863 to 1866. 94 COPPER-BEARING ROCKS OF LAKE SUPERIOR. Tabulation of the results of a microscopic study of the quartzless porphyries of the Keweenaw Series. imen num- ber. Spec: Place. Quarter-section. Macroscopic charac- ters. Microscopic characters. = a) o So 1781 A -| Stannard’s 2616. -. Rock, Lake Superior. Pebble from Albany and Boston Con- glomerate, Kewee- naw Point, Michi- gan. Pebble from the con- glomerate at the National Mine, Rockland, Mich. INIWieee Center & ic af a a 8 55 Aphanitic; dark red- dish-brown; shows no visible porphy- ritic ingredients. SiO,, 65.81 per cent. 33W.| Aphanitic; dark chocolate-brown; conchoidal fracture; holds abundant mi- nute, pinkish, por- phyritic feldspars. SiO,, 65.35 per cent. 16 50 |39 W.} Matrix aphanitic; dark reddish-brown; car- ries minute porphy- Titie tabular feld- spars. In the ordinary light, the matrix of this rock presents a general red background thickly studded with opaque brown ferrites. The only porphyritie ingredi- ents are augites, which are now repre- sented by patches of red translucent, or opaque black ferrite, within which are little remnants of unaltered augite. These ferrite patches often show the crys- talline outlines of the original augites. Elongated holes, worn in the section by grinding, were probably occupied by mi- nute decomposed porphyritic feldspars. In the polarized light, the groundmass presents a considerable proportion of iso- trope matter, in which are occasionally recognizable minute tabular feldspars. Brightly-polarizing, irregularly-outlined particles and clusters of particles in the ground-mass appear to belong to quartz, possibly also to orthoclase. Some of these clusters plainly belong to second- ary quartz. Thelow percentage of silica (65.81), the abundance of altered augite and of ferrite particles, and the scarcity of secondary quartz, all serve to separate this rock from the more acid felsites; while it is separated from the diabase- porphyrites by its higher percentage of silica and rarity of tabular feldspars. Both in the ordinary and polarized lights the section of this pebble resembles closely that of the rock from Stannard’s Rock; the large ferrite patches, representing altered augite, are, however, much less abundant in this rock, which also holds not unfrequent small porphyritic oligo- clases. The groundmass of this rock is much like that of 1781 A, containing, however, rather more secondary quartz. The por- phyritic feldspars are oligoclase. Lith. Baltimor & —WSswoSQsvws YssacosSoD Séhoq Pry daqsod-syvasP §yrh Sx 9Sa0% SAV YrosvsHrO AsssFL wosvoen dA. 939 | urs sssycasS ~oNN0 AS) ssasg BRAD Bos eos \a\xissSasw o'sSsaSS®. (2\sesSo Snow sah SROM ASL Fao Gy Rerog-e}cosD sistas gh Us SVIe SIH SY BV asG ESAS SASSO SaveF wasvsons S of ORNS Yorsas cor feldspar Nose! SRe 1ase. OSLO SH A) x > rSSSWSQHG 99% LSdsSno0h TL rodsSy WS voswydanogsdrasg sod v2gsh ws SUITS QT, saAdo My. HKqzS Ssxsensoq, sos S\ Som BN tas . SAgs5 Sa sosS\on SIs $99G% Gorah & ak YAgqss Narco =e. a ee EEE ee a Rass / Quarts Glass frelusvione @? a Live Ground cane persst X 26 X26 X 400 Portion of Fig ro further entlargect so edh Flomuge xy xX 22 Pigs.1tol2 guartz-porphynes; Frys s3tovs felsttes; for localities see page Xter. 7 guarts porphyr ° iz e pag | Peg. 9 hancl SpEecz mer, reflected leght; Begs. Ji andiwin polarezed fg Rt, alt other frgures v7 ordinary leght o FELSITE AND QUARTZ-PORPHYRY. 101 partially altered glass, I am uncertain. The other occurrence referred to is that of curvilinear aggregations of brown and red ferrite particles, large enough to be seen macroscopically, in the hand specimen, as hair-like markings. These characterize the felsite from the Minnesota coast above mentioned as remarkable for the coarseness of its secondary quartz network. This rock is illustrated in Figs. 15 and 16 of Plate XIII. The porphyritic feldspars in the thin section are found to be either or both of orthoclase and oligoclase. They are always turbid from decompo- sition, and are more commonly red-stained than not. They have always crystalline outlines, or, when they have been eaten into by the still fluid matrix, as is not seldom found to have been the case, at least the remnants of such outlines. In a number of sections the feldspars are seen to have been not only eaten, but also much shattered before the solidification of the surrounding magma. The porphyritic quartzes present all the usual characters of the quartzes of similar rocks the world over. They are random sections of dihexahe- dral crystals (double pyramids due to combination of the two rhombohe- drons), with now and then some development of the lateral (prismatic) faces. The rhombohedral angle being only a few degrees over 90° (94°.15), the sections of these crystals present a nearly square shape.’ Usually they are more or less rounded and eaten into by the matrix, many odd forms re- sulting from this corrosion. In nearly all cases, however, some traces of the original outline remain, with the aid of which, along with the behavior between the crossed nicols, it is always easy to ascertain the erystallo- graphic directions of these eaten crystals. In the series of figures on Plate XIII, I have placed a number of these quartzes with the crystallographic axes in a vertical position so that they may be compared with one another.” Included in the porphyritic quartzes are particles or patches of the red- stained microfelsitic or eryptocrystalline groundmass. In most cases these have had originally a connection with the rest of the groundmass by ‘N. H. Winchell (Ninth Annual Report of the Geological and Natural History Survey of Minne- sota, pp. 21, 33, &c.), has called the dihexahedral quartzes of the quartziferous porphyry of the Palisades and other points on the Minnesota coast, adularia. *Rutley (Study of Rocks, p. 210), speaks of roundish blebs of quartz as characterizing quartz- porphyries generally, but his ‘‘ blebs” are only rounded crystals. 102 COPPER-BEARING ROCKS OF LAKE SUPERIOR. channels through the quartz, either above or below the plane of section. In some cases, however, I have noticed these groundmass inclusions sur- rounded by the quartz in such a way as to render it probable, at least, that they are veritable inclusions of the groundmass dating from the time of crystallization of the quartz. In several sections of North Shore porphyries, and especially in those of the Great Palisades and of Baptism River point on the Minnesota coast, unmistakably genuine inclusions of a true glass are to be seen in the porphyritic quartzes. These glass inclusions are in doubly terminated ‘negative crystals,” conforming in position exactly with the crystal in which they are found, and are of sufficiently large size and thickness to test satisfactorily with the polarized light. They show com- monly more or less of a trichitic devitrification. Two of these glass ‘negative crystals” are figured on Plate XIII, at Figs. 6 and 8. Porphyritic augites, while far less frequent than the quartzes, are yet not very unfrequently to be met with in sections of these rocks. They always have crystalline outlines, or remnants of them, being commonly more or less deeply eaten into like the other porphyritic ingredients. Their chief characteristic is the ferritic decay that they have undergone, the whole mass of the crystal being often represented by an opaque, brown, or deep-red, or black mass of iron oxide. I have already discussed, briefly, the question of the origin of the Lake Superior felsites and quartziferous porphyries, and the same question is referred to hereafter in other connections. Here it is sufficient to say that the marked fluidal structure so often seen, both on the large scale and mic- roscopically; the corroded quartzes; the glass inclusions in these quartzes; the near approach of the groundmass to the glassy condition; the complete identity of these felsitic rocks with others universally conceded to be of eruptive origin, and their very close similarity to the undoubtedly eruptive rhyolites—all combine to make up an irresistible argument in favor of an eruptive origin for these rocks also. As typical localities for these rocks—including only places where they occur as original masses—may be mentioned the following: (1) for the non- porphyritic felsites—Mount Houghton, Keweenaw Point; the central area’ of the Porcupine Mountains, and especially the great ledges in Sec. 35, T. FELSITE AND QUARTZ-PORPHYRY. 103 51, R. 43 W., and again in Sec. 31, T.50, R. 44 W.; the Minnesota coast in the S. W. 4, Sec. 28, T. 56, R. 7 W.; the same coast immediately below Grand Marais; the bed of the Devil’s Track River, Minnesota, for several miles from its mouth; and the islands off the harbor on the south shore of Michi- picoten Island; (2) for the kinds carrying porphyritic orthoclase, but no quartz—the central area of the Porcupine Mountains, where much of the rock is of this character; the N. W. 4 of Sec. 12, T. 37, R. 16 W., in the Clam Falls region, Polk County, Wisconsin; and the Minnesota coast, ten miles above the mouth of Split Rock River; (3) for the quartziferous kinds—the line of the Torch Lake Railroad, Keweenaw Point, Sec. 36, T. 56, R. 33 W.; the hill known as the “North Brother,” near Rockland, Mich., N. E. 4, See. 9, T. 50, R. 39 W.; the bold bluffs in the northern part of T. 49, R. 42 W., Mich.; the central area of the Porcupines, where, however, the prevailing rock is without porphyritic quartz; the bed of Potato River, S. E. 4, Sec. 15, T. 46, R. 1 W., Wisconsin; the mouth of Tyler’s Fork of Bad River, S. E. 4, Sec. 17, T. 45, R. 2 W., Wisconsin; the islands off the north point of Beaver Bay, on the Minnesota coast; the Great Palisades, Baptism River point, and Red Rock Bay, all on the same coast; Bead Island at the mouth of Nipigon Straits on the Canadian coast; and the east shore of Michipicoten Island. The detailed descriptions of the following tabulation cover a sufficient number of occurrences to substantiate the general descriptions above given. Other thin sections of these rocks are briefly described in connection with the detailed descriptions of Chapters VI and VII ‘Mr. M. E. Wadsworth, who has described (op. cit., pp. 113-120) a number of these sections of peb- bles of felsite and of the granite-like rocks which I describe below under the name of augite-syenite, was the first to note the occurrence of secondary quartz, and of an apparently spherulitic structure in these rocks, 104 COPPER-BEARING ROCKS OF LAKE SUPERIOR. Tabulation of the results of a microscopic study of the felsites and felsitic honphyrice of the Keweenaw Series. | Specimen num- ber. 1909... 1908... 1846 1838.. Place. Mount Houghton, Ke- weenaw Point, Mount Houghton, Ke- weenaw Point. Pebble from Eagle River conglomerate; mouth of Eagle River, Keweenaw Point. Torch Lake Railroad, Keweenaw Point. | Quarter-section. W. line. W. line. NW. S. part. Section. Township. Range. Macroscopic charac- ters. nt = 24 19 36 58 29 WwW. 20 WwW. 31W. 33 W. Aphanitic; pink to brick-red; no visible porphyritie ingredi- ents; very hard. SiO2, 76.9 per cent. Difficultly fusible. Aphanitic; hard, light-pinkish; sharp- ly angular fracture ; no porphyritic ingre- dients. SiO,, 77.2 per cent. Matrix aphanitic, pur- plish-red, hard; abundant large black quartzes and flesh-red feldspars. Aphanitic; dark-red, hard; very abun- dant and large, black, porphyritic quartzes reaching two-tenths inch in diameter, and red feldspars two-tenths to one-quarter inch inlength. Some of the feldspars are plainly striated. Re- sembles 1970 and 1846 d. Microscopic descriptions of thin sec- Much non-polarizing matter, through which are seen scattered, when viewed between the crossed nicols, minute bright points and lines; also a few relatively large, scattered nests of aggregated particles of quartz. The whole section is stained with red ferrite, which is also aggregated in numerous irregular, opaque particles. This section differs from the preceeding in containing much less red ferrite, and less non-polarizing matter; and in containing many polarizing parti- cles often arranged in a felt-like mass. Many of the particles are plainly tabular feldspars. The matrix is much stained with red ferrite, and shows but feeble polariza- tion in flocks of small particles ; some small non-polarizing areas. In addi- tion to the general red stain are abund- ant brown and black, opaque ferrite particles. Porphyritic quartzes large, in the usual doubly terminated crys- tals, with embayments and inclusions of the matrix. The porphyritio feld- spars are oligoclase. Augite occurs also porphyritically in particles as large as the quartz, and with rounded contours; these augites are filled with a brown, ferritic .alteration-pro- duet. Matrix irregularly mottled pink and nearly colorless, these mottlings being so arranged as to suggest flowage. The darker portions of the matrix are thickly studded with minute fer- rite needles, so arranged as to empha- size the fluidal structure very strong- ly, especially in the neighborhood of the porphyritic quartzes. The darker portions of the matrix affect the polar- ized light only in a few minute points. The lighter portions, on the contrary, appear to consist of wholly individu- alized quartz and orthoclase confused- ly intererystallized. Calcite is also occasionally seen in these lighter por- a ee eee eee ree ee ee es ee ee | FELSITE AND QUARTZ-PORPHYRY. 105 Tabulation of the results of a microscopic study of the felsites and felsitic porphyries of the Keweenaw Series—Continued. ' z 8 : : 3 S Macroscopic charac- | Microscopic descriptions of thin sec- 28 Place. aes ee ters. , tions. | ; a |SlEl é 7 é & |2\a| 2 } . tions. The porphyritic quartzes are very large and commonly much eaten, with the usual embayments and in- clusions of the matrix. The feldspara are chiefly oligoclase, rarely ortho- clase; both always much clonded : from alteration. There are also pres- ent rare porphyritic augites, largely replaced by a black opaque substance. See Fig. I, Plate XII. 1970..| Pebble from the Calu- 23 | 56 |33W.| Matrix dark reddish- | Differs from the preceeding only in hav- met conglomerate, brown, aphanitic; | ing much less of the whitish individu- Keweenaw Point. sharply angular con- alized areas in the matrix, nearly the choidal fracture; | whole of which presents a brownish very abundant pink staining and produces no definite effect feldspars up to one- on polarized light. The ferrite needles half inch in length, are also somewhat more minute than also black quartzes in the preceeding section. One of the > one-tenth to two-| quartzes carries a sharply ontlined, | tenths inch in di- fresh, brilliantly polarizing augite : ameter; resembles crystal, the augite crystals of the ma- 1846 d. 2514..| Porcupine Mountains, | N. line. | 5 | 50 |43 W.| Aphanitic; pale-lilac; Michigan, 2000 N. no porphyritic in- 700 W. gredients. 2551..| Bed of Carp River,| NW. | 35 | 43 |43W.| Aphanitic; dark pur- Poreupine Moun- plish-red; no por- trix being wholly replaced by a black- ish substance. See Fig. 2, Plate XII. Nearly colorless, faintly tinted with pink; minute tabular feldspars; some networked secondary quartz; some non-polarizing material; opaque fer- rite particles not abundant. Blotched red and colorless ; the reddish tinted portions chiefly non-polarizing, tains, Michigan, 1420 phyritic ingredi- the white portions composed entirely N. 1400 W. ents. of individualized, often relatively coarse quartz and orthoclase; net- worked secondary quartz rare; fer- rite particles not abundant. 2574..| Porcupine Mountains, SW.| 20 | 51 | 42W]| Aphanitic; dark pur- | Thickly studded with minute brown Michigan, 500 N. plish-red; afew mi- ferrite particles, which are also aggre- rn 1450 W. nute dark quartzes. gated into large patches; appear- ance in ordinary light pretty homoge- neous. In the polarized light the ma- trix is seen to be completely saturated with secondary quartz, which pre- sents iteelf in irregularly rounded areas each of which is a closely in- volved network of non-polarizing base and quartz. All of the quartzin one of these areas polarizing together, . it follows that it all belongs to one - individual. A few minute, altered porphyritic feldspars. ee 106 Tabulation of the results of a microscopic study of the felsites and felsitic porphyries COPPER-BEARING ROCKS OF LAKE SUPERIOR. of the Keweenaw Series—Continued. : =} g 2 3 88 Place. ba Ee s $ 2 a 5 2) cS 1247..| Bed of Little Carp | NE. River, Porcupine Mountains, Michi- gan, 1850 N. 600 W. 1259..| Porcupine Mountains, | S. line Michigan, 270 W. 1263..| Porcupine Mountains, | SE. Michigan, 200 W. 1621.) Bed of Potato River, | SE. Ashland County, Wisconsin. 871I.| Mouth of Tyler’s | SE. Fork, Ashland County, Wisconsin. ee ee eee eee & a|2 B/E ie) a|a 20 | 50 9 | 50 32 | 51 15 | 46 17 | 45 | Range. 44W 44W 43W 1W 2Ww Macroscopic charac- ters. Aphanitic; dark pur- plish-red; some mi- nute porphyritic quartzes and feld- spars. Aphanitic; bright-red very plainly banded with lighter shades; porphyritic white orthoclase rather abundant, often ly- ing across two or three bands. Aphanitic; dark-red closely banded with lighter red; no por- phyritic ingredi- ents. Aphanitic; pale lilac- tinted base, thickly studded with white porcellaneous crys- tals of feldspar reaching one-eighth inch in length, and smaller black glassy quartzes. Much altered and soft- ened, aphanitic, brick-red matrix, scattered through which are minute brighter red ortho- clases and very abundant larger quartzes. Microscopie descriptions of thin sec- tions. Matrix stained.with ferrite, and satura- ted with secondary quartz as in the last described. There are also some- what abundant larger quartz areas, apparently also secondary, besides which there are the usual sharply marked quartzes and feldspars, the latter much reddened and altered. Here and there a quite perfectly de- veloped augite crystal is seen. The ferrite particles are arranged so as to indicate flowage. In the thin section the banding is seen to be produced by the presence of much oxide of iron in some bands and absence of it in others; the latter bands are also more highly crystalline, but all of the section presents an un- usual quantity of individualized mat- ter, apparently both quartz and ortho- clase. The bands are non-continuous even in the breadth of a thin section. In the thin section the lighter bands are seen to contain much more and rela- tively coarser secondary quartz than the other bands, which are in turn relatively rich in ferrite particles. In ordinary light the matrix appears of a general gray color, with thickly scat- tered ferrite particles, which, for the most part transmit a reddish light, even when very thick. In polarized light this matrix appears to be satura- ted with networked quartz. The very abundant qnartzes present all the usual characters. The feldspars are all turbid and appear to be wholly orthoclase. Some sections have the ferrite particles and the secondary quartz arranged in indefinite lines so as to suggest flowage. The base is like that of the rock last described, but is penetrated through and through by veinlets of quartz and calcite. The ferritic particles are more thickly crowded in the vicinity of the porphyritic ingredients, and now and then show a tendency to a lineararrangement. Thequartzesare much eaten, and are penetrated to an nil FELSITE AND QUARTZ-PORPHYRY. 107 Tabulation of the results of a microscopic study of the felsites and felsitic porphyries Place. ber. imen num- Spec 8008.) Clam Falls District, Polk County, Wisconsin. 708...) North shore Lake Su- perior, two miles above mouth of Split Rock River, Minne- sota. 711...) North shore Lake Su- perior, one-quarter mile east of 708. 730...) Bed of Split Rock River, Minnesota. 790...| South shore of Beaver Bay, Minnesota. Quarter-section. Nw. NW. Nw. SE. of the Keweenaw Series—Continued. Macroscopic charac- | Microscopic descriptions of thin see- ters. 12 | 37 | 16W| Aphanitic; pinkish- 13 | 54) 9 W. 13 | 54) 9 W. 1| 54/9 W. 12 | 55|8 W. red matrix with mi- nute feldspar faces. Aphanitic ; brick-red, much decomposed and softened. Car- ries minute pink or- thoclases. Light-red; obscurely banded with dark- red ; aphanitio; sub- conchoidal fracture; carries abundant irregular, black, hair-like markings. Aphanitic; dark red; conchoidal frac- ture; carries min- ute red feldspars. Aphanitico; light- gray, banded with non-continuous pinkish bands, the middle portion of each band being oc- cupied by a quartz seam. tions. extraordinary extent by club-shaped masses of the base. The orthoclases are very much reddened and kaolinized. Several inclusions of partially devitri- fied glass were found in the quartzes. A few porphyritic augites, largely al- tered to red iron oxide are contained. The thin section shows a matrix com- pletely saturated with a network of secondary quartz; the quartz network is coarser than usual. Theporphyritio feldspars are wholly triclinic. Matrix largely of non-polarizing ma- terial stained red, and containing min- ute tabular crystals, also areas of sec- ondary quartz. Confusedly inter- mingled with these deeper colored areas are lighter ones, occasionally colorless, in which there is a larger proportion of individualized material, apparently quartz. The section is dotted throughout with minute points of ferrite. The porphyritic ingredi- ents are orthoclase and oligoclase in not very abundant, small, and much altered crystals, some of which pre- sent the appearance of having been much fractured before the solidifica- tion of the matrix. Similar to 708, but with very much more secondary quartz. Near to708 and 711, with the red staining more general ; in other words, there is but little of the lighter tinted, more individualized material; secondary quartz throughout in minute arbores- cent clusters. Colorless, merely varying in transpar- ency. Themore transparent portions, which are distinctly arrangedin bands, are composed of quartz in relatively large areas. The clouded bands pre- sent, in the polarized light, a dark background, thickly crowded with minute polarizing points which are in 108 Tabulation of the results of a nricroscopie studg of the felsites and felsitic porphyries | } Specimen num- ber. 820... 852... COPPER-BEARING ROCKS OF LAKE SUPERIOR. Place. --| Island on north side ot Beaver Bay, Min- nesota, Cedar Island, north shore Lake Super- ior, Minnesota. North shore Lake Su- perior, Minnesota. of the Keweenaw Series—Continued. Quarter-section. Section. Township. Range. Macroscopic charac- ters. NE. Sw. 55 55 8 Ww. 8W. 7W. Aphanitic; conchoi- dal; dark pur- plish-red, banded by indefinite waving bands of light-red. Porphyritic ingredi- ents: quartz, very abundantin crystals one-tenth to one- twentieth inch in diameter, and pink feldspars one-twelfth inchinlength. The feldspars tend to have their longer axes in the direction of the banding. SiOz, 76.83 per cent. Matrix aphanitic, dark purplish-gray, blotched and banded with red; very abundant porphy- ritic pink feldspars one-tenth inch in length, and more minute quartzes. The arrangement of feldspars, and the fine red banding, in- dicate flowage. Aphanitic, pinkish- violet; highly con- choidal fracture ; no porphyritic ingredi- Microscopic descriptions of thin sec- tions. part secondary quartz, but are not all evidently so; these bands also hold abundant minute opaque ferrites. In the transparent bands are quite large irregular patches of a yellowish-green material which might be altered au- gite or epidote, but which all remain dark between the crossed nicols throughout an entire revolution. Matrix nearly colorless, faintly tinted pinkish-gray, cloudy. In the polar- ized light this matrix is seen to be made up of individualized material, in large proportion, saturated with secondary quartz in an arborescent tracery suggestive of the most deli- cate frosting; the filaments of this quartz network polarize together in relatively large areas. Excessively minute, opaque ferrite particles abun- dant. Rare non-continnous bands composed of quartz particles, as in the last-described section, occur, and here again occurs the greenish-gray non-polarizing substance above de- scribed. Large-sized, doubly termin- ated, rounded quartzes are the chief porphyritic ingredients. Matrix very close to that of 818. The patches of the peculiar greenish-gray substance there described are here very plenty; they are often drawn out into long strings, and also occur in small particles dotted over the section so exactly in the manner and with the shapes of the usual ferrite par- ticles, as to suggest the formation of the ferrites from them by alteration. Porphyritic ingredients: quartzes, with the usual characters and large and size; oligoclase. Thisrock and the two preceding are plainly nearer to the glassy condition than uny others described in this list. Colorless, cloudy matrix, completely saturated with secondary quartz in a network coarser than usual; thickly scattered through this matrix are un- ae e a a a — - FELSITE AND QUARTZ-PORPHYRY. 109 Tabulation of the results of a microscopic study of the felsites and felsitic porphyries of the Keweenaw Series—Continued. Specimen num- ber, Place. 853...| Same place as 852. 876... Foot of north cliff of the Great Palisades; north shore Lake | Superior, Minne- sota. Macroscopic charac- ters. ents. This rock is thickly studded with brown and black, eurving, hair- like markings. SiO, 77.12 per cent. Aphanitic ; dark pur- plish-red and light pinkish-red, in inter- twisted curving 2 So 3S gm | nts Behe pa ie 5 3 3 GC |als] & SW. | 28 | 56/7 Ww. bands. NE. | 22 | 56/7 W. Matrix aphanitic; dark purplish-red closely banded with lighter tinted, non- continuous bands, and rows of lighter colored spots. White, kaolinized orthoclases one- tenth inch in length, are the most impor- tant porphyritic in- gredients. More minute quartzes are abundant. Microscopic descriptions of thin sec- tions. usually large particles, and strings of particles, of red and brown ferrite. As already indicated, these strings of particles are sufficiently large to at- tract attention in the hand specimen. See Figs. 15, 16, Plate XIII. Colorless matrix, saturated with net- worked secondary quartz, and thickly studded with particles of red and black ferrite; the great abundance of these particles in portions of the sec- tion, and their nearly complete ab- sence in others, produces a strong banding. Matrix very strongly banded. The mostabundant bands present acloudy, gtay appearance, and are seen in po- larized light to be largely composed of non-polarizing matter, with which are abundant polarizing particles,some of which, atleast, belong to secondary quartz, There are also present in these bands exceedingly minute par- ticles of brown ferrite. Other bands are nearly colorless and transparent, and these are made up chiefly of indi- Vidualized quartz. Still other bands present much of a brown, blotchy stain, and are thickly studded with long, black, ferrite needles. The needles are at times straight, but more often have a marked curvature; and, while they show a marked tendency to fol- low the general directions of the bands, they yet lie across one another in such a way as to suggest the ap- pearance of a brush-fence (compare Zirkel, in Fortieth Parallel Report, Vol VI). The narrow ones of these bands are notcontinuonus even through the width of athin section. Allthicken and thin suddenly, and all are inter- - twisted in various curving forms, mak- ing abrupt turns when coming intocon- tact with the abundant porphyritic quartzes and orthoclases. The bands containing ferrite needles are least continuous and are sometimes found making forms like the letter $ within | 110 COPPER-BEARING ROCKS OF LAKE SUPERIOR. Tabulation of the results of a microscopic study of the felsites and felsitic porphyries of the Keweenaw Series—Continued. ; d ie g S a as} Ag 2 = Macroscopic charac- | Microscopic descriptions of thin sec- oe Place. Dy ala : TS. tions 4 = S|] & & E o =) o|5 E a ® n So n|a | | | | North shore Lake Su- perior, one mile be- low mouth of Bap- tism River, Minne- sota. -| North shore Lake Su- perior; bay below Grand Marais, Min- nesota. Red Rock Bay, Indian Reservation, north shore Lake Super- ior, Minnesota (not Close to 876. porphyritic white kaolinized feldspars are very abundant. The arrangement of these feldspars and of the lighter ma- terial in the matrix tends to produce curving lines. Aphanitic; red, blotched with yel- lowish-white; no por- phyritic ingredients, but minute flashing points, due to the secondary quartz, may be seen in @& bright light. The rockis much altered and softened and comes out in sharp- edged tabular frag- ments. Aphanitic ; flesh-red ; porphyritic red fela- spars and black quar- tzes. other bands. The whole appearance of this banded matrix plainly indi- cates movement while ina fluid condi- tion, and is much the same as com- monly observed in the modern rhyo- lites. The porphyritic quartzes and feldspars present the usual characters, the quartzes carrying often the usual embayments of the matrix, as also well-marked, partially devitrified, doubly terminated glass inclusions, See Figs. 3, 4, Plate XII; also Figs. 9,10, 11, 12, Plate XII. The | In the thin section the faint white banding noted macroscopically is seen to be produced, as usual, by the pres- ence in these bands of relatively coarse quartz and their comparative freedom from the red stain which af- fects the rest of the rock. The usual excessively fine quartz network af- fects the whole rock, and in all por- tions, except the lightest-colored bands, the usual brown, opaque fer- rites are abundant. The porphyritic quartzes and orthoclases present no unusual characters ; the former show very large, doubly terminated glass in- clusions (negative crystals). See Figs. 6 and 8, Plate XII. In the thin section this rock is seen to be completely saturated with the usual quartz network, but shows also num- erous polarizing particles, apparently sndependent of the secondary quartz. Red stain and ferrite particles rather less abundant than usual. In the ordinary light the matrix of this rock is only faintly stained, and is pe- culiar from being strewn with irregu- lar greenish blotches. In the polar- surveyed). ized light the nearly colorless back- | FELSITE AND QUARTZ-PORPHYRY. 111 Tabulation of the results of a microscopic study of the felsites and felsitic porphyries of the Keweenaw Series—Continued. imen num- ber. Spec’ Place. 1540..| North shore Lake Sa- 1728 b perior, Minnesota, 200 paces east 1539. 1728..| North shore Lake Su- perior; north side Bead Island, mouth of Nipigon Straits, Ontario, Canada. A few hundred yards east of 1828, the same rock-mass. Quarter-section. About. Macroscopic charac- ters. | Section. | Township. | Range. 35 | 63 | 5 E. Aphanitic; dark pur- plish-red. Very abundant, much al- tered red feldspars, up to one-half inch in length; also quartzes one-twen- tieth inchin di- ameter. Comes out in thin tabular frag- ments. Matrix dark pur- plish-red, aphanitic; porphyritic, flesh- colored feldspars, one-quarter to one- half inch long, ex- traordinarily abun- dant; quartz also very abundant,rare- ly exceeding one- tenth inch in diam- eter. Resembles 1838, 1846d, 1970, and Michipicoten11. Matrix brick-red, banded with vaguely defined bands of lighter and darker red. The feldspars are less abundant than in 1728, and are whitish and porcellaneous from alteration. Microscopic descriptions of thin sec- tions. ground shows only the usual excess- ively fine quartz network, while the green blotches remain in large meas- ure dark thronghout an entire revolu- tion. Porphyritic orthoclases are of very large size, red-stained and deeply eaten into by the matrix. The por- phyritic quartzes present no unusual characters. In the ordinary light a matrix much like the lighter portions of 1539, ex- cept that red and brown ferrites are thickly clustered in some portions. In the polarized light the distinction between the quartz network and other independently polarizing particles is plainly seen. In the ordinary light the matrix pre- sents throughout a deep reddish- brown stain, produced by thickly- crowded ferrite particles, which, in the immediate vicinity of the porphy- ritic ingredients, present some indi- cations of a fiuidal texture; but, for the most part, the matrix is without such an appearance. In the polar- ized light the matrix is for the most part dark, presenting only very mi- nute, feebly-polarizing particles. The usual quartz network appears to be entirely wanting. The quartzes are much eaten, which is also the case with the porphyritic feldspars. See Figs. 4,7, Plate XIII. Close to 1728, but in the polarized light the background presents more indi- cations of individualization and is pe- culiar for its curvilinear clusters of ferrite particles. The quartzes are extraordinarily large and abundant, and are eaten by the matrix into many peculiar forms. See Figs. 1 2, 3, Plate XIII. 112 COPPER-BEARING ROCKS OF LAKE SUPERIOR. Tabulation of the results of a microscopic study of the felsites and felsitic porphyries of the Keweenaw Series—Continued. | Specimen num- ber. Place. Quarter-section. Section. Township. Range. Macroscopic charac- ters. Microscopic descriptions of thin sec- Py ~ (t) East side Michipico- ten Island. Islands off harbor, south side of Michi- picoten Island. Aphanitic; Matrix dark pur- plish-red, aphani- tic; porphyritic quartzes extraordi- narily abundant, of- ten reaching two- tenths inchin diam- eter. Red porphy- ritic feldspars also very abundant, two- tenths to three- tenths inch in length. Close to 1838, 1846d, 1970, and 1728. light flesh-red; very rough fracture; re- sembles the rock from Mount Hough- ton, Keweenaw Point. The groundmass of this rock is faintly pinkish-tinted and cloudy; it con- tains numerous very minute ferrite particles, which, in the vicinity of the porphyritic ingredients, show crowding and a tendency to linear directions. In the polarized light the matrix shows a dark background strewn with particles and flocks of particles of feebly doubly refracting substances, but only rarely a dis- tinetly recognizable quartz network. The porphyritic quartzes are very large and abundant, and much eaten. The feldspars are also unusually large, are both orthoclase and oligoclase, and are also much altered. See Fig. 5, Plate XIII. The groundmass is nearly colorless, cloudy, and thickly dotted with very minute ferrite particles, which are at times aggregated into waving lines. In the polarized light feebly polarizing flecks dot a dark background, some of which are recognizable as quartz net- work clusters. No porphyritic ingre- dients in the section. *Macfarlane’s Michipicoten Col. No. 11. ‘‘Felsite porphyry.” Rep. of Progress, Geol. Sur. Canada, 1863-1866, p. 142. + Mactfarlane’s Michipicoten Col. No. 13. “Trachytie phonolite.” Ibid., p. 142. Augite-syenite and Granitell—Occurring abundantly as pebbles and boulders in the Keweenawan conglomerates; in great irregular mountain masses in the lower part of the series; and again, in plainly intersecting masses, and even in thin seams in the coarse gabbros lying near the base of the series, on both north and south sides of Lake Superior—are found flesh-red to brick-red rocks, which present a plainly, and often quite coarsely crystalline structure and general granitic appearance. Red feldspars, un- striated alone, or both unstriated and striated together, appear always to make up the bulk of these rocks, and quite commonly are the only macro- scopically recognizable ingredients. Quartz, however, is often visible, and especially in the more coarsely grained and more strongly granite-like Figs pends from Bagle Mountarn , Cook County, hes Fog 7 orclene ref Leght Feg2. peolerzzed fayht Scale 3x d¢eameters. Orthoctasetyy crystals saturated meth corrasron puartz (2). Pigs us desegned to show how numbers ofrnergh boring guertz areas polarvze together Fr9.3 Jrom vein in gébhro, Hice Pornt, Duluth Minn. Ordenary lyht Scale as diameters. Orthocilase decomposed, reddened by trom oxzde,and satura- ted by Secondary guartz. Peg 4 Sram lange area of red rock inthe gabbro of Duluth Minn. Polarzzed Leght Scale af dtameters Orthoclase Wecompasecd ant saturated ele Ee guartz , themurerous areas of which beloreg to only SUX tnrdrviduadls yund d ich exten. | | nd nds 1 | par 3 yusually large, .& VA SAgsS WS HST SYYTO 4 ast SS s< AN redsc sso) X ea) a ROE CTU Kgs seo tSsen \ ays ar ayasws so ee, kod Siqs) Hs ssvsleq wed sewsss HSK 4OAD C3 Sasvgsash vs ari AS) SYx os y svostiorcreay ASate Hodaesyor Wa dtr ds @orsd20h5<0 WERSS gas sssvadog VESTA sdrsosg, pevssod AgsaneYo ebly polarizing yack some of MashosC Yo ov Say ad «5 Koos Sar\o sare aya) STON + Ent asst Malu Avs 30 ondng ses svsaw stot h, eit westaseash is sinot SAgsh Sassxayo LSC aredeasnash es eas SAQA yersscsheO we PEON OD Nine: SS eration Sues Srsragsnas sh sushs ol nO caxsSar bie ohsx0 wots yA Sox shGax Gsroqiworsh ersiaoitsO eu Wsvo oy qsodad KosAw Yo town vosarvosecosse SAY Vsdeasg SAW aWY \use & rranat x8 Sos WaoahsresSscs ‘ , = ac a = z : : dominating eS sake ALOR Watsaarg saat agi ARgsS yranshrO 9) Ses VUE Be osl “Ksiesesbi) | ind of the sqoMtte BAAR eh sent rio Shenoy Ce of the sqoRthhe Bera ites ie | AS 0 *ROSNsgQsenows Ys Wit Aqesss bisesrnfetslows (sosva syred arene Shah, cage oS stro onsbaslo ace sls ¥ BEB): Xo Sossherg eoshaksifs Riss yg, YrMbleTO ram Ges YIES: ’ } e ulaw mass¢ mia itself; — gsNansswdigras svs tery sworn, oS srayr- oSsquikh uw gs} SAQsS yrarshsO AKSSDK SxsK «arcssnsK SsoeshoB MWe j anssosnash y2:sSn0t osarcsssor L0G 2) s¥srehandal Gem Harersed oi orsio0A3 KINDS. BASIC Silica 45 to 52 per cent. (oe INTERMEDIATE KINDS. ACID KINDS. Silica 60 to 78 per cent. oe Summary tabulation of the eruptive rocks of the Kewee Coarse-granular kinds, Olivine-gabbro (B 1). Olivine. Anorthite. Diallage. Titaniferoas magnetite. : Non-orthoclastic, olivine-free gabbro and diabase (in part only) (B 1). Anorthite or labradorite. Diallage or augite. Titaniferous magnetite. Anorthite rock; a special phase (B 4). Silica 45 to 48 per cent. Fine-granular kinds. Grading by increasing fineness of | grain and loss of diallagic cleavage in the augite, which remains coarser than the other constituents, into a Olivinitic diabase and melaphyr (‘lus tled” rocks), B 6 (in large part). Anorthite. Olivine. Augite. = Titaniterous magnetite. Pseud-amygdaloids a special phase. Grading by increasing fineness of grain into —> oe pide ase diabase (in small pa ). Labradorite. Augite. Magnetite. Pseud-amygdaloids a special phase. Grading by loss of olivine, decrease in basicity of the plagioclases, and, in some kinds, by addition of orthoclase, into | Grading by loss of olivine and decrea: sicity of plagioclase, into | Non-orthoclastic olivine-free gabbro and diabase (in part only) (B 1). Labradorite. Diallage or augite. Titaniferous magnetite. Orthoclase-gabbro (in small part only) (B 2). Labradorite or oligoclase. Orthoclase. Diallage and augite. Titaniferous magnetite. Apatite, uralite, common accessories. Uralitic gabbro (B 2). F Hornblende-gabbro (B 3). } Special phases. Silica 48 to 52 per cent. Grading by increasing fineness of grain into ——> “ Ordinary-type”’ diabase (the larger pa Labradorite or citmealegne ces Augite. Titaniferous magnetite. Pseud-amygdaloids a special phase. Grading by decreasing basicity of plagioclase, increase of orthoclase, and introduction of secondary quartz, into | Grading by decreasing basicity of f into < Orthoclase-gabbro (the larger part) (B 2). Gradation forms not known, into —>| “Ordinary-type” diabase (in small part o1 s Oligoclase. Oligoclase. Ps Orthoclase. Orthoclase possibly in a few kinds ( 2 Diallage. Augite. = Augite. Titaniferous magnetite. (These ro © Titaniferous magnetite. never been found to contain over £ Apatite, uralite and secondary quartz, very per cent. silica—rarely so muc 3 - common BecerneeS a5 Pes eben by qnarte eaillbsae ralitic orthoclase-gabbro (B 2). } . ans seud-amygdaloids a special phase. S| Hornblende-gabbro (B 3). Special phases. a Grading by decrease of augitic constituent, and Gradation phases not known, into increase of orthoclase and of quartz, into = Augite-syenite (in part) (A 3). Grading by increasing fineness of | Fine-grained augite-syenite (A 3). 3 Oligoclase. grain, into —> Orthoclase. R Orthoclase. Oligoclase. = Augite (very subordinate). Augite. S Verrite and abundant quartz characteristic Ferrite. 2 accessories. Secondary quartz. 3s a a] Grading by decrease of oligoclase and great in- Grading by increasing amount of quart crease of quartz, into = | Augitegranite (A 4) and granitell or granitic | Grading by increasing fineness of | Fine-grained granitell or granitic porphy = porphyry (A 3) (in part). grain, into —> (in part). 9 Orthoclase. Orthoclase. 2 Oligoclase (not always present). \ Oligoclase. ie Quartz. Quartz. 2 Augite (always more or less thoroughly al- Augite (very sparse, altered to 3S tered to ferrite or hornblende and very chlorite, or uralite). = sparse). Ferrite. = Secondary quartz. = 2 = A Trace page 126, Vol. V, Irving. Series, showing their mutual transitions and relations. Porphyritic kinds, ¢. e., kinds containing some unindividualized matter. Grading, by addition of residuary magma, into — Melaphyrs or ‘“‘luster-mottled”’ rocks of Pum- pelly. Haveattimesalittle residuary magma, but it never amounts to much. Genuine porphyritic kinds of high basicity are unknown. Grading by in- creasing amount of uncrystalline base, and intro- duction of gas vesicles, into —> Grading by decrease in amount of augite and change of the augite into aggregates of rounded grains, into “A shbed"-diabase (B 7) (in small part only) and | this, by introduction of unindividualized ma- terial and increasing fineness of grain, into — D-abase-porphyrife (in small part only) (B 7). Tabular plagioclases. Round augite particles. Magnetite Trresolvable base. Porphyritic plagioclases and rarer augites. Grading by in- creasing amount of unerystalline base, and intro- duction of gas vesicles, into—> | Grading by decrease in augite and general in- Grading, as above, into “Ashbed"’-diabase (in part) (B 7), and this as above, into——> crease in acidity, into | Diabase-porphyrite (the larger part) (B 7). Tabular oligoclases. Round augite particles. Magnetite. Trresolvable base. Large porphyritic plagioclases and rarer augites. Grading by in- creasing amount of unerystalline base, and intro- duction of gas vesicles, into—> | Grading by increasing acidity of the feldspars, decrease in the amount of augite, and intro- duction of much ferritic matter, into | oo .| Grading through increasing fineness of grain, loss of crystalline outlines to the augite, and introduction of irresolvable base, into —> Diabase-porphyrite (in_ part; especially the reddish-brown and jet-black kinds with highly conchoidal fracture) (B 7). Tabular plagioclases. Round augite particles. Magnetite. Trresolvable base, often in very large pro- portion. Much ferritic material in the base. Porphyritic plagioclases and augites. Grading by in- creasing amount of unerystalline base, and intro- dnuetion of gas vesicles, into—> Half glassy vesicu lar kinds. nerals. chlorite, epidote, quartz, r. epidote, &c. 2 a = 4 = | vo | & o R rg a i] = Sok BoS2 de Soaae aloue peas 55g o8as = AY ak aes Ww 2.09 aS 8°95 885 erie = 8'o @ BESZ Sho 3 8S HEt Bagezkae og Slaguk ee o ok wWoLZooa wes ‘=e Bt bot SaSaEEY ze gyeacas a82 3 = 2° ERSSSla Sst Soh Eee. Hed BSeSr as ee aes? 28S PEE RAS ORE Geo as =) . Ses a 3 sale gs* >. lan & S32 £a5 SiS sas s eon, S28 ERS > ~) oa $ SA 2S& SAS Nad 6 3 iS = S Ss ~ S 3 3 3 3 s 2 = = K 4 SS vas = Boe gk Sans os iis gags = Ease 52 an9 eo gHo 2s ms oDwoge 38 Bogard = dle S Sae8 22 Seaesee > aes 3 Sues] 3 BPRS e REzZess Base Grading by still further increase in acidity, in- troduction of orthoclase among the feldspars, and loss of augits in the base, into ' Grading by introduction of felsitic matter, and increasing fineness of grain, into —~> Quartzless porphyries (A 1). Groundmass: Micro-felsitic matter. Crypto-crystalline matter. Ferrite. Tabular feldspars. Secondary quartz. Porphyritic ingredients: Ollgeclasa and orthoclase. Augite with ferritic decay. Grading, by increasing acidity, loss of tabular feldspars in the matrix, and introduction of porphyritic quartz, into | increasing fineness of grain, and Erading by uction of felsitic matter, into—> intro Quartziferous porphyry and felsite. Groundmass : Glass (very little). Crypto-erystalline matter. Micro-felsitic matter. Micro-crystalline matter (subordinate). Ferrite. Secondary quartz. Porphyritic ingredients: J Quartz (corroded dihexahedral pyramids). Orthoclase and oligoclase. Augite (rare). Vesicular kinds not known among the acid rocks. Coarse-granular kinds. Summary tabulation of the eruptive rocks of the Keieenay Series, showing their m nam Series, showin Fine-granular kinds, utual transitions and relations. ——_ a Porphyritic kinds, 7. ¢., kinds containing some Half glassy vesicu- BASIC KINDS. Silica 45 to 52 per cent. Silica 45 to 48 per cent. ‘ Olivine-gabbro (B 1). Olivine. aa jallage. Titaniferous magnetite. Non-orthoclastic, olivine-free (' (in part only) (Bl). Anorthite or labradorite. Diallage or re Titaniferous magnetite, Anorthite rock; a special phase (B 4). abbro and diabase Grading Ss f grain and loss of diallagic cleavage in the angite, which remains coarser than the other constituents, into _ Grading by increasing fineness of grain into —> by increasing fineness of Olivinitic diabase and melaph tled”” rocks), Anorthite. Olivine. Augite. UF (“lustermot- B6 (in large part), Titaniterous magnetite, Pseud-amygdaloids a specini phaso, Grading, by addition of residuary magma, into —_—_> Labradorite. Augite. Magnetite. “ Ordinary -type” di A (B5) Ip wabase (in smi Pseud-amygdaloids a special phase, all part. on] y) Grading by decrease in amount of augite and change of the augite into aggregates of Romie ains, into “Ashbed ”-diabase (B 7) (in small part only) and this, by introduction of unindividualized ma- terial and increasing fineness of grain, into —pP ding by loss of olivine, decrease in basicity ort the plagioclases, and, in some kinds, by addition of orthoclase, into | Grading by loss of olivine and sicity of plagioclase, into | decreasing bya. Silica 48 to 52 per cent. INTERMEDIATE KINDS. — Non-orthoclastc olivine-free gabbro and diabase (in part only) (B 1). Labradorite. | Diallage or augite. — Titaniferous magnetite. Orthoclase-gabbro (in small part only) (B 2). Labradorite or oligoclase. Orthoclase. Diallage and angite. Titaniferous magnetite. fc iw Leone common accessories. ralitic gabbro )e * Hornblende-gabbro (B 3). } special phases. Grading by increasing fineness of grain into —> Labradorite or oligoclase, Augite. Titaniferous 1 magnetite. Pseud-amygdaloids a special phase, “ Ordinary-type”’ diabase (tho larger part) (B 5). Grading, as above, into “Ashbed"’-diabase (in part) (B 7), and this as above, into-——> Grading by decreasing basicity of plagioclase, increase of orthoclase, and introduction of secondary quartz, into | Grading by decreasing basicity of feldspars into | — Silica 52 to 60 per cent. Orthoclase-gabbro (the larger part) (B 2). Oligoclase. Orthoclase. Diallage. Augite. Titaniferous magnetite. Apatite, uralite and secondary quartz, very common accessories. : Uralitic orthoclase-gabbro (B 2). Hornblende-gabbro (B 3). } special phases. Gradation forms not known, into —> “Ordinary-type” diabase (in small part 0 Oligoclase. Orthoclase possi per cent. when silicified by Pseud-amygdaloids & spe t. ACID KINDS. Silica 60 to 78 per cen Grading by decrease of augitic consti U ig stituent, increase of orthoclase and of quartz, ng api | Gradation phe Augite-syenite (in Olinpolase. RAPHE) Orthoclase. Augite (very subordinate), Verrite and ‘aby - accessories, indant quartz characteristic Silica 60 to 70 per cent. {24 25 Le ae Grading by decre r 3 Grease or quate oe oligoclase and great in- | a Grading by increasing fineness of grain, into —> Fine- Orthoclase. Oligoclase. Augite. Ferrite. Secondary ¢ eS Grading by in Augite-granite (A 4) rer elt rag and Orth tise. (in part). igoc! Quint Se (not always present). ugite y ig M4 (always. more or less thoroughly al- to fi . Hats errite or hornblende and very granitell or granitic Silica 70 to 78 per cent. Grading by i i fi acing by increasing fineness of grain, into —> = ‘ Lace page 126 V Page 126, Vol, V, Irving. So —- Fine-grained g/ (in part). Oligoclase. Quartz. Augite (Vv chlorite, Ferrite. Secondary quartz. creasing amount | -anitell or 9! Orthoclase. 0, ery sparse, or uralite) quartz. bly in a few kinds(!). ls) (B 5}. Grading through increasi in, rai loss of crystalline ontlinas CSE aateiar introduction of irresolvable base, into—_» ases not know}, into grained augite-syenite (A 9). of ui alter! into ao raniticp?” F pyrite, to the augite, and | | Tabular plagioclases. | Round augite particles. | Magnetite. Trresolvable base, often in very large pro portion. Much ferritie material in the base. Porphyritic plagioclases and augites. Grading by still further increase in acidity, in troduction of orthoclase among the feldspars, and loss of augite in the base, into Y Grading by introduction of fe ‘creasing fineness of stain, into—> Isitic matter, and | Quartzless porphyries (A 1). Groundmass: Micro-felsitic matter. Crypto-crystalline matter. Ferrite. Tabular feldspars. Secondary quartz. Porphyritic ingredients: Oligaclase and orthoclase. Anugite with ferritic decay. dity, loss of tabular , and introduction of Grading, by increasing feldspars in the porphyritice quartz, into | incrensi ao Grading by 100 of fe), introdue’ ng fineness of grain, and sitic matter, into— + Quartziferous porphyry and felsite. little). ystalline matter. felsitic matter. F -ystalline matter (subordinate). Ferrite. | Glass (ver. Cry Secondary quartz. Porphyritic ingredients: 4 Quartz (corroded dihexahedral pyramids). Orthoclase and oligoclase. Augite (rare). unindividualized matter. lar kinds, Melaphyrs or ‘‘luster-mottled” rocks of P i =a oa : . ! um- | Grad ‘out = elly. Haveattimesalittle residuary magma, pes ea Ss S = a uit it never antonute to much. of mucryatalline ea: uine i Phi ici Sel ves on eX hyritic kinds of high basicity are base, and intro- & 3 nkn duction of gas . a vesicles, into —> £ 2 22 3 aa | Diab oe a ‘abase-porphyrife (in small part only) (B 7). { ‘ sag a ¢ Tabular plagioclases, sa a er fee = 3 Beane augite particles. of uncrystalline s hae Fae aed base, and intro- a7 ks Is esolvable base. duction of gas S.n$ Uex orphyritic plagioclases and rarer angites. vesicles, into—> es 2 a Bo an - ~ ess S23 SSb SBE : : ; aio ES Grading by decrease in augite and general in- ge $5885 creise in acidity, into 3 S242 SE5 “8 2609 1 as on - r=] e2 68 a 3 2 aS im og & ESS Heo ook mse soos MSs Baggee™ Soe : F HRASH 7SO Diabase-porphyrite (the larger part) (B 7). Grading by in- a Agotes g°s Tabular oligoclases. creasing amount Oates $2 gE Rannd augite particles. of uncrystalline| 3°35 aS 83 as = agnetite, base, and intro-| RRA SBE Fae Trresolvable base. duction of gas} .. Baws on Large porphyritie plagioclases and rarer vesicles, into—>| 8 ae8 sos augites. 3 Sok Seg § a ze & ay eas os 3 $42 525 ae Sa> § SAS a & oR x ae meena SND 3 ¢ § & * . . ss ea . 5 Grading by increasing acidity of the feldspars, ~ = decrease in the amount of augite, and intro- 2 > duction of much ferritic matter, into : 3 | * q 4 =- nad BOe ska ace BOG . FY ‘. 4 iy = OS me Diabase-porphyrite (in part; especially the | Grading by in- we Seas reddish-brown and jet-black kinds with creasing amount 525% highly conchoidal fracture) (B 7). of unerystalline eae] base, and intro- ABA dnetion of gas} vesicles, into—>! the acid rocks. Vesicular kinds not known amo . ” . 1 . a + on 1 ™ ’ o , - { . 1 ‘ . ee - ' = ’ . , 4 . 0 =e n ; . — ‘ ‘eS <6 so ~s es vs } ‘ Peal t ree hen sae = Ved re @ tags, \ ial -_ > ye oa oh Paty art ir = POs Se oe ene eS * ‘ 7 ~ + i ad «gues UNITED STATES GEOLOGICAL SURVEY COPPER-BEARING ROCKS OF LAKE SUPERIOR PL.XVI / * gy ‘k -# f v Sah vg ie ON, Beas fe OWT \se es Ta ; A 4 iy! “ht ry Hy hy rm oe A A. Hoen & Co, Lith, Baltimore SANDSTONES ws vost Soosdno osspdubosype op 00h rear RasetstsrGS Ay Lersdessost ya olosd SKQsS SexosubbeO ‘S SAS rons oe ging i Wut : at hints ’ \ if f ha. ey spar; magnetite particles ; and green- ish particles, which are at times re- cognizable as highly altered augite and diallage. In the interstices be- tween the grains, which are from an- gular to round in shape, a fine detrital material is sometimes seen; but for the most part these spaces are occu- pied by infiltrated matter, in the shape of epidote, a greenish chlorite, 132 COPPER-BEARING ROCKS OF LAKE SUPERIOR. Tabulation of microscopic observations upon sandstones, &c.—Continued. men num- ber. Speci 2508..| Silver-bearing rock 2535..| Bed of Upper Carp | -| Union mine lode, Por- ] Place. underlying None- such vein, Porcu- pine Mountains, Michigan. cupine Mountains, | Michigan; top of sandstone underly- | ing “outer trap;” from bed of stream. River ; immediately overlying amygda- loid; Porcupine Mountains, Michi- gan. “4 1 Falls of Bad River, Ashland County, Quarter-section. Nw. Sw. | Section. 19 | Township. 51 51 | Range. 43 W. 42 W. | Macroscopic descrip- tions. Very fine-grained; dark-gray; quartz- ite-like; firm and hard ; effervesces in places with hydro- chloric acid. Very fine-grained ; dark reddish-brown; firm; effervesces readily with hydro- chloric acid. 42W.| Excessively fine- grained; dark pnur- plish-red ; firm; ef- fervesces readily with hydro-chloric acid; finely banded with darker and lighter shades. 3W.| Medium to coarse- grained; reddish. Si0., 69.78 per cent. Microscopic descriptions. calcite, and native copper, all of which, with the exception of the last named, are very irregularly distributed through the section. The copper molds itself sharply around the con- stituent fragments, having in most cases a core of magnetite, an occur- rence suggesting its precipitation by the ferrous oxide of the last-named mineral. The copperalso is occasion- ally to be seen penetrating into the interiors of the more readily decom- posable fragments. Plate XVI, Fig. 1. This rock is composed of predominant quartz fragments, with a smaller pro- portion of porphyry detritus, and a a large one—probably making up half the rock—of infiltrated quartz. There is also some infiltrated calcite, which is very irregularly distributed. A very fine-grained rock; much re- sembling 1792. Larger fragments of feldspar and porphyry matrix are im- bedded in a groundmass, composed of the same materials, with a large pro- portion of quartz. There is also present a notable proportion of basalt- ic detritus. The particles are for the most part quite angular. The interstices are everywhere filled with infiltrated calcite, along with some epidote. Very much like the last rock described, except that itis much finer in grain, and contains a small proportion only of basaltic detritus. Larger angular grains of quartz and feldspars are imbedded in a fine matrix composed of the same mate- Tials, along with much porphyry detritus, largely in a decomposed condition, and an abundant brown ocherous cement. oe mmm puonte ber. Place. Specimen num- 1516J.| Bed of Montreal River, Ashland County, Wisconsin. 1709..; Silver Islet Landing, north shore of Lake Superior, Ontario, Canada. 1709A!| Same place as 1709. DETRITAL ROCKS. § g Oo a 2 ; 3 5g |] Be} 5 3 i y) GE Ss TORE GAGS MET ON LOWLANDS MXS ER > Ss PASS KS Lake Bailey = NS wy AA x » KE SLLLIL LILLE ASS SS CUO GRY woe MSS SEE L2IIPFEEE. - BOONES N NN WN A A eS SWF : aN ant Ne eaeeal ss ce! The Great Conglomerate i Marvines | “tute * “Lake Shore Trap 2 P a a Group C Croup: TRI d St te ee PN AK K uy % KREG 5 RS Q alIX Le Mi) = mh TT wz iy Mh) 'S I MN) My W My Diabase, Diabase - amygdaloid and lustre - mottled Melaphyr, i “Wry yee. ies ; aa : including a number of Conglomerate beds ange Group The Eastern Sandstone Il Phoenix Mine N.2ee W. Eagle River GREENSTONE RANGE | \ 7 R 4 fe . ww ¢ AN Saw WS aN Ws : ee = ‘\ ; A : ; : eK 3 S NA WER ih as GU Rk T OR | 2 CS RWS ON SRS Sy NI AN SANS = Y = a SK ‘) AN XW wy > SER SAQA Sas ORO RSS — SRN SOROS Ts i, BOHEMIAN RANGE mores S.ce¢E— KOER Heads of Tobacco River ~ : EASTERN LOWLANDS : COOOL OD PLP ; S SY PACERS) % S <\ \ . SNS a o fs - rx z WF BEIGE I De Z ¥ : SOR naa ZAUNNW « A ZX rRone < & Wn , \ vo S\ RAS AWS KORE QRRRN SSS ia—— =e : SS We Rs E we ee ANI SINS Oe i. sf SS WY Zo NAO QOS Sit CCL LLL Saas wer NO Ne Se BORER Y * Outer Conglomerate i The Great Conglomerate | : Marvines "Ashbed “Greenstone Diabase, Diabase - amygdaloid and lustre - mottled Melaphyr including “Bohemian Range Group” ' The Eastern Sandstone - ‘Group C" Group B* Group” Group * a number of Conglomerate beds - ; » IV Allouce Conglomerate ae N.42°W. S.42°E— | ; Ge AL KE Meee ek Lf OO OR : - y y, ‘ 7 AOI ISI EISEEIISEEES Z Gy BEE. JERS ? 22 56 Diabases and amygdaloids............-. Sete ve cinibs ePana since tio mae slaaveente sje es 370 @onglomerater2 easene sstecs feel ot Reece ncteecsctietsoces Wale facetemes: 35 Wiahasesvandgamy Pa aloidsrea eS hss cele rials coe arses tists orsiesisieiino sist- see's 1,140 Oonglomerateylitass sac ces 52t-se section (720 - b a, . it an aphaninie -- rphyxitie, ingredien - fine-gramed and oven gue particles and prt : ae af mrpenivaly Sarge 2 eeplish-r red, roak : (255 (14s “YN Ay ad hel . = EOLOGICAL SURVEY Mineral River North and South Lake Superior North and South POR CU BEN & Carp Lake a a = —zy = —_— | pa i ie 46 ity ot f" thw = IOP ON por eee st hh fF -” i pyr a ef = af AY A ES pegs" I Minerval River Tron River B. branch t Little Iron River Tron River TL Little Tron River MOUNTAINS f LINE sf 23-51-43 26-51-43 South 334° East Diabase and diabase amygdaloid im ing narrow conglomerate belts Quartz porphyry and felsite WE ee POSITS 9-50-43 10-50-43 h “AULT ® |= > Sandstone and amygdaloid with a conglomerate. amygdaloid . porphyry conglomerate Diabase moe es COPPER-BEARING ROCKS OF LAKE SUPERIOR PL. xx Iron River Iron River | Diabase and diabase Sandstone and conglomerate OLED SECTIONS ARE LOCATED BY NUMBER ON MAP OF PORCUPINE MOUNTAINS North and South ‘Dark grey sandstone Red sandstone | and black slate , 7 GEOLOGICAL SECTIONS ILLUSTRATING PORCUPINE MOUNTAINS. Scale Too OHO or 1 inch = 333 f ATigoCk Co Lie Balemore. DEES Sabo a Wee O Mu FELSITIC PORPHYRIES OF THE PORCUPINES. 