(1953)

REMANENT IvlAGNETIZATION OF EASTERN UNITED STATES TRIASSIC ROCKS by David Edwin Bowker B. S. Antioch College (1953) SUBI{[TTED IN PARTIAL REQUIREr.ffiNTS FULE'ILLMENT OF THE FOR THE DEGREE OF DOCTOR OF PHILOSOPHY at the MASSACHUSETTS INSTITUTE OF TECHNOLOGY 1960 Signature of Author ••• ~ • or -- ~ •.• y .•. , e/ • ( r". C ••••••••• Department of Geology and Geophysics ...... May Certified by • • • • • • e./.' v. ~ .. (:1. Accepted by•••••••••••••••••••••••••••••• Chairman, Departmental ,.- •• 0 ···· 1960 ........ Thesis Advisor Committee on Graduate Studies ii Massachusetts Institute of Technology Cambridge 39, Massachusetts May 14, 1960 Professor Philip l"ranklin Secretary 0 f the l"aculty Massachusetts Institute of Technology Cambridge 39, Massachusetts Dear Sir: . In accordance with the regulations of the faculty, I hereby submit a thesis entitled, "Remanent Magnetization of Eastern United states Triassic Rocks," in partial fulfillment of the requirements for the degree of Doctor of Philosophy in the Department of Geology and Geophysics. Respectfully submitted, David E. Bowker iii J~ CKNO'VJLEDGJ:lFMT S The author vTishes to express his appreci2.tion 2nd thanks To Professor planning, R. R. Doell for his help end encouragement experimenting, and writing in the of this thesis. Iro D. Greene\'la~t for his assistcffice on the field trips and laboratory vJOrk connected 'Hith this thesis. To the members of the Department their advice, especially To the memb0rs to Professors of Geology preparing Bac~ine Shop for their suggestions. To his wife for her part in the manuscript To .Alice Seelinger for E. l~Jencherend H. Hughes. of the Geology Department time aI}-dm2ny constructive 8~d Geophysics prepa.rc',tion. for the many hours she has spent typing and this thesis. To the National Science ,tt'oundationfor making this \'lorkpossible. iv :REr~ENT I"lAGNETIZATION OF EASTERN UNITED STATES TRIASSIC ROCKS by David Edwin Bowker May Submitted to the Department of Geology and Geophysics 'on 14, 1960, in partial fulfillment of the requirements for the degree of Doctor of Philosophy ABSTRACT Remanent magnetization measurements were made on samples collected from many of the Triassic formations of the Eastern United States. The Nova Scotia igneous rocks were also included. All of the igneous rocks and some of the sedimentary rocks were given an a.c. demagnetization treatment. The results of the igneous rocks are divided according to the three main areas from which the samples were collected: the Nova Scotia, Connecticut Valley, and PennsylvaniaVirginia areas. Except for the Northern Massachusetts sediments, which appear to have been magnetized after deformation, the results of the sedimentary rocks are in reasonably good agreement. The axis of a geocentric dipole field that would account for the remanent magnetization in the sediments is placed within 5 degrees of longitude 105 1/2 E and latitude 65 1/2 N, for a 95% probability. Thesis Advisor: Title: Assistant Richard R. Doell Professor of Geology and Ueophysics v BIOGRAPHY The author, David Eduin BO'Vlker,was born in Richmond, Virginia_, on April 19, 1928. High School, Electrical After graduating in Highland 0prings, in 1945 from High1[md Springs Virginia, School in WasDington, D. C., he attended and graduated the Bliss from there in 1946. After t1<lOyears in the Radar School, Ohio, in 1948. in the U.8. NaV'Jas a student he entered In June, and instructor Antioch Co11ec;e in Yello,.". Syrings, 1953 he received his Bachelor of Science Degree in Physics. ~~ile at P~tioch the author held coop jobs vuth the Airborne Instruments Laboratory, Laboratory, Yellow Springs, Hashington, D. C.; end the Jarrell-Ash The author entered i'.lineola, Ne1vYork; the Kettering Photosynthesis Ohio; the U.S. GeologicB~ ~urvey, M.I.T. Co., Ne1'Ttonville, dassachusetts. in 1953 end has held assistantships Hith the G.B.•G. and the Hock l.laenetics Research Proj ect. During the surmner of 1956, he worked "lith the California Research Corpor[ttion in La Habra, California. vi TlillLEOF CON~JTS ltCKN01iLEDGEr'1ENTS P::J.ge iii •• iv ABSTPJ~CT. I3IfJK-i-RAJ?HY • • LIST OF FIGURES • ix LIST xi OF TABLES INTRODUCTION. 1 Collection A. • 4 l'-1easurement. 5 RN'W~IENT 11AGNETIZATION 7 Igneous Rocks 7 1. Nova Scotia. 7 2. Connecticut Valley Pennsylvania B. Sedimentary • 11 - Virginia. 11 Rocks 1. Connecticut Valley • 2. NevI Jersey - Virginia 17 17 .1l.rea• 20 3. North Carolina • P JiP',T II: P P.LE01VIAGNETI C RE8UL T8 Proposals 27 • 39 for Euture ~ampling. 56 Conclusions. P..PPE~~DIX 11.: INSTRUI.'IENTATION. 1. General. 2. Specimenm1d 59 59 Reference Generator • Input Attenu;:~tor and G. R. Amplifier. 61 69 vii Page 4. 71 Specimen Signal F'ilter •• 5. Reference 11Jnplifierand .tl'ilter. 73 6. Phase Detector. 75 7. P01'1erSupplies. rt o. Accessory lfPPENDIX B: .......... 79 80 Equipment OPERATION 87 ••• 1. Circuit adjustments 87 2. Calibration •••• 87 a. Phase Angle. 87 b. 88 Intensity of Magnetization Measuring Procedure Sensitivity APPENDIX C: 2. 92 •••• COLLECTION 1. Collection. • 93 .AND PREP i~PJ~TION OF SPECIH"ENS . . ... .. Preparation DERIVATION APPENDIX I.rETHOD OF STATISTICllL ft..PPENDIX F: 95 ... 95 97 IUJPENDIX D: E: • OF THE I,Vi.GNETIe VECTOR • THEAT~![ENT • DISCUSSION OF PROCEDURE iillD PESULTS 99 • 105 • 109 1. Collection. 109 2. f.'1easuremen t 109 A.c. Demagnetization •• '•• 110 4. Accepted Demagnetization Results •• 5. Method of Averaging Data •• 6• Geologic 7• Pole Positions • 8. Heat Treatment •• Corrections • .. . . .... • 114 115 • 116 • 117 • 118 viii Page 9. Laboratory Deposition Tests •••••• 10. Origin of Remanent Magnetization 11. Stability 12. Magnetic Reversals 13. Comparison 14. Conclusions ••••••••••••• of Magnetization • • • 120 •• •••••• •••••••• of Pole Positions •••••••• • 122 • • • • • • 124 ... G: IGNEOUS A.~D SEDIlvlENTARY ROCK DATA •• APPENDIX H: CONTWTS ON PHOCEDURE AND CONCLUSIONS •• 1. Rejection Criteria for Sedimentary 2. Influence of Earth t s .If'ield ••••••••• 3. Reduction of Scatter • 121 • • • 123 APPENDIX BIBLIOGRAPHY ••••••••• .. • .... by Geologic Outcrops •••• Correction •• • • • 125 • • • 127 • • • • 144 ••• 144 • • • 146 • • • 150 . . . . . . . . . . . . . . . ••• 152 ix LIST OF r'IGUF..ES Page li'ig. I-I Index Map of Triassic j~eas •••••••• 1-2 Correlation of Triassic Formation America Exclusive 1-3 Nova Scotia Igneous •• 1-4 of North of Canada • 3 .. 8 9 Nova Scotia Igneous (carr. for geol.). 1-5 l'!lass. and Conn. Igneous •• 12 1-6 Mass. and Conn. Igneous (carr. for geol.) •• 13 1-7 .. Pa. - Va. Igneous •••• 1-8 Pa. 15 Va. Igneous (corr. :t'orgeol.). 1-9 Mass. Sedimentary •••• 18 1-10 Mass. ~edimentary 19 (carr. for geol.). I-II N. J. &~d East. Pa. Sedimentary ••• 21 1-12 N. J. and East. Pa. Sedimentary 22 (carr. for geo1.) •• 1-13 Md. a~d West. Pa. Sedimentary ••••• 23 1-14 Ivld.and vJest. Pa •.Sedimentary 24 ... 1-15 Va • Sedimentary. !-16 Va. Sedimentary .... • . 25 . 26 .... 28 (carr. for geol.) • 29 (carr. for geol.). 1-17 N • C. Sedimentary. 1-18 N. C. Sedimentary (carr. for geol.). .. 1-19 Intensity Demagnetization 31 Curve ••• Vector Demagnetization Paths •• 32 1-21 Magnetic Vector Demagnetization Paths •• 33 1-20 Magnetic :B'ig.11-1 Nova Scotia Pole Position - Igneous ••• 11-2 Mass. and Conn. Pole Position - Igneous. 11-3 Pa. ~~d Va. Pole Position - Igneous ••••• .... 43 x Page }i'ig. 11-4 Influence 11-5 of Bedding on Pole Positions N. J., Pa. and Md. Pole Positions - Igneous •• Sedimentary 45 11-6 Va. Pole Positions - Sedimentary •• 11-7 N. C. Pole Positions - Sedimen te.ry• 11-8 Influence 11-9 Average Pole Positions •• 46 .. of Bedding on Pole Positions 47 - Sedimentary • . .. 53 A-I Block Diagra~ of Apparatus •• 60 A-2 View of Apparatus 62 A-3 Coil and bpinner Assembly A-4 0pinner Assembly -5 p.. ••••• •• 63 ........ Cross Section 6it70 Input Attenuator •• A-6 filter Circuit •• 72 A-7 Reference Amplifier and ~~Detector. A-8 Phase Relation ••• A-9 Fanslau Coil End Oven •• 74 ... .. . .. . . . .. 77 81 A-lO Portable t.'lagnetometer•• f'ig. Fig. E'ig • Fig. 1:.8 52 11-10 Triassic Pole Positions f'ig. 44 A~ll Rock Tumbler •• ... A-12 Demagnetization Coil. B-1 Calibration B-2 Intensity Procedure 83 84 .. •• ... 85 90 ... of IJlagnetization••• C-l Portable Drill ••••• 91 96 ....... .... C-2 Specimen Designation ••• D-l Vector Orientations D-2 Schmidt-net H-l Magnetic Vector Demagnetization ...... • EXaJap1e •• .... .. 98 100 102 Paths ••••••• 145 xi LIST OF TP.BLES Page TlffiLE I-I Igneous Rock Data (sites) •••• 34 Sedimentary Rock Data (sites) •• 36 11-1 Average Pole Positions 50 1I-2 Triassic Pole Positions. 1-2 •• 51 G-l Igneous Rock Data (specimens) •• 128 G-2 Sedimentary Rock Data (specimens). 136 H-l Sedimentary Demagnetization H-2 Influence of Geologic Correction Values • ...... .... 147 151 1 INTRODUCTION The continental deposits of Triassic age in Eastern North America are found from South Carolina to Nova Scotia, and occur in several discontinuous generally basins (see Fig. I-l). elongated northward The basins are and in many areas are bordered by faults. The bedding planes in the deposits generally dip toward the dominant fault, such as the eastern fault along the Connecticut Valley basin and the northern fault along the New York-Virginia basin. The basins are quite similar in respect to lithology ture. The sedimentary arkoses, conglomerates, rocks found in the Triassic sandstones, with the Triassic basins include and shales, and several of the southern basins also contain coal seams. interbedded and struc- sediments Extensive basalt flows are in Nova Scotia, the Connecticut Valley, New York, and New Jersey, and all the larger basins have been intruded by basic igneous rocks (mainly diabase). Fig. I-2 is a section of a report by John B. Reeside, (1957), correlating the Triassic through Massachusetts. is given by McLearn continental formations A correlation origin, stratigraphic interest, of the Nove Scotia formations correlation Results of remanent magnetization formations from North Carolina (1953). Since the Triassic sediments are of E'ven within a single basin the results Triassic et al is somewhat difficult. are often subject to doubt. studies on most of these are given in this report. Several areas of however, have not been sampled, mainly the Richmond basin MY. -VA. AREA rRUSSELLJ PALISADE AR£4 ('FONTAINE) SKETCH OF TRIASSIC AREAS 8F EASTERN o I FIG. I-I 100 I N0RTH AMERICA 200 I 300 MILES I I NDEX MAP OF TRIASSIC AREAS I. C. RUSSELL AND J. K. ROBERTS) (after 3 FIG,I-2 (~()l{1{1.~L~\'l"I()N ()F' 'rllI ASSI (~ F'()I{ Mi\'r I (rNS ()F N()l{'rll ,\ MI.~I{I (;A J.~~(;I.,(JSI V I.~ () I.' (;ANAI)A By Love, the Triassic John B. E. Reeside, Jr. (Chairman), P. L. Ap~Hn, H. Colbert, T. GreKory, John H. D. Hadley, N. Bernhard Kummel, P. J. Wa8Ke LcwiK, J. SilherlinK and Karl J. D. ManuelSubcommittee, MRldonRdo-Kocrdell, D. McKee, D. B. McLauKhlin, •.'. W.KMuller, J. A. J.Rcinemund, HodKcrs, It,e I,,"ond V,RG,N,A BO.'11 76 77 Co,roll MARYLANDoftd Fr.lI.rle. COCIftfl.. 78 80 £o.f.mShor. Adam. COllnfy --8-'-- L.bonon YorltC04Infy 82 8J 84 P1.,,'OC'"' r" .. ,oc.". PM••toc.". and L"nco.f., Coun',,, 63 64 Oll"do'JGr'C1,'O". t~ I'.. ~ ~ "' ~~ .... !~<. ~ ~~c ~ "' ~ .... 110 ond CtI'lgJoIfI _ "0" 8l1ek. Cou"fy Coun'", 87 86 Hunf"don Counf, 89 88 50"" ' .. f oftd M'ddl .... cou""" B"Q.nond Po..oie Coun"" Roeltlond Counfy 90 McLou,hllIl PI.,sloc,,,r p",.tocrM PI".Ioc,". 94 ~.cWi-: C"Iocrou. PI. "'OC,". Alpin. G~rmonle Di,trlet typ. lumn numb.r CamplI.r type , Ov.r/ylng PI,I,tooen. Irr II 64 PI""oc,,,. Trlou/e Sfondtud dlvi"on' rflOSSIC /Vorf/tern po,f Jonn7foi1Q.i •• /(0,1Woo. J. T.Ofl rocU c: :0 4: Q: Bntw""N. and QPI7Y '. ~ Rha.tlan Chofl"oc.'o. ",a'."' .c: Q: $".11'''' O'f/OIlOllill. PfIlOCOC.,II. ",,".rlll,1I1 "" "0"., ,o"dlloll,. 0"1 "' ~ ~ 1!I) C"/opllllrll .. bler'tlo"', 1.,Wo,c""O!!. /l"clud.. V''''/Obedi ~t Norian "- co"O'O"'"OI, 6~ 0'*011 of RolJert.J ~ ~~ ~ ~~ :~S ~ t"t .;! G,ltYlbllrQ red Ifloll N... or* 0) Q. 8,u", ..,ek f"''''ol/on (red.hole "'~ 68 .. • • '" ~• ~ el Q. ::J NerrHo~e" 72 811f1RlIfl .flol.ond MOil"'''' 'olld.~". ~t a ~ MOIlfQom.,,, and L.hlQh Stat. MA-SSACHUS£TTS all •• IIrtdf/roy CIOYl'OII,. .,,,.t_. NtOd.t_. 0•• ' C"'O'.OIl. eh,,'.r COun'", NNECTlCUTSOUTH MASS. 93 eloyst""., f',c_, 'H, '''01 •• foc,". 8.,t. and 8~ 08 P,. .. NEW YORK NEW JERSEY PENNSYLVANIA ::J .. Q. o"d 1'0f)1/1I wbb"lIo'u, Corllll •• "orld". Karnian ~ :c C)~ -z-L--- N,."O.ford fO,,,,olIOll g/.b.'1 O"copllyl"'., poll'" .0Ild,tOfll) -1 Pe/llll for IftG IiOil rllb., 50Q,II"., Upper TriasSIC ~J!' g'oup Clotl"c"e. TrIlChyC.'1I1 oo"old •• 1roc",ce,,,, 11011 0 ~ "'e..O.fo,d to'm. (50rtdslo".Ot>d 0'*0,.) !! ....t; PrOl'OCfI,ce,os o'e".'o". P,ol,oeflyeerOI "It" Ladinian 'I 1< uschell<al Middle I (Calcair~ eonchyllen) TriaSSIC Poroe.r"t",. I,I"odo.", Po ,0c.,t1lIt Anisian (vtro/orian) •• Nlco",.tllt bl"o4Il1'lIe Olmo,,' •• IIOuf/1 ""OPopo"oc.ro. p-o""n,o",., .,,",1,. CO'''''''''''' PO,/I'O"u, COII'onll. T"OI"., <I A no.,,,,,II,, mu/"form, • Bunter or Bunt,artd.t.'n (Gr~s biC}a"~) III [II I Prwcomt",o" PrKom"rlO" "' ..'" '02 ,'77,Z13.2", '"" ombr,.,tIolld Pr,comtlno" Z7~ 2..,,,53 P,,,omll"OIl rcom""Oft 10().oo../c"'" Pr,e omb" a" 147.20' '2ts 6,Z7' P-~combrlon to IPrrcomDr'O" 0'<10.."'011 OftdCombr,an '27 'Z9 ~O'IJIC/Ol1 :ue O,dO'lJOC'Of> '44,'4'.2" P~f'('''mb,,(Jn 0"<1 (omb"o, ".e4.ZIZ,J6J Or if/Cion 0 ",Cambflan Combrlon 74,ZI1,3tstJ,3ts' P".combr,on 10,"OO>'ICIO" ZI',Z'4,Z",Z6". J66 ill Scyfhian (Werlenlan) .~ f'em'tI,'OIlU, i' t i~ c: Fl. mlftt}''" KOfllllc""" ~o/ut". X.llodi.eoitl •• fol/ol P,lollo/obu. rOllln40l'" P'OII'I'''''.' rotllltrollt,l VI.fllI"i,.. d.el,i.". Opftlc.rll • C Om",lIl1e OtO(; .rll. 1 r>t,.eo",/K,Of! ",.;;;''';o,pho.,.d Prrcomb,:Oft(?) ,.., _C!!.!!('JVI(lO'" '6,I'O.'~'.ZI6 Low~r T"assic .. ,roc/I/lot• "'.e"oc.'II. "',' '3 ",1" PO'~010'( '7Z roc. S ",'6,'7,16~,I" - - j ",omorP/lo;#rJ rexts PoI«JlOlC ~.",3".J7Z ."oodwllfdi Under/y'M} eferenus rocks fo bibliOgraphy and Northern New Jersey. Although results from the Nova Scotia basalts are included, sediments from this area have not been collected'. '. The purpose of this survey is manifold. 1) Primarily, the results should give a more accurate picture of the earth's magnetic field in the eastern United ~tates during Triassic time. expected that factors which may introduce magnetic studies, i.e., lightning the formations influence errors into remanent strikes, corrections etc., will mostly be averaged out by nIl extensive for geology, survey. 2) 0ince are located in several isolated basins, any systematic of the environment on the remanent magnetism apparent. It is should become 3) All of the areas sampled contained both igneous and sedimentary Triassic rocks. A comparison of the results from these two kinds of rocks will be important, particularly respective 4) Also, the survey may offer values in paleomagnetism. a test for non-dipolar regarding their latitude variations. Collection The samples were collected in the form of one-inch diameter cores. The coring drill was powered by a small gasoline engine and cooled vuth water which was supplied by a small pressurized (this system has since been described The probably error in orientation tank by Graham and Hales, 1957.) of the cores was less than one or t,vo degrees. Approximately eight cores were t~ren from each site (mostly road cuts) with littleconsiderat.ion of the number of igneous flo1'ls. The samples were spaced so as to be representative of the entire 5 outcrop • .An attempt wa.s made to select outcrops from vlidely different locales in order to prevent oversampling anyone formation iI/lore than 530 cores ",ere talcen from 77 outcrops during or region. the survey. Measurement Each core was cut into one or more one-inch long samples. The magnetic moment of each sample was measured with a "rock generator" type magnetometer approximately (emplo~~ng an air-driven 282 revolutions per second. spinner) which rotated at The basic sensitivity I: the instrument was better than 1 x 10 -7 cgsu/cc, 2nd directions magnetization of magnetization greater than 2.5 x 10 -6 cgsu Icc • .All of the igneous samples and some of the sedimentary were given an a.c. demagnetization of the unstable samples treatment to remove part or all components of the remanent magnetization. This "Tas by rotating the slli~pleinside a small pair of Helmholtz coils (supplied by 60 c.p.s. line voltage). The current in the coils was increased to a given value and then slowly reduced to zero. maximum field attainable was 550 Oersteds, which was usually not sufficient procedure sedimentary of could be determined ~~thin a few degrees for samples having intensities accomplished of to complete the demagnetization samples. on the The 7 P ART I: A. RE£f1.At1ENT lvlAGNETIZATION Igneous Rocks According to the results of the remanent magnetization the igneous rocks can be separated into three main groups. correspond to the three principal collected, the Nova Scotia, Connecticut Virginia areas. Valley, and Pennsylvania- of remanent magnetization. to an a.c. field, however, the magnetic behavior quite different. These areas from which the samples were The three groups are characterized their average direction studies, primarily by vlliensubjected of the samples is The data on the igneous rocks is given in Table I-I. 1. Nova Scotia The Triassic basin of Nova Scotia is a long, narrow belt '\vhich borders on the Bay of 1t'undy. The beds dip gently tOvlard the bay at angles up to 15 degrees. ranging from Cape Blomidon The collection Eleven sites were sampled in this area, in the north to slightly sites were spread in an east-west south of Digby. direction so that they would include a large number of flows. The results of the measurements on samples from a given core have been averaged to yield only one direction each core. Fig. 1-3 ShOvlS the direction tion, after a.c. demagnetization, used is the same for all plots. correction of magnetization for of the remanent magnetiza- for the 75 cores. The nomenclature Fig. I-4 is the same plot after for the dip of the beds. The most interesting their behavior feature of the Nova Scotia samples was during the a.c. demagnetization test. It is assumed N • ED • w • • + S • • t E 0 • NORTH- SEEKING DOWN UP RECTIFIED DIPOLE FIELD E9 EARTH'S MAGNETIC FIELD o NORTH-SEEKING o FIG.I-3 NOVA SCOTIA-IGNEOUS 9 N w E S FIG.I-4 