U‘ . "H: ‘ v —"- . CF. “—— ‘MTOMWN MB 6063“: COUNTIES. HICBIGAN mamas FOR ma DEGREE or MS MECKEG’AN STATE UNIVERSITY W‘ILLMMR'OGER MILLER: 1966 LIBRARY ‘ Michigan State 6 C‘ E H T University AESTEACT A GRAVITY InvonlsaTICN OF THE Pi-»RCUPIM‘32 Mair-'JN'I‘QIITS A???) fiIUAC‘EfléT AREA, CNTCRAGQN.AND GCGEBIC CURTIES, MICHIGAN By Hilllam Roger Killer A gravity study coneieting of 23a observation points was made of the Porcupine Mountains and neighboring area in the Northern Peninsula of Michigan. A Bonguer gravity anomaly map, superimposed on a geologic moo by White, 1962, is presented. Toe Keweenew fault, a5 defined by closely spaced, parallel gravity contours, extends completely across t 3 study area. Gravity lows can be correlated with the Preeque Isle and Iron River eynclinea. A linear gravity high north of the Keweenaw fault delineates the high- ensity, Portage Lake lava series. Tw parallel series of closely spaced gravity contours correlate with the thite Pine fault and suggest another fault northeast of and parallel to the White Pine fault. The "cross—profile" method was attempted to Be; -.;re.te the residual from the regional gravity anomaly, but was found to be unsatisfactory. The "smooth-contour" method was attempted and was found to be eatieractory. The Talwani two-dimensiotal method was used to comr pute anomalies from bodies of assumed geometric config- urations and density contrasts to fit the reeifiual anomalies. Variation in the regional gravity is attributed to thickeninr of the lavas dovn~dip. A GRAVITY INVESTIGATION CF THE PCRCUPINE JCUUEA NE AND AuuLVhCT AREA, CHTGIL“ GON‘AR “"““IC COUXT ”3, B'ICnITA E}! William Weger Miller A ‘KEEIS Submitted to Michigan State University in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE Department cf Geolouy L 00 w 9‘ M3 Am‘hgh ’AJ -Jb-r}_v- “1‘: I‘ The s. er wig hes to off er his sincere tflunks to Dr. Eilliam J. Hinze whe Snrwesned tuia study and who provided many useful eu3zestions and criticisms. The anther 13 else indebted to Dr. Juetin Zinn and Er. James a. Trow for their advice during the study and to Dr. Barnett T.£sndefur who reviewed the meruscgift. fishy thanke are due Mr. D. H. fierritt for his assist.ance in writing computer programs and for criticisms of this study. Also acknowledged are Messrs. John Kleener, Jefles Clmstead, George Secor, Gary Servos afii Norman iingard. The assistance and information provided by M ears. H. J. Hardenber3 and R. E. Reed of the C c103- ical Survey Division 01 the Stat e cf chigan also is greatly appreciate . Acke ~1eC3ement is due Kr. Josenh Meagher of the Ontonagon County Road Commission for access to the reed profiles in the study area. The writer is especially grateful to his wife who has greatly aided in the collection, red ction and inter- pretation of the data. 11 TABLE CF CG NTENTS “new—“m Ammonmwrimo. . . . T233175 CF COIET‘ISE'ETS . . . LIST or $231.33 . . . . LIST or FIGURES . . . LIST OF PLATES . . . . I "moms: ISBN Nature and Scope . Previous Work . . Location . . . . . Clifzmte o o o o 0 Physical Geography Industry . . . . . General . . . . . Stratijraphy Q o . StrUCtureo o o o o FIELD PRL CED"RE Instrumen . . . . Sta.t10ns o o a o o Elevaticns . . . . Drift . . . . . . Rock Sampling . . LABORATC FY PROCE-URE Rock Densities . . Reduction of Data. “ources of Error . iii Page ii iii vi vii t-H—r KEN-1343‘ ‘J 15 20 20 21 21 A C. T113313 CF CQNI‘EECS (continued) INTERPRETATION Geneml...o.... GE‘aVity :mp o o o a o 0- : o o o o o : ISOlati-G‘n Of ADOMliCS . g a g g Q o o . Interpretaticn of Profiles . . . . . . . CCIICLUSICTIB o o o o o u o o o o o o o a c o o SUGG ESTICLS IvCR FURTHER STUDIES 0 o u . . . . BU “:4 UU-LJLILT‘I O o O o o o o o o 0' a o o I o a 0 1V I O O O Fag 2'; 110 e LIST OF TABLES ABLE Page 1. Generalized Geologic Column. . . . . . . . 12 2. Densities determined in this study . . . . 27 3. Densities determined by various workers. . 30 h. Densities used in reduction cf data. . . . 3O 5. Latitude corrections . . . . . . . . . . . 32 6. Principal facts. . . . . . . . . . . c . . 35 LIST OF PLATE Plate 1. Bouguer gravity and generalized geologic map. . . . . . . . . . . In Pocket 2. Regional gravity and location Of prOfileB map ¢ 0 u o o o o a o In POCkEt vii INTRODUCTION I-Iature and Scope The Porcupine Mountains are an arcuate spur of the Xeweenawan Trap Range in the northwest corner of Ontonagon County, in the Northern Peninsula of Michigan (Figures 1 and 2). They are the result of an anomalous geological structure in the Keweenawan rocks on the south shore of the Lake Superior Basin. This structure is an arcuate dome, parallel to Lake Superior. It interrupts the normal succession and dip of the rocks. Although the regional geologic picture is known, limited outcrops and accessability and lack of explor- ation drilling have hindered detailed geological mapping and geophysical investigations. To contribute to our geologic knowledge of the area, 29h gravity stations were established in the Porcupine Mountains and adjacent area. The known geology was correlated with the Bouguer gravity anomaly map. Limited quantitative calculations were performed on the resulting anomalies to better define the geology. Previous Work The geology of the Lake Superior Region has been studied for over a century. Logan (1853) was the first to recognize the succession of rocks commonly accepted toss 3y. The historical uecni.lm€ht of Lake Superior geology is well summarized by Irving (1383) and by Van flies and others (1911). ‘1 :ive stu3y of the rocks of (A The first comprghe Xe; ,‘e. awan s$e on the BCith shore of lake Superior was carried out t3 Lane (1911). Ha described the strati~ tor 3hr in detail and tabulated rock sensities. Later Butler and hires: (1W 9) r:ao oe contributions concerning the petrolor5"7 eno ore astonits of roe ks of tie Keweenaw Peninsula. More rte mztly, Leith (1933) and Broderick 3rd others (19% 6) summarized work Gone Sines 1900 in this important cclper produoi n5 area. Unfortunately, most of these workers were griz4r11y toncerxwu w.lth the :at1ve copper district to the northeast, and gave little attention to the Porcupine N'ounta- n area, the area covered by this study. -.auen (195)) Banwlri :=3d the :ork done in the :i' ity of the folouplie Loanta_ns ané cescrioed the rhyolite ex:osei in the are3. white (193%) described the geology of the White Pine coyper deposits. Later, 1957, he described the regional tectonic setting of the Michigan copper oistrict and in 19b2 me pped the Nonesuch shale from Black River, on the MichiganwWisconsin border, to Calumet, Michigan. Hamolin (1961) stueieo the paleoaeograpny of the sedimentary rocks of Upper Keweenawan and Cambrian ages. Aldrich (1923 applied goophysioal methods to the study of the Keweencwan rocks of northern Wisconsin. Brouerick (1928) found electrical and magnetic methocs applicable to mappin; faults and lava flows in rocks of Keweenawan age in E1- .J Li hlgan. Theil (13;6) and bacon (1957) illustratefi che relatlorchip of Bouguer 5P3V‘ty anomalies to geology of the south chore of Lake Superior. Incll correlates the "mlccontinent gravity high" with the firuvity anomalies over the Kewecncwan of wlsconsln. The regional gravity study by Bacon gnome; a cimilar high in the Northern Peninsula of Mich144n. Recently the U. 6. Geologica Slrvey (1934) hrs releasco an acromagnetlc 3 ap of porn of Lho otlcy area. ECGRAPHY Location The study are is shown in Figures 1 and 2. It consists of the western two-thircs of Cntona~on County and the adjoininfi area of Gogebic Cetnty in the Earthern Peninsula of K chig3n . It includes. pp. mxi.m3.tely gm square miles betwe- en parallels W60 30' and hSO 55' north and meridians 890 15' enl 900 00' west (Fi3ure 2). Michige State highways E~283 and M~64 and Unitas d States hizhway US-hfi make tte e3 65 of the area eccessable. The City of Ontonsgcn lies in the northeast corner of the area. Climate The climate of the area is t’rrorrd by its prox- imity to Lake Superior. Autumn and Spring are lat 3r than in other areas at the same latitude. The mean annual temperature is near #00 F. Th~ winter average is near 230 and the summer everafg is near 550 F. Highs of 1000 F and lows of -300 F have been recorded. Variations in the daily temperature of hO-SO F0 are not uncommon. The average annual precipitation is near 30 inches, with snowfall in excess of 100 inches per year. 976° 8T9° : I: 0 8I7° BIG 0 KEWEENAw LAKE SUPERIOR 47°— —47° HOUGHTON I o N I H T I E I3 I BARAGA I—I . ) I I l l G -- —-——-—J ' I8 I“*—-‘I*— - —- -_JI I—— I \n l____‘{ I MARQUETTE . J . . | ALGER ‘ I MIC/WI IRON [—‘“-—-7 . . SCHOOLCRAFT —- 644/ ‘ ' j“ _ 3____]_1 ' L460 W/SC | l I‘ . I460— 0N8 IDICKINSON, J' I . ”V FIAT] DELTA , Ll SCALE I . r 3 1 . 