211 and non-polarizing, while thickly studded through this are minute particles of quartz, a number of which polarize together, thus showing that they are parts of one crystal. The section thus has a peculiar mossy appearance in polarized light. This quartz is doubtless secondary, but the particles are larger and more nearly like those of the original quartz than usual. The few porphyritic quartzes and feldspars present the usual characters. Much black dust is present in blotches and lines, and is in part undoubtedly mag- netite. The dark purplish quartz-porphyry (2574) from See. 20, T. 51, R. 42 W. (500 N., 1150 W.), holds a few minute original quartzes, and shows under the microscope a matrix which in the ordinary light appears nearly homogeneous and thickly dotted with minute brownish and blackish part- icles, but in the polarized light presents an appearance analogous to that of the last rock described, except that the secondary quartz is in much more minute particles, large numbers of which polarize together. Orthoclases occur among the porphyritic ingredients, and a very interesting relation was noted between one of the orthoclase crystals and one of the original quartzes, the latter having grown around the end of the former. A few minute augites occur in the matrix. A closely similar rock (2586) appears in large exposures on the upper part of the stream which enters the southeast end of Carp Lake, in the S. W. 4, Sec. 23, T. 51, R. 43 W. The sections of the dark purplish- red rock (1247 and 1248) from the bed of Little Carp River in the north- east corner-of Sec. 20, T. 50, R. 44 W., appear much like the last described, having not very rare original quartzes and orthoclases, and abundant second- ary quartz, some of which is arranged in curving concentric lines, appa- rently emphasizing a structure in the original rock. These sections show much fine ferrite, and now and then a quite perfectly developed augite crystal. The ferrite particles in places appear to indicate flowage. The ledge on the south line of Sec. 9, T. 50, R. 44 W., 270 paces west of the southeast corner, shows a very plainly banded felsitic porphyry (1259) with not rare, white orthoclase crystals which often lie entirely across two or three bands. The banding is produced by lighter and darker shades, and is quite irregular and wavy. Under the microscope the banding is seen to be produced by the presence of much red iron oxide in some bands, and its absence or relative scarcity in others. The bands are quite without regularity or continuity, 212 COPPER-BEARING ROCKS OF LAKE SUPERIOR. the white bands being merely irregular rows of light blotches. The indi- vidual blotches do not average more than a small fraction of an inch in length, the red material closing together between them. Under the micro- scope both light and dark portions show little sheaf-like aggregations of orthoclase, which mineral in the whiter portions is often larger than in the red. A good deal of the usual secondary quartz and ferrite are present. The porphyritic orthoclases are much decomposed and reddened, and are not very abundant. Another banded rock (1263) is shown in one of the numerous north- easterly trending ledges of the southern part of T. 51, R. 43 W., near the southeast corner of section 32. Thisis a dark-red felsite without porphyritic ingredients, looking much like a dark-red quartzite, with close and quite regular bands produced by variation in depth of color. Under the mi- croscope the thin section shows but little coloring matter. The lighter bands are seen to be composed of rather coarser particles than the others, while the banding is further emphasized by fine lines of thickly crowded ferrite particles. The base appears to be composed of individualized orthoclase and quartz, and some little quartz that appears as if secondary, but there is none of the irregular mossy or radiating or concentric structure produced by secondary quartz, such as noticed in other sections, the base presenting a remarkably homogeneous, finely crystalline appearance The numerous samples brought from other ledges within the porphyry area of the Poreu- pines do not indicate the existence of any other phase of the porphyry than those described above. The limits of the Porcupine porphyry area are pretty well determined by exposures, more especially on the north and northwest, where the ex- posures of the different rocks often lie quite close together. Thus in sections 30 and 31, T. 49, R. 44 W., the Presqu’ Isle River exposes diabases and amygdaloids of the ordinary type, and the latter rock is seen again in the southwest of section 19. In the northeast of section 19 and the northwest of section 20 are large exposures of red felsite and felsitic porphyry, while in the middle of the west side of section 18 are seen the amygdaloids and diabase belonging to the belt north of the porphyry, the north and south limits of which on the Presquw’ Isle are thus indicated. Again, at the rapids of Little ies. PORPHYRY AREA OF THE PORCUPINES. ata Carp River, in the northeast corner of Sec. 20, T. 50, R. 44 W., the contact of the porphyry with the overlying rock is in sight. The high ridge of porphyry in the east part of section 31 and the southeast of section 30 of the same township proves that the boundary of the overlying belt of diabase and diabase-amygdaloid makes here a considerable deflection to the west- ward from a straight line drawn between its positions on the Little Carp River in See. 20, T. 50, R. 44 W., and in the west part of Sec. 18, T. 49, R. 44 W. Sec. 32,7. 51, R. 44 W., exposes porphyry largely in the south- eastern and southern portions, and diabase in the western and northern, while in the stream at the northeast corner of this section, lilac felsite and amygdaloids are largely exposed at only 200 paces from each other. South of Carp Lake, in sections 23 and 22, the porphyry and overlying rock are largely exposed at points not far apart, and several exposures of the two rocks between here and the junction in the N. EK. 4, Sec. 32, serve to fix this part of the boundary quite closely. The road running east and south from the head of Carp Lake, through sections 23 and 24, crosses ledges both of the porphyry and its overlying rock. In Sec. 30, T.51, R. 42 W., the limit is again found in the northeast quarter of the section. Further south- east, in T. 51, R. 42 W., there is some doubt as to the exact limit of the porphyry to the eastward, or rather, the position of its overlying rock is left in doubt by lack of exposures; besides which some doubt is introduced by the uncertainty as to where the fault lying south of the porphyry ends. Closely approximated exposures of the porphyry and amygdaloid on the south fix the southern limit very closely in sections 3, 4, 5, and 6, T. 50, R. 43 W. In the eastern part of T. 50, R. 44 W., a gap without exposures leaves the exact position of the eastern limit in some doubt, as indicated on the map. The porphyry and felsite ledges are so generally distributed over the area colored for those rocks as to indicate that they underlie most of its extent, but in one place a large exposure of a rather coarse-grained very highly crystalline gabbro, such as is frequently asso- ciated with porphyry and felsite on the north shore of Lake Superior, was noted. This is on the south line of Sec. 3, T. 50, R. 44 W., 1,150 paces west of the southeast corner. The ledge is 100 feet high and 200 feet long in a southwest direction. 214 COPPER-BEARING ROCKS OF LAKE SUPERIOR. In attempting to trace the porphyry of the Porcupine Mountains east- ward we find that across T. 49, R. 43 W., the region where it would lie is mostly drift-covered, but that in the northern part of T. 49, R. 42 W. there are large exposures of quartzose porphyry occupying a belt one to two miles in width, and trending east-north-east across the township to the northeast corner. T. 50, R. 41 W. is next crossed by the belt in its south- ern portions, without many exposures. One is reported by Mr. B. N. White at the center of Sec. 21, T. 50, R. 41 W. Across the middle sec- tions of T. 50, R. 40 W. the government surveyors have written the words, “‘red slaty trap,” which are evidently meant for the red porphyry. The same words are used in the plat of T. 50, R. 39, for the quartzose porphyry already described. Westward from the Presqu’ Isle River to the Montreal I have no knowledge of any porphyry exposures. The country is mostly low and the rocks covered where the porphyry would be expected to appear. Beyond the Montreal it reappears, as subsequently described. North and west of the porphyry area of the Porcupine Mountains there is everywhere found a belt of basic rocks having a surface width of from about one-fourth to one-third mile, and a thickness varying from 300 to 500 feet. Toward the middle of the thickness a porphyry-con- glomerate is included, with a thickness of over 60 feet. The basic rocks of the belt are in very regular and rather thick flows, some half dozen beds appearing to make up the whole thickness. Among the massive portions of the beds a very fine-grained, dark-red, compact and semi-conchoidal ° rock is abundant, occurring both above and below the intermediate con- glomerate. Under the microscope the slices of this rock, from points far apart along the length of the belt, show the characteristic arrangement be- longing to Pumpelly’s melaphyrs. Olivine, plagioclase, magnetite and augite are the ingredients in order of age. The augite occurs in crystals including numbers of the small plagioclases, while the magnetite and the olivine are crowded into the spaces between the augites, the latter mineral being usually much altered to both red (hematite) and green (serpentine) sub- stances. Another rock of this belt—occurring in some places in two layers, one above and one below the intermediate conglomerate, and in others only above that horizon—is an aphanitie dark-gray to black or reddish-brown rock NS IV fron River \We Lake Superior _ : a South 36%°East PORCUPINE MOUNTAINS East and West VIL So Mineral River N | Take Superior & iB a 2 ! FL EA SZ — : a ann FF p ey < y senereeseaeeataar arse oO LY a SSS 10 b-a- nH 2-4 27m — aL a2 a 23 50 — aa 36 50 — 42 1—40 —42 Wasa) pap — a2 2-40-42 | 2) -a9—a2 30 — 49 — 42 North and South Diabase anid diabase- Sandstone and Diabase and diabase- Sandstone and Dark gray sandstone Red sandstone. The Eastern sandstone. ring and felsite. anygdaloid, with a conglomerate. amygdaloid. conglomerate. and black shale. iglomerate belts, porphyry conglomerate. 1 2 + 5 6 Bee ZZ Sections are located by nuonber on map of Porcimme Mowtains. Atlee & Code, Bultinane GEOLOGICAL SECTIONS ILLUSTRATING THE STRUCTURE OF THE PORCUPINE MOUNTAINS. Scale io0000 or Linch = 8333 feet. waco INNER TRAP BELT OF THE PORCUPINES. 215 with few or many porphyritic feldspars. The thin sections show this rock in some cases as a typical ashbed-diabase, with a few porphyritic orthoclases, and in others as a true diabase-porphyrite. The latter presents very numerous porphyritic orthoclases in an excessively fine base, in which there are portions which polarize only very feebly or not at all, and in which minute tabular plagioclases with rare augite, magnetite and ferrite particles are the only recognizable ingredients. Some of the beds are of the ordinary type of fine-grained diabase, and the amygdaloids present no unusual characters. The rocks of this belt can be seen to best advantage on the upper Carp River, in sections 19 and 30, T. 51, R. 42 W.; on the road from Union mine to Carp Lake, in Sec. 24, T. 51, R. 43. W.; along the course of the stream south from the same road in the NE. 4, Sec. 23, T. 51, R. 43 W.; in the NW. 4 of the same section along the larger stream which runs into Carp Lake near its southeast corner; and on the Little Carp River in sections 17 and 20, T. 50, R. 44 W. On the upper Carp the junction with the overlying conglomerate is seen at 450 paces north and 1,630 west of the southeast corner of Sec. 19, T. 51, R. 43 W., where the strike is northwest, and the dip north- east 25°. Hence up stream to the junction with the in- cluded conglomerate at 282 paces north and 1,630 west of the same corner the ex- posures are nearly continu- ous and show much of the fine-grained reddish meia- 7 7ATr 3 400 paces lo phyr, besides several bands -_— 34%. of amygdaloid and diabase of Fic. 4.—Map of exposures on upper Carp River, Porcupine Mountains. One inch=90 paces. the ordinary types. Thethick- ness between the two conglomerates is about 200 feet. The upward course of the stream follows the junction with the lower conglomerate to a point 216 COPPER-BEARING ROCKS OF LAKE SUPERIOR. 100 paces north and 1,520 paces west of the section corner, the conglomer- ate forming the southwest bank, and the diabase the northeast, as indi- cated in the accompanying sketches, Figs. 4 and 5. AL ZZ ~ Ee a ale ae 5 < ee Ss pels hee SoH, mes - Sor oe 2 ee ee Ss Soe = ‘y Bs Bie.) HT iis Frag. 5.—Cross-section on line CD of Fig. 4. At the last point indicated, B of Fig. 4, the stream makes a sharp turn westward, and the diabase is faulted against a reddish diabase-porphyry, carrying orthoclase and triclinic feldspars as porphyritic ingredients, and having a confused, much altered base in which the minute tabular plagio- clases are, however, very abundant. The whole rock is permeated by lit- tle strings and patches of calcite. Further up the stream, in the northwest part of section 30, and as far as a point 1,675 paces north and 1,590 west of the southeast corner of the os S << SRS ISS ae Fic. 6.—Section on line AB of Fig. 4. latter section, other basic beds are seen in place, including two or three amy gdaloids, some reddish melaphyr and a heavy bed of diabase-porphyry. All of these beds, from the junction of the upper conglomerate, trend north- west and dip northeast 25°. Still further up the stream, in section 30 (1,420 N., 1,400 W ), the true felsitic porphyry begins to show. Judging by the surface width and dip angle, the thickness on this stream between the up- per conglomerate and the last amygdaloid is as much as 600 feet, but some of the apparent thickness may be due to the faultings spoken of. The two streams in Sec. 23, T. 51, R. 43 W. do not expose the upper conglomerate, but present above the lower conglomerate some 400 feet in thickness of very regularly-bedded melaphyrs and amygdaloids, including much of an exceedingly fine-grained diabase of the ashbed type, which at times carries numerous porphyritic orthoclases, and runs then into a diabase- } { u INNER SANDSTONE OF THE PORCUPINES. 217 porphyry. The exposures on the Little Carp River in sections 17 and 20, T. 50, R. 44 W. extend nearly continuously between the upper conglomerate and the red quartziferous porphyry below. The strike here is north and south, and the dip some 15° westward. The entire thickness between the con- glomerate above and the quartz-porphyry below is some 280 to 300 feet, a considerable reduction on what is seen further east. The junction with the upper conglomerate is seen in section 17 (160 N., 1,000 W.). Between this point and the lower conglomerate there is a thickness of only some 75 to 100 feet, much of which is made up of a dark-brownish diabase-porphyry. The lower conglomerate is seventy-five feet thick, and below it comes a suc- cession of amygdaloids and fine diabases to the junction with the quartz- porphyry below, which occurs at 1,850 paces north and 600 west of the southeast corner of section 20. Southeast of the exposures on the upper Carp River in sections 19 and 30 of T. 50, R. 42 W., the belt of country in which the continuation of these basic rocks would be expected is without exposures, so far as known, except two of conglomerate, which from their position and character may very well belong with the median conglomerate of the belt I am now de- scribing. One of these is in the creek-bed in See. 32, T. 51, R. 42 W. (840 N.50 W.). A thickness of sixty feet is here seen, striking northwest, and dipping northeast 20° to 25°. The pebbles are large, usually from ten to one hundred pounds in weight, and are composed almost entirely of purple quartz-porphyry and felsite. The other point is in See. 29, T. 51, R. 42 W. (950 N. and 1,450 W.), where there is a large show of a conglom- erate similar to the last, striking N. 10°-15° E., and dipping S. E. 30°. The broad sandstone and conglomerate next succeeding in the Porcu- pine Mountains region, which I regard as the equivalent of the main or Great Conglomerate of Keweenaw Point, has not been seen in any one section across its width. Its existence as a single great layer is inferred from scattering exposures and from the topography. Its upper and lower limits are well seen in a number of places, but its middle portions underlie lowland and are but little exposed. The layer is largely sandstone, the conglomeratic portions occurring at the base, near its union with the under- lying amygdaloid. The rock is made up of the usual reddish porphyry 218 COPPER-BEARING ROCKS OF LAKE SUPERIOR. detritus, often permeated by secondary calcite. The upper portions of the layer are best seen in the face of the great cliff which forms the north side of the valley in which lie Carp Lake and Carp River. This cliff extends nearly continuously across T. 51, R. 43 W., a distance of over six miles. The crown of the cliff is from 800 to 1,000 feet above Lake Superior, and from 400 to 600 feet above the valley of Carp Lake. The base of the cliff is marked by a long slope of fragments fallen from the diabase and amyg- daloid that form its upper portions, but through the greater part of its length there is a perpendicular face of about 400 feet above the talus. The base and lower portion of the cliff are composed of sandstone and conglom- erate, but toward the east the sandstone rises nearly to the top of the cliff, while on the west side of the township it is found only at its base. At Carp Lake, which lies at about 400 feet altitude above Lake Superior, the cliff reaches 1,000feet above the same level. Here the sandstone rises to about 400 feet above Carp Lake, while in the eastern part of section 13 it rises almost to the top of the hill. Other places where the top of the layer may be seen are on the tram-road from the Nonesuch mine to Lake Superior, in Sec. 27, T. 51, R. 42 W., at 1,050 paces north and 1,500 west, and again in the same section at 1,850 north, 1,600 west. At the latter point a creek follows the junction between the sandstone and overlying diabase for some distance. The lower portions are exposed on the upper Carp River, S. W. 4, Sec. 19, T. 51, R. 42 W.; on Little Carp River, S. W. 4, Sec. 17, T. 50, R. 44 W.; on the stream in the N. E. 4, Sec. 13, T. 49, R. 45 W., and on the stream in the S. W. 4, See. 15, of the same township. ; As marked on the map and sections of the Porcupine Mountains, this layer has a thickness of some 1,800 or 1,900 feet. It is possible that in the middle of the thickness there may be some interstratified diabases and amyg- daloids, but the existence of the long low valley of Carp River, under which lies all of the thickness about which there is any doubt, and the entire ab- sence of exposures of any such rock on the Carp, Little Carp, and Presquw’ Isle rivers, where they cross this belt, seem to forbid such a supposition. In the region of the Montreal River a number of interstratified diabase flows make their appearance, but they are to be seen on every crossing river. Next in order to this conglomerate in the Porcupine Mountains comes OUTER TRAP BELT OF THE PORCUPINES. 219 the second belt of basic rocks, with a thickness of some 300 to 400 feet. The rocks of this belt are finely exposed in the great cliff which stretches in a curving direction entirely across T. 51, R. 43 W., on the north side of the Carp Lake Valley. As already explained, to the eastward these rocks are found just capping the cliff, and then extending toa relatively long dis- tance down the north slope of the mountain; as, for instance, in Sec. 13, T. 51, R. 42 W., where this belt has a surface width of over half a mile. Further west the junction with the underlying sandstone is lower down in the face of the great cliff, the belt descending but a short distance down the north slope of the mountain, and as a consequence presenting but a narrow spread on the map. Beyond T. 51, R. 43 W., to the westward, this belt pursues a course at first southwest and then more nearly south through T. 51, R. 44 W.; T. 50, R. 44 W.; T. 50, R. 45 W., and T. 49, R. 45 W., to the Presqu’ Isle River, where there isa sharp bend to the westward, as indicated on the map. The best exposures are on the Little Carp, in Sec. 18, T. 50, R. 44 W., and on the Presqw’ Isle, in sections 14 and 15, T. 49, R.45 W. On both streams the junction with the overlying sandstone is exposed, and both streams make falls over the basaltic rocks, those on the Presqw’ Isle reaching a height of twenty-five feet. Eastward from T. 51, R. 43 W., this belt continues on an easterly course for some three miles, and then, turning, pursues a tortuous southerly course to the south side of T. 51, R. 42 W., whence, turning again ab- ruptly, it runs westward through the northern sections of T. 50, R. 43 W. Here it is found to come directly in contact with the central porphyry of the Porcupine Mountains, some 2,500 feet of rock that appears on the north side of the mountains being now absent, at least at the surface. This peculiar behavior I regard as the result of a fault, as indicated on the sec- tions of Plates XX and XXI. The peculiar serpentine course of the belt through T. 51, R. 42 W. is not conjectural, having been very satisfacto- rily made out from the locations and inclinations of a number of expo- sures. Moreover, it corresponds entirely with the courses marked out for the overlying belts. In the vicinity of the Unien mine, on sections 27 and 22 of T. 51, R. 42 W., both upper and lower limits of the belt are well exposed. 220 COPPER-BEARING ROCKS OF LAKE SUPERIOR. The beds of which this belt is composed are very sharply defined and regular, with strongly marked vesicular or amygdaloidal portions, and — massive, often semi-columnar, lower portions. The massive rock is very fine-grained and commonly of a chocolate-brown to reddish-brown hue. Very often it carries mottlings, or pseud-amygdules, of dark-green chlorite, epidote and calcite. Nearly all appears to carry olivine in a much altered condition, and many of the sections show the characteristic arrangement of relatively large augites free from magnetite or olivine, but including num- bers of plagioclases, while the interspaces are thickly studded with mag- netite and altered olivine. One of these is figured on Plate X, at Fig. 1. The amygdaloids do not present any peculiar points. Dark-green chlorite, epidote, calcite, laumontite and prehnite appear to be the com- mon fillings. At several points these amygdaloids have been worked for their copper, but unsuccessfully. Next in order in the Porcupine section comes a thickness of over 3,000 feet of red sandstone with imbedded conglomerates. The sandstone, which is of the usual porphyry detritus, very greatly predominates over the con- glomerate, the latter being disposed in the sandstone in very thin and ir- regular bands. The pebbles are, as usual, of porphyry and felsite, but pebbles of the basic rocks are not excluded. The exposures of this sand- stone in the Porcupine country are too numerous for description. It is the best exposed belt of rock in the region, being seen in its entire width. It evidently includes no belts of crystalline rocks. Iron River exposes it largely, especially in the east half of Sec. 24, T. 51, R. 42 W. Little Iron River and Union River make large exposures in the same township. The whole thickness may be seen by following the coast line in T. 51, R. 42 W., and T. 51, R. 43 W.; and again from Lone Rock to the Presqu’ Isle River. Numerous exposures are met with in the woods north of the Carp River Valley cliffs, while Carp and Little Carp Rivers, in T. 50, R. 45 W., and the Presqw’ Isle, in Sec. 9, T. 49, R. 45 W., expose the entire width. The same sandstone is seen at a number of points in the eastern part of T. 50, R. 44 W., east of the north-and south porphyry ridges of the cen- tral and western parts of that township. Next in order comes the belt of dark-colored sandstone and shale OUTER SANDSTONES OF THE POROUPINES. 221 which has been traced already from the vicinity of Portage Lake to the Ontonagon River. As further east, so also in the Porcupine region, this layer consists of a series of alternating dark-gray to black clayey shales and dark-gray sandstones ; all dark-colored because of their comparatively large content of basic detritus. Calcite is very often found in the matrix, and one phase consists almost exclusively of basic detritus with calcite cement. The total thickness averages about 600 feet, varying somewhat from this figure. On the map of Plate XIX the belt is marked as very irregular in the surface width, the irregularity arising from the numerous changes it undergoes in direction and amount of inclination. At the Nonesuch mine, 8. E. 4, Sec. 1, T. 51, R. 43 W., the shale is seen with a thickness of over 200 feet, trending N. 45°-50° E., and dip- ping S. E. 28°. Near the base of the shale is the sandstone seam, 4 feet thick, worked at the Nonesuch mine for its copper. This rock is a dark greenish-gray, fine-grained sandstone, which in the thin section is seen to be composed in some measure of basic detritus, along with porphyry detritus, and numerous single quartzes. The basic detritus appears in the shape of much decomposed red- and green-stained particles, showing both feldspathic and augitic ingredients. A good deal of magnetite is pres- ent, and native copper is very abundant, for the most part clustered around the magnetite particles. In a few places secondary calcite lies between the grains. The thin section of this rock is figured at F ig. 2, Plate XVI. Beneath the copper-bearing sandstone there come a few feet of shale, also carrying some copper, and beneath this some two and a half feet of a light- gray sandstone, harder than usual, beneath which again is the great sand- stone layer previously described. The thin seam just mentioned as occurring at this junction has been traced for a number of miles in the valley of Iron River, and is the one which has attracted so much attention in this region for the silver it con- tains. Under the microscope it is seen to differ from the Nonesuch copper sandstone, and, indeed, from the rock of the shale belt generally, in that it contains some water-deposited (secondary) quartz between the grains, which consist, as usual, of mingled porphyry and basic detritus and quartz particles. Calcite has also been deposited more or less plentifully 222 COPPER-BEARING ROCKS OF LAKE SUPERIOR. in the interstices of the grains, and in some sections is the only indurating material. From the Nonesuch mine eastward the shale belt runs through the southern parts of sections 6 and 5 of T.50, R. 42 W. In the latter section the lower layers, including the Nonesuch bed, which is here also well charged with copper, are exposed on Mineral River at 250 paces north and 450 west of the southeast corner, with a southerly dip of 40°. From here the course of the belt makes a wide bow through sections 4 and 3, T. 50, R. 42 W., and sections 31 and 30 of T. 50, R. 41 W., to Mineral River, in Sec. 25, T. 51, R. 42 W., where itis seen exposed (1,200 N., 200 W.), with a northeasterly dip. In the same section, on Iron River (1,750 N.,800 We), the junction with the underlying sandstone is again seen, and both rocks make here a sharp turn from a northwesterly to a northeasterly course, the dip at the same time being changed from a northeasterly direction to a southeasterly one. The course of the belt is next on a bow to the eastward through Sec. 19, T. 51, R. 41 W., returning to Iron River in the 8. E. 4, Sec. 13, T. 51, R. 42 W. Here Iron River crosses the whole width of the belt, exposing both the underlying and overlying sandstones. The dip here is 35° east of north, and the thickness of the belt 600 feet. From here the course is westward to Little Iron River, in the 8. W. 4, Sec. 13. At this place there is a sharp synclinal, the belt turning abruptly and showing southerly dips. Return- ing now eastward to Iron River, the junction with the overlying sandstone is found in the northeast quarter of the same section (1,150 N., 250 W.), Thence to its mouth, Iron River is constantly on the layers of this belt, an anticlinal occurring near the N. E. 4 of Sec. 13. The turns of the shale and of its overlying and underlying sandstones will be best understood by an inspection of the sections of Plates XX and XXI, and of the strike and dip notes of Plate XIX. At the mouth of Iron River the shale belt passes into the lake with a northwesterly trend, the junction with the overlying sand- stone appearing just at the mouth of Iron River, and with the underlying on the lake shore on the west side of the N. E. 4 of the N. W.4, Sec. 12, T. 51, R.42 W. In all of these exposures between the Nonesuch mine and the mouth of Iron River the subordinate bedding of the shale stratum remains NONESUCH SHALE BELT IN THE PORCUPINES. 223 very much the same as at the former place, viz: a main body of dark-gray shale, varying a good deal in fineness in different layers, and occasionally becoming a sandstone; near the base a bed of sandstone, recognizable as the ‘Nonesuch vein,” and below this always the light-gray calcitic sandstone known as the “silver belt.” On the lake shore, just southwest of Lone Rock, in the northern part of Sec. 26, T. 51, R. 44 W., the shaly belt appears again, with the usual characters and a considerable thickness. It is terminated eastward by a heavy dike of olivine-diabase, on the east side of which the sandstone is filled with calcite, the calcite being a vein following the course of the dike, which is N. 40° W. ‘Thin sections of the shale and sandstone exposed here show them to be just the same as those exposed to the eastward. West of this point the shale belt remains under the lake as far as the mouth of Presqu’ Isle River. Here it reappears, at first trending only a little west of north, with a dip slightly south of west, but changing rapidly as the river is ascended to a more nearly westerly direction, with a flat southern dip, the amount lessening to 5° in the southern part of Sec. 30, T. 50, R. 45 W., between which point and the lake the river makes a series of falls over the shale and interstratified sandstone. From here the course of the belt is east and south, the shale and its underlying sandstone appearing in large exposures along a small creek in Sec. 34, T. 50, R. 45 W., with a N. 10° W. strike and a westward dip of 10°. Hence the course continues southerly for about a mile, when an abrupt turn westward is made, the belt crossing the Presqu’ Isle in the southern part of Sec. 4, T. 49, R.45 W. The exposures are nearly con- tinuous along the river during its course through this section. At the line between sections 4 and 5 the overlying sandstone is horizontal—being at the bottom of the synclinal here crossed by the Presqw’ Isle. A little further up stream a perceptible northerly dip begins, and at the junction with the shale, somewhat north of the middle line of the section, this has increased to 7°, with a due east and west strike continuing. Further up stream the dip steadily increases, and at the section line, where is the junction with the underlying sandstone, is as much as 20° Returning now to the Nonesuch location, the shale belt may be traced 224 COPPER-BEARING ROCKS OF LAKE SUPERIOR. by large exposures westward through sections 12 and 11 of T.50, R 42 W. Further west, in the N. E. 4 of Sec. 8, it is found trending still more to the south of west. South of here, in this township, the shale has not been observed, but a series of observations on the underlying sandstone, as recorded on Plate XIX, serve to fix the course of the belt very accurately. The uppermost rock in the Porcupine region is the main mass of sand- stone of the Upper Division of the series. It is seen at the mouth of Iron River, overlying the shale; again, in a similar position, on Iron River in the 8. E. 4 of See. 13, T. 51, R. 41 W.; and at several points in the low ground south of the Porcupines—for instance, on the upper part of Mineral River, near the south line of Sec. ®, T. 50, R. 42 W., and on the upper Iron River, near the south line of section 18, in the same township. On the west side of the Porcupine Mountains the same rock appears on the Presqu’ Isle in Sec. 32, T. 50, R. 45 W., and Sec. 4, T. 40, R. 45 W. In tracing the several rock belts which overlie the central porphyry in the Porcupine region east to the Ontonagon and west to the Montreal, I have to depend upon the geological notes of the township surveyors, upon the few facts given by Foster and Whitney, and upon the data communi- cated to me by Mr. B. N. White, of Ontonagon, who has a wide familiarity with the Ontonagon region. Moving eastward, then from the Porcupine . area, I note first an exposure of the black shale on the headwaters of Min- eral River, in the center of the N. E. 4 of Sec. 34, T. 50, R. 43 W., where the dip is 40° to the north. Eastward from here the course of the belts makes a good deal of northing, the “trap” ledges marked on the township plats as occurring near the N. E. corner of Sec. 5, T. 49, R. 42 W., at the falls near the N. W. corner of Sec. 34, T. 50, R. 42 W., and again near the middle of the north line of the same section, marking the course of the upper trap band. In T. 50, R. 41 W., Mr. White finds the Nonesuch shale as far north as the center of section 14. The same explorer reports red felsitic porphyry at the center of section 21; so that we have here a width of just one mile for all the belts between the porphyry and the black shale. This narrowing may be due in some measure to an increase in the dip angle, but must be chiefly caused by the thinning of the two intermediate conglomerates to the com- COPPER-BEARING ROCKS OF LAKE SUPERIOR F i OuNe RN blob K - , a eee aa ae aes LAS J A N8PtL eee gd J ‘s i? lh H i D e a RN a e id & NZtL - 4 2G Lhe a meridian A Hoen® Co.Lith, Baltimore MICHIGAN AND NUMAKAGON LAKE WISCONSIN. it, ithe Western fo rikontel Sandstone ‘The Eastern Horizontal Sandstone KEWEENAW = SERIES The Main Body of Sandstone The Black Shales | E The Outer Conglomerate Sendstone and Conglomerate Diabase, Diabase daloid, Melaphyr, with a few coarse imbedded thin Conglom- erates Ge GE EB Coarse grained Gobbro 6 | } Felwite and Quarts porphyry LOWER > DIVISION Granitic porphyry Granite penetrating the Coarse | Gabbro and Huronian Schists HURONIAN Mica- schists, Slates, Magnetic rocks ete HBB LAURENTIAN Os Sneins, Mica gneiss ae Gi € mite ete Scale snoiomo or Linch « 4735 miles UNITEO STATES BEOLUGICAL SURVEY mae Dh es soeaiae al 5 guaeeaaue atts Yin yy Yj ee areeeuaras Vs o ae SY Bea. L i . Gg Aha os _~ mee COPPER~BEARING ROCKS OF LAKE SUPERIOR PL.xxit i; ) “A UT ie i ~ m = 2 ‘ ; IVER ‘ . S Fae " GEOBOGICAL MAP OF THE REGION BETWEEN THE ONTONAGON RINE MICHIGAN anp NUMAKAGON LAKE WISCONSIN - eeeon BAST AND WEST CONTINUATIONS OF THE PORCUPINE BELTS, 225 paratively small thickness which they are observed to possess east of the Ontonagon. In T.50, R. 40 W., the exposures indicate the continuance of the same conditions. The shale shows in the N. W. 4 of the S. W. 4 of See. 18, again in the the N. W. 4 of the N. E. 4 of Sec. 15, and again near the south quarter-post of section 11. These exposures, with those already noted on the other side of the Ontonagon, in See. 7, T. 50, R. 39 W., serve to fix the course of the shale belt across this township at a little north of east for the first two miles, then about N. 15° E. for two and a half miles, and then N.30° E. to the Ontonagon River. ‘Red slaty trap and conglomerate” are marked on the township plat as occurring within a mile of the shale, and the succession is evidently the same as already noted to the east of the Ontona- gon, viz: black shale, sandstone and conglomerate, traps, conglomerate, traps, porphyry. North of the black shale the main body of sandstone is everywhere the surface rock to the lake shore. Westward from the Porcupine Mountains the upper belts are more easily traced. Following the coast line westward from the mouth of the Presqw’ Isle, the main sandstone of the Upper Division forms the coast as far as the west line of T. 49, R. 46 W., just beyond which the black shale, which may also be seen a short distance up Black River from the mouth, appears at the coast for a short time, soon retreating from it again. From this point the main body of sandstone forms the coast continuously to the Montreal River. In this distance the layers trend more to the south than the coast line, which thus is constantly reaching a higher horizon. At the same time the dip angle rapidly steepens, being 45° about midway in range 47, and néarly 90° at the mouth of the Montreal River. It thus results that on the Montreal as much as 10,000 feet of the main sandstone is crossed by the lower reaches of the river, for some ten miles to the east of which stream it often forms bold cliffs forty to seventy feet high. On Black River there are falls in the N. W. 4 of Sec. 15, T. 49, R. 46 W., over conglomerate and sandstone, which belong with the broad conglomerate beneath the shale. The conglomerate at the falls near the S. W. 4 of the 8. W. 4 of the same section belongs with the Carp Lake band, and the “trap” at the falls just above in the N. E. } of Sec. 21 with the underlying diabases of the band fol- lowing just above the porphyry of the Porcupine region. The “ trap-rock” 15L8s 226 COPPER-BEARING ROCKS OF LAKE SUPERIOR. of the old Chippewa location, 5. W. 4, Sec. 22 of the same township, evi- dently belongs with the main mass underlying the porphyry. When the Montreal is reached, instead of finding one broad conglom- erate between the outer or Carp Lake trap, and the belt next the por- phyry, we meet with a succession of alternations of sandstone or red shale and diabase. It has already been indicated that even in the Porcupine Mountains the inner conglomerate may hold an interstratified diabase band, and a few miles west of the Presqu’ Isle there certainly is one. Further west the sandstone and beds of basic crystalline rocks must dovetail into one another in some such manner as indicated on the map of Plate XXII. Exposures belonging to these trap bands are met with on the west line of the N. W. 4 of Sec. 34, T. 49, R. 47 W.; on the west line of the S. W. 4 of Sec. 31 of the same township; and on the south line of See. 34 of T. 49, R. 48 W. Further back from the lake shore there are other exposures belong- ing to the Main Trap Range, as far south as and nearly in contact with the underlying iron-bearing slates. The section displayed on the Montreal River is next to be described. Ascending the Montreal River from the mouth, vertically placed ledges of red sandstone and red sandy shale belonging to the main body of the Upper Division, are the only rocks seen up to the 8. E. 4 of the N. E. 4 of See. 20, T. 47, R. 1. E. (Wisconsin), two and a half miles above the mouth. Here begin exposures of the black shale and its interstratified sandstones. The shale of these alternations is dark-purple to black, very soft and clayey, and quite regularly laminated. The shale layers run from ten to fifty feet or more in thickness, and are quite subordinate in abundance and thickness to the associated sandstones into which they grade. The sandstone is dark- gray to brown, very close-grained and compact, and often appears macro- scopically like a fine-grained, crystalline rock. This rock forms massive ledges in the bed and on the sides of the stream Under the microscope it appears much the same as the sandstones at the same horizon in the Poreu- pine and Ontonagon regions, but some sections show an unusually small amount of porphyry detritus, being almost wholly made up of basic frag- ments, with the calcite cement. THE MONTREAL RIVER SECTION. 227 After crossing a thickness of these beds of some 350 to 400 feet—a much smaller thickness than was noted farther east—a broad belt of coarse conglomerate is crossed. The constituent bowlders are largely of the sev- eral kinds of acid porphyries, but there are many of the basic igneous rocks of the system. Much calcite is present between the bowlders and sand grains, and also occurs in veins of some size. The vertical bedding is well brought out by the few intercalcated sandstone seams. This conglomerate is exposed in cliffs several hundred feet high, forming the walls of the nar- row tortuous gorge through which the Montreal River passes at the middle of Sec. 20, T. 47, R.1 E. It is plainly enough the equivalent of the outer sandstone and conglomerate of the Porcupine Mountains. In the latter dis- trict this stratum has a thickness of some 3,000 feet, but at the Montreal it is not more than 1,200 feet. Next in descending order on the Montreal is met an alternating series of thin and very regular beds of fine-grained diabase and red sandstone and shale The beds of the crystalline rocks are sharply defined from each other by very strongly developed amygdaloids or vesicular portions. The lower portions of the diabase flows are characterized by a very distinet columnar structure at right angles to the bedding. The finest exhibition of both amygdaloids and columnar structure is to be seen at the head of the upper falls, where at low water there is a very large surface of bare rock. The following tabulation, copied from my report on the Geology of the Eastern Lake Superior District,! serves to show the main facts with regard to these alternations. It should be said that detailed microscopic examina- tions would possibly prove some of the layers to be melaphyrs: Thickness in feet. lis JDSTRING cass bAOG) pepe U BOCOUn CORTE es AaeodieEsCOSoo.cncoorm5ooc. 20 TI. Red shaly sandstone......-. .----+ 22sec cere ee cece eee teen eee ee es 10 TWh. TSG 5 a2 Samat Sone Gaon edeU CHASER enone DoRtedn coonnaaa chs Ubpace 4 IV. Sandstone and shale, including the following subdivisions: (1) thin laminated red shale, 4 feet; (2) purplish, lumpy, fine-grained sand- stone, 8 feet; (3) like (1), 24 feet; (4) like (2), 6 feet; (5) like (1), very bright red, 14 feet; (6) like (2), 5 feet; (7) bright red clay shale, 14 feet; total .... ..--..------ --- 202 cee cnet te eee etree 41 1Geology of Wisconsin, Vol. III, p. 191. 228 COPPER-BEARING ROCKS OF LAKE SUPERIOR. Thickness in feet. V. Diabase, including the following subdivisions: (1) amygdaloid, with abundant amygdules of prehnite, laumontite, calcite and chlorite, and with seams of laumontite and large patches of calcite, in the more thoroughly altered portions, having at base a heavy laumon- tite and calcite seam carrying copper, on which some mining has been done, 25 feet; (2) pseud-amygdaloid, 5 feet; (3) compact portion with distinct columnar structure, the rock having on fresh fracture a grayish color and distinctly-crystalline appearance, though very fine grained, 70 feet; in all .......-.........-----.. 100 VI; Covered s2sc< i elnd ks ic Saat eee tee eee see eters 185 VII. Diabase, with subdivisions as n V..... .------.-.-----------. ------ 92 Vill Red sandstone andishale= ace eee oe eee ee eee eer 20 IX. Diabase, with subdivisions as in V; compact portion dark chocolate- brownyes-4-. - ees a HOA Soe Jonna oon eC Oks, coer 50 X. Reddish conglomeratic Senin REP eS ciyas DoS aoS Tato RDA eaoe 60 XI. Diabase, including : amygdaloid, 10 feet; compact portion, 20 feet; in all 30 XII. Diabase, including: amygdaloid, 5 feet; compact portion, 20 feet ; in all 25 XIU. Diabase, with usual subdivisions ...-..--...---- ---..--- S6655 Gosnnae 10 DOIG LOIN NGM nage dae Bo oSoOnbonocddckeccbeScsepoeos SancelGascnd coe} 33 XGV, Red: sandstone amd Shaler. = ee = eta aos lal etal ee tete tate etek tote teeter 60 XVI. Diabase, with usual subdivisions ....-..-. Lats Pp Se Rae, Ga.s BNR See 60 KVL. Red: sandstone and! shale ~o <2 9 tee eee eee eee 20 XVIII. Compact, dark greenish-gray diabase, with amygdaloid at top, and showing a tendency to a cross-columnar structure ............-.. 21 XIX. Diabase, including: (1) amygdaloid, in many places showing a tondeney to cross-columnar structure, some bands almost completely made of amygdules, and others with but few, 15 feet; (2) compact por- tion; hightycolummary.s feet sy ariel eter eee elo eee 23 XX. Diabase, including: (1) amygdaloid in distinct bands, as in-XIX, some of the bands showing a change to laumontite and calcite, the amyg- dules, in order ot abundance, being prehnite, pink orthoclase, orthoclase and calcite, orthoclase, prehnite and calcite, 11 feet; (2) compact portion, with columnar structure, 10 feet; in all .... 21 XXI. Diabase, including: (1) amygdaloid,in many places altered into laumon- tite seams, 2 feet; (2) ee portion, 30 feet; in all ............ 32 XXII. Rediciaaaee sebueed Seek Doce Pe eee emt 5 XXIII. Diabase, without amy eanlaid « eipysibjekels wise: n Siaysle =< atee SEE eee eee 10 XXIV. Diabase, including: amygdaloid, mostly covered, 15 feet; compact por- tion, 40: feet’; inlall. <\..30s6 (2 Secn sob ace ole ays ee eee 55 XXV. Covered... scabs. amiyceioseigereecele octane sb Saree eee eee eee 185 XK VI, (Redishate sa.25) se eee sided Weacarateld, ne Si eee eter eee eee 40 Total... vic sas, siaisieiecethe cs eid lela iets Se Een eee 1, 212 These layers are exposed along the stream as far as the crossing of the Lac Flambeau trail, near the east line of Sec. 21, T. 47, R.1 E. They THE MONTREAL RIVER SECTION. 229 undoubtedly include the equivalents of the outer trap, the Carp Lake conglomerate and sandstone, and more or less of the inner trap, with its conglomerate, of the Porcupine Mountains, but with a greatly decreased total thickness, which effect is wholly produced by the thinning of the sandstone and conglomerate. On the Montreal River the included detrital beds are nine in number, with a total thickness of 290 feet, as against some 1,900 or 2,000 in two (or three?) layers in the Porcupines. The diabase flows, however, evidently increase in number and total thickness between the Porcupine Mountains and the Montreal River. Through the eastern part of T. 47, R. 1 E., and southern part of T. 47, R.2 E., the Montreal is unfortunately without exposure. In this in- terval one would look for the extension of the Porcupine Mountains por- phyry, and such a rock has been seen west of the river in the N. W. part of T. 46, R.1 E. In this interval must also lie a large proportion of the beds which make up the Main Trap Range, further east. On the Upper Montreal, and its tributary, the Gogogashugun, in T. 46, R. 2 E, there are again quite large exposures, continuing with but little break to the junction with the underlying Huronian schists. ‘These layers must in large measure correspond to those of the South Range of the region east of the Montreal, and in a measure to those which in the Ontona- gon region and farther east are buried beneath the Eastern Sandstone. One of the northernmost of these beds is a narrow one of red felsite-por- phyry, exposed on the Gogogashugun, near the south line of section 8. Immediately beneath it comes a succession of beds, many of which are composed of a black conchoidal-fracturing aphanitic rock of the ashbed type, while still further south to the junction with the Huronian a peculiar dark-greenish diabase is the prevailing rock. ‘The former of these two kinds of rock may be seen largely exposed along the Gogogashugun in its passage through Sec. 8, T. 46, R. 2 E., along the Montreal in sections 2 and 11 of the same township, and in a number of large ledges between the two rivers. The green diabases show on the Flambeau trail, in section 19, on the Gogogashugun, in section 16, and very largely at the falls on the Montreal, in sections 11 and 14 of T. 46, R.2 E. These greenish to greenish-gray diabases are quite peculiar, and resemble closely rocks seen in the South 230 COPPER-BEARING ROCKS OF LAKE SUPERIOR. Range of the Ontonagon country, at what must be nearly the same horizon. They are furnished with imperfectly developed amygdaloids, quite char- acteristic of which are elongated (spike) amygdules, composed of quartz, epidote and chlorite in combination. The pronounced green color is due to the large amount of chlorite which is present, both as an alteration-pro- duct of the feldspars and in large green pseud-amygdules. A section of one of these rocks is represented at Fig. 3, Plate VIII. The entire horizontal width of the Keweenaw Series on the Montreal is some 50,000 feet. Allowing for supposed flatter dips in the lower por- tions, we may estimate the thickness at 33,000 to 35,000 feet for the Lower Division, and about 12,000 for the Upper Division. As already indicated, this estimate for the Lower Division will be too great if the influence of the Keweenaw fault should extend so far as this, but it does not seem that the discrepancy can be more than two or three thousand feet at the outside. In the vicinity of the Potato River, which crosses the series some ten miles west of the Montreal, along the strike, several important changes are to be noted. In the first place, the lower strata of the Upper Division and the upper strata of the Lower Division are greatly thinned. The black shale, with its accompanying sandstone, has thinned from 400 to 250 feet, and its underlying conglomerate from 1,200 to 800 feet, while all that is left of the 290 feet of sandstone and shale, which on the Montreal River are inter- stratified with the uppermost diabases, is one little seam of shale ten feet in width. This thinning of the sandstones is of course simply a continuation of the thinning process already described as obtaining between the Poreu- pine Mountains and Montreal River. Now, however, a thinning of the crystalline members also has begun, the entire width of the Lower Division in the vicinity of the Potato being only some six and a half miles, as compared with seven and a half miles on the Montreal, and with the same high dips. But a yet more remarkable change is the apparent substitution of more or less coarsely crystalline gray to black gabbros for all the fine-grained diabases of the lower 10,000 to 12,000 feet of the Montreal section. This is a change which first begins on the Gogogashu- gun River, where a few ledges of the coarse gabbro are seen between broad belts of the finer kinds. On the Flambeau trail, in the western part of T. THE POTATO RIVER SECTION. 251 46, R. 2 E., the coarse rocks appear more plentifully, and by the time the Potato River is reached the finer rocks have nearly or quite disappeared. These coarse rocks, as shown elsewhere, are much like the coarse gabbros of Duluth and the Saint Louis and Cloquet rivers, which they resemble, moreover, in being cut by masses of brick-red granitic porphyry, a large exposure of which rock is to be met with, for instance, on the old Ironton trail in the northern part of Sec. 8, T. 45, R. 1 W. For the rest, the Potato section is chiefly made up of ordinary types of diabase and melaphyr. At least two bands of felsite and quartziferous porphyry are included. One of these, in the southern part of T. 46, R. 1 W., is evidently the same as that noted on the Gogogashugun, See. 5, T. 46, R. 2 E., while the other much broader band, which is exposed on the river in sections 14 and 15 of T. 46, R. 1 W., appears to belong with the porphyry of the Porcupine Mountains. ‘The rock of the latter belt is largely a true quartziferous porphyry, with a lilac-tinted matrix, in which are thickly scat- tered minute black quartzes, one-twentieth inch in diameter, and whitish kaolinized feldspars, one-tenth to two-tenths inch across. Faint white lines are occasionally seen, and the whole aspect of the rock is very much that of the rock at the Great Palisades on the Minnesota coast. Ten miles farther southwest, along the strike, Bad River crosses the series, and here the changes are carried to a yet greater extreme. The plack shale and underlying conglomerate have thinned respectively to 125 and 350 feet, while the entire width of the Lower Division to the underlying Huronian is only some 17,000 feet, of which 12,000 feet are taken up by the coarse gabbro. The remaining 5,000 feet are made up chiefly of the typical fine-grained diabase and diabase-amygdaloid; but two beds of quartzose porphyry are included, the lower one of which is evidently the same as the broad belt of the Potato River section. One porphyry-con- glomerate has been noted in this thickness. Beyond Bad River the general trend of the formation changes abruptly to a westerly direction, but otherwise the conditions remain much as ob- served on that stream, as far as the Brunschweiler River, save that the gab- bro below expands to a great width. In the townships between Bad and Brunschweiler rivers the gabbro makes such frequent exposures—those 22 COPPER-BEARING ROCKS OF LAKE SUPERIOR. on the line of the latter stream being almost continuous from the head of Bladder Lake to the contact with the overlying fine-grained diabases—that there can be no doubt as to its occupying the whole of the width indicated. It is in this vicinity that the coarse gabbro appears to occupy a position of unconformity to the underlying Huronian slates.’ A few miles west of the Brunschweiler the coarse gabbro exposures begin to have scattered among them others of the usual fine-grained dia- bases, and beyond range 6 west the gabbro is no longer met with. It thus terminates to the westward much as it does to the eastward. The entire length of the belt occupied by these coarse gabbros is some 40 miles, its width ranging from 14 miles to 45 miles. Three principal phases of the rock occur, viz: orthoclase-free gabbro, orthoclase-gabbro and hornblende-gabbro. The first of these is bluish-gray to black, and ranges from below medium-grained to very coarse-grained, the crystals reaching several inches in length. The usual constituents are a very basic feldspar—which, judging from the angles, is commonly near anorthite—dial- lagic augite or true diallage, titaniferous magnetite, and olivine. There are sundry alteration-products often present, but the rock on the whole is a very fresh one. The second variety of gabbro is found especially in the more northern portions of the gabbro belt, forming apparently continuous bands, which have in some cases been traced for a number of miles. It is a red- and black-mottled, or red-, black- and gray-mottled rock, and com- monly quite coarse-grained, though never reaching the extreme degree of coarseness sometimes shown by the orthoclase-gabbro of the Saint Louis. It is also marked by very abundant and noticeably large grains of titan- iferous magnetite. Oligoclase and orthoclase, both much altered and red- stained, diallage commonly largely altered to greenish uralite, and beyond this to chlorite, titaniferous magnetite and very abundant apatite are the ingredients. Still a third variety, forming a belt or belts some 15 miles in length, near the junction with the Huronian, belongs to what I have called horn- blende-gabbro in Chapter III. This rock is peculiar in containing much deep-brown intensely dichroic hornblende, which, however, I think can be 1See pp. 144, 156. i ’ UPPER SANDSTONES IN THE BAD RIVER COUNTRY. 233 satisfactorily proved to be secondary to the augitic constituent. Macroscop- ically it is medium-grained, and from black- and white-mottled to nearly black in color. The constituents are labradorite, augite, hornblende, titan- iferous magnetite, apatite, uralite and diallage; with a little biotite, chlorite and quartz. In the townships west from Bad River, within the gabbro belt, low exposures of a coarse, pinkish granite are often met with, and precisely sim- ilar exposures are found in the area occupied by the upper mica-schists of the Huronian. This granite is intrusive, cutting both the gabbro and the upper Huronian schists. It is a true biotite-granite, consisting of ortho- clase, oligoclase, quartz very rich in large bubble-bearing cavities, and rather rare biotite. Thus far, for the region west of the Montreal River, attention has been directed to the Lower Division of the Keweenaw Series, and to the lower- most members of its Upper Division. These lower rocks form the mass of a highland or range which, on the Montreal, is only some two miles from the lake shore, while on Bad River it lies twenty miles back of the coast, leaving in front of it a broad lowland, underneath which lies the main mass of sandstone of the Upper Division. On the Montreal most of the thickness of this upper sandstone is in sight, and on the Potato, Bad and Brun- schweiler rivers some hundreds of feet of its lowest portions are to be seen. On the Montreal, Potato and Bad rivers it stands vertically or nearly so, with a slight inclination to the north, the northern dip flattening somewhat in the higher layers. On the Brunschweiler a perceptible flat- tening of the whole series has begun. Throughout most of the lowland underlaid by these sandstones they are covered by red lacustrine clays, but at two points—on Bad River in See. 25, T. 47, R. 3 W., and on White River in the N. E. 4, Sec. 6, T. 46, R. 4 W.—they appear in great force, inclining now to the southeastward. Qn Bad River, a thickness of 2,000 feet is in sight, trending N. 60° E., and dipping S. E. 38°; and on White River, 300 to 400 feet, with a N. 40° E. trend, and 25° S. E. dip. These southward-dipping sandstones indicate the existence of asynclinal in the Upper Division of the series, and explain the wide surface spread of the upper sandstones in this region. 234 COPPER-BEARING ROCKS OF LAKE SUPERIOR. Srction V.—NORTHWESTERN WISCONSIN AND THE ADJOINING PART OF MINNESOTA. This region was examined in considerable detail for the Wisconsin Geological Survey in the years between 1873 and 1879, by Messrs. Sweet, Strong and Chamberlin. The results of their work are given in Vol. III of the Geology of Wisconsin, which volume also contains brief descriptions by Pumpelly of a number of the specimens collected. A special trip was also made for this work by Mr. R. McKinlay under my directions, in the valleys of the Snake and Kettle rivers of Minnesota, with especial refer- ence to determining the manner in which the Keweenawan rocks and the Lake Superior basin terminate westwardly. From the data collected by these several investigators I compile the following brief account of the region, adding some conclusions of my own. This region includes two distinct belts of the Keweenawan rocks. One of these is a continuation of the belt we have been following all along from Keweenaw Point, with the dip as usual to the north and west, while the other is a parallel belt made up of strata presenting a southerly or south- easterly dip, and forming the northern side of a synclinal trough, which extends entirely across Wisconsin to the Minnesota line. The axis of this synclinal, where it first strikes the lake shore near the Montreal River, trends about southwest; beyond Bad River for some 35 miles it runs nearly due west. Turning then again, it follows a southwesterly course for about 80 miles, when it changes to a nearly due south course in the valley of the Saint Croix River, where the north and south belts finally unite, under- neath the newer Cambrian sandstone of the Mississippi Valley. In this region the two main divisions of the series are plainly recognizable. It thus follows that the Upper Division, with its great thickness of soft sand- rock, occupies the middle of the synclinal, while the ridges on each side are composed of the resistant crystalline rocks of the Lower Division. The Southern Belt; Numakagon Lake to the Saint Croix “River—In the southern belt, including the northward-dipping rocks, with the one excep- tion of the conglomerate at the base of the Upper Division, the only expos- COPPER-BEARING ROCKS OF LAKE SUPERIOR PL. XxIll ED STATES GEOLOGICAL SURVEY I. n N. 35° W. throug Silver mountain Main trap range Fault = ay » It 5 Silver af: ler Sandstone Keweenaw series, upper deiviston Kowveenaw serves , lower adtviston Huronian I. N. 28° W. through Agoge Maw range bic and Carp lakes. 