NOVA SCOTIA-IGNEOUS CCORR. forGEOLJ 10 that the remanent magnetization is composed of a "soft" component, uhich can be removed by placing the sample in an a.c. field and then slo\'llyreducing the intensit:>rof the field to zero, and a "hard" component, which 1vill not be erased during the removnl of the "soft" (1958) and Creer (1958) The results of As and Zijderveld component. indicate that 1lllstablecomponents can be removed by partial a.c. de:!D.agnetization • .ll'ig. I-19 is a plot of the relative intensity the remanent magnetization samples. The corresponding magnetization of during the demagnetization of several paths of the directions of the remanent is shown in ~lg. 1-20, (for the sake of simplicity the points have been connected by straight lines). Considering N::~35-1, it is noticed that the magnetic vector tends to vary about an average direction for a.c. field intensities variations, however, are relatively greater th8n 100 Oersteds. large. Ns65-2 shows a similar tendency to vary, at first to a lesser degree. the variations become much greater. The Above 100 Oersteds At somewhat lower a.c. field values Ns64-1 begins to vary in the same plane as Ns65-2. Many of 'the samples did not exhibit any obvious patterns behavior even though their magnetization of could be easily changed. Sa.l1lples from outcrops having very little scatter in their remanent magnetization directions, by the a.c. fields. of "soft" components' such as No. 13, were relatively unaffected A comparison of heat treatment and a.c. field treatment from outcrop No. 5 gave similar results. (for the remov,u on some of the samples 11 2. Connecticut Valley Eight of the outcrops the four principal sampled in the Connecticut igneous flows: the Deerfield Valley represent lava of Northern IlJlassachusetts (4), the Talcott lava (2), the Holyoke lava (1), and the Hampden lava (1). is ShOvffi A plot of the remanent magnetization in It'ig.1-5 and Fig. 1-6 (after correction Because the direction of the earth's magnetic upon the location of the site, the influence is shown ,dth respect to the pole positions of its significance direction for dip of beds). field is dependent of the bedding in Fig. 11-4. correction A discussion is given in Part II. For the most pc..rt,the demagnetization lavas was similar to those of Nova Scotia. far from ideal, in that the direction of the Connecticut V8~ley The results were still of magnetization seldom stayed ,vithin a fev; degrees of an average value during the demagnetization procedure. As a result of the demagnetization of magnetization a northerly magnetization tests, the average dlrection for each outcrop treated was moved a few degrees in direction. The reduction in scatter of the remanent was the most significp~t. 3. Pennsylvania - VirF-(inia Unlike the Nova Scotia and Connecticut rocks of the Pennsylv8~ia It'iveof the outcrops - Virginia Valley areas, the igneous area are mostly intrusives. sarnpled are in the eastern part of Pennsylvania, and two are in the western part. The three Virginia outcrops are located in the Potomac area. The remanent magnetization directions are shovm in Fig. 1-7 and 12 • • •••• )tc£f I X'c'J- •• • • /t17 X'••• •• ... XCI 0 • • • • 0 x M~ • • • • • • l!c3 ED X M8 • W • 0 + S .FIG. I-5 MASS. AND • CONN.-IGNEOUS • E 1:1 N ., . }' • ~cLf .. ~(~ ... : • • • 0 '>(~8 +. w. • • •xl\. JM~ .M? • •• • • • • • XCI I ~C3 $ • •• • • • XM7 • • • S FIG. 1-6 MASS. AND CONN.-IGNEOUS (CORR. for GEOL.) E 14 N w E S FIG. 1-7 PAt AND VA. -IGNEOUS 15 N • • • .. x.• ••• V~~X~¥ PI' •• , • pC'. •••• x. •• .R ~~ ••• •• ~P'I • xv;' .: • • # •• • ;3 .Q(V6 •• • • • + w E S FIG. 1-8 PAt AND VA. -IGNEOUS (CORR. for GEOLJ 15 Fig. I-8. The bedding correction, horizontal position, which restores the beds to a has reduced the dip of the remanent magnetization and has also reduced the scatter. Although the demagnetization tests reduced the scatter within several outcrops, affected their average direction The demagnetization assumption of magnetization. of these sa~ples agrees very well ~dth the that the total remanent magnetization "hard" and a "soft" component • paths of three samples. they hQrdly is composed of a .ti'ig. I-21 shows the demagnetization vmen the peak value of the a.c. field was increased by small increments most of the relative exhibited the curious hump that appears vector has reached a stable direction intensity curves just after the magnetic (see Fig. I-19). is also evident in the Nova Scotia and Connecticut This feature Valley intensity plots, although in some cases it is not as clearly developed • .The accepted on the intensity trough. predicted value of demagnetization, curves, usually Hence, the elimination from the intensity magnetization shown by an open circle occurs at the bottom of the first of the "soft" component can often be curves as well as from the direction of plots. The average intensities of magnetization in the Nova Scotia, Connecticut Valley, for the igneous rocks and Pennsylvania - Virginia areas are 9.8, 10.0, and 9.7 (x 10-4 cgsu/cc) respectively. average values seem remarkably constant These since the intensity variations mnong the samples from a given area were gre~ter than lOOx. The difference in the direction these three areas is certainly of remanent significant. magnetization One possible for expla~ation is that when the rocks wera formed, they failed to acquire a remanent 17 magnetization hypothesis, in the direction of the applied field. six randomly oriented samples were heated to about 650°C and allowed to cool in the earth's magnetic from the following outcrops: Except for a difference in orientation, tion. To test this field. The samples were NS13(2), M6(1), M9(1), P14(1), Vl(l). of 2 to 3 degrees, accounted for by the error the samples acquired the same direction Although the test was not conclusive, of magnetiza- it seems to eliminate this possibility. B. Sedimenta~r Rocks The data on the sedimentary of the formations rocks is given in Table 1-2. in the New Jersey - Virginia IV!Ost area and in the Deep River area of North Carolina have been sampled. In the Connecticut Valley only the Northern Massachusetts l<[eresampled. 1. Connecticut sediments Valley Five outcrops of Turners Falls sandstone Longmeadow and one outcrop of sandstone were sampled in the Massachusetts area. The results are given in Fig. 1-9 and F'ig. I-IO. The scatter of outcrop No. 5 was reduced demagnetization in a 20 Oersted field. slightly by partial With a 50 Oersted field the scatter of the 1ongmeado1'1 sandstone was not only reduced, but the average direction due west, bringing of magnetization was also changed about 10 degrees the results into better agreement 'idth the Turners 1"a.11ssandstone. Because correction the attitudes of these beds do not differ greatly, the for dip does not constitute a good test for stability. 18 • , • •~J ~ 3.><iJt •• ••• • ,. • ()e• • • X • • .4 ED • + W s FIG. 1-9 MASS,~SEDIMENTARY E 19 w E s FIG. 1-10 MASS.- SEDIMENTARY (CORR. for GEOLJ However, the influence of the axial dipole field seems to be more evident here thrn with any of the other sedimentary The Connecticut and, according on the Deerfield because of the addition then that the magnetization of irotftfrom the lava. of the.sediments a chemical process which reflects the influence magnetic fields. been plotted Thus, pole positions in Part II. 20 degrees northeast 2. diabase (1952), they are much redder near the to Willard contact, probably is probable Valley beds are resting formations. It represents of post-Triassic .for these sediments The average pole position have not would lie about of Massachusetts. New Jersey - Virginia Area The results from the New Jersey - Virginia Fig. 1-11 a.Dd li'ig.1-12 show the remanent divided into three groups. magnetization directions of eastern Pennsylvania the directions for the Lockatong plots for Virginia, in the Potomac, formations r'ig. 1-13 and r'ig. 1-14 shaH and New Jersey. and Maryland. The direction which contain the results Scottsville E'ig. 1-15 and Fig. 1-16. Roberts and Brunswick for the Gettysburg: and New Oxford formations western Pennsylvania sandstone area have been and Danville No distinction of of magnetization from outcrops located areas, are shovffiin has been made bet1'leenthe and shales in this area (nor in the other areas); (1928) did make such a distinction, Several of the outcrops ment 1nth field intensities slightly, unaffected. responded to a.c. demagnetization of 20 - 50 Oe. but the average direction however. treat- The scatter was reduced of magnetization Most of the outcrops would have required was relatively field 21 N • • J"1. • .x, • • J"Lf • )( •• • • • • J'J., • • >( :[3 •XPI3 • .)( • •0 • •ED •• • ,•• • • •• • • )( 'IS' W • • • • + • J( PI~ 0 S FIG. I-II N.J. AND EAST PA.-SEDIMENTARY E 22 N pt5' • E9 X W • • • • • + E xPI~ S FIG.: 1-12 N.J. AND EAST PA.-SEDIMENTARY (CORR. for GEOL.) 23 N • •• o Md3 y I' I •• •Xpg • • •• W · M'~ • • ~ .~f>'-•• •• x. · .X., '.0 .: ••• ~ • • .)( •• •••• ~Plp5' • • XP7 • + • • • • • • S FIG. 1-13 MD. AND WEST PA.- SEDIMENTARY E 24 N • •_.Pf.~tlf~ .~ X.~~ ..~, .., : • .. • • fiId_~)(PJ.' ~ • . ~PJ.. • • • • • 0 xP7 • • 0 ED • • + W FIG. I-14 XP8.• • • MD. AND WEST PA. - SEDIMENTARY E (CORR. for GEOLJ 25 N • • .. • • : ~II • • •• -?- 7 •• • • • • • ~ : -X" - ... . - Xt7 • >('-( xq •I~ W • . " • c:.• to¥. /rp• .,. .. •• • • • •• •x" •• • X $ 1'1 • • • )(8 •• •• + • E ~ Ie • • • • • • • x• • • • 3 • • • 0 • S FIG. 1-15 VA.-SEDIMENTARY 26 . ... ... • •• • • • ~ • ').. •• 'X, • . ... .X7 • , . • . . .... • II • l'f~ •••• • XI" ~ • (7/)0 • • • • ._ • • • • • o • • • • • • X8 $ ~ q • • o • + w • • • • • • • • • X • &.I • • ~ 3 • • • • • • • • S FIG. I -16 VA.-SEDIMENTARY (CORR. for GEOL.) in excess of 550 De. to complete the demagnetization intensities test. It seemed, however, that the a.c. treatment brought the average direction much better agreement, of magnetization wOQld have of the outcrops into and also reduced the scatter vdthin each outcrop. It may be noticed in the magnetization plots that some of the cores show a tendency toward reversed magnetization. whether the magnetization was reversed of ma~netization the outcrop was labeled reversed Table 1-2). committal, moved toward the reversed If the movement was in the normal direction, the outcrop '\'lEtS sediments, If direction, (noted by R under remarlcs in labeled norm3~. that some of the outcrops contained magnetized several samples in fields up to 550 De. from each outcrop were demagnetized their directions or normal, fo determine or non- It is possible, both normally of course, 2nd reversely since only a few samples were tested in most cases. The bedding corrections suggest that the remanent magnetization of most of the outcrops has been stable since deformation because the scatter among the outcrops was reduced. 3. North Carolina In the Deep River Basin of North Carolina, s&~pled to represent magnetization formations. formations is more clearly developed were The remanent plots are sho'\'ffi in Yig. 1-17 and in li'ig.1-18. revers8~ pattern mentary the three sedimentary nine outcrops The here than in the sedi- of the New Jersey - Virginia occur in both the Pekin and Sanford formations. areas. Reversals 28 FIG. 1-17 N. C. - SEDIMENTARY 29 N -. • • • • • • • 0 • • • $ • • • • w • • • • • + • • XL{ X5 • • • • • •• • • • 'X7 E • • - • 0 • 4'.. - .. • • • • • 00 • S FIG. 1-18 N, C,-SEDIMENTARY (CORR, for GEOL.) 30 The remanent magnetization of outcrop No. 8 was originally scattered between the normal and reversed hemisphere of the plot). directions After demagnetization 550 De. field the magnetization the evidence was not conclusive, (in the lower treatment was more clearly reversed. there was an indication in a Although that the reversal was not a complete 180 degrees from the normal direction. The demagnetization treatment was not sufficient the "softu components had been completely Since the bedding corrections remanent magnetization for stability. removed. do not reduce the scatter of the in this area, they cannot be used as a test When an overall comparison the several basins, the bedding evidence of stability to indicate when corrections (see Part II). is made, however, betv!8en offer much more conclusive 31 P68-1 P71-1 2 4 3 5 NS35-1 o 234 D.mcl9netlz~tlon FIG. 1-19 INTENSITY 5 Intensity C)( 100 0 •• :> DEMAGNETIZATION CURVES 32 w / / + E NS64-1 s FIG. I -20 MAGNETIC VECTOR DEMAGNETIZATION PATHS 33 E s FIG. 1-21 MAGNETIC VECTOR DEMAGNETIZATION PATHS TABLE I-I IGNEOUS" ROCK DATA No. cis Formation Geologic Attitude Stk. E Dip Location Long. W 0 NS2 NS3 NS4* NS5* NS6-' NS7* NS8* NS9-' NS10 NSll* NS12* NS13M6* 10 JJE.' M9* Cl~ C2 C3* C4* Jill 4/10 8/24 9/32 2/12 6/38 5/16 7/14 7/17 7/15 7/12 8/15 North Mountain It It 11 It tt II "tt n II It II " " II II II II II at 11 " 8/16 4/6 7/9 8/13 Deerfield 8/12 6/7 6/8 3/5 Hempden .Talcott " n II II Ho;l:yoke 35 lOW 35 10 W 121 10 S 51 10 N 70 14 N 74 9tN 74 9~N 68 5S Approx. Flat 23 bE Approx. Flat Approx. Flat 67 52 180 175 37 34 20 10 179 25 20 E 10 S 170~ 170~ S S E E 9~-E 9~ I 11 Lat. N 0 f II Ixl0 4 cgau/oc 45-13-40 64-23-31 45-13-45 6Lv-25-55 45-18-49 64-31-34 45-13-23 6Lv-30-57 45-13-51 6Lr47-50 45-05-11 64-45-50 45-05-52 65-04-24 45-02-26 65-13-"" 4ir54-1tJ 65-19-05 44-52-36 65-52-35 4Lr37-07 65-55-30 4Lr36-44 8.9 5.7 21 8.7 8.3 6.8 3.9 15 12 12 5.8 72-33-06 72-33-18 72-35-05 72-34-01 12 64-23-iIJ 6 95 # 28~ 20~ 35 35~ 16 9~ :~~3 8 12t k 137 4.7 7.1 54 4.5 29 42 345 59 24 2 667 5t 105 13 1.5 42-36-51 42-36-50 42-32-20 42-29-03 9.8 Z7 15 8.3 80t 72-45-03 41-53-53 72-43-00 L.J.-26-18 72-50-04 41-~-1.IJ 72-49-00 41-42-27 18 8.1 7.6 1n4 6t 11~- 9 15 5 Pole Position Long. E Lat. N 71! 98~ 153! 11$ 346~- 119t 26 40t 70t 74 59~ 70 74t 77t 71 68t 22i- 67 75t 61t 50t 7 43 17# 51t 24 330~ ~~ 72 57 22 625 44 71 347 77t 58'"2 64 4f:> 58 58 75 52~ TABLE I-I (cont.) No. cis Formation Geologic Attitude Stko E Dip P6 ~* P1O* Pll P14--- P16 Vl* V5* V6fi ~ * cis e95 k 7 8/12 6/7 8/8 9/15 8/10 diabase 34 tl 65 75 75 It Lat. N C> I " 77-05-21 39-58-41 n 55 12N 15 N 15 N 15 N 15 N 80 .30 N n 25 30 W 77-31-01 .39-olv-07 u It n 8/19 6/6 n 15/24 8/14 8/16 25 W , Long. .W 0 P3 Pole Position Location 70 II 15 It 13 10 W 76-54-50 75-32-13 75-32..19 75-28-01 75-19-36 74-57-50 40-03-29 40-20-36 40-21-10 40-16-02 ~23-31 40-20-18 77-3~25? 38-44-59~ 15 W 77-48-1$ .' 38-31-45, IxlO 4 cgsu/ss 7.J" 27 11 6.3 3.8 2.7 15 12 4 7.4 Samples required &c. demagnetization treatment Cores/Samples Angular radius of Fisher circle of confidence (95% probability) Precision factor Location questionable 6 95 4 3t 8 2~ 3 3 10 k 176 3.94 48 396 Long. E Lat. N 93 120 . 68 131~ 117 62t 66~ 389 327 1;8 151 63t 71t 62t 52t 125 62 14- 77 11 26 12t 20 136~ 102 172t 353t 58~ 88 TABLE I-2 SEDIMENTARY ROCK DATA No. cis Forma.tion Geologic Attitude stko E Dip Location Long. W Lat, N 0 Ml M2 M3 M4 M5* Ml1* NJl~" NJ2 NJJ NJ4 Turners Falls 7/7 II 11 4/4 u II 9/9 11 8/11 11 11 8/28 4/8 Longmeadow .. 7/7 Lockatong 11/13 Brunswick 8/11 6/9 Lockatong " P12 P13 P15 8/10 Gettysburg 9/11 New Oxford 8/8 " 10/14 Gettysburg New Oxford 5/5 u 10/14 n 7/7 Brunswick h 2/2 13/16 Lockatong Mdl Md2 MdJ 9/12 Gettysburg 15/20 "u 6/6 Pl* P2 P4-' P5 P7 P3 " I U 0 I " IxlO 5 cgsu/cc 42-36-22 42-36-20 42-36-23 108 2.7 42-36-/~ 39 S 15 S 72-31-41 72-31-39 72-31-25 72-33-05 72-.3 I-Ii> 72-31-44 42-37-21 42-17-08 3.0 105 1.1 65 70 62 75 7 N 7 N lON 15 N 74-55-07 75-01p.Q8 75-04-06 75-03-45 40-30-46 40-27-29 40-27-07 40-25-58 3.9 206 3.5 2.6 44 25 43 70 72 30 21 W 10 W 36 N 40N 24 W 20 W 14 N 15 N 7W 77-16-/+6 77-07-59 76-58-13 77-01-30 76-52-48 76-45-56 75-27-03 75-27-33 75-09-40 39-49-ll 39-45-40 39-58-02 40-02-05 40-01-43 40-02-55 4O-ll-30 4O-lLv-57 40-28-40 101 57 74 31 N lON 30 N 77-20-00 39-40-53 77-13-/4-9 39-/.0-55 77-18-23 39-43-13 71 73 76 45 27 S 35 $ 30 S 99 65~ 19 55 48 33~ e95 k # I~ Pole Position LongoE LatoN Remarks 104 16~ 43 36 .18 104 6t 1 7~ _ 002 _6 69 46 71;; 10 __.-lxlO 6~- 106 0.18 0.47 1.6 1.4 1.2 54§35 40 2.3 2.6 1.7 6 3 23ir 43 19~ 58 2.9 2.3 3.3 227 1.9 71 161 13 107t 66 8It 139~ 105~ 122 illt 196 216~ 219 139 63t 65 73t 61} N 69 N N 73~ 61~ 3# 14t - 8 138~ 70 37} 104 62-fi- 91 115 61:t 52~- N N N N R R R N R N N N W ~ TABLE I-2 (cont.) Geologic Attitude No. V2 V3 V4 V7 VB V9 VI0 Vll V12 V13 Vl4 V16 V17 V18 NOl Ne2 N03 NC4 N05 NC6 NC7 NC8* N09 cis Formation " 8/14 Pekin u 8/12 14/28 Sanford II 12/24 8/9 Cumnock 8/16 Sanford 9/18 7/9 Pekin N Normal R Reversed " " 29 5 14 7 51 86 15 I.IJ 149 31 45 41 46 49 15 44 25 68 99 70 74 105 25 IxlO 5 Long. W Lat. N 0 sedime.nts 6/7 It 8/14 8/13 "II 7/7 I,' 9/12 9/21 " 2/2 It 11/16 3/5 Border Gong1. n u 4/4 4.7 sediments. 10/12 ",~ 9/l2 It 8/10 6/12 Stk. E Dip Pole Position Location t .. 0 r II 31 VI 27 W 22 W 6<\W 2, 14 N 9 N 19 W 11 VI 19 W 23 W 45 N 28W 32 N 30 N 77-37-J.B 77-38-28 77-36-26 78-04-04 78-15-18 78-16-01 78-31-21 78-37-46 79-08-23 79-10-43 79-18-15 79-4J.-1O 79-41-32 79-41-36 lOE 10 E 20 E 7 S 12 S 18 S 17 S 15 S 79-29-10 35-23-00 79-25-55 35-26- /f-5 79-22-09 35-27-27 79-15-45 35-27-31 79-14-38 35-32-28 79-1/v-40 35-31v-13 79-12-201 35-27-501 79-12-101, 35-2B-20~ 79-00-10 , 35-37-45 ' 14E 39-01-36 38-49-32 38-47-06 3S-18-30 38-n-Q3 38-10-34 37-49-22 37-44-46 36-57-24 36-54-38 36-49-43 36-37-45 36-37-11.