3 I 0 MILES 50 I MENOM|NEE LAKE MICHIGAN 910° 819° 818° 817° 816° FIGURE I. AREA OF INVESTIGATION 10 .0 <3” PO E32 32 Roads -—I-{§3——— Towns 0 !\ LAKE SUPERIOR ONTONAGON SCALE . MI es ’/ O ,/ w: ,., ,, ,, —-‘—~\_ .r E /./' \ I \\I.D /‘ PORCUPINE '\ ,' +— / . I \\ / MOUNTAINS "I II T \'\ J— T J— / T ‘I T ‘L T ‘1‘ L—45045' N. , /~'/ \ 46°45I / ./‘/ ‘ z /' /'/ o . L0 / / X / / / F- /. I + fr I. + I ‘- 6 I 1) / (33 V-”/ 0% (I; BERGLAND + + ‘“ + 1) L (2) I / M28 //- _____ l/ // In / 'QI' // ‘3» R45W/ R44W 0f R43W FIGURE 2, DETAIL MAP OF AREA OF INVESTIGATION Physical dew: mphy An extensive description of :he phseicel geo:. ;raphy of the er -!n is given by Martin (Von Rise, 1911). Only a brief resume will be attempteo here. The most prominent topCZrophic features in the area are the Keweenawe “T p Re nge and t.e fore fine Mountains. The overall relief in the area is ggrooter then 1300 feet, varying from 602 feet above mean sea level (the mean elevation of Lake Sap erior) to 1333 feet above mean sea level in the Porcupine Mountains. The Keweenewon Trap Range is a northeastward trenoih3 homoclinal r1639, elop1n3 northwest. It extzrda from the northern e633 of T. #9 N., R. 40 w. to the south- west corner of the study area. The mean elevation of this fo-ture is near 1530 feet above sea level. The wei.ll relief is near 503 foe b. The highest point is 1775 feet above mean sea level at the Ber3lend fire tower. The top03rephy, the result of differential erosion of the more resi'w ant lave.s and the les 8 roeietant ..... sedimentary rocks, is ru33ed. Transverse water gape out the rio3es in many pieces. The Porcupine meantoihe are in the northwestern part of the area of investi3ation. They are an erouate, convex northward spur of the Keweenauan Trap Range and are parallel to Lake Superior. The north slope is rela- tively steep, and increases some 800 feet above lake level less than two miles inland. The mean elevation of the Porcupine Mountains is about 1500 feet above mean sea level. The average local relief is near 300 feet. The highest point in the Porcupine Mountains is an un- named peak, 195o feet above mean sea level. South of the Keweensusn Trap Range is a broad, relatively flat plain. It has an avera3e elevation of 1300 feet above mean sea level. The local relief is 100 feet. North of the Keweenswan Trap Ran3e a flat plain gently slopes toward Lake Superior. The southern portion of the area is drained by the Ontone3on and Presque Isle Rivers. They flow northward through gaps in the Trap Range at either end of the stuoy area. Streams on the northern slopes of the Trap Range generally flow northward toward Lake Superior. They ere perpendicular to the strike of the rio3es and have relatively small drainage basins. The lsr3est of these streams, the Iron River, drains an oblate shaped basin between the Porcupine Mountains and the Trap Ran3e. The Carp and Little Carp Rivers drain the main part of the Porcupine Mountains. They follow subsequent valleys until they cut the rid3es in the southern part of the Porcupine hountsins. Several of the streams show evidence of stream piracy, indicating fluctuations in the drainage of the area. During Pleistocene time, the area woo covered by the Chippewa and Kewoenaw lobes of the Wiscoooin ice sheet (Leverett, 1929). ExoePt for several of the valleys which have been deepened and widened, the topography is believed to be much the some now as it was before glaciation. Drift in the Trap Range is thin where present. Most of the lower elevations are covered by relatively thin drift or glaoiolacustrine deposits. Industry The major industry in the areas is mining, with lesser importance given to agriculture, lumbering and tourism. be native copper deposits in the area were first exploited by prehistoric Infiiana (Drier, 1951). Mining by the "white man" did not begin until aboot lfiflo, (Butler and Burbank, 1929). Since that time mining activity has fluctuated considerably. The White Pine copper mine is the only deposit presently being exploited. Agriculture is limited to dairy farming and root and hardy orchard crops. The lm'u’oering is primal—11y of pulpwood and minor hardwood. Tourism is rapidly becoming an important industry. .I The Precambrian rocks of the Lake Superior region can be subdivided into three distinct groups or systems, separated at most places by major unconformities. They are overlain in places by Paleozoic rocks and generally are concealed by glacial debris of Pleistocene age. The Upper Precambrian is the predominate age of rocks in the study area. It is a thick sequence of relatively unmetamorphosed, interbedded lava flows and sedimentary rocks. These rocks are called the Keweenawan series. They are conformable with rock units of earlier and later age. The Lake Superior structural basin and the Keweehaw fault are two major structural features which control the structures in the study area. Stratigraphy The formations in the study area are: the Portage Lake lava series of Middle Keweehawan age; the Copper Harbor conglomerate, the Nonesuch shale and Freda sand- stone, the lower units of the old Oronto group (Thwaites, 1912), of Late Keweehawan age. The youngest unit in the area is the Jacobsville sandstone which is late Keweenawan 10 11 or Cambrian in age and has been correlated with the Beyrielo group of Wisconsin. A generalized geologic column is given in Table 1. The Portage Lake lava series (White, 1933) is a thick sequence of basalt and sndesite flows, with a few interbedoed rhyolitic conglomerates and, locally, rhyolites. It comprises the four groups of Irving (1C83); the Bohemian Range group, the Central Mine group, the Ashbed group, and the Eagle River group. The Bohemian Range group is a sequence of amyg» daloidal basalt flows. It contains subordinate con- glomeratic beds and rhyolites. It attains a thickness of 10,000 feet. A basal conglomerate rests unconformsbly on the Animikie or Middle Precambrain rocks (Allen, 1915). The Central Mine group is a similar sequence char- acterized by thick lava flows. Associated with these flows are minor interbedoed rhyolitic conglomerates and thin ssh beds. The Ashbed group is described as a series of inter- bedded lava flows and subordinate coarse, sedimentary rocks. In the Porcupine Mountains the lower part is a thick sequence of rhyolite (Thuden, 1950). The Eagle River group, a 2000 foot sequence or basic lava flows, is interboooed with minor amounts of rhyolitic conglomerates. The total thickness of the Portage Lake lava series 12 TABLE 1.. GENERALIZED GEOLOGIC COLUMN CENOZOIC Quarternary glacio-fluvitile deposits - —————————————————— unconformity -—--~~ ---------------- PALEOZCIC (7) Cambrian Jacobaville sandstone ----- 7-----7-----?- unconformity -?---~~?~-~--?~-*--?~- PRECAMBRIAN Keweenawan Upper Oronto group Freda sancetone Nonesuch shale Copper Harbor group Outer conglomerate Lake Shore trap Great conglomerate Lower Portage Lake lava series Eagle River group Aahbed group Central Mine group Bohemian Range group ................... unconformity -~m~---~-u~~-~—*O~-u-~- Huronian 13 is 25,000 feet at Houghton, Michigan but it thins wests ward. It is probably no more than 5300 feet thick in wisconsin. The Copper Harbor conglomerate is the thickest and most persistent conglomerate of the Keweenawan sequence. It can be traced from Keweenaw Point to Black River on the Michigan-Wisconsin border and further west. In the Porcupine Mountains it is 5000 feet thick and comprises three distinct units, known in the older litera- ture as; the Great and Outer conglomerates which are separated by the Lake Shore Traps. Lithologically the sedimentary units are poorly stratified conglomerates, containing minor interbedded, medium to coarse grained, arkosic sandstones. These units interfinger and pinch _ out in relatively short distances. The ratio of sandstone to conglomerate is unknown due to absence or continuous exposures. El-Kjalidi (1950) found a predominance of sandstone in measured sections on the north flank of the Porcupine Mountains. The Lake Shore traps are a 300-h00 root series of basic lava flows. They form the escarpment overlooking Lake of the Clouds in the Porcupine Mountains. A sharp lithologic break separates the Copper Harbor conglomerate from the overlying Nonesuch shale and Freda sandstone. These units are a series of silty shales, siltstones and sandstones, several thousands of feet thick. The Nonesuch shale is predominately a flaggy, grey to remulqu~rfij a b81464 grey to \ ripgla 4444 .1 0 .1. A 1-3 O “13.2"va .bwA ~~M or cont taut heavy greenifih-grey, Z? 1’11}; 1 Er vironmert , gag mineral 11 iltaconw, 3?3 feet thick, winh inter- allty fihfilES. The praaence muflcracka 4414449 4 fihnllow mmrine 41413 Celtai Eonresis~ fir s41tea 444 ular detri: 48 44:;454 6340514104 near to the 404444. 