3 Fault Porcuptnr Fauk Eastern Sandstone Se S.E.. Heweena SUS upper Aiveston Keweenan z SETTES dower diviston lower division Heweenau serves upper diviston Keweenaw series, Laurentian Huronian (Gnewss, granite ete) Il. N45 W. through the mo uth of Montreal river. TAKE SUPE Keweenaw Serves: Muronian Keweenaw sertes lower division upper division Laurentian (@newss qrantte elt } IV. N.27° W. through Long lake. Douglas Co Copper range > ea abet Western SEOEN W. lake Long serves, lower division Keweenaw series, upper division Keweenaw vertes, lower division Laurentian Huronian Heweenaw ( Gnetss, granite ele) Ws Across the S! Croix valley from Chegwatona t Clam lake. fotsdam Sandstone _ W. Potsdam Sandstone A Hoon ® Co SiO. Bainere Keweenaw sertes, lower division Hurontian Se THE REGION BETWEEN PORTAGE LAKE AND THE S* CROIX RIVER. GENERALIZED GEOLOGICAL SECTIONS OF = a ery > a . . 2 NUMAKAGON LAKE TO THE ST. CROIX RIVER. Zap ures are altogether of the beds of the Lower Division. The relative positions of the exposures, and the bedding directions observed at them, show that immediately west of the district last described, or in ranges 6 and 7 west, a rapid flattening of the northern dip takes place, and a proportionately great widening of the belt of country occupied by the formation. In range 7 west this width is as much as 9 miles, the dip flattening to 35° in the lowermost belts and to 25° in the upper belts. Farther west the dips flatten still more, getting as low as 10° to 15°, and the surface width becomes as much as 12 to 15 miles. As to kinds of rocks, the exposures are sufficiently frequent to show that the constitution of the Lower Division of the series is the same in this region as farther east. The greatly predominant rocks are the usual plainly bedded fine-grained diabases with their amygdaloids. Melapliyrs or olivine- diabases are rarer, but occur somewhat frequently. Interleaved porphyry- conglomerate and sandstones have been observed at a number of points, while massive quartz-porphyry is occasionally to be seen. No coarse gab- bro has been observed anywhere between Numakagon Lake and the Saint Croix River. A A rather unusual phase of diabase is the diabase-porphyry of the ledges in sections 26 and 27 of T. 36, R.16 W. These rocks, “in a greenish-gray, fine-grained matrix have a greater or less amount of red feldspar in porphy- ritic crystals, one-thirtieth and one-eighth inch in diameter.” The specific gravity is 2.90.° Under the microscope the porphyritic crystals prove to be a somewhat altered triclinic feldspar, while the groundmass is chiefly made up of smaller plagioclases. Intermingled with these are fibrous, greenish, feebly dichroic or non-dichroic particles, which prove to be altered (uralitic and viriditic) diallage; epidote, in quite abundant grains; titanic iron largely altered to a white substance ; and pseud-amygdaloidal chlo- rite. Closely related to this, and evidently at about the same horizon, is the dark greenish-gray porphyritic rock so largely exposed at the Dalles of the Saint Croix, in T. 34, R. 19 W2 In this rock porphyritic brown ‘See Geology of Wisconsin, Vol. III, pp. 41,42; 46-48; 391-395 3 399-428, for lithological deserip- tions and complete local details. . *R. Pumpelly, Geology of Wisconsin, Vol. III, p. 41. * Geology of Wisconsin, Vol. III; also A. Streng and J. H. Kloos in Leonhard u. Geinitz Jahrbuch fiir Mineralogie. 1877. 236 COPPER-BEARING ROCKS OF LAKE SUPERIOR. plagioclases and pseud-amygdaloidal epidote, chlorite and quartz are im- bedded in a groundmass consisting principally of plagioclase, with which are augite, commonly much changed to viridite, magnetite or titanic iron and epidote. This rock passes into a true amygdaloid, and is associated, as is also the similar rock of T. 36, R. 17 W., with diabases in all respects like the common types of Keweenaw Point. It is of considerable interest that rocks closely allied to these are found at a similarly low horizon on Silver Mountain, in the South Range of Michigan, and again on the Minne- sota coast of Lake Superior. In the vicinity of Saint Croix Falls, as also again on the upper Saint Croix, and on its tributaries, the Kettle and Snake, in Minnesota, the Ke- weenawan rocks are visibly overlain by the horizontal fossiliferous basal or Cambrian sandstones of the Mississippi Valley, the sandstones lying horizontally in the erosion hollows of the previously tilted Keweenawan beds. As this is a matter of great theoretical importance, we may quote at some length from Professor Chamberlin’s descriptions of the Saint Croix rocks.’ The other places referred to are described in subsequent paragraphs. At and in the vicinity of Saint Croix Falls, and southward from there to the neighborhood of Osceola Mills, there are numerous and very fine exposures of the Cop- per-bearing series and of the overlying Potsdam sandstone. * * * * Forthe greater part, they lie in the immediate valley of the Saint Croix river, and owe their exposure to the erosive action of that stream. The valley here is some 400 feet (aneroid) below the higher plateaus that approach the stream, within a mile or two on either hand. The Copper-bearing rocks appear in the slopes of the valley, at heights ranging up to 200 feet or 300 feet. * * * * * * * * * Just below Taylor’s Falls, the river has cut a deep vertical gorge in the trappean rock, forming the beautiful and picturesque Upper Dalles. About two m-les below this a similar caton has been formed, constituting the Lower Dalles. The walls within these Dalles are almost absolutely vertical, and instead of showing worn faces, like the slopes above, present the regular rough surfaces common to fissure planes. It seems very probable that the original worn surface of the gorge has been riven and thrown down by the action of the frost and the undermining of the stream. * * * * * * * * * * In this vicinity, the relation of the Potsdam sandstone to the copper-bearing rocks is most satisfactorily shown. * * * * * * * * * On the N. W. 4 of See. 12, T. 33, R. 19 W., Osceola, there is an exposure of hor- izontally stratified sandstone in the side of a small ravine, and within a few feet is an 1Geology of Wisconsin, Vol. III, pp. 415-421. CHAMBERLIN ON THE ROCKS OF ST. CROIX FALLS. 237 exposure of melaphyr' of the Keweenaw series. The sandstone is quite hard and compact, but the stratification is undisturbed, and there is no indication of met- amorphism. A short distance farther north, the road passes over an exposure of melaphyr on which the sandstone is seen deposited in direct contact with it. In the south part of the village of Taylor’s Falls, near the summit of the ridge, is a remarkable exposure of the Potsdam in connection with the Keweenaw series. Its occurrence is illustrated in Fig. 7, but somewhat idealized. All that is seen is an outcrop of melaphyr, and, on the exposed face, a conglomerate formed of rounded and water- worn fragments of melaphyr. These frag- ments are of all sizes, and the cementing ma- terial is a ferruginous sandstone of Potsdam age, containing occasional Lingulepis shells. In the vicinity of the melaphyr the greater part of the conglomerate consists of its fragments. After inspecting the locality, it seems evident that the melaphyr was an exposed cliff in the Potsdam sea; about whose base large and small water-worn fragments of the melaphyr were collected, and, the interstices being filled Fie. aes unconformable contact be- with sand, solidified into the conglomerate as tween Keweenawan diabase-porphyry,and Pots- itnow appears. The junction of the two forma- dam sandstone at Taylor’s Falls, Minn.; after tions is not well exposed, as the sandstone *'°"% graduates into the conglomerate, and the latter is banked up against the uneven sur- face of the melaphyr. The unconformability, however, cannot be doubted. * * * * * * * * * On the west side of the river, about half a mile above Taylor’s Falls, when the water is low, the junction of the Potsdam and Keweenaw formations may be found. * * * * The fossiliferous blue shales of the Potsdam are horizontally deposited on a melaphyr, containing small specks of pyrites. The melaphyr breaks out in thin pieces, having the shales firmly attached. The junction is marked by a dark line about one-eighth of an inch thick, which seems to cement the two formations. * * * * * * * * * The foregoing facts, corroborated as they are by much other data gathered from the vicinity and other parts of the district, and elsewhere, make it certain that the Copper-bearing series was subjected to much erosion during and previous to the for- mation of the Potsdam sandstone, by which valleys were cut into it to the depth of at least 300 feet. This, doubtless, represents but a small proportion of the total erosion which the series had suffered in the pre-Potsdam period. This locality presents the most clear and unequivocal evidence that the Copper- bearing series is much older than the Potsdam sandstone of our state, so much older, indeed, that there was time for the very extensive wearing down of the former before the latter was deposited. The crystalline rocks of the Copper-bearing series of this locality, while varying somewhat, possess a general similarity, and are not diversified by conspicuously dis- tinct beds of different kinds of rock, as has been found to be usually the case in other 1Rather a porphyritic diabase, according to the nomenclature adopted in this yolume.—R. D. I. 238 COPPER-BEARING ROCKS OF LAKE SUPERIOR. extensive exposures of the formation. So true is this, that it is quite difficult to dis- tinguish the true bedding planes. * * * ¥* ¥ * So * * * In addition to these vertical planes of division, which are generally quite smooth and uniform, but not persistent to great depths, there is another prominent set which are much less smooth, but much more persistent and constant in direction. The surface of the layers separated by these joints is nearly uniform to the general view, but in detail is slightly uneven and undulatory, as though the separation took place not through the fracture of a homogeneous rock, but by separation along a natural division plane, These planes are usually separated by several feet. They are confidently believed to represent the dip of the igneous beds. It is not presumed that all of the layers so formed represent separate overflows of molten material, much less distinct periods of eruption; but that in the flowage and outspreading of the igneous matter, a somewhat parallel arrangement of the not perfectly homogeneous substance took place, giving rise to an obscure pseudo-stratification, sufficient to influence the jointing that subse- quently took place. At the same time, the fact that the beds at different horizons pre- sent different textures, and, in a subordinate degree, different mineralogical composi- tion, would seem to favor the belief that the several hundred feet of the formation exposed in the vicinity of Saint Croix Falls, represent a considerable number of dis- tinet but closely successive overflows; all, perhaps, belonging to one great period of eruption. The latter statement seems to be demanded by the lithological similarity of the rock, the slight distinction between the beds, and the absence of detrital deposits between them. Notwithstanding their obscurity, however, the beds give to the out- crops the distinctive step-like or trappean contour that has been previously described and figured. This is best seen in the exposures about one mile east of Saint Croix Falls (N. E. 4 of Sec. 29, and N. W. 4 of Sec. 28, T. 34, R. 18 W.), where the inclined ledges follow each other with much regularity and persistence, giving to the profile of the cross-section a serrate outline, notwithstanding the fact that the glacial agencies acting from the northwest tended to plane down the edges of the beds. It is upon the persistence of these inclined ledges, taken in connection with par- allel lithological belts, that our determination of the dip, a matter of some theoretical interest at this extremity of the formation, is mainly based. The average of a large number of guarded observations gives a dip of about 15° W. by S. This inclination to the south of west is quite an interesting fact, however it may be interpreted. To the writer it seems to signify, taken in connection with other observations, that the trough of the Lake Superior synclinal, at this western extremity, curves rapidly south- ward, and is connected, over a sort of saddle-back anticlinal, with the broad strati- graphical basin that stretches southward into Minnesota; and that the igneous beds overlap this figurative saddle-back, so as, on their margin, to really lie in the southern or Mississippi basin. This low anticlinal is supposed to lie a little north of Saint Croix Falls, and to be the low, flattened extremity of the Laurentian and Huronian heights that lie to the eastward—the saddle-bow of our illustration. The unconformity shown by Messrs. Sweet,’ Strong,” and Chamberlin? to obtain in the Saint Croix Valley between the fossiliferous Cambrian 1 Transactions of the Wisconsin Academy of Sciences, Arts, and Letters, Vol. IT, p. 40. 2Geology of Wisconsin, Vol. III, Part VI. KEWEENAW POINT AND ST. CROIX ROCKS COMPARED. 239 sandstones and the bedded melaphyrs and amygdaloids upon which they lie being so plainly indisputable, the latest advocate of the old idea of the con- temporaneousness of these sandstones with the copper-bearing or Kewee- naw rocks has been driven to question the correctness of the identification of the bedded diabases and amygdaloids of the Saint Croix Valley with those of Keweenaw Point.’ It is therefore proper that I should insist here that this identification is also indisputable; and that it is so because of the absolute identity in nature and structure of the rocks of the two regions, and because the Keweenaw belts have been followed continuously from the eastern end of Keweenaw Point to the Saint Croix River. In support of the first of these assertions, I have to advance the follow- ing facts. The predominant fine-grained basic rocks of the two regions are so completely the same in mineral composition, even to the alteration-pro- ducts, that thin sections of rocks from the two districts placed side by side are not distinguishable from one another. The only approach to an excep- tion to this statement is the somewhat greater prominence of prehnite as an alteration-product on Keweenaw Point than on the Saint Croix” The rocks of the two regions present precisely the same amygdaloidal, pseud- amyegdaloidal, and compact phases. The amygdules are made of the same minerals in both, associated in the same ways. Native copper occurs in the Saint Croix Valley in the same manner, and with the same associates as on Keweenaw Point. Here and there an exposure may represent a dike so far as can be perceived, but almost everywhere the Saint Croix Valley rocks present precisely the same bedded structure as seen in those of Ke- weenaw Point. This is displayed, not only in the common step-like con- tours of the exposures, but the individual beds may be readily separated from one another, each bed often showing sharply marked its upper 1‘“ Notes on the Iron and Copper Districts of Lake Superior,” by M. E. Wadsworth. Bulletin of the Museum of Comparative Zoology at Harvard College. Whole series, Vol VII. Geological series, Vol. I, No. 1, p. 107. 2Compare R. Pumpelly, Geology of Wisconsin, Vol. III, p. 36. ‘‘While the absolute identity of the diabases and melaphyr and of their varieties and amygdaloids, and of the interbedded porphyry conglomerates of the Wisconsin area with those of Keweenaw Point is evident, I am struck by the com- parative scarcity in the former, of one of the most important forms of alteration that abounds in Michi- gan; I have found in the four collections but one instance of change of feldspar to prehnite.” With regard to this it should be said that the specimens from Wisconsin examined by Pumpelly included very few from the uppermost belts of the Lower Division, which carry prehnite much more commonly. 240 COPPER-BEARING ROCKS OF LAKE SUPERIOR. vesicular and lower compact portions. Moreover, where the dip is high and the exposures are large, as on the Snake and Kettle rivers of Minnesota, there is to be seen a continuous series of beds, in all many hundred feet thick and in every respect similar to the alternations which obtain on Keweenaw Point. The same interstratified porphyry-conglomerates and sandstones are met with in both regions, and in both regions carry at times native copper. Interbedded original felsitic porphyries also occur in both regions. In support of the second assertion, as to the actual continuity of the Keweenaw Point and Saint Croix rocks, I have to say, in the first place, that the evidence of this continuity is precisely the same for the distance between the Montreal and the Saint Croix, as for that between the Montreal and Keweenaw Point, or even the distance between the eastern part of Kewee- naw Point and its western portion at Portage Lake; that the continuity has never been disputed for the two latter distances; and that it should there- fore be accepted at once for the first-named distance. The evidence for all the distance between Keweenaw Point and the Saint Croix is just as strong as that ever appealed to to prove the continuity of geological formations anywhere, save in those very rare and exceptional regions where the rocks are completely bare. This evidence consists in the frequent recurrence, at short intervals, of the same kinds of rocks, with the same structure and stratigraphiecal arrangement; and such evidence is forthcoming in the present case. From Keweenaw Point to the Saint Croix, the formation has been traced mile by mile with a constant recurrence of precisely the same bedded basic rocks, with the same amygdaloidal and compact portions to the beds, of the same associated felsitic porphyries, of the same interstratified porphyry- conglomerates, and of the same native copper in veins, altered amygdaloids and conglomerates. The same division of the series into a Lower or prevail- ingly eruptive member, and an Upper or detrital member, is also everywhere present. From Keweenaw Point to the region of Long Lake, some even of the subordinate members are recognizable as continuous. For the par- ticulars of this evidence, I refer to the detailed descriptions of Foster and Whitney’s report, of Vol. III of the Geology of Wisconsin, and of the present work; to the United States Land Office township plats; and to the 22 / 3 | eee fF exrtends a the Tiver T 42 N T, 41 N, : 9 Horizontal (Potsdam stipdstone | 3 | I z ae | i ee Date bc Mission Sta 40 IN, 1.39 N. thw il Horivantal Misdam watdsto A Boon $ SS. Li. Baknmcere ' MAP SHOWING POSITION OF THE EXPOSURES OF KEWEENAWAN ROCKS AND POTSDAM SANDSTONE ; ALONG THE LOWER PORTIONS OF SNAKE AND KETTLE RIVERS, MINNESOTA . KEWEENAWAN ROCKS ON SNAKE AND KETTLE RIVERS. 241 collections of the Wisconsin Geological Survey, and of the survey made for this report. If this evidence does not constitute proof of continuity, then no geological formation in the United States has ever been proved to be continuous for more than a very few miles—rarely for more than a mile— except in the plateau region of the western territories. In the distance between Numakagon Lake and the Saint Croix it is difficult to estimate the total thickness of the Keweenawan rocks. The Upper Division is not exposed on this side of the synclinal, and the position of the junction with the older rocks is rendered uncertain by heavy drift accumulations. Judging, however, from the dip and strike observations, and from the outside limits between which its surface spread must lie, it appears probable that the Lower Division of the Keweenaw Series must have here a total thickness of from 25,000 to 30,000 feet. The Northern Belt; Snake River and Kettle River District, Minnesota.— The western end of the trough in the Keweenawan rocks is concealed by the unconformably overlying Cambrian sandstone and limestone. The final termination southward must lie on the Saint Croix, about half way between Hudson and Osceola, the exposures continuing down to the latter place. Rounding the turn and moving northward now on the Minnesota side of the Saint Croix, we find the Cambrian sandstone completely con- cealing the older rocks until Snake River is reached in township 39. Here, on the lower portions of Snake and Kettle rivers, and on the Saint Croix in the vicinity of the mouths of these streams, typical Keweenawan rocks are again exposed on a large scale with a trend but little east of north and a high easterly dip. Snake River enters the Saint Croix on Sec. 30, T. 39, BR. 19 W... we miles below the mouth of the stream, in the N. W. 4 of Sec. 7, T. 38, R. 19 W., there are cliffs of horizontal Potsdam (Cambrian) sandstone 50 feet high, in which the rock is the usual crumbling, quartzose, light-colored sandstone commonly seen in the Mississippi Valley. The same rock. is ex- posed on the Snake River in the southern part of Sec. 36, T. 39, R. 20 W. Above this, Snake River is without rock exposures until Sec. 24, T. 39, R.21 W. is reached. From here there are exposed continuously in the bed and on 16LS 242 COPPER-BEARING ROCKS OF LAKE SUPERIOR. the banks of the stream to the dam at Chegwatona Lake, near the east line of section 27, beds of diabase and diabase-amygdaloid, with interbedded porphyry-conglomerates, trending N. 10° to 20° E., and dipping 60° to 75° south of east. The rocks, as shown by the thin sections, are in every respect identical with the fine-grained diabases and diabase-amygdaloids of Ke- weenaw Point. The following is an account, kindly furnished by Professor T. C. Chamberlin, of the succession displayed at this place.t His measure- ments were only rapid pacings, and his examinations did not begin quite so far down stream as the last ledges located by Mr. McKinlay. The locality was, however, visited after having studied in detail the adjacent Wisconsin formations, and the observations were made especially with reference to the relations of these rocks to the Wisconsin and Michigan series, and, so far as general structural questions are concerned, were entirely conclusive in the judgment of the observer. 1. The uppermost exposure examined, 7. e., the one lowest down the river, the dip being eastward down stream, is a diabasic amygdaloid, much altered, con- taining malachite. The exposure is low and small. 2. Ten paces up the stream, 7. e, westward, there is a similar but less amygdaloidal rock in low exposures. 3. Fifteen paces further there occurs a similar rock which continues exposed for 26 paces. 4, This is succeeded by a conglomerate of the Keweenawan type, having a surface exposure of between 6 and 7 paces. This is followed (underlain) by about 8 paces of mixed conglomerate and amyg- daloid, that, for want of time, was not studied with sufficient thoroughness to determine its true nature. It appeared, however, to consist of the shattered fragments of the upper vesicular portion of a lava flow mingled by wave action with water-worn pebbles of more distant derivation. 6. This is followed by about 45 paces of diabase, more or less amygdaloidal, and be- longing to the more common type of Keweenawan diabases. . This is underlain by conglomerate of the common Keweenawan sort, having a surface width of about 12 paces. . This is succeeded by diabase and amygdaloid, more or less concealed and varying in character, for a space of 79 paces. 9. This is followed (underlain) by a reddish very amygdaloidal rock, which, in 6 to 7 paces, graduates into 10. A bed of the common Keweenawan diabase, which has a surface extent of 12 paces. , 11. This is succeeded by a reddish-brown amygdaloid for 10 to 12 paces. 12. Then follows a dark-gray diabase, including red diabasic rock, for about 12 paces. 13. This is followed for about 10 paces by amygdaloidal rock. 14. This again by diabase for 23 paces. or =I io) 'From unpublished notes, made in 1878. KEWEENAWAN ROCKS OF SNAKE AND KETTLE RIVERS. 243 15. Then follows a mottled igneous rock for 44 paces, graduating into the common dia- basic trap. 16. This gives place to a coarse red conglomerate of pronounced Keweenawan type containing porphyry pebbles. It has a surface width of 35 paces. 17. This is underlain by amygdaloidal diabase for 12 paces. 18. There follows this again a coarse red Keweenawan conglomerate with associated shale. This presented favorable conditions for definitely ascertaining the strike and dip, which were found to be, strike, N. 10° to 15° E.; dip, 60° east- ward (E. 10° to 15° 8). This stratum has a surface width of 10 paces. 19. Under this lies a fine-grained diabase, with a surface exposure of 18 paces. 20. This gives place to a band of amygdaloid, 3 paces across, followed by trap of vary- ing character for a width of: 75 paces. A gap, estimated to exceed one-half mile, ensues, in which there appeared to be no exposures in the north bank of the river. On the south side, rock with harmonious dip could be seen at some points, but it was not visited. ; At the dam at the outlet of Chegwatona Lake there are much altered amygda- loids and diabases in alternating series that strike from N. to N. 10° E., and dip from 60° to 70° eastward. The amygdaloidal bands are conspicuous, but not sufficiently sharply defined to give very precise strike and dip, but they harmonize well with the undoubted observations given above and the more general ones made along the whole section, so that the attitude of the series is perfectly certain. The rocks, whether com- pact diabases, amygdaloids, or conglomerates, are typically Keweenawan in aspect, and leave no room for doubt that they belong to the copper-bearing series and form the western and perhaps terminal margin of the Lake Superior synclinal trough. Native copper occurs in these rocks on Snake River both in the con- glomerates «and some of the bands of altered amygdaloid, and in such quantity near the surface as to promise success to mining enterprise. Returning now to the Saint Croix River, we find, on ascending from the mouth of the Snake, an exposure of the horizontal light-colored Potsdam sandstone in Sec. 30, T. 39, R. 19 W., and inthe N. W. 4 of Sec. 29, ledges of the usual fine-grained diabase striking north and south. On the N. E 4 of See. 20, are again flat-lying ledges of a fine-grained diabase, apparently striking north and south with a very low eastern dip. At this place native copper has been obtained in a small trial shaft near the river edge. The lower part of the shaft penetrated to an amygdaloidal layer.’ The usual light-colored horizontal Potsdam sandstone is exposed near by. Kettle River enters the Saint Croix near the 8. E. corner of Sec. 8, T. 39, R.19 W. From this point the upward course of the stream is nearly due north for some three miles, this direction being apparently induced by the north and south strike of the rocks. In this distance are some five or 1Geology of Wisconsin, Vol. III, p. 427. ray , 244 COPPER-BEARING ROCKS OF LAKE SUPERIOR. six long, low diabase ledges at the edge of the stream, apparently with a north and south trend. In the N. W. 4 of the N. W. 4 of Sec. 32, T. 40, R. 19 W. the east bank of the stream shows a diabase ledge 15 feet high and 35 rods long. Just opposite, on the other side of the stream, is a flat- lying reddish conglomerate. Porphyry conglomerate occurs again on the east bank of the river near the center of the 8. E. 4 of Sec. 29, T. 40, R. 19 W., and again in a large exposure a mile farther up stream in the N. E. 4 of the S. E. 4 of Sec. 19, where it plainly lies at a very flat angle. These three exposures appear all to be part of the same conglomerate bed. Six hundred paces up stream from the last exposure, typical diabase and dia- base-amygdaloid are in sight. Above this point the river is without exposure for about five miles, the upward course of the stream in this distance making over three miles of westing. On the north line of Sec. 3, T. 40, R. 20 W., however, large expos- ures of diabase begin again. Through Sec. 35, T. 41, R. 20 W. the river pursues a nearly southerly course, and on the east side, continuing for over half a mile, is a west-facing cliff 10 to 30 feet high of the typical fine-grained diabase. The east slope of the ledge is gradual, and the strike and dip are plainly to be made out, as respectively N.6° E., and 50° K. On the north line of the same section, and again in section 22, similarly-pliiced ledges are largely exposed, the river making in this distance about a mile of west- ing, so that between the south line of T. 41, R. 20 W. and the expos- ures in section 22 the river crosses a mile in width of Keweenawan beds, with an average eastern dip of 50°. The last place is of great interest, for only 309 paces north of the stream, and directly in the course of the north- ward-trending diabases, is a cliff of horizontal light-colored Cambrian sand- stone 40 feet high and several hundred paces in length. The occurrences at this point are represented in Figs. 8 and 9. Four miles west of here, on the line of the Saint Paul and Duluth Rail- road, near Hinckley, the same light-colored sandstone is quarried. The exposures in section 22 are the last of Keweenawan rocks seen in ascending Kettle River. Six miles farther north, however, near the south line of Sec. 22, 'T. 42, R. 20 W., the horizontal light-colored Cambrian sand- stone begins to make large exposures, which continue without break, either . Y UNCONFORMITY ON KETTLE RIVER. 245 in the bed of the stream, or in cliffs 20 to 75 feet high, on either side, for 5 miles, to the north line of Sec. 35, T. 43, R. 20 W. Above this for 33 miles the sandstone does not appear in the river, but is seen here and there ec. COT. on hillsides near the stream. Through sections 11 and 3, T. 43, R. 20 W. the sandstone reappears in the stream, the last exposure found lying 200 paces south of the north line of section 3. From this point up stream for some nine miles no exposures were found. Then, through sections 9 and 4, of T. 45, R. 20 W., and 32, 29, and | 28, of T. 46, R. 20 W., frequent out- eae crops of mica-schist are met with in, NRO W OSs ota, : the hillsides near the river. These briefly-stated facts with regard to the region of the Snake and Kettle rivers, further illustrated by the map of Plate XXIV, will serve to render certain three very important F, i 4 Scale 1)mile to 4. inches. conclusions, viz: (1) the diabases and Gh post ees diabase-amygdaloids and interbedded Fie. 8. —Map of Exposures on Kettle River, Sec. os . 22 teal wives CONN cs Minnesota. Scale 4 inches to porphyry-conglomerates Ou tMISMCIS= theme: trict are in all respects like those of Keweenaw Point; (2) the light-colored horizontal Cambrian sandstones overlie these beds unconformably; (3) these Keweenawan beds, with a trend but little east of north, present an easterly dip which at from 5 to 8 miles west of the Saint Croix reaches 50° to T° and which flattens rapidly eastward, becoming very low on the Saint Croix Fic. 9.—Section on line A B of Fig. 8. Scale, horizontal, 8 inches to the mile; vertical, 300 feet to the inch. itself. The first two of these conclusions are but confirmations of those reached farther down the Saint Croix, but the last is of the greatest interest 246 COPPER-BEARING ROCKS OF LAKE SUPERIOR. and importance in its bearing upon the structure of the western termination of the Keweenawan trough, as is shown in a subsequent chapter. The exposures of Huronian schists on the upper Kettle River, taken together with those at Moose Lake, on the Saint Paul and Duluth Railroad, and those at Thompson, on the Saint Louis River, are also of great interest, since they form a line beyond which it is certain that the Keweenawan rocks cannot pass to the westward. Upper Saint Croiz.—For 30 miles above the mouth of the Kettle River the Saint Croix shows no rock of any kind. Then come large exposures of southeastward-dipping sandstone, extending for many miles along the stream. I quote in this connection from Professor Chamberlin’s description :* From See. 4 (I. 43, R. 13 W.) to the southern line of the county? (Sec. 33, T. 43, R. 14 W.), the bed of the stream? is almost continuously composed of sandstone and con- glomerate. The greater portion of this is the common red sandstone of the series. The lower mile and a half is conglomerate, and probably corresponds in stratigraphical equivalence to the conglomerates of Sees. 27 and 14, T. 44, R. 13 W., above-described, as it lies in the line of strike, and bears a similar relation to the crystalline strata on the northwest. By consulting the map, it will be seen that from Chase’s dam to the county line, a distance of about 11 miles, the river runs an almost direct course, and with slight interruptions is bedded on sandstones and conglomerates. A casual glance will show that the stream runs closely with the strike of the strata. A more careful study makes it appear that the river crosses the strata at a very small angle, passing from higher to lower beds. Near the county line, however, the river turns southward and pursues, for about three miles, a southerly course. This brings it over higher (geo- logically) strata. For a little more than a mile, however, it is bedded in drift, but near the north line of Sec. 9 (T. 42, R. 14 W.), the sandstone of the series reappears in the bed of the river and extends across it, causing rapids and forming occasional low exposures in the banks. The ledges show fine ripple-marks and occasionally rain- drop impressions. They are more indurated and seem to contain more quartz and less argillaceous material than those previously described. This sandstone again becomes concealed at the south line of the section, but reappears in the bed of the river in the Indian village in the N. W. 4 of the N. W. 4 of See. 21, (T. 42, R. 14 W.), about a mile below. These are probably the highest beds of the Keweenaw group exposed in the district. Next immediately underlying this sandstone and conglomerate series, so far as the outcrops show, there appears to be a diabase, little exposed, underlaid by a stratum of easily-recognized melaphyr, forming at the surface outcrops along a belt lying parallel to the sandstones. This is the typical Keweenaw melaphyr described by 1Geology of Wisconsin, Vol. III, p. 424-427. 2? Douglas County, Wisconsin. The Saint Croix. al UNITED STATES GEOLOGICAL SURVEY OPPER-BEARING R OF LAKE SUPERI R.AVW. R.XAIV W. R.Xxm1 Ww. | Maarten ee y ine: Diabase a s Diabase Meagdatoctt ] | ae Ditthase, “47 7 J LLongloyertite Adloo § Oo 1i8. Baltimore MAP SHOWING POSITIONS OF EXPOSURES OF KEWEENAWAN ROCKS IN THE UPPER ST CROIX VALLEY, WISCONSIN, {TDN of RPaAtT “Pr Op tart? WCET WAT. TIT BASED ON REPORT OF MOSES STRONG -GEOLOGY OF WISCONSIN, VOL II Scale 2.3 miles to 1 inch. ee eee Way « «4 4 @ ROCKS OF THE UPPER ST. CROIX. 247 Professor Pumpelly on page 32, and identical with stratum 108 of the Eagle river section. It is found in the N. E. 4 of Sec. 14 and the N. W. 4 of See. 27, T. 44, R. 15 W., the N. W. 4 of See. 28, T. 43, R. 14 W., and at the falls on Chase’s brook, in the N. E. 4 of the.N. W. 4 of See. 16, T. 42, R. 15 W. The first three of these may be joined by a nearly straight line about 12 miles in length, whose course will be about N. 48° E., or nearly the average observed strike. If this line be projected it will pass to the southeast of the melaphyr exposure on Chase’s brook, and, if extended in the opposite direction it will pass about an equal distance from an outerop of precisely similar rock found on Moose creek, in the N. E. 4 of the N. W. 4 of Sec. 2, I. 44, R.13 W. It would appear highly probable, then, that the first three exposures belong to the same stratum, and that the remaining two represent a lower bed. This is confirmed by the existence of a similar melaphyr near the center of the west line of the N. W. 4 of See. 21, T. 43, R. 14 W., and also one in the S. W. 4 of Sec. 10, either of which might readily be referred to the lower bed, though it is not so apparent that both could. Entering more into detail, we observe that the outerop of the melaphyr in the N. W. 4 of the N. E. 4 of See. 27, T. 44, R. 13 W., rises only about 10 feet high and forms the bank of a creek. The rock agrees completely with the description of the typical Keweenaw rock previously referred to. The formation crops out quite continuously along the stream as far as the forks in the N. E. 4 of Sec. 28. Here it is found to be dark, coarse-grained, rather soft, containing much chlorite, and crumbling readily on weathering, and no longer possesses the distinctive melaphyr characters. On the line between Sees. 22 and 27 we, however, find the typical melaphyr again. Following the line of strike into the S. E. 4 of the N. E. 4 of Sec. 14 of this township (T. 44, R. 13 W.), we find on Moose creek the same melaphyr. Its dip here appears to be about 18° to S. 309 EK. A few yards below the ledges are traversed by veins of epidote, with some indications of copper. The rock is here very amygdaloidal, carrying chlorite as a cell-filling, dip 20°. A few rods below we find a heavy, firm, fine-grained, dark-greenish, diabase-like rock. The surface of this presents very finely preserved glacial grooves, having a direction S. 15° W. Some are wide and shallow, while others are narrow, sharply-defined hair lines. In the N. W. fof the S. E. 4 of this section there are also some small ledges of fine-grained diabasoid rock, and in the S. W. 4 of the S. E. 4 of the section we encounter the con- glomerate before described. Following up Moose creek to Sec. 2, we find in the N. W. tof the S. E. } first a very hard, fine-grained, nearly black diabase, above which, about 100 yards, there appears a coarser crystalline diabase and diabase pseudo- amygdaloid, containing patches of epidote, quartz and considerable calcite, though the rock is not generally amygdaloidal. There are to be found occasionally specks of mala- chite. The dip measurements were 17° and 2098S. E. The ledges are much fissured and broken in all directions. Near the center of the section, low ledges, along the west side of the stream, exhibit a coarse-grained rock, somewhat resembling the mela- phyr found farther up the stream, presently to be described. Above this in the N. W. 4 of the section, there first appears a diabase of medium grain and greenish-gray color, and about 100 yards farther up, on the left bank of the stream, a low outcrop of soft, very dark, diabase pseudo-amygdaloid, containing chlorite, quartz, orthoclase and 1 See Geological Survey of Michigan, 1869-1873, Vol. I, Part II, p. 186. 248 COPPER-BEARING ROCKS OF LAKE SUPERIOR. prehnite. About an eighth of a mile above this, and only a short distance below the town line, the west bank of Moose creek exposes the typical melaphyr previously men- tioned, characterized by a dark-green color, fine-grain, peculiar irregular fracture and large reflecting surfaces of satin-like luster. Passing due southwestward about seven miles into the S. W. 4 of Sec. 6 we en- counter a dark, fine-grained diabase, occasionally amygdaloidal, with calcite. A vein about two inches wide was observed, which carried considerable native copper in films and small particles, associated with calcite and epidote. In the rock there are also parti- cles of epidote carrying copper. These are in the bed of the brook, and overflowed in high water. A short distance above, the rock becomes softer and contains large amyg- dules of chlorite with frequently a core of calcite. These ledges extend along the stream for about half a mile. At the dam, near the town line, there is a ledge of highly- altered diabase-amygdaloid containing calcite, chlorite and epidote. * * * * * * * * * To the west of the center of Sec. 8, T. 43, R. 13 W., there is a fine exposure of conglomerate, having a dip of about 14° in a direction 8. 50° E. It is traversed by two regular systems of joints on courses N. 34° HK. and N. 56° W., by reason of which it is eut into regular cubical blocks. Judging from the drift, the western portion of the S. E. 4 of the adjoining See. 5 is underlaid by conglomerate. Passing over an interval of about five miles, in which no outcrops are known to exist, we find in the S. E. 4 of Sec. 6, T. 43, R. 14 W. a wide, low, northeasterly- trending ridge, presenting bared rock at one point, which appears to be a diabase of very fine, close grain, and dark color, coated with a thin, light-colored crust due to weathering. In the N. E. 4 of See. 9 of this township there is a ridge composed of rather soft, fine-grained, dark, reddish-brown diabase amygdaloid (specimen 425), weathering to a dirty lilac hue. It appears to be much altered. This ridge, in common with those of the vicinity, presents an abrupt declivity on the northwest and a gentle slope in the opposite direction, the same phenomenon observed so frequently on the opposite side of the Saint Croix Valley, but reversed in direction. It is scarcely nec- essary to repeat that it is due to the inclination of the strata whose projecting edges form the ridges. In the S. W. 4 of Sec. 10 (T. 43, R. 14 W.) there is a similar ridge composed of melaphyr, and already referred to. A short distance south of this, in the adjoining sec- tion (N. W. 4 of Sec. 15), there is a similar ridge, but of diabase, beyond which is still another, the rock of which is a dark brown and black, hard, fine-grained crystalline diabase, containing occasional amygdules of chlorite. It resists weathering well, and only shows a thin, light, dirty grayish coating of weathered substance. The trend of these ridges is northeasterly with the strike of the strata. In the 8S. W. 4 of See. 15 (T. 43, R. 14 W.), in a large hill, there is a small denuded area of rock, of hard, close, minutely crystalline texture, reddish-brown coler, and rough, uneven fracture. It contains scattered aggregations of chlorite. It appears to be an altered melaphyr. In the 8. EB. 4 of Sec. 17 (L. 43, R. 14 W.) there is a long ridge of melaphyr that appears to be a continuation of that above noted in Sec. 10, and is probably to be correlated with that in Sec. 2, T. 44, R. 13 W., and that at the falls on Chase’s brook, Sec. 16 (T. 42, R. 15 W.). There is a like rock found near the center of the west line of the N. W. 4 of Sec. 21. ROCKS OF THE UPPER ST. CROIX. 249 In the S. W. 4 of Sec. 22 (T. 43, R. 14 W.) there is an outcrop of a fine-grained, hard, reddish-brown, crystalline rock, probably a diabase. It forms the nucleus of a hill. In the 8. E. 4 of the N. W. 4 of Sec. 28 there is a small uncovered area of typical melaphyr, which probably belonged to the same stratum as those situated in Sees. 14 and 27, T. 44, RK. 13 W., as already stated. From this point, for a distance of about 30 miles down the Saint Croix, no exhibitions of rock in place of any kind are known to exist. The following is a description of the same district by Mr. E. T. Sweet:! In the banks and channel of Moose river, on Sec. 2, T. 44, R. 13 W., there are low ledges of melaphyrs and diabases, dipping 18° 8. 35° E. These are conformably overlaid by fine conglomerates and coarse sandstones. The pebbles of the con- glomerate have nearly all been directly derived from the underlying crystalline rocks, and are held together by a coarse, red, sandy matrix. None of the very coarse or bowlder conglomerates noticed on the northward-dipping belt, in Ashland county, and on the Saint Croix river, were observed here. In following Moose river southward, towards its mouth, several small exposures of the fine conglomerate were seen, but it apparently has no great thickness, for it soon grades into coarse, reddish sandstone, and that finally, after reaching the Saint Croix, into quite fine-grained, red sandstone, often somewhat argillaceous. The most northern exposure of this sandstone on the Saint Croix, is at the head of a small lake about a mile above the mouth of Moose river. The outcrop is in the east bank. The layers are hard and thin, and contain many red argillaceous spots. Indurated smooth slabs come out readily. A few of the layers are finely ripple- marked. The strike is N. 53° E. and the dip 1498S. This place is a short distance below Chase’s dam, on Sec. 36, T. 44, R. 13 W. For five miles along the Saint Croix below Moose river, a few small exposures only are seen. On Sec. 8, T. 43, R. 13 W. the sandstone is exposed in the banks five or six feet high. At the first considerable exposure, the rock is fine grained, very thin bedded, and argillaceous. Circular red- dish and bluish spots of indurated clay are of frequent occurrence in the layers. The strike is N. 55° E. and the dip 13° S. There are two well-marked systems of joints; one trending N. 28° W., and the other N. 55° KE. THE MINNESOTA COAST. 263 porphyry. In the gap between this gabbro and the slate on the Saint Louis, the base of the Keweenaw Series lies concealed. The Saint Louis River slates at Thompson, eight miles west of Fond du Lac, trend N. 85° E., and have a dip of some 30° to 40° southward. Far- ther down stream, towards the junction with the overlying sandstone, they trend somewhat more to the northeast. The gabbro does not exhibit any sign of bedding. However, the trend of the hills which it forms in the southeast part of T. 49, R. 15 W., is about N. 46° E., and near Duluth still more to the north. Eighteen miles north of Duluth, on the Cloquet River, in the southern part of T. 53, R. 14 W., the same gabbro reappears. It seems to form a belt running at first northeast and then more and more to the north until it finally takes a nearly northerly course. So far as these facts go there is no definite evidence of unconformity between the gabbro and the Saint Louis slates. The appearance is rather the other way. In the eastern part of the city of Duluth we begin to find plainly bed- ded rocks flanking the coarse gabbro on the east, and for the entire dis- tance to Grand Portage Bay these bedded rocks prevail, as also back in the country for many miles. They are diabases of several kinds; amyg- daloids; typical luster-mottled melaphyrs, or fine-grained olivine-diabases; coarse-grained gabbros, belonging chiefly to the orthoclase-free kinds, but including also orthoclase-gabbros; anorthite-rock; felsites; quartz-porphy- ries; granitic porphyries; porphyry-conglomerates; and red sandstones and shales. In other words, we find here precisely the same rocks that characterize the Keweenaw Series on the South Shore. Detrital beds are here relatively rare, and the layers thin, as compared with those of the Ke- weenaw Point series, but we have here to do with quite low horizons which are in general comparatively free from detrital layers. At Duluth, as already said, the trend of the layers in sight on the coast is at first even slightly west of north, with an easterly dip of 45°. These are rapidly changed for a due northerly trend, and 25° easterly dip, and these again, by the time the mouth of the Lester River, which is 54 miles below Duluth, is reached, for a N. 30° E. trend, and a 15° S.E. dip. Be- tween Lester and French rivers, the strike directions make more and more easting, becoming finally, on French River, 124 miles below Duluth, N.50° E., 264 COPPER-BEARING ROCKS OF LAKE SUPERIOR. the dip remaining at 15° S. E. From Duluth to French River the coast line trends about N.50° E., so that in this distance the rock beds, running more to the north than the coast line, intersect it at an angle which varies from 55° near Duluth to nearly 0° at French River. One interesting result of this relation between the trend of the strata and that of the coast line is the production of points projecting southwestward and formed of the harder beds. It is these projecting points, with other smaller ones along the Minnesota coast, that have been represented by Norwood as formed of a series of dikes. As shown below, dikes exist here, but they are relatively very infrequent, and nearly always of small thickness. From Duluth to French River, then, there is a constant ascent in geological horizon, and the thickness crossed cannot be much less than from 8,000 to 9,000 feet. From French River to Burlington Bay there is again a somewhat more northerly trend in the rock beds, but since the coast line here also runs more around to the north, the dips at the same time flattening to 10° and even 6°, there is not much added in this distance to the thickness above given. After Burlington Bay is passed, the strike begins to cut the coast more sharply, and by the time Split Rock River is reached, 45 miles below Duluth, fully 10,000 feet of thickness have been crossed. In the vicinity of Split Rock River the layers strike nearly due north, cutting the coast at an angle of 35°; but half way between Split Rock River and Beaver Bay, coast and strata are again trending together, at about 40° east of north. Below Beaver Bay, again, the strata turn away from the coast to the northward, and for some two miles below Baptism River strike only a very few degrees east of north, and by this time the coast must have crossed fully 16,000 feet in thickness of rock beds. Be- yond the last point, however, both coast and strata begin curving more and more around to the east, the two coinciding at N. 50° E., somewhere between Petit Marais and Two Islands River. In the vicinity of Two Islands, Cross, and Temperance rivers, are the highest strata met with anywhere on the Minnesota coast, or, indeed, on the entire north shore of the lake, with the exception of Isle Royale. In the 80 miles between RELATIONS OF TRENDS OF COAST LINE AND STRATA. 265 Duluth and Temperance River, the coast line has crossed some 17,000 feet of strata. Two miles below Temperance River, in Sec. 28, T. 59, Rents W.,..& descent of the coast line in geological horizon begins to be perceptible. This descent continues without interruption for a distance of 70 miles, or to the end of the Minnesota coast, at Pigeon Point. From Temperance River to Grand Portage both coast line and strata curve more and more to the eastward, but the strata change direction more rapidly than the coast line, so that they cut it at a small angle all the way, producing points like those described as characterizing the coast line west of Temperance River, but with the difference that the points now project eastward, instead of to the southwest At Grand Portage, the Keweenawan beds striking out under the lake, the Huronian or Animikie slates appear from beneath. The Minnesota coast line, looked at as a whole, presents a sort of flat crescentic shape, with the concavity towards the lake. The same is true of the courses of the strata, but the crescents formed by them have a much smaller radius, and hence intersect that formed by the coast line, trending more to the north at the Duluth end, and more to the east at the Grand Portage end. In following the coast, then, from the slates of the Saint Louis River to Grand Portage, we ascend in geological horizon to a point near Two Islands River, and from a point just east of Temperance River descend again to the same slates at Grand Portage. Since the exposures are almost con- tinuous, the coast line thus gives a complete cross-section of the whole thickness of Keweenawan beds present in northeastern Minnesota. Since the junction line between these Keweenawan strata and the underlying slates makes quite a large angle with the lake shore at both ends, and since the prevailing dips are so flat, it follows that the first-named rocks spread far back into the country. At the mouth of the Brulé River they lie some 12 miles back; at Grand Marais 18 to 20; at the middle of the crescent, near Manitou River, 30 miles, at about which distance they remain until near Duluth and the Saint Louis River. The slates themselves have about the same flat position, so that they, in their turn, spread over a wide belt of country. Equally simple with the general structure as thus laid down, is the , 266 COPPER-BEARING ROCKS OF LAKE SUPERIOR. general stratigraphical succession displayed on the Minnesota coast. Cer- tain groups of beds are plainly to be made out, and in many cases minute stratigraphical measurements could be made in detail through thicknesses of thousands of feet. Of course, the greater the detail attempted, the greater would be the obstacles met with, in the way of faults—which are numerous along the Minnesota coast—thinning out of beds, corrugations of beds, and similarity of lithological composition between different layers. All of the Keweenawan beds of the Minnesota coast belong to the Lower Division of the series. The same statement applies to all of the Ke- weenawan rocks of the North Shore, except a small area at the southeast corner of Isle Royale. The following are the subordinate groups of beds into which I have subdivided the Keweenawan rocks of the Minnesota coast, with a total thick- ness of upwards of 20,000 feet. The thickness of the first group is so un- certain, and indeed irregular, that it is difficult to give an approximately cor- rect estimate of the total thickness. Above the lowest group, as already said, the thickness appears to lie between 17,000 and 18,000 feet. In all probability, 22,000 to 24,000 feet would not be very far from the truth as an estimate of the total thickness. ; I. Tue Saint Lours RIvER GABBRO AND ASSOCIATED RED PORPHYRIES.— These rocks are chiefly coarse orthoclase-gabbro, but include also ortho- clase-free gabbro, and a very few beds of fine-grained diabase. Red augite-syenite and granitic porphyry occur in large areas, constituting at times the entire mass of hills. Felsitie porphyries occur, but more rarely. Similar rocks, similarly associated, occur at the same horizon about the headwaters of Poplar, Cascade, and Brulé rivers, but are not found where they should appear at the Grand Portage end of the coast, though it is quite possible, and even probable, that some of the overflows of coarse gabbro found capping the slates of the Thunder Bay country belong here. The thickness of this group is difficult to estimate, but is probably not overstated at 6,000 feet. Il. Tae Dutura Grour.—This group is a succession of heavy but sharply-defined beds of very fine-grained but aphanitic rocks, belonging to the ashbed type of diabases, and to the diabase-porphyrites. A very few SUBORDINATE GROUPS OF THE MINNESOTA COAST. 267 beds of rather coarse-grained orthoclase-free gabbro are included; and there is a little interleaved detrital matter. Thin amygdaloids of peculiar character cap many of the beds of the upper two-thirds of the group, but the amygdaloidal character never reaches so great a development as in some of the succeeding groups. This group is distinctly recognizable at both ends of the coast, and at points in the interior, wherever its course has been crossed. Its thickness lessens as it is followed eastward; but at Duluth it is not far from 5,000 feet. Ill. Tue Lester River Grovr.—This is a succession of heavy, distinct beds of fine-grained brown rocks, largely of the ashbed type. Diabase-por- phyrites, some of the ordinary diabases, rare beds of coarse-grained gabbro, and two or three belts of granitic porphyry are also included. Amygda- loids are almost unknown, and no detrital material has been observed. The rocks of this group are known at both ends of the coast, and at intervening points in the interior. The thickness is about 2,600 feet. IV. Tue Agate Bay Group.—This is a succession of relatively very thin beds with very highly vesicular, stratiform amygdaloids, which must make up two-thirds of the thickness of the group. The prevalent non- amygdaloidal rock is a fine-grained, olivine-bearing diabase or melaphyr. Towards the base are a number of layers of diabase-porphyrite, also with strongly developed amygdaloids. Thin seams of reddish sandstones and conglomerate are also included. This group forms the coast line for a distance of some 35 miles below the mouth of Lester River, and has been traced some miles farther east by exposures in the back country, but it does not appear at the eastern end of the Minnesota coast, having appar- ently quite thinned out. This fact is in accordance with the general law of thinning towards the east, which is obeyed by all three groups below, and by the one above. The thickness of the group is about 1,500 feet. V. Tue Beaver Bay Grour.—This group is especially characterized by a predominance of black, coarse-grained, olivine-bearing gabbros in very heavy layers without amygdaloids, and by the great abundance and prominence of its included red felsitic porphyries and granite-like rocks. There are, however, very considerable thicknesses included of fine-grained ashbed-diabase’, with and without amygdaloids, while the ordinary fine- 268 COPPER-BEARING ROCKS OF LAKE SUPERIOR. grained diabases with amygdaloids are not excluded—though they are rarely met with. No detrital material has been observed. In following the coast line eastward the beds of this group are crossed in ascending order between Split Rock and Baptism rivers, a distance of some 18 miles; and in descending order in the 28 miles below Grand Marais; besides which are also exposures of the same beds in the intervening country back of the lake shore. In its eastern extension this group does not exceed 4,000 to 5,000 feet in thick- ness, but to the west it must fully reach, if it does not exceed, 6,000 feet. VI. Tue Temperance River Grour.—This is a succession of very dis- distinctly and thinly bedded fine-grained -diabases and melaphyrs, with strongly developed amygdaloids, and several seams of detrital matter, in the shape of red shaly sandstone and conglomerate, one sandstone layer exceeding 200 feet in thickness. Towards the base of the group are some layers of dense ashbed-diabase and diabase-porphyrite. The rocks of this group form the coast line from a point two miles below Baptism River to Grand Marais, a distance of 50 miles. They are the highest rocks seen on the Minnesota coast, and have a thickness in sight of some 2,500 to 3,000 feet. In giving more detailed accounts of these several groups, it will be most convenient to take them up in ascending order, considering in each case first the more western exposures, and then the eastern extensions. The Saint Louis gabbros and porphyries—The rocks of this group form a bold range of hills, extending from Duluth in a 8. 46° W. direction, seven miles on the north side of the Saint Louis River. They have also been car- ried northward from Duluth to the Cloquet River, and up that stream nearly to township 55, a distance of over 25 miles; the belt, as a whole, having apparently at first a northeasterly, then a northerly, and again a north- easterly trend, where left on the upper Cloquet River. How wide the belt is remains quite uncertain, a broad area of country without exposures lying west and north of it; but, judging from the relative positions of the west- ernmost exposures of the gabbro, and the easternmost of the underlying slates in the neighborhood of Fond du Lac, the width cannot there exceed two miles, if it reaches that distance.1 Equally a matter of inference is the ‘Directly north, or even northwest from Duluth, one can travel on gabbro and intersecting red rock for some miles, but this is because the belt here trends northward. COARSE GABBROS OF THE ST. LOUIS RIVER. 