> 36-38-10 cgsu/cc 5.1 0.8 18 6 4.8 0.59 1.2 6 95 k Long.E # 202 15 3.9 81 607 2.4 125 242 242 91t 7 312 152 15 32'~ 7 21~ W 104 4.2 203 6 1xl.Cr 1.4 3.0 3.6 201 7St 6 1• .3 25 14 65 54 15 3 42- 6.6 4.4 1.5 0.98 ~8 0.92 0.79 1.5 ':-12 63 13 74~ 216~ .57 28 2.9 1.5 lAO 0 12~ 9~ 37 77 19~ lOir 5.9 16 1.5 1.5 9.4 330 2.7 30.3 34 13# 159 227 282t 73 16s... 297l 265~ '17t 249 'Z/9 92t LatoN Remarks 59 -25 82 70ir 67 72 72 62 40 6It 70 71t 3J~ -38 N R N N N N 'N N R N N N R R 53~ N 12~ N 8 N -2.3 58 R N -33:r R N -13t 59~ R 38 39 PALEOMAGNETIC RESULTS PART II: It is assumed in this analysis that the geomagnetic during Triassic field oriented time approximated on average to that along the earth1s axis of rotation. has sho"\'mthat the relative rotation that even if a permanent non-dipole in the out by observations Since the deposition over period of long, the average remanent magnetize_- tion of samples collected through rock formation (1959) Runcorn field could be generated a long time at the earth's surface. rocks is relatively f a dipole of the core and mantle infers core, thenon-8.Y.ial parts l\Touldbe averaged sedimentary 0 field acting should represent a considerable thickness the axial magnetic of course, that the magnetization is stable). of one field (prOvided, It is, however, also expected that the remanent magnetization of the igneous rocks may show the influence of secular variations of the magnetic The location of the north-seeking wpich would have produced latitude (A) i\ position. magnetization The magnetic in a given core, inclination (1) and the are related by: Tan I where pole of the dipole field, the remanent has been obtained for each core. field. = 2 Tan A is the latitude of the site location 'tvi th respect to the pole By the method of Fisher (1953), the circle of confidence (for 95% probability) was c8~cuJ_ated for the pole positions of each outcrop. _The data is given in Table I-I -and Table 1-2. The circles of confidence projection of the northern are also plotted on an equal-area polar hemisphere of the globe. Since the 40 latitudes of most pole positions the circles of confidence introduced tion. are greater than 60 degrees north, are actually plotted as circles. The error is very small end should in no way affect 8n interpreta- vJhen the pole position corresponding occurs in the southern south pole is plotted. hemisphere, South poles are indicated the by open circle plots with dashed circles of confidence. The pole positions for the igneous rocks are plotted Fig. 11-2, and :F'ig.I1-3. The only agreement seems to be those pole positions present magnetic Valley among the three are2.S which reflect the influence before Blld 2.fter bedding for some of the more stable outcrops and Pennsylvania - Virginia and closed points respectively, It is possible of the field. Fig. I1-4 shows the pole positions corrections in Fig. II-I, areas. They are ShOl'Inby open and are joined by straight then that the magnetization been stable since deformation. in the Connecticut lines. of these tvJO areas has The bedding correction for the Nova Scotia samples was too small to be of any significance. :F'ig.11-5, Fig. 11-6, and Fig. 11-7 give the pole positions the sedimentary influence rocks. of the bedding Fig. 11-8, like Fig. 11-4, shOl-vSthe correction and indicates tion in most of the sediments may have been stable Except for the Maryland areas, such as Ne1'l Jersey, Virginia, conclusively considered for area, the geologic that the magnetizations as a whole, however, 8l1d that the magnetizasince deformation. corrections made in local North Ca.rolina, do not ShOll are stable. the evidence Hhen the areas are is much more convincing. Since all of the igneous rocks were given. an a.c. demagnetization test, the author did not feel justified in eliminating any of 41 o 90E FIG.II-I NOVA SCOTIA POLE POSITIONS -IGNEOUS o FIG. II-2 MASS. AND CONN. POLE POSITIONS -IGNEOUS FIG. II -3 PA. AND VA. POLE pas IT IONS - IGNEOUS 90E FIG. 11-4 INFLUENCE OF BEDDING ON POLE POSITIONS-IGNEOUS 45 FIG.11-5 N. J'J PA, AND MD. POLE POSITIONS - SEDIMENTARY o 90E FIG.11-6 VA, POLE POSITIONS -SEDIMENTARY 47 80 FIG. 11"7 N.C. POLE POSITIONS .. SEDIMENTARY 48 eo o FIG. 11-8 INFLUENCE' OF BEDDING ON POLE. POSITIONS -SEDIMENTARY the results in the final analysis. To obtain the final circle of confidence, the Fisher statistical treatment positions of the outcrops. vlas applied to the pole This was done for each of the igneous areas becnuse of the basic differences in their pole positions. The results are given in Table 11-1. The tendency of pole positions tilth small circles of confidence to group together by non-Triassic suggests thQt the results may be unduly pole positions some outcrops is unstable). influenced (i.e., the remanent magnetization Any selection of pole positions of according to the size of the circle of confidence vJill, of course, be arbi trar-y. Tvlany of the sedimentary outcrops vJere eliminated from the final analysis for one of the follovJing two reasons: 1. The remanent magnetization was partially reversed. 2. The remanent magnetization contained unstable components that might have been removed by partial a.c. demagnetization • Eliminations based on the second reason were somewhat arbitrary only the more obvious cases have been excluded. was made on the follovrlng outcrops: NJl, 2, . and The final analysis 3, and 4; PI, 2, 5, and 13; Mdl, 2, and 3; V2, 7, 11, 14, and 16; NC2, 6, and 9. The final data is given in Table II-I. The average pole positions are plotted in Fig. 11-9. Triassic pole positions based on measurements by other investigators are given in Table 11-2 and Fig. 11-10 for comparison. data is reproduced from an analysis by Irving (1959). This SO TABLE 11-1 AVERP_GE No • .A:rea POLE POSITIONS Pole Positions Long. E Lat. N Type No. of outcrops B-95 k 'Igneous 11 10 1/2 20 77 1/2 78 1/2 15 15 40 61 1/2 1 N.S. 2 Conn. Valley n 8 3 Pa-Va If 10 8 1/2 33 129 67 1/2 4 NJ-NC 19 5 47 105 1/2 65 1/2 Sediments Before a final opinion can be expressed about the geomagnetic field in the eastern United states during Tirassic explanations for the differences res~lts must be considered. differences in the sedimentary Four possible time, several and igneous reasons for the follow: 1. Igneous rocks represent hence were influenced a. small interval of time 2nd by the local magnetic field more so than by the average dipole field. 2. The igneous poles represent the geomagnetic r8ndom walk positions field (see Green, 1958), which are averaged out in the sedimentary 3. 4. results. The igneous rocks ,..,ere not magnetized origin2~ly the direction field. of the earth's magnetic The igneous rocks (and perhaps the sediments) magnetically of unstable. are in 51 TABLE II-2 TF~ASSIC POLE POSITIONS Pole Positions No. Cormtry Rock Unit 'Long. Lat. dX d~ Remarks 7 6 12 N&R 143 E 43 28 12 R Lavas and sediments Connecticut IIalley 88 E 55 8 15 N&R " Lavas Connecticut 90 E 54 6 11 N 50 It Brunswickian formation of Newark Series 9.3 E 63 3 6 N 51 II 107 E 55 KgomaSeries 44H 54 Brisbane 37 H 39 46 England 47 Ne~lRed Sandstone France Red sst. 48 U.S.A. 49 Springdale 52 Bechuanaland 53 Australia dX ~f the Vosges and d 4 Valley sst. tuff. 131 E N are the semi-axes. of the ovals in the direction of and perpendicular pole and the site. 5 10 N N & R of confidence to the great N circle of the poles, joining the 52 o 90E FIG. II - 9 AVERAGE POLE POSITIONS .- : o 9O\\' 180 FIG.II-IO -Triassic pole positions.Cdfter IRVING) .. . ; 54 A discussion 1. of the above four points follows: It is not possible to set a time limit on the formation period of the igneous rocks. Connecticut However, since the three lava flovls are separated. by several hundred feet of sediments (see Krynine, that the deposition thousand years. 1950), it seems likely period required at least several If this is true, and if the magnitude of the geomagnetic secular variations more recent times (see Johnson, resembles that of 1948), then it is probably that the average pole position of the Connecticut Valley lavas represents the 2.:x:ial dipole field (of course, this is based on just a few samples in time). Further, the pole position lavas and sediments, that the sediments of the Connecticut No. 48 in ~'ig. 11-10, indicates are in fair agreement vrith those from other areas, whereas they should agree more closely ~~th the lavas. If the magnetization sediments was caused by a long-term, chemical process, differences the various sedimentary 2• of the post-depositional in the polar plots of formations may be smoothed out. .Although the random walk theory is a possibility, it seems that there shoQld be some evidence of it in the sedimentary deposition formations, CE'ill particularly be quite rapid. since continental Chemic2.1 magnetization may have the SEme effect as that mentioned above. 55 3. At first this seemed an attractive hypothesis, but the heating experiments It is unlikely, described moreover, such as anisotropy that any physical of magnetization could be so uniform l~rge areas. in Part I ruled it out. susceptibility (Grabovsry, as to give consistent If the rocks possess mechanism, 1959) results over considerable the remanent maglletization may be dis- torted slightly (Kalashinikov, 1959). Such distortion should, however, be averaged out by s2~ples collected over large areas. 4. p~though corrections for geologic attitude indicate that some of the igneous rocks have been s tnble since deformation (see Fig. II-4), there is still the possibility that they were unstable before deformation. The close agreement betvJeen the pole positions sediments 1<liththose of the Pennsylvania of most - Virginia igneous rocks further suggests that intrusive may be more stable than extrusive F'rorothe above discussion rocks rocks. then, it appears thE'.tpoint 3 is the least valid, whereas points 1, 2, and 4 are still quite possible. It must also be remembered that the a.c. demagnetization a basic difference The direction Connecticut in the magnetic stability of remanent masnetization tests reveal of the igneous rocks. in most Nova Scotia and Valley igneous smnples can be changed appreciably by applying a.c. fields of less than 100-200 Oe., whereas this cannot be done 1-liththe Pennsylvania - Virginif~ igneous samples. Thus, 56 point 4 may be better taken. Proposals for !!uture ::lampling Although this survey has been quite eA~ensive several hitherto unknovm features of the remanent the East Coast Triassic sufficient northern mab~etization of rocks, there are still several areas of interest to warr2nt further sampling. New Jersey lavas and sediments they may be the same age. Connecticut, and has revealed well as a more complete Because the are similar to those in An investigation of these, as survey of the IVleriden }t'ormation of Connecticut, may be very enlightening. Since the igneous rocks of Nova Scotia give pole positions are different from those of the sedimentary t he sediments in this area will also be important. Although basins, it is doubtful that findings such as the Dan Hiver and Richmond final results, comparative formations, 2. that survey of from any of the smaller basins, will a1ter the it will never the less be worth while to make measurements on the rocks in these areas. Conclusions Several important conclusions, some of which are very tentative, may be dralom from this survey, based on findings Triassic rocks and not necessarily applicable from the East Coast to other areas. They include the follo~rlng: 1. Results of sedimentary rock measurements from several basins are in close agreement and indicate that factors which might introduce errors into magnetic studies are either negligible or consistent in their influence. 2. Igneous rocks may not be as reliable rocks for p~eomegnetic A.C. demagnetization as sedimentary interpretations. tests can improve the results from both igneous and sedimentary rocks. 4. Results from small numbers of srunples may be indicative (i.e., the data given in Table 11-2), but extensive s?~pling is certainly more valid. 5. It seems evident that during the Upper Triassic the geomagnetic approximated field over the eastern United St2.tes on average that of a dipole. of tIllS dipole intercepted The axis the earth's surface in the vicinity of Long. 105 1/2 E and Lat. 65 1/2 N. 58 APPENDICES 59 APPENDIX A: 1. INSTRUMENTATION General The apparatus is of the "rock generatorn type (Johnson, 1938; Nugata, 1943; Bruckshaw, 1948; Graham, 1955; Doell, 1955; Hood, 1956) in which the specimen, in the form of a one-inch diameter cylinder one-inch long, is rotated near a coil. rock sample generates "an alternating The magnetic momentof the voltage in the coil which is analyzed for phase and amplitude to determine the direction of magnetization and the intensity of magnetization, respectively, of the-specimen. A block diagram of the apparatus is shownin Fig. 11.-1. The signal generated in the specimen coil is fed into the attenuator and then into the battery-operated General Radio amplifier. the signal is sent through a filter li'romhere and into the phase detector unit. The photocell and light chopper located at the base of the spinner generate another alternating reference signal. voltage, referred to as the The photocell maybe rotated about the spinner and in this way the phase difference between the specimen signal and the reference signal can be varied. reference aplifier This signal is fed into the and phase detector unit which contains a filter that is matchedto the one in the circuit associated with the specimen signal. Various methods for generating the reference signal and measuring the phase have been described in the literature. The spinner arrangement described by Graham(1956), is similar to the apparatus here, while the detector circuit is similar to that UU ,;,; > > rt)U) Ort) O. Q. :::> (/) a: ~ Q. ...J 0 u "0 ~ Q: ci 4: a.. ~ a: w l..J - u. 4: W lI- Z 4: a.. '0 u. LIJ a: c []! u LIJ ILIJ I 0 ~ u LIJ a.. (/) t::J a.. z LLI (/) a.. ~u U o ex:: C\I CX) C\I L Q. en @ II) Q. 0 CD C\I C\I u (/) 0 z LLI C) U ..:( Cf) ::> ~ <{ 0:: 0... <{ a.. 0 l.J... ~ <{ a:: C9 <{ - 0 ~ U 0 --1 CD I « (!) l.J... 61 described by Hood (1956). apparatus in which the components ~. li1ig.A-2 is a photograph are as follows: A. Spinner assembly B. Decade attenuator C. General Radio amplifier D. Calibrated E. Reference Ft. Oscilloscope G. Air pressure regulator H. 300 vol t power supply I. 6•.3 volt filament supply J. Ref erence lamp power supply attenuator and filter amplifier and detector Specimen and Reference A. unit and on-off control Generator The spinner and coil assemply the components of the measuring are sho.. m in tig. A-3, in which are as follows: Specimen pick-up coils B. Specimen holder c. Reference light chopper D. Reference photocell assemply E. Spinner base F'. Phase dial Fig. A-4 is a cut-away drawing of the spinner assembly, and shows details of the various parts. The specimen coils actually consist of two coils each, connected in such a manner that the current flow induced in the inner coil is opposite to that induced in the outer coil. The radii and number of 62 FIG. A-2 VIEW OF APPARATUS 63 FIG. A-3 COILS AND SPINNER ASSEMBLY ---------COIL SUPPORT ------------- -COIL FRAME ----------------!ALANCING -- --- COIL~ ------------PICKUP COILS (pr-wound) - --- ------------------SPECIMEN - --- -------------------- HOLDER -SPECIMEN I I z o -METAL ,----- --- ---- -- - - - --------- --- -- ---PHOTO-TUBE - --------- -LAMP ASSEMBLY --------LIGHT o BOX CHOPPER --SPINNER ----;--- - -SPINNER ---------AIR BASE INPUT ----SPiNNER BASE SUPPORT o - ---- - - ---BASE PLATE -PHOTO-TUBE LIFT FIG. A-4 SPINNER ASSEMBLY CROSS-SECTION 65 turns of the coils are designed to give zero flux linkages through the double coil system. Considering a concentric pair of coils with rectangular crosssection, when H is not a function of r, it can be shown that the current induced in the coils is proportional to the quantity . (r32 + r33 - rl3 - r3), where rl and r2 are the J.IlIler and outer radii 4 of the inner coil respectively, and r and r are the inner and outer 3 4 radii of the outer coil, respectively. (Although the coils used do not have rectangular cross-sections, they can be divided into several smaller units for the purpose of meeting the above requirements.) Thus, if this quantity is made to equal zero, there will be no currents induced in the coil system by a uniform field H. This is very convenient for eliminating the effects of stray 60 cycle fields in the laboratory and also for removing any signals that may be induced by the coils vibrating in the earth's field. The coils were balanced for this condition by experimentally determining the number of turns that were required an the outer coil. This condition does not exist for curved fields, however, so the coils are made as small as conveniently possible. Since the current induced in the coils is a function of R (the distance from the magnetic source .to the windings) it is apparent that the signal induced in the coils by the rotating specimen is not made zero by the two opposing coils because there are m~y more flux linkages in the inner coil system than in the outer one. The e.m.f. of this double coil, due to the rotating specimen, is more than 50 per cent of that which is produced by the inner coil alone. The inner coil has been p i-wound to decrease the distributed 66 capacitance betweenthe windings and thus to increase the natural resonant frequency of the coil. This eliminates the possibility that there maybe undesirable amplitude and phase versus frequency effects near the operating frequency. A consideration of the signal to noise ratio will necessarily involve the input tube in the amplifier. The statistical voltage , produced in the input of an amplifier of bandwidthWis: E n = 12.7 x 10-11 ~ \'l(R + R ) t c where Rt is the equivalent noise-resistance R is the grid resistance in the first c For a rectangular cross section coil, of the first tube and grid (the coil resistance). assumingthat the windings are symmetrically placed in horizontal and vertical rows, the coil resistance R is given by: c w~ere.,e is the width of the coil and,fJ and a are the conductivi ty and circular area, respectively, of the wire used in the vlinding. ~"'ora given coil size the voltage induced in the coil by the rotating specimenis proportional to the numberof turns in the coil, or inversely proportional to a. Therefore, the signal to noise ratio is proportional to: or 1 V W(Rta2 + (7f 2-f/ / 4) (r~ - ri» 67 Once r2 and rl have been chosen, (which is, of course, arbitra~) it is clear that the signal to noise ratio increases with a decrease in a. The inner coil was woundwith number40 gauge wire and contains approximately 25 thousand turns, whereas the outer coil was wound with number38 gauge 'Wireand contains about 8 thousand turns. total resistance The of these two coils is 24 thousand ohms. bince there are two sets of coils, the combinedresistance of the system is 48 thousand ohms. Obviously the voltage induced in the over-all system is twice that induced in either coil pair alone. The reason for two pairs of coils is to increase the input signal to the amplifier and also to reduce the effect of the position of the spinner on the voltage output. The reference signal generator consists of a Clairex type Cl - 2 photocell, a 3 volt ngrain of wheatll lamp, and a light chopper. The photocell and lamp assembly maybe raised and turned at right angles to facilitate starting and stopping the spinner. The photocell mount is attached to the base plate which supports the spinner The entire assemply can be rotated through 3600, base. permitting the phase difference between the reference and specimen signals to be varied. The spinner is of the Beams(1930) type, in which the specimen holder spins freely in air without bearings. This type of mechanism permits high speeds that otherwise would have been difficult attain. to The spinner and spinner base are cone-chaped; the spinner has an angle 0( of 101.5 degrees and the base has an angle J9 of 91.5 degrees. Air holes inside the base are oriented at an angle 68 and create a vortex of air which causes rotation of the spinner. The result of the Bernoulli effect, produced by the narro~dng of the air passage near the edge of the spinner and spinner base, keeps the spinner in its place. The specimen holder stands on a shaft about 6 inches long and is attached to the spinner. This permits the coils to be shielded from the air blast at the base of the spinner, which may cause an undesirable vibration of the coils. It also helps to minimize coupling between the coils and the reference to be rotated a full 360 degrees. photocell generator and allows the Of course, it also allo'\-'ls the specimen holder to be much closer to the coils. The spinner is usually steadied by hand until it is brought up to about half speed, at which time it stabilizes without supports. quite satisfactorily and spins freely It was fotU1d that the spinner 'iauld also perform with a cloth bearing located near its center of gravity (8:pproximately the middle of the Shaft.) With this cloth bearing the spinner may be started and stopped without having to be supported. The spinner base is held in place by four springs. The friction between the spinner base and the bottom plate, and the three tygon tubes which feed air to the spinner base tend to damp out any oscillatory motion that may be initiated during the starting procedure. Several different materials were used for the specimen holder, but most of these proved unsatisfactory. and paper bakelite, lucite, and fiberglass Materials such as linen could not withstand the added impact that occurred when a rock specimen broke during the 69 spinning operation. The most satisfactory material used was laminated West African mahogany, which was chosen in preference to other woods because of its high strength to weight ratio. rfhe cap of the specimen holder was made from Du Pont nylon or Du Pont delrin .. .Another holder was constructed entirely of delrin, and preliminary tests indicate that it is quite satisfactory. 