1:4 coitfict 4444444 244 N?! L4;h Lhfile 41: -44 Frags as: 44044 13 grafisziaral. £49 Fce13 4411 agrzeg, fine Lo 445144 3441444, r44 40 greeniah—gvey arkose I: 4444142 ulnar amcunts of Pfid to green, 53-1?) 53.5.. 111111? {340113 188 3.115»: siltstoncs. is gvmerally C01L14.-‘J 40 be tae 3044;.4t formation of the K4 04:14;n 69044444. Accu44t4 may. brewer 4 of the Llikkrnsu of tfia F4443 444 not .4 tt‘IbJ emssurca I". th13 T44 JUUODS *h UAd 804thanst Of «0 graineu, 134 fE Gt 13143.2? kufifis of 1n,ogo feet a Kemeensw fault. 44144, (4444114, 1961). 498114414, however, data frcm £344~ ear the For44pine war1“*x (344411 , 1953. ville 344484344 comprlaca the rec 4 unit 3 rate It 15 a medium to £1 quarszose Eandstcné. It is #900 L:,“ ;’ ya I It haa been correla with 444 Bsyfield group in 418004414 and is believca to 114 ec4aen rocks cf Keweauaaan and Croixian 4343. 840443 4 L9 contacts have been £0444 , its relationship with t?18 44 ,u w 144 rhyolltes rzaw I441r5114 occur 14 4 viz-1v13 Fl“ :4\.‘.£} asudatona 16 atlll conject drfil. and other 'iuio rocks on t: 3K4443~ 11 cefinit4ly Kewveerawan 11thologlcal units (RLod, 153%). The exact relction of these bodies to the se*lr ntary rocks is not fully kncwn. However, they could be sources for Some cf the rhyLlitic CChIlDI; cr- ates of the KesoeneLLn series. r: L 1 l *4. ex r4 9» 3x“ (a (D g) (Y: "3 9 93 cf (:1 “j ”t uperior occupies clinal structure, the Lake Sup (rior ELsin, in the southern Canadian Shield. The periphery cf the western half of the basin is composed of rocks of Keweenawan age. Except for a subordinate fold in the Porcupine Mountains, the beds dip toward the center of the basin. They are steerer on the south then on the north limb. R general flattening of dip oc urs from the base to the top of the Kewoenauxn section, with thick:- ing of t. e units down~dip. These factors indicate a depositional basin. Furthermore, bent pipe smygdules (Butler Ln1 erbL nk, 1:29) iniicete that the lava flowed from the center toward the mar31n of the basin. However, foreset bedding and pebble imbrication in the Upper cheezsws (Hemblin, 1338 and 1951) indicate stream flow from the ergin to the cen- ter of the basin. {bite (1957) CXplains this LperLnt erLLLx by a relatively flat basin floor and generally continuous downwarping. when lave accumulation keeps pace with subsijence, the floor remains flat end the lava spreads l6 outward. This causes the streams to flow parallel to the basin and to pond at the margins. When extrusion is interrupted, continued subsidence of the basin will cause the streams to flow toward the center of the basin. Later eruptions will flow from their source to the lowest point in the basin and from there outward. Folds he south limb of the Lake Superior Basin is quite irregular; broad, transverse snticlines and synclines plunge down-dip toward the center of the basin. Many minor fluctuations occur on these major flexures. The Porcupine Mountains are an arcuste dome, parallel to Lake Superior. They are connected to the Keweenawsn Trap Range by a saddle. Theden (1950) confirmed the presence of rhyolite in the center of the Porcupine Mountains as previously mentioned by Butler and Burbank (1929)- The Iron River syncline lies between the Porcupine Mountains and the Keweenswan Trap Range. It is assymet~ ric and strikes northeast. It is truncated on the north- east by the White Pine fault. The beds on the north limb are near vertical and locally overturned. The Presque Isle syncline is on the west flank of the Porcupine Mountains. It plunges northwest. Several other folds exist. Many are the result of drag along faults. They vary in size from a few feet, to several miles in magnitude. 17 Faults The Keueehcw fault is a high snfile re- verse fault. It strikes northeast and dips northwest. It has been mapped along the southern edge of the Kowce~ nswan Trap Range from the ehé of the cheeraw Peninsula to the northern edge of Lake Gogeblc. A broad throu5h~ like area exists between the cheehaw fault on the north and the South Trap Range and Precambrian highlands to the southeast. This trough is 5enerclly thought to contain a wetgc of Jccobsville sandstone deposited prior to deformation. Figure 3 is the postulated configuration of the fault and associated sedimentary wngo. The rocks are offset in many places by other faults. The majority of those are transverse faults associated with post~dcpositional deformuthh. Ltho (1911) notes the occurrence of longitudinal strike onc clp faults. The White Pine fault, s major trcrsvcrse fault, strikes northwest and dips steeply northeast. It is a right—handed tear fault. Lateral displacement is only about one mile and vertical displacement is only a few hundreds of feet (white, 1934). Other faults in tre area are minor. Figure A is a generalized structure map or the area and shows only the magcr structural features. KEWEENAWAN TRAP RANGE A . J COBSVILLE PORTAGE LAKE SANDSTONE \ LAVA SERIES UPPER .. O) P OR TA GE \ EWEENAWAN LAKE \ LAVA SERIES FIGURE 3. THE KEWEENAW FAULT 19 9 Scale . LAKE SUPERIOR (5 miles 70 PRESQUE +ISLE SYNCLINE H— + + + 7// -|— + ‘7‘ ‘§‘k~_—?_E\Egifll?’_— . FIGURE 4. SIMPLIFIED STRUCTURE MAP OF STUDY AREA FIELD PROCEDURE Instrument The gravity observations were taken in the study area during July and August, 1963, employing Worden gravimeter no. 99. The gravimeter measures the relative acceleration of gravity with a sensitivity of 0.01 maels, which is about one part in 100 million of the earth's acceleration of gravity (930 gals). The meter has a linear calibration constant of O.99h(5) meals per scale division and a range of about 80 mgsls without resetting. Stations Gravity stations (Plate 1), were placed at one-two male intervals along the existing road system. They were plotted from U. 8. Geological Survey, 15 minute, topo- graphic maps with an accuracy of 0.1 miles. Transporta- tion to the majority of the stations was by automobile. However, foot traverses were made to remote areas where necessary. One foot traverse was made along the shore of Lake Superior on the Lake Superior Trail from the east end of Porcupine Mountain State Park to the mouth of the Presque Isle River, a distance of 15 miles. Elevations were ascertained for this traverse with a hand level using Lake Superior as a reference datum. 20 Gravity hose stations (Figure 5), located on or near easily accessoble reeds, war: chosen to minimize travel time and the number of t mes the gravi.ucter need ed to be reset. They were tied to each o cher by the method of looping (Figure 5). Station."A" was chosen as the primary bees and the othe.rs as secondary bones. The study was adjusts d to th c"intcrnotionel gravity datu.’ through the Ber .1end end Lgrefi 1d gravity bases cf Professor Lloyel Bacon (Hinze, 136%). Elevations The majority of the gravity stations were placed within 50 feet of U.S. Goologioel Survey or U.S. Coast " or at road intersections and Geodetic Survey "bench marks with known elevations. Elevations for these ste tions were determined with e hand level and have on accuracy of;f' 2 feet. Elevations at road int rsections given on U. S. Geological Survey topo.r ep oiic m.1ps, with e 20 foot contour interval have an accuracy of f 2 feet (I ’Ieye r, 1963). The remeinde r of the station es vere established at rood or trail intersections and the elevations interpolated from the 20 foot contour interval. It is the author's opinion that these elevations have an accuracy of at least 2} 20 feet and might approach f 10 feet. Drift The elastic properties of the working parts of the The number of lines betwbeen sftctidons indico:es Tthe C Affil— num er 0 irect grovi y les -0 (4" o p T ’J‘ T ‘L T D T L “L .4 g H 0 R3 2 . M 0 o + ‘4‘ JV ’+ + J +— .4 is Z + L + +- E‘" ‘L ,_ __ a _ A F'/05N h 6’ . CD . ' O 2 i \. K0 R45W ~1: R44W + R43W + R42W + R4IW + R4ow' FIGURE 5. GRAVlTY BASE LOOPING 23 gravimeter and temperature variations cause changes of readings with time. This change is called drift. Control of this drift was accomplished by one of two methods. For automobile traverses, stations of known gravity (base stations) were occupied at least once every two hours. The gravimeter readings were then plotted versus time and the indicated drift removed from the stations read between the base stations. This method assumes linear drift and is called the "base-check” method. Figure 6 is a typical daily drift curve. On foot traverses, the "rate" method (Woollard, 1958) was used. This is accomplished by occupying any given station at least twice during each traverse. In this case, each station was read at least twice during a period of one-half hour. The rates of drift are then plotted and the indicated drift removed in a manner simi- lar to the "base-check" method. Rock Sampling Samples of various lithological units were collected at several sites throughout the area. Limited outcrops made sampling of all unite difficult. Only the more resistant unite (those that were well exposed) were sam~ pled. The Nonesuch shale was sampled at the Nonesuch mine and in the white Pine mine. The conglomerates were sampled at various exposures along the shore of Lake 8:3 ES 360 .83: .w 339... ON m. «50... .25... t. N. o. 0 «Son eEom of .0 523330 3:65 o 253.com 29.6 zoom "who: m II— _.0 I —.O I. IIIIN.