269 inclination of the mass as a whole; judging from the adjacent rock beds this is some 45° southeastward from the western extremity to near Duluth; about the same amount eastward at Duluth, and a good deal less than this to the south of east on the Cloquet. No sign of anything like subordinate bedding can be seen in the rock itself. It is massive and irregularly jointed, making great ledges facing in different directions, and furnishing bare, rounded summits to the hills which it composes. The prevalent type of the gabbro of this belt and the kind constituting the hills at Duluth is of a light-gray color, and very coarse-grained, single feldspar crystals sometimes reaching even an inch or two in length. The augitic ingredient is plainly in greatly subordinate quantity, and often on a fresh surface its presence cannot be detected at all. On exposed surfaces, however, the weathering generally brings it out, and then it can be plainly seen to fill the spaces left between the feldspars. Titaniferous magnetite is also often perceptible to the naked eye in large particles. Less commonly the grain is finer and the color darker, the augitic ingre- dient at the same time becoming more plentiful. In the thin section the predominant feldspar is seen to be a plagioclase belonging near the oligo- clase end of the series. There appears also to be always a younger feld- spar present, which has the character of orthoclase and fills corners between the plagioclase crystals, around whose contours it moulds itself sharply. Streng and Kloos found 1.61 per cent. of potash in the rock, which they very properly regarded as belonging to orthoclase. The spaces between the feldspars are filled with a diallage which is always more or less altered to greenish uralite. The alteration in many sections is carried beyond uralite, to chlorite. The magnetite is very large, abundant and titaniferous. Apa- tites of large size are found in all sections. Biotite is a not uncommon accessory. Olivine is absent from all sections. A large-sized figure of the thin section of the Duluth rock is given on Plate VI. 1 Microscopic descriptions of the Duluth gabbro have been hitherto published by Streng (Ueber die Krystallinischen Gesteeine von Minnesota in Nordamerika—Leonhard u. Geinitz, Neues Jahr- buch fiir Mineralogie, Geologie und Paleontologie, 1877, p. 113), and N. H. Winchell (Eighth An- nual Report of the Geological and Natural History Survey of Minnesota, 1880, p. 22). Streng calls the rock ‘‘hornblende-gabbro,” regarding the hornblende as primary. His conclusions are summed up as follows: ‘‘The hornblende-gabbro of the Saint Louis River at Duluth consists of a greatly pre- 270 COPPER-BEARING ROCKS OF LAKE SUPERIOR. Farther west on this gabbro belt, as for instance on King’s Creek, N. E. 4, See. 12, T. 49, R. 15 W., the rocks appear largely to belong to the olivine-bearing, orthoclase-free kinds, having at the same time a very basic feldspar. The red rocks that occur so largely associated with the gabbro of Duluth lie in it very irregularly, and form nothing like distinct belts, so far as I could make out. They may be seen in great patches, hundreds of feet square, and surrounded on all sides by the gabbro, and again, as at the quarry near Rice’s Point, in irregular veins from two to three inches to sev- eral feet in width. Much the most abundant kind of these red rocks is one which presents macroscopically a wholly crystalline texture, and a pinkish color mottled with green. Pink feldspar facets, now and then striated, quartz, and a greenish mineral may all be made out with the naked eye. Under the microscope the rock is seen to be chiefly composed of reddened orthoclase, but similarly reddened oligoclase, greenish hornblende, quartz and magnetite are also present. The quartz occurs both in quite large dominating plagioclase (labradorite), little orthoclase, some hornblende, diallage, magnetite, and titanic iron, and holds also very minute quantities of chalcopyrite and epidote, which is at times asso- ciated with quartz.” My study leads me to agree in the main with these conclusions. I take, how- ever, the hornblende to be wholly uralite, the plagioclase to be more often nearer oligoclase than labradorite, and the iron oxide ingredient to be wholly titaniferous magnetite rather than both mag- netite and titanic iron. The epidote, quartz, and chalcopyrite are so rare as not to deserve mention in any general description of the rock. The following analysis is given by Streng: SiQg .25 a2 22 Se.oed/b5 ssecise cass Sees owes se ew Sees cis sdeeisetemsaneweeeae sestecee 49.15 ANS Os, o:- Sico:c aethrec Sheharya eres oeiee Seensee See ace etes oe tera 21.90 Fe,03 Sees poesoss osteo ssseso cos SseeSoSss so scoebocshosesss cossenoncess 6. 60 FeO «20258 d2iscjos det See ace cones eee oo eee ae Renee eee eee 4, 54 OaO .52 5-2 aerccecis. sd acacteamban tes ener sasareeisa tt oer eee erce este ee ieerears 8. 22 IS 0 eee eee eee Ker SON aS Sao coos eas ona seeesedatocediaccodcoes 3. 03 KgO «.c2cosciratadiswiters cad Soe seca aoe tee ate etna en eiee mee eee eee renee 1. 61 NasO) co ciceccisesce cc os cee basco cess cme t eneEmee snes tena meee eee eee 3. 83 gO) 252 Sas cos oases esse wen cote anne ete winteeeelodSeseiseiocte <-idisoereae cece 1. 92 100. 80 PyO5. - ced own Jb cock tee Ses See cee ee ee er eee eters sisteadeceteleeteeaae 0. 33 TiOg «65 scenns ssmeisc aden se ea eee sete ne CEE Oe ee eee eer ee eee ee ee 0. 18 Winchell finds that the ‘‘ chief ingredients, which are always present, are plagioclase and pyrox- ene, but the latter is sometimes very small in amount.” He finds ‘‘also titaniferous iron, generally magnetic, almost always present, and sometimes in quantity sufficient to render it an iron ore of low grade, * * * Pyrite, caleite, epidote and chlorite also existin some parts, * * * especially as geodes, nests, and vein-fillings, or as products of change. The plagioclase ‘‘is provisionally taken for labrador- ite,” but in some places it is said to appear ‘‘more like anorthite.” The pyroxene is taken to be diallage, much of it ‘‘ fibrous from incipient change, the products being ferrite and viridite.” Hornblende and uralite are not mentioned. The iron oxide is considered to be titanic iron, although magnetic, because of the presence of the white decomposition product. RED ROCKS OF DULUTH. 271 patches and again in little strings running through and through the feld- spars, in the usual manner of secondary quartz. A number of these small patches of quartz lying near each other will polarize together, showing that they are part of one individual. Moreover, the same is true of the larger quartz areas, and numbers of small particles lying near them, so that all of the quartz is considered to be secondary. This secondary quartz is fre- quently scattered through the feldspars in such a manner as to present the appearance of graphic granite, and again it is arranged in irregularly radi- ating lines. Chlorite is often present as an alteration-product of both feld- spars and hornblende. No base finer than the rest of the rock was observed, so that the name should apparently be syenite, the quartz being taken as secondary. Since the hornblende is probably uralite, as in the similar rocks of other parts of the extent of the formation, the rock is probably an augite- syenite. We have in this rock precisely the same as is found in many peb- bles of the porphyry-conglomerates of Keweenaw Point, and such as is found massive again along other portions of the Minnesota coast. Another kind, less common than the foregoing, presents a red matrix with little green or black in it, but numerous facets of red feldspar difficult to distinguish from the matrix, save in certain positions. This is a true “oranitic porphyry,” standing between the granites and felsites. Under the microscope it appears originally to have been composed of a minutely crystalline base; but the whole is now saturated through and through with secondary quartz. Less common than either of the foregoing, but still forming quite large patches in the gabbro, is another red rock which presents to the naked eye an aphanitic light-red matrix, in which minute orthoclases are very sparsely scattered. Underneath the microscope it shows a nearly white matrix so thoroughly saturated with secondary quartz that it is often difficult to tell its exact original nature. The quartz is arranged in arborescent clusters and in crossing forms, and all of a cluster will polarize together. Numer- ous black particles, some of them undoubtedly magnetite, others more mi- nute and hair-like, are contained; also porphyritic crystals of orthoclase and augite. The whole section is dotted with minute brownish particles. One or two minute porphyritic quartzes were observed. The rock is plainly 272 COPPER-BEARING ROCKS OF LAKE SUPERIOR. enough a felsitic porphyry, with various products of devitrification in the base. These three varieties of red rock, thus described as occurring at Duluth, are evidently but different phases of the same rock, and without much doubt are connected with each other in the mass, though this was not proved in the field. The exposures of gabbro on the Cloquet River regarded as belonging to this belt are on Sec. 10, T. 54, R. 13 W. (270 N., 1,500 W.); on See. 5, T. 53, R. 13 W. (1,700 N., 2,000 W.); at the falls on the N. E. 4, See. 18, T. 53, R. 13 W. (1,650 N., 700 W.); at a number of points through See. 36, T. 53, R. 14 W,; in the S. E. 4, Sec. 35, T. 53, R. 14 W. (75 N., 600 W.); and about the falls in the S. E. 4, See. 34, T. 53, R. 14 W., where the show- ing is a very large one. The rock seen at these points is pretty uniform in character, and is a very fresh olivine-gabbro. It is light-gray in color, very coarse-grained, and composed chiefly of very fresh plagioclase (anorthite). Quite fresh diallage fills in the spaces between the feldspars. A few large, fresh olivines occur here and there in the section. 'Titaniferous magnetite is abundant and large-sized, and biotite occurs in a few small scales. From the last exposure examined on the Cloquet, in Sec. 10, T. 54, R. 13 W., it is some eighty miles in a N. 50° E. direction to the vicinity of Brulé Lake, where Mr. Chauvenet found again a large development of coarse gabbros and red granitic porphyries. ‘The intermediate country has not yet been surveyed, and is well-nigh unknown, save to the Indians. There can be little doubt, however, that the same belt runs through. I am informed by Professor N. H. Winchell that he found such rocks on what would be the line of this belt in making a northwesterly traverse from the mouth of Poplar River. Some sixteen miles back from the mouth of Baptism River in a northwesterly direction, Messrs. Campbell and McKinlay found a granitic porphyry, which may belong to the same belt, but the country was low and swampy, and no other exposures were in sight. The exposures about Brulé Lake, and the headwaters of Brulé and Cascade rivers are on a grand scale, and of great interest. To reach them my assistants, Messrs. Chauvenet and McKinlay, started from the lake shore at Grand Marais, Sec. 21, T. 61, R. 1 E.; went thence northwest to Devil’s ROCKS. OF BRULE LAKE AND EAGLE MOUNTAIN. Die Track Lake, in the southern part of T. 62, R. 1 W.; canoed this lake to the western end; portaged to Cascade River in Sec. 26, 'T.62, R.2 W.; and thence ascended Cascade River to its source in a series of small lakes, in the south- ern part of what would be T. 63, R. 2 W., if the country had been surveyed. They crossed in this ascent a series of distinctly bedded diabases and amyg- daloids, dipping southward at a low angle. The lake which forms the source of Cascade River lies in what would be about Sec. 2?, T. 63, R. 2 W. Thence they took a W. N. W. course to Brulé Lake, which lies east and west, with a length and width respectively of about ten and two miles. The shores of the lake are bold and rocky, and exceedingly irregular in outline. The rocks assigned to the horizon now under description were found first on and about Eagle Mountain, which lies ten miles north and two west of the northeast corner of T. 62, R. 2 W., or somewhere about the S. E. 4 of Sec. 22, T. 63, R. 2 W. It rises abruptly on the east side of a small lake to a height of 450 feet, or to upwards of 1,500 feet above Lake Superior. The mountain is a bold mass of bright red rock, and from its summit may be seen numbers of other elevations composed of the same red rock. This rock is a granitic porphyry, and over most of the mountain presents an appearance closely resembling that of the second kind of red rock men- tioned as occurring at Duluth, while it is precisely similar to rocks seen cutting coarse gabbro at the same low horizon in the Bad River country of Wisconsin. It presents to the naked eye the appearance of being chiefly made up of small red feldspars, but there are areas which will not reflect any light. No other mineral is to be detected. Under the microscope the section presents precisely the same appearance as that of the Duluth rock, being made up of reddened orthoclases and matrix, the latter now so thor- oughly saturated with secondary quartz arranged in bunches of radiating lines, that its original nature is difficult to decide. The quartz also pene- trates some of the recognizable orthoclases, many of which are, however, without it. One or two particles of greenish hornblende were observable; minute black particles also occur. Near the top of the mountain a more dense kind than usual was noticed, which turned out to be a true felsitic por- phyry. No line of demarkation was noticed between the kinds. All about 18 Ls 274 COPPER-BEARING ROCKS OF LAKE SUPERIOR. the mountain the rock appears as if massively bedded, with an east and west trend, and a 10° to 15° southward dip. Eastward from Eagle Mountain three or four miles the red granitic porphyries were again found exposed. On the foot of the mountain on the south, moderately coarse dark-gray ortho- clase-gabbro was in place, appearing to underlie the granitie porphyry. Leaving Eagle Mountain, the course of the party lay in a northerly direction, through a string of four lakes. In the second of these, Pike Lake, massive ledges of gray gabbro 10 to 30 feet high run along both sides of the lake. This gabbro is very coarse, much weathered and iron- stained, and shows a great deal of very coarse titaniferous magnetite. Under the microscope it is seen to be closely allied to the Duluth gabbros, from which it differs, however, in having more orthoclase, a less-altered diallage, and in containing quite a little secondary quartz. The same rock continues largely exposed to the end of the last Jake in the series in about what would be Sec. 15, T. 63, R. 2 W. From the last lake the trail leads through a gorge 10 miles in a direction slightly north of west to Brulé Lake. The walls of the gorge average some 50 feet in height, now and then rising into cones of bare rock 100 to 150 feet high. They are often not more than a few rods apart. That on the north is for most of the distance red granitic porphyry, and that on the south at first the coarse gray gabbro of the lakes below, while nearer Brulé Lake it is composed of a finer-grained brownish- gray orthoclase-gabbro. In this rock there is a good deal of augite with crystalline outlines, it having formed before the feldspars, besides diallage with the usual relation to the feldspars, which are both oligoclase and ortho- clase. There is contained a great deal of titaniferous magnetite in black rods. Brulé Lake is a sheet of water some ten miles in length by two in great- est width, with an exceedingly irregular outline, and numerous rocky islands. The lake lies in a rock basin, and its shores, especially the northern, rise into bold cliffs, and the whole landscape is unequalled for beauty anywhere in the Northwest. There was not enough time spent here to work out any details, but enough was seen to learn that the rocks lie in distinct belts trending slightly south of west. At the northwest corner a red granitic porphyry like that of Eagle Mountain has a great development. South THE DULUTH BEDS. PA, from here are belts of fine-grained ashbed-diabase and of a diabase-porphyry with a fine-grained to aphanitic gray matrix and large red crystals of a tri- clinic feldspar. Still south of these belts are others of a medium- to very coarse-grained gray gabbro. One of these belts, consisting of a medium- grained kind, with much whitened feldspar, and much magnetite, can be traced for several miles from the end of the lake, through a line of islands to the north shore. Still south of these belts, and appearing both in the islands and on the northeast shore, are again others of a red granitic por- phyry, running into a true quartz-porphyry; of fine-grained ashbed-diabase, and of a very coarse orthoclase-bearing gabbro like that seen farther south towards Eagle Mountain. The gabbro sheets overlying the slates of Pigeon River and Thunder Bay, and above alluded to as possibly belonging to the same general hori- zon with the Duluth gabbros, are described in connection with the slates.’ The Duluth Group—tThe rocks in the neighborhood of Duluth which I assign to this group were found exposed in the streets of the town itself, along the lake shore to the mouth of Chester Creek, and on the hillside in the triangular area between the latter creek and the lake shore. As ex- plained on a previous page, these rocks trend at first west of north, and then about north to and beyond Chester Creek, dipping at first 45° eastward, but near Chester Creek not more than 20°. The whole thickness displayed is not far short of 5,000 feet. With the exception of two thin beds of a moderately coarse, black gabbro, and a little interleaved detrital matter, all of this thickness is made up of a succession of very fine-grained to apha- nitic, gray to brown rocks, which are frequently porphyritically developed, with red and more rarely white feldspars as porphyritic ingredients; and which, in the upper two-thirds of the thickness often present amygdaloids as the upper portions of the flows. These amygdaloids have commonly a light-brown or reddish-brown matrix, and amygdules which are prevailingly epidote; but amygdules of epidote and quartz, of epidote and calcite, and of a green earthy substance, evidently a decomposition-product, also occur. A general epidotic decay is often presented in the shape of reticulated strings and blotches of epidote through the amygdaloids, and even, to some 1See also Chapter VIII. 276 COPPER-BEARING ROCKS OF LAKE SUPERIOR. extent, in the more compact portions of the beds. The amygdules are rela- tively small and not very thickly strewn. They are frequently elongated in a common direction and ina very striking manner. The same amygda- loids which exhibit this elongation of the amygdules in a common direction show also other signs of having flowed as lava, such as flowage lines, ropy texture in a common direction, etc. The most interesting of these phenom- ena is, however, an appearance of stratification presented on a weathered surface, which is evidently directly connected with the viscous flow of the original lava. As to the thickness of the layers of this series at Duluth, it may be said that the thickness of the lower layers is exceedingly difficult to determine, the rock exposures showing the same material of great widths, and there being no amygdaloids. Evidently the thicknesses are very considerable, probably measured even by hundreds of feet. Higher up, however, the layers become plainly thinned, and alternate more rapidly, and in the upper third of the series amygdaloids and compact portions alternate with each other quite rapidly, as is well seen along the shore west of Chester Creek. An examination of a large number of sections of these rocks under the microscope showed them all to be closely the same, varying only in texture and fineness of grain. The main ingredients in all are plagioclase, augite and magnetite. ‘The triclinic feldspar occurs both in the ground- mass and as the chief porphyritic ingredient, the reddish crystals showing frequently and plainly the striation to the naked eye. In both, measure- ments give the low angles indicative of oligoclase. The porphyritic erys- tals are commonly filled with brownish particles of ferrite, and are nearly always more or less thoroughly dulled by alteration. The augite is only rarely fresh, generally showing more or less of a change to a greenish, non- polarizing, viriditic substance, with which change there is also connected the formation of much magnetite in small particles. It exists both as a filling to the spaces between the feldspars, and in little rounded granules, the latter phase being especially characteristic of the finer-grained kinds. Magnetite is present, however, not only as an alteration-product of the augite, but also occurs abundantly in all sections as an original constituent. Besides these main ingredients, there are also to be observed apatite, which occurs THE DULUTH BEDS. ree im many sections in the usual slender needles; epidote, which in many sec- tions is abundantly present in the groundmass, at times to such an extent as to form pseud-amygdules, besides occurring as a true amygdule in the amygdaloids; quartz, also as an alteration-product, associated with the epi- dote, and also in some of the excessively fine-grained kinds as true infil- trating secondary quartz.’ Olivine is absent throughout. These rocks then are to be called, according to their texture and degree of crystalline development, fine-grained diabase, porphyritic diabase, diabase-porphyrite, and diabase-amygdaloid. The two beds of gabbro above alluded to are in strong contrast with the rest of the rocks of this group. They show a black, rather coarse, highly crystalline, rough-textured rock, which in the thin section is seen to be made up of anorthite; diallagic augite, very coarse and abundant, partly fresh and partly altered to viridite and uralite; and very coarse magnetite or titanic iron. . With the exception of the last rocks described, Professor N. H. Winchell, if I understand him correctly, would regard all of these fine-grained rocks, and especially the amygdaloidal and porphyritie phases, as metamorphosed shales and sandstones, and as altered from the red sandstone of Fond du Lac, to which, as a result of alteration, he also refers the granite, granitic porphyry, and felsite of the Duluth gabbros, and indeed of the whole Minnesota coast. The usual proofs are present that the rocks now under description are entirely original and have flowed as lavas. These are, in brief, completely crystalline texture in most kinds; presence of some origi- nal non-polarizing base in some of the porphyritic kinds; complete absence in all of any traces of fragmental texture; true gas vesicles in the amygda- loids; elongation ot these vesicles in a common direction; flowage lines 1QOne variety of the Duluth fine-grained rocks A. Streng has described in some detail under the name of ‘‘melaphyr-porphyry,” the term melaphyr being used for any older plagioclase-augite rock. (A. Streng und J. H. Kloos: ‘‘Ueber die Krystallinischen Gesteine von Minnesota in Nord Amerika,” in Neues Jahrbuch f. Mineralogie, ete., 1877, p. 42.) It is evidently the rock which is largely exposed near the elevator in East Daluth, N. E.} of the 8. E. ¢ Sec. 27, T. 50, R. 14 W., and again—the same belt—on Brewery Creek, at 250 paces north and 100 west of the southeast corner of See. 22, T. 50, R. 14 W. It presents a very dense groundmass, with very thickly scattered porphyritic crystals of red feldspar, mostly triclinic. The following is the analysis given by Streng: SiO,, 50.03; A1,Os, 15.38; Fe.O3, 11.78; FeO, 3.90; CaO, 5.39; MgO,3.60; K20, 1.14; Na.O, 5.01; H20, 2.73; COg, 0.98=99.94; P20,, 0.33. His analysis shows the essentially basic nature of this porphyry, which Messrs. Streng and Kloos class with the somewhat similar rock from Saint Croix Falls, Wisconsin. 278 COPPER-BEARING ROCKS OF LAKE SUPERIOR. and ropy texture in the amygdaloids; and division of the beds into lower compact and upper vesicular portions. To these we need only add that should we look on them as of detrital origin, we must do the same for all the amygdaloids of the Lake Superior basin, and for all of the crystalline rocks with which they occur. This would leave us only a few insignificant dikes to regard as of eruptive origin. Between the Keweenaw Point dia- bases and amygdaloids and those of Duluth there is no difference as to the general nature—-the origin of the one is the origin of the other. True detrital material was, however, observed interbedded in the Du- luth series at two points; one of these was low down in the series, on the hillside above the Catholic church at Duluth, where a small exposure of a very finely laminated argillaceous slaty rock is to be seen; the other is on the lake shore between Brewery and Chester Creeks, where may be seen a light-brownish, quite plainly bedded fine-grained sandstone composed of a mixture of basic and acidic detritus, the former predominating. Several small dikes were observed cutting the beds of this mem- ber on the lake shore between Chester Creek and Duluth. These dikes trend with the strata, but cut across them at right angles to the bedding. They are composed of a fine-grained black rock, which, near the middle of the dike, is plainly crystalline, while towards the sides it is aphanitic. This rock has not been examined under the microscope, but is precisely the same macroscopically as that of some similar dikes occurring five miles further down the coast, below the mouth of Lester River, which is a very highly augitic diabase, without olivine, and with but little magnetite. Since these beds make so large an angle with the coast near Duluth, they depart rapidly inland. So far as our limited explorations went inland, the belt of country under which they are supposed to lie is largely low and without exposures, lying back of the first or lake range of bold hills. Fol- lowing the range line between ranges 11 and 12 north seven miles from the crossing of Knife River in the 8. W. 4, Sec. 6, T. 52, R.11 W., Mr. McKinlay found no exposures, but eastward from the last point three miles, in the N.W.4 of the 8. W. 4, Sec. 4, T. 53, R.11 W., he found a large exposure of a very fine-grained massive gray rock, with porphyritic triclinic feldspars, which both to the naked eye and under the microscope resembles closely the gray THE LESTER RIVER BEDS. 279 Duluth rocks, to whose horizon it may reasonably be referred. The rocks of the upper Cascade River, and the east end of the Minnesota coast, which may belong in part to the member now under description, are considered after the next two members are described. The Lester River Group—The third member of the succession on the Minnesota coast I have divided from the second by a rather arbitrary line. Its beds were seen best exposed on the lake shore from a point be- tween Chester and Tischer’s Creeks, in Sec. 24, T. 50, R. 14 W., to a point about two miles below the mouth of -Lester River, in Sec. 34, T. 51, R. 13 W.; along Lester River, and in the woods west of the river, in Sees. 4 and 5, T. 50, R. 13 W., and Secs. 29 and 33, T. 51, R.13 W.; along French River, in Sees. 6 and 7, T. 51, R. 12 W.; in scattering ledges in the woods in the southern part of T. 53, R. 11 W., north of Knife River; and again along Encampment River, in Secs. 3, 10, and 11, of T. 53, R. 10 W. This group is made up chiefly of beds of fine-grained to nearly black, dark-gray, brown, or reddish-brown compact rocks, occasionally porphy- ritic with reddish plagioclases; but this character is not so marked as in the preceding group. No detrital material was observed, and only one or two amyedaloids, although feebly developed pseud-amygdaloids occur more frequently. A few coarse-grained beds are included, and there are two or three belts or areas of red granitic porphyry. Several narrow dikes were seen on the coast, like those of the Duluth Group, and, like them, trending with the general direction of the beds, now altered from what it was near Duluth. The prevalent fine-grained beds were best seen on Lester and French Rivers. At the mouth of Lester River and for some distance below, and again up the river for half a mile, are large exposures of a very fine- grained, dark-brownish to dark-greenish, compact, very heavy rock, with a few minute porphyritic feldspars. The chief constituent is a plagioclase, in minute tabular crystals, which never give higher angles than for oligo- clase. Quite subordinate in quantity are the minute particles of augite, many of which are largely altered to a greenish substance, with which is also associated more or less magnetite, evidently as a product of alteration. 280 COPPER-BEARING ROCKS OF LAKE SUPERIOR. Original magnetite and rare and small porphyritic oligoclases complete the list of constituents. The rock belongs to Pumpelly’s ashbed type. The southeast dip, at 10°, can be plainly made out in this rock at the mouth of the river. Ascending Lester River, lower layers come to view. Near the middle of the west line of the N. W. 4 of Sec. 4, T. 50, R. 13 W., the rock is very fine-grained, of a dark brownish-gray color, and under the microscope presents the typical appearance of Pumpelly’s melaphyrs, namely, large augites, including numerous tabular plagioclases (oligoclase), and with numerous olivines, altered to greenish and brownish substances, magnetite, and much red ferrite in the spaces between the augites. Near the northwest corner of the section a coarse band is crossed. Next, through the greater part of Sec. 33, where the river makes four falls, whose height aggregates some 80 feet, the rocks are very dense, dark brownish- gray diabases, alternating with red- and dark-green-mottled varieties. These are seen in the thin section to be the usual pseud-amygdaloidal diabase, holding augite, often fresh, but often altered to a dark-green substance, much reddened plagioclase, magnetite, pseud-amygdaloidal chlorite, and occasional porphyritic oligoclases. In Sees 6 and 7 of T. 51, R. 12 W., French River makes nine falls over the rocks of this group, the individual falls running from 6 to 70 feet in height. Between these falls the river rushes down an inclined plane nearly on the slope of the S. E. dip. The rocks in sight are largely fine-grained, rough-textured, luster-mottled kinds, ranging from black to bright red in color, according to the amount of secondary peroxide of iron present. They are very highly augitic, with much magnetite and olivine in minute particles, wholly altered to a green substance, between the augite grains. All specimens show rare and small porphyritic oligoclase, and there is often pseud-amygdaloidal chlorite. The rock at the falls in the N. W. 4 of Sec. 6, beyond which the river was not ascended, is very dense, with conchoidal fracture and of a dark-brown to nearly black color. Its thin section shows the common characters of this variety, viz, predominant plagioclase (oligoclase) in small tabular crystals, and the augite in minute rounded particles. One amygdaloid was noticed on French River, near the north line of Sec. 7, and 730 steps west from the northeast corner of THE LESTER RIVER BEDS. 281 ~ the section. The amygdules are thickly crowded, small, often elongated, and chiefly composed of radiating laumontite in the specimen brought away. The fine-grained, conchoidal-fracturing, brownish rock, with accompanying laumontitic amygdaloid, seen on Encampment River, in the.S. E. 4 of See. 10, T. 53, R. 10 W., is probably to be placed with the fine-grained rocks of the Lester River Group. It was not possible to determine whether all of the coarse-grained rocks of the Lester River Group are interbedded flows and not dikes, but most of them are plainly the former, and the rocks of those exposures whose relations were doubtful are in all respects identical with those of the undoubted beds. As an example may be mentioned the rock quarried below the mouth of Chester Creek. The thin section of this rock is figured at Figs. 3 and 4 of Plate II, and is further described in the table on page 46. It is a medium-grained, highly crystalline, black, rough-textured, olivine-gabbro or diabase, consisting chiefly of anorthite and diallagic augite, and containing also large particles of olivine and titaniferous magnetite. Externally it presents a luster-mottling, such as is seen in the finer rocks, and from the same cause. It is the same rock that forms the few coarse beds of the Duluth Group, the uppermost amygdaloids of which group it closely overlies. It forms a bed of very considerable thickness, and can be followed along the lake shore for many rods, varying somewhat in coarseness of grain. A similar rock closely overlies the fine-grained dia- base of the mouth of Lester River. In it the olivines are more highly altered, being almost wholly changed to a brownish ferrugimous substance. This layer can also be traced for a long distance on the shore. Similar rocks show again on French River, near the north line of Sec. 7, T. 51, R. 12 W., and in a great ledge 200 feet high on the west line of the S. W. 4 of Sec. 26, T. 53, R.11 W. The rock on French River occurs plainly in- terbedded with the fine-grained rocks already described. It is moderately coarse in grain, gray, minutely spotted with red, and of a rough texture. It consists chiefly of anorthite, diallagic, very fresh augite in large crystals, each one of which includes several detached areas, and olivine, which occurs in large patches crossed by black, brown, and red bands of iron- oxide. The thin section is represented in Figs. 1, 2, and 4 of Plate III. 282 COPPER-BEARING ROCKS OF LAKE SUPERIOR. The rock in Sec. 26, T. 53, R. 11 W., forms a ridge which presents a bold cliff to the northwest and a gradual slope to the southeast. Macroscopic- ally it is somewhat different from any of the foregoing, presenting a very light-gray color, mottled with darker shades, but the thin section shows that it is essentially the same rock, and that the differences are due to smaller amounts of augite and to the great freshness of the rock. Even the very large olivines are unusually fresh, being traversed only by a few rifts bordered by a greenish alteration-product. Coarse-grained, rough- textured black olivine-gabbro belonging to the Lester River Group forms the barrier rock of the falls of Encampment River in the N. E. 4 of See. 10, ALI 5 Sy kul OB Ws Another kind of coarse-grained rock is presented in the ledges on the west line of Sec. 28, T. 54, R.13 W. This is an orthoclase-gabbro, carry- ing orthoclase, oligoclase, diallage, augite in long-twinned blades, apatite and a good deal of secondary quartz. Externally it is brownish-black and resinous-looking from alteration, and peculiar for its long-bladed augite crystals. The thin section of this rock is pictured in Figs. 1 and 2 of Plate V. The red porphyries of the Lester River Group can be best seen on the lake shore both above and below Lester River. The importance of the place not being realized at the time, sufficient attention was not given to it to determine the relation of these red rocks to those adjoining them. Some of the specimens brought away show a medium-grained, highly crystalline rock, which in the thin section looks as if it might be a very greatly altered orthoclase-gabbro. Quite a little augite, much of which is fresh, is con- tained, and the reddened feldspars are filled with secondary quartz. Other specimens show a rock more like the granitic porphyry of Duluth, and others again are distinctly felsitic porphyries. Even the latter kinds are saturated with secondary quartz, and all kinds so much altered that the original condition of the matrix is not easy to determine. At one point below the mouth of Lester River a coarse, black olivine-gabbro includes patches and vein-like bands of the red rock, in this case one of the more distinctly crystalline and augite-bearing kinds, while a few rods farther along the shore the same red rock forms the whole face of the exposure. Some of the bands of red in the black gabbro are only a few inches wide RED ROCKS AND DIKES OF THE LESTER RIVER GROUP. 283 and have serpentine courses, intersecting one another. There can be no doubt that the rock and conditions are the same as observed in the case of the red rock penetrating the gabbro at Duluth. The red rock below Lester River becomes more and more fine-grained as it is followed down the coast, until it presents the appearance of a felsite, with distinct red orthoclases. Still farther it is much weathered and earthy, with seams of calcite and large sized ‘“‘vugs,” lined with fine crystals of the same mineral. In the same vicinity it is thickly dotted with amygdule-like spots of white calcite, one-fourth inch in diameter. Whether these are true amygdules or replace- ments has not been determined. ‘True quartz porphyry and granitic por- phyry are exposed along Encampment River in the N. W. 4 of Sec. 11, T. 53, R. 1 W., with a width of 400 paces. This belt lies at or near the sum- mit of the Lester River Group Below Lester River these red rocks were observed to be cut by sev- eral narrow dikes, 10 to 20 feet wide, and trending N. 45° to 50° E., or with the strata. These dikes were marked by a very strong cross-jointing, and near the walls by a close-jointing parallel to the walls. In the middle of the dikes the rock is black, fine grained, but highly crystalline, and rough in texture. ‘Towards the sides where the jointing parallel to the walls comes in it is aphanitic, dark-green in color, and greasy from the presence of chlorite. A section of the rock from the middle portion shows augite predominating, partly fresh, and partly altered to a brownish substance, in areas enveloping numbers of minute plagioclases (labradorite), just as in the ‘‘luster-mottled” melaphyrs of Pumpelly. Magnetite is present in small particles, and besides the viriditic and ocherous material, evidently resulting from a change of the augite, there are other particles of some- what similar material, usually of a deeper tint, lying between the augites in small rounded forms which show no tendency to polarize together. These are evidently altered olivines, and the resemblance to Pumpelly’s luster- mottled rocks, save in unusual fineness of grain, is thus complete. The section of the finer-grained rock from the side of the dike shows it to be the same, except that it is in an excessively fine condition, has its augite largely changed to a chloritic substance, and contains some non-polarizing base. 284 COPPER-BEARING ROCKS OF LAKE SUPERIOR. The Agate Bay Group—The Agate Bay Group of beds is finely dis- played in its entire thickness of some 1,500 to 2,000 feet, along the lake shore for a distance of some 84 miles, between a point in the 8. W. 4 of See. 34, T. 51, R. 13 W., a mile and a half below the mouth of Lester River, and one in the S. E. 4 of Sec. 14, T. 54, R. 9 W., two miles above the mouth of Encampment River. These beds are also to be seen exposed on French, Knife, Encampment, and Gooseberry rivers, for short distances from their mouths. The most striking external characteristics of this group, as compared with those previously described, are the relative thinness and distinctness of its beds; the great number of highly vesicular amygdaloids, which must make up more than half the entire thickness of the group; the pe- culiar appearance of subordinate stratification presented by both amygda- loidal and compact portions of the layers, when weathered; the prevalent fine grain of all save one or two of the beds, and the presence of two or three thin layers of red sandstone, shale and conglomerate. The lower beds of this group, which are to be seen along the shore in Sees. 34, 35, 24, and 26, T. 51, R. 13 W., trending more to the northward than the coast and dipping southeast about 15°, are somewhat peculiar. The rocks exposed about the lower part of Encampment River in Sec. 11, T. 53, R.10 W., appear also to belong here, as do, in part, those along the shore for two or three miles above the mouth of the same river, the broad bay into which this river empties setting back far enough to reach these lower layers. The non-amygdaloidal portions of these lower beds are composed largely of very dense conchoidal-fracturing diabases of the ashbed type, some having a dark-greenish to black color, while others have a more reddish-brown color, when the grain is excessively fine. There is often more or less unindividualized material, when the rock becomes a diabase-porphyrite. Other layers again have the compact portions a coarser rock, often much altered and crumbly, and of various purple and brown shades. These are the usual Keweenawan fine-grained olivine-free diabases. The amygdaloids of all these beds are plainly marked. They carry chiefly laumontite, calcite and quartz in the cavities, which are often of large size (4 to 4 inch), smooth-walled, and elongated in a common direction. Many are empty, and being thickly strewn, the result is a completely honey- THE AGATE BAY BEDS. 285 -~ combed rock. In one place, about two miles below Lester River, one of the hard reddish-brown dense beds above referred to was furnished not only with an upper, but with a basal amygdaloid, in which the cavities were large, smooth-walled, and quite regularly oval, often empty, or lined with drusy quartz. A fine showing of one of these hard beds is to be met with on the coast near the center of Sec. 22, T. 53, R. 10 W., about ten miles above the mouth of Encampment River. Here is a bold cliff 25 feet high, of the hard, dense, light-brown rock, which below is without amygdules, but which as it is traced up the cliff becomes more and more amygdaloidal, finally becoming a highly vesicular amygdaloid, with large cavities elon- gated in a common direction, and carrying saponite, calcite and laumontite. Under the microscope the non-amygdaloidal portion of this rock is seen to be chiefly composed of tabular plagioclases (oligoclase) set in a brownish, iron-infiltrated matrix which will not affect the polarized light. Augite is present only in very rare minute rounded grains and in a few porphyritic crystals. Particles of magnetite and porphyritic oligoclases complete the list of ingredients. The rock is a diabase-porphyrite with the augite nearly or wholly wanting. Some of the less dense beds showed pseud-amygdaloidal phases, with pseud-amygdules chiefly of a dark-greenish chlorite, and at several points on the shore of Sec. 25, T. 51, R. 13 W., a crumbling pseud-amygdaloid was found with a light reddish color, mottled with dark-green chlorite pseud-amygdules, and presenting at first sight, especially on cross fract- ure, a strong resemblance to a reddish sandstone, with angular grains. This resemblance is heightened by the fact that the rock has a bedded appearance. A careful examination, however, of the weathered surface of the rock shows that it probably has a completely crystalline texture, and this is abundantly proved to be the case by the thin section, which shows that the rock is nothing but one of the usual pseud-amygdaloids, of inter- locking crystalline texture, and with no trace of fragmental origin. This rock would undoubtedly be taken for a sandstone by most observers at first sight. 286 COPPER-BEARING ROCKS OF LAKE SUPERIOR. The remaining two-thirds of the Agate Bay Group forms the most of the coast from Talmage River to beyond Gooseberry River, in which dis- tance there is, on the whole, an ascent of the coast line in geological horizon; but there are minor descents and ascents according to the relations between the irregularities of the coast and the trends of the strata. The dips are flatter than further east, never exceeding 10°, and sometimes sinking to 5° for considerable distances. he prevailing rock of the non-amygdaloidal portions of the beds is fine-grained and olivine-bearing, having nearly always the characters of Pumpelly’s melaphyrs, 7. e., large augites including num- bers of minute plagioclases, and much olivine and magnetite crowded into the spaces between the augites, the olivine generally altered into a reddish or greenish material. Though generally much finer-grained than the typ- ical melaphyr of the Greenstone of Keweenaw Point, these rocks often show, in the less altered portions, which are then quite black in color, a distinct luster-mottling. In less fresh kinds there is a tendency to weather to a semi-nodular surface, the augite resisting decomposition better than the interspaces. These more altered kinds run through various shades of brown and red, more or less mottled with green. There is a good deal of variation as to coarseness of grain in different beds, and an extreme coarse- ness carries the rock into a true olivine-gabbro, which plainly enough, as may be seen even with the naked eye, is a phase of the fine-grained mel- aphyr. Such a rock presents itself on a large scale, with bedding surfaces hundreds of feet in length and width shelving into the lake at a low angle, along the coast between Sucker River Bay and Knife River, in the north- east part of T.51, R.12 W. Sections of this rock are figured on Plate III. Encampment Island, a mile east of Encampment River, is again formed of one of these coarser kinds, which also can be seen forming a distinct layer between finer-grained beds, on a cliff side in the north half of Sec. 22, T. 53, R. 10 W,, 50 to 75 feet above the lake. The amygdaloids of the upper two-thirds of the Agate Bay Group are very strongly characterized. In the first place they are very highly vesic- ular; the vesicles are always small and often so closely crowded that when the amygdules are dissolved from them the rock is almost as open as well- raised bread. The common amygdules are laumontite, saponite, and cal- - THE AGATE BAY BEDS. 287 cite. This seems the order of abundance for the whole group, but in sep- arate layers either one or the other of the first two may predominate. The small, rounded, white or greenish-white spots of saponite are very char- acteristic. Prehnite is a much rarer amygdule, and agate still rarer. An- other equally important characterisijc is the stratiform appearance taken on by these amygdaloids. This appearance, which has received some notice on a previous page, is also found, though to a less extent, in the interbedded massive layers, or rather in the massive lower portions of the beds of which the amygdaloids form the upper portions. In both amygdaloids and compact portions this stratiform appearance is especially brought out by weathering. This was seen beautifully illustrated at the mouth of a creek on Sec. 15, T. 52, R. 11 E., about two and a half miles above Agate Bay. The creek enters the bay over the low shore cliff, into which it has worn its way back for some distance. Just where the water flows over it the rock is hard and massive, without trace of stratiform appearance, but on either side it may be traced distinctly into the usual obscurely stratiform material. At a little distance an exposed cliff presents much the appearance of a series of sedimentary beds, as for instance a set of rather heavily bedded sandstones alternating with shales; indeed, these rocks, as already indicated, were long ago called ‘“‘metamorphic sandstone and shale” by Norwood, and are now regarded as such by N. H. Winchell. But a closer study shows that here, as everywhere, both heavier and thinner layers are made up of rocks identical with the amygdaloids and diabases of Keweenaw Point, whose completely interlocked crystalline condition in the lower portions, and highly vesicular condition in the upper portions—the massive and vesic- ular parts grading into one another—abundantly prove their origin as lava flows. The lower portions of the beds have, too, very frequently, a well- marked columnar structure, another characteristic of the Keweenaw Point flows, and of flows of eruptive rocks generally. As already said, microscop- ically, these rocks are olivine-bearing augite-plagioclase kinds identical with the Greenstone of Keweenaw Point, even to the peculiar crowding between the augites of the olivine and magnetite particles. They are also the same rocks, only finer in grain, as the coarse black diabases which Norwood and Winchell themselves regard as eruptive, and—which will be 288 COPPER-BEARING ROCKS OF LAKE SUPERIOR. taken by some as still more conclusive proof of eruptive origin—they are identical, even to the same crowding of the olivine in the interspaces, with the rocks of the narrow dikes found along the coast westward to Duluth. As shown below, the rock of the dikes observed cutting the Agate Bay beds themselves is a true luster-mottled melaphyr. The subordinate layers, of which both amygdaloids and compact por- tions appear to be made up, are never regular or persistent, and in this respect there is a contrast with the subordinate layers of true sedimentary rocks, the most irregular of which are never so irregular as these. When in the field it was thought that the peculiar combination of resemblances to sedimentary beds and to the usual eruptive rocks of the region shown in these stratiform amygdaloids and associated massive layers, might find ex- planation in the origin of the amygdaloids as volcanic ashes,’ 2. ¢., frag- mental volcanic material stratified by water. In this case the amygdules might be pseud-amygdules, which could of course originate as well from fragmental basic material as from the same material in the original massive condition. But the study of specimens, and more especially the micro- scopic study of thin sections, which develops the wholly non-fragmental character of the material, and the true vesicular nature of the amygdaloids, show that such an idea is wholly untenable. The following section, made out along the cliffs just west of Agate Bay, serves well to show the sort of succession everywhere to be observed in these stratiform beds The section could have easily been extended both up and down, but is sufficient as an illustration. The layers dip some 6° to 8° to the southeast. The order is an ascending one. IA. Massive, vertically columnar layer of a medium-grained, distinctly at crystalline, purplish rock, mottled dark and light on a weathered surface. Sparsely scattered pseud-amygdules of calcite and laumontite, and of chlorite, are contained. The thin section shows plagioclase; augite, inclosing plagioclases; magnetite; olivine, wholly altered to red oxide of iron and a green substance, and crowded with the magnetite between the augites; and pseud- amygdules of a pale greenish substance. Grading into the over- lying rocks by increase of abundance of amygdules. Thickness seen Sbove water is. ctt sete e a ee cee eee eee ees tater 5 ‘Norwood seems to have had this idea with regard to some of these beds, though most of them he regarded as ‘“‘metamorphic shales.” See Owen’s Geological Survey of Wisconsin, Iowa, and Min- Desota, p. Jol. THE AGATE BAY BEDS. 289 IB. Stratiform laumontitic amygdaloid, the irregular and non-continuous layers less than six inches in thickness. Matrix much as in fore- going; finer grained. Amygdules small, not exceeding } inch, thickly crowded, of laumontite, calcite, saponite. Thickness... -- 10 IIA. Massive, vertically columnar layer, of a rock similar to that of 1A., but finer grained. In places laumontite amygdules or pseud-amyg- dules run through the whole thickness. Subordinately stratiform when weathered. Thickness.................. See heir sie es 3 IIB. Stratiform amygdaloid like 1m. Thickness ........... x SEE ate 6 — 9 IIIA. Massive, vertically columnar layer of a rock closely resembling that of IA., but showing under the microscope larger olivines and more pseud-amygdaloidal chlorite. Exceedingly irregular in thickness, expanding and contracting suddenly from a few inches to several feet, and vice versa. Thickness from 4 inches to..-...--.--.--- eas ITB. Stratiform laumontitic and calcitic amygdaloid; subordinate layers a TEWeINGHessuhiGk. ME NICKNESS tere [acy ete Sere eater aera ial init 6 a IVA. Massive, vertically columnar layer like IA., ILA., IllA.; exceedingly ; irregular in thickness, running from nothing to.......---..-.--- 2 IVB. Stratiform laumontitic amygdaloid, the amygdules larger than usual, reaching 4 inch, and evenl inch. Thickness..... .............20 = VA. Massive, vertically columnar layer; rock like that of I4.; very irreg- Wibie, WUNRIESS, WOW NINE? iO) sond0s boocobee ceoo {See oL coe ecce 2 VB. Stratiform laumontitie and calcite amygdaloid; layers so thin as to near sielhe “WNC 6S isscbéeadeccoo cbcnoe deaaeo cdaseones Bibs 5 VI. Massive, vertically columnar layer, somewhat amygdaloidal towards EOP ROC Ka lc UACm een NTC IMESS ie ere asjois siaistelctetolelaini= Seoteey nsayeten ay eis 15 VII. Red shaly sandstone; very irregular in thickness; running away down into crevices in the underlying massive rock, and in places curi- ously intermingled with the overlying amygdaloid. Thickness ... 2 to3 VIII. Stratiform laumontitic amygdaloid, layers at times very thin. Thick- MGSS mises a efetas sre Bos Bete SSIS BR Ee Aa IO GODS Ae aoorE Shee sta e 10 IXA. Massive layer, with the vertically columnar structure strongly marked, of a fine-grained dark-gray to nearly black rock, which under the microscope is seen to be one of the usual olivine-bearing mela- phyrs, peculiar only in unusual fineness of grain. This layer forms the greater part of the face of the west point of Agate Bay. It is exposed in an immense surface, sloping towards the lake, as much as a quarter of a mile in length, and at times several hundred feet wide. As one walks over this great surface the ends of the col- umns, which show in cross-section, are finely displayed, and are seen to lack, as usual, the regularity of the basaltie columns of some regions. They are made by the intersections of several systems of joints, here quite close, and have varying numbers of sides 19LS 290 COPPER-BEARING ROCKS OF LAKE SUPERIOR. and varying sizes. Many of the columns are triangular. posed of minute particles of Fic. 13.—Sandstone ‘‘ veins,” Minnesota coast—plan. quartz with other porphyry detritus, together with here and there dark-colored particles and particles of triclinic feldspar which probably are from some of the basic eruptives. When first seen these apparent veins of sandstone showed no connection with any other sandstone, but a few rods farther down the coast the amyg- daloid in which they occur was found overlain by the remnant of a thin SANDSTONES AND DIKES OF AGATE BAY GROUP. 293 red sandstone layer, or rather conglomerate, the pebbles being wholly of amygdaloid. Proceeding down the coast, the next sandstone met with is the seam already described in the section given of the succession at Agate Bay. This sandstone is much like the one last mentioned, descending in the same way far down into the crevices of the underlying rock, and inter- mingled curiously with amygdaloid. It is only two or three feet thick. Still farther down the coast, on the N. E. 4, Sec. 32, T. 5”, R. 10 E., red shaly sandstone was noticed occurring with stratiform laumontitic amygda- loid, as represented in Fig. 14. The sand- stone layer with which this must connect was not seen here. At the projecting point near the 8. E. corner of Sec. 1, 53, R.10-W., thin sandstone seams are to be seen interleaved Fic. 14.—Sketch of cliff on Minnesota coast, showing penetration of fissures of amygdaloid by sandstone. with the melaphyr, and on the shore of See. 32, T. 54, R. 9 W., two and a half miles above the mouth of Gooseberry River, is a remnant of a porphyry-conglomerate—the pebbles small, usually less than one-eighth of an inch across, and subangular—with abundant calcareous cement. A very few narrow dikes, much like those of the Lester River Group, were observed cutting the layers of the Agate Bay Group. One of these is to be seen on the shore of Sec. 34, T. 51, R. 13. W., two miles below Lester River. It corresponds in trend with the bedded rocks which it cuts, but lies at right angles to the dip. It is composed of a dense black rock, which has not been examined microscopically, is very strongly and closely cross- jointed, and is only a foot wide. A very prominent dike, five feet wide, is seen in the cliff on the shore of Sec. 15, T. 53, R. 10 W. Fig. 15 shows the occurrence of this dike, which is composed of a very fine-grained, black, luster-mottled melaphyr, the thin section of which looks much like that 294 COPPER-BEARING ROCKS OF LAKE SUPERIOR. of the Greenstone of Keweenaw Point. It consists chiefly of very fresh augite in relatively large areas, inclosing numbers of tabular plagioclases (an- orthite), and having in the inter- spaces, which are chiefly occupied by the same tabular plagioclases, many small altered olivines and ' particles of magnetite. The dike is strongly cross-jointed, save at the edges, which are traversed by joints parallel to the walls, and are com- posed of an aphanitic rock, much altered to chlorite. The rocks tra- versed are the usual stratiform Fic. 15.—Dike traversing stratiform amygdaloid and amygdaloid and columnar mela- columnar melaphyr, two miles below Lester River, Minnesota coast. phyr of the Agate Bay Group. Equivalents of the Duluth, Lester River, and Agate Bay Groups at the east end of the Minnesota coast—At the eastern end of the Minnesota coast there intervenes, between the Huronian slates and the base of the Beaver Bay Group, which next overlies the Agate Bay beds, a space only three and a half miles wide, measured at right angles to the east and west strike. With the flat dip prevalent in this region this width cannot include a total thickness of more than 3,000 feet, while at the Duluth end of the coast there lie between the same horizons the whole of the Duluth, Lester River, and Agate Bay groups, a thickness of some 9,000 feet; not to speak of the Duluth gabbros, which must add several thousand feet more. Forty miles west of Grand Portage, however, about Brulé Lake, in T. 63, R. 2 W. and R. 3 W., the gabbros are present in full force, while between them and the lower limit of the Beaver Bay Group there is a width of 10 miles, within which space, supposing the dip to be not more than 10°, a figure which the observations along Cascade River show to be closely right, there is room for a much greater thickness of the Duluth, Lester River, and Agate Bay groups. The small thickness on the lake shore near Grand Portage is probably to be ROCKS OF CASCADE RIVER. 