3. Input Attenuator and G. R. iunplifier A circuit schematic of the input attenuator is show in 1t'ig.A-5. The output terminals of the'coil are connected to the primary of the input transformer, a UTe type 0 - 4, via a 6 foot shielded cable .. The transformer eliminates the necessity for grounding one side of the coil to the attenuator chassis and helps to reduce the effects of undesirable electrostatic signals generated by the spinner. The secondary of the transformer is connected to the attenuator selector which has two positions for attenuation, one position direct coupled and one position for amplification. rfhe multiplication factors for positions 1 through 4 are approximately x 1/100, x 1/10, xl, and x 10 respectively. An amplication of x 10 on position powered type lLE3 vacuum tube. 4 is supplied by a battery- The input signal is applied directly to the grid and the output is capacitive coupled from the plate. The signal experiences a phase change of 180 degrees when this amplifier is used, which must be taken into consideration. The output signal from the attenuator circuit is then applied to a General Radio type 1231-B battery-operated amplifier. The 7fi 4 cOil Input I I ~ , o , 0 30 , ---------, _-------------r---------, 2 ' o . I 21 UTC 0-4 w/A..(.-metal shield Cap. In mlcro-fdrade FIG. A-5 INPUT ATTENUATOR 10 71 maximum gain of the amplifier is 86 db and there are tvro attenuators built into the unit. One of these is a variable always set for maximum gain during the operating other has two settings, labeled front panel. position < 0.03 volt and These two settings are referred B, respectively, procedure. <1 The volt on the to as position A and curve (see li'ig.B-2). on the calibration The output of the G. R. amplifier gain control and is is applied to the specimen signal filter circuit. 4. Specimen Signal Filter :B'ig.A-6 is a schema.tic of the specimen The basic components with a variable of the circuit are a cathode-follower attenuator, a cathode-follower signal filter circuit. a bandpass filter, input an on-off switch, and output. Both cathode followers vacuum tubes with decoupled are of the biased type, employing plate circuits to minimize of 60 cycle ripple in the power supply voltage. 6J5 the influence The load resistor in -the cathode circuit of the input tube is a ?l ohm, 10 turn, 0.1% linearity potentiometer which serves as a variable dial on this control is linearly turn representing 100 divisions. in the specimen amplifier circuit, attenuator divided into 1000 divisions, The each Thus, there are three attenuators circuits; a 2 step attenuator attenuator. a 4 step attenuator in the G. R. 2mplifier, in. the input and a variable in the filter circuit. The filter is used to improve the signal to noise ratio of the specimen signal and hence to increase detector. dependence, Since the filter introduces it is necessary the sensitivity of the phase a phase shift versus to incorporate frequency a ma.tched filter in the + 300v dmp. Input I .I I output 100 ~ ~~~et. I~ · ~ Cdp. In mlcro-fdrdds Filter FIG.A-6 - Burnell FILTER Co. type BIF Bandpass CIRCUIT 2 73 reference amplifier. The filters were supplied by the Burnell with a 6 db grain) according to the Company(type ElF bandpass filters following specifications: 1. Center frequency 287.5 cycles 2. Less than 0.5 degrees relative phase shift within 5 cycles either side of the center frequency 3. Stable within a 60 - 100 degree temperature range Considering amplitude variations as well as phase variations, operating frequency for the filters the best 1'1aSfound to be about 282 cycles. The on-off swltch removesthe specimen signal from the grids of the detector tubes while the phase meter is being adjusted for zerosignal condition. The switch is left in the on position during the operating procedure. The output cathode-follower couples the signal to the phasesplitter located on the chassis A in Fig. A-2. 5. Reference Amplifier and !I'ilter " The reference amplifier and phase detector circuits are on the same chassis; a schematic of this unit is shownin .trig. A-7. The output signal from the photocell is applied to the input of the reference amplifier where,it is converted into a symmetrical square wave and then applied to the suppressor grids of the 6SJ7 detector tubes. The main componentsof the reference amplifier are a 12AU7 low gain input amplifier (approx. x 10), a bandpass filter, gain control, a variable a 6SJ7 high gain amplifier (approx. x 100), an overdri ven 6J5 amplifier and a 6H6 clipper. The clipper eliminates the positive 74 200K lOOK 6H6 +300 470K I I ~ MonItor o 2 ou tput , ....... ...... ......'1 Filter Input oI ~, t I ~ I I I I I I I I ..... ..... .. I ) ", ... Cap. In micro-farads Filter - Burnell Co.type BI F bandpass FIG. A-7 REFERENCE AMPLIFIER AND 9f-DETECTOR 75 part of the output voltage which otherwise would drive the suppressor grids of the detector tubes into the conduction region. All the amplifiers are of the RCtype, and each plate circuit decoupled from the B+ line in order to eliminate 60 cycle ripple. is lfhe gain control permits the symmetryof the square wave output to be varied slightly, but other than this it serves only to prevent the voltage on the grid of the 6J5 from becomingtoo large. The bandpass filter, as mentioned previously, specimen amplifier filter is matched to the so that the phase vs. frequency response of the two units will be identical., 6. Phase Detector The phase detector circuit includes the 6J5 phase-splitter the two 6SJ7 detector tubes sho"min .il'ig. A-7. signal is converted by the phase-splitter amplitude, but differing and The specimen input into two signals of equal in phase by 180 degrees. The amplitudes of these two signals are balanced by t he two 27Kohm, 1%wire-\'lOund resistors; (it was not found necessary to match these signals better than 1%). The outputs from the phase-splitter are then applied to the control grids of the detector tubes. The two 6SJ7ls were .selected beforehand for similar characteristics so as to minimize balancing problems. have a common resistor, IIlhecathode circuits shunted by a 500 micro-farad capacitor, which biases the tubes for class A operation. have a common connection. The screen grids also A 25Kohmpotentiometer connected to the 300 volt lead varies the plate load resistance permits the two plate voltages to be equalized. of each tube and thus In this way the 76 phase meter (a Simpson 25 micro-amp, zero-center connected through two l30K ohm resistors balanced for zero-signal condition. to the plates, amplitude is being turned on or off when the incoming signal applied to the suppressor turn the tubes on and off at regular intervals. during the half cycle when the reference a negative specimen signal grids serves to In other words, signal has zero voltage the detector tubes behave as class A amplifiers, signal applied to the control grid will be amplified circuit. switch is is unknown. The reference amplitude, can be The meter sensitivity used to short the meter when the equipment and also to lower the sensitivity meter), which is and any in the plate However, during the half cycle when the reference voltage amplitude, there will be no conduction signal has through the tube, and the plate voltage will rise to the full B+ value A complete mathematical the capacitors analysis given by Hood (1956) involves connected between the plates actually acts as a biased commutator, is given by Nagata (300 volts). and ground. 'The circuit however, and a simple analysis (1943). The phase sensing action of this circuit may be best understood by considering the action of only one of the detector tubes. is a diagram of the voltage appearing one cycle of operation. Assuming l\'ig.A-a at the plate of the tube during that the phase meter has been balanced for zero current flow when no signal is applied to the control grid, the plate voltage during the on-time will be some steady d. c. value, say 150 volts (case I). Now, if a pure sine wave is applied to the control grid, and it is in phase ~d.th the reference signal, the ~I >1 '0 ~. >1 '0. > I > 0 + U") 0 0 It) + > LIJ « cJ) u w « cJ) u UJ cJ) « u UJ « cJ) u (f) z - 0 « .1- n:: .-J W (j) w « a.. I I ro « . - (!) l.1... 77 78 average plate voltage during the on-time "Iill becomeless positive (case II). Conversely, if there is a 180 degree phase difference between the two signals, positive the average plate voltage will becomemore (case III), and if the phase difference is 90 degrees, the average plate voltage will be unchanged (case IV), i.e., 150 volts. Variation of the average plate voltage about the zero signal reference line is therefore proportional to cos tt, where e is the phase difference between the control grid and the suppressor grid signals. The current flow through the phase meter will also be proportional to cos -e. The sensitivity of this circuit can be doubled by simply applying a second signal, 180 degrees out of phase with the first signal, to t he control grid of a second tube and connecting the meter between the two plate circuits. becomesmore positive, Whenthe plate voltage of one tube the other plate voltage becomesless positive and the phase meter current will be twice that produced by one tube alone. The use of two detector tubes has the added advantage that variations in the B+voltage, the filament voltage, etc., minimum effect on the stability of the circuit. have a The deflection of the phase meter is obviously dependent upon the amplitude of the specimen signal, but independent of the amplitude of the reference signal. The capacitors connected between the plate circuits and ground cause the plate voltage to assume a d. c. value approximately equal to the average plate voltage during the on-time of the tube. This changes the phase meter current from a pulsating d. c. to a steady d. c. current. By varying the amountof capacitance the response 79 time of the meter can be varied; that is, the time r~quired for the meter to indicate a change of phase. capacitors permanently Except for the 4 micro-farad in the circuit, the capacitors are used only when the noise level becomes large enough to m~~e the meter indications unstable. Any control grid signal which is not a harmonic of the reference signal will cause the plate voltage and more negative, harmonics to vary alternately the average variation Also, even will be averaged to zero since there are an equal number of positive and negative However, it is clear that odd harmonics and will therefore fundamental half cycles during the on-time of the tube. will not be averaged to zero, il1terfere vdth the phase detection of the frequency. The specimen signal bandpass odd harmonics detector. being zero. more positive filter reduces the amplitude so that they do not disturb the operation The filter also minimizes the phase sensing action of the circuit. 7. regions, Obviously, control grids must be well shielded from the reference prevent of the phase the noise level which could have driven the detector tubes into the cut-off or saturation limiting of the the signal to interference. Power Supplies A Heathkit model PS-3 power supply delivers volts at 30 milliamps filaments Heathkit to the amplifier a regulated and detector units. 300 The require 6.3 volts d. v. at 3 amps and are supplied by a model BE-4 battery eliminator. As mentioned previously, the G. R. amplifier and the input 80 amplifier have their ownbattery power supplies. The G. R. uses a type 6TA60Battery while the input amplifier uses t1'TO type C batteries g. and one type N60battery. Accessory Equipment Rotation of the specimen is controlled by a 'Vlatts air pressure regulator, shownin Fig• .8.-2. The frequency is monitored by observing the Lissajous figures produced on an oscilloscope by the reference signal and a 282 c.p.s. signal from the audio oscillator. Whenthe two signals have the samefrequency, the Lissajous figure consists of one stationary loop. Fig. A-9 is a photograph of the Fanslau coil used for attaining a magnetic field-free region. The diameter of the larger feet and each coil contains 20 turns of wire. coil is 4 A 6 volt battery eliminator supplies approximately I ampof current to the coil, amount sufficient to null the earth's magnetic field. A discussion of the design. of a li'anslau coil is given by Chapmanand Bartels The furnace, located inside the :F'anslaucoil, an (1940). has non-inductively woundheating coils and is powered by a 110 volt variac. Temperature in the oven is controlled by a ]loxboropotentiometer controller (using a thermocouple) which turns the variac voltage on and off. The variac is adjusted for minimumpower requirements at the desired temperature and thus tends to minimize temperature variations as the thermocouple turns the current on and off. The magnetic field inside the Fanslau coil is measured by a nux-gate type zero-field magnetometer (Serson, 1956). The magnetometer and the flux-gate detector unit are labeled A in Fig. A-9, and a 81 FIG. A-9 FANSLAU COIL AND OVEN 82 transistorized schematic of the circuit (supplied by Serson) is shown in Fig. A-IO. This unit is capable of measuring fields of less than 1 gamma and is more than adequate for its intended use. It was found that the magnetic field in the laboratory often varied as much as 1000 gammas, and it was necessary to periodically adjust the current in the Fanslau coil. reduce the effects of 1£0 these field variations on cooling rock samples, a rock tumbler was used, (see Fig. A-ll). The holder holds six samples and will just fit inside the oven. When the rocks are ready to be cooled the holder is placed on the table of the tumbler, one end resting on a bearing and the other end resting directly on the table. When the bearing supports are turned, the holder also rolls on the table, thus producing rotation about two axes. From the point of view of the rock specimen, a d. c. field appears as an a. c. field, the frequency being determined by the rate of rotation. The radius of the largest end plate on the holder was made to differ from the radius about the vertical axis of rotation in such a way that the holder seldom repeats any of its positions. An air turbine is used to rotate the unit at several turns per second. For the a. c. demagnetization experiments a one-sample tumbler was used inside a small Helmholtz coil (see Fig. A-12). The cross section of the coils is approximately 3/4 inches square and the mean radius is 2.5 inches. Each coil contains 250 turns of No. 16 nyclad wire and they are connected in series. The current is supplied by a variac capable of delivering over 10 amperes. field inside the coils is about 550 Oersted. At maximum current the The heat generated by v ~ z . > N U) + o + - o + III 'D .a o x tV o X tV 'D .a o en o ~ o III en 'D "0 l- 'D '+I o I- o E c a.. 'D u "0 C Eo cn E~ 'D~ ~v L: + en -N =0 ex> N' Z N ~ ~O +N "0 c o E..., EN 'U v ~- to 0 • V ~ Z o - I Z (f) o (f) 0:: W v t- 0:: W ~. W t- o « W Z 19 ~ ~ w en <! t- o:: o a.. o I « 19 LL 83 84 FIG. A-II ROCK TUMBLER 85 FIG. A-12 DEMAGNETIZATION COI LS 86 the resistance in the windings limits the maximum field that can be produced. The coils were originally designed to slide apart on runners so as to produce a continuous decrease in the field intensity between the coils. This was found to be unnecessary however, so they were set apart at the proper distance, and the variac was used to raise and lower the field intensity. The tumbler is turned by a small a. c. motor that applies power to the outer rim of a large disk. adjustable rheostat, The motor speed is varied by an which is usually set to rotate the tumbler from five to ten revolutions per second. 