° II .Illun.o I ‘HUO cuogsngg ewes 25 Superior as well as on the south flank of the Porcupine Mountains. Basic rocks were collected from the escarp- ment overlooking Lake of the Clouds and from scattered exposures in the Keweenawan Trap Range. Fresh, unseat.- ered samples are necessary for reliable density measure- ments. However, fresh samples were not always obtainable. Therefore, a certain amount of error has been introduced. LABORATORY PROCEDURE Rock Densities Lane (1911) compiled a list of densities for Keweenawan rocks of Michigan. He used values previously determined by hacFarlane (1885), Marvine (1873) and others. Recently Theil (1956) discussed the density relation- ships of gravity anomalies with Keweenawan rocks in northern Wisconsin. Mack (1957) also studied densities of Wisconsin rocks. Density values presently accepted by Professor Lloyal Bacon (Hinze, 1964) are incorporated into this study. Densities were measured of rock specimens collected by Thaden (1950) and by the author. The densities were determined by the normal method of loss of weight in water. More than one determination was made for each specimen. The first measurements were of initially dry samples, the second after soaking for a period of one week, and the third after soaking for a period of one month. Some of the samples disaggregated with soaking. Gradual increase in densities was observed with soaking, especially the more porous units. This increase may he explained by saturation of the more permeable rocks. The densities determined by the author are given in Table 2. The densities determined by the writer are 25 mp.mamw.m or.m mw.~unn.m mm.m n Nod-z. . wo.ma0®.m em.w a shone hodhoqsm 0x69 m>.muhm.m mw.m mm.mama.m mm.« a noun nosuoeoz fidAwd med. owluannd mmd a 888 23 «0 o3 _ x In. unmashmsoawcou mmdéfi Qua m neoofifluouux madden mad. 8.9.5...“ 5d Sdumfim 8d a «52 nonnoaoz _sohh manna nosoocoz a».mumh.m :>.m m>.muhm.m m>.m mm.m:¢m.m mm.m m ends scam «page scum oases nosaocoz "wanna mo.mL.m.m oozm using.“ mm.“ d” swqem 9E“. was nsddussom scansohom .333" 3an mm.~aoe.m mm.m m nooocefiflooadz ohmammd and Eddie wmd mtmummd mm.m 2 Emma .5333 . ncddnasoz endogenom 1.: _ A. Q 4 . .t l I ! "outgoing" _ N can: cecal . _ . 54... dog {E1 1. same .an 11 £338. : ed “3.1103 Em i a: house use i A3 .358 as” A _ 53% ans. 5 umfifiofio 333.8...m Spas .aaadb uwndmdoa ummnwda an» smacks» «Saab cwhdmdma amazed an» ma oqun any and «cans oaumenuund wnp ad £405 on» «wonamdma umHQEdm no hopes: on» ma nonuddznon was 5.: .npcos H.96u umxdom moagadm A.m .383 A no.“ 6832. madam TN .5 2733 335m. A.” 3m.m..mo.m $.m 5.m..$.m 8.m 8.9.8...“ Ed 3 $38333 mafiflv maddpcsoz madazohom no nusow ”mwaoumucwm nunlufl _qqnu _n¢jl .mon 34 l 9233 and 85. 50m Am MW33 Em a: .333 35 _ A3 .333 33 v 131 3 «6.3203 333 ads 5 393333 33338:...“ 033. N) C J appreciably different from those determined by others wha have studied the rocks of Keweenawan age Table 3). 30 Table 3. Densities as detarminsd by other workers and by the author. Lane Theil Basen Miller Sandstones and Shales ---- 2.30-2.35 2.25 2.35 Conglomerates 2.73 --------- --~- 2.65 Rhyolite 2.60 --------- 2.67 2.55 Basic rocks 2.87 2.91 2.90 3.00 Table h. Densities used in Reductisn Lithalogy zDenS; g/bc Sandstones and Shalea 2.40 Conglomerates 2.60 Rhyollte 2.55 Basic Rocks 2.90 3333333 only 3 1131331 n3333 cf axpcsurcs 3333 3’3313d and those that 3333 3333131 333 the m3re r3313t333 units, thcy are net r3 {~233 rztativa 3? £33 toial 33333: n. Ther3~ £333, tfze 333313 33 33333333 333p333331y not 33312313 valid. to be 332313333 2ith 3333 gravity Stu 3133 of Kewcen3Jan rocks, the 333313133 3333 in this 33333 are thoae 333d by {333338.r L13331 £3 _3n (Table 5). cepticn are the 333313 33 33f the ri~3lite and th 33 33133333333. Radactlo n of Data Cb33rv3d gravity data mast be redu3c~3 to r33 x.ve the effects of latitude, elevatien, and 3333 distribution. The reduction 13 accorflin; t3 the equatian: EB”¥o*-fig/W*8Kl3;~ where g3 a *33933r g4 33 3y 3 ”33,3: 50 a 3333rvei gravity; 399 thecretic31 333 13331 gravity: 3? a free air correction; an n 3033333 3r 3333 correction; 333 3T u terxm in car mirm The 3335333 gravity 333331y 13 the r zvifiy value that exists after tha $333333 C3rr3cticn has been 3331131 to a level d3tum.(AGI 61333333, 1350). It 13 the differ* 3333 between he calculat3d tnsflr9*1331 333 £33 cbaerved gravity at the station 3133. {1? {0 Observed gravity is the measured acceleration of gravity at any point. It is computed by multiplying the meter readings, corrected for drift and adjusted to the primary base of this study, by the meter calibra- tion constant. The theoretical sea level gravity or latitude cor- rection removes the effect of the decrease in the socel- eration of gravity from the equator to the poles. It is expressed by the ”1930 international gravity formula": 3.9:- 978.0149(1 ,1 0.305325231251329 - 0.000005951112329) where 978.049 is the mean sea level gravity at the equator and 59.15 the gravity at latituoe‘Ou Nettleton (lQHO) has shown that differences in lat- itude corrections are negligible for small latitude changes. The correction factor used in this study is the average of the corrections for the least and the greatest latitudes of the study area. The latitude correction is added to the observed gravity if the station is south of the primary base latitude and subtracted if it is north. Table 5. Latitude Corrections Correction Factor Latitude (mg/3;) (mg/ft) Least latitude Ado 30' 1.3052 0.0002471 Greatest latitude #60 55' .3041 0.0002469 Mean 1.30#65 o.oooen7 U) u) the free air correction compensates for the eleve- tion of the 5ruvity station obote a comhon 18% l :2 mxm. It is founu ty multiolying the elevation of the station above the datum by the vertical ruuicxt of gravity, 0.33’.05 musls per foot. The Bou5uer or mass correction compensates for the mass distribution between the station end datum. It is found by multiplyin5 the elevation of the station above datum by 0.01276 m5sls per foot, where is the tens- ity of the mass between the station and datum. Different densities for the Bou5uer reduction were ssi5ned to the 5rsvity s cations accordin3 to the 5e0105* as mapped by White (Plate 1). rr e data was recuccd to a datum of 600 feet above mean sea level, the approximate level of Lake Superior. As stated by VSJK (1956): "1. If the density of the surface rocks varies, the effect of the topography cannot be elim- inated from the 5rsvity data by computin5 the Bouguer correction with a constant Consity. 2. Bou5uer corrections with varying density must be used only to the datum s arface of the topo« graph. (the lowest elevation in the stuoy Terrain corrections account for the variations in the Bou5uer assumptions (Nettleton, 1940). The; were cetermined accordin5 to the method outlined by Hammer (193 9). Only zones E-K it elusive were founc to be applicable to the study area. These zones include the area between Circles with radii of 553 feet to 32,490 feet ”.14 i. d away from each station. Because of their promeity to major topographic features, 25 per cent of the grav- ity stations were selected for terrain corrections. The corrections were applied only where they exceeded 0.1 mgal. All calculations in the reduction and interpreta~ tion of the date were performed by the CDC 3600 digital computer. Exceptions were the drift and terrain correc- tions. The original data and the computer programs are on file at the Department of Geology, Michigan State University. The principal facts for the gravity bases are given in Table 6. Sources of Error U. 8. Geological Survey, 15 minute topographic maps at a scale of 1/62500 were used to locate stations for latitude corrections. The location accuracy is g 0.1 miles, which creates a gravity effect or about ZLG.13 mgals. Elevation errors vary from d 2 to A 20 feet and introduces a maximum error of t 0.13 to (f 1.26 mgals in the reduction of the data. The combined errors resulting from observation and removal of drift are estimated to be no greater than A;Q.l mgals. Terrain results in a maximum error of 0.1 mgals. An accuracy of d:0.50 mgals was sought in this sur- vey and undoubtedly has been achieved for the majority of .oomH .cooem .o .q no escapees seam .mhsousoo Bonn copcflothch coapo>eam .oc\m Ne. w .hudmsov .qsz Bruno .