295 assigned in part to actual thinning, such sudden thinnings being easily explicable when the rock layers are nearly altogether of eruptive origin; but also, in part, to some non-conformity with the underlying slates. How- ever, the whole question of the way in which the Duluth, Lester River, and Agate Bay groups extend to the eastward is one which will have to be further studied in the interior along the various rivers entering the lake— especially along Brulé, Cascade, Poplar, and Temperance rivers. Cascade River was examined by Messrs. Chauvenet and McKinlay above Sec. 26, T. 62, R. 2 W., but this was not far enough down stream to determine the existence or non-existence here of the Agate Bay beds. The first rocks met with by Mr. Chauvenet on the Cascade were found just where he first struck the river in Sec.'26, T. 62, R.2 W. Here, for about half a mile, there are exposed in the bed and on the sides of the river, beds of a dark-gray to reddish-brown aphanitic rock with conchoidal fracture, much like some of the dense brown rocks of the Lester River Group. The only thin section made showed a diabase-porphyrite, composed chiefly of minute tabular plagioclases with a good deal of a matrix which shows but a feeble, flickering light when revolved between the crossed nicols. These rocks are quite plainly bedded, dipping southward at about 9°. In places they seem to show a subordinate structure parallel to the bedding, while most exposed surfaces are so weathered as to fall in showers of small frag- ments when struck with a hammer. One or two vesicular layers were noted, the vesicles smooth-surfaced, elongated, one-sixth to one-fourth inch in length, and either empty or lined with drusy quartz. Continuing the ascent of Cascade River, no more exposures were found until reaching the falls in section 10. In the vicinity of these falls the rocks succeed one another in the following descending order: (1) dark-gray very fine-grained rock, resembling the fine-grained diabases of the Duluth and Lester River groups, not examined under the microscope; (2) brick-red quartz-porphyry; (3) medium-grained, black gabbro or luster-mottled mel- aphyr. The last rock forms the barrier over which the river falls. Five hundred feet above the falls comes in a medium-grained, brownish-gray orthoclase-gabbro, the thin section of which resembles closely that of the peculiar orthoclase-gabbro of the Lester River Group seen largely exposed 296 COPPER-BEARING ROCKS OF LAKE SUPERIOR. on the west line of See. 28, T. 51, R. 13 W. Itshows labradorite, orthoclase, pale-greenish-brown augite—often in twinned blades—titaniferous mag- netite, apatite and a good deal of secondary quartz. The next rock noted was half a mile up stream at the 40-foot fall, which is somewhere near the southern part of Sec. 11, T. 62, R. 2 W. These falls are over a very fine- grained, grayish-brown rock, resembling the predominant gray diabases of the Duluth Group. There are strong appearances here of a southern dip at an angle between 10° and 15°. Above these falls for three-fourths of a mile the river is expanded into a lake; then comes another fall over the same compact, gray rock, which is exposed also above the falls on a large scale. The thin section of a specimen taken from the bed of the river above the falls bears out completely the external resemblance to the Duluth gray diabases. For a mile above this fall the river is again a lake, at whose upper end are again exposures of a fine-grained, gray to black rock, with luster-mottlings one-eighth inch across. The prevalence among the rocks of the upper Cascade of fine-grained diabases closely resembling those near Duluth and Lester River; the occur- rence among them also of quartz-porphyry, coarse-grained black gabbro, and of the peculiar orthoclase-gabbro with augite twins; the nearly com- plete absence, so far as observed, of amygdaloids; the geographical posi- tions of the exposures with regard to the older rocks about Brulé Lake and Eagle Mountain, and the newer ones on the lake coast—all combine to render it highly probable that we have here to do with the eastern exten- sions of the Lester River and Duluth groups. The exposures at the eastern end of the Minnesota coast between the base of the Beaver Bay Group and the Animikie slates are unfortunately not continuous, having between them long beaches. The base of the Beaver Bay Group intersects the shore about six miles above Portage Bay Island. Below here for about a mile were observed numerous exposures of a very dense brown, conchoidally fracturing rock, which is plainly bedded, and dips 8° to 10° south, with a due east and west trend, the rock appear- ing in a series of eastward projecting points, which make an angle with the lake shore of about 45°. The layers are distinctly columnar, and are often much shattered by close jointing, which in places is almost like a slaty cae ie 4 — ROCKS OF PORTAGE BAY ISLAND. 297 structure, the rock coming out in thin slabs. The intervening beaches are presumably occupied by amygdaloids. This compact rock resembles, both externally and beneath the microscope, some of the conchoidally fracturing layers of the Agate Bay Group (as for instance that above described as occurring on the shore near Silver Creek, Sec. 22, T. 53, R. 10 E.), and also some of the layers of the beds of the Duluth and Lester River groups. Below these brown rocks no exposures were found for about a mile, when, four miles above Portage Bay Island, dark-gray, fine-grained diabase pseud-amygdaloids alternate with amygdaloids in which the matrix is dark gray and the amygdules rather sparse and large and chiefly of stilbite and calcite. Similar rocks are seen again after a long beach, at about three miles above Portage Bay Island. After this another long beach intervenes, beyond which there is first a low, irregular exposure of a coarse-grained black gabbro, which is possibly a dike, and then, just at the west point of Grand Portage Bay, dark-gray, medium-grained diabases with amygdaloids like those just described. These gray diabases and amygdaloids are not much like anything else seen on the Minnesota coast. On Portage Bay Island still lower rocks are visible. On the northeast corner of the island are the uppermost beds of the Animikie Group, seen near the water’s edge. Overlying these beds, and forming the mass of the island, is a considerable thickness of an aphanitic black rock, which under the microscope appears to be made up chiefly of augite in aggregations of rounded grains and magnetite particles. The plagioclases are subordinated to the feldspars in quantity, the proportion varying in different sections. Fic. 16.—Generalized section of Portage Bay Island, Minnesota coast. Some sections show more or less of an isotropic material penetrated by minute plagioclases, as in the matrices of many of the amygdaloids. Other sections show numerous chlorite pseud-amygdules. In one place near the 298 COPPER-BEARING ROCKS OF LAKE SUPERIOR. eastern point of the island this rock was seen weathering out into little spheroids usually under half an inch in diameter. These black rocks are somewhat peculiar, and although allied to the ashbed-diabases of the Du- luth Group, they differ in the very high content of rounded augite particles, in which respect this rock differs, indeed, from any other as yet examined from the entire extent of the Keweenaw Series. The uppermost rocks of the island are coarser grained, and include rather coarse olivine-diabases, and at least one bed of an orthoclase-gabbro which, in the thin section, looks just like that of Lester River. It is difficult to decide just how to correlate these eastern rocks with those near Duluth. It is evident that in a general way they resemble the rocks of the Duluth and Lester River groups. The resemblance to these groups of the brown and gray diabases of the coast above Portage Bay is very strong. On the whole, since the peculiarly characteristic stratiform olivine-bearing beds and associated shaly amygdaloids of the Agate Bay Group are not seen here at all, I am disposed to regard that group as having thinned out to nothing, and to divide the rocks that are seen here between the Lester River and Duluth groups, which must also, of course, have greatly thinned, if this reference is a correct one. Beaver Bay Group—The Beaver Bay Group was made out from the coast cliffs between Split Rock River and a point about two miles below Baptism River; from numerous inland exposures for five to eight miles back from the mouths of Beaver, Baptism, and Temperance rivers, and from the coast cliffs between Grand Marais and a point in the Indian reservation, about four and a half miles above the western point of Grand Portage Bay. This group is characterized by the great predominance of coarse-grained rocks, next in abundance to which are felsitic and quartziferous porphyries and granite-like rocks. Dense brown and gray diabases of conchoidal fracture occur to some extent, while amygdaloids and fine-grained diabases of the ordinary type, though rare, are not excluded. While the prevalent coarse-grained rocks of the group are plainly enough flows, exhibiting the usual flat lakeward dip, and while the same is clearly true of much of the porphyry, there are other places where there is BEAVER BAY GROUP. 299 much difficulty in determining the positions which these rocks occupy. Some of these places are difficult because, between the porphyries and the nearest bedded basic rocks, there are gaps without exposure, such as shingle beaches along the coast, and these gaps are either so long that the relations of the rocks can only be guessed at, or else they are so short that it is hard to see how one rock can pass under the other. So many of these cases proved tractable under further study that there remains but little doubt that in nearly all the porphyry would be found plainly enough to overlie or underlie the other rocks in a regular way. In yet other cases, however, vertical contacts between the two rocks were found, and while these con- tacts are in some cases demonstrably due to faulting, in others this is not so evident, and there are certainly places where the coarse-grained basic rocks look much as if intrusive, while the red granite-like rocks always present this appearance. Undoubted dikes occur cutting the por- phyries, and that much more frequently than in any of the preceding groups, but they are always of fine-grained rocks, unlike the associated coarse-grained kinds. The aphanitic, brown and gray rocks above referred to, as well as the rare amygdaloids and associated fine-grained diabases, are always plainly bedded. No rocks distinctly of detrital origin were observed in the group. On the whole, the group may be briefly described as made up of bedded coarse basic rocks, with interbedded fine-grained basic rocks, only rarely amygdaloidal, and also of interbedded acid porphyries in very irregular areas, which are individually limited in extent, contracting suddenly from several hundred feet in thickness to nothing. The whole group is much faulted; fine-grained diabase dikes are not uncommon, while gabbros and coarse-grained granite-like rocks are present in intersecting masses. The total thickness is probably understated at 6,000 feet. In describing this group more in detail, I find it most convenient to fol- low its exposures from west to east along the coast, taking the different kinds of rocks as they come. Beginning on the west, the basal bed of the group is a felsite, forming the bold point one and one-half miles above the mouth of Split Rock River. For some distance both east and west of the mouth of this river the rocks trend far around to the north, west of the river lying nearly 300 COPPER-BEARING ROCKS OF LAKE SUPERIOR. due north, and to the east of it changing gradually more towards the N. N. E. The coast line is trending here as a whole just about N. E., but subordinately it gives a number of long trends corresponding to the more northerly trend of the rocks, as shown in Fig. 17. Until this unusual amount of northing y Scale 1 mile to 2 inches. Fic. 17.—Sketch-map of rock exposures near Split Rock River, Minnesota coast, T. 54, R. 8 W. in the strike is realized the exposures in this vicinity are confusing. The following is the succession of strata roughly made out for some four miles along the coast in the neighborhood of Split Rock River. There are prob- ably some gaps in the succession, and the thicknesses given are only the roughest approximations. Nevertheless, the section in its general features is correct, and will well illustrate the nature of the lower beds of this group SECTION NEAR THE MOUTH OF SPLIT ROCK RIVER. 301 Feet. I. Red felsitic porphyry.—This rock shows finely on the coast two miles above the mouth of Split Rock River, where it forms a very striking red cliff 30 to 50 feet high. Close inspection of the cliff shows run- ning through it a sort of banding which is brought out by narrow whitish strings, and also by lighter and darker shadings in the general red color of the mass. These bands curve up and down in the most irregular manner; for a while they will seem to be nearly horizontal, and then will suddenly change to vertical, and indeed to all sorts of directions within a few feet. That they represent a fluidal structure there can be little doubt. There is no tendency to split parallel to this banding. Under the microscope the thin sections show a matrix closely resembling that of the quartz-por- phyry of the pebbles of the Calumet conglomerate of Keweenaw Point, figured on Plate XII, Fig.2. It presents a reddish splotehy appearance, the minute ferrite particles which give the color being very irregularly distributed; and appears to be made up largely of what Rosenbusch calls erypto-crystalline matter. With this are par- ticles which may be orthoclase, and a good deal of quartz, arranged in the peculiar ramifying way that characterizes the secondary quartz of the granitic porphyries. Scattered through this ground mass are numerous minute black particles. The porphyritice in- gredients noted are comparatively small crystals of orthoclase and oligoclase, no quartzes having been observed. On the lake shore ~ this porphyry has not been observed in contact with either the underlying or the overlying rocks, being separated from them by beaches. Two miles north, however, on Split Rock River, the con- tact with the underlying melaphyr is very nicely exposed. The dip here is to the east 18° to 20°, and several other observations along Split Rock River show the same eastern dip. At one point on the Split Rock River, about one and a half miles from the lake, the porphyry is cut by a dike, six feet wide, of a very fine dark- gray rock. The dike trends with the strata, nearly north and south, and dips at right angles to them, or 70° west. Thickness Of thissporphyry.]2 22 see ss cass 22 3 Soe see eee emseee 600-700 II. Ashbed-diabase and diabase-amygdaloid.—Several layers (not more than four) each with an amygdaloid, of a very dense, light-gray to dark brownish-gray, conchoidally fracturing rock, which, in the thin see- tion, shows tabular oligoclase (measurements on four different slices failing to find any angle above 25°); augite in aggregates of rounded particles; and magnetite, as the chief ingredients. In sections of the densest kinds there are areas which have little or no action between the nicols, and which appear therefore to be glass. More or less brown ocherous matter appears in the sections, the amount varying directly with the amount of brown tinge pre- sented by the rock macroscopically. Of the two amygdaloids seen, 302 COPPER-BEARING ROCKS OF LAKE SUPERIOR. one, which is exposed on the strike for several hundred feet at the foot of a cliff, on the first point above the mouth of Split Rock River, shows a weathered, greenish, earthy matrix, and rather sparsely scattered amygdules of laumontite. The other amygda- loid, seen on the face of the first point below Split Rock River, has a brownish, aphanitic matrix, and is so highly vesicular that the vesicles touch one another. These vesicles are small, very smooth- walled, elongated in a common direction, partly empty, but for the most part filled with amygdules of chalcedonic quartz, laumontite, or chlorite. These layers occupy a surface width, measured from west to east, of over half a mile, and must have a thickness, there- fore, of abileast S00 teetaes teem eer-eeee aia ae ere eet eee UI. Dark-gray to black gabbro.—This layer or series of layers forms the coast line for about a mile in the S. E. 4 of Sec. 6 and S. W. 4 of See. 5, T.54,R.8 W. The lower layers are rather fine-grained to medium- grained, dark-gray to nearly black, rough-textured, and marked by strong luster-mottlings. The thin section shows labradorites ar- ranged in curving lines, which are evidently the result of flowage. The augites are relatively large, and inclose each countless minute feldspars. The magnetite is unusually abundant, being so thickly crowded between the augites as to render these interspaces nearly black. Quite large fragments of the rock are raised by the magnet. Though olivines are generally present in these luster-mottled rocks, none could be detected here. This section is figured on Plate VIII, Fig. 4. Higher layers become coarser in grain, and of a rougher texture, with less marked luster-mottlings. In the thin section of this coarser rock the augites are strongly diallagic and still larger than the plagioclases, but not nearly so much so as in the previously described rock. They are usually fresh, though occasionally altered to chlorite. Good-sized olivines, partly fresh, but generally traversed by broad brown and green bands of alteration, are here abundantly present. Still higher up, near the top of these layers, the grain becomes quite fine again, but no thin sections have been examined. Near the middle of the 8S. E. 4 of See. 5, T. 54, R. 8 E., this gabbro is interrupted by a vertically placed mass of excessively coarse- grained anorthite-rock. The cutting mass is from 50 to 75 feet wide, and bears north and south. It shows on both sides of a little square-angled, rock-walled bay, on the south point of which it rises as much as a hundred feet above the lake. On both sides of the cutting mass the black gabbro is filled with large angular masses of the same coarse anorthite-rock. The included masses reach sometimes many tons in weight, and in some places predominate over the including gabbro, which then appears as if veining the coarser rock. At the west angle of the bay the included masses are nearly absent, and the gabbro resumes its usual vertically col- umnar appearance. At the north angle of the bay the anorthite- 800 SECTION NEAR THE MOUTH OF SPLIT ROCK RIVER. rock rises again to a height of over 150 feet. The inclusions of angular masses of the anorthite-rock in the gabbro indicate the more recent origin of the latter, and this conclusion is borne out by the thin section made from a specimen taken at its contact with the gabbro, in which the relatively fine gabbro surrounds the ends of the anorthite crystals, as the base of any porphyry does the por- phyritic crystals which lie imbedded in it. Since the strike is now trending somewhat more around to the northeast, and the dip at the same time flattening somewhat, this gabbro probably does not exceed in thickness Ssome....-............ Be erainisteteeiete sero tees IV. Ashbed-diabase and diabase-amygdaloid—The compact portions of this layer, which is a dark-gray or brownish-gray compact rock, macro- scopically like the rock of II, is largely exposed along the coast, in the N. E. 4 of Sec. 5, T. 54, R. 8 W., and See. 33, T. 55, R. 8 W. The overlying amygdaloid, which is seen at several points, has an aphanitic, dark-gray matrix, not unlike much of the compact rock below, while the amygdules are wholly of light pink laumontite lying in elongated, smooth-walled, closely crowded vesicles, aver- aging from ¢ to ? of an inch in greatest length. The amygdaloid is 26 feet thick, and the whole thickness of the layer probably not HIGIRS) UNE 5 .dc0n oboche pagb cbo UOC Hoe TE Gbcot oe aeoshoEsoarcomende V. Olivine-gabbro.—This gabbro is in sight, directly overlying the above de- scribed amygdaloid at several places along the shore of See. 33, T. 55, R.8 W. It is a medium-grained to rather fine-grained, dark- gray to black rock, much like that of III. The thin section shows numerous rather fresh olivines; large diallagic augites, often includ- ing many plagioclases (labradorite); and titaniferous magnetite. This layer shows a strongly marked columnar structure at right angles to the bedding, and in places the columns are even cross- jointed, so as to show a rude ball-and-socket jointing. In places also weathering brings out distinctly a spheroidal structure. At a projecting point in the N. W. 4 of the N. E. 4 of See. 5, T. 54, kh. 8 W., this layer is crossed by a mass of coarse white anorthite- rock similar to that above described, and in the vicinity the gabbro holds numerous angular masses of the anorthite-rock. Thickness OP HAS TENG, QW Gnas oe coou cocoon og eoobecocoEde We cobra teistee See VI. Red quartziferous porphyry.—The rock of this layer is to be seen at the point in the northern part of Sec. 33; T. 55, R.8 W. The thickness OP UNS JERE IEPA SOUS 66665 Sh cen noooGEcshon ocegus cosaco as acS HOS Total thickness of the section............-- EOOSUBS Seaaas 303 900 100 100 100 2, 600 The granite-like rock forming the end of this point may also be part of the last layer, and faulted down into its present position, but from its 304 COPPER-BEARING ROCKS OF LAKE SUPERIOR. crystalline character is rather to be regarded as an intersecting mass. This rock resembles closely in the hand specimen a moderately coarse flesh- colored granite, much more closely than the similar rock at Duluth. Large cleavage facets of pale flesh-colored feldspar make up most of the specimen, which shows also quite distinctly large quartz areas. There are also indefi- nite dark-colored patches of small size. Under the microscope, however, the rock is seen to be essentially the same as that at Duluth, from which it differs chiefly in its relatively small amount of ferric oxide. The section is almost entirely made up of feldspars (orthoclase with a little oligoclase) and quartz, which occur both in quite small and quite large areas relatively to the feldspars. All of these areas are, however, included within the feldspars, never filling corners between them as with true granite; and since many areas polarize together within the mass of one or more feldspar crystals, it is evident that the quartz is all Jater than the feldspars, i. e., either secondary to them, or filling spaces left in them by some solving process. From the last point noted in the foregoing section (near south line of Sec. 28, T. 55, R. 8 W.), to the red rocks of the south point of Beaver Bay (S. E. 4, Sec..12, T. 55, R. 8 W.), a distance of eight and a half miles, the only rock noted was a very dark-gray to black diabase or gabbro, now olivine-bearing, now not, always very highly augitic, and often showing a very coarsely nodular weathered surface, resulting from the resistance to weathering of the very large augites. Usually the exposures are low lake- ward-dipping surfaces; but in the N. W. 4, Sec. 27 are cliffs of the black rock 150 feet high. A rude columnar structure is often visible. For a while the high dip, 18° to 20°, is continued, but more to the south of east than before, and soon it flattens, and the trend becomes more nearly parallel to the shore-line. At Beaver Bay a red granite-like rock and a quartziferous porphyry suddenly appear again among the black rocks. The occurrences are very interesting, and much like those described as presenting themselves at the close of the above detailed section (N. E. 4, Sec. 33, T. 55, R. 8 W.), but more difficult to reduce to order. Fig. 18 is a sketch map of Beaver Bay, show- ing the exposures of the different rocks. The common black rock of the vicinity, as seen for instance along the ROCKS OF BEAVER BAY. 305 bed of Beaver River, and on the south point of Beaver Bay, is the same as that already described as showing for some miles along the coast above Beaver Bay. It is a moderately coarse, very dark-colored, and often nearly black, very highly crystalline rock, in which the three common ingredients— augite, anorthite, and titaniferous magnetite—can often be seen with the naked eye. The very dark color is due to the great abundance of the augitic ingredient, which, while commonly subordinate to the plagioclase x g % Sip ~ : Ushbed- diibase and granitic porphyry. LAH Orthoclase= (boro weitle Tine - 3 A | olivine a ro and telsite Y lf ji / al [ | Fic. 21.—Section of wall DE of Fig. 20. of plainly bedded fine-grained diabase, laumontitic amygdaloid, and luster- mottled melaphyr. These are terminated by a narrow ravine 15 feet wide and 100 feet deep, the east face of which is made up of the pink felsite which forms the rest of the point. This face is beautifully slicken-sided, being polished in some places to a glassy surface, and marked from top to 312 COPPER-BEARING ROCKS OF LAKE SUPERIOR. bottom by grooves and striz inclining 5° to 15° away from the vertical, towards the north. The red rock of this wall and of the rest of the point is a pink to purple felsite, often showing many lines of a lighter color than the rest, and seamed with strings and veins of calcite. The bedded dia- bases and amygdaloids of the bay seem to have been let down by faulting into their present position between the two walls of red rock. Beyond this bay to the northeast the felsite of its northern point forms the lake coast for about a mile, in which direction it presents a very dis- tinct and rather low southeastward dip (15°) with a trend more around to the north than that of the lake coast, so that new layers succeed each other somewhat quickly, and the total thickness of the felsite mass must be very considerable. The general southeastward dip has at times superinduced upon ita bowing, by which for short distances the rock will appear to plunge underneath the water at a high angle. Calcitic veins, and at times a gen- eral calcitic decay, affect the rock in many places, but much of it is with- out the calcite. Where the flat lakeward dip is plainest there is often a well- marked columnar structure at right angles to the bedding. At one point on the shore of the 8. W. 4, Sec. 28, T. 56, R. 7 W., this felsite presents somewhat interesting appearances. The ledges here are very large, forming a cliff 20 feet high for a distance of many hundred feet, with broad surfaces shelving into the water at an angle of about 15°, and affected by a strong columnar cross-jointing. The rock of the upper lay- ers is aphanitic, but of a rough texture and a flesh color. Thickly dotting it are very fine, dark-colored, hair-like lines, forming curves and curls of various forms, the whole appearance suggesting strongly that of a thin sec- tion of some modern rhyolite or of some glassy rock with hair-like bodies.’ Under the microscope this rock is seen to have a matrix which is completely saturated with quartz, in the ramifying and network forms which indicate a secondary origin. The original matrix appears to have had some minute feldspars, but much of it seems to have been without crystalline structure. The hair-like bodies resolve themselves into linear clusters of red and black particles of ferrite, which I take to be the alteration-product of some orig- inal constituent, either crystalline or unindividualized. They are certainly ‘Compare Zirkel, Microscopical Petrography, Plate VII, Fig. 1, and Plate IX, Fig. 1. é THE BEAVER BAY GROUP. 313 not products of infiltration like the so-called dendrites, since they run through and through the mass of the rock. They appear to me to furnish one more point of resemblance between the ancient felsites and quartz- porphyries and the modern rhyolites, and are another proof of the erup- tive origin of these rocks. Yet another proof of an eruptive origin is furnished by the rock of the Fic. 22.—Flowage structure in felsite, Minnesota coast. lower layers of this cliff. There are here large surfaces hundreds of feet square in which a fluidal structure may be seen on a large scale. Light- colored, pale-pinkish felsite and dark-brownish felsite are twisted together in various curling and snake-like forms; the mass as a whole dipping, as usual, 15° to the southeast. The contrast between the colors is very strong. The lighter material is the most abundant, and includes the darker. Fig. 22 represents an area of 20 by 28 inches. Some of the dark-colored bands are a foot or two in length and an inch to three inches in width, from which 314 COPPER-BEARING ROCKS OF LAKE SUPERIOR. size they run down to mere threads. The brown bands themselves are often streaked with lines of the lighter kinds. Under the microscope both light and dark kinds are seen to be felsites with a quartz-saturated base precisely like that of the rock of the upper layers above described, and to differ from each other only in the amount of red, black, and brown ferrite particles con- tained. The ferrites are not arranged in lines as in the peculiar rock of the upper part of the cliff. Beyond this point the felsite continues to be the coast rock through section 28, but in the northeastern part of this section, and the southeastern of section 21, it becomes involved with a black diabase, the diabase first ap- pearing to intersect it, and then to become peculiarly intermingled with it in irregular areas. Finally the black prevails, with here and there a vein of the red, forming one of the usual rudely columnar flows of moderately coarse black diabase. These confused rocks, which were not examined thoroughly enough to warrant further description or conclusions, terminate at a shingle beach in the bay above the Great Palisades. The rock exposures about the Palisades are of the greatest interest, because of their bearing on the question of the relation of the acid and basic flows of the series. Since we have here a great flow of quartz- porphyry unmistakably overlying a succession of plainly-bedded fine- grained diabases and amygdaloids, it follows that all idea of the greater antiquity of the acid as compared with the basic rocks of the Lake Supe- rior region must be abandoned. This is a conclusion clearly indicated in all parts of the Keweenaw Series, but the exposures are here so fine and so unequivocal that I have described them already in some detail in con- nection with the general part of this report. The description need not be repeated here, but a few details may be added. All along this part of the coast the layers are trending more and more away from the coast line towards the north, as a result of which the harder rocks form points pro- jecting towards the southwest. Two of these points, both formed of quartz- porphyry, are shown on the accompanying sketch-map. They are the Great Palisades and the bold point just below the mouth of Baptism River. Each has a shorter side trending east and west, and a longer side trending well THE GREAT PALISADES OF THE MINNESOTA COAST. 315 around to the north, longer in the latter case than the former because of the increased amount of northing in the courses of the strata. % S Scale 12xm1le to 2 inches. Fig. 23.—Sketch-map of exposures in the vicinity of Baptism River, Minnesota coast. The south side of the Palisade Point shows the following section. A of this section is an amygdaloid, with dark-brown aphanitic matrix, just rising from the beach and here and there capped by a thin seam of red detrital matter. B is a flow-bed made up of 50 feet of massive, cross- a6 COPPER-BEARING ROCKS OF LAKE SUPERIOR. columnar, fine-grained, chocolate-brown, semi-conchoidal diabase, with sparse laumontite and calcite amygdules increasing in number above, and AG Ios. ay ot Sl eel [7 Th, a Phd Le 4 Co l = A ee WA My) pitied ALY Watley lire Fic. 24.—Section on south cliff of the Great Palisades, Minnesota coast. A, amygdaloid; B, columnar diabase-porphyrite; C, mingled amygdaloid and detrital matter; D, columnar diabase-por- phyrite; E, amygdaloid; F, quartz- porphyry. 6 feet of true amygdaloid, of which the upper 3 feet is highly vesicular. C is a thin seam (6 inches) of mingled amygdaloid and detrital matter. D is another great flow of diabase, made up of 1 foot of basal amygdaloid or vesicular portion, 30 feet of massive cross-columnar diabase, as above, the sparse amygdules gradually increasing in number upwards, and 10 feet of true amygdaloid (E) growing more and more vesicular upwards. The compact diabase of these beds belongs with the diabase-porphy- rites, the augite being a quite subordinate ingredient, while there is often much non-polarizing matter. A specimen from the upper bed yielded 47.9 per cent. of silica. In the upper or amygdaloidal portions of these beds are scattered small hard red patches, a few inches across. At times these patches are round, and appear at the first glance somewhat like the pebbles of a conglomerate, but they are more often irregular and are mingled curi- ously with the surrounding diabasic material. Some of the apparently rounded particles are plainly seen, even by the naked eye, to fill original vesicles, often of relatively large size, and in these cases are either on the outer wall of the vesicle with calcite within, or have between them and the wall a lining of calcite and laumontite. In the thin section this material is easily seen to be fragmental, being composed of subangular quartz grains, with some reddish interstitial matter. It is possibly this reddish matter that has caused Norwood and Win- chell’ to speak of the existence here of conglomerate and breccia rocks, 1 Owen’s Geological Survey of Wisconsin, Iowa, and Minnesota. Philadelphia, 1852, pp. 259, 362- 364. Seventh Annual Report of the Geological and Natural Hist. Survey of Minn., p. 10. THE GREAT PALISADES OF THE MINNESOTA COAST. 31% which I myself failed to find. All I could find was a series of plainly- marked flows, with massive columnar lower portions and upper vesicular portions as strongly developed as anywhere in the typical region of Ke- weenaw Point. The red detrital material appears to me to always occupy the open spaces of the scoriaceous upper portions of the lava flows. In the thin section it is invariably sharply defined from the matrix, which always presents the usual appearance of the diabase-amygdaloids. ‘The whole occurrence is closely like that of the ashbed rocks of Keweenaw Point, both as to the curious intermingling of scoriaceous amygdaloid and detrital material, and as to the peculiar kind of diabase forming the lower portion of each flow.’ Above these beds comes the mass of quartz-porphyry which forms the Great Palisades. The entire thickness of this porphyry is over 300 feet, but in the section under description only some 50 to 75 feet are in sight. The base of this mass of porphyry presents a most peculiar appear- ance. For a thickness of some 5 feet it is much weathered, and calcified— the contact line of the dissimilar rocks having evidently been the course of altering waters—and shows a strong appearance of contorted lamination, which is often intensified by the calcitic alteration. This peculiar alteration is the same as that which affects, in a less prominent degree, higher portions of the mass, as is very distinctly seen in the thin section. The feldspar crystals are found following the curving lines and again obstructing them. The quartzes are much smaller than the feldspars, and are in the usual doubly terminated crystals, with embayments of the matrix. There are also contained in the quartzes fine glass inclusions, in regular shapes cor- responding to those of the containing crystal, and affected by a hair-like devitrification. Figs. 11 and 12 of Plate XIII represent this laminated por- phyry, and Figs. 3 and 4 of Plate XII, the rock at the northeast end of the Palisades. All of these figures represent those portions of the rock which show the flowage structure most plainly. The columnar char- acter of this rock is very noticeable, and is of especial interest, since a 1Jt should be repeated here that both Norwood and Winchell regard the amygdaloids, the diabases that go with ‘them, and all of the felsitic porphyries as altered sediment. Compare Eighth Annual Report of the Geological and Natural History Survey of Minnesota, p. 26. 318 COPPER-BEARING ROCKS OF LAKE SUPERIOR. columnar structure is far less common in rhyolitic rocks than in basaltic.’ The columns are peculiar. The intersecting joints do not lie at the same angle with the vertical, but incline slightly toward each other, so that they intersect in depth. This is especially well seen on the south side of the Palisades, and is roughly indicated on the accompanying figure. Of all of the quartz-porphyries of the Lake Superior basin the Pali- sade rock presents the strongest appearance of sedimentary origin, on ac- count of the lamination it shows, especially in its lower portions. This lamination presents great irregularities, but in places, while changing many degrees in inclination within a few feet, it preserves for quite long distances the same general direction. Nevertheless, as shown in a previous chapter, this rock, like all the other porphyries of the Lake Superior basin, is of eruptive origin, and the lamination is that which often characterizes felsitic porphyries and rhyolites the world over. A mile and a half above its mouth, in the S. E. 4, Sec. 10, T. 56, R. 7 W., Baptism River makes falls over a quartziferous-porphyry much like that of the Palisades. rom its position it appears not impossible that this rock belongs to the same belt with that of the Palisades. Below the Palisades for about a mile the coast is formed of a coarse, black, very highly olivinitie gabbro, with strongly marked vertically columnar structure. The diallages are large, producing a nodular weath- ering, and often show a shining metallic cleavage surface. The vertically columnar structure of this rock renders it evident that we have here to do with a flow and not a dike, from which it follows that there must be a fault between this rock and that of the Palisades, it being so different from the beds which belong beneath the Palisade porphyry. Beyond this rock again, and separated from it by a short beach, comes in a fine-grained, dark-brown ashbed-diabase with highly vesicular amygdaloids, the vesicles elongated in a common direction. After a short beach of only 20 paces, this is re- placed on the shore by a purple felsite, behind which it passes, forming the bed-rock of Baptism River a short distance above its mouth. At the mouth of this river the purple felsite is the cliff rock, and at E is faulted against 'See illustrations to Clarence King’s 40th Parallel Report, vol. i, plate xxi, and vol. ii, plate xxiii. ROCKS NEAR THE MOUTH OF BAPTISM RIVER. 319 fine-grained diabase and amygdaloid, which in turn pass, with a steep dip, underneath the quartz-porphyry of the bold point C. The rock of the latter point is precisely the same as that of the Pali- sades. It shows the same violet-tinted base, the same quartzes with glass inclusions, the same very abundant orthoclases, the same strongly columnar structure, and the same lamination. Here, however, the lamination shows much less tendency to confine itself to one direction, and therefore is less likely to be mistaken for sedimentary lamination. The point as a whole shows a very distinct dip to the eastward, and yet on the long face C D, parallel to the trend, where the laminze should look horizontal, were the rock a sedimentary one, they wander up and down in a wholly aimless manner. At the point D, where this rock ends on a small beach, its lamine dip 60° S. 65° W., while just beyond across the beach they dip 80° north of east. Here the porphyry is highly charged with calcite, which has impregnated it in cross seams, and along the lamination, and in places there is a general calcitic decay, large white pseud-amygdules of calcite dotting the rock. At D F of the map of Fig. 23, this porphyry passes beneath plainly bedded diabases and amygdaloids. This horizon I have selected as the base of the Temperance River Group. The close similarity of the Palisade porphyry to that of the point just below Baptism River, and of the diabases immediately underlying these porphyries to one another, suggest that the two points are but portions of one layer faulted apart. Beyond the point last described, in descending the coast, the Beaver Bay Group strikes back into the country, having between it and the shore a constantly widening strip of the beds of the Temperance River Group. The exposures, by which has been made out the continuance, in this region, of the Beaver Bay Group, until it emerges again on the shore at Grand Marais, do not merit any particular description. They are the usual steep- backed ridges, with flat lakeward slope, composed of the common black gabbro. The exposures below Grand Marais which I have referred to the Bea- ver Bay Group may also be more rapidly passed over. The dips here are not more than 8° to 10° lakeward, and the trend much more to the east 320 COPPER-BEARING ROCKS OF LAKE SUPERIOR. than that of the shore, being at times even due east. Since the coast line itself is trending here only some 20° to 25° north of east, it follows that each bed makes a yery long exposure on the coast. Felsite and quartziferous porphyry have a great development between Grand Marais and the Brulé River, the ledges on the coast being usually comparatively low and often partly concealed by shingle beaches. On the Devil’s Track River, how- ever, the exposures are on a grand scale. Quartziferous and granitic porphyries show again in the vicinity of the large bay in the east part of T. 62, R. 4 E., and again at Red Rock Bay in the Indian reservation (S. E. 4, T. 63, R. 5 E.). The remainder of the coast between here and Grand Marais is formed chiefly of coarse black gabbro. In the angle of the coast immediately below Grand Marais, 8S. W. 4, Sec. 21, T. 61, R. 1 E., red felsite is cut by dikes of dark-colored rock, and the same thing recurs for two or three miles down the coast, the dikes pro- ducing projecting points and the felsite weathering down into shingle beaches. The shore-cliff just beyond Grand Marais is red felsite for a length of sev- eral hundred paces in a northeasterly direction. At the southwest end of the cliff is a broad dike composed of a medium-grained olivine-diabase, of which the surface presents a mottling like that of the luster-mottled mela- phyrs. The olivine is wholly altered to a brownish substance, but the other ingredients are quite fresh. Near its junction with the red felsite this rock becomes finer in grain, until at the contact it merges into an aphanitic dia- base-porphyrite, with much greenish alteration chlorite. At the northeast end of this cliff is another broad dike of similar char- acter, with two or three narrow ones, from a mere seam to one or two feet in width. The rock of these narrow dikes is a dense diabase-porphyrite with much non-polarizing matter in the base. The felsite cut by these dikes presents a quite distinct, though irregular, dip towards the lake, and has the usual wave-like pseudo-lamination markings. It presents the appear- ance of a hardened mud rock more here than at most points where the felsites were observed. In the thin section is shown a base with much non- polarizing material, with the usual ferritic devitrification-product, and much BEAVER BAY GROUP BELOW GRAND MARAIS. Ba | arborescent and netted secondary quartz. Calcite seams permeate much of the rock, and, in many places, the weathering has so affected it that a slight blow of the hammer on the face of the cliff will bring down showers of angular fragments. This peculiar result of weathering is very charac- teristic of the Lake Superior red felsites. The large exposures of red felsite on the Devil’s Track River have already been alluded to. From the mouth of the river nearly to the north line of See. 3, T. 61, R. 1 E., the exposures are almost continuous and the cliffs occasionally rise to a height of 150 feet. There is often an appear- ance of lamination, and across these markings a strong columnar struc- ture is frequently seen. The thin section shows the usual non-polarizing base, with ferrite particles and net-worked secondary quartz. Below the Devil’s Track are long beaches of felsite shingle. In See. 9, T. 61, R. 2 E., typical brown ashbed-diabase and diabase-porphyrite form the shore, and at one point show a capping mass, five feet thick, of curi- ously intermingled sandstone and amygdaloid. From this point to the mouth of the Brulé River red shingle beaches are interrupted occasionally by exposures of brown and red diabase-porphyrite. Many ledges show no macroscopically visible porphyritic ingredients, but are porphyrites because of their content of non-polarizing base; others show numerous large por- phyritic oligoclases and augites. In the groundmass in some slices more or less secondary ramifying quartz is seen, when we have a transition to the rock recognized in the pebbles of the South Shore conglomerates as a non-quartziferous porphyry. Below the Brulé, coarse olivine-gabbro forms the coast for a number of miles, lying in flat, often cross-columnar flows. Just below the mouth of the Brulé this rock is peculiar, on account of its great richness in brassy- lustered diallage and its very large olivines, which are sometimes one-fourth to one-third of an inch across, and always altered to a black, resinous-looking substance with a concentric scaly structure (hyalosiderite). Below the large bay in the northeast part of 'T. 62, R. 4 E., these coarse rocks are interrupted by beaches with detached ledges of dense, brown diabase-por- phyrite. One exposure, near the west line of See. 12, T. 62, R.4 E., shows a red crystalline rock, which macroscopically presents a mass of red feldspar 21L 8 322 COPPER-BEARING ROCKS OF LAKE SUPERIOR. crystals, marked in places by a network of black lines. Under the micro- scope this rock turns out to be composed entirely of crystalline matter; reddened oligoclases and orthoclases, completely saturated with secondary quartz, making up most of the section. The black markings mentioned resolve themselves into altered augite blades, with whose alteration is con- nected the production of much magnetite. Numerous large apatite needles are included. Below the mouth of the river forming the western boundary of the Indian Reservation, coarse olivine-gabbro forms the coast as far as Red Rock Bay, a distance of some five miles, lying in beds with cross-columnar structure, flat lakeward dip, and easterly trend. In many places this rock shows in a marked manner the luster-mottling due to the presence of rela- tively large diallages, including many feldspars. At Red Rock Bay, in the Indian Reservation (southeast part of T. 63, R. 5 E.), these black rocks give place again to red felsite and quartziferous porphyry. The display of these acid red rocks here is very large and among the most interesting of this class of rocks in the Lake Superior region. The red rock at the bay is commonly atrue quartziferous porphyry, with a base in which much non-polarizing matter is mingled with the usual ferrite particles, and saturated with arborescent secondary quartz. On the high point of red rock in the bay, areas of a slightly differently colored rock are included in the general red mass. Under the microscope the rock of these areas shows a base in which quartz and orthoclase are distinctly individu- alized in good-sized particles, The bold red bluff from which the bay takes its name shows no trace of banding, but at the point beyond the bay the curving and twisting pseudo-lamination so often seen in these red porphy- ries is shown on a large scale. For short distances the rock will appear like a much-contorted schist, and then again will pass into the general structure- less mass. When seen, the banding is as often vertical as horizontal. In this vicinity the red rock is cut by a heavy dike, of which part is represented in the accompanying figure. This dike shows for several hundred feet along its length, and with a width of some 75 feet. The junctions with the adjoining rock are sharp, occasionally showing irreg- ularities, as in the figure. In places patches of red rock clinging to the top i TEMPERANCE RIVER GROUP. 323 of the dike suggest that we have here its original top. The rock of the dike is a very dense, dark greenish-gray diabase-porphyrite, with a tendency to become somewhat coarser in the middle. The silica content of this dike- rock is very low, being only 45.88 per cent. The whole dike is intersected by two sets of very strong transverse joints, which dip respectively S 134° and E. 694°. These are cut by others parallel to the walls of the dike and Piz sey ee Se ZA OS S = bse lt7™~ zit Fee | aby. 7s ~—7 a >i LU: pp aaron | DF REE NY SE TIC zis ts USAIN IN DS A SF ENIRCIN NURS / ify [el L~— SOIR SATIN NR COPS ISS RNS, as LOSE N TG Se LSE ISS ENE NTI Pee . ~¢~5 ge esse ANNE A/S SSNS Bee BS Sig ee aS SSN Ea Sy [a BG i ay SIN es ae ae Fia. 25.—Dike in quartz-porphyry, Red Rock Bay. the whole mass looks much like a pile of books. About one-fourth of a mile farther down the coast another dike, of more completely crystalline diabase, cuts the red rock, which soon after ends, being replaced by the rocks which I have already described in connection with the Duluth and Lester River groups. Temperance River Group.—The rocks of this group are displayed along the coast from a point a mile and a half below the mouth of Baptism River to Grand Marais, a total distance of some 50 miles. The total thickness appears to be upwards of 2,000 feet. The highest beds of the group form the coast between Petit Marais and Temperance River. As already described, the beds of this group, where they first appear in descending the coast, just below Baptism River, trend sharply to the north, and even due north for a while, after which they swing around more to the east of north, the coast line and strata trending together for a long distance. The easting in the trend of the layers continuing to increase at about two miles below Temperance River, they finally begin to trend more to the east than the coast line, so that from this point to Grand Marais, 324 COPPER-BEARING ROCKS OF LAKE SUPERIOR. where the base of the group comes to view, there is a steady descent in geological horizon. The usual lakeward dip, of course, holds throughout the extent of the Temperance River Group. The angle ranges from 6° to 30°, and on the whole the inclination, especially in the western portion, is rather greater than usual. In its kinds of rock the Temperance River Group, on the whole, con- trasts strongly with the preceding one; indeed, with all of the Minnesota shore groups, except the Agate Bay Group, with which it has some charac- teristics in common. The rocks forming the greater part of its thickness are dark-brownish, fine-grained diabases of the ordinary type, in thin layers, with strongly developed vesicular or amygdaloidal upper portions, and often with a more or less plainly marked columnar structure in the lower por- tions. Much less common, but still occurring in a number of layers, are fine-grained, blackish olivine-diabases or melaphyrs, with the typical luster- mottlings. They are also furnished with amygdaloids. Layers of ashbed- diabase and diabase-porphyrite of conchoidal fracture, and furnished with amygdaloids, also-oceur, especially toward the base of the group. Several seams of reddish sandstone and shale are included, one layer exceeding 200 feet in thickness. Peculiar conglomerates also occur. The whole suc- cession presents much the appearance of some of the layers in the middle and upper portions of the Keweenaw Point series. The prevailing diabase and melaphyr of this group do not merit any especial description here, since they are only repetitions of what have already been described in full for other parts of the extent of the formation. They make many very interesting exposures, among which may be mentioned as especially fine those of the shore of sections 36 of T.57, R. 7 W., and sections 30 and 31 of T.57, R.6 W.; that of the mouth of the Manitou River; and that of the point on the east side of Pork Bay, where may be seen a black luster- mottled olivine-diabase or melaphyr, which, under the microscope, shows all the characters of this rock as found in the typical region of Keweenaw Point. Another fine exposure is that of the bay in the 8. W. 4, Sec. 21, T. 58, R. 5 W., where quite a succession of diabases and amygdaloids is in sight, including one or more beds of luster-mottled melaphyr. Those of the ROCKS AT MOUTH OF TEMPERANCE RIVER. 325 “Two Islands,” which are columnar rocks with the outline of Fig. 26, and of the mouth of Temperance River, are also very instructive. Fic. 26.—Profile of island at mouth of Two Islands River. The last-named place is possibly the most interesting of all. A short distance from its mouth the river makes several falls, the first one into, the rest along the course of a narrow gorge, which sometimes reaches 50 feet in depth, but is so narrow that in places one can step from one to the other of the overhanging walls. The gorge is a succession of well-smoothed pot- holes broken into each other. There are displayed here a number of very thin layers, the massive columnar portions often not exceeding two to four feet, and the very strongly developed amygdaloids running even below these figures. A number of these beds have very plainly marked basal amygdaloids, with relatively sparse spike amygdules. At two or three hori- zons, streaks of red sandy shale were noticed between one of these amyg- daloids below and a massive layer above. The detrital matter is often in mere films, and at times is entirely absent. In places it is found to have aggregated in irregularities of the underlying amygdaloid, when for a short Fig. 27.—Section on Temperance River. distance it may have something of a thickness. This is finely displayed on the northeast side of the basin at the mouth of the river, as shown in the following section, which represents a wall some 80 feet long and 20 326 COPPER-BEARING ROCKS OF LAKE SUPERIOR. high. The whole appearance at this place reminds one strongly of the alternations at the upper falls of the Montreal, on the South Shore,’ save that the beds are thinner on Temperance River than on the Montreal. The peculiar irregularities to which these eruptive rocks are subject were well seen in a cliff side below Temperance River, where ‘ Fig. 28 was drawn. The ashbed-diabases of this group are only met with at low horizons, being found on the aa coast not far below Baptism River, and again at Grand Ma- rais. Immediately overlying BLY. the quartzose-porphyry of the > Lees Beaver Bay Group, C of Fig. Perse -) NS : : Ne fe 23, is found the succession indicated in the following dia- Fig. 28.—Section on Minnesota Coast, near Temperance 2’am (F ig. 29), in which the River. The columnar portions are the lower massive por- * A = tions of the flows; the dotted parts the amygdaloids or lowest lay te brown, ae ha vesicular upper portions of the flows. nitic diabase- porphyrite, with conchoidal fracture, and containing 52.56 per cent. of silica. The next is a black, medium-grained olivine-diabase or melaphyr, containing 50.76 per cent. of silica, with the olivine wholly altered to a green and brown substance, and furnished above with an amygdaloid, and the uppermost Fic. 29.—Section on Minnesota Coast, near Baptisin River. layer is a heavy one of brown diabase-porphyrite, resembling that at the base of the section, but not quite so dense in grain, and carrying 57.87 per ‘Geol. of Wis., Vol. III, p. 191. DETRITAL ROCKS OF THE TEMPERANCE RIVER GROUP. 327 cent. of silica. Just where the sketch was taken the dip lakeward was unusually high. Further down the coast it soon flattens again. The rock constituting the point at Grand Marais is again all ashbed- diabase, though for the most part coarser-grained than that described above. It has a brown color, is exceedingly dense and hard, and shows a well-marked cross-columnar structure in places. In the thin section it is seen to contain much augite, both in the round particles characteristic of the ashbed-diabases, and indicative of relatively rapid solidification, and in particles whose con- tours are determined by the pre-existing plagioclases. It is thus a well- marked intermediate stage between the diabases of the ordinary type and of the ashbed type. Besides the tabular plagioclases of the matrix there are also present larger porphyritic plagioclases. The strong resistant power of this rock is shown in the existence of such an exposed ledge as that which forms the protecting reef of Grand Marais Harbor. The rock is in part more dense than that represented by the above description, and, to judge from the numerous angular fragments on the shingle ridge forming the east side of Grand Marais, must graduate downwards into an aphanitic diabase-porphyrite. The detrital rocks of the Temperance River Group were noticed at several points along the coast. The westernmost of these is in the N. E. 4, Sec. 11, T. 56, R. 7 W., where a thin seam of red shale, with very irregu- lar thickness, holds balls and fragments of amygdaloid, and occasionally has amygdaloidal material strangely mixed up with the red sand of the matrix. This seam overlies a porphyritic amygdaloid, which graduates downward ‘nto a true ashbed-diabase, and is overlain by an excessively vesicular thin amygdaloid. The whole occurrence, then, is an exact repetition of the ashbed of Keweenaw Point, the same peculiar dense diabase being fur- nished with the same peculiar scoriaceous amygdaloid. What appears to be the conglomerate just mentioned, but thickened, is seen in a vertical wall 36 feet high at the bottom of a bay in the extreme northeast corner of section 11. The overlying and underlying rocks are not seen here, but at its eastern extremity this conglomerate comes into abrupt vertical contact (the contact being seen on a wall 30 feet high) with a dark brownish-gray, fine-grained rock. This rock the thin section shows to be a typical luster- 328 COPPER-BEARING ROCKS OF LAKE SUPERIOR. mottled olivine-diabase or melaphyr, the olivine in which is wholly altered to a reddish and greenish material. This rock is alluded to further on. Just above Manitou River, Sec. 10, T. 57, R. 6 W., 15 to 20 feet of red shaly sandstone may be seen overlain by an amygdaloid, and this in turn by a columnar diabase. Numerous fragments of amygdaloid and decom- posed diabase are contained in the sandstone. The fragments are all angu- lar and under an inch in diameter. The occurrence of seams of red shale at the mouth of Temperance River has already been mentioned, and the peculiar irregularities to which these seams are subject shown in Fig. 27. A mile and a half below the mouth of Poplar River, in the northwest corner of Sec. 35, T. 60, R. 3 W., six feet of a conglomerate are seen overlain by black melaphyr or fine-grained olivine diabase. The pebbles are larger below, reaching four inches in diameter, and are principally of red felsite. Many are, however, of various types of amygdaloid and diabase-porphyrite. Several thin sections were made of these pebbles, and in all the amount of non-polarizing unindividualized matrix seemed unusually large, suggesting the possible origin of these balls as volcanic scoriz. At the mouth of the creek in the 8S. W. 4, Sec. 19; T. 60, R. 2 W., the following section was noticed; the order is an ascending one: 1. Highly vesicular amygdaloid -----..