87 APPENDIX B: 1. OPERATION Circuit Adjustments The electronic units are allowed to warm up for some time until their tube characteristics have stabilized. This is particularly important with regard to the audio-oscillator since it sets the frequency standard for the frequency-sensitive apparatus. After the spinner has been brought up to speed, the oscilloscope is used to observe the output of the reference amplifier. The reference amplifier gain control is first turned to its minimum position, then it is slowly increased until the output becomes a symmetrical square wave. The specimen signal is next removed from the detector tubes by the on-off switch in the specimen filter circuit. The meter switch is then set for maximum sensitivit~Tand the meter balance control is used to zero-center the phase meter.' It is usually necessary to check the meter balance periodically during the initial measurements until the instrument has become completely stable. If at any time the meter can not be balanced to zero, a better selection of detecting tubes has to be made. 2. Calibration a. Phase Angle The relative phase angle of the circuits is determined by measurement of a one-inch wooden cylinder containing a piece of magnetized drill rod mounted parallel to and centrally located between the ends of the cylinder. This simulated specimen is oriented in the holder so that the north-seeking pole of the magnet points toward the 88 "0" reference mark inscribed alignments inside the holder. When the circuit have been made, and the spinner is brought up to the correct speed, the phase meter will show a deflection. amount of deflection attenuators. can be controlled by the specimen amplifier The phase dial is then rotated until the meter indicates a null reading. Since there are two positions 180 degrees apart on the graduated phase dial which give a null reading, to establish observed. The maximum a convention whereby This is accomplished it is apparent it is necessary which pole is being by having the needle of the meter move from left to right, as the null position is approached, 1-Thenthe angle indicated by the phase dial pointer is increased. When the meter indicates the correct null position, from its holder and rotated until a degrees comes dial is loosened opposite the pointer. The dial is then secured in place. In order to minimize orientations measurement errors such as phase-dial of the specimens in the holder, two measurements for each component shifts, incorrect etc., it is best to make of magnetization. The second is made with the specimen rotated 180 degrees axis directed toward the "0" reference direction the phase mark. of the component of magnetization about the The angle between the in the plane of rotation an~ the reference mark is then 360 degrees minus the phase dial reading. This technique is used during the calibration procedure as well as during the specimen measurements. b. Intensity Nagata of lVlagnetization (1943) has can be approximated shown that the magnetizat.ion of a rock specimen by a small dipole located at the center 0f the 89 specimen. In order to calibrate the intensity of magnetization indicated by the attenuator settings in the specimen amplifier circuits at a given maximum meter deflection, a small coil of known radius and number of turns takes the place of the specimen. A known alternating current passing through the coil will simulate in the pick-up coil the effect of the rotating dipole. A block diagram of the calibration equipment is shown in Fig. B-1. The maximum induced magnetic moment of the test coil, i.e., when the current is maximum, will be equal to t he moment of the rotating dipole which produces the same effect in the pick-up coil. This is given by: c.g.s. units where: r = E = r.m.s. voltage across coil and attenuator R = N = number of turns in coil radius of coil total resistance of coil and attenuator If a cylindrical specimen, which is 1 inch long and 31/32 inches wide, produces the same signal. in the pick-up coil as does the test coil, then the component of magnetization of this specimen is: IV! = s Y27rr 2 NE lO(12.04)R c.g.s. units/c.c. The calibration curves, shown in Fig. B-2, represent the intensity of magnetization required to deflect the phase meter full scale to the right for the given attenuator settings, assuming that the phase dial is adjusted to read the proper maximum. LIJ a:: ..... LL :I: cf) I '&. cf) LIJ a:: a: < > Q. +.::> c ..... U LIJ < ~ ~ u.: LIJ-o °c I '0 a:: u u a: ..... => cf) LIJ 's.. cf) U LIJ 0.. ....J 0 u cf) ..... ....LIJ a: w :J W o o U a: 0.... z o ~ a:: en -.J <! U I en <..9 l.L 90 91 102 C) z 0 .-( w a: ...= 0 a. z a: => .... I 0 - 10 A2 A3 AI Mult. by AI ---------10-1 A2 - --- ---10-2 A 3 - - - - - - - - - 10-3 Setting 8 I - - - - - - - -- 82 - - - - ----83 - - - ------ 10-1 10-2 10-2 INTENSITY FIG. B-2 (CGSU/CC) INTENSITY OF MAGNETIZATION 92 It maybe noticed in li'ig. B-1 that the reference voltage is not taken from a point that mayv~ in amplitude during the calibration. Also the phase shift network should be adjusted periodically for maximum deflection. 3. fJieasuringProcedure Whenthe spinner is rotating at the proper frequency and the phase meter has been zero-balanced, the methodof measurementis as follows: 1. The specimen signal attenuators are set for low sensitivity and then the on-off switch is turned on. 2. The phase dial is rotated until the meter shows a maximum deflection to the right. 3. The attenuators are then adjusted until the meter reads full scale. 4. The phase-dial is rotated until the meter is nulled. the phase-dial pointer indicates 'When an increase in angle, the meter deflection should movefrom left to right, insuring that the proper pole is being measured. The frequency will have to be monitored carefully full scale and null readings of the meter. 1. during the The data obtained is: The attenuator settings are converted by Fig. B-2 into the intensity of magnetization of the componentin the plane of rotation. 2. The phase-dial reading gives the angle, about the spinner axis and in the plane of rotation, between the nOli reference 93 mark and the componentof magnetization in this plane. This angle is measured counter-clockwise whenlooking into the holder. 4. Sensiti vi ty The sensitivity static of the instrument is limited by the electro- signal generated whenthe spinner rotates minimize this signal, in air. the spinner is coated with silver In order to circuit paint and a wire brush is connected to ground and allowed to rub against the shaft. In this mannerthe amplitude of the signal can be kept below 5 x 10-7 c.g.s. units. This means that measurementsof moments 6 c.g.s. units/cc can be madewith errors in direction of of 2.5 x 10- less than 10 degrees. The amplitude and phase of the electrostatic signal usually remained constant during the time required to measure a specimen completely. Henceit is possible to remove this componentfrom the measurementsand further increase the sensitivity. This was seldom done, however, since most of the rock specimens had a relatively intensity high of magnetization. Whenthere is no electrostatic signal present, and this is indeed a rare occurrence, the backgroundsignal is 1 x 10-7 c.g.s. Occasionally, neighboring laboratories units. create frequencies at or near the operating frequency, and cause the phase meter needle to move slowly from one side to the other, the rate depending upon the difference between the two frequencies. Whenthis happens the variable attenuator is used at as low a setting as possible so as to increase the signal to noise ratio, since most of the stray signal is induced 94 in the circuitry and not in the pick-up coil. Of course, when this effect becomestoo large, the equipmentcan not be operated. - 95 APPENDIX 1. C: COLLECTION AND PREP iillATION Or~ SPECIIvlENS Collection One-inch diameter rock cores are drilled twelve-inch portable diamondcoring drill McCulloughchain-saw engine. a gear reduction unit, diamondcore drills poweredby a small The engine, originally has been converted to direct equipped with drive because the muchbetter at higher speeds, and also because the reduction in weight is significant. the drill in situ using a The water required to cool is supplied by a three gallon garden-spray tank. Depending on the length of the cores, whichvary from two to ten inches, anywhere from one to three tanks of water are required to collect eight cores. This methodof collecting specimens was first described by Grahamand Hales (1957). ,It'ig.C-l is a photograph of the engine and the orientation device. The orienter slides into the hole, with the core still intact, and then the compassis leveled by rotating the barrel and by adjusting the dip indicator. The top side of the core is markedby running a brass rod along the slot in the barrel of the orienter. The azimuth of the downdip direction of the line is recorded, as well as the dip of the core, and then the core is broken loose and the top and bottom are carefully marked. The cores are designated a ccording to state and numberof core. Whenthe rocks are too friable engine becomesinoperative, to permit drilling, or whenthe samples are collected by hand according to the technique given by Doell (1956). 96 FIG. C-I PORTABLE DRILL 2. Preparation The cores are cut into one-inch lengths, and are numbered marks: consecutively. starting at the bottom, Each specimen then has two orientation a vertical line along the side and a mark identifying The coordinates of the specimen the top. (see Fig. C-2) are designated as follows: 1. The z axis is parallel to the cylinder axis and is directed positive upwards. 2. The x axis is perpendicular to the cylinder axis and is directed positive toward the reference line. 3. The y axis is directed positive so that the system is right-handed and orthogonal. Samples collected by hand are drilled in the laboratory the core is perpendicular to the surface of the sample, the orientation line being scribed on the up-dip the core is the complement side of the core. Hence the dip of of the dip of the sample. The errors in orientation than one or two degrees. of the cores are probably no greater However, errors in orientation samples are much larger, .perhaps more than five degrees. core-drilling technique so that of hand Thus, the is not only much faster than hand sampling, but is also much more accurate. 98 +z ORIENTATION LINE +y x+X FIG. C - 2 LINES SCRIBED ON BOTTOM SPEC IMEN DESIGNAT ION 99 APPENDIX D: DERIVATION OF THE Only three orientations IvIAGNETIC of the specimen in the specimen holder are required to obtain the direction vector. VECTOR and magnitude of the magnetic For increased accuracy, however, six different orientations are measured and the twelve data obtained are averaged to yield three angles and three intensities. Each specimen orientation gives the following two data: 1. The angle between the componentof magnetication in the plane of rotation 2. and some reference axis of the specimen. The magnitude of this componentof magnetization. The orientation of the axes with respect to the specimen has been shownin Fig. C-2. The system used to describe the magnetic measurementsis given in It'ig. D-l, where 1\1 is the magnetic vector and is, of course, directed toward the north-seeking end. A, B, and C are the componentsof lVi, lying in the planes normal to the x, y, and z axes, respectively. X, Y, and Z are the componentsof lying along the x, y, and z axes , respectively. IV! 0\ x is the angle measured from the +y axis to the componentA in a right-handed sense. Similarly, 0{ 0<. y is measuredfrom the +x axis to the componentB, and z is measured from the +x axis to the componentC. For the first measurementthe specimen is oriented with +x directed toward the "0" reference mark on the holder and +y directed upward, parallel direction to the axis of rotation. (900 from "0"). the ~gle 0{ y. The z axis is in the "90" The data obtained are the componentB and The specimen is then rotated until -y is directed 100 +z +v -~---------------+x FIG. 0-1 VECTOR ORIENTATIONS 101 upward and +z is directed toward "90"; +x remains in the original position. Thus, B is once more measured, 360 minus c{ y. The two measurements but the angle obtained is are averaged to give the final value for B and 0< y. average values for A, C, c( x, and c;( z are obtained Accordingly, following "all the procedure Upvlard pOSe given in Table D-l. "90" Angle measured pOSe +x +y -z +x -y +z +y +x +z +y -x -z +x +z +y +x -z -y Component measured O<y B 360 - d.. y clx B A 360 - c:< x c(z A C 360 - O<z C Table D-l Since A2 B2 C2 M2 it = = = = + z2 x2 + Z2 x2 + y2 x2 + y2 y2 + Z2 follo'Vls that 1/2 Thus the amplitude of the vector lVl can be obtained from the measurements A, B, and C. F'inally, vuth respect the direction of the vector 1/1with respect to the geographical coordinates is obtained to the axes 2nd graphically +z -Z UP DOWN -y FIG. 0-2 SCHMIDT-NET EXAMPLE 103 with the aid of the Schmidt equal-area projection. The Schmidt projection is preferred to the stereographic projection since a unit area on the sphere remains nearly constant after projection. .feature is desirable in the application of the statistical This methods f described ,in appendix E. The plotting procedure used here followed that of Doell (1955). In contrast to the technique of Graham(1949), wherebyonly one hemisphere is used for plotting, both hemispheres are used. distinguish between the two, solid circles rro and solid lines were used for plots on the lower hemisphere, and open circles and dashed lines for plots on the upper hemisphere. The orientation of the axes on the Schmidt-net are shownin Fig. D-2, where the x and y axes are in the plane of projection and the +z axis is up. The angle q z defines the plane containing the z axis and the . vector lvi, represented by line OA, which intersect s both the upper and the lower hemispheres. The angles 0( x and 0<. y define t\'lOmore planes which should intersect at a common point along OA. tion the projected point P obviously lies In this illustra- on the lower hemisphere. This gives the direction of the magnetic vector Mwith respect to the specimen coordinates. However,the projections do not always meet at a common point. Whena small triangle is formed, giving an estimate of the error in the measurements, the meandirection largest is taken a s the center of the circle than can be inscribed inside the triangle. :F'orall of the measurementsreported in the survey the error was less than 10 - 15° and in most measurementsit was less t~an 1°. 104 In order to obtain the direction of !vI in situ, the specimen coordinates have to be oriented in the position they had in the field • .Florthis the N-S geographic axis is marked so that the +x axis assumes the correct declination; down-dipdirection i.e., the angle between the of the specimen core and geographic north. axis is then rotated about the y axis until inclination, movingpoint Pinto P'. The z it has the proper The original bearing of the magnetic vector is nowrepresented by point PI, with respect to the N-S axis. The dip of the vector is referred to as positive when directed downwardand negative whendirected upward. The angle of declination reads clockwise from north. Corrections for bedding orientations which restore the specimen to its pre-deformation position can be madein a similar manner. The strike of the bedding plane is marked with respect to the N-S axis, and then the strike axis is movedinto alignment with the axis of the Schmidt-net. 'Whenthe z axis is rotated about the strike axis, by an amount equal to the dip of the bed, point pi will moveinto the position of the magnetic vector before the deformation (not sholomin :Flig.D-2) For a more complete account of the use of the Schmidt-net for rock-magnetic problems, the reader is referred to Doell (1955). 105 APPENDIX E: lvIETHOD OF' STATISTICAL TREATlilFl~T A certain amount of scatter is usually of remanent magnetization present which is determined samples taken from any given body of rocks. of such.~ocks may reflect the influence present during the time of formation, the average direction of the geomagnetic was developed treatment calculated of magnetization position direction is given below. is applied, hOlvever, the average of the north-seeking pole of a geocentric this direction dipole of magnetization in The pole position of this dipole field lies in the of the horizontal the relative latitude (A) Tan I where I is the inclination latitude this for each core is used to locate the field that would have produced the core. error of this average by Fl~her (1953), and has been used throughout Before fisher's treatment geographic from the several for the solution of this problem report •. An outline of this treatment direction field it is of interest to determLne of magnetization A statistical from the different bince the magnetization samples, a1'1d also an estimate of the probable direction. in the direction component of the remanent vector, and is given by = 2 Tan A. of the magnetic of the outcrop location vector and A is the with respect to the pole position. The stereographic or Schmidt equal-area projection can be used in the determination of the pole positions (see Grahmn, 1955). Thus, for each outcrop, there is a set of N pole positions, l'ihereN is equal to the number of cores t8ken from the outcrop. In . 106 practice, these pole positions are plotted sphere such as the Schmidt equal-area that the Schmidt net represents the longitude and latitude from the projection equal-area projection. of the pole position of the earth, can be read directly the polar plots in Part II are projections). therefore define a set of unit vectors, from the center of the unit sphere to the points in question. fisher has shown that the average direction vectors, represented vectors. in space of the resultant, Let 1.]. and m.]. be the longitude th unit vector, v ]..• = = = z.]. xi y. ]. where z. is the vertical component of R, follovring equations: and latitude, sin m.]. , cos cos Ii' and ffi. ]. 1, 2, ••N), respectively, cas m. sin 1. ]. J. of vi directed toward longitude zero), and y. is the horizontal ]. 90 E (positive I R/ , the longitude R, lVI, can be calculated = Then 'of v. directed toward longitude J. such unit R, of the N unit J. (positive towa.rd longitude The magnitude 1'1 component of v. (reckoned positive J. xi is horizontal of a set of by the points P.]