%u«>epn seamsom .mEnaoo huamumo AAA 0 m 3' Ln ma cs(£m mo .mudmcon «qua seeps poem 00w sound «madam was» .hud>shm hoswzom A.N .mssfioo hpdecnm Ue>henno CH osfio> moan eacma moH x m.m A.H mm.mma are: cocoon no, .:N© mmmd 3. mm mm m. mm m: ozaad mm.m I too: titttt mm .mc w Goad m. mm @m m. mm m: Omim A3 Nc.mm oo.m ho.m I ma.omh mac H.hm mm H.m: w: m aw.aea oe.m o>.men mm.emw mama a.mfi em H.mm me o Hm.mmu os.m m:.mN- mm.emo mama m.mm ow m.mm we 2 Nm.:« oe.m Nm.HH- mm.mmh ass m.mm on m.me we 2 mo.mm oo.m mw.~H- mm.mme mama o.~m aw m.mm m: 4 mm.wfiu ow.m Ho.Naa mo.mew cam” o.mm ow H.Hm o: a em.m om.m N>.mmu ms.map mafia o.mm cw H.He a: a om.m oe.m aw.mm- afl.mms new e.mm em «.3: a: : ms.mfi- o:.m mfi.emu no.3ao mmmfl m.Ne em 0.3m we a ms.HH- 0:.m am.mwa ofl.mwm mama m.mm cm m.mm a: a 00.: c oo.m ne.mw- mw.ocm ommfi m.em cm m.mm on a em.om ow.m Ha.mfl- mo.mne mrm m.em mm o.oe a: o ee.flm oe.m mo.: . om.oee manhav m.mm em m.ez me o efl.mm oe.m mm.mfi- .ema Mme m.om em m.~m a: m Ho.em oa.m mo.m . .wws wfiw m.om em m.om we < 5 E w.m2to Aacwa.un mamas. huu>cso Apcv :«2 was ad: was coup IILuMQM¢mmmauwsqswce stomach, cm>nmnno >on wesudwcou messaged -asm epoch adqaondum...w canoe ’ ’ v the stations. However, individual stations may be in error by i 1.6 angels. INTERPRETATION General Bouguer gravity maps reflect variations in the Bouguer gravity anomaly resulting from horizontal changes in density. These changes are caused by surface and subsurface geology, deep-seated structures, and regional as well as local changes in lithology. The variations in the Bouguer gravity anomaly can be areally large with gentle gradients or can be local with abrupt changes and are the combined effect of shallow and deep-seated sources. Deep—seated, as well as shallow, widespread sources (wide- spread with respect to the size cf the area of investi- gation) produce broad, areslly large anomalies with generally gentle gradients. These broad anomalies are called the regional gravity anomalies. Local anomalies with abrupt changes in gradient are called residual gravity anomalies. ravity Map Plate 1 is the Bouguer gravity anomaly map drawn at a tee mgal contour interval and superimposed on the geoloiic map as adapted from.White (1962). The median gravity anomaly value is — 33 mania. This value is appreciably lower than the average or zero mgals observed 37 “8 ufi .» d from a regional gravity study of the same area by Bacon (1957). This difference is explained by the use of a reduction datum of 600 feet above sea level instead of the sea level datum that was used by Bacon. The total variation in gravity is 75 mgals. The gravity values increase from south to north. They vary from.- 78 mgals in the southeastern part of the study area to a maximum of - 2 mgals on the north side of the Porcupine Mountains. The correlation of the observed graVity anomalies with the geology of the area is excellent. However, inadequate station density in some remote areas limits the complete reliability of the correlation. A linear gravity high occurs over the high density basic flows of the Keweenawan Trap Range. A well defined gravity low exists over the Iron River syncline. An ill—defined low of lesser magnitude occurs over the Presque Isle syncline and extends to the northwest out of the study area. A broad gravity low defines the trough south of the Keweenaw fault. A series of closely spaced contours parallel the Keweenaw fault. They indicate that the fault excencs completely across the study area. Parallel to the White Pine fault are a series of closely spaced contours. A similar anomaly exists six miles northeast of the White Pine fault. These two anomalies delineate an elongate positive gravity feature, several miles long, which strikes northwest. It may represent a horst-like structure. An east-west trending gravity high occurs south of Ewen in the vicinity of sections 26—29, T. #8 N.. R. 40 R. It could originate from an elongate intrusive in- to the sedimentary rocks, or it may represent an old ridge of Keweenawan lavas buried beneath the Jacobsville sandstone and glacial debris. A series of tightly grouped contours extends south- west across sections 3, 8 and 18. T. fl9 N.. R. #4 w. It correlates with a fault previously mapped by White. A fault mapped as extending across sections 4, 10 and 15, T. &9 N.. R. #4 w. is not defined by the Bouguer gravity anomaly map, probably because of inadequate station coverage. A flexure in the Bouguer gravity contours in sec- tions 9~ll and 14-16, T. 49 N.. R. #2 w. represents a gravity minimum that correlates with a body of rnyolite mapped by Wright (1939). It has a magnitude of about five mgals. Several other variations exist in the Bouguer gravity anomaly map. However, more detailed station coverage is necessary for further interpretation or these anomalies. 40 Isolation of Anomalies There are many methods of isolating the residual gravity anomalies from the regional gravity picture. Only the graphical methods were considered in this study, because of inadequate station coverage and inconsistent station spacing. Several sets of cross~profiles were drawn from the Bouguer gravity anomaly map to isolate the residual anom- alies, but, this method was not utilized in the final analysis because a great many interpretations were found to be plausible and it was impossible to determine which interpretation was most correct. In view of the uniform gravity gradient that exists in the area of investigation, ' was used to isolate the method of ”smooth-contouring' the residual gravity anomalies from the regional picture. This method involves drawing smooth contours over the anomalies connecting the regular spaced contours on the margins of the study area. Plate 2 is the map of the regional gradient of the Bouguer gravity. It shows that the gradient increases at a rate of 2 mgals per mile northward. This increase can be attributed to the thickening of the lava flows down-dip. In general, the contours roughly parallel the strike of the Keweenawan rocks. bl Intersretation of Profiles Seven profiles (Plate 2) were drawn normal to the strike of the regional gravity and the anomalies to be studied. The Talwani two~dimensional method (1933) has used to compute anomalies from bodies of assgmed geomet~ ric configuration and density contrasts to fit the resid- ual anomalies. Several assumptions were made in fitting the computed anomalies to the observed residual gravity anomalies. They are: l. The residual gravity anomalies obtained from the "smooth-contouring” method are the true residual gravity anomalies. 2. The densities used in the reduction of the gravity data are valid. 3. The density contrasts between the inferred bodies and the host are correct. h. The bodies that produce the gravity anomalies which satisfy the observed residual gravity anomalies are geologically reasonable. Profiles A~A' to F~F' inclusive were drawn to study the depth extent and the geometric configuration of the Keweenaw fault and the adjacent trouih to the south containing the Jacobsville sandstone. There are several factors which influence the position and shape of the gravitational field over a fault. among tieee are; the magnitude and depth of the density contrast that exists between the upthrown and downthrown sides #2 of the fault, the dip of the fault, and the throw of the fault. The Keweenaw fault may produce two possible sources of density contrasts. Near the surface, there exists Juxtaposition cf the low density Jacobsville sandstone to the south up . 2.h g/bc) with the high density lava flows to the north.