- 2... on oe eee ne mae ee 2 feet. 2. Fine-grained diabase, including (a) basal amygdaloid, 1 foot; (b) less amygdaloidal, 1 foot; (¢) massive portion, 8-12 feet; (d) very irregu- lar summit amygdaloid, 6 inches to 2 feet; in all about............. 15 feet. 3. Red shaly sandstone, bunchy, irregular, mingled with the amygdaloid, IHNEN WG aeaccaac w rd) Sw Sis ca evap ain font aration Oe Sra OPE IOUS < CRIM rea 2 feet. 4, “Amygdaloidl) cinerea sectors eco oe ice rer erstennie or oe ee ae einen eeterereas 4 inches. 5. Sandstone: os 225 <2 heehee oe kc were co syareeree aerate eiaeis eval Ses eee errr 6 inches. G:, Amy daloid ia: feecertesrercriee elas epee eae eee eae Foasnaes soso Sbs6 2 feet. Te, SANASbONGE sero < x ov “Any stl % v AVA NODIdiN YL yewnosum sass Pr ym aan] 1S « id SOTOULE New ~ % 4 5, %y “e pl terngy % Srey nh SHOOY ONINVAd-Yadd090 AVE MOVIE 4 Pl owe aw ow? BA p] UopPuIYyseM PI bd | tial 777 tap tPY OFEmES Nous . _ Avg uaastfanyi _— AOE TSATY a PI wonsy k ookeg uodSanyge AZAYNS WOl01039 S3LVLS G3LINN ISLE ROYALE TO NIPIGON BAY. 329 probably worn out in this sandstone, of which it is supposed that only the uppermost parts are in sight. Good Harbor Bay, four miles below, has certainly had this origin, the sandstone concerned being, however, a lower layer. At the latter place both underlying and overlying rocks are in sight, the former in a low ledge on the northeast shore of the bay, the latter in a vertical exposure of 20 feet. The sandstone is 225 feet thick, of which 120 feet may be measured in detail. The whole thickness dips 9° east of south. The Temperance River Group is almost free from dikes, another feature which it has in common with the bedded diabases of the upper part of the Keweenaw Point series. One of aphanitic black rock, six feet wide, and with cross-columnar structure, was noticed cutting amygdaloid near the base of the group on the shore at the east side of Sec. 11, T. 56, R. 7 W. In the same vicinity, Sec. 11, T. 56, R. 7 W., at two points, masses of red augite- syenite were seen in vertical contact with the diabases of the Temperance River Group. It is possible that these are faulted up from the under- lying Beaver Bay Group, though they look like cutting masses. The high bluff known as Carlton’s Peak, Sec. 20, T. 59, R. 4 W., near Temperance River, shows at its summit numerous large angular fragments of anorthite- rock, such as has already been described in connection with the Beaver Bay Group. None was seen that could be certainly regarded as in place; nevertheless, the mountain is, without much doubt, composed of this rock, and I should regard the rock as having antedated the Temperance Group flows rather than as a cutting mass. SEcTIoN Il.—ISLE ROYALE TO NIPIGON BAY. All along the eastern part of the Minnesota coast, as described in the preceding section, the Keweenawan beds strike away towards the lake from the coast line, so that finally, at Grand Portage Bay, the older slates come out to the shore. The Keweenawan beds reappear, however, in Isle Royale, having exchanged their easterly course for a more northeasterly one! while concealed by the lake. This change already begins to be per- 1§ee the red lines of Plate XXVIII. 330 COPPER-BEARING ROCKS OF LAKE SUPERIOR. ceptible on the Minnesota coast before reaching Grand Portage, and shows also in the Lucille Islands, off Pigeon Point, the outer one of these islands being formed of a typical Keweenawan diabase. The following brief account, with the accompanying map of Plate XXVII, will serve to present the main features of the geology of this region. So far as Isle Royale is concerned, I have had to depend upon the report of Messrs. Foster and Whitney, read in the light of a familiarity with most of the remainder of the extent of the formation, not having visited the island myself. The detailed topographical map of the island, by the United States Lake Survey, aids not a little in the understanding of the structure. The region from Thunder Bay to Nipigon Bay I have examined myself, and am thus able to draw information more satisfactorily from the descrip- tions of Logan, Macfarlane, and Bell, as well as to judge of the correctness of the views advanced by these writers. ISLE ROYALE. Isle Royale is a very long, narrow island, trending in a general north- easterly direction. Irom point to point the island is just 45 miles in length; but from the Rock of Ages, the farthest outlying reef to the southwest, to the Gull Island rocks on the northeast, is 57 miles. The island varies in width from three to eight miles. It does not lie exactly in a straight line, but curves from N. 65° E. in the southwest part to N. 53° E. in the north- east part. On the southern side of the southwestern end is quite an area of low land, underlain by sandstone and conglomerate, dipping some 8° to the southeast. This sandstone evidently belongs to the Upper Division of the series. ‘The remainder of the island is made up of very regularly bedded crystalline rocks, with here and there an interstratified conglomerate, all dipping southward at an angle which has not been satisfactorily determined, but which, probably, does not often exceed 25°. The whole shape of the island, both as to outline and topography, expresses the geological structure in a most striking manner. It is traversed from end to end by a series of parallel ridges, which present always a steep, often a precipitous side towards the north, and a gradual slope towards the ‘Since the above was written, N. H. Winchell has published some notes on the geology of Isle Royale, especially on the south side of the island. Tenth Annual Report of the Geological and Natural History Survey of Minnesota, pp. 49-54. ISLE ROYALE. 331 south. These ridges are, of course, made of the heavier, more resistant layers. They seldom reach 500 feet above the lake level. The inter- mediate linear valleys are worn in the softer amygdaloids and other less resistant rocks. At the ends of the island these valleys are occupied by long, narrow extensions of the lake, and between them the ridges continue, constituting the so-called “fingers” of Isle Royale. Ridges and valleys both change in trend as the island is followed to the northeast, as does the island itself as a whole, and this is evidently due to a similar curving in the trend of the underlying rocks.’ It is evident, from the descriptions of Messrs. Foster and Whitney, that we have here merely a repetition of what is seen everywhere else in the course of the Keweenawan rocks. They describe the beds as exceed- ingly well marked and mostly thin, and as provided with strongly-devel- oped vesicular portions, and lower portions which are often columnar. The more coarsely crystalline kinds of which Foster and Whitney speak— such as that of the ridge along the northwest shore of the island, and that of Blake’s Point, at the northeast—evidently belong with the coarse gabbros of this memoir; while the porphyritic kinds which they mention as occur- ring at several points would appear to belong with my diabase-porphyrites. They say nothing, however, of the occurrence of red rocks, which might be quartziferous or granitic porphyries, although one would expect such to occur, especially on the north side of the island. One occurrence which they describe is of interest, namely, the sandstone veins running down from an overlying sandstone into the cracks of an amygdaloid at the mouth of Chippewa Harbor, on the south side of the island. The same thing may be seen at many places on the Minnesota coast, as already indi- cated. THUNDER BAY TO NIPIGON BAY. As shown in the following chapter, the slates of the west and north- west sides of Thunder Bay, and again those of Pie Island and Thunder Cape as far around as Silver Islet, belong with the iron-bearing rocks of the South Shore. The east shore of Thunder Bay, however, and the whole of the peninsula between Thunder and Black bays, are occupied by a 1See, also, Chapter IX. 332 COPPER-BEARING ROCKS OF LAKE SUPERIOR. series of quartzose sandstones, dolomitic sandstones and red marls, which plainly belong at the base of the Keweenaw Series. According to Logan,’ the whole thickness of these rocks is between 800 and 900 feet; Bell, how- ever, from later study, making it between 1,300 and 1,400 feet. The fol- lowing is the succession, as given by Bell:? Feet. Alternating red and white dolomitic sandstone, with a red conglomerate layer at the bottom, oceurring on Wood’s location, Thunder Cape*............-..--. 40 Light-gray dolomitic sandstone, with occasional red layers and spots and patches of the same color. These sandstones occur along the southwest side of Thunder Bay and on Wood's location == Je. cam sem care steelers aie sine ) Pilot Light 1 —, me Delle ya ries eT ee ee ae te i & be ‘ dy y + by mr "i ( j —" eae et i “a S OF LAKE SUPERIOR PL. XXxvIll Lie — to approad, and sometimes two or more sepresent the lower drvistan the orange lines the uppar VUsLON | tie blue tines represent the unde || lines are based on observation. where broken The formations newer han te Kaweenawan are passes under therm For more complete explanation see chapuer Xx Es Lower and Upper Silurian and Devoraan Limestone [EY viene Cotored Cambrian (Potsdam) Sandstone (GHEY Reatisn SPE ria dstarie (Acronndcontinnation of 2) Scale avntnon orlinch= 31.565 miles. { Caribou Ti a sar oo ee t/ ISLAND yg Light L ‘Outer Id Co “= a“ " op voce fa. 7 Sf Michiean 1a ; hight, House {Madedrane 7” ir Channel <4 Pouite 1 House See} | WHLTR. vrs y. v - WAY, Hi corcapeg Troquas. > A Hoon Co, Lith Baltimare RUCTURE AND EXTENT OF THE KEWEENAWAN TROUGH. . oP ep ene or eee ae ey we See Lh os ee 7 THE LAKE SUPERIOR SYNCLINAL. 411 1873, while at the same time modifying them in some respects, and develop- ing a number of new facts with regard to the structure and course of the synclinal. The most important modification was that with regard to the supposed occurrence of horizontal Potsdam or unconformably overlying sandstone in the trough of the synclinal. On my map of 1874 I had marked such a sandstone as occurring along the upper Saint Croix, as indicated by the descriptions of Dr. D. D. Owen,’ but this sandstone was subsequently shown by Sweet? to belong in the Upper Division of the Keweenaw Series, it being in fact but the westward continuation of the south-dipping sandstones of White and Bad rivers. The upper Saint Croix was again further examined by Sweet and Strong in 1876, and the sandstone in question found to be underlain conformably by fine-grained diabases and melaphyrs with interbedded conglomerate and sandstone. My map and section of 1874 had also shown horizontal sandstones filling the trough of the synclinal in the Bad River country. This conclusion was based on an observation by Dr. I. A. Lapham, which subsequent ex- amination by myself failed to verify. There then remained, to indicate the presence of this newer sandstone in the trough of the synclinal, only an exposure of flat sandstone on the shore of Lake Superior at Clinton Point, four miles west of the mouth of Montreal River; and this, as shown on a previous page, is rather to be regarded as the eastern termination of the horizontal sandstone of the Apostle Islands and of the coast of Bayfield County. The chief new developments as to the structure and course of the syn- clinal, resulting from the later work of the Wisconsin Survey, were (1) the connection by Strong of the Keweenaw Range of north-dipping rocks with the similar rocks of the Saint Croix by exposures all across the previously wholly unexamined interval between that river and Numakagon Lake; (2) the determination of the comparative flatness of the northward dip across this interval; (3) the determination by Chamberlin of a curve to the southward of the belts of this range, with a flat westerly dip, in the imme- 1Geological Survey of Wisconsin, Iowa, and Minnesota, p. 161. 2“‘Notes on the Geology of Northern Wisconsin,” by E. T. Sweet. Trans. Wis. Acad. Science, Vol. III, 1876. 412 COPPER-BEARING ROCKS OF LAKE SUPERIOR. diate vicinity of the Dalles of the Saint Croix, of the similar southerly course with high easterly dip of the Keweenawan beds of Snake River, Minnesota, and, as a consequence, of the southerly direction of the axis of the synclinal near its final termination; and (4) the determination by Sweet of the existence of a southward dip in the Saint Louis River slates, and the consequent probability that the Huronian rocks form the bottom beds of the synclinal. In Vol. IIT of the Geology of Wisconsin, published in 1880, I embod- ied these points in a brief discussion of the structure of Northern Wis- consin, accompanied by a map, which I now modify only as to the exact extent of the upper sandstones of the Keweenawan, and as to the western extension of the horizontal sandstone of the lake shore, which, on the map of 1880, was made by misprint to extend to the north side of the Saint Louis River at Duluth. No such sandstone is to be seen near Duluth. At the beginning of my study for the present memoir, North Wisconsin had been shown to be traversed by a broad synclinal in the Keweenawan rocks, possibly also in the Huronian, which was presumably the continua- tion of the Isle Royale-Keweenaw Point depression. The exact nature and position of the western termination of the synclinal, the relation to the synclinal of the rocks of the Minnesota coast, and of the Porcupine Mount- ains, and the behavior of the depression to the eastward of Isle Royale, were all points left in doubt, though it appeared exceedingly probable that the entire western half of the Lake Superior basin is a synclinal depression affecting both Huronian and Keweenawan rocks. Now, however, I feel able to announce with confidence that the entire lake basin, including not only the western half, but the eastern half as well, is a synclinal depression; that this depression certainly affects the Kewee- nawan rocks throughout their entire extent; that it as certainly affects in very large measure the underlying Huronian rocks, which, while they are greatly folded where extending without the limits of the depression, within its limits form without folds its bottom layers; that the axis of the depres- sion has, like the lake itself, at first a northwesterly and then a southwest- erly direction, with minor bends corresponding to the several bends in the axis of the lake; that the eastern termination of the depression is buried THE LAKE SUPERIOR SYNCLINAL. 413 beneath the newer formations in the vicinity of the Sault Saint Marie; that the western extension passes on to the south shore of Lake Superior with _a course curving more and more to the southwest until, at the termination in the Saint Croix Valley—and therefore without the present hydrographic basin of Lake Superior—it becomes nearly due south, the exact termina- tion here again being buried beneath the newer horizontal Cambrian for- mations; and that, in the region of the Porcupine Mountains of Michigan, _and the Douglas County Copper Range of Wisconsin, there are minor folds superinduced upon the grand synclinal, accompanied in the former case at least, by further complications, due to faulting. The evidence upon which these conclusions are based is to be found in (1) the nearly constant dip inwards of the Keweenawan strata towards the middle of the basin; (2) in the frequently similar dip of the Huronian; (3) in the constant order of Upper Keweenawan, Lower Keweenawan, Huronian, and gneiss with granite and folded crystalline schists, met with on all sides on going from within the supposed trough outwards; and (4) in the parallelism between the courses of the Keweenawan belts of the North and South Shores, and of the shore line with these belts. The details of the evidence under the first three of these heads are given in Chapters VI and VI, and on the maps and sections of Plates I, XVII, XVIII, XXII, XXIII, XXVI, and XXVII, and need not therefore be repeated here. That under the fourth head, however, needs some fur- ther remarks. In the first place it is to be observed that the drawings, from which the accompanying maps of Lake Superior, Plates I and XXVIII, are reduced, are much more accurate than any previously made with geological data, being compiled directly from the maps of the United States Lake Sur- vey, from Captain Bayfield’s chart, and from the United States land-office plats; and that, consequently, correct ideas may be obtained from them as to the courses of the coast and other topographical lines, and of rock belts. Directly north of the east and west portion of Keweenaw Point, be- _tween Agate Harbor and Copper Harbor, with its east and west rock belts, dipping north, we find the east and west part of Isle Saint Ignace again made up of east and west rock belts, which now, however, dip to the south. West- ward from Agate Harbor and Eagle Harbor, on Keweenaw Point, the coast 414 COPPER-BEARING ROCKS OF LAKE SUPERIOR. line of the Point and the course of the constituent rock belts swing around to the southwest. Correspondingly, we find, on the North Shore, a southwest trend (participated in by rock belts, coast lines, and lines of islands), begin- ning in the western part of Isle Saint Ignace, and continuing through the peninsula which forms the south side of Black Bay, through the adjoining islands, and through Isle Royale. Isle Royale does not lie on a straight course, but on a curving one, its outlines, projecting points, ridges and rock belts at the western extremity trending 10° to 12° more to the south than at the eastern extremity. This curvature to the westward is continued to a nearly due westerly direction in the rock belts, projecting points and other topographical features of the Minnesota coast between Pigeon River and Grand Marais, although the coast line in this distance trends as a whole some 20° south of west. The counterpart of this swing to the west is found on the south shore of Lake Superior in the course of the Main Trap Range and its constituent rock belts, and of the coast line between Fourteen-mile Point and Black River. West of Black River, the Main Trap Range of the South Shore and its rock beds curve again to the south of west, and as Bad River is neared the direction is only some 30° west of south. The corresponding curvature on the North Shore is to be found in the distance between Grand Marais and Split Rock River. For much of this distance the coast line follows the trend of the strata, until the latter comes around to only a few degrees west of south, when the rock belts depart from the coast, and run with a eastward curvature over to the South Shore. Still further west, both sides of the synclinal are on the South Shore, the strata, and with them many topographical features, on both sides, trending at first well around to the west, and then more and more towards the south, until the termination is reached in the Saint Croix Valley. Beyond Copper Harbor to the eastward, on Keweenaw Point, the point and its strata begin to swing around to the south of east, and this direction is continued on Manitou Island, and in Stannard’s Rock, which is, as pre- viously shown, a mass of quartzless porphyry. Parallel to this curving course is the coast line of the lake between Huron Bay and Marquette. Now on the North Shore, in the line of islands lying south of Nipigon j Ces ee a el) —~ MN bg Pt a sa Bie THE LAKE SUPERIOR SYNCLINAL. 415 Bay, and in the rock belts composing them, a similar curvature to the south of east is begun. That this continues until it becomes nearly or quite a southerly course is shown by the trend of the northeast coast line of the lake, which is composed of the older rocks, between the Pie and Michipi- coten Island, where the Keweenawan rocks again appear. The parallelism of the northeast coast, of the line marked out by the eastern end of Keweenaw Point and Stannard’s Rock, and of the south coast between Keweenaw Bay and Marquette, looks also the same way. Still further to the east, the South Shore shows only rocks newer than the Keweenawan, but at the east end of the lake a continuous belt of the latter rocks is marked by Michipicoten Island, Capes Choyye and Gargantua, Pointe Aux Mines, the peninsula of Mamainse, the coast of Batchewanung Bay, and Gros Cap, the beds always dipping lakeward. The most striking thing about this belt is its parallelism to the lake coast behind it, and the consequent abrupt turn, at more than right angles, in the Michipicoten bight. In the map of Plate XX VII and the accompanying sections of Plate XXIX, I have attempted to summarize the facts bearing upon the subject of this chapter, and to generalize from them to the structure of the syn- clinal. The spaces between the red lines of this map are each supposed to represent 2,500 feet of rock thickness, the spaces being narrow where the dip is high, and correspondingly broad where it is low. The lines were constructed by first platting out the spaces in those districts where actual measurements had been made of strike and dip, the width of each space being made to correspond to the width of the surface outcrop of a 2,500- feet thickness at the measured angle of dip. Where actual thinning on a large scale had been proved by careful measurement to exist—e. g., on Keweenaw Point—the lines were approached on this account also to the determined amount. Then the broken connecting lines were sketched in, taking into account the general lithological characters of different horizons —often recognized for over a hundred miles—the relations of the belts to the junction with the Huronian below and to the line between the Upper and Lower Divisions of the Keweenawan, and the angles of inclination and trends indicated by the nearest exposures. 416 COPPER-BEARING ROCKS OF LAKE SUPERIOR. The spaces between the lines do not, of course, represent single con- tinuous beds, or even, in many cases, groups of beds, for in their course around the lake such beds must constantly thin out and be replaced by others. The spaces are, however, designed to cover the same general horizons, so far as practicable. Of course there must be many imperfections in such a map, under the very best of circumstances, for not only do the courses of the belts under the lake have to be hypothetical, but, from the general similarity of the beds of the Lower Division at very different horizons, there must always be more or less doubt as to the correctness of the connecting lines, even on the land. Then, again, the map is very irregular as to accu- racy in those places where the courses and inclinations of the beds can be marked out. On Keweenaw Point, for instance, the detailed measurements of Pumpelly and Marvine make it possible to locate the courses of the 2,500-feet spaces with far greater minuteness of detail than it is possible to show on such a map as this. From this downwards there is every degree of accuracy to cases where the lines are purely hypothetical. Notwithstanding all these defects, the general correctness of the struct- ure of the great synclinal indicated by the red lines appears to me to be beyond question. One objection that I anticipate to this map is that it is an attempt to apply the methods used in studying sedimentary beds to a series largely formed of eruptive ones; to which I have to answer beforehand that this series is just as much made up of layers as any sedimentary one, and that in a sedimentary series beds thicken and thin and disappear just as here. The map and sections do not show the nature of the bottom of the trough. I believe this bottom to be made up of Huronian slates below, resting upon the older gneiss, and of Keweenawan strata above, but both greatly thinned, since the eruptive rocks, which constitute so large a part of these groups around the edge of the basin, appear to me to have reached the surface there. The simplicity of the synclinal has been further complicated by faulting. The fault to the south of the Keweenaw Point Range, it seems probable, may have been connected with a sudden change in the dip of the strata from a flat to a steep lakeward inclination. It seems a plausible WWity se =e in Ah. v iat ‘a ‘ os. Ag Through Burling! piiein beds bay, aa Heweenawan series, lower div Through Two Island River ar K £E s Through mouth of { Ss. U Through Pie Island a upper division | North and south == upper division | North and south ee \Keveenaw series, upper divisto GEOLO GICAL SECT Scale 500000 ail ie Bay and Atkins Lake SAAR IOR Western. 5 e east end of Stockton's Is Stockto uv Pi SE Hewemnaw series, upper le River and Ontonagon. P E naw series, upper division mouth of Eagle River. Eagle Re. e D Rk} KEWEENAW PO Keweenaw series. igh Mt. Houghton. bh Michipicoten Island. te wf @ = OF THE LAKE S - 7891 mules . £ , ~@ s = Hevenaw serves, upper division Kewenay pistks,, te ete aries, Huronian G ness, granite ele lower duision (Tren bearing series) “ Two Island River G A K Keweenaw series, lower duiswon (naire, granile ade. Huroran be (Anmikte group ) Through mouth of Brule River and Ontonagon. Ont eg Cr Mare trap range “ S.26°E Basten sandstone R E ee U Ss Huronian Aron bearing series Brule River } L Heweenaw series, lower dwiston Keweenaw series, upper division lower divisor Keweenaw’ series, * te cle: Huronan Gneiss, J Animikie group | W Through Pie Island and mouth of Eagle River. Eastern sandstone Eagle Ru: R KEWEENAW POINT Muronian Gneass, qrante ete ISLE SUPE RT 0 R? ROYALE a S Murontian Tron bearing series) k " A us Keweenaw series, lower duvision LAKE | THUNDER, pp, ja ei par 1 eee Heweenaw serves, Upper division Keweenaw serves lower duis. Huronian { Anamilete group.) \) North and south Uwough Mt. Houghton. Eastern sandstone KEWEENAW, R a ePOUN TN al a7 A K Wy J C P Huronwan Gness, granite ete Aron. bearing series division dwision , Keweenaw sertes, lower ISLE IGNACE « L upper | NIIMGON BAY | st Teween aw Serwes, lower dwision Hewvecnaw sees, VE Helde Be group LGA south through Mien p: chipicoten Island . Lover: Trenton. and Gneumnate North and E Maynestan groups Muronian Iron bearing serias) Keweenaw serves lower dzvesion A oon sos te yeries, Upper Havenaw 3ENE -)) GEOLOGICAL SECTIO , soo or Li Scale 500000 OF THE LAKE SUPERIOR SYNCLINAL. speculation that this fault is met at a large angle by another, coming from the southeast, at a point behind the line from the end of Keweenaw Point to Stannard’s Rock, the junction of the two being the lowest part of the dislocation. Behind the Porcupine Mountains, as previously shown, is again a fault, of much smaller ex- tent, which is again connected with a fold, though a sub- ordinate one. I have also already indicated the prob- ability of the existence of a fault on the north side of the Douglas County Copper Range of Wisconsin. The connection of the belts of this range with those of the North Shore is one of the least satisfactory parts of the map of Plate XXX. It is evident, however, from the trends on the North Shore, and in the Douglas County rock belts, that some such connection must exist, though whether with so much of a fold as I have indicated is not so plain. The relation of the Huronian to the synclinal is a point of great interest. Beyond question, in the western half of the Lake Superior basin, it bottoms the great trough, for its beds are found dipping inwards on both sides; on the North Shore at a low angle, and on the south generally at a high one. It appears highly prob- able that the eastern part of the trough is similarly bot- tomed by the Huronian. The Huronian beds are, how- ever, here found, just without the rim of the synclinal, folded in a complicated manner; for instance, beyoud the western end of the trough in Minnesota, in the iron regions of Michigan, on the east shore of Lake Supe- rior, and about the head of Lake Huron. Other folded schists, which possibly belong with the Huronian, occur in Canada, north of Lake Superior. The con- nection of these folded beds with the unfolded is a structural problem still needing investigation. So far 27 LS ‘usu doledng oyv7yT JO UoMoas [voeTodAyT—' ge “DIT 7 oly ee swrips nf Aeopuoanyy PIPT0T ~ ti Xf S \ ‘SISNPS' MDPUOLNIT DP] OT 418 COPPER-BEARING ROCKS OF LAKE SUPERIOR. as present knowledge will allow, it has been discussed in the previous chap- ter. In the preceding generalized hypothetical section of the Lake Superior basin, which may be looked on as taken across from the Pigeon River region of the North Shore, through Ontonagon, the South Range, and the Meno- minee region of Michigan and Wisconsin, but not on a straight line, and not drawn to any scale, I have attempted to bring out the following points: (1) the synclinal structure of the lake basin; (2) the partial unconformity of the Keweenawan to the unfolded Huronian; (3) the supposed relations of the folded and unfolded Huronian; (4) the limitation of the Keweenawan outwards by the higher Huronian land; and (5) the origin of the Keweenawan eruptive rocks through fissures arranged around the rim of the trough. If this sketch represents actual conditions, then the downward bowing of the great trough, which subsequently was filled with the Keweenawan accumu- lations, was begun in the Huronian and continued through the Keweenawan. Accompanying this downward bowing was a crumpling of the Huronian to either side of the broader bow—and this crumpling, so far as this sketch is concerned, may have taken place in large measure before the Keweenawan —and an extravasation of molten matter around the rim of the trough. CHAPTER x; THE COPPER DEPOSITS. No special investigation made of the copper deposits.—Different kinds of copper deposits.—Cupriferous sandstones and conglomerates.—Cupriferous amygdaloids.—Epidote belts.—Transverse veins.— Similarity in origin of the several forms of copper deposit.—Source of the copper, and cause of its precipitation; different views.—Rules to guide the explorer for copper.—Portions of the Keweenaw Series favorable and unfayorable to the occurrence of copper.—Prospects of future developments of copper without the present producing districts: in the Bad River country of Wisconsin; between Bad River and the Saint Croix; in the Saint Croix Valley; on the Douglas County Copper Range; on the Minnesota side of Lake Superior; on Isle Royale. A special study of the copper deposits of the Keweenaw Series formed no part of the plan of the investigation upon which this memoir is based. These deposits, were, of course, already the best known things about the series, and any study made with the hope of adding materially to the facts collected by the numerous geologists who have hitherto written upon them would have occupied far more than the whole time at com- ‘mand. For the sake of rounding off the subject, however, I may appropri- ately offer a general account of the structural and genetic relations of these deposits, adding a few general considerations of an economic bearing as a guide to the future explorer for copper, both within and without the present producing districts. All the workable deposits of copper heretofore discovered in the Lake Superior region fall into one or other of two classes, which we may term belt or bed deposits, and transverse vein deposits. The first class includes the cupriferous conglomerates and sandstones, the cupriferous amygdaloids, and most, if not all, of the so-called veins carrying much epidote and coin- ciding with the bearing of the formation ; the second class includes those veins which traverse the formation in a direction more or less nearly at right angles to the bedding. No copper has ever been observed in connec- tion with the acid eruptives of the series, nor have any workable deposits been discovered in the massive non-vesicular diabase beds, except as dis- tinctly subordinate to, and directly connected with, the amygdaloid deposits or epidote courses, and always accompanied with an extreme degree of alteration. 419 420 COPPER-BEARING ROCKS OF LAKE SUPERIOR. The conglomerate and sandstone deposits are simply portions of the beds of these rocks, in all respects of the ordinary character, save that they are impregnated with the native copper. Cupriferous deposits of this char- acter are for the most part confined to the thin conglomerate beds which are interstratified with the ordinary diabase flows; but one cupriferous bed of sandstone is known within the upper or purely detrital division of the Ke- weenaw Series, and separated from the nearest trappean flow beneath it by a thickness of many hundred feet of sandstone layers. This is the belt of dark colored sandstone and shale in which occurs the Nonesuch copper bed of the Porcupine Mountains. This belt has been traced from Keweenaw Point to Bad River, a distance of about 150 miles; and has been found to contain copper at a number of points in the vicinity of the Porcupine Mountains, and again on the Montreal River, the boundary line between Michigan and Wisconsin. In the cupriferous conglomerates and sandstones the copper occurs as a cementing material, and as a replacer of the constituent grains, being in all cases plainly of secondary origin, and a result of deposition from an aque- ous solution. Moreover, the cementing copper itself, 7. e., that which is to be seen in the thin section between the constituent grains molding itself sharply around their contours, is often also plainly a replacer of still smaller constituent particles. In the case of the Nonesuch sandstone of the Poreupine Mountain region a large proportion of the particles of cementing copper have within them a core of magnetite. It is indeed not improbable that in all cases the cementing copper is not a deposit in the original inter- spaces of the fragmental particles, but is always a replacer. In the thin sections of these cupriferous conglomerates the larger par- ticles of porphyry matrix, and fragments of the feldspars, are found to be replaced by copper in varying degrees, the metal in the case of the feldspar fragments tending to follow the cleavage directions. In the famous con- glomerate of the Calumet and Hecla mine in the Portage Lake region the copper has not only saturated the matrix, but has also entered into and more or less completely replaced large-sized pebbles and even bowlders several inches to a foot or more in diameter. Hundreds of such bowlders are picked each day from the heaps of rock, before it is taken to the stamps CUPRIFEROUS CONGLOMERATES AND AMYGDALOIDS. 421 In these bowlders the copper has replaced both the matrix and the porphy- ritic feldspars, occurring in the latter, when the replacement has not been carried very far, often along the cleavage lines only. Pumpelly has shown that the deposition of this copper has always followed other great changes in the condition of the porphyry fragments, and notably the replacement of both matrix and feldspars by chlorite and epidote; these minerals hay- ing in turn been replaced by the copper. This relation, between copper, epidote and chlorite, is one which exists also in the altered amygdaloids; and the source of the constituents of these minerals may be found either in the particles of amygdaloid matrix and other basic materials which not unfrequently occur in the conglomerates themselves—in the Nonesuch sand- stone forming a predominating quantity—or in the overlying trappean beds, from which they may have descended along with the infiltrating carbon- ated waters. The ordinary cupriferous amygdaloids, such as those which are so largely mined about Portage Lake, are, as Pumpelly was the first to show, simply the more or less completely altered and copper-saturated upper vesicular portions of the old lava flows, and are neither independent layers, nor “veins” parallel with the formation. The copper has been introduced into these amygdaloids during one of the later stages of a long chain of replace- ments, whose history has already been briefly outlined, as worked out by Pumpelly, on a previous page. Several paragraphs of his descriptions may appropriately be quoted again in the present connection. Considerable portions of the bed have lost every semblance of an amygdaloid, and consist now of chlorite, epidote, calcite, and quartz, more or less intimately asso- ciated, or forming larger masses, of the most indefinite shapes, and merging into each other. Sometimes portions of partially altered prehnite occur. In places, considera- ble masses of rich brown and green fresh prehnite filled with copper occur; but, as a rule, this mineral has given way to its products. To this process the copper-bearing beds of Portage Lake—wrongly called lodes —owe their origin. Considerable portions of these beds are but partially altered amygdaloids, containing amygdules of prehnite, chlorite, calcite or quartz, with more or less copper; other portions are in the condition described above. In the still amygdaloidal portions, the copper was deposited in the cavities and in cleavage-planes of some minerals, and replaced calcite amygdules, ete. But in the confused and highly altered parts of the bed it erystalized free, where it had a chance; more generally it replaced other minerals on a considerable scale. It formed, in 422 COPPER-BEARING ROCKS OF LAKE SUPERIOR. calcite bodies, those irregular, solid, branching forms, that are locally known as horn- copper, often many hundred pounds in weight; in the epidote quartz, and prehnite bodies, it occurs as thread and flake-like impregnations; in the foliaceous lenticular chloritic bodies, it forms flakes between the cleavage-planes and oblique joints, or-in places—and this is more particularly true of the fissure veins, which we are not now considering—it replaces the chloritic, selvage-like substance till it forms literally pseudomorphs, sometimes several hundred tons in weight. The copper in these deposits is not restricted to that portion of the bed which was originally vesicular, but runs from it downward irregularly into the originally compact portions, following always a great alteration of the rock. The copper, however, tends always to be very irregular in distribu- tion, and, even in the longest worked and most reliable amygdaloids, has frequently to be searched for through many feet of barren rock. In this search the diamond drill is now extensively used, the miners being guided in its use by the occurrence of seams of calcite and epidote, and other alteration forms, which, when followed up with the drill, are often found to lead to pockets containing much copper. In one class of amygdaloids, those of the ashbed type,—which I agree with Wadsworth in regarding as merely very highly scoriaceous and open lava flows, into whose interstices the intermingled detrital material has sub- sequently been washed—the distribution of the copper is sometimes more uniform than in the ordinary cupriferous amygdaloids, so that the whole of the bed may be broken down and taken to the stamps, as is done for instance at the Atlantic mine. _ The copper deposits of the Ontonagon region have not had the study given to them that has of late years been devoted to those of the Kewee- naw Point and Portage Lake districts; so that it is not possible to be quite so positive in our statements in regard to them. The copper of this region never occurs in transverse fissures, but either lies in irregular accumula- tions—often solid masses many tons in weight—associated with much epidote and calcite, distributed along the course of diabase beds, or else occurs with more persistent and vein-like aggregations of epidote and cal- cite. The latter coincide always with the bearing of the formation, and commonly also with its dip, but in some cases, as for instance in the once famous Minnesota mine, dip at a higher angle than that of the formation, EPIDOTE COURSES.—TRANSVERSE VEINS. 423 which they consequently slowly traverse in depth. According to Foster and Whitney, deposits like that of the Minnesota mine show another indica- tion of a vein-like character in the shape of slickensided and generally sharply defined walls The “vein” at the National mine is also peculiar in lying at the base of one of the great lava flows, and immediately above a conglomerate bed, while coinciding with them in both bearing and dip. It is evident, even with our present knowledge of the deposits of the Ontonagon district, that their history has been essentially the same as that of the Portage Lake deposits. In the case of that copper which occurs irregularly distributed, along with epidote and calcite, throughout certain of the trappean beds, the process of replacement has gone on irregularly, because of some irregularity of texture in the original rock. Deposits like that of the Minnesota mine may have resulted from the deflection of the altering waters along the course of a pre-existing but not open fissure; the “vein” being in this case, as before, a replacement, at least in large mea- sure, of original rock substance. . The transverse veins have been mined for copper on Keweenaw Point only, where they are found varying in width from mere seams to 10 and even 20 and 30 feet. For the most part, however, they do not exceed one to three feet in width, the expanded portions being met with where they traverse the amygdaloidal or otherwise open textured portions of the flows. The same veins which, in the amygdaloid and looser textured diabases, are expanded and often rich in copper, will, when in the more compact and massive beds, such as the well-known Greenstone, contract to mere seams without metallic contents; and the same is in large measure true of their intersections with the sandstone belts. The veins lie always very nearly at right angles to the trend of the beds which they traverse, standing always very near the perpendicular. Quartz, calcite and prehnite make up the common veinstone, but they are mingled with more or less of the wall rock of the vein, which frequently predominates greatly over any true veinstone. The veins are in fact for the most part not sharply defined from the surrounding rock, but consist in each case of a network of smaller seams traversing the shattered wall rock. Veins composed almost wholly of calcite are not unknown, but they are never productive of copper. The 424 COPPER-BEARING ROCKS OF LAKE SUPERIOR. copper in these veins occurs both in smaller fragments and minute particles intimately mixed with veinstone, and again in masses many tons in weight. The larger masses frequently are found to contain within them portions of the wall rock. Nearly all of the productive mines based on these transverse veins are working directly beneath the Greenstone, the layer which is described in a previous chapter as constituting so prominent a feature in the geology and topography of Keweenaw Point. This position of the mines is one not due to the non-occurrence of copper elsewhere on the course of these veins, but results from the fact that further south they become buried be- neath a heavy coating of drift, while to the northward they pinch out and become barren in the broad Greenstone belt. These veins, on account of their transverse position to the bedding of the formation, of their often slickensided walls, and from their carrying often a true veinstone, have commonly been regarded as ‘true fissures.” That they are on the lines of pre-existing fissures or transverse cracks in the formation there can, I think, be no doubt; but they are not true fissure veins in the sense that the veinstone and metallic matter oceupy, along with wall-rock fragments, original fissure space. I see in them simply the results of a rock alteration entirely analogous to that which has brought about the deposition of copper and its associated veinstone minerals within the cupriferous amygdaloids. They are alteration zones which traverse, instead of following, the bedding, simply because the drainage of the altering waters has been given this direction by the pre- existing fissures. All of the phenomena of these veins coincide completely with this view: the common occurrence of wall rock within the vein, or rather the embracing of the wall rock masses by the vein; the replacement of wall rock by copper masses; the occurrence of wall rock within these masses; the expansion of the veins and their greater richness where travers- ing the more readily alterable amygdaloids and looser textured diabases; their contraction and barrenness within the compact and less readily changeable Greenstone; and the coincidence of the paragenesis of the vein minerals with that of the cupriferous amygdaloids, are all facts better explicable on this view than on any other. ORIGIN OF THE COPPER DEPOSITS. 425 Thus the differences in origin of the several classes of copper deposits —conglomerate beds, cupriferous amygdaloids, epidote veins parallel to the bedding, and “fissure” veins transverse to it—which at first sight seem to be great, on closer inspection for the most part disappear. They are all the result of the percolation of carbonated waters, which, in the lines of fissure, the open textured amygdaloids, and the nearly equally open con- glomerates, found the least resistance to their passage, and at the same time the greatest susceptibility to their altering power. This susceptibility de- pended partly upon the very openness of these different rocks, but also, in the case of the amygdaloids, in the presence of a large proportion of glass basis, the most readily alterable substance among rock constituents. The source and the cause of the arrest of the copper which was carried in with the altering waters are other and more difficult questions. Its home has commonly been regarded as being within the mass of the trap- pean flows themselves, with which it is supposed to have come to the sur- face. Another view is that it was originally deposited in a sulphuretted form along with the detrital members of the series, from which it was sub- sequently leached, partly in the shape of a sulphate, but principally as a carbonate and silicate. The latter is the view which Pumpelly has elabo- rated;! to whom also is due the credit of having advanced the only satis- factory view as to the cause of arrest of the copper in the places where it is now found. He has shown the existence of an intimate relation between the precipitation of the copper and the peroxidation of the ferrous oxide of the augitic constituent of the basic rocks; a relation so constant as to ren- der irresistible the conclusion that in this ferrous oxide is to be found the precipitating agent of the copper. To this I would add that the ferrous oxide of the magnetite, and of the unindividualized magma of the vesicular layers, has also been concerned in this reaction. While this explanation of the precipitation of the copper seems satis- factory, we have too little to go upon in deciding between the two views above referred to as to the source of the metal. Too few signs have been observed of the existence of copper in the upper sandstones of the series, such as would be expected were this its home, to allow of an easy acqui- 1Geology of Michigan, Vol. I, Part ILI, p. 43. 426 COPPER-BEARING ROCKS OF LAKE SUPERIOR. escence in Pumpelly’s view. On the other hand, the trappean rocks them- selves are for the most part devoid of copper, except such as is plainly secondary. Copper in a sulphureted form I have, however, observed in the coarse gabbros of Duluth, in the green uralitic gabbro of Mount Bohemia, and in similar coarse rocks in one or two places on the north shore of Lake Superior. It is commonly said that copper occurs in the conglomerates and sandstones only where it could have leached directly downwards from an overlying trappean mass; and with one exception the statement is undoubtedly correct. The exception is that of the Nonesuch cupriferous sandstone, which is, however, a very important exception, since this rock not only has no overlying diabase, but is separated from the near- est trappean flow beneath it by many hundred feet of detrital material. As previously shown, this sandstone is unusual for its large proportion of basie detritus. Its copper can only be connected with a trappean source by supposing it to have formed part of this detritus in the sulphuretted con- dition, and afterwards to have been dissolved and redeposited in a native state. This is a supposition which would seem on the whole, however, to be rather more violent than to regard the copper as having come from the overlying sandstones, and as having been arrested in its descent on meeting a layer so rich in basic detritus as to be able to furnish the requisite supply of precipitating agent. From the facts and theoretical considerations thus given, may be for- mulated a few simple rules to guide the explorer for copper in the regions traversed by the Keweenaw Series. Thus the explorer, should he be searching for transverse veins, should bear in mind that epidote, prehnite and chlorite are the favorite associates of the copper; that veins carrying a greatly predominating quantity of calcite are not likely to be cupriferous ; that laumontitic veins have hitherto not proved to be sufficiently rich for exploitation; that a vein which may be very rich and wide in the amygda- loidal or other soft and easily decomposed rocks will pinch to a mere seam and become barren within the massive and more compact layers; that, hence, the intersection of a vein with such amygdaloidal or other soft beds should always be searched for; that the copper occurs in these veins with extreme irregularity; and finally, that a vein found traversing decomposed EXPLORING FOR COPPER. 427 amygdaloid beds with the favorable veinstone, even though it show only a little copper at surface, is worthy of examination. Should our explorer be looking for cupriferous belts, he should see that they are well defined ; that they present evidence of much alteration such as is above indicated; and that one or more of the favorite associate min- erals of the copper are present. These favorable indications, along with a more or less well preserved amygdaloidal character to the rock, and the presence of some copper at surface, are sufficient to warrant further exam- ination. In searching for these belts care should be taken not to be misled by the occurrence of seams of native copper without veinstone along the joint cracks of an unaltered massive diabase, and of isolated pockets of epidotic and calcitic material carrying some copper. In the case of sandstone and conglomerate deposits the explorer is to bear in mind that thus far they have been found only where a thin seam of conglomerate is directly overlain by a trappean mass; or if away altogether from the trappean beds, only in sandstone which is very rich in basic det- ritus. Beyond this, there is nothing to guide him except the finding of the copper itself. Any one of the numerous conglomerate seams which from Keweenaw Point to Minnesota are everywhere interbedded with the pre- vailing basic flows, might become cupriferous at any point along its course. Large portions of the Keweenaw Series may be thrown out of the ques- tion in considering the possibilities of future discovery of copper in the Lake Superior region. Thus the whole extent of country occupied by the Upper Division of the series, with the one exception of the Nonesuch sandstone belt, appears to be non-cupriferous. The extent of the Upper Division is indicated on the accompanying maps. Again, all of the belts and areas of acid eruptive rocks, such as the central area of the Porcupine Mountains, and the great spread of red rock in the Brulé Lake country in Minnesota, are without copper. The same is true also of all belts and areas of coarse- grained basic rocks, such as the great area of coarse gabbro in the Bad River country in Wisconsin and the similar area which occupies so large a belt of country between Duluth and Brulé Lake in Minnesota. The favor- able phase of the formation for the existence of copper in any form of deposit is the thin and regularly bedded one, with well-developed amygdaloids. 428 COPPER-BEARING ROCKS OF LAKE SUPERIOR. Thus far native copper mining has proved profitable within the limits of the State of Michigan only, and it seems to be true also that all or nearly all of the producing deposits have been opened on and worked by the ancient miners, whose attention was of course attracted by those deposits which by the accidents of erosion had been left prominently exposed. It is incredible that even in the long-settled districts of Michigan all of the workable deposits of copper have been discovered. Thus on Keweenaw Point the valley south of the Greenstone Range, in which lie buried beneath a surface coating of drift the equivalents of the Portage Lake cupriferous beds, has never been explored by trenching or mining opera- tions. The same is in a measure true of the Bohemian Range of Keweenaw Point. ; Without the boundaries of the State of Michigan, the attempts at copper mining have been but feeble, and utterly inadequate to prove or disprove the existence of workable copper deposits. In Wisconsin native copper has been met with all along the course of the southern Keweenawan belt from Montreal River to the Saint Croix. Running from the Montreal, in Sec. 2, T. 47, R. 1 E., southwest and west, is a belt of distinctly bedded and often amygdaloidal diabases in which copper has been seen in greater or smaller quantity both in crossing veins and in altered diabase belts, at the crossing of each stream, the intervening areas being drift covered At the crossing of Montreal and Bad rivers this belt is worthy of further exam- ination.’ Beyond Bad River, to the southwestward, float copper is exceed- ingly common, and traces of it are here and there met with in the ledges themselves. Unfortunately the country is one covered with heavy drift accumulations, through which only the harder and more enduring, and therefore non-cupriferous, beds ordinarily project. The indications are that, but for the overlying sheet of drift, this region would be as productive in copper as that of Keweenaw Point. Rounding the turn at the western end of the great Keweenawan syn- clinal, in the Saint Croix Valley, we find the drift covering lighter, and here, in the vicinity of Snake and Kettle Rivers, and thence northeastward into Douglas County, in Wisconsin, are found plainly bedded diabases and ‘See Vol. III, Geol. of Wis., pp. 205, 206. COPPER IN WISCONSIN AND MINNESOTA. 429 amygdaloids carrying copper with interbedded cupriferous conglomerates. The region is one which in the early days of mining excitement on Lake Superior was so remote and inaccessible that the flood of copper hunters which at that time spread west from Keweenaw Point failed to reach it. It still lies almost wholly unexplored, while promising more to the copper hunter than any other portion of the entire extent of the formation outside of the State of Michigan. Further north and east from the district last described lies the Copper Range of Douglas County, Wisconsin.’ This range has already been fully described on a previous page as to its position and structural characters. Copper has been found along its course in a number of places, chiefly in epidotic altered amygdaloids, and the general structural characters are such as to indicate the possibility of the occurrence of copper in quantity along this belt. Some little mining has been done at several points, but not enough to lead to any satisfactory conclusions. On the Minnesota coast of Lake Superior, copper has been met with at only two or three points. Of the five subordinate groups into which I have divided the rocks of this coast, only two, the Agate Bay and Tem- perance River groups, are of such a nature as to encourage the expectation that copper might be found in them. The great thickness which makes up the other three groups—and the same is true of considerable portions of the two groups named—is for the most part composed of very massive compact beds such as have never yielded copper on the South Shore. The beds of the Agate Bay and Temperance River groups are often thin, much altered, and highly amygdaloidal, and might perhaps be found to carry here and there workable deposits of copper. The distribution of the rocks of these two groups is approximately shown on Plate XXVI of this volume, from which it will be seen that the extent of country within which there is any likelihood of the discovery of copper in this region in the future is a small one, lying for the most part in the immediate vicinity of the lake shore. It is also to be observed that the most probable mode of occurrence for copper within this restricted area is the amygdaloid belt, the form in which occurs the copper of French River, where the metal is associated with eee eee eee 1See Chapter VI, p. 250. See also Geol. of Wis., Vol. III, pp. 357, 362. 430 COPPER-BEARING ROCKS OF LAKE SUPERIOR. much prehnite; that such amygdaloid belts will dip towards the lake at a very flat angle; and that cupriferous conglomerates are not to be looked for. Isle Royale is the only remaining portion of the copper-bearing rocks within the territory of the United States. It has long been known to be cupriferous ; the copper occurring here in the three forms of transverse veins, epidote courses and amygdaloid belts. Thus far mining has never prospered on the island. It can, however, hardly be said that the ground has as yet been sufficiently tested. NOU Se NOTE 1. (Page 13, line 1.) N. H. WINCHELL ON THE GEOLOGICAL POSITION OF THE COPPER SERIES. Since this was printed, N. H. Winchell has published (Tenth Annual Report of the Geological and Natural History Survey of Minnesota, pp. 123-126) a more definite statement of his views as to the geological position of the Copper-Bearing Series, which he places, as before, as the equivalent of the Potsdam Sandstone of New York, regarding the Eastern Sandstone, however, as in part newer than, and unconformably superposed upon, the Copper-Bearing Series. He had not before stated definitely his views as to the position of the Eastern Sandstone. See further as to this, Note 22. NOW Ea: (Page 14, foot-note.) LITERATURE LIST. Mr. M. E. Wadsworth’s bibliography of Lake Superior Geology, referred to in this foot-note, covers references, not only to the Copper-Bearing Series, but to all other formations represented in the Lake Superior region. It is arranged alphabetically, and brought down to 1880. The references in the literature list of this volume are all taken directly from the originals, my indebtedness to Mr. Wadsworth’s bibliography consisting in its having led me to a number of references which might otherwise have been overlooked. NOTE 3. ADDITIONS TO LITERATURE LIST. (Page 18.) Insert, as last reference under 1854: Wuitney, J.D. Metallic Wealth of the United States. Philadelphia, 1854, 510 pp. (Page 21.) Insert under the year 1871, as the second work: Koos, J.H. Geologische Notizen aus Minnesota. Zeit. der deutsch. geol. Gesell., 1871. Ae 432 COPPER BEARING ROCKS OF LAKE SUPERIOR. (Page 23.) Insert under 1880 the following additional reference: Irvine, R. D. The Mineral Resources of Wisconsin. Trans. Am. Inst. Min. Eng., 1880, viii, 478-508. (Page 23.) The following works, referring more or less fully to the Copper-Bearing Rocks, have appeared since the literature list was printed: 1882. POWELL, J. W. Report of the Director of the U. 8. Geological Survey, for the year ending June 30, 1881. Contains a brief preliminary announcement (pp. xxxi- xxxix) of some of R. D. Irving’s most important results. WINCHELL, N. H. Tenth Annual Report of the Geol. and Nat. Hist. Survey of Min- nesota, 254 pp. 18883. . CHAMBERLIN, T.C. Geology of Wisconsin, Vol. I, Part I. General Geology, 1-300. Irvine, R. D. Mineralogy and Lithology of Wisconsin. Geology of Wisconsin, Vol. I, Part II, 309-361. NOTE 4. (Page 32.) CHRONOLOGICAL RELATIONS OF THE DIFFERENT CLASSES OF ERUPTIVES OF THE KEWEENAW SERIES. The facts upon which is based the statement of page 32, to the effect that no such chronological relations are found to obtain between the Keweenawan eruptives of dif- ferent degrees of acidity as are said to hold true in so many Tertiary and Post-Tertiary voleanic regions, are given in various places in subsequent pages of the memoir. It will, however, be convenient to summarize and classify them here briefly, including the results of some analytical determinations made since the memoir has been in type. The chronological relations referred to as obtaining, according to the geologists who have examined them, in many Tertiary and Post-Tertiary voleanic regions, and notably in those of the western cordilleras, consist in this, viz, that the eruptives of different acidity have followed one another in a certain unvarying order. The earliest eruptives of any one district are found to have been of rocks of intermediate acidity. Next in order have come rocks of high acidity; whilst last of all have been erupted those of low acidity, ordinarily known as “basic.” Among the Keweenawan eruptives there has been no such chronological relation. The facts upon which this conclusion is based may be classed under the following heads: (1) the positions of the different kinds of eruptives in the stratigraphy of the series; (2) the occurrence of acid flows directly and visibly superposed upon basic flows; (3) the occurrence of flows of in- termediate acidity overlying acid flows; (4) the occurrence of flows of intermediate acidity overlying porphyry-conglomerates; (5) the occurrence of flows of intermediate acidity overlying basic flows; (6) the intersection of basic by acid rocks. On the other hand we may cite as showing not only the absence of the ordinary Tertiary order, but the failure of order of any kind; (7) the occurrence of basic overlying acid flows; (8) NOTES. 