. on a unit sphere (i is given by the direction of the i of the unit If it is assumed a north polar projection (for instp~ce, The pole positions directed on a projection upwards), zero component toward longitude 90 E). of R, L, and the latitude from x., y., and z., by the use of the J.]. ]. of 107 f 1 L = Tan- M = 1 Sin- ~l i 1 Yi/ Xi Ii /[<!l [ Zi The confidence xi)2 + C!l yi)2 + of this average direction <!. Zi)2] 1/2} can then be determined from 1 - Cos IR I ,R l - N - e- - this report). 6', can be calculated is the semi-angle 1 } 1l1sher (1953) level (p is taken as 5 percent where P is the desired probability throughout f( 1. ) l/n-l (p The "radius of t4e circle of confidence," from the above equation. ,r'orP = 5 percent, e of a cODe whose apex lies at the center of the unit sphere and 1rlhoseaxis is the vector R, within which the true lies for 95 percent of such determinations. direction on the size of N in this equation, limitation size of N - R should not exceed 2. large this restriction of negligible p~ the if N is moderately is importance. of the directions of v., k, can be ~ from k For a uniform distribution numbers but theoretically need not apply, since the error introduced estimate of the precision calculated However, There is no as the precision N - 1 N - r'isher (1953) R k is nearly one, and approaches increases. estimate of the precision, If reversals = Although 6' gives a direct k has been included are present high in the results. in any of the measurements, more feasible to consider the probability it is that the average direction 108 R lies along an axis, and not only in one direction. words, all of the unit vectors, vi' can be considered positive. Althoughsomeof the samples in this report definitely reversals, In other indicate there are no clear cases where both reversals and normal directions of magnetization are contained within the same outcrop. Thus, this point is not applicable to any of the results. 109 ft2PENDIX F: 1. DISCUSSION OF PROCEDUP~ ili~DF~SULTS Collection ft~l samples from Nova Scotia and some from Massachusetts collected during the summer of 1956. during the follovdng summer. were all other sa.mples were collected Most of the s8mples were tal(en from road- cuts and quarries because the equipment limited the survey to easily accessible areas, ~~d also because these outcrops were relatively unweathered. depending An~vhere from 2 to 14 cores were collected from each site, on the extent of the exposure and the ease of coring. Although Nova Scotia sediments vlere originally to be included in the survey, they were found to be too friable and the coring technique could not be used. To test for stability of the remanent magnetization in rocks it is desirable to collect samples from several sites \dthin the same formation which have significantly different bedding attitudes. Since the beds of most Triassic basins generally dip tOl'lardone side of the basin, selection of sites with large differences somewhat difficult. of strike and dip was }'urthermore, the number of sites available road sides was limited. From collections along made over large areas, however, it is possible to infer that the magnetization has been stable since the beds were deformed. :2. l'Jleasurement The interval of time between the collection specimens ranged from several months to a year. and measurement of the This was not important, however, since most of the specimens were given an a.c. demagnetization 110 test. Any isothermal imparted components of magnetization to the specimen during this interval All of the measurements apparatus. comparison of this instrument, by A. Cox at the University of results indicated determinations amplifier gain, caused by battery the sensitivity A of magnetization deter- Due to slight variations and tube replacements, of the instrument of the specimens, value of the a.c. demagnetizing some of the weak sediments. in the errors in 'tiasadequate for the it set a limit on the maximum field that c01Lld be used in treatll1g For specimens with magnetization of less than 2.5 x 10-6 cgsu Icc, the error in the direction of magnetization therefore specimens may va:ry as much as five per cent. original measurements intensities type Berkeley. were ~~thin a half degree, and the intensity were wi thin one per cent. Although several of California, that the direction minations the intensity uere thus removed. were made with a "rock-generator" To test the accuracy were measured that maY have been measurements the specimens might be greater than 10 degrees, could not be demagnetized and much below this level. 3. A.C. Demagnetization Creer (1959) and :As (1958) have demonstrated to reduce the scatter in remlli"'1.ent magnetization bring the results into better agreement other sites, by treating The influence (1958). results, and also to vuth those determined from the samples in an a.c. demagnetizing of a.c. fields on isothermal-remanent and on thermo-remanent Rimbert that it is possible magnetization Im~ components magnetization (Tru1) has been studied can usually field. be removed by from most (IRrvl) 111 rocks by treatment however, in relatively is much more difficlut low intensity a.c. fields. Tru~, to remove by a.c. demagnetization. this respect, the relative stabili ty of chemical magnetization too well knovm, although in some cases its behavior In is not is not unlike a Tlli~(see Haigh, 1958). If a rock specimen contains a "soft" component ''lhosedirection can be easily changed, it, is necessary component before the original direction be determined. of magnetization, Many of the specimens of remanent to remove this magnetization can examined in this report are Imown to have acquired an IRI\1component "Thile in the laborato~J. Thus, it is probable that many of these specimens acquired an IRH component in the field. During the demagnetization field was controlled procedure the intensity by a variable auto-transformer. was varied in finite steps, and not continuously, were performed demagnetization treated. to determine tests. of the a.c. Since the field several experiments whether this affected the resuJ_ts of the Several specimens from the same core were In one case the a.c. field was reduced by the transformer, in the next case the fie~d was reduced by sliding the demagnetizing l coils apart very slovlly. l he specimens gave similar results. for one specimen, the field was increased then reduced alternately related variation Hence, it is assumed in steps of 10 Oe., and by one of the two methods. in the demagnetization ilso, There was no path of the specimen. that the demagnetizing apparatus does not bias the results. Fig. 1-19, Fig. I-20, and tig. 1-21 show some results demagnetization tests that were made on igneous specimens. of the They are 112 representative of many of the specimens, of the remanent magnetization but not all. The behavior in the Nova Scotia and Pa - Va rocks, when subjected to a.c. fields, is a point of considerable Specimens interest. from the Pa - Va area gave similar res~lts, whereas mens from Nova Scotia responded speci- in a variety of l'laysto the a.c. field treatment. In general, the remanent magnetization of the Pa - Va igneous rocks was quite stable in a.c. fields above 20 - 100 De. deflection of the remanent vector was probably a "soft" IRI~ component. the direction due to the removal of Some of the specimens of remanent magnetization The initial experienced w'hen left in the laborutory for long periods, but after a.c. field tests the resultant was always the same. intensity Specimens responded After the initial demagnetization fields, the remanent vector remained of an average direction a change in direction in low w~thin about 5 degrees during further demagnetization. from several Nova Scotia outcrops, such as NS 13, to the a.c. field tests in a similar manner. of the remanent vectors about an average direction The variations were, however, slightly larger than those for the Pa - Va specimens •. &s a rule, the sma~ler the circle of confidence the remanent magnetization for a given outcrop, in the presence of a.c. fields. ~lany of the Nova Scotia specimens were relatively a.c. fields, as is sho'tffi in ]'ig. 1-20. the "soft" component, usually required For instance, unstable in Except for the removal of a.c. field intensities to displace the more stable of 100 - 200 De. 1"ere the remanent vector by large amounts. the remanent vector of specimen number NS 18-3 remained 113 within 10 degrees of its original below 100 Oe. direction for field intensities Above this value the vector was deflected more than 180 degrees. There is a possibility magnetization, resulting that the change 'in the direction from the a.c. field tests, was a random phenomenon. To test this hypothesis, was repeated several times at the same field intensity of specimens. the demagnetization In most cases the remanent few degrees of an average value. the remanent vectors continued direction as before the test. in the direction understanding of the remanent properties vector was often of the beds. of this phenomenon. in the direction Valley igneous of remanent magnetization the a.c. test were quite large, although for this variation ~ Belshe has experienced tests performed therefore Triassic An of the rocks may lead to a better rocks are more closely related to the Nova Scotia rocks. tendency was It was not possible Judging by the a.c. field tests the Connecticut variations ~dthin a to change in the same to relate this plane with the geologic attitude of the physic?~ for a number vector remained confined to a plane, such as that in fig. 1-20. analysis procedure 1Vhen the field intensity increased The variation of resulting there was no obvious to be confined to a plane. similar results on igneous rocks. in a.c. demagnetizing This pattern of behavior not unique in the Nova Scotia and Connecticut lavas. Some of the is Valley from 114 4. Accented Demagnetization Results There are several ways to proceed vuth the a.c. field tests for a given outcrop. They are: 1. Select one specimen from each core, subject them to an a.c. demagnetizing field, and increase field intensity by regular intervals. Fisher circle of confidence of magnetization the a.c. Determine the for the average direction after each successive When the circle of confidence a.c. test. is reduced to a minimum value, proceed vuth the demagnetization of the remaining specimens at the same field intensity. 2. Proceed as above, treating each core independently,. ho't>Iever.v!hen the remanent an average direction, vector begins to vary about treat the remaining with the same field intensity. specimens The circle of confidence does not have to be determined. 3. Select only a few representative specimens the average a.c. field intensity required. The labor involved in the first method is, obviously, If the outcrop is not homogeneous, etc., it is possible demagnetizing Scotia specimens that too-large in some specimens. considerable. i.e., contains several flows, also that the cores require different fields, and it is apparent and determine intensity in the case of the Nova a.c. fields 1iLll produce instability The second method is more reli8.ble for the Nova Scotia and Connecticut VCJ~ley specimens. The greater stability of the Pa - Va igneous rocks makes it possible pattern for only a few specimens. subjected to a demagnetizing It may be possible to determine The remaining the demagnetization specimens are then field of the accepted intensity. to improve the results slightly by a more careful treatment of the samples, although it seems very improbable that the improvement 5• "dll be significant. IV!ethodof Averaging Data It has been the practice specimen represent of many investigators to let each one unit of data in the final analysis. ~or instance, pole position number 50 in .r'ig.11-10 was determined the remanent magnetization from results of 71 specimens taken from 21 samples. If the specimens are taken along a direction the bedding plane there is some justification represent sediments. a different perpendicular in having interval of time during deposition If the specimens each specimen of the are taken along the bedding plane, then this is probably not the case. of time may be represented to With the igneous rocks, an interval by each flow. E'or many of the outcrops sampled during this survey, specimens from the same core had remanent magnetization very well, yet the average directions directions that agreed for the cores were significantly different. Thus, if each specimen is given the same 1veight in the statistical treatment, the average direction the outcrop \v.illbe displaced most specimens. of magnetization for in favor of the core containing the 113 In this report the author prefers basic sampling unit. to let the cores represent Thus the specimen magnetizations to obtain one direction of remanent magnetization the were averaged for each core. 6. Geologic Corrections For the sedimentary at, or near, each core. beds, a strike and dip determination The bedding plane of each core was then corrected to a horizontal the same position was made position, presumably orienting the core in it had before the bed was deformed. It was found that the average direction of remanent magnetization was about the same, whether the cores were corrected an average correction individually was applied to the entire outcrop. average strike and dip determination or Since an was believed to be more reliable, this method was used on all the outcrops. The geologic attitude of the beds at each outcrop is given in Table I-I and Table 1-2. Corrections geologic for the igneous rocks were more difficult attitudes were not always obvious. because the In many instances the strike and dip had to be inferred from neax by sediments. There is a possibility about an axis perpendicular that the outcrop may have been rotated to the bedding plane. results will contain an error which is difficult seems improbably, prominent If this is so, the to evaluate. It however, that this type of deform2~tion is very in the eastern United States Triassic beds have dips of less than 35 degrees rocks. Most of the and folding is not very extensive. It is hoped that any errors caused by inaccurate corrections are averaged over an extensive area. geologic out by the large number of observations made 117 7. Pole Position The dipole formula was used to obtain the pole position geocentric dipole field that would account for the direction remanent magnetization were determined statistical of a in a given core. The respective for each core within an outcrop, treatment of the pole positions and then Jl'isher's was applied to obtain the average pole position and the circle of confidence at the 95% probability level (see Appendix E) • 'rlhisdata is given in Table I-I and Table 1-2, and the pole plots are given in Part II. The average pole position and for the sediments, for the outcrop. was determined by averaging the pole positions The fact thax poles .iLth small circles of confidence lie close together, are generally for each of the three igneous areas, whereas the poles with larger circles of confidence scattered toward the present that the final results may be in error. geographic pole, suggests Any selection on the angle ~95'or based on the relative stability of poles based of the respective specimens when subjected to a.c. fields, will, of course, be arbitrary. Since all of the igneous rocks were given the same treatment, author feels that none. of' the results can be eliminated the from the final analysis. This was not the case vuth the sedimentary tests could not be completed. "soft" components final results. Many outcrops of remanent magnetization which appeared to contain were not included in the It is believed that more complete a.c. tests will bring the results of such outcrops final average. rocks because the a.c. into better agreement vuth the 118 8. Heat Treatment It is possible to remove "soft" components of remanent magnetization from rocks by applying heat and then allowing in a zero-field (Doell, 1956). region the rocks to cool This test was applied to one specimen from each core of outcrop number NS 4 in order to determine the relative merits of the a.c. field vs. heat treatments. specimens were heated to successively intervals) higher temperatures and allowed to cool inside the li'anslaucoil. magnetization was determined after each application tests were continued beyond 600°C, magnetite. The intensity at this temperature. The (25°C The remanent of heat. above the curie temperature of magnetization of ,,,asreduced almost to zero (The rock tumbler was not available and it was not possible The at this time, to keep the field inside the ~"anslau coil at a zero level.) The a.c. field test was applied to the remaining results of both tests "1ere essentially roughly corresponding specimens. alike, '\'v1.th a 20 De. The field ~l.C. to 300°C. Although the tests may be equally valid, there are several reasons for preferring.the approximately a.c. method. The heat test requires t't'lO hours to heat and cool a group of specimens. this time the earth's field has to be critically test requires only a minute or so per specimen, .field is of no consequence. applications destroying ~urthermore, nulled out. During The a.c. and the earth's it is possible that heat may induce chemical changes in the specimens, either or altering the remanent magnetization. The pasic difference in the pole positions for the three igneous areas suggests that the rocks may not have acquired a remanent 119 magnetization in the direction were cooled. Kalashinkov the magnetic susceptibility of the earth's field at the time they (1959) and Grabovsky (1959) have sholffithat of the rock m~y account for the divergence between the vector of the remanence and the earth's magnetic field which has caused this remanence. To test the significance of this hypothesis, each of the igneous areas were randomly of the earth's field. the oven was accurately The declination determined. field could not be determined of the field inside The dip and the intensity unlikely difference .A. discrepancy for by the orientation that the magnetic of the at the exact site of the specimens. the same direction • could be accounted from inside the oven, The results showed that each specimen acquired in approximately specimens 650 °C, and then allowed to cool in the heated to approximately presence oriented t\'lO error. susceptibility a remanent vector of about 2 degrees Thus it seems is responsible for the in the pole positions. The intensities of magnetization were slightly different. The intensity was about 20% less than.the the Massachusetts acquired by the above specimens of the Nova Scotia specimens original value, specimens was increased whereas the intensity about 200%. The intensity of the Pennsylvania and Virginia Since the intensity of the applied field was not lrno\'m,it is not possible to m~~e any inferences field during Triassic article by Thellier earth's magnetic times. specimens was increased about the intensity The interested about 100%. of the geomagnetic re~der is referred to an (1959) for an account of the intensity field during the geologic of and historic of the past. 120 9. Laboratory Deposition Tests In order to obtain some indication of the magnetization sediments may have acquired in deposition, North Carolina sandstone were po~uered tory. that the several specimens-of and redeposited in the labora- This work vias performed by D. Greenewal t of the Department. The remanent magnetization tometer. was measured with an astatic A brief description of the procedure type magne- and the results are outlined below. Several specimens were ground to a povmer. Then the powder was allowed to fall through water to separate those grains which remained for more than 5 seconds and less than 30 seconds. The grain size was found to va~J from 0.1 to 0.02 roms. in diameter. The in suspension powder was redeposited in still water in the earth's magnetic The water was then drained away gradually to dry. and the sediment v[as allovled Specimens tEJcen from this deposit were found to have a magnetization magnetic field. which roughly coincided in declination with the earth's field, but which had a dip some 10 to 30 degrees less than The intensit3T of magnetization the magnetic inclination. vIas several times gre2,ter than that of the original rock before pOvldering. Similar experiments performed with Triassic sediments Englend have been reported by Clegg, et a1 (1954). the variation from In their results in the dip was about 8 degrees and the intensity about three times as great as that of the original rock. that the lower magnetic was They suggest intensity of the natural specimen may be accounted for by turbulence intensity of the earth's field since Triassic during deposition or by a rise in the time, or it may also be due to the decay of the remanent magnetism has found decay times comparable (1943) ,dth time •. Nagata to this in the remanent magnetism of igneous rocks. 10. Origin of Remanent IViagnetization The information acquired from the deposition the sediments may well have become magnetized some cases this could have occurred The primary magnetic materi8~s and hematite. The magnetite tests indicates that before cementation. In on deposition. in the sediments were magnetite occurred as detrital fragments whereas the hematite was more often present in the form of a pigwent. Evidence that this form of hematite ffiC'.y be magnetic and can be reliable for paleomagnetic Their investigation the llips indicated work is given by Hargrave of Jurassic red limestones and ,tl'ischer(1959). and radiolarites from that hematite was the only magnetic material present. Howell, et al (1958) experimented w~th Triassic rocks from Arizona and their results suggested that PQrt of the remanent magnetization may have been due to the presence hematite is cooled below -20°C magnetization. low temperatures Since it is difficult on the rock-generator with the Triassic Tests made by D. Greenewalt, to measure specimens with such type megnetometer similar rocks included using the astatic that the hematite may have been contributing magnetization. when it loses part of its remanent specimens become heated quite easily), been performed of hematite; (because the experiments have not in this report. magnetometer, to the remanent indicated 122 Krynine (1950) regarded the Triassic red beds as sediments derived mainly from red soils produced rocks in the source area. by weathering of the silicate Thus, the red color is of primary origin and represent~ physical and (or) chemical deposition. found these conclusions to be in general agreement (1955) Reinemund with conditions observed in the Deep River basin of North Carolina. 11. Stability of lv1.agnetization The fact that many of the rocks show a uniformity of magnetization indicates long period of time. some degree of magnetic Of course, the geologic in direction stability corrections over a gave evidence that most of the rocks have been stable since deformation. That the magnetization remains stable over short periods confirmed by repeated measurements of some of the specimens had been stored with their magnetic axes oriented Some of the rocks were unstable field. In most cases the unstable a.c. field treatment; comparable not possible to obtain accurate results. a minority of the earth's could be removed by acquired IRM components time (10 min.) w~ich in random directions. in the presence components some specimens to the measurement of time was and, therefore, in times it was These samples represented however and in most cases they were not included in the final results. The relative instability of the Nova Scotia and Connecticut igneous rocks, when subjected to a.c. fields, results may not be reliable. In contrast, suggested that these the Pa - Va igneous rocks were verJ stable and their results were in good agreement results of the sedimentary rocks. Valley with the 123 12. Magnetic Reversals Many of the sedimentary direction rocks were magnetized with a mean downward dip. in the remanent magnetization in a Northerly Considerable scatter ~ms present of some rocks, however. In general, the scatter was downward and confined to a plane vrhich contained direction of magnetization the present of the stable rocks and the direction earth's field. of ~fuen given an a.c. field test many of the scattered remanent vectors moved toward a reversed Although the tests were not concluSive, a.c. field intensity, the the reversals direction. due to the upper limit of the appeared to be slightly less than 180 degrees. Reversals were found in most of the sedimentary there were no cases where both normal and reversely specimens were found uithin the same outcrop. formations, magnetized During the a.c. tests the remanent vectors of some specimens were deflected perpendicular to the plane of scatter; was considered in a direction in this case the magnetization to be normal. There are several reasons for believing caused by a physical or-chemical that the reversals effect of the type envisaged Neel (1949, 1952), and were not due to a reversal geomagnetic but were by in the main field. 1. The revers2.1s occured throughout the Triassic rocks, but there was no evidence of rocks with a stable, reversed magnetization. Many of the normally showed no influence magnetized rocks of the present earth's field and were quite stable in a.c. fields; i.e., some of the New Jersey sediments. 121 2. l\ianyof the rocks vuth normal magnetizations scattered in a nearly reversed direction. were Conversely, many of the reversed rocks were scattered toward the normal direction. Thus, the earth's field was not the only factor influencing mechanism 3. the scatter; the reversal seemed to have some influence, Two minor points, vlhich mayor also. may not have a bearing on the issue, are: a. Reversed rocks generally of magnetization. had a weaker intensity ''Illy should the reversed field always be ,."ea.ker than the normal geomagnetic b. field? No reversed and normally magnetized specimens "Tere found within the same outcrop. Clegg, et al, found the same pattern of scatter rocks, and apparently or normally magnetized there was no physical specimens. committal on the reversal in the English Triassic difference Ii'orthe most part they ,vere non- issue. luthough the above points suggest a reversal the evidence is certainly in the reversely in the rock itself, far from being conclusive. At present, the issue is still open to further criticism. 13. Comparison of Pole Positions fig. 11-10 ShOvlS the Triassic pole positions determined by other investigators. United States rocks are slightly given in this report. that have been The pole positions determined from southw"est of the final pole position 125 Poles No. 48 and 49 include results from 'the igneous rocks of the Connecticut Valley. Since these rocks are considered it is safe to assume that these poles are unreliable. determined agreement from the Brunswickian with the results reported Pole No. 51 (Springdale position formation to be unreliable, Pole No. 50, in New Jersey, is in good here for the same formation. sandstone) has the same longitude as the pole given in this report; the latitudes differ by about 10 degrees. With respect to the Triassic pole positions English and United States sedimentary rocks, the longitude is somewhat less and the latitude difference than previously the relative thought to exist. significance Irving 14. from difference is som81vhat more than For a comprehensive of the pole positions, drift and polar wandering, as determined discussion on as regards continental the reader is referred to an analysis by (1959). Conclusions One very important concerned result that became evident the relative values of the igneous paleomagnetic determinations. The sediments results whereas the igneous rocks did not. by this survey and sedimentary rocks for gave fairly consistent For the reasons given in Part II, it was assumed that the igneous rocks were not as stable as the sediments, and hence their results were not included in the final analysis. The pole positions given in Fig. 11-10 led Du Bois, et al (1957) to conclude that (1) small samplings CCln results from both igneous and sedimentary be quite reliable, and (2) rocks laid down at the same 126 time are in agreement. difference Concerning point (1), it is noticed that the between the pole position (determined rocks) given in Fig. 11-10 and the pole position survey, is about half the difference United States pole positions. small samplings from United States determined from this. between the English and the For this reason the author feels that can also be misleading. is obvious from the pole positions That point (2) is in error given in ~'ig. 11-9. 12'7 lUJPENDIX G: IGNEOUS AND SEDINENTlffiY The remanent magnetization ROCK DATA data for the igneous a~d sedimenta~J rocks is contained in Table G-l and Table G-2. The follovrl.ng information is given: Outcrop No./ average intensity of a.c. demagnetizing when used, e.g., NS 4/20 field, Oe. No. specimen designation; core-specimen D.M. - Direction of magnetization; declination is east of north, dip is positive dOvffiward. \Vhere two directions are given for one specimen, the flrst is the original direction of remanent magnetization and the second is the direction after a.c. demagnetization. I Intensity of remanent magnetization to tviO significant figures (cgsu/cc). N. Pole North seeking pole of a dipole field that would produce the average direction each core. of ma~~etization The longitude is east and the latitude is positive north. in 12:8 T.ABLE G-l IGNEOUt) ROCK DATA Ixl04 DeL No. N. Pole No. 69t 71t 1Lv-1 24# 25t 2 1~ 2t 16~ 3 338 15-1 9t 352t 2 10 360 3 340.t 338t 4 3# D. M. IxlO4 N. Pole NS 2&3 2 3-1 2 3 4 4-1 2 5-1 2 3 4 6-1 2 3 7-1 2 3 4 8-1 9-1 2 27 22t 22~ 22t 23t 35 34t 37 37 37 38t 1# 1# 16 34t Zit 29~ ~ 29 26t 52t /JJ~ /JJt 45 1$ 57t 58 50 50t 51 53 44 45t 45t 60 56 53 60 47t 51 51 28.0 7.5 9.3 8.1 8.1 10.0 9.2 li.O 11.0 11.0 10.0 7.8 7.7 9.3 5.5 6.0 6.0 5.1 6.9 4.2 4.6 83 65 47 73t 52 66 99 68 57 75t 13 2 8~68 69 70 NS 1/20 Oe. 10-1 2 26 351t 2Jt 335t :3 24t 351 11-1 328t 6t 2 310 341 3 6t 13 12-1 2 45 39 45 31 42 34 53t 43 61 26 44 /IJ ~t 6Oj65 67t 5It 357t 63 13-1 99i- -28 2 103 -Zl 3 100 -21 96 -30 6.6 152!- 6# 4.6 6.5 4.6 6.7 4.3 506 . 132 70 2.8 6.1 4.7 6.3 2.6 5.6 265 7ict O.~ 5.7 1.8 6.7 6.7 6.5 4.9 16-1 34 -lot 71 46t 51 65t 71 46 3.4 1.3 46t 44t 1.5 4.5 101 3.5 1.8 3.8 1.1 47 41 52 47t 47 55 50 84 43t 46t 61 J{;. 48 35t 3J.6 31 2 346t 36 27 346 3 350i- 38t 30 354 4 346 36t 344t 31t 17-1 3ftt 198 83t 168 77* 7t 55t ;"9 4.2 0.84 3.9 1.0 5.2 3.1 5.0 1.4 7.2 6.4 7.2 5.6 7.7 5.8 7.3 5.5 156t 59t 126 70 194 30 213t 26 NS 5/20 Oe. 18-1 2 3 4 19-1 2 20-1 2 3 4 5 6 7 8 356t 9t ot 359 300i 297 280 288t 288 285t 282 r 28# 287t 281t 22.0 25.0 24.0 24.0 16.0 13.0 5'S! 17.0 21.0 57 20.0 56 56 22.0 56 22.0 20.0 58 56 22.0 57t 21.0 56 47 51 49 31 34 129 D. M. No. IxlO4 21-1 34?k -2:7 11.0 7.1 350t 13 2 358t -69 26.0 3M3 4 7.3 3 328 -64 39.0 6.6 345t 8 22-1 358~ 53 11..0 12~ 48t 7.7 2 353 48t 16.0 8.5 10~ 46 23-1 36~ 35 18.0 2 :'25t 37 14.0 24-1 24t 60 9.1 6.3 23 44 2 23 57 7.9 6.1 25t 47 9.1 3 18 59 4 15 54 11.0 5 8t 51t 13.0 8.4 15t 1$ 6 10 52 13.0 13t 43t 8.0 25-1 315t 34 16.0 314 33 14,0 2 321 27t 1500 317t 36 18.0 314 3 33 19.0 313 37 17.0 26-1 353 59 50.0 352 57 15.0 2 355t 57t 6300 355t 5'4- l~O 6 27-1 339 2 330t .3 331t 4 337t 5 331 6 352 7 347 28-1 16~2 15t 9 3 N. Pole 132 44 105 68 71 L.8t 87 66 60 59 61t 57t 59 55t 57 4 .348t 60 5 343t 65 8.9 8.6 9.2 9.8 9.0 8.5 8.8 7.3 8.7 8.9 8.3 8.9 N. Pole 30 62 0 181 41t 92 7# NS 55 57 56 D. M. IxlO4 NS 7/10 Oeo 29-1 69~ 66 8.2 60t 58 6.3 2 70fi 63 7.3 6.5 50~ 59 3 ' 291-2 65t 12.0 9.4 33~ 64 4 14- 71 702 M3~ 65t 6.1 8.6 5 51t 56 51t 53t 6.0 6 39~ 61 8.0 63 5.7 4# 7 50t 6# 81 45} 61 5.5 8 7.9 50t 67 30-1 344t 66t 6.6 344 61t 5.3 2 325t 66 6.2 349t 63Q- 5.8 3 332t 74 7.0 336t 67t 5.4 31-1 61t 74 4.4 307t 83 3.2 2 Bot 78 7.3 36t 77t 1.4 3 87t 76 8.3 42t 69~ 3.4 8.2 4 ~ 78 83 ~1 144~ 5 9~- 73 7.9 6 ,:89~ 84t 8.1 7 322 -15 7.3 321t 66 3.4 32-1 481- 57 6.4 69¥2 57 5.4 2 44t 61 7.1 56t 51t 5.3 3 47t 66 905 6.8 LJ.t 6# 4 6# 65 S.3 57 64 5.9 6.8 5 69t 65 5.2 6# 65 6 51t 66 6.8 7 59t 64t 6.1 8 7.3t 66 6.5 33-1 33 75 8.6 7t 59:! 9.1 2 63;t 74 9.2 7.3 9t 65 No. 164 65 125 73 l81t 74 282 80 23 55 96 80t 130 No. D. Me Ixl04 33-3 102 76 352t 64 Illt 75 9)- 61 102t 68 31 64t 121t 77 7# 73 182t 64 174 44 172~ 113 154 66 aot 52 170 51 174.t 33 155 51 169t 72t 150/r 68 lloO 709 9.7 7.2 9.5 6.3 8.9 9.0 15.0 2.9 16.0 2.9 12.0 3.6 5.5 6ct3 5.9 1.9 4 5 6 7 34-1 2 3 4 5 N. Pole 307 4 2 36-1 2 3 4 5 37-1 2 3 38-1 2 3 39-1 2 3 l31 -11 30t 60 346t 45 32 44 265 17t at 70i26* 18 344 51 259t 19 207 54 262 18~ 357 35 249i- 18 2411 81 8 68 80 271~ 23t 68t 177t 76~ 15 66t 327t 73t 342 62t 335t 78 323 83t 71 3ut 351t 64 322t 51 355t 52 322t 63 349 48 31St 64 347 52 D. M. 40-1 33~ 48 41-1 27t 54t 2 24t 53t 3 20t 56 42-1 16t 51t 2 20t 50 43-1 2l 52 44-1 lot 60 1 2 62 22' 45-1 359/r 65 2 358 59 46-1 37t 61t 2 4J.t 6# 3 22t 61 Ixl04 8.2 1.4 1.4 1.6 4.3 3.7 3.2 5.4 5.3 5.5 6.0 2.7 2.9 3.4 N. Pole 36t 29t 57t 66~ 4St 70t 40t 68t 355t 81~ 316 85 6 61 42t 64t 40 68 41t 63t 49 7}~ NS 10 NS 8/100 Oe. 35-1 No. NS 9 60 11.0 1.6 3.4 0.83 12.0 14# 1.3 13.0 0095 12.0 0.88 13.0 0.70 15.0 66 2.1 0.47 1.8 0.42 1.2 0.29 1..0 197 1.6 3.7 1.1 5.5 1.5 138 3.9 1.7 1..1 1.8 3.7 1.6 63 68t 47-1 2 30 48-1 30 24 33 28~ 31 29t 2 49-1 2 3 4 5 50-1 2 3 82t 4 51-1 ~ 52-1 53-1 2 28 28,t 26 17t 21t 10 20t 25 30t 28t 53 52 54k 55t 51 .51t 54 52~ 53 61 50~ 53 58 55! 58 57t 59 19.0 16ctO 12.0 12.0 19.0 18.0 18.0 15.0 15.0 12.0 -17.0 14.0 16.0 15.0 12.0 15.0 16.0 47 72 35,t 70t 31 67 NS 11/15 De. 77 54-1 7t 50 2 359 44 3 67t 55-1 56-1 2 7t 50 17 26 8 16 11 1St 68t 19.0 19 47 11.0 18.0 11.0 17.0 10.0 14.0 10.0 11.0 5.8 1300 5.5 34 62 20 68 56 66 57 62 55 64t 55 66 62 70 59t 131 D. No. Me 68t l8i 64t 8 68t 56-3 354 57-1 2 IxlO4 9 11 6 58-1 352 9 59-1 3l8t 1St "9.6 5.6 9.7 5.2 6# 8.8 71 5.l 58'~ 69t 8.2 6.3l 500 ~t li.O 3.0 54 64t 8.6 62 3.0 8.2 64t 62 3.6 67 11.0 5.4 14t 6# 8.5 17,t 70 23t 59t 4.5 2 322 16 60-1 43 32 2 26 3 NS 12/20 Oe. 61-1 344 2 345t 62-1 337 2 338 63-1 33# 61.-1 224 331 2 137 33 65-1 302t 324 2 298 329 66-1 349 336 67-1 352 349 2 357 343~ 44 18.0 43t 20.0 52t 10.0 52 11.0 47 5.2 6.7 34 69 2.4 69t 6.5 66 2.1 62 8.2 614- 4.0 52 6.5 62 ,"0 22.0 52t 50t 6.6 64t 14.0 52t 1...6 62 14.0 4.1 50 N. Pole 1% 78 11 75 32 69t 17 69-1 70-1 71-1 2 26 49 30t 45 26t 45 30 44 31t 42 3.3 3.1 4.4 6.7 6.5 2 .3 73-1 7ir1 2 3 75-1 2 3 30t 30t 43 42. 28 2fr} 34 30! 29t 25 46 43 45 2# Li3 28t 44t 44 49 50 500 5.1 5•.3 6.5 7.7 7.7 704 63 5.8 6..3 0 N. Pole 51 ' 60 55 48t 61t 58 52t 66 67 M 6/10 Oe. 39-1 1~ 11 3~2 1~ 12 19t 5 40-1 16t 18 17 10 2 18 19 8 17 6 41-1 27 23t - 3 2 22t . 8t 25t - 7 3 24 5t 24t- # 42.-1 14 11 15 -11 2 12t lOt 11 2 43-1 22 5t 21 ~ 4 2 26t 6t 27 - 5 44-1 19! - 3t20 -14 2 2l-5t 22 -17 45-1 18 It 16t - 8 2 28 -6 21t -10 46-1 26 38t 15t 17t 18 151t 67 174 68t 171 310 63t 81 213t 67 173 67 157 73 50 50 5# 50 Ixl04 D.M. 72-1 NS 13 68-1 No. 64t 60 62~- 58 9.0 8.0 907 8.9 8.2 6.9 9.1 80 1100 8.7 9.2 9.0 10 0 9.3 14.0 14.0 16.0 l200 9.7 9.1 10.0 83 15.0 12.0 15.0 12.0 7.2 5.4 8.2 6.4 27.0 9.6 45~ 43!- 41 45 0 50t 40 0 58t 49 51 ItOt 64 41 59 43 0 33t 45 132 No. IxlO4 D.M. N. Pole M7 47-1 2 48-1 49-1 2 50-1 10 19~ 358 4 1 359 28t 30t 53 25 13 56 10.0 9.1 11.0 7.9 5.9 15.0 33t .5.# 242t 62 50t 66t 340 45 M8 51-1 52-1 53-1 2 54-1 55-1 56-1 2 57-1 196 13 4.2 269 -18 18.0 4.2 23t 33, 30 29 5.0 12 8.6 33 338~ 52'1.. 10.0 81t 732 0.60 106 52 1.2 91 74 99.0 M9/50 De. 26 58-1 27 59-1 22t 18 2 3# 24 60-1 30 29 61-1 87t 2 62-1 63-1 2 64-1 2 65-1 2 40 27 1'4- 6.3 3.9 7.9 6.2 8.9 6.2 8.0 6.8 J(J 4.2 25 31 27t 1St 8 29 9 87 25t 31t 5t 22 66~ l7t 56 95 57'~ 36 J2, 106 4lt 60 26 68 37 3.4 . 3.7 304 9.0 6.1 7.8 3.4 8.6 2.9 8.4 46 24 3.1 72 40 8.0 48 2.9 34 73 59 14.0 4.7 56 46 65 57t 13.0. 