(p - 2.9 g/bc). This gives a density contrast of 0.5 g/bc which should result in s gravity low south of the fault. In addition, a density contrast may occur at depth between the lava flows and the underlying basement rocks. If this deep-seated density contrast exists, it should be reflected in the Bouguer gravity anomaly, either as a negative anomaly on the north side of the fault or by a plateau in the gravity gradient. This, however, is not evident on the Bouguer gravity map. Several explanations may be offered for the apparent lack of anomaly due to a deep~sested density contrast. The Juxtaposition of the lava flows with the basement rocks may be at such great depths, that the gravity effect is too wideSpresd to be identified in the Bouguer gravity anomaly. In addition. the density con- trast may be too small to have any detectable effect on the Bouguer gravity. Also, the dip of the fault may change with depth resulting in an anomaly whose effect ”3 is not evident near the surface trace of the fault. Because there is no reflection of a deep~seated density contrast evident on the Bouguer gravity anomaly map, it is assumed that variations on the Eouguer gravity map are caused by near surface structures. Profile A-A' (Figure 7) originates in section 3h, T. 48 N., R. #5 w. and extends north-northwest to section 28, T. 49 N., R. #5 W. The anomaly has a minimum value of - 17 mgals. A 3100 foot wedge of sediments could cause a gravity anomaly that would fit the residual anomaly. Profile B-B' (Figure 8) extends from section 33, T. 48 N.. R. an H. to section 29, T. kg N., R. as w. A simple wedge of sedimentary rocks 2300 feet thick would acrount for the 20 mgal anomaly which is shown. Profile C-C' (Figure 9) begins in section 3h, T. AB N., R. R3 w. and extends to section 30, T. 59 N., R. 33 W. his 23 mgal anomaly is an unusual one to fit. All geologically reasonable geometric configurations failed to account for a large deficiency of gravity over the northern portion of the profil). Study of topograpi 0 maps and aerial photographs reveals a circular shaped hill which shows marked topographic similarities to exposures of rhyolite further east. It is concluded that a rhyolite body with a density of 2.55 g/hc occurs in T48 N,R45W JACOBSVIL LE SANDSTONE Flgure 7. Over Profile REGIONAL GRADIENT OF GRAVITY—— '— BOUGUER GRAVITY RESIDUAL ANOMALY COMPUTED ANOMALY T49Nfi45W ____ PORTAGE LAKE LAVA SERIES Scale (3 Mae? [0 Gravity and Inferred Geolcgy A-A' 1+5 —207 --30 .J ,MGALS #40— MGALS _20 .. REGIONAL GRADIENT 0F GRAVITY - — '- BOUGUE R GRAVITY “- R ESIDUAL ANOMALY— COMPUTED ANOMALYC) [T48N,E244w T49N,R44w JACOBSVILLE PORTAGE LAKE SANDSTONE LAVA semes Scale G kfeet IG Figure 8. Gravity and Inferred Geology over Profile 8- B' MGALS KFEET _20 q _30 -. -lO-r s REGIONAL GRADIENT OF GRAVITY——— / / BOUGUER // —— / GRAVITY // / / / RESIDUAL ANOMALY COMPUTED ANOMALYG) [T4e~, R43W IT49N.R43 W RHYOLITE JACOBSVILLE PORTAGE LAKE SANDSTONE LAVA SERIES \ Scale \ b kfeef I10 Figure 9. Gravity and Inferred Geology over Profile C-C' 37 this part of the area. The residual anomaly is satisfied by a wedge of sedimentary rocks 3800 feet thick plus a body of rhyolite 1000 feet thick. The geometric configu- ration of the rhyolite used to fit the anomaly suggests a possible intrusive body. Profile D-D' (Figure 10) extends from section 35, T. #8 N., R. #2 H. to section 2§, T. #9 N., R. #2 w. A 3300 foot wedge of sediments is believed to cause this 17 mgal anomaly. The north side of this wedge, the Keweenaw fault. appears to be vertical. Profile E—E' (Figure 11) has a total anomaly of 21 mgals. It begins in section 9, T. #3 N., R. #1 w., and extends northwest to section 14, T. #9 N., R. #2 w. A wedge of sediments #700 feet thick fits the anomaly very well. I The largest of t.ese anomalies, 33 mgals, occurs over profile F~F' (Figure 12). This profile extends from section 30, T. 49 N., R. #0 w., to section 21, T. 50 N., R. hl w. A 6100 foot wedge of sediments would account for this anomaly. The geometric configuration of the trough of Jacobsville sandstone as determined from the interpre- tation of the gravity profiles is different from that normally postulated and as illustrated in Figure 3. The north side of the trough, which is the Keweenaw MGALS MGALS -301 -40* -50 J .40q ~ S REGIONAL GRADIENT OF GRAVITY— — — OBSERVED GRAVITY —— / / / / / RESIDUAL AnouALv —— c aneureo ANOMALYO T4e~,R42w JACOBSVI L LE SANDSTONE \‘ _ T49N, R 42w PORTAGE LAKE LAVA SERIES r Scale j 0 kfeei l0 Figure IO. Gravity and Inferred Geology over Profile D-D' 49 S N’, I/ / / // // / m REGIONAL GRADIENT 'J-so , g '7 or GRAVITv—— — z ‘6‘” BOUGUER GRAVITY -704 O O o— (D ngIo- ESIDUAL GRAVITY : coueurEo manor 0 -204 2-I T46N T49N R4Iw|R42w A JACOBSVILLE PORTAGE LAKE he”: SANDSTONE LAVA SERIES m U I]. X -2-4 . Scale fl 0 kfeef l0 '4‘ Figure II. Gravity and Inferred Geology OVOI’ Profile E-E' MGALS MGALS R4OW R4|W JACOBSVILLE SANDSTONE KFEET Gravity and REGIONAL GRADIENT OF GRAVITY -— — —- BOUGUER GRAVITY RESIDUAL ANOMALY —-—— COMPUTED ANOMALY Q T49N TSON PORTAGE LAKE LAVA SERIES Scale 0 kfeet IO Inferred Geology F — F' OS 51 fault, is found to dip south, possibly at a high angle, rather than north. There are several possible explanations for this interpretation. It is generally believed that the Keseenaw faulting occurred in port-Jacobaville time (Hamblin, 1958). If the faulting occurred as a series of parallel faults instead Of one major fault, the resulting an maly could be misinterpreted as due to a vertical or south dipping fault. More detailed gravity investigations Over the Keweenaw fault may reflect the presence of parallel faults in the Boujuer gravity anomaly. As is readily evident from the gravity profiles, there is an apparent change in dip of the fault from the west to the east end of the study area. The dip of the fault apparently changes from.near vertical, east of Lake Gogehic, to south on the western side of the lake. This may be the result of change in the dip of the fault or it may be eviflence of the fault dying out and changing to a monoclinal ridge. An alternative interpretation that may explain the configuration of the trough south of the cheenaw fault, suggests that deformation is concurrent with deposition. If this is the case, each vertical movement of the fault will result in deposition of elastic material to the south from the upthrown side of the fault. This will result in a wedge of sediments similar to a baJada. The density of this wedge will decrease away from the source as a function of sorting (Kane, 1361). This change in densityn .av result in a Bouguer gr utity that mar be interpreted as a fault with a south Sip. The above interpretations are only ,entative because of the fiifficolty in éefining the regional gradient of gravity. Several attorots were re no to de~ crease the apparent egional graiient of gravity. This would stee ,osn tle reci.nai gravity profiles a:. d res ult in a gravity interpretation nearer to that of Figure 3. However, such attempts re salted in re5ional 5raiie.ts that did not fit the ctseived gradient of the Bougner gravity. The regions oriflient of gravity used in this interpretation is assured to be valid. However, extension of he survey to the wsst and South ngy result in better resolution of the re5iona gradient of g,'ra Lity and better definition of the retiflual anomalies. Proi ”ile G~G' (FL are 13) be gins in section 32, T. MS N., R. he u’. and extends north-northwest across the Iron Riv er w‘nclinc to t- e north slope of the Porcupine Mountains in section 17, T. 51 E., R. as W. A residual low of 13 m5als exists over the troxsh south C'f the Keeeenaw fault. A low of £5 mgals exists over the Iron River syncline. A3000 foot wei5e of seiimentary rocks fits the 53 s N O "" / r / / ‘0’ / / / / / .. OT / / / / REGIONAL GRADIENT / / OF GRAVITYJ— —— / / -4O_{ / / / / BOUGUER GRAVITY -604 0 a 7 o - 9 9 g . e ‘3 - _ a 4' \ ' IO 1 ‘ a Q 4 ‘ a RESIDUAL ANOMALY —— ~20— " v 3 5 6 c ‘4’ COMPUTED ANOMALY O -304 R42W R43W T48N T49N T49N TSON R43WlR44W‘T5IN 2 1 NONESUCH SHALE 3 SL JACOBSVILLE PORTAGE LAKE “ RH A SANDSTONE LAVA SERIES YOLITE FRED SANDSTONE RHYOLITE Scale (3 kfeel lb -44 Figure l3. Gravity and Inferred Geology over Profile G—G' 5N Presidusl anomaly south of the Keweenaw fault. The configuration of the Iron River syncline is relatively well known te the base of the Name such st5le. The 5e0- metrio configuration we 1 for the Ir 3 River syneline is $4 e triangular shaped bevy 3530 feet deep and six miles wide, as determined from a structure*ccntour map by Kerdenter; (1351). A Cm :e'ity of 2. h 5/ho 9:33 used for the N: nesuch shale erzd the overlyin5 Fre1a sendetcne. however, the enemely computed to the base of the Nonesuch shale reSulted in a 5revity 13? e ency wlw n compared with the residual gravity anomaly. Pn ad1itiornel anomalous source must be used to fit the observed anomaly. Rhyolite is found in drill holes soutli end mithin th ercn Fiver syncline and in the ForCL5iee Fountains. Consequently, a bedy of rhyolite is proposed to help account fer the anomaly. Tre density of the rtyolite was assumed to be 2.55 B/bc. The body of rhyolite roughly parallels the base of the Nonesuch shale. To the south of the syncline the rhyolite is two miles across strike and appears to thin to no more thzan 2500 fe et thick under the syncline. It extends to the Porcupine Fountains where it attains a thic11.ess of 1593+ o 2360 feet. Because of limited (‘1' I'J‘ statien coverage, e cor £15 ration of the rrvolite in the Parcupine IZc*:ta ins proper meet Le coneidered as tentative. CONCLUSICES l. A Bougue‘ gravity enomely mop has been preyered for the study area which shows some of the most interesting gravity anomalies that occur in rocks of Keweennwen ego. 2. In general, the gravity map correlates very well with the geology es mapped by White (1E52). 