433 the occurrence of basic flows superposed upon intermediate flows; and (9) the inter- section of acid by basic rocks. (1.) Lhe position of the different kinds of eruptives in the general stratigraphy of the series.—Acid rocks, while on the whole decidedly affecting low horizons in the series, here and there occur at quite high ones, as, for instance, in the Poreupine Mountain region (pp. 155, 206—224, and Plates XIX, XX, and XX1J), and on Michipicoten Island (pp. 155, 342, 343). In the latter case the acid rocks occur at the summit of a series of over 18,000 feet of plainly bedded eruptive flows, both intermediate and basic, with interstratified conglomerates and sandstones. But, wherever occurring, at low horizons or high, the beds of acid rocks have commonly above and below them basic beds. The instances of such an occurrence of acid rocks are altogether too numer- ous for all to be here referred to. I may merely mention the following cases: Mount Houghton, on Keweenaw Point (pp. 181-183, Plates XVII, XVIII), is a mass of red felsite, having both on the south, or below it, and on the north, or above it, great thicknesses of basic flows. The belt of red porphyry which forms so prominent a feature to the west of the Ontonagon River, and as far as the Bad River in Wisconsin, has in a similar manner basic flows both above and below it (pp. 199, 209, 220, 231, Plates XXII, XXIII. See also Geol. of Wis., III, pp. 195, 198, Plate XVI, and Atlas, Plate XXII). On the Minnesota coast the larger number of flows of acid rocks occur in the subordinate series of beds which I have called the Beaver Bay Group (pp. 298- 323). Both above and below the Beaver Bay Group occur great thicknesses of basic flows (Agate Bay Group, Temperance River Group, pp. 267, 268, and Plate XX VI); besides which, within the Beaver Bay beds themselves, the acid rocks are found over- Jain and underlain by basic flows. But not only is it plain from their stratigraphical relations that the acid and basic eruptives alternated with one another in formation; the flows of intermediate acidity also evidently alternated, as to time of formation, with both basic and acid flows, for the beds of intermediate acidity occur at many horizons throughout the series. For instance, the peculiar, resinous-looking diabase-porphyrites of the south side of Michi- picoten Island (pp. 86, 87, 343), having about 60 per cent. of silica, lie above many thousand feet of basic flows. Numerous instances of the occurrence of sub-basic diabase-porphyrites on the Minnesota coast might also be cited in this connection, as, for instance, the brown diabase-porphyrite, with strongly-developed amygdaloid, which forms the shore cliff one mile below the mouth of Silver Creek, NE. 4 Sec. 22, T.53, R. 10 W., Minnesota (pp. 80, 54, 285). An interesting case of the interstratification of a rock of intermediate acidity with basic kinds is furnished by the trap belt which overlies the felsitie porphyry of the Porcupine section (pp. 209, 214, 217, Plates XIX, XX, XXI). This belt has a surface width of one-fourth to one-third miles, and a thick- ness of from 300 to 500 feet. Towards the middle of the thickness a porphyry-con- glomerate is included, with a thickness of over 60 feet. The rocks of this belt include diabases and diabase-amygdaloids of the ordinary types, and luster-mottled melaphyrs. Interstratified with these, both above and below the intermediate conglomerate, are layers of a diabase-porphyrite which is distinctly of intermediate acidity, containing, so far as determined, about 60 per cent. of silica. Clearly, then, we have here an acid porphyry succeeded by flows of a wholly basic material, following which come, in as- cending order, arock of intermediate acidity, others which are completely basic, a por- 434 COPPER BEARING ROCKS OF LAKE SUPERIOR. phyry-conglomerate, basic flows, again more rocks of intermediate acidity, more basic rocks, and finally a great thickness of porphyry-conglomerate and sandstone. No possible explanation of this section can be offered by which a succession of intermedi- ate, acid, and basic eruptions can be made out, for even if the acid porphyry lying at the base of the section should be taken as intrusive, and therefore possibly subsequent to the overlying rocks, there remains the intervening porphyry-conglomerate to prove the existence of acid porphyries prior to the eruption of both the intermediate and basic rocks of this belt; whilst the diabase-porphyrite cannot in any way be made out as antecedent to all of the basic rocks with which it is immediately associated. It should be said that in all cases here cited of the occurrence of rocks of inter- mediate acidity, care has been taken to refer only to those in which the intermediate acidity is plainly an original character, and not in any measure one due to a subse- quent infiltration of secondary quartz. The question might arise in some minds as to whether the cases here cited of the indiscriminate stratification of acid, intermediate, and basic rocks might not be due to the subsequent intrusion in the form of sheets of all of the basic rocks concerned. That some of the basic rock beds of the series, and especially those formed of coarse- grained rocks, may be of an intrusive nature, has been indicated in the memoir (pp. 27, 144), though definite evidence of this is lacking. However this may be, in the present connection, care:has been taken to consider only those basic rocks which are furnished with well-developed amygdaloids and are consequently the results of flowage at the then existing surface in each case. Indeed, should we, for the sake of argument, admit—what Ido not at all believe—that all of the basic and intermediate beds which are not furnished with amygdaloids are intrusive, those furnished with amygdaloids being always taken as surface flows, we should immediately find ourselves at the saine result, namely, that there has been no definite order among the eruptions of different acidity. Many more instances than are here mentioned might be cited, but it is thought that those given are sufficient for the sake of the argument. The Huroniap, beneath the Keweenawan, contains many beds of eruptive mate- rial. True acid rocks are extremely rare, if indeed they occur at all, but basic and intermediate eruptives are plenty. There is much doubt, with our present knowledge of them, as to how far these eruptives are intrusive, and though it is not deemed prob- able, some of them may be intrusive sheets, contemporaneous with the surface flows of the Keweenawan. Many of these beds partake of the folds of the folded Huro- nian and hence antedate the folding. On the whole, it now seems probable that by far the greater part of the Huronian eruptives preceded all of the Keweenawan eruptives, acid and basic. (2.) The occurrence of acid flows directly and visibly superposed upon basic flows.— Acid rocks directly overlying basic flows are met with m several places on the Min- nesota coast, but in the case of the Great Palisades, fully described in the memoir (pp. 146-148, 314-318, Figs. 23 and 24), the occurrence is so striking and conclusive that no others need be cited. To the descriptions given in the memoir, I may merely add here that analytical determinations made since these descriptions were in type show that the diabases {or rather diabase-porphyrites, since they contain much non-polarizing matter) underlying the quartz-porphyry of the Palisades belong with the more basic of NOTES. 435 the basic rocks, having less than 48 per cent. silica. Of course the presence of strongly- marked amygdaloids and of intervening red shaly seams proves that these diabases succeeded each other regularly as flows at the then-existing surface, and that the last of them was succeeded in turn by the flow of the quartz-porphyry which makes up the mass of the Palisades. (3.) The occurrence of flows of intermediate acidity immediately overlying acid flows.— The porphyry of the Palisades just alluded to, or another flow closely like it, at the mouth of Baptism River, passes under a series of beds seen in a single cliff, in which the succession is as follows, beginning below: (1) brown, aphanitie diabase-porphyrite, with 52.5 per cent. of silica, thickness not measured, but under fifty feet; (2) black olivine-diabase, with crowning amygdaloid, and containing 50.76 per cent. of silica; and (3) brown diabase-porphyrite, with 57.87 per cent. of silica, and also furnished with a crowning amygdaloid. Thus, overlying a quartz-porphyry, we have im order a sub- basic, a basic, and an intermediate flow. (4.) The occurrence of flows of intermediate acidity overlying porphyry-conglomer- ates.—Intermediate flows are of course often met with at horizons in the series higher than occupied by beds of conglomerate. In the ease of the inner trap belt of the Por- cupine Mountains (pp. 214-217) a diabase-porphyrite, with 60 per cent. of silica, very closely overlies a porphyry-conglomerate, a small thickness of basic flows separating the two. (5). The occurrence of flows of intermediate acidity immediately superposed upon basic jlows.—A number of occurrences of this kind are to be met with among the Agate Bay and Lester River beds of the Minnesota coast (pp. 267, 279-294), but the only case in which the silica contents of the adjoining rocks have been determined is that of the cliff side one mile below the mouth of Baptism River, cited in the last paragraph, in which case an olivine-diabase, with 50 per cent. of silica, is overlain by a diabase-porphy- vite with 58 per cent. of silica, both rocks being plainly surface flows, since both are furnished with well-developed amygdaloids. (6.) The intersection of basic by acid rocks.—Coarse olivine-gabbro is intersected by granite in a number of places in the Bad River region of Wisconsin (Geol. of Wis., III, pp. 168, 183-193; this vol., p. 125). The coarse orthoclase-bearing gabbro of Da- luth (49 per cent. silica) is intersected by granitic and other acid porphyries (pp. 270- 272). Granite-like rocks, apparently intersecting basic flows, occur at several points on the Minnesota coast (pp. 303, 305, 310, 329). On the Bohemian Mountain, on the north side of Lac La Belle, Keweenaw Point, red granitic porphyry apparently inter- sects a melaphyr (p. 184). (7.) The occurrence of basic flows overlying acid rocks.—The quartziferous porphyry of Baptism River, already several times cited, is closely overlain by a basic flow, and a number of other instances are to be met with on the Minnesota coast. In the region of the Ontonagon River and the Porcupine Mountains (pp. 206-225), and again in the Bad River region of Wisconsin (Geol. of Wis., pp. 195-198, and Atlas, Plate XXII) are sim- ilar occurrences. (8.) The occurrence of basic flows overlying those of intermediate acidity A number of cases of this occur among the Agate Bay beds of the Minnesota coast (pp. 284-294), and the same thing is met with in the inner trap belt of the Porcupine Mountains, as already described. 436 COPPER BEARING ROCKS OF LAKE SUPERIOR. (9.) The intersection of acid by basic rocks.—Dikes of basic rocks are to be observed cutting acid porphyries at a number of places on the north shore, as for instance near Lester River (p. 283), at Beaver Bay (p. 307), at Grand Marais (p. 320), near Red Rock Bay (p. 322). In the last case the dike-rock is a diabase-porphyrite with only 45.8 per cent. of silica, whilst the rock intersected is a typically developed quartz-porphyry. NOTE 5. (Page 32.) COMPARISON BETWEEN TERTIARY AND KEWEENAWAN ERUPTIVES. In a first brief announcement of the results of my study of the Keweenaw Series (Report of the Director of the United States Geological Survey for the year ending June 30, 1881, p. xxxiii), Director Powell says that the acid eruptives of the Kewee- nawan “are regarded by Irving as ancient rhyolites and trachytes, from the degrada- tion of which the conglomerates of the series have resulted.” In the notes I furnished the Director as to my results, I had not meant to convey the meaning that I regarded the Keweenawan acid eruptives as lithologically identical or equivalent with the Ter- tiary rhyolites and trachytes—though his words perhaps might be so understood— but merely to indicate that they occupied the same general position as to acidity and general lithological charaeters among the Keweenawan eruptives as are occupied among the Tertiary eruptives by the rhyolites and trachytes. My acquaintance with the Tertiary eruptives is too limited to allow of my passing an opinion on the accuracy of the view commonly accepted by the most eminent lithologists of the day, viz, that the Tertiary eruptives are always distinct and deserving of separate names from those that preceded Tertiary time. NFO}, E16: (Page 32, eighth line from bottom; also page 138, last paragraph.) VOLCANIC ASH IN THE KEWEENAW SERIES. Mr. A. R. GC. Selwyn has published (Science, Vol. I, No, 1, February 9, 1883; also, Vol. I, No. 8, Mareh 30, 1883), since this volume was in type, a statement that volcanic ash exists in the Keweenawan rocks of Michipicoten Island, but he has not yet pub- lished any description of this material. Macfarlane, in his descriptions of the Geology of Michipicoten Island (Geol. Surv. Canada: Report of Progress, 186366, p. 138 et seq.), Speaks of “ breccias,” which, as I understand him, are the rocks to which Selwyn refers. Macfarlane describes the breccia in one case as consisting of ‘ small fragments of melaphyr, some fresh looking, but the greater part bleached to a reddish-gray color, inclosed in a reddish-brown earthy matrix, consisting most probably of finely commi- nuted melaphyric material, as it is readily fusible before the blow-pipe.” In another case he speaks of ‘a trap breccia, composed of fragments of dark-brown melaphyr, cemented together by a brownish-red trappean sand.” Ihave not observed anywhere on the south or north shores of the lake any rocks which resemble these, if I under- stand Macfarlane’s descriptions correctly, unless they are somewhat like the Nonesuch sandstone of the Porcupine Mountains. I have said in the text that this sandstone may be in part of volcanic ash nature. Though it is not impossible that the Michipicoten NOTES. 437 breccias may, in part at least, have originated as volcanic ash, I imagine that it would be exceedingly difficult to prove such an origin for them. Constant avgularity of the particles might perhaps point that way, but a genuine vesicular character to each fragment would be about the only proof of such an origin, and in such ancient rocks, so profoundly altered as these must be, it would be extraordinary if angularity and vesicular character should be preserved. Dr. T. S. Hunt writes me that he observed nothing on Michipicoten Island that reminded him of the typical voleanic ash of such regions as those of Vesuvius and the Eifel, and suggests that these brecciated rocks may be due to the disintegrating effect of waters upon material extravasated beneath the sea. Such an origin is, of course, possible, and it may be true in a measure also of the common red sandstones of the Keweenaw Series, though these are very plainly in large measure composed of water-rolled and water-worn fragments. But, whatever the origin of the Michipicoten breccias may be, I have never met with anything just like them on either the north or south shores of Lake Superior, if Iunderstand Macfar- lane’s descriptions correctly. NOLE (Page 39.) PLAGIOCLASTIC INGREDIENTS OF THE KEWEENAWAN BASIC ERUPTIVES. Since this volume has been in type, a number of separations, by Thoulet’s specific gravity method, of the plagioclastic ingredients of the several kinds of Keweenawan basic rocks have been made by my assistant, Mr. C. R. Vanhise. These separations were undertaken with the view of determining whether only one plagioclase feldspar, as indicated by the optical method, or more than one, is concerned in the make-up of the Keweenawan basic eruptives. The investigation is not yet completed, but so far as it has gone it has tended to strengthen the conclusion already arrived at, namely, that only one plagioclase feldspar is ordinarily present, except in some of the por- phyritice kinds, in which the porphyritic plagioclases are different from the microliths of the groundmass. Especially in the case of the coarse olivine-gabbros and olivine- free gabbros did the experiment confirm the conclusions before arrived at, namely, that only one plagioclase is concerned, and that commonly lies, in its silica content, between anorthite and labradorite. The silica determinations made upon the separated plagi- oclases in no case showed less than 46 per cent. But if we accept, as it seems almost necessary that we should do, Tschermak’s theory of the nature of the intermediate plagioclase feldspars, this high silica content is easily explicable on the view that only one feldspar is concerned. Tschermak’s view is still further confirmed by the fact that, in every instance where the optical measurements stood near the border between anorthite and labradorite, the silica content also more nearly approached that of labradorite. See also Note 10 for the results of experiments made with the coarse anorthite- rock of the Minnesota coast. 438 COPPER BEARING ROCKS OF LAKE SUPERIOR. NOTE 8. (Page 46.) NATURE OF THE FELDSPATHIC INGREDIENT OF GABBRO FROM CLOQUET RIVER. The feldspar of specimen 1103, separated from the other ingredients by Thoulet’s method, gave 52.40 per cent. of silica, or almost exactly that of labradorite, the feld- spar indicated by the optical measurements, as will be seen by reference to the table on page 46. NOTE og. (Page 50.) NATURE OF THE FELDSPATHIC INGREDIENT OF THE GABBRO FROM NEAR THE MOUTH OF NIPIGON RIVER. The feldspar of specimen 1752, separated out by Thoulet’s method, yielded 49.28 per cent. of silica. The optical measurements indicate anorthite. A separation of the feldspars into two parts by Thoulet’s method was tried, but without success. NOTE ro. (Page 113.) SECONDARY QUARTZ. The secondary quartz of the orthoclase-gabbros (p. 51), augite-syenites, and granitoid porphyries of the Keweenaw Series (p. 113) is chiefly of the kind called by Fouqué and Lévy (Minéralogie Micrographique, p. 193), “‘quartz de corrosion.” Some of the secondary quartz of the last-named rocks may also correspond to their “ quartz globulaire” (op. cit., p. 194), but I find nothing in their descriptions or figures which recalls the peculiar arborescent secondary quartz so commonly met with in the matrices of the Lake Superior felsitic porphyries (p. 92). NO GSE, ata. (Page 59.) ANORTHITE-ROCK, Since this account of the rock of the anorthite bowlders and masses, met with inclosed in the olivine-gabbro of the Minnesota coast, was put in type, the following analytical determinations have been made upon the anorthite: | | 22 B 729 |729A|729B| 822 }822A| (single | 822 C | | crystal.) Silica (Si Oz). --...----- Alumina (Als Oz)...-- seoseee Iron protoxide (Fe 0). Famer(CaiO)ec-- ---ee= Magnesia (Mg 0) ..-.. ee Potash (Ke QO) ..-...--. nocBacel hes Soda (Naz O).....-- a Water (He 0) .--...... | No. 729 is from a great mass of anorthite surrounded by black olivine-gabbro, near the mouth of Split Rock River, on the Minnesota coast (see p. 59). The sample for the NOTES. 439 analysis was broken from all parts of the specimen, care being taken to select parti- cles free, so far as could be detected, from any included substance. Nos. 729 A and B, are from portions separated by Thoulet’s method (iodide of mercury solution). At a specific gravity of 2.713 a very few dark-colored particles separated out. On grad- ually diluting (by the slow addition of water, and mixing after each addition) no more fell until the specifie gravity was reduced to 2.691, by which time two-thirds of the powder had separated out. This was drawn off and constitutes 729 A. On continuing the dilution the deposition continued, until at 2.663 specific gravity nearly all the powder had fallen. This was then drawn off and constitutes 729 B. Thus the depo- sition was a continuous process from 2.713 specific gravity to 2.663 specific gravity, and there was no sharp separation. This, taken together with the similarity between the silica percentages of 729 A and 729 B, seems to indicate the simplicity of the feld- spar, whose crystals were so large that on crushing each must have been broken into many thousand pieces, so that the deposited material could hardly have been compound because of an interlocking of crystals. Two thin sections of 729, in addition to the ones described on page 59, were made, and the following angular measurements obtained from the feldspar individuals: Angles on opposite sides of & ELOSEERAicEs Whole angle. 83° 38° 71° 31 36 67 31 28 59 33 25 58 24 29 53 39 38 77 32 34 66 No. 822 is from a large, bowlder-like mass included in the black olivine-gabbro of the Minnesota coast two miles below Beaver Bay (p. 61). The complete analysis is made upon material carefully selected from all parts of the hand specimen; the silica determination of 822 C being upon less carefully selected material; $22 A is the mass of the powdered rock separated out by Thoulet’s method at 2.70 specifie gravity, a very small portion being left suspended ; 822 B is a single erystal very carefully separated from the rock. From these figures, and especially from the close correspondence of the silica content of the single crystal with that of the powdered rock, it is evident that there is no admixture of feldspars in this case. ' The following additional optical measurements were made from new sections of $22: Angles on opposite sides of Whole angle. eross-hair. ) 24° 47° | 3B 23 52 33 25 48 40 41 81 28 zs = 3 7 37 22 60 24 25 49 33 36 69 30 29 59 32 35 67 33 20 62 440 COPPER BEARING ROCKS OF LAKE SUPERIOR. Although these investigations plainly indicate that there is only one feldspar con- cerned in this rock, yet this feldspar does not correspond in composition to typical anorthite, which contains, according to Dana, silica, 43.1; alumina, 36.9; lime, 20; equals 100. This composition corresponds, for R: B®: Si, to the quantivalent ratio 1:3:4; whereas the analysis above given gives a ratio of about 1: 2.4: 4.15. Since a single crystal, showing no sign of interpenetration by other feldspar individuals, or of admixed impurity of any kind, gave nearly the same silica content as shown in the complete analysis, it appears evident that the latter is the true composition of the anorthite composing the rock now under consideration. Dana gives a number of analyses of anorthite which are closely like the one given above. If the view of Tschermak as to the nature of the intermediate triclinic species be accepted, then, of course, the composition expressed by this analysis requires no further explanation. NOTE 2. (Page 72.) ERRATUM. T. 51, R. 42 W., should read T. 51, R. 12 W. NOW Ee 3. (Page 82.) DIABASE-PORPHYRITE OF THE PORCUPINE MOUNTAINS. Specimen 1245, diabase-porphyrite, contains 59.75 per cent. of silica. NOTE 14. . (Page 84.) DIABASE-PORPHYRITE OF THE GREAT PALISADES. Specimen 884, from the compact portion of one of the flows underlying the quartz- porphyry of the Great Palisades, contains only 47.90 per cent. of silica, and is hence one of the most basic of this class of rocks. NiO Ens). (Page 85.) DIABASE-PORPHYRITE FROM TWO MILES BELOW THE MOUTH OF BAPTISM RIVER. Specimen 907, diabase-porphyrite, has of silica 52.56 per cent. 1 System of Mineralogy, p. 339. NOTES. 441 NOL EF) «6. (Page 109.) COMPOSITION OF QUARTZ-PORPHYRY OF THE GREAT PALISADES. Specimen 876, representing the quartz-porphyry of the Great Palisades of the Minnesota coast of Lake Superior contains 71.10 per cent. of silica. NVOLLD Ey 7: (Page 110.) QUARTZ-PORPHYRY OF BAPTISM RIVER POINT. Specimen 902 has 73.87 per cent. of silica. NOTE 18. (Page 152.) ERUPTIVE MATERIAL IN THE UPPER DIVISION OF THE KEWEENAW SERIES. A slight exception to the general absence of eruptive material from the Upper Division of the Keweenaw Series is found in the olivine-diabase dike described on page 223, A small exposure of diabase was also noted among the sandstones of the Upper Division on the Saint Croix River in Sec. 35, T. 44, R. 13 W., Wisconsin, by the late Moses Strong (see Geol. of Wis., p. 424). It is not evident whether this exposure repre- sents a thin intercalated seam or a dike. Both these occurrences are in the lower part of the Upper Division of the Series. NOTE 19. (Page 224, line 14 from top of page.) ERRATUM. T, 40 should read T. 49. NOTE 20. (Pages 253-258.) THE UNCONFORMABLE CONTACT OF BLACK RIVER, DOUGLAS COUNTY, WISCONSIN. The quotations here given from Mr. Sweet’s descriptions of this contact are per- haps not extensive enough to bring out all the important facts. As the occurrences on Black River and on the other streams of the vicinity have a very considerable impor- 442 COPPER BEARING ROCKS OF LAKE SUPERIOR. tance, I add three cross-sections of the gorge (constructed from Mr. Sweet’s descrip- tions), whose southwest wall is represented in Fig. 10, with the design of bringing out more distinctly the relations of the exposures here seen. we Fic. 37.—Cross-sections of gorge of Black River, Douglas County, Wisconsin. I, at about 4 of Fig. 10; I, at 5o0f Fig. 10; III,at 7 of Fig. 10. Scale natural, 200 feet to the inch. These cuts will serve to make plainer Mr. Sweet’s reading of the structure at this point. If the reading is correct, of which I have no doubt, it is evident not only that we have to do here with an unconformable contact, but also that the newer sandstone is here deposited within the sinuosities of the old coast-line. NGO MEE 2-1. (Page 316.) DIABASE-PORPHYRITE OF THE GREAT PALISADES. The compact diabase-porphyrite of the layer immediately beneath the quartz- porphyry of the Palisades contains 47.9 per cent. of silica. NOM E22; (Page 350.) GEOLOGICAL POSITION OF THE COPPER-BEARING ROCKS. The question of the equivalency of the Copper-Bearing Rocks with geological formations of other regions is not directly touched upon in the discussions of Chapter VIII, in which I have contented myself with an attempt to demonstrate their complete distinctness, structurally, from any of the immediately associated formations and their consequent right to a distinct name, of at least local significance. I have shown that they are not Huronian, and that at the same time they are separated by a great uncon- formity from the overlying fossiliferous Cambrian sandstones, with which they come in contact. Heretofore most of the differences of opinion in this connection have been upon these very points. A number of writers, and especially Messrs. Foster and Whitney, maintaining the unity of the Keweenaw Series and the Cambrian sandstones above re- ferred to, and maintaining at the same time the equivalency of these sandstones with the so-called Potsdam of New York, have been led to include the Copper-Bearing Rocks also with the Potsdam sandstone. On the other hand, those who have maintained the pre- Potsdam age of the Copper-Bearing Rocks, including the writer of this volume, accept- ing the reference of the overlying sandstones to the Potsdam of New York, have NOTES. 443 thought it sufficient, in order to establish their point, to show the existence of a great unconformity between the Copper-Bearing Rocks and the overlying sandstones. A; Recently, however, two writers, Messrs. Selwyn! aud N. H. Winchell,? while ad- mitting the existence of this unconformity, and the consequent distinctness of the Copper-Bearing Series from the overlying sandstones, have yet maintained the Cam- brian age of the former rocks. These two writers, however, differ somewhat between themselves, Selwyn merely maintaining that the Copper-Bearing Rocks, along with the overlying Cambrian sandstones and the underlying Animikie slates, “oceupy the geological interval elsewhere filled by those divisions of the great Paleozoic system which underlie the Trenton Group,” without more definitely parallelizing them with the older Paleozoic formations of the Eastern States. He also says that he prefers “to. call them all Lower Cambrian, which includes the Potsdam sandstone and the Primor- dial Silurian.” Winchell, on the other hand, would make the Copper-Bearing Rocks the direct equivalent of the New York Potsdam, while regarding the sandstones which uncon- formably overlie them, 7. ¢., the “Eastern” and “ Western” sandstones of this volume, and the fossiliferous Cambrian sandstone of the Mississippi Valley (his Saint Croix sandstone), as later than the New York Potsdam. Stated in his own words, the follow- ing are Winchell’s conclusions: 1. “The Taconic Group was correctly established by Professor Emmons, though its limits, stratigraphically and geographically, were at first wrongly defined by him. 2. “The Georgia Group of Vermont, and the Animikie Group of Thunder Bay, and the Acadian of New Brunswick are the equivalent of the Taconic of Emmons. 3. “The Taconic has the true Primordial fauna of Barrande. 4, “The Potsdam, which lies conformably above it in the east, is represented by the rocks of the Copper-Bearing Series in the west. 5. “No fossils, representing the true Primordial fauna, have yet been discovered in the west, nor have any been found in the western representative of the Potsdam. 6. “The ‘second fauna’ of Barrande is found in the Quebec Group of Canada, and in the Saint Croix sandstone of the west, lying in each case above the Potsdam sand- stone.”® Elsewhere! Winchell suggests the probability of a former continuity, in the region north of Lake Superior, of the Animikie slates and the schists, which in that region have been called Huronian, a position which I have regarded in the preceding pages as muck more than probably true. If it is so, and Winchell’s reference of the Ani- mikie to the Taconic of Emmons is correct, then the Huronian and Taconic are also the same, which would extend Winchell’s use of the term Cambrian over the Huronian as well as over the Copper Series. Into a diseussion of the question as to how far downwards the term Cambrian should be stretched, I have no desire to enter at length, since I think it would be a profitless one. I will only say that, in using the word Keweenawan, I have never designed to give to this term a scope equivalent to that of the terms Cambrian, Silurian, &e., but 1Science, Vol. I, pp. 11, 221. 2Yenth Annual Report of the Geol. and Nat. Hist. Surv. of Minnesota, pp. 123-136, also Science, Vol. I, p. 334. 3Tenth Annual Report of the Geol. and Nat. Hist. Surv. of Minnesota, pp. 135, 136. 40p. cit. pp. 90, 94, 95; also Science, Vol. I, p. 834. 444 COPPER BEARING ROCKS OF LAKE SUPERIOR. have merely designed to indicate by it the entire structural distinctness of the Copper- Bearing Rocks from the oldest of the fossiliferous Cambrian sandstones of the region, as well as from the underlying Huronian. I may also add that it appears to me very unreasonable to stretch the term Cambrian over such an unconformity as subsists between the last-named sandstones and the Keweenaw Series, and yet more to stretch it over the unconformity between these sandstones and the Huronian. Everywhere throughout the Northwestern States, where the Cambrian sandstones come in contact with the Huronian, there is evidence of an enormous time-gap between the two forma- tions. As one illustration of this relation, out of many that might be cited, I may mention the occurrences in the Baraboo region of Wisconsin, where a great series of quartzites, including siliceous schists and immense beds of a felsitic porphyry, are overlain by the fossiliferous Cambrian sandstones in such a manner as to prove beyond all question that the time which elapsed between the two periods at which these forma- tions were deposited was sufficiently great to cover, (1) the folding and alteration of the older series, measuring upwards of 20,000 feet in thickness; (2) the denudation of the elevations of land thus produced to such an extent that ridges approaching in height the highest existing mountains of the globe were entirely removed, and depres- sions made in their place ; and (3) the depression of this area beneath the sea and the wearing by wave action of the older rocks to supply the material for the newer. Now the older of the formations in this case I take to belong, beyond question, to the same horizon as that to which belong the Animikie slates and the Huronian rocks of the Lake Superior region generally. Certainly no one ever has referred or ever would refer them to a lower horizon, while Winchell even regards them as the equivalent of the New York Potsdam and of the Copper-Bearing Rocks of Lake Superior. Inasmuch as neither the Huronian nor the Copper-Bearing Series has thus far afforded any fossils, it does not seem to me reasonable to extend to them, in spite of these great unconform- ities, the name of Cambrian, even though the fossiliferous rocks immediately overlying them be not, as Winchell has argued from their paleontology, the equivalents of the oldest of the typical Cambrian divisions of Barrande. But, however this may be, it seems sufficiently evident that Winchell’s reference of the Copper Series directly to the horizon of the New York Potsdam is untenable. If I understand him correctly, he supports this reference by three kinds of evidence, stratigraphical, lithological, and paleontological. The stratigraphical evidence con- sists in the occurrence in the east of the following succession, in ascending order: (a) A series of slates, sandstones, &e., of considerable thickness, and carrying Barrande’s first fauna, conformably succeeded by (b) the typical Potsdam sandstone, of very incon- siderable thickness, with only a very few fossils, grading up into (¢) the Calciferous Sandrock, in which, and in whose continuation in Canada, is found a large fauna, cor- ” responding to the second fauna of Barrande. The members of this succession he parallelizes, respectively, with (a) the Animikie Group (and hence with the Huronian of the Lake Superior country generally), (b) the Keweenaw Series, and (c) the Saint Croix sandstone, including the Eastern Sandstone of this volume, and the lowest fossiliferous Cambrian sandstone of the Mississippi Valley. Now, not to speak of the grave doubts which still hang about the relations of the older rocks in the Hastern States, there are serious objections to this scheme of stratigraphical equivalence: (1) It disregards the entire absence, so far as known, of fossil remains from the Ani- NOTES. 445 mikie and Keweenawan rocks, which are often full as favorable in nature to the oceur- rence of such remains as their supposed equivalents in the east. (2) It disregards the unconformity between the Animikie (and Huronian generally) and the Keweenaw Series, which unconformity finds no parallel in the eastern series, as given by Win- chell. (3) It disregards the immense and tar more striking and pronounced uncon- formity met with in the western succession between the Keweenaw Series and the overlying sandstones, which break not only finds no parallel in the east, but is to be contrasted with the gradation of the New York Potsdam into the overlying Calciferous Sandrock. (4) It parallelizes the Keweenaw Series, which approaches a thickness of 50,000 feet, of which fully 15,000 are of purely detrital matter, with a sandstone only a few hundred feet thick. The lithological evidence advanced is hardly worth discussion, because of the well- recognized untrustworthiness of such evidence when applied to the comparison of rock formations at long distances apart. Winchell’s assertions, however, of a lithological correspondence between the New York Potsdam and the Keweenaw Series will not bear examination. In his own words, the New York formation “is a red or gray loose sandstone, often tilted or faulted, also metamorphosed, and then having the name of quartzite.” We look in vain in it for the great beds of porphyry-conglomerate, the immense thicknesses of basic and acid eruptive rocks, and the black shales of the Ke- weenaw Series. Even the sandstones of the two formations do not approach each other in character, those of the typical Potsdam being described as distinetly quartzose, whereas those of the Keweenaw Series are only very subordisately so, being composed almost wholly of fragments of the feldspars or felsitic matrix of the acid eruptives of the same series. The occurrence in the Keweenaw Series of beds of metamorphic origin, including ‘ gneiss, syenite, and hard, red quartzites,” as stated by Winchell, I do not admit. Gneiss is never met with. Peculiar red rocks, to which the name of sye- nite may be applied, are met with in the series, but are plainly of an intrusive nature. Rocks to which the name quartzite could be applied I have never seen; certainly they must be very rare, if they occur at aH. Portions of sandstone beds locally indurated by a quartz infiltration I have occasionally seen, but such rare and unimportant oceur- rences would hardly warrant the mention of quartzite as a characteristic of the forma- tion. On the other hand, there is a distinct similarity between the typical Potsdam as described and the so-called Potsdam of Central Wisconsin, where a quartzose compo- sition, with local indurations due to quartz infiltration, and local developments of red sandstone, often of considerable thickness, are prominent features. The paleontological evidence advanced by Winchell consists in the occurrence, in the Calciferous Sandrock of New York, and in its extension into Canada, of a fauna nearly allied to that of the lowest fossiliferous sandstone of the Mississippi Valley. Accepting the statement as to this similarity so far as it goes, I have to say, (1) that the evidence is too meager to establish a complete equivalency between the Calciferous Sandrock and the Mississippi Potsdam; (2) that even if it were not so, it would remain to show that the Potsdam itself is not merely a downward continuation of the Calcifer- ous, the few fossils that occur in it being insufficient to disprove this relation, while the grada ‘ion of the Potsdam into the overlying Calciferous is a distinct indication of such a relation. In conclusion, then, I have to say that it seems to me quite plain that the horizon 446 COPPER BEARING ROCKS OF LAKE SUPERIOR. of the New York Caleiferous and Potsdam together is represented in the west by the following succession, given in descending order: (a) The Lower Magnesian Limestone, grading, by alternations with sandstone, and decrease of calcareous matter into (b) the basal sandstone of the Mississippi Valley, of whose total thickness of about 1,000 feet, from one-half to two-thirds, is quartzose and non-caleareous, and whose lower- most portions are equivalent to (c) the Western Sandstone and to the Eastern Sand- stone of the Lake Superior region, while it is regarded as probable that the lowest portions of the last-named sandstones are at a lower horizon than any met with in the Mississippi Valley. Probably the New York Potsdam finds its near equivalent in these lowest sandstones and in the lowest portions of that of the Mississippi Val- ley, while the Calciferous Sandrock is represented in the West by the upper half of the last-named sandstone, which alone is fossiliferous, and by the Lower Magnesian Limestone. The question then arises as to whether the Keweenaw Series is the equivalent of any of those fossiliferous rocks which in the east are said to be beneath the typical Potsdam. A discussion of this question, however, would hardly be profitable, until the stratigraphical relation of these eastern formations to the true Potsdam is more satisfactorily made out. When any such discussion is undertaken, however, it will be necessary to keep constantly in mind the great unconformity between the Keweenaw Series and the western representative of the Potsdam sandstone. NOTE 25. (Page 417.) ERUPTIVES OF THE ANIMIKIE GROUP. The cut on page 417 does not differentiate the eruptives of the Huronian from the rest of the series. Some of these eruptives may of course have been contemporane- ous, or nearly so, with those of the Keweenawan, having been formed intrusively, while at the same time those of the Keweenawan above were poured out at the sur- face. The Huronian eruptives are commonly without amygdaloids, which may, of course, be because of their intrusive nature. Still, they ordinarily partake of the folds of the folded Huronian, and must therefore have preceded the Keweenawan erupt- ives at least in large part. * ll PINS Bree Acid original rocks, 91-126, 144-151. ———, Age of, 12, 13. ——-—, Absence of copper in, 426. ——~—, Chronological relation of, to basic eruptives, 32, 432~ 436. ——-—, Classification of, 91. ——-, Distribution of, 155. ——~—, Frequency of, 91. ——-—, Huronian and Keweenawan compared, 405. ——~—, Kinds of, 112-125. ———-—, augite-syenite, &c., 112-124. ———~— felsite and quartz-porphyry, 95-112. ———-—, granite, 125. ———~—, quartzless porphyry, 91-95. ———, Summary of, 126. ——~—, Views on origin of, 12, 150. Agate Bay, Amygdaloids of, 137, 287-289. ——, Olivine-diabase of 72, 76, 287. ——, Section at, 288, 289. Agate Bay Group, 284-294. ——— at Agate Bay, 72, 288-290. ——-—, Amygdaloids of, 136, 286-289. ——_—, Anorthite-rock of, 292. ——~—, Bedding of, 288. ———, Copper possibly present in, 429. ——_-, Dikes of, 293, 294. ——— at Encampment Bluff, 47, 285. ——— at Encampment River, 284, 285, 291. ——~—, Faults in, 290, 291. ——— on French River, 284. ——— on Gooseberry River, 286, 293. ——— near Lester River, 292. ——~—, Olivine-diabase of, 76, 286. —— —, Relation of acid and basic rocks of, 435. ———, Sandstone of, 292, 293. —— — on Split-Rock River, 291. ———on Talmage River, 286. ——-—, Thickness of beds of, 290. ———, Thinning of, at eastern end of Minn. coast, 294, 298. ——-—, Warping of beds of, 290. Agate Harbor, Trends and dips near, 178, 413. Agogebic Lake, Eastern Sandstone at, 360. —-—, Lower Division at, 158. Albany and Boston mine, Augite-syenite pebbles of, 115, 118, | 119, 190, 191. ——-—, Conglomerate of, 190, 191. ——-—, Dip of strata at, 187. ———, Quartzless-porphyry of, 94, 191. Albite in olivine-diabase, 70. Algoma mine, Ferruginous sandstone of, 374. Allouez mine, Dip at, 187. Alteration of augite to chlorite, 43, 64, 79. ——— diallage, 52. ——— ferrite, 79, 98, 102, 114, 125, ——— green substance, 71, 89. ——— hornblende, 56, 114, 125. ——— magnetite, 41. ——— uralite, 52. —, epidote-quartz of amygdaloid, 199. — of feldspars to chlorite, 64, 89. ——— through prehnite to chlorite, 64. ——— to prehnite, 89. — — glass-base in quartz-porphyry, 101. —— ——ferruginons prehnite, 89. * ——— in olivine.diabase, 70. —— olivine to biotite, viridite, and tale, 39. ----— greenish substance, 38. ——— magnetite (?), 39. —— orthoclase to chlorite, 51. — — plagioclase to chlorite, 51. ———-— green substance, 71. ———— prehnite, 46. ——prehnite to chlorite, 89 ———— chlorite, calcite, and green earth, 89. ———— epidote and calcite, 89. ———— orthoclase, 89. —, Pseud-amygdaloidal, 63, 64. — of uralite to chlorite, 52. Aminicon River, Orthoclase gabbro of, 52, 54. ——, Rocks of, 255, 256. Amygdaloids, 87-91, 134-139. —, Absence in Huronian, 403, 445. —, Alteration of, 89, 90, 199. —, Amygdules of, 135, 136. —of ashbed-diabases, 183. —, Characteristics of, 135, 136. —, Constituents of, 88, 89. ——, Ferrite of, 88. ——, Plagioclase of, 88. —, Copper, deposition in, 90, 421, 422. —, Distribution of, 155. —, Fluidal structure in, 83. —, Matrix of, 87, 88. | —, Pumpelly on, 89-91. —, Relations of, to diabase-porphyrites, 87, 89. —, Stratiform, 137. Amygdules of amygdaloids, 89, 90. —, Elongation of, 136. Analcite of amygdaloids, 90. Animikie Group, 367-386. —-—, Bell on “crowning overflow " of, 381, 382. —.—, Contact of, with Keweenaw series, 157, 297, 405. (447) 448 INDEX. Animikie Group, Dikes of, 144, 367, 368. —~—, Dike-rock from, 372, 373. ——at Grand Portage Bay, 297, 369. — —, Interbedded diabases of, 373, 374, 445. ——at Kaministiquia River, 380 ——, Limits of, northern and western, 384. ——at Lucille Islands, 369. ——on Mesabi Range, 382-384. ——at Pigeon Point, 369, 370, 379. ——on Pigeon River, 370, 382. ——at Pokegoma Falls, 383. ——~-—, Portage Bay Island, 297. — —, Relation of, to granites of Mesabi Range, 399. — ———, Hnuronian, 443, 444. — — — — Keweenaw Series, 297, 385, 405, 443-445. —— —— South Shore Huronian, 385, 386. ——on Saint Lonis River, 262, 384. —— at Silver Islet, 378. —— on Thunder Bay, 371-379. —_—, Views on age of, 157, 385, 443. —_--—--— criticized, 385, 386, ——on Wauswaugoning Bay, 368, 369. Anorthite-rock, 59-61. —— in Agate Bay Group, 292. —in Beaver Bay gabbro, 310, 436, 440. —, Characteri&tics of, 59. —, Constituents of, 59, 438-440. — differs from European gabbros, 59. —, Localities of, 59. —, Mode of occurrence of, 59. —at Split Rock River, 302, 438, 439. —, Tabulation of observations on, 59-61. Anorthite of anorthite-rock, 59. —, Analyses of, 438, 440. —, Determination of, by Thoulet’s method, 438-440. —of olivine-diabase or melaphyr, 70. —of orthoclase-free gabbro, 40. Anse aux Crépes, Keweenawan rocks of, 348, Apatite of diabase-porphyrite, 79. —of hornblende-gabbro, 57. —of orthoclase-gabbro, 52. — of orthoclase-free gabbro, 43. Apostle Islands, Sandstones of, 153, 154, 365. Argillite of Nipigon Lake Basin, 340. Ash, voleanic, Absence of, in Keweenaw Series, 32, 138, 139, 436, 437. Ashbed-diabase of Bohemian Range, 183. —, Distribution of, 155. — of Eagle River section, 171-173. — of Lester River Group, 279, 280. —, Origin of name, 138, 173. —, See Diabase-porphyrite. Ashbed Group of Keweenaw Point, 140, 171-178. ———-~—, Characteristics of, 138. -—--- , Section of, 186. ——-—— — , Thickness of, 178. Atlantic Mill, 130, 192. Augite of amygdaloids, 88. ——anorthite-rock, 59. ——augite-syenite, 114. —— basic original rocks, 37, 38. — — diabase-porphyrite, 78, 79. — ——(porphyritic), 79. ——olivine-di base, 70. —— olivine-free diabase, 63, 64. —— orthoclase-gabbro, 41, 42. Augite of orthoclase-free gabbro, 52. —— quartz-porphyry (porphyritic), 102. ——quartzless porphyry (porphyritic), 93. Augite-syenite, 112-125. — of Beaver Bay, 122, 306. —— Brick Island, 369. —, Characteristics of, 112. —, Constituents of, 112-115. ——-—, angite, 114. ——-, feldspars, 112, 113, 114. ——-— , ferrite, 113. ——-—, hornblende, 113. ——-—, magnetite, 114. ——-—, quartz, 112, 113. —— —-—, secondary, 113, 114, 438. —, Localities for, 115. — of Mount Bohemia, 184. —, Name of, 115. —, relations of, 115. — of Saint Louis River Group, 270, 271. —, Tabulation of observation on, 116-124. — of Victoria Islands, 372, 373. —, See Porphyry, Granitic. Azoic Rocks, Reporton. See Hunt, T.S. Bad River, Augite-syenite of, 115. ——, Gabbros of, 40-41, 144, 154, 155, 231, 377, 435, 436. ——, Granite of, 233, 435. ——, Hornblende-gabbro, region of, 56. ——, Lapham on sandstone of, 411. ——, Orthoclase-gabbro of, 52, 54. ——, Orthoclase-free gabbro of, 44, 45. ——, Quartz-porphyry of, 103, 150, 231, 433. ——, Relation of acid and basic rocks on, 435. ——, Sandstone of, 132, 231. ——, Sources of information on, 207. ——, Thickness of Keweenaw Series on, 231. ———~—, Lower Division on, 158. Baptism hiver, Bay, and vicinity, Ashbed-diabase of, 318, 326. ——-—, Augite-syenite of, 116, 123. ———, Beaver Bay Group on, 298, 318, 319. ——-—, Diabase-porphyrite of, 85, 326, 440. ——~—, Felsitic-porphyry of, 110, 318. ——-—, Gabbro of, 272. ———, Quarta-porphyry of, 102, 103, 147, 158, 314, 318, 319, 447. ———, Relation of acid and basic rocks of, 435, ———, Temperance River Group on, 823, 326. Baraboo, Relations of Huronian and Potsdam at, 444. Bare Hills, Felsite of, 149, 182. Bare Point, Ashbed-diabase of, 375. Barrande, J., Western equivalents of 1stand 2d faunas of, 443. - Basic original rocks, 35-91, 134-144, ——-—, Age of, 12, 13. ———, Amygdaloids of, 134-139. ———, Characteristics of, 134-144. ——-—, Classifications of, 35, 37. — ——, Coarse-grained, 37-6". ———-—, anorthite-rock, 59-61. —— ——, hornblende-gabbro, 56-58. —— ——, orthoclase-gabbro, 50-56. ———-, orthoclase-free gabbro, 37-50. ———, Dikes in, 143. ——~—, Dip of, 141, 142. ——~—, Effect on topography, 141. ——--, Extent of single beds, 140. ——~—, Fine-grained, 61-91. —— — —,amygdaloids, 87-91. eo a INDEX. Basic original rocks, Fine-grained, ashbed-diabase, 77-87. —— —-—,diabase-porphyrite, 77-87. ————, olivinitic diabase and melaphyr, 68-77. —— — —, olivine-free diabase, 61-68. ——— in Huronian and Keweenawan, Similarity of, 402,403. ——-, Material for study of, 36. — ——, origin of, Views on, 11. ———, Pumpelly’s description of, 35. — ——, Relation of, to acid rocks, 148, 432-436. ——-—, Rosenbusch’s classification of, 35. ——-—, Thickness of beds of, 134, 141. Batchewanung Bay, Course of Keweenaw Series at, 349. ——, Huronian of, 400. ——, Keweenawan rocks of, 348. Battle Islands, Course of Keweenaw Series at, 334. ——, Sandstone of, 336. Bayfield, H. W., 5. —, Paper by, 14. Bead Island, Quartz-porphyry of, 103, 111, 346. ——, Quartzless porphyry of, 95, 304 Beaver Bay and vicinity, Anorthite-rock of, 61, 310, 439, 440. ——-—, Ashbed-diabase of, 84, 305, 308. ——~—, Dike of, 307, 436. ———, Gabbros of, 42, 43, 48, 49, 305, 306, 309. ——-—, Granite of, 304, 306. ———, Granitic porphyry of, 122, 306. ——-—, Magnetite of, 51. ——-—, Olivine-diabase of, 308. ———, Quartz-porphyry of, 99, 100, 103, 107, 108, 306, 307. Beaver Bay, Islands in, Anorthite-rock of, 307. Beaver Bay Group, 295-323. ——-—, Acid and basic eruptives of, 433, 436. ——-—, Anorthite-rock of, 61, 308, 310. ——W— at Beaver Bay, 107, 108, 304-309. —— —— Beaver River, 306-308. ——-—, Characteristics of, 207, 298, 299. ——-, Diabase-porphyrite of, 83, 84, 308, 440, 442. ———, Dikes of, 320, 322, 323. — ——, Felsite of, 108, 109, 110, 310, 31 1, 320-322. ———, at Grand Marais, 319, 320. ———, Granite of, 304. ——-—, at Great Palisades, 109, 314-318, 434, 435, 440. ——~—, Limits of, 298. ———, Quartz-porphyry of, 107, 108, 314-318, 440. ——— at Red Rock Bay, 110, 322. ———— Split Rock River, 107, 299-303. ——-—, Thickness of, 299. ——— at T. 56, R.7 W., 108, 310, 311. Beaver River, Anorthite-rock of, 60, 306. —-—, Diabase-porphyrite of, 83, 308. ——, Gabbro of, 306, 308. ——, Orthoclase-free gabbro of, 48, 49, 306. Bell, R., on Animikie Group, age of, 385. ———~, crowning overflow, 382. ———-—, at Gunflint Lake, 382. ———-, stratigraphy of, 380. —on Huronian Rocks of Pic River, 401, 402. —— Kaministiquia slates, 374. —— Keweenaw Series, age of, 12. —— Nipigon Lake Basin, 27, 408. —, Publications by, 21, 22. —on Pigeon River dikes, 370, 371. — — Rainy Lake schists, 397. —, Referred to, 5, 6, 10, 400. — on Saganaga Lake schists, 397. —on schists, age of, 395. 29LS . 449 Bell on Thunder Bay schista, 396. ———— sandstones, 157, 332, Béte Grise Bay, Augite-syenite of, 117. ———, Eastern Sandstone on, 185, 353, 362, 363. — —— Olivine-diabase of, 72,74, 184. ——-—, Median Valley rocks on, 179. Big Trout Bay, Dikes of, 371. ——-—, Dike-rock from, 372. Bigsby, J.J., 5. —, Publications of, 14, 17. —on Rainy Lake schists, 397. Biotite, Alteration-product of olivine, 38. — of granite, 125. — — orthoclase-free gabbro, 43. —— orthoclase-gabbro, 52. Black Bay, Dikes near, 333. —_—, Dip of strata on, 333. —-—, Lake Superior synclinal on, 414. ——, Lower Division on, 160. —-—, Porphyry of, 337. ——, Sandstone of, 24, 128, 156, 336, 337. ——, Relation of sandstones and diabases near, 334. Black and Nipigon bays, 331-338. ——-—, Amygdaloids of, 334. ——-, Detrital rocks of, 336. ——~-—, Diabases of, 334-336. ——-—, Relation of rocks of, to Keweenaw Point rocks, 336, 837. ———. See Nipigon Bay, Black Bay. Black Point. See Caribou Point. Black River (Mich.), Lower Division on, 208. ——, Shales of Porcupine Mountains on, 225. ——, (Wis.), Rocks of, 251-254, 441. Black Sturgeon Lake, Sandstone, &c., of, 340. Black Sturgeon River, Contact of sandstone and gabbro on, $33, Bladder Lake, Contact of gabbro and Huronian on, 232. —-—, Olivine-diabase of, 38. Blake, W. P., Paper by, 18. Bohemian Mountain. See Mt. Bohemia ond Bohemian Range. Bohemian Range, 179-186. ——, Augite-syenite of, 115, 116, 117, 145, 184. —-—, ‘‘Chlorites” of = diabase-amygdaloids, 285. ——, conglomerates of, Source of, 186. ——, Diabases of, 183. ——, Diabase-porphyrite of, 81. ——, Felsite of, 104, 182, 183. —~—, Foster and Whitaey on, 180. ——, Hunt on, 180. —-—, Jackson on, 180. ——, Kinds of rock of, 181. —~—, Localities on, 181. —-—, Lac la Belle to Delaware mine, 183, 184. ——, Mt. Bohemia, 181, 184, 185, 435. ——, Mt. Honghton, 181, 182, 433. ——, Orthoclase-gabbro of, 53. : — —, Olivine-free diabase of, 67. ——, Relatiomto. Keweenaw Series, 181. ——, Summary on, 186, 187. —-—, Thickness of beds of, 187. ——, Whittlesey on, 180. —~—, See Bare Hills, Lac la Belle, Mt. Bohemia, Mt. Hough- ton. Brick Island, 369. Brooks, T. B., 5. —on gneiss and schist, interbedded, 400. 450 —on Huronian greenstones, 394. —on relation of Keweenaw Series to Huronian, 407. —, Publications of, 20, 21, 22. Brulé Lake, Chauvenet’s and McKinlay’s visit to, 272. ——, Diabase of, 275. ——, Duluth gabbro at, 294. ——, Gabbro of, 56, 272. ——, Porphyry of, 124, 272. Brulé Range, Rocks of, 257. Brulé River and vicinity, Beaver Bay Group on, 321, 322. — ——, Orthoclase-free gabbro of, 38, 44, 49, 144, 321. Brunschweiler River, Flattening of dips at, 233. ——, Orthoclase-gabbro of, 54. ——, Quartzless porphyry of, 93, 95. ——, Gabbros of, 232, 233. ——, Upper Division on, 153. Burlington Bay, 264. Burt, W. A., and Hubbard, B., Paper by, 16. Cabmous Neiding Point (Island near), Diabase-porphyrite of, 338. Calciferous Sandrock, 351, 443, 444, 445. Calcite of diabase-porphyrite, 79. — of sandstones, 128. —veins, 423. Calumet and Hecla mine, 188. See Conglomerate, Calumet. Calumet Conglomerate. See Conglomerate, Calumet. Cambrian, extent of term, 443-445. : Cambrian Sandstone of Mississippi Valley, 234-250, 366. ——, Extent of, 366. ——, Relation to Keweenaw series, 366, 443. — —, See Eastern Sandstone, Potsdam, Wiscons.n, North western. Campbell, A. C., 3. — on Beaver Bay Group, 309. —— North Shore, 262. —— Mamainse, 348. —— Porcupine Mountains, 207. —and McKinlay on Baptism River Rocks, 272. Canadian Naturalist, 335, 378, 405, 432. Canada, Geology of, 3, 374, 377, 385, 386-390, 400, 401, 402. —, Geological Survey of, Report of 1848, 390. ---—--— — , 1863-'66, 400, 436. ----- , 1866-"69, 123, 157, 339, 340, 374, 380, 381, 385. a , 1870-"71, 402. —--—-—-- , 1872-"73, 382. Cape Choyye, Keweenawan rocks of, 347, 415. Cape Gargantua, Keweenawan rocks of, 347, 415. Caribou Island, Olivine-gabbro near, 375. ——, Upper Division at, 154. Caribou Point, Olivine-diabase of, 72, 77, 328. ——, Sandstone of Temperance River Group at, 328. Carlton's Peak, Anorthite rock of, 59, 329. ——, Origin of, 329. Carp Lake, Felsite of, 210. ——, Porphyry and diabase of, 213. ——, Sandstone (inner) of Porcupine Mountains at, 213. Carp River, Conglomerates of (T. 51, R. 43 W.), 215-717, 220. —-—, Diabase-amygdaloids exposed on (T, 51; R?42 W.), 215. —-—, Diabases of (T. 51, R. 43 W.), 215-217. ——, Felsites of (T. 43 R. 43 W.), 105. ———— (T.51 R. 43 W.), 106, 210. ——, Outer sandstone and conglomerate of Porcupine Mount- ains on (T. 50, R. 45 W.), 220. ——, Sandstone of (T. 51, R. 42 W.), 132. ——, Stratigraphy on (T. 51, R. 43 W.), 215-217. Carp River. See Porcupine Mountains. INDEX. Cascade River, Diabases of, 296. ——, Diabase-porphyrite of, 85, 295. ——, Duluth and Lester River Groups on, 296. ——, Gabbro of, 56, 295. ——, Quartz-porphyry of, 295. —— visited by Chauvenet and McKinlay, 273, 295. Castle Danger, Agate Bay Group at, 290. Cedar Island, Felsitic porphyry of, 108, 306, Chamberlin, Prof. T. C., 4, 5, 7, 10, 11, 410. —, on Keweenaw series of Northwestern Wisconsin, 234. —— St. Croix Valley, 236-238, 411, 412. — — Snake River diabases, 242, 243, 412. ——, Publications of, 23, 432. Chase’s Brook, Melaphyr of, 247. Chassells, J., 4, 197. Chauvenet, W. M., 3, 262. —, on Brulé Lake rocks, 272. —— Eagle Mountain rocks, 145, 273. — — Eastern Sandstone, 359, 360, —— Hungarian River (sandstone of), 354. — — Porcupine Mountains, 207. —— Torch Lake railway (sandstone of), 358. . —and McKinlay at Cascade River, 295. ———— Brulé Lake, 272-274. ——— — Eagle Mountain, 273. Chegwatona Lake, Diabases of, 243. Chester, Prof. A. H., Assistance of, 4. — on the Mesabi Range, 383, 384, 398. — — Vermillion Lake schists, 397-399. ~ Chester Creek and vicinity, Diabases of, 276, 277. ———~—, Dikes of, 278. ———-—, Gabbro of, 277. —— —-—, Lester River Group at, 281. ———~-, Rocks of, 275-278. See Duluth. Chlorite of amygdaloids, 90. —— olivine-free diabase, 64. —— orthoclase-free gabbro, 43. —— sandstones, 128. Chief’s Bay, Nipigon Lake, Limestones of, 340. Chippewa Harbor, Sandstone of, 331. Chynoweth, B. C., 4. Clam Falls District, Diabase-porphyrite of, 83 —-—, Felsitic porphyry of, 103, 107. Cloquet River, Gabbros of, 44, 46, 268, 269, 272. ———-—, Feldspar of, 438. Conglomerates, 127, 151. —, Copper in, 420. —, Extent of, 151. —, Huronian, 386-388. —, Origin of, 127. ——-, Foster and Whitney on, 8 ——-—, Houghton on, 9. —, Pebbles of, 127, 167, 168, 195, 196. —, Porphyry, Distribution of, 155. —, Source of materials of, 31, 32, 186, 195, 196. —--—--—— , Foster and Whitney on, 31, 32. —, Variations in composition and structure of, 151. Conglomerate, Albany and Boston, 118, 119, 151, 190, 191. —, Calumet, Alterations in, 195. ——, Copper of, 420, 421. ——, Pebbles of, 105, 195-196. ——, Sandstone of, 130. —, The Great, at Eagle River Section, 167-169. ———~, Montreal River, 227-229. ——-—, Ontonagon River, 199. INDEX. Conglomerate, Great, on Porcupine Mountains, 209, 217, 219. ———-— Portage Lake, 191, 192. —, Thickness of, 177, 182, 186. —, Inner, Extent of, 215-217. , Kingston, 176. —, Outer, 151, 179, 186, —— on Bad River, 231. ——on Manitou Island, 179. —— — Montreal River, 226. ——— Porcupine Mountains, 220, 224. , ——— Potato River, 230. ——, Thickness of, 186. Contact of acid and basic rocks, 148, 432-436. —-- at Great Palisades, 147, 314-318. ——Animikie slates and interbedded diabase, 374. —— Eastern Sandstone and Lower Magnesian limestone, 351. —— Houronian Quartzites and Cambrian Sandstone at Bara- boo, 444. —— Keweenawan gabbros and Huronian, at Bad River, 155, 156. —-----— near Bladder Lake, 232. —-—-—--— on Saint Louis River, 263. —of Keweenawan Series with Animikie Group, 157, 405. oo at Grand Portage Bay, 297, 367. —— on Thunder Bay, 376. a Saint Louis River, 263. ——-———-— — at Silver Islet Landing, 378, 379. —----— Cambrian (Potsdam) sandstone, 366. = SS on Kettle River, 244. SSS eS at Taylor's Falls, 237. ———— Eastern Sandstone, 185, 204, 353-361. SSS SS on Béte Grise Bay, 353, 354. la ms Douglas Houghton River, 355, 356. se ae se Gratiot Lake, 354. ——— — —— — Hungarian River, 354, 355. —_-——— in Michigan (T. 50, R. 39 W ), 359, 360. ===> on Lac La Belle, 354. ——————-—— Ontonagon River, 203-205, 359, 360. SSeS SS Portage Lake, 359. ---—-— Huronian, 155, 156, 404-408, —— —— — —_ in Bad River Region, 155, 156, 231, 232. SE at Bladder Lake, 232. ——-—-—-—-—— Nipigon Lake, 408. ee re of North Shore, 405, 406. —_— ——— —— South Shore, 404, 405. ——— Western Sandstone on Douglas County Copper P Range, 250-259, 366. — —limestone and trap of Nipigon Lake, 369. —— sandstone and gabbro on Nipigon Bay, 333. ———— — Nipigon Lake, 339. —— Western sandstone and Saint Louis River slates, 263. Copper of amygdaloids, 90, 419-425. ——, ashbed-diabase, 122. ——, sandstones, 128. — in conglomerates, 420. Deposition of, 420-422, 425, —, Modes of occurrence of, 251, 419. —, Occurrence of, on Douglas County Copper Range, 251. ———-— Keweenaw Point, 423, 424. ———— Ontonagon River, 423. ———-— Portage Lake, 421, 422. —, Origin of, 425, 426. —, Possible productive area for, 427-429. ————— in Isle Royale, 420. —————— Michigan, 427. —, Productive area for, Minnesota, 428, 429. 