3. The positive anomalies correlate with the lava flows of Keroenewen age. h. The major gravity lows between the Porcupine iounteins and the Keweenewen Trep Range and south of the eweenaw feult correlate with the Iron River syncline and the trough of Jeoobsville sandstone, respectively. 5. Gravity profiles drawn over the Keweenew fault indicate a decrease in throw from northeast to southwest varyin5 from 6000 feet north of Ewen to 3000 feet west of Lake Gogebic. The dip of the fault appears to be south instead of north as previously postulated. 6. The Bouguer gravity anomaly mop indicates the Keweenaw fault extends completely across the study area. 7. There is no apparent effect of a deep-~eeted density contrast that might occur with the Keweenew fault on the Bouguer gravity map. 8. A gravity anomaly exists that correlates with the White Pine fault. A similar anomaly occurs six miles U1 Cx northeast of the white Pine fault. S. A gravity ancmaly exists that correlates with an Lzz-named fault which extends southwest t'"wLbl Lectlons 4, 3 anl 13 in T. aj K., 3. 44 R. 13. The Iron Riva? syncllne may be unicrlain by a thick rzw Llite to iJ tifit extends into the Porcupiae Lcuntains. It 1. QJLC- BLLD feet thicx under the syncline, 1530 fee t thick in the Fare Lyi: a Mountains and extwnds fLr SLLG distance to the south of the syncllna. ll. The method of oreganprofilin; does nLt apper to be asplicable to tn: study area. cwever, smooth- cuntourlng proved adequate. 12. The regional gradient of gravi J, which increases ncrthward, can be attrLbLLei t3 LLicreLlLQ cf the la 33 d3wn-dip. 13. The awlllLLLiLl of gravity ntethods to the in- vest14ation3 of Precaqulan Terrane3 is a uLele tool for geological explcration. SUGGESTIONS FOR FUTURE WORK 1. A detailed sampling of the various lithologic units should be attempted, using both available well cores and outcrops. The subsequent densities obtained should be applied to the original data collected by the author if significantly different from the values used in this study. 2. Several detailed profiles are necessary to study the Keweenaw fault for possible solutions of the apparent southerly dip of the fault. 3. Among the many causes of variation in the Bouguer gravity anomaly map which warrants further investigation are the White Pine fault and associated anomaly to the northeast, and the faulting which occurs in the wouthwest part of the study area. h. A detailed field mapping and petrological study of the rhyolite which crops out south of the Iron River syncline is in order. 5. Several gravity stations should be placed in critical points of the survey area to increase the validity of this study. 6. The survey area should be extended to the east euui west for better resolution of the regional gradient Of the Bouguer gravity. 57 58 7. The area should be extended to he soqth to inc the South Trap Range to study the thickness of the Jacobs- ville sandstone and its relationship to the lava flows. on? T"! YM‘f'F1'.’T/. f»? s '3‘? uuuA-JCT:D .LJ...J..J.V‘..'--_ g.$ Adams, F. D., 1909, The basis of Precambrian correlation: J‘Dur. (1991., V. 17’ p. 103-22 . Aldrich, H. R., 23, Hague tic surveying;G on the copoer- bearing rocks of Liaco usin: horn. 3ol., v. 18, p. 5=5£nn 0574. Allen, R. C., and Barrett, L. P., 1915, Basel c>n~lrnerate of Keween wan series urcenfcraablt with Ctsso group: Jo ur. Geo 1., V- 23: Po 639 ‘703- , 1315, Contributions to the Precambrian geology of I‘ECI‘f “LQI'D h110h1;2an and 911000115312“: £1011. G601. C-Ld Biol. Survey, pu‘. 18, geol. series 15, p. 13-164. American Geelclg is al Ins-titute, 1960, _51 9;331_Cf Geology agdgfi'let 1W-19‘0233 American deol. last. ., Hashington, D. C. .- '-._ Bacon, L. 0., 937, Relationship of gravity to ooolo tical «tractors in Kiohigan's Upper Peninsula: in Goal ojical Exploration, Institute Lake Superior Geol., Mich. Co lege Min. Tech. Press, p. 58-53. , 1363, Futolr.a-3 $~bldéic structire in the accts~ ville-Gay area of the Keweenaw Peninsula, as inter— ;reted from geophysical data: Institute LaEce L‘uperim Geol., Proc. 6th Ann. Ktng., p. 8. Bateman, A. M., 10 H50, - vflf'i” E! :trel rtoosit 3: John ‘Jiley and Sons, 150., has York, 9le. roderick, T. M.. 1929. Zoning in sicniean c opcr deobsits and its significance: Econ. Geol., v. 2 , p. 1L9-162, , 1931, Fissure vein and lcia relatio. Lira in B.ichi; copper deposits: Econ. Geol., v. 26, p. ONO-355. , 13 35, Differentiation in lavas of the h oh "an Ker ‘0' Cm). s3.” G‘JOl. 3J0. IEKIXEPICS. EH11]... V. “r5, p. 503-55 r'Q .) , 33?, Ma ghetic surveys in Mich ;;;an copper country: ECC'D. G001:’ v. 3"“, p. 531. kn \I.‘ Broderick, T. M., and Hc-hl, C. D., 1928, bedorv ical methods applied to cxoloration and geologic mapping in the Iichizan copger dist r1 t: Econ. Geol., V. J! Do 408-514- '0 d' , 1935, Differentiation in traps and ore opooi Lti on: Econ. deol., v. 30, p. 301-312. Broderick, T. E., and Iiohl, C. D., and Eidomiller, H. N., 1948, Recent contributions to the geology of the Michigan copper district: Econ. Jeol., v. Ml, Do QVS‘YEB- Butler, E. 3., a-nd Darbank, U. 3., 1929, The copes r depcsits of Lichi 5an: U. S. Geol. Survey Pro i. Paper 1L4, 283p. Calumet and Hecla Consolidated Copper 00., 1C,2‘, Genetic classification of the Michi9ma1 copper depo si to: Econ. Geol., v. 24, p. 325- 323. Carlson, C. 0., 1232,31tumen in Nonesuch formation of Kewecna :an series of Northern Eichigan: Am. Assoc. Petroleum Geologists Bu11., v. 10, p. 737-780. COI'hNall, H. Jig, 19831, b$fikvrelltidtiun in Pauly. 1.8.: 1.3.3 or tf‘ri. Keweenawan series: Jour. 6601., v. 59, p. 151-172. , 1957, Minor elements in Keweenawan lavas, Michigan: Gecchim. et Cosmochim. Acta, V. 12, p. 293-224. Dom‘élasg 0. Va, and Tilonfls, Go Do’1'357' a pOC.>lu1.e (1m in of native copper: Econ. Geol., v. 52, p. #52” ~457. Drier, R. W., and DtTumole, O. J., 1959, Pnehictorin cor‘er 4r‘q .A’v‘. “Oiw-hw ’ w;¢i"::* E '1. ‘ I?“ .u C: .LL‘qu' 31.1.0! “.21.. . DuBcis, P. M., 1155, Paleomagnetic measurements of th Kewcena awan (Lich): Nature, v. 175, p. 5co- 507. Eddy, G. E., 1933, Magnetic surveying of the copper country of Northern hichigan: Compass, v. 113, p. 117'119 . Fisher, James, 1929, Historical sketch of the Lake Superior ccpper district: Lake Superior min. Inst. Proc., v. 27, p. 54-b7. Gordon, w. 0., 1905, The Black River section near Bessemer: Mich. head. Science Rept., V. 7. p. 108-195. 61 Grcut, F. F., at. 81., IFSI. Precazbrian stratigraphy of.Minneseta: 6331. $00. ham? 33 3311., v. 62, pt. 2, p. 1:,17-le{3. ruck, H3msr, 31F, 633133? 3! the F13r1 an C3ppsr dist: EM. kin. Jffiurg, v. 13-3 J, p. _’~L. ”it" Q‘Jo Jim-2113. I: K... 1‘5“: 3 £1313 .3 :521’1'3333615" ":':**.:.,:3:.:; 13:32:12: 3: I ha. Geno-t: W. 13.3., 33 ~31. {aier-fi‘] 3.1%, , 1F51, Paleo~r33513 evolutifin 3f 1? e LaVS S"r3r13r r31313n frnm.13te r'gweenawan time to late Cam3313n time: 0331. See. Amsrica 3311.. v. 72, p. 1-18. lam-mm 31:33.1 :6, 111373, Terrain cams-3313213 far gravy meter 333313n3: Gm nxvfii 3, v. R, p. 134~l 4. Har~~nbarg, H. J., IFCJ, Pevaozm 11 CCFmIni 3:133. Heilasjed, c. 8., 133340, 31:15:13" 7.23233: 3.: Pmntiza~ hall, Inc., Ln513320d cm. 2., gay Jergcy. 1:13.33 'v, ”0 Jo, 1 jQL, ?uP£OP.&1 CC): .3431Elcat1: -n¢ Earnetcin, O. M., 1"3, Unp'b115hed mrs er' s thec1s, E13h1:_an Stat a University. 323cm 121m B. V' .C., 1923, Laka Sctcrirr’cnfl~"*~1‘*ax G331. S-oc. Amaricg.3u11., v. 34, p. £3?‘L73. Hatch: c138, H. 0., Rooney, w. J., 33d Fishcr, J3m33, 192;, Earth reslsfi 1v1ty megx vrrmw is in trae Lake $3perior coppar country: Amrrica Inst. E 1n. Ict. En3., C333Ly31331 Prespecting, p. 51*67. Ifil‘thhu J- Lu 1C” 5‘3: Q2" 733’ " 1' ‘ fi"“3“£m73"3£;:33 ‘UI" "T’V— UhiVfi‘rcity 1111311215 rFEEEo, 1:19 Lima, lilo, 313;). Ho'dhton, D3u5laa, 1873. Ll:h313:" (cf tha upger Pew“ ins 313): Rich. 6331. 133 3, p411. 2, p. 2;;*¢.C. Kubb.1‘1 , L. L., IEFB, Ke‘: 33333 P31.3It, 133 particular reference to the £3131: sea and tre;S.r 33 "“313331 r0331 8: filth. GQOI. 3-31.1'1’9‘, 1331;.5. p't. 2, :39. IZ3b3r, N. K., 135?. 