451 Copper, Productive area for, Wisconsin, 427, 428. —, Pumpelly on origin of, 425. —, Rules for exploration for, 425, 426. — in sandstones, 128, 420. —, Sulphuretted, in gabbro, 426. —in transverse veins, 423, 424. Copper Creek, Keweenawan rocks of, 254, 255. Copper Falls mine, Sandstone of, 129, 180, 171. Copper Harbor, 151, 186, 413, 414. ——, Dip of strata at, 178, Credner, H., Publications of, 20, 21, 22. — on relation of Eastern Sandstone and Keweenaw Series, 363. Current River, Diabase-porphyrite near, 375. Dacotah Mine, 189. Dana, J. D., on composition of anorthite, 440. Dawson, J. W., Publication of, 18. Delessite of amygdaloids, 90. Deroux, H., Publication of, 19. Des Cloizeaux on determination of plagioclase feldspars, 39. Desor, E., Publication of, 17. Detrital Rocks, 127-133, 151. ——. See Conglomerate, Limestone, Sandstone. Devereaux, J. R., 4. Devil's Track Lake, visited by Chauvenet and MeKin- lay, 273. Devil’s Track River (coast near mouth of), Felsite of, 103, 321. —— —, Quartz-porphyry of, 149. Diabase, Olivine-, (coarse-grained). See Gabbro, Orthoclase- free. Diabase, Olivine-, (fine-grained), and Melaphyr, 68-77. ——of Agate Bay, 76, 287. ——, Alterations in, 70, 71. —— of Béte Grise Bay, 74, 185. ——— Caribou Point, 77, 328. ——, Characteristics of, 68, 71. ——, Color of, 69. ——, Constituents of, 69,70. ———-—, Age of, 70. ———-—, augite, 70. ———-—, magnetite, 70. ———-—, olivine, 70. ————, plagioclase, 69. ————, pyroxene, 70. — —, of Eagle River section, 73, 170. ——— French River, 75, 76, 279, 280. ——— Gooseberry River, 76, 289, 290. ——, Graduation of, into coarse olivine-gabbro, 69. ——, Grain and texture of, 69. — —of Greenstone Group, 73, 174, 175. —-— — Knife River, 76, 279. ——— Lac La Belle, 74, 183. ——— Lester River, 75, 280. ——— Moose Creek, 75, 247-249. ——— Porcupine Mountains, 74, 214, 215. ——— Potato River, 74, 231. ——, Pumpelly's descriptioa of, 69, 70. —— of Silver Creek, 76. ——, Specific gravity of, 69. ——near Split Rock River, 76. —— of Saint Croix River, 75, 243. ——— Totogatig district, 75. Diabase, Olivine-free, (coarse-grained). clase-. Diabase, Olivine-free, (fine-grained), 61-68. ——-—, of Bohemian Range, 67, 183. See Gabbro, Ortho- 452 INDEX. Diabase, Olivine-free, Characteristics of, 61-66. ———, Color of, 62, 63. —— —, Constituents of, 63. ae , augite, 63. -—----—— , Magnetite, 63. ——— , plagioclase, 63. —— — of Copper Creek 67, 254. —— — — Eagle River Section, 66, 67, 170. ———— Fond du Lac mine, 67, 251. ——~-—, Frequency of, 65, 66. ———, Localities for, 65. ———, Modes of occurrence of, 62. ——— of Montreal River, 67, 68, 227. ———, Pseudamygdaloidal, alteration in, 63, 64. ———, Pseudomorphism in, 64. 65. ———, Pumpelly’s description of, 61-66. ——-—, Tabulation of observations of, 66-68. ———, Texture of, 63. —— —, Types of, 61. ——— of Union mine, 67, 219. Diabase Orthoclase-free, (coarse-grained). See Gabbro, Orthoclase-free. Diabase-porphyrite and ashbed-diabase, 77-87. ——, Amygdaloids of, 79. ——near Baptism River, 85, 326, 440. ——, Base of, 78, 79. —— of Beaver Bay, 84, 305. —— —— River, 83, 308. ——— Bohemian Range, 81, 183, ——— Cascade River, 85, 295. ——, Characteristics of, 77. ——, Color of, 77, 78. ——, Constituents of, 78-80. ———-—, apatite, 79. ————, calcite, 79. ———~—, chlorite, 79. ———— , epidote, 79. ———~—, oligoclase, 78, 79. —— ——, orthoclase, 78, 79. ———-— silica content, 79, 440, 442. ——, Copper in, 422. ——, Distribution of, 155. —— of Duluth, 80, 83, 275-277. ——— Eagle River, 171-173. ——— Encampment Bluff, 84, 285. ——— French River, 83. ——near Great Palisades, 84, 316, 442. ——, Grain and texture of, 77. —— of Knife River, 84, 279. —— — Lester River, 279, 280. ——— Little Carp River, 82, 215, 217. ——, Localities for, 80. — — of Michipicoten Island, 85, 87, 344-346. ——— Porcupine Mountains, 82, 215-220, 440. ——— Portage Bay Island, 85, 296-298. ——— Potato River, 83, 231. ——— Red Rock Bay, 85, 323. — —, Relations of, to ashbed-diabase, 78. ————— olivine-diabase, 78. —-—---—— orthoclase-gabbro and quartzless porphyry, 79. ——near Split Rock River, 84, 301, 303. —— of Suffolk mine, 81, 176, 177. ——, Tabulation of observations on, 83-87. Diallage. See Augite. Dieffenbach, O., Publication of, 19. Dikes, 143, 144. Dikes of Agate Bay Group, 287, 293, 294. — of Animikie Group, 144, 367, 368, 372, 373. —— Basic Rocks, 143. —— Beaver Bay Group, 299, 306, 307, 320-323. —— Big Trout Bay, 371, 372. —— Black and Nipigon Bays, 334. —— Chester Creek, 278. —— Duluth Group, 278. —— Grand Portage Bay, 367. —— Hat Point, 368. —, Huronian, 389. —of Kaministiquia River, 374. —— Lester River Group, 283. — — Mamainse, 143. —— Minnesota Coast, 143, 278, 283, 294, 301, 306, 307, 320-323, 829, 384. —— Pigeon Bay, 372, 373. —— Pigeon Point, 370. —— Pigeon River, 371. — — Porcupine Mountains, 223. —— Red Rock Bay, 322, 323. —— Saint Louis River, 384. —— Silver Islet, 378. ~—— Silver Islet Landing, 379. —— Split Rock River, 301. —— Temperance River Group, 329. '—— Thunder Bay, 370. —— Thunder Cape, 376. —— Victoria Islands, 372. —— Wauswaugoning Bay, 368, 369. Diorites, 393, 400. Dog Lake, Schists of, 396. Doré River, Huronian Rocks of, 401. Douglas, J., Paper by, 21. Douglas County Copper Range, 250-259. ———— on Aminicon and Middle Rivers, 255-257. ———— in Bayfield County, 257, 258. ———w—on Black River, 251-255. or Copper Creek, 254, 255. ————, Copper of, 251, 428. ———-—, Lower Division on, 159. ———~—, Relation of, to Keweenaw Series, 251. ————, sandstone of, Age of, 259. ———_— , Western sandstone on, 259, 366. Douglas Houghton River, Eastern Sandstone on, 185, 355, 356. ——-—, Wadsworth on rocks of, 255, 363. Duluth, Diabase-porphyrite of, 80, 83, 275-247. —, Granitic porphyry of, 116, 119, 263, 270-272, 435. — Orthoclase-gabbro of, 51, 53, 55, 269. — Orthoclase-free gabbro of, 44, 46, 277. —, Quartzless porphyry of, 95. —, Western Sandstone absent at, 412. Duluth Group, 155, 275-279. ——, Absence of copper from, 426. — —, Characteristics of, 266. —— on Chester Creek, 275. ——, Dikes of, 278. é ——at Eastern end of Minnesota coast, 294. ——, Origin of rocks of, 277. ——. See Duluth. Dupes, J. A., Publication of, 18. Dutton, T. R., Publication of 15. Eagle Harbor, 413. ——, Sandstone of, 128. ——, Topography at, 17%. Eagle Mountain, Granitic porphyry of, 116, 124, 145, 273, 274 ae INDEX. Eagle Mountain, Orthoclase-gabbro of, 53, 56. Eagle River Section, 167-178. ———, Amygaloids of, 170-172. ———, Ashbed Group of, 171-173. ———, Diabases of, 170. ——— Diabase-porphyrite of (beds 45, 65, 66), 80. ———, Extent of, 141. ———, Great Conglomerate of, 166-168. ---—- » Pebbles of, 93, 104, 115, 118, ———, The Greenstone of, 174, 175, 178, 187. ———, Kingston Conglomerate of, 177. ———, Limits of, 166. ——— Marvine’s Group ‘‘A” of, 173, 174. ——-—, Melaphyr of (beds 22, 69, 87), 66, 67, 170. —-——, Olivine diabase of (greenstone beds), 73. ——— Orthoclase-gabbro of (bed 94), 52, 53, 174, 175, 176. ——-— Orthoclase-free gabbro of (beds 96, 107), 44, 45, 175. ——-—, Phenix Mine Group of, 175, 176. ——-—, Pumpelly on, 62, 168, 175. ——-—, Sandstone of, 169, 171. ——-—, Summary of, 177, 178,. ———, Thickness of, 178. Eames, H. H., on East coast of Lake Superior, 27, 347, 349. —-—, Publication by, 20. Eastern Sandstone, 351-365. ——, Age of, 12, 351, 352. ——, at Béte Grise Bay, 185, 353, 354. ——, Clay holes in, 185, 357. —-—, Conclusions regarding, 365. —— on Douglas Houghton River, 355, 356. —-—-excluded from Keweenaw series, 24. ——, Extent of, 351. ——, Foster and Whitney on, 361, 362. ——on Hungarian River, 354. ——on Lake Agogebic, 360. ——-— Portage Lake, 185, 359. ——, Relation of, to Mississippi Valley sandstone, 351, 442-445. ————— Keweenaw Series, 360-365, 442-445. ----— Trenton limestone, 352. ——— —— Western Sandstone, 366. —— on South Range, 360, 361. ——, Theories as to, 361-365, 442-445. ——on Torch Lake Railroad, 356-358. ——, Wadsworth on, 354, 355, 357-359. ——, Winchell on, 442. Edward Island, Sandstone conglomerate and trap of, 336. Egleston, F., Publication of, 22. Emerson, L. G., 3, 202. Emmons, E., Taconic Group of, 443. Encampment Bluff, Diabase-porphyrite of, 84, 285, 433. ——, Olivine-diabase near, 76. —-—, Orthoclase-free gabbro of, 47, 286. Encampment River, Agate Bay Group on, 284, 285, 289. ——, Flowage structure in rocks of, 291. —-—, Lester River Group on, 279, 281-283. Encampment Island, Orthoclase-free gabbro of, 286. English Lake, Hornblende-gabbro of, 58. Epidote of amygdaloids, 89, 90. —— diabase-porphyrites, 79. —— sandstones, 128. Eruptives, Acid. See Acid original rocks. —,Basic. See Basic original rocks. —, Tertiary, Order of, 432. —-—, Relation of to Keweenawan, 436. Faults in Agate Bay Group, 290, 291. —— Beaver Bay Group, 312. 453 Faults at contact Eastern Sandstone and Keweenaw Serica, 865. — of Douglas County Copper Range, 258. — at Great Palisades, 319, —on Hungarian River, 355. — — Keweenaw Point, 158, 205, 365. ———~—, Foster and Whitney on, 361. ———-—, End of, 208. ————0n Montreal River, 230. ————, Effect of, on South Range, 205. — of the Keweenaw Series, 416, 417. —— — North Shore, 142, 290, 291, 312, 319, 329. ——— Porcupine Mountains, 219. —— Temperance River, 329. Feldspars of amygdaloids, 88. — — augite-syenite, 112, 113, 114. —— diabase-porphyrite (porphyritic), 79. —— granite, 125. —— olivine-diabase, 70. —— quartz-porphyry, 98, 101. ———-— (porphyritic), 97. ——quartzless porphyry, 92. —, Methods of determining, Des Cloizeaux’, 39. ————, Thoulet’s, 437, 438, 489. —, Nature of, 39, 437-440. —, Silica content of, 437-440. —, Tschermak’s theory of, 437-439. Sce Plagioclase, Felsites, 95-115. —, Banding in, 97. — of Bare Hills, 182. —— Beaver Bay Group, 311, 312. —, Characteristics of, 95-102. —, Color of, 96. —, Constituents of, 98, 102. ——-—, augite, 102. ——— ferrite, 98, 101. ——-—, ‘‘greenish substance,” 100. —-—-—, orthoclase, 99. ———, quartz, 99. ————, secondary, 99, 100. —, Flowage in, 97, 98. —, Glass-base in, 99. —, Localities for, 102. —, Matrix of, 96-98. — of Little Montreal River Bay, 183. —of Michipicoten Island, 343. —of Mount Houghton, 182, —, Origin of, 102. —of Porcupine Mountains, 212. —, Porphyritic ingredients of, 97, 98, 101, 102. — Rosenbusch on, 96. —of Stannard’s Rock, 197, 198. —, Tabulation of observations on, 104-115. —. See Porphyry, Quartz-. Felsitic porphyry. See Felsites. Ferrite of amygdaloids, 88. — —augite-syenite, 113. —— felsites, 99, 101, 102. —— orthoclase-free gabbro, 41. —— quartz-porphyry, 98, 100, 102. —— quartzless porphyry, 92. Fire Steel River, 200. Flambean Trail, Gabbros of, 236. Flint Steel River, 200. Flowage-structure in felsitic porphyry, 139. — in amygdaloids, 88, 139. 454 Flowage-structure in basic rocks, 81, 139. —of Beaver Bay Group, 149, 313. —— Great Palisades, 317, 318. —— Red Rock Bay, 322. Fond du Lae, 26. —, Sandstone of, 262. Fond du Lac Mine, Olivine-free diabase of, 68, 251. Fortieth Parallel, Geological exploration of, 98, 109, 312. Foster, J. W., Publications by, 18. Foster, J. W., and Whitney, J. D., 2, 5, 6, 197. ——— on acid eruptives, 12. ———W— Bohemian Range, 180, 185. —— —— conglomerates, origin of, 30, 31. —-—- , pebbles of, 31. — ——— Eastern Sandstone, 361, 362. ——— — Isle Royale, 330, 331. ———— Keweenaw Series, age of, 12, 352, 442. —— —— Lake Superior synclinal, 410. ———— Mount Bohemia, 184. os Houghton, 149, 183. ———— pebbles of conglomerates, 31. —— —-- Pigeon Point, 370. ———— Porcupine Mountains, 207, 224. ——-—, Publications of, 16, 17, 18. ——— on Saint Croix Valley, 240. ———— sandstone of Béte Grise Bay, 185, 353, 354. ———— South Range, 204, 205. —— ——Stannard’s Rock, 197. — ——— traps, origin of, 9. Fouqué, F., and Lévy, A. M., on secondary quartz, 438. French River, 264. ——, Agate Bay Group on, 284. ——, Diabase-porphyrite of, 83. ——, Lester River Group on, 279-281. — —, Olivine-diabase of, 72, 76, 280. ——, Olivine-gabbro of, 281. Gabbro, Hornblende-, 5€-58. — of Bad River country, 232. —, Characteristics of, 56. —, Constituents of, 57. —, Localities for, 56. —, Tabulation of observations on, 57, 58. Gabbro, Olivine-. See Gabbro, Orthoclase-free. Gabbro, Orthoclase-, 50-56. —of Aminicon River. ——Bad River, 54, 144, 155, 156, 232, 233. —— Brunschweiler River, 54, 230, 231. —— Cascade River, 56. —, Constituents of, apatite, 52. ——-—, augite, 52. ——-—, biotite, 52. ———, copper sulphide, 52. —— —, chlorite, 52. ——-—, iron sulphide, 52. ———, magnetite, 51. ———, orthoclase, 51. ——-—, plagioclase, 51. ———, quartz, secondary, 51, 438. — ——, titanic acid, 51. —, Distribution of, 154. —, of Duluth, 51, 53, 55, 269. —— Eagle Mountain, 56, 273, 274. —— Eagle River Section, 53, 174, 175, 176. — Frequency of, 50. —, Grain of, 50. — — Lester River, 55, 981, 282. —, Mode of occurrence of, 52. INDEX. Gabbro, Orthoclase-, of Mount Bohemia, 53, 184. — — Pigeon River, 372. — — Silver Islet, 378. —, Tabulation of observations on, 53-56. —of Thunder Bay, 376. Gabbro, Orthoclase-free, 37-50. —of Animikie Group, 368, 379. — — Bad River, 45, 232. —— Beaver Bay Group, 48, 49, 302, 308. —— Brunschweiler River, 46, 230, 231. —— Brulé River, 38, 49, 144, 321. —, Characteristics of, 37. —, Constituents of, apatite, 43. ———, augite, 42, 43. ——— biotite. 43. ——-—, chlorite, 43. —— —, ferrite, 40. ——-—, iron oxide, 41. ——-—, olivine, 37, 38. ——-, plagioclase, 39, 40. © ——-—, prehnite, 43. ——~-—, titaniferous magnetite, 41. —— -—, viridite, 43. —, Distribution of, 154. —of Duluth 46, 277. —— Eagle River section, 45, 175. —— Encampment Bluff and River, 47, 286. —, Localities for, 43. —, Luster-mottling of, 42. —, Mode of occurrence of, 43. —of Nipigon Bay, 50, 333, 334. —- Pigeon Point, 370. — —— River, 371, 372. —— Potato River, 45, 230. —— Saint Lonis River, 268, 270. —, Specific gravity of, 38. —of Split Rock River, 49, 302. — Tabulation of observations on, 45-50. —— Thunder Bay, 371, 376, 277. Gaujot, E., on Bohemian Range, 180. Geological Report, Copper Lands, &c. See Foster and Whitney. Glass-base, 96. ——of felsites, 99, 100. Gogogashugun River, Diabase, &c., of, 229, ——, Quartzless-porphyry of, 93. Good Harbor Bay, Sandstones of, 329. Gooseberry River, Agate Bay beds at, 289, 290. ——, Conglomerate on, 293. ——, Felsite of, 231. ——, Olivine-diabase of, 76. Goose Point, Olivine-gabbro near, 375. Grand Falls. See Kakabika Falls. Grand Marais and vicinity, Beaver Bay rocks at, 298, 319, 320. ——~—, Felsite of, 103, 110. ——v—, Reef at harbor at, 327. —-—— Relation of acid and basic rocks of, 436. — —, Temperance River Group at, 324, 327. ——, Titanic acid in rocks of, 52. ——, Titaniferous magnetite of, 51. ——, Topography near, 141, 142. Grand Portage, 330. —— Bay, Animikie Group at, 297, 367, 405. ———, Gabbros of, 297. ——— Erosion of Huronian beds at, 405. Granite,125. — of Bad River, 144, 233, 435. sellin iia ita isin ia as insu alia nti alia g pment — Biya INDEX. —, Characteristics of, 125. Granite, Constituents of, augite, 125. ——-—, feldspar, 125. ———, hornblende, 125. ——-—, quartz, 125. —of Duluth, 270-272, 435. —, Eruptive and non-eruptive, 395. —, Huronian, 389, 390. —, Inclusions in, 125. —of Kakabika Falls, 375. —at Lake Shebandowan, 396. —, Localities for, 125. —in Menominee Region, 394. ——Mesabi Range, 383, 899. —north of Thunder Bay, 396. —, Relation of Animikie beds to, 399. —, Relations, 125. Granitell. See Augite-syenite and Porphyry, Granitic. Granitic porphyry. See Augite-syenite and Porphyry, Gra- nitic. Gratiot Lake, 164, 186. Gratiot River, 165, 187. Great Conglomerate. See Conglomerate, Great. Great Conglomerate Ridge, 164. Great Palisades, 146-148, 314-318. ——, Diabases of, 315, 316, 317. ——. Fluidal structure of felsites of, 98. ——, Diabase-porphyrite of, 84, 316, 440, 442. — —, Glass inclusions in rocks of, 102. ——, Quartz-porphyry of, 103, 109, 146, 147, 317, 318, 440. ——, Relation of acid and basic rocks of, 435. Great Palisades (near), Gabbro of, 318. —-—, Diabase-porphyrite of, 36, 80, 84, 318. Greenstones, Huronian, 389, 390. Greenstone Range, 164, 165. Greenstone, The, 61, 71, 73, 87, 154, 164, 187. ——, Alteration of, 70. —— at Eagle River section, 174, 175. ——, Extent of, 140. ——, Pumpelly on, 69, 70, 174. ——, Thickness of, 178, 187. ——, Thinning of, 187. ——, Veins in, 424. Gros Cap, Amygdaloid of, 349. ——, Felsite of, 349. ——, Huronian rocks of, 401. ——, Lake Superior synclinal at, 415. Gull Island, 330. Gunflint Lake, Schists of, 399. Hall, C. W., Publications of, 18, 23. Hancock, Sandstones and shales near, 193. Harbor Island, Trap of, 401. Hat Point, Animikie Group at, 368. Hill, E. P., 163. Hinkley, Potsdam sandstone near, 244. Hodge, J. T., Publication by, 16. Hornblende of hornblende-gabbro, 56, 57. ——aungite-syenite, 114. —— granite, 125. —, Uralitic nature of, 114, 396. Hornblende-gabbro. See Gabbro, Hornblende. Houghton, D., 5. -- on conglomerates, 9. ——, Eastern Sandstone, age of, 352. ——, Keweenaw Series, age of, 12. —, Publications of, 14, 15. — on traps, origin of, 10. 455 Hubbard, B., 5, 16. Hungarian River, Eastern Sandstone on, 354, 355. ——, Faulting on, 355. ——, Wadsworth on rocks of, 363. Hunt, T.S., 5. —on Animikie Group, 157, 384. ————, age of, 385. ——, Bohemian Range, 180. —— Diabases, origin of, 10. —— Huronian of Thunder Bay, 377, 405. — — Keweenawan of Thunder Bay, 332. —— Nipigon Group, 157. —, Publications of, 19, 20, 21, 22, 23. — on quartz-porphyry of Nipigon Straits, 31. —— Volcanic ash, 437. Huron Bay, 414. Huronian, Marquette, and Menominee, 392-395. ———, Diorites of, 393. ———, Gneiss of, 393. ———, Granite of, 394. — ——, Greenstones of, 393. ——, kinds of rock of, 393, 394. ——-—, Relations of, to Penokee Huronian, and Animikie Group, 894, 395. ———, Schists of, 393. Huronian, Original, 386-391. ——, Characteristics of, 386-389. ——, Dikes of, 389. — —, Eruptives of, 390, 434, 445. ——, Relation of, to Animikie Group, 385, 386, 390, 391, 399, 443. 445. —--- , Lake Superior synelinal, 416-418. Huronian, Penokee, 391, 392. ——, Relation of, to Animikie Group, 392. Hyperite of Macfarlane, 377. Tron River, Nonesuch shale belt on, 221, 222. ——, Outer sandstone and conglomerate of Porcupine Mountains on, 220. ——, Sandstones, &c., of, 222. Ironton Trail, Diabase porphyrite of, 83. ——, Granitie porphyry of, 231. ——, Orthoclase-gabbro of, 53. Isle Royale, 65, 164, 329-331, 414. ——, Area of, 27. — —, Copper of, 430. ——, Height of, 331. ——, Sandstone of, 331. —-—, Thickness of Lower Division on, 159. ——, Topography of, 330. ——, Upper Division on, 154. —— vein, 189. Isle St. Ignace, 27, 334, 335, 413, 414. Jackson, C. T., 5. — on Bohemian Range, 180. —— diabases, origin of, 10. ——, Keweenaw Series, age of, 12. —, Publications of, 15, 16, 17, 18, 19, 20. Julien, A. A., 23, 35, 45. —on alteration-products of olivine, 39. ——orthoclase in gabbros, 41. —, Publication of, 23. Kakabika Falls, 374, 375. ——, Animikie slates at, 330. Kaministiquia River, Animikie Group at, 371. —-—, Dikes on, 374. 456 INDEX. Kaministiquia River, Ferruginous slates and sandstones of, 374, 380. Kettle River, 243-245. ——. See Snake River. Keweenaw Bay, 163. ——, Eastern Sandstone at, 351. Keweenaw Fault. See Faults. Keweenaw Point, 163-197. ——, Area of Keweenaw Series on, 27. ——, Ashbed Group on, 171-173. ——~, Authorities on, 163, ——~, Bohemian Range on, 179-187. ——, Dimensions of, 163. —— east of Eagle River, 166, 167. 2—— from Eagle to Gratiot rivers, 187. —— at Eagle River Section, 167-178. — —, Eastern Sandstone on, 185, 351-360. ——, Elevations on, 164, 165. — —, Faults on, 166. ——, East of Gratiot River, 164-165. —— at Gratiot River, 187, 188. ——, Great Conglomerate of, 177. ——, Greenstone of, 174, 175. ——, Kingston Conglomerate, 177. ——, Lake Shore Trap of, 178, 179, 186. ——~, Lower Division on, 157, 158. ——, Marvine on stratigraphy of, 167. ——, Median Valley, Rocks of, 179, 187, 188. ——, Outer Conglomerate of, 151, 179, 186. ——, Phenix Mine Group, 175, 176. ——, Portage Lake to Gratiot River, 195, 196. ——, Portage Lake Section, 188-195. _ ——, Relation of Keweenaw Series and Huronian on, 406, 407. ——, Ridges of, 164, 165. ——, Section of eastern part of, 186. ——, Transverse copper veins of, 423-425. ——, Thickness of Lower Division on, 157, 166. ——, Topography of rocks of, 164-166. ——, Upper Division on, 153. Keweenaw Series, Acid rocks of. See Acid original rocks. ——, Age of, 12, 13, 431, 442-445. ——, Area of, 27. ——, Ash, voleanic, absent in, 32, 487. ——, Authorities on, 4, 5. ——, Basic Rocks of. See Basic original rocks. ——~—, Chronological relation of eruptives of, 32, 432-436. ——, Conglomerates of. See Conglomerates. ——, Copper deposits of, 409-429. See Copper. ——, Contact of, with other formations. See Contact. ——on East Shore. Chap. VII. See East Shore. —-—, Eruptives of. See Acid and basic original rocks. ——, Extent and general nature of, Chap. I. ——, Faulting of, 416,417. See Faults. —-—, Foster and Whitney on, 7-9. ——on Keweenaw Point. See Keweenaw Point. —-—, Literature of, 14-23, 431, 432. —-—, Lithology of, Chap. IIT. ——, Lower Division of, 154-160. Sce Lower Division. ——in Michigan, Chap. VI. See Michigan. ——— Minnesota, Chaps. VI, VII. See Minnesota. — —on North Shore, Chap. VII. See North Shore. —-—, Porphyry conglomerates of, Chap. II. ——, Relations of, to newer formations, 351-366, 442-445. ee older formations, 367-409, 442-445. ——on South Shore, Chap. VI. See South Shore. ——~, Upper Division of, 152-154. See Upper Division. ——in Wisconsin, Chap. VI. See Wisconsin. King’s Creek, Gabbro of, 46, 270. Klapetko, F., 4. Kloos, J. H., Publication by, 431. See Streng. Knife Falls, Animikie slates of, 384, Knife River and vicinity, Agate Bay beds on, 284, 286, ——-, Diabase-porphyrite of, 84. ——-—, Lester River Beds on, 279. ——/—, Olivine-diabase of, 76. — —, Olivine-gabbro of, 286. Labradorite of augite-syenite, 113. ——olivine-diabase, 70. ——(porphyritic), of diabase-porphyrite, 79 —. See Anorthite. Lac La Belle, 164, 179, 181, 184, 185. — —, Ashbed-diabase of, 183. ——, Eastern Sandstone at, 354. ——, Olivine-diabase of, 74, 184. ——, Orthoclase-gabbro of, 53. —-—, Porphyry-conglomerates of, 183. ——. See Mount Bohemia. Lake Agogebic. See Agogebic Lake. Lake Shebandowan, Schists of, 396. Lake Shore Trap, 178, 179, 186. Lake Superior, Dimensions of, 26. ——, East Shore of, 27, 347-349. ——, Generalized Section of, 417, 418. ——, North Shore of. See North Shore. ——, South Shore of. See South Shore. —— synclinal, 410-418. S ——-—, Wisconsin Geol. Survey on, 410-412. Lapham, IL. A., 411. L’ Anse, 163. Lester River, Agate Bay Group near, 292, 293. ——, Diabase-porphyrite of, 84, 155, 279. ——, Dikes near, 283, 293. ——, Lester River Group oa, 279, 280. ——, Olivine-diabase of, 75, 280, 283. ——, Olivine-gabbro of, 282. ——, Orthoclase-gabbro of, 55, 56. ——, Porphyries of, 282, 283. ——, Sandstone near, 292. Lester River Group, 279-284. ——-—, Characteristics of, 267. ——-—, Dikes of, 283. ——— in Eastern Minnesota, 294. ———, Limits of, 279. ——-—, Localities for, 279. Limestone, 24, 128. —, Huronian, 386-388, —, Keweenawan, of Nipigon Lake, 340. Little Carp River, 213. ——~—, Diabase-porphyrite of, 82. ——-—, Diabases of Porcupine Mountains on, 215, 217. ——-—, Outer Trap-belt of Porcupine Mountains on, 219. ———— Sandstone-belt of Porcupine Mountains on, 220, ——-—, Quartz-porphyry of, 106, 211. — ——, Stratigraphy on, 216, 217. Little Iron River, 222. Little Montreal River, 164. Little Montreal River Bay, Felsite of, 182. Locke, J., Publications of, 15, 18, Logan, Sir William, 5, 6. —on acid eruptives, 12. —— Animikie Group, age of, 388 ———, relation of, to Huronian, 390. ——— _—, stratigraphy of, 379. —— Black and Nipigon Bays, 334-336. etal “a tvebintes ee eS ee ee ee ee ee eee INDEX. Logan on ‘crowning overflow,” 381, 382, —— East Coast Keweonawan, 347, 348. ———— Huronian, 401. —-— greenstones, Huronian, 389. —— Kaministiquia River slates, 374. —— Keweenaw Series, age of, 13, 341, 344. —— Michipicoten Island, 24, 343. ——Nipigon Group, 157. —— Original Huronian, 386-388. —— Pic River Huronian, 401. —, Publications of, 15, 16, 17, 20. —,on Thunder Bay, 330, 332. ———-—,, sandstone, 332. —— ——, schists, 396, 397. ———-—, schists west of, 374. Lone Rock, Nonesuch shale belt near, 223. Lower Division, Keweenaw Series, 152, 154-160. ———-—, on Bad River, 158. ——-—-——— , Gabbros of, 155. ----— Black and Nipigon Bays, 160. — Douglas County Copper Range, 159. ———— Isle Royale, 159. ———-—,Nipigon sandstone of, 157. ———-—, on Ontonagon River, 158. ———-—, in Saint Croix Valley, 159. ———~—, Thickness of, 157-160. Lucille Islands, 330. ——, Animikie Group at, 369. ——, Keweenawan diabase on, 369. Macfarlane, T., 6. —, on Animikie Group, 385, —— ‘Crowning Overflow,” 382. —— East Coast Keweenawan, 347, 348. —— Mamainse, 160, 348. —— Michipicoten Island and its rocks, 85, 86, 87, 93, 112, 160, 341-346, 436, 437. —— Origin of traps, 10. ———— felsites, 12. —, Publications of, 20, 23. —on Silver Islet, 378. — — Thunder Bay rocks, 332, 377-379, 405. Magnetite of augite-syenite, 134. — —diabase-porphyrite, 78, 79. — — olivine-diabase, 70. —— olivine-free diabase, 62. —— orthoclase-gabbro, 51. ——orthoclase-free gabbro, 41. Main Trap Range, 165, 187, 188, 198, 201, 208, 229, 414, Mamainse, 160, 348, 415. —, Dikes of, 143. Manitou Island, Outer Conglomerate on, 179. ——, Kind of strata on, 414. Maniton River, Temperance River Beds on, 324, 328, Marcon, J., 5,11. —, Publications of, 16, 17. Marquette, 414, 415. Marvine, A. R., 5, 7, 10, 21, 52, 163, 416. — on amygdaloids, origin of, 11. —— Calumet Conglomerate, 195. —— Eagle River Section, 167-178. ——rocks of Houghton and Keweenaw Cos., 188. 457 Mather, W. W. on Stannard’s Rock, 197. Maw-ske-quaw-caw-maw River, Augite-syenite of, 124, 321, 822. ——, Orthoclase-gabbro of, 49, 322. McIntyre, 380, 381, McKay's Mountain, 374. McKinlay, R., 3, 262. —on Beaver Bay Group, 278. —— Duluth Group, 278. —— Snake and Kettle River district, 234. —--South Range, 360-366. —. See Campbell, Chauvenet. Median Valley, Keweenaw Point, 179, 187, 188. Mendota Mine, Diabase of, 184. Melaphyr of Pumpelly. See Diabase, Olivine — grained). —— Macfarlane, 85, 87, 93. Menominee Region. See Huronian, Marquette, and Menomi- nee. Mesabi Range, Animikie group at, 382-384. ——, A. H. Chester on, 383. ——, Granite of, 383. ——, Schists of, 398, 399. Metasomatic Development of Rocks of Lake Superior. See Pumpelly. Michigan, Keweenaw Series in, Chap. VI. ———on Keweenaw Point, 163-198. ——-— from Portage Lake to Ontonagon River, 198-201. ———on the South Range, 201-205. ———. See Bohemian Range, Eagle River Section Eastern Sandstone, Keweenaw Point, Portage Lake Sec- tion, Sowth Range. Michigan, Geological Survey of, 31, 44, 52, 65, 73, 80, 91, 188, 189, 190, 191, 195, 197, 247, 351, 352, 359, 360, 406. Michipicoten Bight, 347, 413. Michipicoten Island and vicinity, 341-346, 415. ——, Amygdaloids of, 345. ——, Area of Keweenaw Series on, 27. ——, Diabases of, 343. ——, Diabase-porphyrite of, 78, 80, 85, 87, 433. —-—, Dip of rocks on, 343. ——, Felsite of, 103, 112, 343, 346. ——, Lower Division on, 160. ——, Macfarlane’s specimens from, described, 85, 86, 87, 93, 112, 342-346. ——, Peculiar “breccias” of, 436, 437. ——, Quartz-porphyry of, 93, 112, 346. —-—, Relation of acid and basic rocks of, 433, 434. —-—, Stratification on, 341. ——, Thickness of rocks of, 342. Michipicoten River, Huronian rocks of, 400. Microfelsite of Rosenbusch, 96. Middle River, Rocks of, 256. Mineral River, Nonesuch Shale Belt on, 224. Minnesota, Area of Keweenaw Series in, 27. —, Authorities on, 262. —, Course of rock-belts in, 265. —, Dikes of, 143, 264, 278, 283, 293, 294, 301, 306, 307, 320-323, 329, 384. --, Duluth to French River, 264. —, French River to Split Rock River, 264. —, General structure of, 140, 265. —, Lakeward dip of rocks of, 141. —, Lake Superior coast of, 262-329. —, Mesabi Range, 382-384, 398, 399. —, Snake and Kettle River District, 241-246. —, Split Rock River to Grand Portage Bay, 264, 265. , (fine- 458 INDEX. Minnesota, Subordinate groups of, 266. —, Temperance River to Grand Portage, 265. —, Thickness of Lower Division on, 159. —. See also Agate Bay Group, Beaver Bay Group, Duluth Group, Lester River Group, Saint Louis River Gab bros, Temperance River Group. — —-—, Rocks of, 266. —, Geological Survey of, 7th Annual Report, 138, 142. ———-—, 5th Annual Report, 138, 145. ———-—, 9th Annual Report, 101,382, 398. ————, 10th Annual Report, 399, 442, 443. — mine, Copper vein of, 422, 423. Mission Creek, Animikie slates of, 262. Montreal River, Diabase, &c., of, 229. ——, Amygdaloids of, 136. ——, Lower Division on, 158. : ——, Olivine-free diabase of, 16, 67, 68, 229. ——, Sandstones of, 133, 225, 404. ——, Sources of information on, 207. ——, Upper Division on, 153. Montreal River Section, 226-230. Moose Creek, 247, 249. —-—, Olivine-diabase of, 75. ——— free diabase of, 68. Mosler, C., Publication by, 23. Mosquito Lake, 163. Mount Bohemia, 184, 185. ——, Anugite-syenite of, 115, 116, 185, 435. ——, Olivine-diabase of, 184. ——, Foster and Whitney on, 184, --—, Orthoclase-gabbro of, 52, 53, 184. Mount Houghton, 181, 184. “ ——, Felsite of, 102, 104, 182, 183, 343, 433. ——, Foster and Whitney on, 31, 149, 183. ——, Quartz-porphyry of, 149. Miiller, A., Publications of, 18. Murray, A., 400. ——, Publication of, 15. ——, on Thunder Bay schists, 396, 397. National mine, Copper vein of, 423. —-—, Quartzless porphyry of, 94. Neebing, Animikie Group at, 380. New Hampshire, Geology of, 40, 51. Nicholson, H. A., Publications of, 21. Nipigon Bay, Contact of sandstone and gabbro on, 333. ——, Gabbro of, 44, 50, 333, 334, 438, ——, Lower Division on, 160. ——, Sandstone of, 128, 333, 336. Nipigon Group, Hunt on, 157. Nipigon Lake and Basin, 338-341. ——, Age of rocks of, 341. ——, Augite-syenite of, 339. ——, Limestone of, 24, 128, 340. ——~, Relation of Keweenaw Series and Huronian on, 408. ——, Sandstone, 24, 339. Nipigon Straits and Islands in, 334, 338, Nouesuch mine, 221. ——, Copper of, 420. ——, Sandstones of, 131, 132, 221. ———, Basic detritus in, 128. — Shale Belt, 221-224. — —— on Iron River, 222. — — — — Little Iron River, 222. ——-— Lone Rock at, 223. ——-— on Mineral River, 221. — — —— Presqu’ Isle River, 223. Nonesuch Shale Belt in T. 50, R.39 W.; R.40 W.; R.41 W., 224, 225. ——-—possibly like ‘‘breccias” of Michipicoten Island, 436. North Brother, 103. North Shore of Lake Superior, Agate Bay Gronp, 284-294. ——, Beaver Bay Group, 298-323. ——~, Black and Nipigon bays, 331-338, ——, Characteristics of, 260, 261. ——, Conglomerates of, 30. ——, Distribution of Keweenaw Rocks on, 261-266. ——, Duluth Group, 275-279. ——, Isle Royale, 330, 331. ———— to Nipigon Bay, 329, 330 ——., Lester River Group, 279-283. ——, Minnesota coast, 261-329. ———-—, east end, 294. ——, Nipigon Lake, 338-341. —-—, St. Louis River Gabbros, 268-275. ——, Temperance River Group, 323-329, ——, Thunder Bay to Nipigon Bay, 331-338. Norwood, J., 5. — on diabases, origin of, 10. —— dikes, 143, 264. — — Douglas County Copper Range, 258. —— Great Palisades, 316. —— Metamorphic sandstone or shale, 138, 287, 288. ——, North Shore rocks, folding of, 140. Olivine, Alteration of, in basic rocks, 39. — of anorthite rock, 59. —— basic original rocks, 38. ——melaphyr, 69-71. —— orthoclase-free gabbro, 38. Olivine-diabase. See Diabase, Olivine-. Olivine-free diabase. See Diabase, Olivine-free. Olivine-gabbro. See Gabbro, Orthoclase-free. Ontonagon River, 155, 198-201. ——, Copper of, 422. ——, Eastern Sandstone on, 359, 360. ——, Falls of, Exposures at, 302. ——, Keweenawan rocks of, 199. ——, Lower Division on, 158. ——, Outer Conglomerate on, 149. ——, Quartz-porphyry on, 150, 199, 433. ——, Sandstones of, 199, 200. —-—, Stratigraphy on, 198, 199. ——, Thickness of Keweenaw Series on, 201. ——, Trend of strata east of, 208. —-—, West Branch of, 203. Ontonagon, and Montreal Rivers, Country between, Dip of strata of, 208. ee , Eastern Sandstone of the, 208. —-—--—--—— , Stratigraphy in, 207, 208. -----—— , Union of South and Main ranges in. 208, —-—-—--—. See Porcupine Mountains. “Ordinary type” diabase of Pumpelly. See Diabase, olivine- free. Orthoclase of augite-syenite, 113. ——diabase-porphyrite, 78, 79. ——felsites, 99. ——hornblende-gabbro, 57. ——olivine-diabase, 69. ——orthoclase-gabbro, 51. ——quartzless porphyry, 92. —(porphyritic) of quartzless porphyry, 93. ——quartz-porphyry, 99. ~~ wa } INDEX, , Orthoclase-free diabase (coarse grained). See Gabbro, Ortho- clase-free. Orthoclase-gabbro. See Gabbro Orthoclase. Orthoclase-free gabbro. See Gabbro, Orthoclase-free. Osceola, Contact of Keweenaw Series and Potsdam Sandstone in, 236, 287. Otter Head, Huronian of, 400. Owen, D. D., 5, 37, 403. —on Fastern Sandstone, 351. —— Keweenawan rocks, 112. ——St. Croix Sandstone, 411. ——, Publications of, 17. —. See Norwood. Owen, R., on Pigeon River dikes, 370, 371. Pebbles in augite-syenite, 112. —of Albany and Boston Conglomerate, 94, 190, 191. —— Calumet and Hecla Conglomerate, 105, 195, 196. —— National mine, 94, 190, 191. Peninsula Bay, Trap of, 401. Penokee Huronian, 391, 392. Percival mine, 257. Petit Marais, 264. ——, Temperance River Group at, 323. Phenix Mine Group, 175, 176, 178. Physical Geology of Lake Superior. See Whittlesey. Pic Island, Trap of, 401. Pie, The, 415. Pic River, Huronian of, 401. Pie Island, 331. Pigeon Bay, Animikie Group on, 372-374. ——, Dike-rock from, 372. ——, Gabbros of, 372. Pigeon Point, Animikic Group at, 369, 370. Pigeon River, 414. ——, Acid eruptives of, 372. —— Animikie Group on, 370-372. —-—, Dikes on, 371. ——-—, Rocks of, 372. ——, Gabbros of, 371, 372. Pike Lake, Gabbros of, 274. Pike River, Slates of, 401. Pine Rapids, Sandstone of, 249. Plagioclase of amygdaloids, 88. ——augite-syenite, 113. — — hornblende-gabbro, 57. —— olivine-diabase, 69. —— olivine-free diabase, 63. ——orthoclase-free gabbro, 39, 40. ——-—, Angles of, 39, 40, 439. See also Tabulations of obser- vations of various rocks. Point Magnet, 334. Pointe aux Mines, 347, 349, 415. Pokegoma Falls, Animikie Group at, 383, 384. Poplar River, Rocks of head-waters of, 145, 272. ——, Temperance River Group on, 328. Porcupine Mountains, 65, 206-224. ——, Authorities on, 207. —— Basic Belt of, first, 214-218, 432, 435. ————, second, 219, 220. ——— belts, continuation of, 224-226. ——at Carp River and Little Carp River, 215-217. ——, Diabase-porphyrite of, 82, 215, 440. - ——, Dike of, 253. ——, Fault of, 219. —-—, Felsites and quartz-porphyries of, 99, 102, 103, 105, 106, 343, 150, 209-214. 459 Porcupine Mountain, Formation of, 206. ——, Height of, 209. ——, Lower Division on, 209. ——, Melaphyr of, 214. —-—, Nonesuch shale belt in, 221-224. ——, Olivine-diabase of, 72, 74, 214. ——, Olivine-free diabase of, 67. ——, Porphyry of, 150, 209-212, 432, 433. ————, Central, 208, 209. ———-—, Distribution of, 210-212. — ———, Limits of, 212-214. ——, Sandstone of, 131, 132. --—-—, Inner, 217, 218. ———, Outer, 220, 224. ——, Stratigraphy of, 208, 209, 413. ——, Townships 50 and 51, R. 42 W., Conglomerates of, 217. ——, Upper Division on, 153, 209. Pork Bay, Temperance River group at, 324. Porphyrite, Diabase. See Diabase-porphyrite. Porphyries. See Acid original rocks. Porphyry-conglomerates. See Conglomerate, Porphyry. Porphyry, Felsitic. See Felsites. Porphyry, Granitic, of Albany and Boston Conglomerate, 118, 119, 190, 191. ——-—Baptism River, 123, 272. ——— Beaver Bay, 122, 306. ——— Béte Grise Bay, 117. ——— Duluth, 119, 270, 271. ——— Eagle Mountain, 124, 273, 274. —-—— — River conglomerate, 118, 168. ——— Maw-ske-quaw-caw-maw River, 123. ——— Minnesota, T. 56, R.7 W., 122. ——— Mount Bohemia, 116, 184. ——near Split Rock River, 121. ——— Tischer’s Creek, 120. See Augite-syenite. —, Quartz, near Baptism River, 110, 318. ——of Beaver Bay, 106-108, 307. — —— Bead Island, 111, 346. ——— the Calumet Conglomerate, 105, 195, 196. ——— Cedar Island, 108, 306, 307. ———Eagle River Conglomerate, 104, 165. ——— Grand Marais, 110, 391. — —— Great Palisades, 109, 314-818. ——— Little Carp River, 106, 210. ——— Michipicoten Island, 112, 346, ——— Potato River, 106, 231. ——— Porcupine Mountains, 42, 51, 105, 210, 211. — ——Red Rock Bay, 110, 322, 323. ——— Stannard’s Rock, 197, 198. ———Torch Lake Railroad, 104, 196. ——— Tyler's Fork, 106, See Felsites. —, Quartzless, 91-95. —— of Albany and Boston Conglomerate, 94, 190, 191. —-—, Base of, 92. —— of Bead Island, 95, 304. ———Brunschweiler River, 95. ——, Characteristics of, 91, 92 ——, Color of, 92. — —, Constituents of, 92, 98. ——-—, augite, 93. ——-—, feldspars, 92, 93. ——-—, quartz, 92, 438. —— of Duluth, 95. — —, Flowage structure in, 93. 460 Porphyry, Quartzless, Localities for, 93. —— of National mine, 94. ——, Phases of, 91. ——, Relation of, to augite-syenite, 92. —— Silica content of, 92. ——, Tabulation of observations on, 94, 95. Portage Bay Island and vicinity, 296-298. ———-—, Animikie Group on, 297. ————— , Diabase-porphyrite of, 78, 85, 297. Portage Lake, Amygdaloids of, 189, 345. ——, Amygdaloids (cupriferous) of, 421, 422. ——, Conglomerates of, 93, 190-192. ——, Copper deposits of, 420-422. ——, Dip of strata on, 187. ——, Nonesuch Shale belt on, 193. ——, Sandstone of, 130, 131, 185, 192, 193. —-—, Thinning of beds on, 187. ——, Upper Division on, 153, 193. Portage Lake Section, 188-195. ———, Conglomerates of, 32, 190, 191. ———, Exposures of, 188. ———, Great Conglomerate of, 191, 192. ——-—, Marvine on, 188. ———, Pumpelly on, 188-190, 194. ———, Sandstone of, 192, 193. ——-—, Shales of, 192, 193. ——-—, Stratigraphy of, 189. ———, Summary of, 194, 195. ———, Thickness of, 188. ———, Upper Division on, 192, 193. Potato River Section, 230, 231. ——-—, Diabases of, 74, 83, 231. ——~—, Felsitic porphyry of, 103, 106, 231. ———, Gabbros of, 45, 231. Potsdam Sandstone of New York, Relation of, to Keweenaw Series, 443-445. ———-—, Western «quivalents of, 442, 445. ————. See Cambrian, Sandstone. Powell, J. W., Publication of, 431. —,on Tertiary and Keweenawan eruptives, 436. Praysville, Diabase-porphyrite of, 81, 176, 177. Presq’ Isle River, Diabase of, 212. — ——, Limits of Porphyry on, 212. ———, Lower Division on, 208. ———~, Nonesuch shale belt on, 223. ——-—, Outer sandstone exposed on, 220. —— —, Outer trap exposed on, 219. ———, Upper Division on, 220. Prehnite in amygdaloids, 89, 90. —— olivine-diabase, 71. —— olivine-free diabase, 65. ----— (amygdaloidal), 64. — — pseudamygdaloids, 62-66. Pyroxene. See Augite. Pumpelly, R.., 2, 5, 7, 10, 163. — on amygdaloids, 88, 89, 135, 136, 416. ———, copper in, 421, 422. ——-— of melaphyrs, 87. ——augite-diorite, 56. —— ashbed-diabases, 61. —-— basic original rocks, 135. —-— Calumet Conglomerate, 195. --— conglomerates, pebbles of, 31. —— Des Cloizeanx’ method, 39. —— diabases, origin of, 11. —— diabase-porphyrite, 77, 83, 235. INDEX. Pumpelly on Eastern Sandstone, relation of to Keweenaw Series, 360, 362, 363. —— granitic porphyry, 110. ——hornblende-gabbro, 56. —— Keweenawan sandstones, nature of, 30. —— Keweenaw Series, age of, 13. ——-——, relation of, to Huronian, 106, 107. —— melaphyr, 68-70. —— olivine-diabase, 68-71, 73, 74. — — olivine-free diabase, 60-66. —— ‘ordinary ” diabase, 61. —— orthoclase-free gabbro, 45. —— orthoclase-gabbro, 53, 54. ——the Porcupine Mountains, 207. ——— Portage Lake Section, 188, 189. —— Pre-Cambrian erosion of Keweenawan rocks, 363. —— pseudamygdaloids, 60-66, 135. —, Publications of, 21, 22, 23. —onrocks of Saint Croix Valley, 239. Quartz of amygdaloids, 89, 90. ——augite-syenite, 112, 113, 114. ——diabase-porphyrite, 79. —— granitic porphyry, 112, 113, 114. — (secondary) of felsites, 99, 100, 211, 438. ——, Fenqué and Lévy on, 438. —— of orthoclase-gabbros, 51. ——— augite syenite and granitell, 113, 114, 438, ——— quartzless porphyry, 92, 438. — of hornblende-gabbro, 57. —(porphyritic) of quartz-porphyry, 93, 102. Quarzites, Animikie, 367-386. —, Huronian, 386-388. Quartz-porphyry. See Felsites and Porphyry, Quartz-. Quartzless porphyry. See Porphyry, Quartzless. Rainy Lake, Schists of, 397. Red River Road, Animikie Group on, 380. Red Rock Bay and vicinity, Beaver Bay Group at, 320. ———-—, Diabase-porphyrite of, 85, 323. ———-—, Dike near, 322, 323, 436. ———~—, Felsites of, 322. ————, Gabbro of, 322. ———-—, Quartz-porphyry of, 103, 110, 322. Red Rock Post, Gabbro of, 333. Report of Geological and Mineralogical Survey of Mineral Lands of United States in Michigan. See Foster and Whitney. Rice Point Quarry, 119. See Duluth. Rivot, L. E., 5. —on origin of traps, 10. —, Publication of, 18. Roche de Bout, Diabase of Island near, 338. Rockland (National mine), Quartzless porphyry of, 94. Rocky Run River, Sandstone of, 249. Rogers, W. B., Publication of, 15, 19. Rominger, C., 5. — on Eastern Sandstone, age of, 352. —— Keweenaw Series, age of, 12. —, Publications of, 21, 22. Rosenbusch, H., on augite-syenite, 115. —— basalt, 37. —, Classification of plagioclase-augite rocks by, 35. -—, Nomenclature of rocks adopted, 28. —, Nomenclature of felsites, 96. Rutley on quartz-crystals in quartz-porphyry, 101. Saganaga Lake, Schists of, 397. St. Croix, Dalles of, Diabase-porphyrite of, 235, 236, INDEX. St. Croix River, Authorities on geology of, 240. ——~—, Contact of Potsdam sandstone and Keweenaw Series on, 236-288. ——-—, Diabase exposures on, 243. ——-—, Lower Division on, 159. ———, Prospects for copper on, 428. — ——, Relation of rocks of, to Keweenaw Point rocks, 239- 241. ———, Sandstone of, 243, 411, 443, 444. ———, Termination of Lake Superior synclinal on, 411, 412, 414, ——-—, Upper Division on, 153. | Saint Louis River Gabbros, 156, 268-275. ——_—, Augite-syenite of, 270. ——— at Brnulé Lake, 274, 275, 294. —— —, Characteristics of, 266. ——— on Cloquet River, 268, 269, 272. ——-—, Dip of, 269. ———at Duluth, 269-272. —— —— Eagle Mountain, 273. ——~—, Extent of, 268. ——-—, Felsitic porphyry of, 271, 272. Saint Louis River, Animikie Group on, 262, 384, 412. ——~—, Dikes of, 384. ———, Gabbro of, 263. See Saint Louis River Gabbros. ———, Sandstones of, 262. Sand Point, 178. Sandstone of Animikie Group. See Animikie Group. —,Cambrian. See Cambrian. —, Eastern. See Eastern Sandstone. —, Keweenawan, 127-133, 420. ——of Agate Bay Group, 292, 293. ——— Albany and Boston Conglomerate, 130. ——— Atlantic Mill, 130, 192. ———Bad River, 1382, 227, 233. ———Batchewanung Bay, 348. ——— Black Bay, 24, 128, 156, 333, 336, 337. ——— Cape Choyye, 347. ——— Calumet Conglomerate, 130. ———Caribou Point, 328. ——— Carp River, 132. _ —— Constituents of, 127, 128. —— of Copper Falls, 129, 130, 171. ——, Copper in, 420. ——of Eagle Harbor, 128. ——— Eagle River Section, 169, 171. ——— Good Harbor Bay, 329, ——— Isle Royale, 331. ——— Lester River, 292. ——— Montreal River, 133, 225, 404. ——— Nipigon Bay, 333, 336. ———— Lake, 24, 339, 340. — —— Nonesuch Mine, 131, 182, 221. ——, Nonesuch sandstone belt, 221-224. ——of Ontonagon River, 199, 200. ——— Pointe aux Mines, 347. —— —Porcupine Mountains, 132, 215-217, 220, 221. ——-— Portage Entry, 193. —--- , West of, 200. ——— — Take, 192, 193. ———St. Croix River, 246-250. = Silver Islet Landing, 133, 378. ——— Temperance River, 385. ———Thnunder Bay, 156, 157, 333, 376, 377, 411. ——— Upper Division, 152-154. —-—, Veins of, in diabase, 139, 140, 292, 293. ——-of White River, 233. 461 Sandstone, Potsdam. See Potsdam. —, ‘‘Metamorphic.”” See Norwood. —, Nonesuch Belt. See Nonesuch. —, Western. See Western Sandstone. Sault Ste. Marie, 413. Sawteeth Mountains, 142. Schists, shales, and slates, of Batchewanung Bay, 400. ——, Grand Portage Bay, 247, 367, 405. ——, Gunflint Lake, 399. —— Hat Point, 368. —— Kaministiquia River, 374, 375, 380. —— Lucille Islands, 369. —— Mesabi Range, 382-384. —— Michipicoten River, 400. —— Mission Creek, 262. ——Nipigon Lake, 408. —— Pigeon Bay, 369-374. —— Pokegoma Falls, 383, 384. —— Rainy Lake, 397. — — Red River Road, 380. —— Saganaga Lake, 397. —— St. Louis River, 262, 384. —— Slate Islands, 401. — — Thompson, 262. —— Thunder Bay, 375-380, 396, 397. —— Wauswaugoning Bay, 368. — — See Animikie, Huronian, Nonesuch, Porcupine Mts. Science, Vol. I., 441, 442, 443. Section of Animikie Group (Bell), 380. —on Agate Bay, 288-290. —on Bad River, 232. —— Eagle River, 177, 178. —of Huronian (Logan), 386-388. —on Keweenaw Point, 186, 187. ———of Lake Superior Basin, 417, 418. — on Minnesota Coast, 266. — — Montreal River, 227, 228. —— Ontonagon Section, 198-201. —, Penokee Huronian, 391, 392. —on Portage Lake, 194, 195. — — Potato River, 230, 231. — — Snake River, 242. —— Split Rock River, 301-303. —— Temperance River Group, 328. —— Thunder Bay (Bell), 332. ——T. 60, R. 2, W., 328. Selwyn, A. R. C., on Michipicoten Island, Specimens from, 4, 342, —, Publication of, 23. Shales. See Sandstone schists. Shumard, B. F., Publication of, 17. Silver Creek, Diabase-porphyrite of, 80, 84. ——, Olivine-diabase of, 76. ——. See Encampment Bluff. Silver Islet, Dikes of, 378. —-—, Slates of, 331. Silver Islet Landing, Dikes of, 377. ——-—, Sandstone of, 133, 378. Silver Mountain, 202, 203. Simpson’s Island, Sandstone of, 336. Slate Islands, 401. Slates. See Schists. “Slide, The,” of Eagle River, 175. Snake River, Chamberlin on rocks of, 242, 243. —-—, Conclusions regarding rocks of, 245, 246, 412. —-—, Sandstone of, 240. See Kettle River. 462 ? INDEX. South Range, 201, 208. ——, Dips of rocks of, 202, 204, 205. —-—, Eastern sandstone on, 360. ——, Foster and Whitney on, 204. ——, Limits of, 201. ——on Montreal River, 229. ——— Ontonagon River, 203. ——, relation of, to Keweenaw Fault, 205. —— —— Main Range, 204, 205, 208. —— at Silver Mountain, 202, 203. South Shore Rocks, Eastern sandstone, 351-365. ———, Haronian, Marquette, 392-395. ———~—, Penokee, 391, 392. ——~—, Michigan, 161-229. ——-—, Minnesota, 234-259. ———, Wisconsin, 224-259. South Side Mine, 189. Spar Island, Dike of, 273. Special Report on Trap Dikes, &c. See Hunt, T.S. Spencer, J. W., Publication of, 23. Split Rock River and vicinity, 301-303. ——-—, Anorthite-rock of, 59, 60. ———, Augite-syenite of, 116, 121. — —-—, Beaver Bay Group on, 298. --—-—, Diabase-porphyrite on, 84, ———, Felsites of, 107, 291, 301. ———, Granites of, 304. ———, Olivine-diabase of, 76, 291. —— —, Orthoclase-free gabbro of, 48, 302. Stannard’s Rock, 197, 198. ——, Felsite of, 93, 94, 197, 198. ——, Foster and Whitney on, 197. — —, Mather on, 197. Stevens, W. H., 163. Streng, A., and Kloos, J. H., on diabase-porphyrite, 235. ———on Duluth Group, 277. ——-—, Saint Louis gabbro, 269. ——-—, Publication of, 22. Strong, M., 5, 7, 11, 35, 44, 410. —on Saint Croix Valley, 238, 411. —— Wisconsin, Northwestern, 234. Stuntz, G. W., on Mesabi Range, 399. Sucker Bay, Orthoclase-free gabbro of, 43, 47, 286. Sucker Brook, Orthoclase-gabbro of, 373. Sucker River, Olivine-diabase near, 72, 76. ——, Orthoclase-free gabbro of, 47. Suffolk Mine, 81, 176, 177. Sweet, E. T., 5,7, 10, 11, 35, 44, 410. —on Black River Rocks, 251-258, 441. —on Douglas County Copper Range, 250-258. —, Publications of, 22, 23. — on Saint Croix River, 238, 249, 411. —— Saint Louis Slates, 412. —— Wisconsin, Northwestern, 234. Synclinal, Lake Superior. See Lake Superior. Taconic Group, Winchell on Western Equivalents of, 443. Tale, alteration product of olivine, 39. Taylor's Falls, Contact of Potsdam Sandstone and Keweenaw Series at, 236-238. Temperance River and vicinity, Anorthite-rock of, 59. ——-—, Beaver Bay Group on, 298. ———, Geological descent of strata at, 264, 265. ———, Temperance River Group, 323, 325, 326. Temperance River Group, 323-329. — — —at Baptism River, 326. Temperance River Group, Beaver Bay Beds of, 318, 319 — ——, Caribou Point, 328. ---- , Copper possibly in, 424. ——-—, Characteristics of, 265, 324. -— — _—, Detrital rocks of, 327-329. —— —, Dikes of, 329. ——-—, Dip of beds of, 324. ———, Faults of, 329. ——-—at Good Harbor Bay, 329. ———— Grand Marais, 327. ——— — Manitou River, 328. ——.- -— Poplar River, 328.: ———— Temperance River, 325, 326. ——-—, Thickness of, 323. Thompson, Saint Louis slates at, 262. Thompson Island, Dike of, 373. Thoulet, J., method of determining feldspars, 437-440. Thunder Bay and vicinity, Animikie Group on, 375, 380. ———, Chert of, 375. ———, Dip on, 333. ———, Dolomitic sandstone of, 376. ———, Erosion on, 377, 405. —— —, Interbedded diabases of, 375. ———, Keweenaw Series, 331-333, 403. ——-—, Parallelism of Huronian and Keweenaw Series on, 405. ———, Sandstones of, 156, 157, 332, 383, ——-—, Schists of, 331, 376, 396. ---- , Age of, 397. ———. See Thunder Cape. Thunder Cape, Dike of, 376. ——, Olivine-gabbro, 377. —-—, Slates of, 331, 376, 378. Tischer's Creek, Augite-syenite of, 120. ——, Lester River Group near, 279. Titanic acid in orthoclase-gabbro, 52. Titaniferous magnetite. See Magnetite. Tobacco River, Eastern Sandstone on, 354. Topography affected by basic rocks, 141-143. Torch Lake, Eastern Sandstone near, 185, 359. Torch Lake Railroad, Eastern Sandstone on, 356. ——-—, Quartz-porphyry of, 103, 104, 186, 196. ———. See Conglomerate, Calumet. Totogatig District (T. 44, R. 9W.), Olivine-diabase of, 75. ——(T. 42, R. 11 W.), Diabase-porphyrite of, 83. Township, Michigan, 46, R. 39 W., 203. ———,R. 41 W.., 202, 203, 204, 360. ——, 48, R. 36 W., 202. ———, R. 43 W., 105. ——-—, R. 44 W., 201, 202. ——, 49, R.36 W., 202. ——-—, R. 42 W., 103, 214. ———, R43 W., 214. ———, R. 44 W.., 212, 213. ———, R. 45 W.., 218, 219, 220, 223, 224. ——-—, R. 46 W.., 225. ———, R.47 W,, 226. ———. R. 48 W., 226. ——, 50, R. 39 W., 94, 103, 199, 200, 214, 225, 359, 360. ———, R. 40 W., 199, 214, 225. ——-—, R. 41 W., 214, 222, 224. ———, R. 42 W., 217, 222, 224. ———, R. 43 W.., 105, 131, 209, 210, 213, 224. ———, R. 44 W., 82, 103, 106, 209, 211, 213, 215, 217, 218, 219, 220. — Neel INDEX. Township, Michigan, 50, R. 45 W., 219, 220, 223, 224. ——, 51, R. 35 W., 352. ——-—,R. 38 W., 199, 200. ——-—,R.41 W., 222, 224. ——-—, R. 42 W., 67, 72, 74, 105, 132, 209, 211, 213, 215, 217, 218, 219, 220, 222, 224. —— —, R. 43 W., 82, 103, 106, 209, 210, 211, 212, 213, 215, 216, 218, 219, 220, 221. ———, R. 44 W., 213, 219, 223. ——, 52, R. 35 W., 359. ——, 54, R. 33 W., 359, ———, R 84 W.., 959, ———, R48 Ws; 182. ——, 55, R. 33 W., 94, 118, 119, 187. ——, 56, R. 31 W., 67, 176. ——-—, R.33 W., 103, 104, 105, 130, 183, 196, ===, Rh. 84 Wi, 198, ——, 57, R. 31 W., 81, 176, 188. ———, R. 32 W.., 187. ——, 58, R. 27 W., 183. —— —, R. 28 W.., 72, 74, 182. ——-—, R. 29 W., 53, 74, 81, 104, 116, 117, 181, 183. ———, R. 30 W.., 128. ———, R.31 W., 53, 66, 67, 73, 104, 118, 129, 130. SS SLED ent —, Minnesota, 38, R. 19 W., 241, 243. ——, 39, R. 20 W., 241. a Rol Wie eel ——, 40, R. 19 W., 244. ee OO Wing 24d ——, 41, R. 20 W. 244. ——, 42, R. 20 W., 244. ——, 43, R. 20 W., 245. ——, 45, R.20 W., 245. ——, 46, R. 20 W., 245. ——, 48, R. 6 W., 262. ———, R.15 W.., 262. ———, R.16 W., 384. ——, 49, R.15 W., 46, 263, 270. ee Rel Wieceee — —, 50, R.13 W., 55, 75, 84, 279, 280. ———, R. 14 W., 46, 55, 83, 95, 119, 120, 279. ——, 51, R. 11 W., 76, 84. —— —, R. 12 W., 47, 72, 75, 76, 83, 279, 280, 281, 286. —— —, R.13 W., 53, 55, 56, 84, 279, 284, 285, 292, 293, 296. ——, 52, R. 11 W., 76, 278, 287. ail Wray 20> —=——, 58, Ril W., 283. ——~—,R.10 W., 47, 48, 76, 80, 84, 279, 281, 282, 284, 285, 286, 291, 292, 293, 297. ———, R. 11 W.., 278, 279, 281, 282. Rede, 2 lee ———, R. 14 W.., 46, 263, 272. ——, 54, R. 8 W., 48, 59, 60, 84, 300, 302, 303. ———, R.9 W., 76, 107, 284, 290, 291, 293. === Ri13 W.., 272, 282. ——, 55, R.7 W., 49, 61, 309. ——~—,R.8 W., 48, 49, 60, 61, 83, 84, 107, 108, 121, 122, 303, 304, 305, 309. ———, R. 26 Wi, aes. ——, 56, R.7 W., 84, 85, 97, 100, 103, 108, 109, 110, 116, 122, 146, 310-318, 327, 329. ———,R.8 W., 49, 309. ———, R. 25 W., 384. ——, 57, R.3 E., 38. eG Ws Oe Township, Michigan, 57, R.7 W., 123, 824. ——, 58, R.5 W., 324, 325. ——, 59, R. 4 W., 265, 329. ——, 60, R. 2 W., 77, 828. ———, R.3 W., 328. = Fe 19 Wr BEo ———, R. 13 W., 382, 383. ——, 61, R.1 E., 110, 272, 320, 321. ———, R.1 W.,, 273. ———,R.2E., 321. ——, 62, R.1 W., 145. ———,R.2 W., 53, 56, 85, 145, 273, 295, 206. ———=, Ri8iwa dds: ———,R.3 E., 49. ———,R.4 E., 124, 320, 321. ——, 63 R. 1 W., 145. ———, R.2 W., 56, 124, 145, 278, 274, 204. ———,R.3 W., 145, 294. ———,R.5E., 49, 85, 110, 111, 320, 322, —, Wisconsin, 33, R. 19 W., 236. ——, 34, R.18 W., 238. ———,R.19 W., 235. ——, 36, R.16 W., 235. ——— R17 Wi, 206. ——, 37, R. 16 W., 103, 107, 203. ———, R..17 W.., 83, 208. —--,42,R.11 W., 83. ———, R. 14 W.., 246, 249. ——-—, R.15 W., 247, 248. ———, R.16 W.., 249. ——, 43, R.13 W., 246, 248, 249. ——-—, R.14 W., 75, 83, 246, 247, 248, 249, ——, 44, R.3 W., 45, 46, 56, 58. ———,R.4 W., 46, 56. ———, R.5 W.., 46, 56, 58. ——-—, R. 6 W.., 54, 56. ———,R.9 W.., 75. ——-, R.13 W., 68, 72, 75, 246, 247, 248, 249. Se aye eas: ——, 45, R.1 E., 45. ———, R.1 W.., 45, 58, 231. ——-—, R.2 W., 45, 54, 103, 106. ———, R.3 W., 46, 56, 57, 58. —— —, R.4 W., 46, 54, 57, 58, 93, 95. ———, R.5 W., 46, 56. ———, R.6 W., 46, 56. ——,46R.1E., 67, 229. ———, R.1W.., 53. 74, 83, 103, 106, 231. ——~—, R.2E., 68, 93, 229, 231. ——-—, R.4W., 238. ——, 47, R., 1 E., 68, 133, 226, 227, 228, 229, 427. ==, RB, 220: ———, R.3 W., 132, 233. ay Ev LL Ws, 200 ——-, R. 12 W., 256. ———,R.13 W., 255. =——, R. 14 W.., 68, 252, 254. —-—, 48, R.10 W., 257. ———, BR. 12 W., 53, 54, 256. ——, 50, R. 6 W., 258. Se Was OTs Trap belt, Porcupine Mountains, Inner on, 214, 215, —-—-—-—-—— , Outer on, 218-220. Trenton limestone, 352. Tschermak, G., Theory of feldspars, 437, 440. Two Islands River, Temperance River Group on. R25. 463 464 Tylor’s Fork. See Bad River. ——, Quartz-porphyry of, 103, 106. Union Mine, Olivine-free diabase of, 67, 219. — —, Outer trap belt exposed at, 219. ——, Sandstone of, 132, 220. Union River, Outer sandstone exposed at, 220. ——, Trends of strata on, 200. United States Lake Survey, 330. Upper Division, Characteristics of, 152-154. —— Eruptives of, 152, 440. ——on Isle Royale, 154. ——— Keweenaw Point, 153. — —— Montreal River, 153. ——— North Shore, 154. ——— Ontonagon River, 199. ——— Porcupine Mountains, 153, 208. ——-— Portage Lake, 153, 193. —— in Wisconsin. —— without copper, 426. Vanhise, C. R., on uralitic hornblende, 396. —, Determination of feldspars by, 437-440. Veins, Calcitic, in Greenstone, 424. —, Nature of, 424, 425. —, Transverse, 423-425. Vermillion Lake, Prof. A. H., Chester on rocks of, 398. ——, Schists of, 397-399. ———L—, Relation of, to Huronian Animikie Group, 397. Victoria Island, Dike rock of, 372. Viridite an alteration product of olivine, 39. — of orthoclase-free gabbro, 43. Von Buch on origin of conglomerates, 8. Wadsworth, M. E., 5. — on ashbed-diabase, 138, 422. —— bibliography of Lake Superior Rocks, 14, 431. —— diabase origin of, 11. —— Douglas Houghton River, sandstone of, 356. — — Hungarian River, sandstone of, 355. —— Keweenaw Series, age of, 12, 13. —, Publication of, 23. : —on relation of diabases of Saint Croix Valley and Kewee- naw Point, 239. ——relation of Eastern Sandstone and Keweenaw Series, 363-369. —— Torch Lake, sandstone of, 357. Wausan, Huronian rocks of, 400. Wauswaugoning Bay, Animikie Group on, 368, 369. Western Sandstone, 153, 154, 365, 366. —— Characteristics of, 365, 366. —— Extent of, 365. ——, Relation of, to Eastern sandstone, 366. —----— Mississippi Valley sandstone, 366. See Douglas County Copper Range. White, B. N., 3.4. White on Porcupine Mountains, 207, 224. INDEX. White on South Range, 202. White River, Sandstone of, 233. White Fish River, Sandstone of, 351. Whitney, J W., Publications of, 16-18. —. See Foster and Whitney. Whittlesey, C., 5, 17, 19, 22, 44. —on Bad River Country, 207. —— Bohemian Range, 180. —— Douglas County Copper Range, 258. —— Montreal River, 207. ——Poreupine Mountains, 207. —, Publications of, 17, 19, 22. Wichmann, C., Diorites of, 393. —on Huronian greenstones, 394. ———, Marquette and Menominee, 394. Williams, C. P., 163. Willis, on quartzites of Pokegoma Falls, 384. Winchell, N. H., 4, 5, 7, 101. — on acid eruptives, 12. —— Animikie Group, 382, 397, 399, 443. ——diabases, origin of, 10. —— Duluth granite, 145. ——— Group, 277. —— Eastern Sandstone, 431. —— faults of North Shore, 142. —— Great Palisades, 316. —— Gunflint Lake, 382, 399. —— Keweenaw Series, age of, 12. ———— Relation of to other formations, 443-445. —, ‘‘Metamorphic shales” of, 138, 287. —on Pigeon River dikes, 370, 371. ———— hills, 382. ——Poplar River granite, 145. —, Publications of, 20, 23, 431. —on Saganaga Lake, 399. —— Saint Louis River gabbro, 269, 272. — —Thunder Bay schists, extension of, 397. —— traps, ll. —— Vermillion Lake schists, 397. Wisconsin, Area of Keweenaw Series in, 27. —, Possible copper of, 427. —, Potato and Bad River districts, 230-234. —, Northwestern, Diabase-porphyrite of, 235, 236. ——~, Sources of information on, 234. ——, Stratigraphy of, 234. ——, Southern belt of, 234-241. ——. See Douglas County Copper Range. See Taylor's Falls. —, Geological Survey of, 2, 7, 35, 39, 41, 44, 45, 46, 52, 54, 56, 63, 69, 74, 77, 89, 105, 125, 156, 207, 227, 235, 251-258, 365, 383, 391, 392, 393, 394, 398, 404, 410, 411, 412. Zirkel, F., on rhyolites, 98, 109. ——trichites, 312. i=) SMITHSONIAN INSTITUTION LIBRARIES MAN 3 9088 01363 2112 lll