5 333 3~33313 3? 3:23 (:151 .13 of tire Ironmood 1: on £33m3t133 3f’F13h1:_an and 1333 313: E00“. G801o, V. 54’ p. 8:3‘118. 62 Irving, R. D., 1833, The copper-bearing rocks or Lake Superior: U. 3. Gaol. Survey Mon. 5. #639. Irving, 12.13., and Chamberlain, T. C., 1885, Observations on the Junction between tho Eastern candctonc cud tho Kewecncwan uric: on Kouunaw Point, Lek. Supt-ion U. S. Geol. Survey Bull. 23. 124p. Irving, R. D., and Van Hiac, C. 3., 1892, The Poncho immbenring uric: of Michigan and Wisconsin! U. S. 0901. SW Hon. 19. 5334p. Juana. J. 3.. 1960. W: M» Publilhing 00.. Import Bosch. Col onus. Jamisonfl. L. 19188, 4 s The entomon Harald Puss, Ontomgon, lichigcn, 2389- Kane, M. P., and Pakiccr, L. C... 1961, Geophysical study of lubaurfaco ultimatum. in louthom Owens Valley. Californiu Geophysics, v. 26, p. 12-26. El-mlidi, H. 3., 1950, Unpublished mater'a thesis: Michigan State University. Kotlimvcakii, B. V., 1962, Evaluating the cccmcy of a gravimetric survey: in Applied Googéhyaica, USSR, Foreman Press, New York, 9. 139.1 . Inna, A. 0., 1898, Geological rcport on 1310 Roycl, Michigan: Mich. Gaol. Survey, pub. 6, pt. 1, 2819. ,______, 1909. Geology of the Porcupine lountaina, Michigan: Mining World, v. 30. p. 1115-1117. ______, 1911., chcenann uric: of lichignn: Mich. Gaol. and Biol. Survey, pub. 6, goal. car. it, 9839. ____, 1916, Th. Kewecnaw fault: Gaol. Soc. Ameriu M]... '0 279 :1- 93’1000 ________, 1923, Geotnem or Lake Superior copper country: Geol. Soc. America. Bull., 1. 3b, 1:. 703-720. Lam, A. 0., and Gordon, w. 0., 1907. A geological action from Beacon:- down Buck Rim: Inch. Gaol. Sumy cht. 1906, p. 397'507. 63 Lang, 8. S., 1919, Porphyry intrusion: of the hichigan copper country: Eng.‘nin. Jour., v. 107, p. 452. Lawson, A, C., 1916, The correlation of tho Precambrian rocks or the region of the Great Lakes: Calif. University,Dept. aeol., Bull. 10, p. 1-19. Leighton, M. w., 195%, Petrogcneeie of a gebbrogranoghyre complex in northern Wisconsin: Geol. Soc. Amer c 81111., V0 65, De 401-M2e Leith, c. x.. 1927, Lake Superior Precambrian (11198.): Geol. Soc. America Bull., v. 38, p. 110-111, 9- “9-752. Leith, c. K., Lund, R. J., and Leith, Ardrew, 1935, Precambrian rock. or the Lake Sugzrior region: U. s. 0801. Survey Prof. Paper 1 . 3%. Leverett, Frank, 1929, Morainee and chore lines or the Lake Superior basin: in Shorter contributions to General 0103:, U. 8. Goal. Survey Prof. Paper 15“: Po -720 Logan, w. 8., 1863, Report on the geology of Canada: Canadian Geol. Survey, Rent. Prog. 1863, 983p. Longwell, C. 3., 19h3, Geological interpretation of gravity anomalies in the eouthern New England- Hudeon Valley region: Geol. Soc. nitric: Bull., 7. 5h, 9- 555'590. Longyear, C. 8., 1917, Results of drilling in the Nonesuch formation between White Pine and Lake Superior: in Mineral Resources of Michigan, Geol. and Biol. Survey, pub. 24, geol. Ber. 20, D. 19‘20. Macrarlane,‘Thomae, 1866, On the rocks and cupifcrous beds or Portage Lake, @ichiganx Canadian Gaol. Survey, Pros. R'pte 1803'1%5, p. 1‘9’161‘0 MaCR, Jo We, 1957' UUDUblinm mam.‘ “188183 University of Wisconsin. Marvine, A. 3., 1873, Correlation of the rock! of Boughton and KoueenaW'Countiee, Michigan: Mich. Geol. Survey, publ. 1, pt. 2, p. 97-61. 69 Marvine, A. R., 18738. General structure and lithology of the Eagle River section, Michigan: Hich. Geol. Survey, publ. 1, pt. 2, p. 95‘140. Meyer, H. J., 1963, Unpublished master's thesis, Mich. State University. Miller, W. 3., 1923, Precambrian folding in North America: Geol. Soc. America Bull., v. 3#, p. 679-702. Nettleton. L. In. 191:0, WW' Hearse-Hill Book Co., Inc., New‘York, Now‘ank. _____,-l9&2, Gravity and magnetic calculations: Goo- physics, v. 7s D. 293°310. Niggli, Paul, 1952, The chemistry of the Keweenauan lavas: Amrican Jour. Sci., Bowen Volune, pt. 2’ D. 381*“12. Nishio, Kerijiro, 1919, Native copper and silver in the Nonesuch formation, hichigant Econ. Gecl., 'e 1“: P. 324'33“. Rand, J. R., 1957. Copper mineralisation at the White Pine mine, Ontonagon County, Michigan: in Geological Exploration, Inst. Lake Superior Geol., Mich. College Min. Tech. Press, p. 17-25. Reed, R. C., 196R, Personal Communication. Roberts, E. E., l9h0 New data on eons problems of Keeeenaw Point (M1ch.), Lake Superior gang.): 0801. 306. Amrio. BUIle, Ve 51) D. 1902e Rominger, c. L., 1876, Observations on the Ontonagon silver mining district and the slate quarries of Enron Ba : Mich. Geol. Survey Rept. 3: Pt. 1, p. 151-106. Seaman, W. A., 1929, Geological and magnetic field work in the Keueenaean of the liohigan copper country: Lake Superior Min. Inst. Proc., v. 27. p. 155-159. sinuous, Gene, 1961!, Gravity survey and geological interpretation, northern lbn‘York: Geol. Soc. America Bull., v. 75. p. 81-98. Spirorr, Kiril, 1952, Residual minerals in Keweenawan congloeerate: Rocks and Minerals, v. 27, p. 2&3-246. 65 Spurr, J.“ a., 1920, The copp er ores of Lake Superior: Eng. and Min. Jour., v. 110, p. 355-357- Stoiber, R. E., 1955, winoral zoning in the Portage Lake lava series, hHichi'an Copper district (abs. ): Econ. 66010. V. 50, p. 101. _____J 1959, gdule mineral zoning in the Portage Lake lava series, Michigan copper district: Econ. Geol., v. 54, pt. 1, p. 1250-1277, pt. 2, p. 1hL4-lh60. Sullivan, C. J., 1557, Classification of metalliferous provinces and deposits: Canadian Inst. Min. Zet. Trans., v. 60, p. 333-335. Taiwani, Manik, Yorzel, J. L., and Lsndesman, Mark, 1959, Rapid gravity computations for two-dimensional . bodies with application to the Mendocino submarine frsfiture zone: Jour. Geophy. Research, V. 6a, p0 9'59- Thaden, R. E., 1950, Unpublished master's thesis, Michigan State University. . Theil, Edward, 1956, Correlation of gravity anomalies with the Keueenawan geology of Visconoin and Minnesota: Geol. Soc. America Bu11., v. 67, p e 1079- 1100 e Thiruvathukal, J. V., 1953, Unpublished master's thesis: Michigan State University. Tyler, S. A., et. a1., 1940, Studies of the Lalo Superior Precambrian by accessory mineral methods. Geol. Soc. America Bu11., v. 51, pt. 2, p. 1929 1538. United States Geological Survey, 196h, Aeromagnetic map of the Bergland and part of the White Pine Quadrangles, Ontonagon and Gogebic Counties, Michigan. vagk, Raoul, 1956, Gouguer corrections with varying surface density: Geophysics, v. 21, p. 1004-1020. van Rise, C. 8., et. al., 1909, Precambrian geology of North America: U. S. Geol. Survey Bull., 350. 9399. _____, 1911, Geology of the Lake Superior area: U. S. Geol. Survey Mon. 52, 641p. 66 Wadsworth, M. E., 1891, The south Trap Range of the Keweenawan series: American Jour. Science, v. #2, p . “17”“).9 e White, W. 5., 1952, Imbrication and initial dip or Keweenawan conglomerate beds: Jour. Sed. Petr., v. 22, p. 189-199. , 1953, Stratigraphic sections in the vicinity of the White Pine copper mine: U. S. Geol. Survey Preliminary Rept., Open file, Lansing Michigan. , lesh, The White PirefCopper deposits: Econ. Geol, v. #9, p. 675*710. , 1957, Regional structural Betting of the Michigan native copper district: in Geological Exploration, Inst. Lake Superior Geol., Mich. College Min. Tech. Press, p. 16.18. White, w. 8., and Cornwall, H. R., and Swanson, R. w., 1953. Bedrock geology of the.Ahmeek Quadrangle, Michigan: U. S. Geol. Survey Quad. Maps, 61-27. White, H. 8., and Wright, J. 0., 1962, Geologic maps showing outcrops of the Nonesuch shale from Calumet to Black River, Michigan: U. S. Geol. Survey open file rept., 1962. Whitney, J. D., 18#9, Notes on the topography, soil geology, etc., of the district between Portage Lake and the Ontonagon (Lake Superior region): U. 8., Slat Cong., let Session, Senate Exec. doc. 1, pt. 3 and House Exec. doc. 1, pt. 3, p. 6&9-701. Hoods, T. 8., 1919, The porphyry intrusions of the Michigan copper district: Eng. Min. Jour., n. 107, p0 299-302- Woollard, G. P., 1943, Transcontinental gravity and magnetic profile of North.America and its relation to geologic structure: Geol. Soc. America Bull., , v. 54, p. 7&7-790. , 1951, Annual report of the special committee on the geophysical and geological study of con- tinenta;.1§SO-1051: American Geophy. Union Trana., v. 32, p. 634-6R7. 67 Woollard, G. P., 1958, Results for a gravity control net- work at airports in the United States: Geophysics, v. 23, Po 520-535. Wright, F. E., 1909, The intrusive rocks of Mount Bohemia, Michigan: Nich. Geol. Survey Sept. 1908, p. 355-402. Wright, F. E., and Lane, A. C., 1909, Preliminary geological map of the Porcupine Mountains and vicinity: Mich. Geol. Survey Kept. 1908, p. 11. ram”! Elm, .ll." 1‘ 1 1"] ‘1