53t 44t 3.7 275 -38 0 198t 53 46165 73 355 55t 81 298'~ 38 12t 59~ 48t 75 49 No. D. M. C 1/50 Oe~ 1-1 20 67 4t 56~ 2 12 61 2 54 2-1 28 51 17 39t 2 39 49t 5t 38t 3-1 52 44 5 33~ 2 57 43 57 43 4-1 24 57t 22t 51 2 28t 48 28t J.j!, 5-1 276t 51t 19 53 6-1 22 56 9 40 7-1 324 62 4 44 8-1 46 23 2 '56 Ixl04 N. Pole 20.0 6.7 17.0 4.4 18.0 4.5 19.0 500 15.0 200 1~0 3.3 17.0 200 19.0 2.6 34 614- 59 57l 4lt 46 35t 50 33t 53t 60 59 58 63t 34~ 6st 81 5It 7St 59 68 53 50 34.0 3.2 19.0 2.4 9.8 5.6 20.0 609 C2 6.3 44 66 39t 31 64 31 37t 38~ 37t 23 36t 9-1 2 10-1 11-1 7t 20t 15 25 12-1 13-1 14-1 1 46 13t 39 25 17 3/150 Oe. 15-1 350t 338 16-1 67 23 2 20 19 17-1 173 358t 18-1 7 5 19 7 16 24 605 l2.0 2.4 503 60S 7.8 16.0 70 73 63t 55t 153 79 11.0 21 3.1 2.2 3.1 4.5 4.2 12.0 5.1 63t 338 72 6oi- C 22t 52 -29 59 74 60 73 71 69 83 5.6 407 31<Jt 54 13a No. D. M. 19-1 175 158 20-1 274 358 2 273 354 50 64 47 71 58 70 IxlO4 602 N. Pole 9 78 337 74 2.7 9.6 3.4 10.0 3.8 c 4/100 Oe. 8 22-1 14 2 12 17t 3 J2 19 23-1 J2t 24-1 24t 15 23 1St 26 16t 37 11 22 10 17 43t 19 4.1 3.3 4.1 3.0 4.2 3.0 3.9 2.5 3.9 2.2 75 50t 81 55-t 76t 5lt P3 21-1 22-1 23-1 2 24-1 25-1 2 26-1 2 27-1 28-1 2 11 39 12 46 26 25 26 24 18t 22 42 20 26 28 25 4# 46t 45 47 1+2 42~ 37 40t 40t 9.2 7.0 7.1 6.3 5.0 8.9 7.8 8.3 7.8 6.9 7.3 . 6.9 no 86 63t 67 69 91 100 71 7,* 118 93:r 66 82 82t 6# 67 P 6 47-1 354 2 359 48-1 354 49-1 358t 50-1 350 51-1 350 52-1 356 35 33 36 38 32 35 45 60.0 55.0 52.0 14.0 0.22 0.36 6.3 ll5 6J.t 120 112 6ck 64 125 126 121t 58t 60 67t No. D. Me IxlO4 N. Pole P 9/50 Oelt '~-1 27 30t 69-1 352 342 70-1 350 344 71-1 305 349t 72-1 332 345 73-1 348 347t 74-1 338 344 75-1 350 345 P 10/50 Oe. 76-1 ot 359 2 359 358t 77-1 356 357 2 357t 357l 78-1 354 356t 2 35# 356 79-1 354 357 2 358 359 80-1 341 357 2 346i 358t 81-1 338 353 82-1 326t 349 2 333 343 83-1 338t 1* 81,-1 3531 356t 59~ 907 54 6.3 57 1600 49 9.4 56~' 12.0 602 4~! 78~ . 18.0 51 6.8 809 58t 47 5.8 51 11.0 6.8 43 51 10.0 5.9 '45.4 4.6 53 67t 1'4- 63t 138t 62 134t 67 138 63t J33 62?r 138t 62 144 67t 5.8 4.8 5.2 4.6 4.0 3.4 3.2 2.9 7.4 6.4 6.8 6.1 2.9 2.6 3.7 3.4 6.5 6.1 5.8 5.1 9.3 6.3 7.9 5.6 7.7 5.7 ill 63 11# 63t 115 59t 113 62 1J3 64 122 63 ]35 63 li.O 109 67 6.0 6.6 5.1 118 65 ~1t 40t 41 ~.~ 41 '43~ 42 44 42 35t 34t 35t 34t 40t 40 ~t 40t 37 41 40t 42t 41 41 40t 44 44 46 50 46 49 44 134 IxlO4 D. M. No. N. Pole P11 85-1 86-1 2 87-:;J. 88-1 89-1 90-1 91-1 2 92-1 353~ 348 348 354 360 343 352t 355 354 353 P 14/S0 Oe. 16 103-1 8t 2 3 5# 58 53 1 52 53~ 61t 57'~ 53! 59 wt 105-1 2 106-1 2 107-1 2 3 108-1 109-1 2 3 110-1 2 3 129t 2.1 3.7 3.8 500 4.3 S.o 69t 117~ 159 137 132 7l:~ 71 72 72 142 74 33it ilJ 9 ilJ 14 39 17t 34t 12t 38 8t 33~ 10 33~ 7t 30t 6t 32t 7.t 35 358t 33t 356~ 30t 354 31 3 34t 6 31 16 37t lot 37'i12t 34 12t 37'~ 15 111 D. M. 125-1 322t 126-1 312 127-1 330 128-1 316 129-1 338t 130-1 348 0/7 63 2.6 2.9 2.6 2.1 2.2 2.6 111 63 lot 41 28 1,-1 6 3t 7 5-1 lot 2 7 12 2~9 2.4 2.4 2.6 2.3 2.3 2.5 3.0 2.5 351 7 2-1 23~ 15 2 '19~ 3-1 3.0 91t 65 lloi 61t 2.4 9St 2.3 . 2.7 2.4 2.9 2.4 101 2.4 204 2.7 112t 2.5 3.1 2.5 3.2 3.5 93 2.3 2.2 2.6 2.2 3.1 204 63 ,,6-1 359t 9 2 352t 4 1 7-1 6t 2 352t 5 8-1 360 9-1 2 60 59 63t 1+2. Ixl04 13.0 N. Pole 153 163 145l 160 137 136 53 71 39~ 6.4 L..2 38 50 14.0 LJ. 11.0 47 12.0 43 10.0 122 61 122 66t 35 15.0 34t 6.4 2.8 36 27t 2.5 30 26.0 31 16.0 28 24.0 .29~ 1600 42t 6.3 1..2 38 1$ 8.2 J.Ot 4.4 L.2~ 10.0 32 5.7 8.7 46t 4.7 38 11.0 47i 83 66 115 5et 107 61 125 62t 44t 18 0 0 44 43t 16.0 18.0 44 11.0 71t 12.0 47t 45 51 46 V 1/20 Oe. 1-1 2.9 38t 2 38t 358t 35 2 37 1~ 4# 20 43 27t 39t 6].38 2 2t 32 358t 35 1 31 3t 31t ~ 4.4 2.5 104-1 300 2 71 6% ilJ 34 9'2 35t 10 132t 143 37 13 12t 3.9 2.5 3.6 No. P 16 10 349 ot 355 352 10-1 10 7 6 2 11 11-~ 339t 336t 2 337 343t 12-1 332 353t 13-1 at 8 608 36t 47 8.9 4.8 44 8.2 45 47 5.2 7.4 38 4.8 3# 37b: 7.9 4.2 32t 50 12.0 40 6.6 46 1200 40t 6.6 51 1000 43 5.4 53! 11.0 46 64.0 120t 61 117 63t 147 59 115 61t 152 4~ 14# 57 13# 65 135 No. 14-1 D. Mo IxlO4 2t 25.0 21.0 28.0 11.0 11.0 5.8 8.6 5.1 7 2 328 8 15-1 359 4 2 358 4t V 5/20 Oe. 38-1 351 351 39-1 3 355 2 145 40-1 325 320~ 2 329 327 41-1 332t 334 2 339 339~ 42-1 341 328 43-1 298 316 2 30~ 34ll 44-1 320 328 2 322 3IB! 45-1 312 321 2 304 310 38 3.3 44 38t 43 ~~ 44.! 39 N. Pole 119 . 62 129 2# 5.9 125 3.8 4.3 127t 44~ 3.3 5.0 38t 40t 4.2 182 53~ 4.2 47 2.6 403 55 52t ~'.3~0 36 4.5 157'~ 3~3.4 4.1 45 413.5 51 183 3.9 3.4 51t ~~6 187t 58t 51'2 2.7 3.2 55 2.8 44 1.8 184 set 45 53t 60 53 60 59i 58 72t 52 57 55 56 51 108 3.9 3.9 . 4.1 195t 4.1 2.6 2.6 471;; V 6/20 Oe. 46-1 59 55 56 2l~ 42~ 20t 61t 24 55! 6 63 2J~. 52~ 34~ 355t 2 16 47-1 2 7.9 505 130 78 71 85 5.6 5.0 6.6 3.9 805 5.5 12t 19~ 51-1 101 81 46 2 28 52-1 99 38 2 76 31 66 53-1 50~ 2 75t 71 3 .68 50t tv 56t 43t 39 51~ 53-t 51~ 52 Ixl04 11.0 ~5 7.B 4.5 8.9 A.5 8.6 4.7 5.1 1..5 7.1 4.6 803 504 7.3 4.7 6.7 4.6 5.7 5.4 7.0 5.3 6.0 5.2 53 7 25 28 1.4 0.62 2.4 1.9 D. M. 339~ 352 2 355 2t 49-1 46 26 2 42 50-1 28t 21t 40 46t 62 Noo 48-1 62 56~ 65 50 49 49 51 50~ 72t 60 75 75 76t 73 66 59 6<Ji N. Pole 156 . 76k- 65 80t 188 85 268 60i 350 82 1 59~ 12 91-1 92-1 143 148 2 30B 93-1 334 very unstable 136 TABLE G-2 SEDI~illNTARY ROCK DATA No. M D. M. Ix105 1 1 2 3 4 5 6 7 8 broken 360 43 J2I 2 2 354 40 48t 50 51t #40 7 50 13 M3 14 15 16 17 18 19 20 21 22 3t 3~ 354 53 359t 4S broken 7t 56 355 30 345 1.$ 342 59 3AB 52 351 4# 1 50 358 52t 351 58 351 47t 1.1 1.7 1.7 1.7 2.4 1.7 2.0 2.6 2.1 3.5 2.4 1.5 0.87 0.96 1.2 1.5 1.3 2.1. 1.2 2.0 M4 23 24 25a 25b 250 25d 26 27 28 332 347t; 3~ 33# 343 345t 349i 342 330 64 55 59t 59 60 58 4* 65t 68t No. 29 30 -'M 2 9 10 11 12 N. Pole 3.4 1.8 2.3 2.2 2.3 2.3 1.5 2.2 1.9 M 5/20 D. N~ 350 71 70 5Ei Ixl05 5.0 7.6 Oe. 31-1 339t 55 5 45 2 354 5# 0 42t 8 55 3 358 49t 32-1 357 52 2 356 1# 33-1 lot 50 6 53t 2 52t 6~ 55t 3 352 72 344 63 4 17 .50t 5t 51 4 55 34-1 2 ot 50 1 3 4 358 56 35-1 350 57t 2 347t 56t 3 354 56 36-1 346 58 344 59 6 59! 2 346 &J 3 354 61 342 59 37-1 358'~ 6J~ 2 360 66t 3 It 61 8 61 4 5 7t 60 38-1 359t 54 357 56 2 14 55! 4 53 3 7t 50t 2 53 4 10 65t 2 59 6t 56f 0.64 0.57 0.62 0.61 0059 0.57 0.57 0.54 104 102 1.3 1.0 1.7 1.1 1.2 1.1 1.6 2.0 1.7 1.8 106 1.7 1.8 1.7 1.6 1.5 1.6 1.7 1.6 2.4 200 1.7 1.9 1.6 1.6 2.1 1.6 1.8 1.9 2.2 1.7 2.2 N. Pole 137 No. M Ix105 DoM. ll/50 Oeo 74 1St 67 6 54 75 40 28t It 57 76 14 39~ 2 5# 77 15 64 16 62 N. Pole 1.1 0.79 1.6 0.91 1.8 1.3 0.85 0.62 i 350 4 4 359 358t 7t 360 4 5 6 7 ItJ 35 34 22 33t 7.4 3.9 2.4 509 3.0 2.6 38t 108 28t 32 2 10 9 28 10 11 7 43 17 28 28 12 13-1 2 14 15 16 17 18 2t 9 40 43t 4# 131 loot 100~ 108t 111 93t 109 53 42~ 29~ 39 36 2~ 39 g,t 1;2 36~ 40 broken 3.0 2.4 2.8 2.6 2.9 2.9 2.5 2.8 2.1 2.} 2.2 3.1 IxlO5 25-1 2 26 1St .46t 17 33 12 52t 3.1 ~2 2.7 27-1 2 28 29-1 2 30-1 65t 65 6# 57 62 tot 66t J 2 .8-1 D. M. N. Pole gO 65 85 75 0.71 0.94 16.0 OGt 49 0.49 0065 0.53 1.3 3.0 168 53t 147 140 50t 44 136 52 2.2 L7 1.7 113t 65 130 68 119t 6# 122 63t J4 J 1 2 3 No. 63 65 64 77 90 .. ..-:.3# 54 76 59 56 59t 51 " ' 102 89 89t 43 61t 66 69 56 347 295 333 336 335 335 2 3.46 26 31 18 32 44 45 31 2l~ 8t 42 14 66 67 P l/50 Oe 1. 12 36 6 42~ 2 _356 43 3t.52 3 16 38t 3t 43t 4 357t 49t 1t 43 5-1 51- 38t 13 30 8 2 LJ. 13t 29 6-1 31 63 3~ 45t 2 35 58 27 63 7 50 67t 28 57 8 44 67 26 51 49~ 79 81t 66 1.8 2.1 1.8 0.94 0.87 1.3 1.5 1.4 1.6 1.3 L1 105 1.4 0.61 0.35 0.63 0.33 91 58 80 75t 88 77t 83t 72t 83 104 69 J 3 28 19 47 20 35 45t 21 355t M:> 22-1 broken t1 2 23 355 4% 2~1 lit 65 2 15 6&} 4.0 3.8 5.0 3.2 2.6 206 55t 45t 124 130 70 66 61t 70 71t 87 P2 17 9 10-1 19 2 359t 11-1 349~ 2 17 33 43 32 42t 39 0.57 0.58 0.51 0.56 0.63 66 119~ 70 138 No. 12-1 2 14 13 15 16 17 18 19 20 Ixl05 D. 1-1. N. Pole P8 .58 too weak and unstable " II II tt " 47t 5t 20t 339 13 12t 353 Il 56 53 53 46 41 " It 11 It tt U 0.27 0.28 0.20 0.54 0.58 0.88 127 90 172t 118 103 140 74 84 60 81 75 65 P4 29 30 31 32 ~ 33 34 35 36 too weak and unstable <1 x 10-6 46 P7 . 53 54 55 56 57 13t 270 21$ 310 274 17 61t 49 4lt 43 38 4J.t 59~ 52 45 52 50 46t 50 '4- 58 42 58 L{l 34 1.5 1.2 2.1 2.7 105 1~ 135t 109 9# 55t 5~ 57 58 108 1.4 105 1.6 1.8 1.9 103 1.4 103 0.17 0.28 0.17 0.10 0.18 131~ 63 103 66 95t 64 95t 65 64 1l0~ 58 203t 210 187 196 1St 99 59-12 60-1 2 61 62-1 2 63 64 65 66-1 2 67 D. Ixl05 M. 2l7t 193~198 213 214 283 335 304 322t 276 205 272 278 35 13t 8 24 17 12 39t to 56 73t 47 3 61t 66 68 0.52 0.41 0 36 0.59 0.57 0.45 0.45 0.51 0.56 0.56 0033 0039 0.57 0.35 N. Pole 234 -28 255 -33 0 t 237, -29 191 182 20t 49b; 196b; 56 10/1 21 205 -.38 .31 146 88 21$ Pl2 P 5 37 353 38 354 39-1 13 2 13 .40-1 20t 2 27 LJ. 15 42 30~ 4.3-1 31~ 2 31 44 31t 45-1 .32 2 .30 No. 0 .38 13 96b; 65 93 94 95 96 9? 98 99 100 208 - 6 228 -lot 346 69 247 66 broken 238 - 3 238 -22 6 284t 200 207 0.58 0.76 246t -41 223t -33! 179~- 77 245 16 102 LA 2.8 217 -24 209 -31 184 10 1.4 1.3 140 138 0.50 0.21 0023 0.14 1.5 0.23 0.63 0.75 1.0 104 212 26 207t P13 101 102 352 347 59 40 73t 66 P 15 111 too 6 47 113 114 333~115 265 116 250 117 34 118-1 354 2 305 119-1 215 2 296 3 281 112 weak 64 42 65 33 59~ 45 68 81t 8t 66 55 102 86 53 65 208t 7 230 14 40 64 64 239~224 5t 139 No. 120 121 122 123 124 N. Pole 514- 2.0 171 58 2.:5 222 200 -22 3.6 253t 169 lit 2.0 298 8 187 2.1 'Z74 346 264 Md 1 1-1 343 2 343 3 343 2 353 3-1 3'Zl 2 342 4 352t 3~ 5 6 352~ 7 359 8 21 9 IxlO5 D.M. ok 62 1.0 65 66 54 50 56 1.0 42 5# 1.1 3.9 3.0 2.9 2.5 2.0 31j- 3.7 48 3.5 1.0 65 1.9 54 71 20 -56 -iJ. -1,,4 No. Md 3 26 27 28 29 30 31 D. N... 19t 360 333 34# 7t 352 sat 57t Ixl05 0.42 0.46 2% 49~ 37t 0.46 3.5 3.0 2.3 16-1 359 38t 2 359t 40 17 360 36Q8 18 35t 19 2 'Zl 20 2 ~ 21 4 32 3.5 3.9 4.5 4.0 6.7 7.8 50.3 -24 N. Pole 89~ 117 67t 65 1.30 lot 51 102 61t 119t 53 112 110t 6CJt V2 104 63t 130 62t 108 57 wi- 63t 110 51 98 59t 63t 65t 94 62t 132 58 128 58 117 li5t 140~ 117t 61 55 61t 58 V3 22-1 Md 2 10 11 12-1 2 32 9 2# 7t 16 6 30 13 359t 37t 14 1t 20 15-1 16t 3It 2 1St 29 16 broken 17 13 26 18-1 5~ 31 2 11 33 19 9~ 32 20 14t 37t 21 5 34 22-1 13 29~2 27t 23-1 11 20t 362" 2 18 35~/ 2 .J. 4 25 8 25 25 18 2.9 3.2 2.9 2.7 2.5 3.0 1.8 1.9 6.1 2.1 75 91 61~58'~ 95 58 lilt 113 63t 56t 75! 60t 85 58t 93~ 63 2.1 1.9 1.9 1.8 2.3 2.5 2.1 2.5 3.1 2.8 90 81 100 86 63 65t 63 60i 73~ 63 99t 59 93t 59 203 :2 184 23 1Sl3t 24-1 17St 2 174 25 195 26-1 189 2 194t 27-1 243t 2 228 28-1 195 2 202t 29-1 217t 2 216 V4 71 30 31 205 32-1 88 2 45 33-1 17t 2 24 3iv-1 37t 2 17 54t 29 23 12 0034- 250 -25 0.39 0057 248 -37 100 270 -42 14 1.1 74 0.33 0.94 28 22t 1.2 0.41 4J. 38t 0.45 5l:t 1.1 32' 0.83 ~ 1.4 27 1.2 LJ. 68t 20 55 57 46 50t 52 51 236 7t 254 -37 217 -13 242 -22t 230 -25 0.82 279t 62 2.2 242t -34 1.8 323 65 1.5 li5 77t 1.5 1.6 1.2 1.1 li5t 83 140 Ix105 N. Pole D. M. 35-1 358 67~ 0.70 144 77 2 26 38t 1.1 36 20 53t 1.5 147 79 66 80t 37-1 34 1$ 2.6 2 32t 49 2.8 No. V7 .54 55 56 57 58 59 60 71;;32t 3 Z7 357t 33 18 31 12 49 3 18 Zl ~ 5.3 9.1 5.5 2.7 3.4 94 103 118 69 65 68 66 4.7 3.2 103 62 68 76t 80t 75-1 2 76-1 2 77-1 2 77a-1 2 156 140 104 85 110 107 I:x105 N. Pole 80 I$t 3 200 9 1.6 38 1.6 313t -15 43 1.4 72 0.55 330 LJ.t 69t 0.71 114- 0078 355t - 5 16 0.74 V 10 78 79 348 15 37 No. D.M. lei 11 to 1.0 1.8 98t 71t 61 56t 63 64 60~Eo 51 184 65 73 Vll V 8 61 62-1 67t 43 2 45 63-1 36~ 2 33 64 154 65 J.o~ 66 36 67 36 68-1 1# 2 29 69 69 56 47 42t 36~ 34 49t 49 57t 53 52t 51t 67 0.70 0.56 0.63 1.0 0.73 0.50 0.55 0.55 0.53 0.67 0.32 0.39 357 30t 5# 59r J$ 59 296 34 27 34t 66~ - 5 65 74t 70 76 336 62 80-1 28 2 2# 3 27t 81 24 82 17t 83 19 84 352 85 10~ 86 14 87-1 22 2 22t 88-1 22 2 32 89-1 16 2 12 24 90 36 35 31 2.3 1.9 4.3 5.7 28 25 8 31 15t 30 22 23 35 31 30 210\36 6;, 1.9 605 6.7 5.1 5.3 7.1 6.9 4.1 75 73 127 87 81 67 ~ 57 64 58 55 62i 107 1.5 81 64 2.0 60 65 1.5 1.8 3.7 2.7 1.8 180 - 1t 4.2 V 9 70-1 2 71-1 38~3~ 281~ 2 285 3 303 72-1 2l 2 20 :3 5 73-1 358 8 2 53t 60 45 53! 66 53 57 56 52t 56k 65~ 3 24t 74-1 3~.# LJ.t 2 350t 39 0074 0.72 22 0.41 207t 0.44 0.59 1.1 1.0 0.96 68 1.3 '17 67t tv 12 35 9~1 2 79 1.7 95-1 119 2 126 96 316 20 31t 50t 19'7t 37t 331 83 1.5 1.8 1.6 282 - 2 286 - 4 140t 65 V13 97 98 99 100 weak and unstable -1% 141 D. No. V 14 101 360 1 102-1 2 12 103-1 7 2 21 104-1 2 45 28 V 15 105 106 V 16 107 108-1 M- In05 68t 0.74 1.6 1.7 1.1 1.7 1.4 66~ 1.4 49 42t 52t 82t 67 N. Pole D. M. No. 13nt 55t 124 57 V18 126 127 164 129-1 128 60~ '. 147,t 69 2 130 131 132-1 2 133 122t 36 150 -13 346 Z7 200t 11 201t -13 359 66 Z72 60t 239 32 219 31 319 70 Ixl05 N. Pole 0.51 2.8 0.72 2.7 6.3 1.9 1.7 2.3 0.80 1.6 32# 14t 319~ -37t 128 51 249 -4J. 1.7 1.5 1.8 1.2 1.0 1.3 276 -47 160 67t 195 29 217t - 9 181 52t broken 1 1-1 187t 35 2 197 38 2-1 189i 16t 2 201 41 3 71t 55 Lr1 196 17~2 195t 22 5 19~ 17t 6-1 183 27t 2 189t 25 7-1 185 16 2 186t 18 8-1 174 15t 2 179 18 NC 26 53 tIJ 2lt 2 15t 62 109-1 13 59 2 lit 63t 110 19t 59 111 .3L.Ot 56 112 16t 37 113 358t 61t 11 114 7 115 3t 58 116 354t 68t 1.9 2.7 3.1 103 76 141t 75 2.4 2.8 154 3.1 5.3 2.5 3.0 3.7 3.3 2.5 134 75 161 57 93t 64 158t 65t 84 49-~ 147t 68t 173~- 64t 70t 269 -38t 353t 26 263 -42 1.0 260 -40~ 104 0.'l7 278 -41 1.3 1.3 277 -35 1.2 1.6 290 -47 1.1 NC 2 V 17 117 118 119-1 2 ]20 121 122-1 2 123-1 2 124 125 352 47 3L.Ot 47 189t 38t 177t 48 170t 1.$ 12t 46 40t 16 14- 13 3 44t 6 41 20t 52 It 53 4.6 2.4 4.3 5.1 2.8 1.3 4.9 5.3 3.2 3.4 1.6 3.8 138t 58 1L.8 52t 249 - 6 46 2t 44t 120 62 13~ 63t 70t 257t 113 110 65t 35 3# 7t 16.0 7 15.0 10 87 57 5.2 7t - 4 11-1 356t 2t 4.7 102t 63 2 358 4.9 4 12 6.2 29 -10 61~ 45 0.61 128 67 346 13 11~ 22}-10 14 74 IIJ 4.3 15-1 31 - 3 3.1 57t 46 2 26 - 7t 3.8 10 - 9 88 54 16-1 7.7 8 -11 2 7.8 9-1 1$ 2 46 142 No. Irl05 D. M. N. Pole NO3 17-1 2 18-1 2 19-1 2 20-1 2 21-1 2 22-1 2 332t 3t 15# 155 153t 152 102 95 51 - 6 - 9i 3 5 3t 6 17 23 35 1$ 33~" 16 - 4 14t 3 6.1 6.3 3.9 ~5 3.5 3.3 3.9 3.7 4.4 2.7 5.3 5.6 120 326 59t 37-1 -57t 38-1 2 39-1 2 40-1 2 41-1 2 42-1 2 43-1 2 44-1 2 45-1 2 46-1 2 47-1 2 L.8-1 2 328t -57 5 -tt 18t 32 73 53 NO 4 23-1 2 24-1 2 25-1 2 26-1 2 27-1 2 28-1 2 29-1 2 30-1 2 31-1 2 32-1 2 33-1 2 34-1 37 '6 43t 36 129 129 105 98 279 277 54 1;0 319t 31$ 172 173 177~ 194 289 193 302 31;0 227 2 143 35-1 176t 2 172t 36-1 65 2 158 55t 52t 20it 21 9 5 23 28 8 6 26 55 51t 4l 14 11t 29 50 41 16 43 25 75 70~ 2 4 76 73t 0.40 0.40 1.0 106 5.4 5.0 0.89 0.92 4.2 404 0.84 0.67 0.33 0.62 0.91 0.72 0088 0.77 0.63 1.0 0.82 1.0 0.74 0.89 3.1 2.7 0.94 0.65 348 6ti 31 45 345l-30~ 353t - 3t 191 8 20It 2 D. 162t 1CJl 205 164 160 178t 176 194 219 215 241 274 178~Z76 53 181 224 229t 174 187 202 21;7"t 7 289 M. &>t 27t 33 4# 49~ 49 39~ 40 32t 4J.2 75 67 52!83 59~ 43 56 69~ 28t 45 34 59 69 55 IrlO5 N. Pole 1.1 1.1 2.1 2.1 103 1.7 2.3 1.8 0.69 0.66 0.38 0.50 0.70 0.73 0.48 0.90 0.45 0.33 0.88 1.1 0.90 0.57 0036 0.50 274 -37 271~ -iIJ 288t -33 274 -i;fJ 241 -31 245~ 6 273 -15 300 -lot 251 -13 279t -42245t -25 248 21 90t 92 9# 93t 95~ 98t 106~ 55t 54 57t 58 58"2&>t III 61 9 41t 70 292 -50t 279 -37t 233t -17t 181t No. NO 5 56 NO 6 49 6t -14 50 6~-- -16k51 4 -ll,t 4 - 9 52 53 3 -8 54 1~-9t 55-1 357 - 7t 2 357 - 4 56 355 - 4 5.4 4.6 5.3 6.1 5.3 503 502 3.6 2.6 58t 285 -13 290t -58 303! 13 NO7 57-1 220 20 2 308 56t 58-1 51t -49 2 67 -49 59-1 303 87 60 2 255 60-1 248t 38t '2 2&> 41 0.63 0053 0.95 0.90 0.50 0.71 1.7 103 234 -11 15 -51 262 ot 226~ - 9 143 No. 61-1 2 62-1 2 63-1 2 64-1 2 D. M. 259 265 205t 208 .30.3 314 29 126 50t 45 21t 1~ 37,t 34 72 70 Ixl05 N. Pole '0.43 0.65 228t - 1 2.2 246~ -45 1.8 0.94 206~ 28 0.73 0.42 310 7t 0•.33 Ne 8/550 Oe. 65-1 142 178 2~ 29t 38t 29 55 .36 62 6.3 7# 57 62 1.3t .39i 2 1iJ. 198 66-1 5i208t 1 2 161t 67-1 214 1.38 2 202 228t 68-1 26~ 177 2l 2 29t 50t 164 72t 69-1 303 78t not .32 2 343 55 155 47t 70-1 352t 22t .332 74t 2 337~- 38 182 20 21 46t 71-1 110 54 2 l7t 36 332 57t 72-1 175 200 32 2 200t 50 1.89 20 73-1 320 73t 165 28 2 250 74 151 42t ~t 1.3 0.98 10.3 1.1 0.75 0.58 0.98 0•.39 1.0 0.18 1.1 0.66 0.84 0.28 0.96 0.35 0.jJ) 0.69 0.67 0.52 0.88 0.18 0.59 0.64 0.53 0.21 0.55 0.38 0.56 0.57 0.44 0.51 0.76 0.17 0.59 0.39 268t -46 267 -32t 255 -45 284 -37t 323 -25 267 -26 29# 25 259~ -/let 303 -q No. Ne D. M. Ixl05 N. Pole 9 74-1 357 - .3 2 # 75-1 2r 2 32Sf 4 76 5 - 3 77 16~ 14t 78 2 355 broken 79 80 9 10~ 81 10 II 3~t 1•.3 1.4 2.3 2.1 1.3 1.1 1.2 1.4 1.5 92 57 141 55 92~ 64 109 55 57 59 77 72t 5~ 59 APPENDIX 1. H: COI\1MENTS ON PROCEDURE Rejection AND CONCLU~IONt) Criteria "for Sedimentary Outcrops The final analysis of the sedimentary pole positions include the data from many of the outcrops. These outcrops were rejected on the basis that they contained unstable remanent magnetization did not components of which could not be removed with demagnetizing fields as high as 550 De. Several of the magnetic vector demagnetization paths for some of the igneous rocks are shown in Part I. noticed that the magnetic vector generally during the demagnetization been removed. vary randomly about an average many sedimentary demagnetization moves in a given direction procedure until the unstable ~urther demagnetization component has causes the magnetic vector to direction. The magnetic vectors of outcrops also moved in a constant direction procedure. It is However, after demagnetization during the in fields as high as 550 Oe, many of these showed no tendency to vary randomly, indicating that part of the unstable As an example of this behavior component still remained. several of the magnetic vector paths for outcrop number NC 8 are plotted in fig. H-l. The initial direction is given, as well as the directions after demagnetization in fields of 250 Oe and 550 De. values of the demagnetizing field fell along these paths. Intermediate Although the vectors seem to be moving toward the same area it is clear that further demagnetization is required. Hence, when the magnetic vector continued to move in a given direction after the application the outcrop was rejected. of 550 Oe demagnetizing fields, N 64-1 ,, I I +!,, w E I I , 60-1 ~, ,, ,,4, ,, " ,, ,, , " ",, ,, ,, ... , ,, , J s FIG. H-l MAGNE~'IC VECTOR DEMAGNETIZATION PATHS Even if larger demagnetizing fields had been available may not have been possible to remove the magnetic intensity the unstable components it still because was approaching the limit of the instrument (2.5 x 10 -6. cgsu Icc for 10° accuracy.) Also, in the 10 -7 cgsu I cc range, the magnetization (see ~agata, 1953). may not be meaningful Table H-l contains the original direction direction after demagnetizing of magnetization and the in 250 Oe and 550 Oe fields, respectively, for several samples from each outcrop. Those outcrops which were rejected because of the above criteria are marked vuth an asterisk 2. Influence of Earth's Field The average direction of magnetization in Part I. for each outcrop is shovm It is possible that the present dipole field) has influenced the outcrops. (*). the direction earth's field (or axial of magnetization of some of This is evident in Part II where it is noticed that several of the circles of confidence include the magnetic dipole axis. It is doubtful, however, that this influence has affected the results to any extent. The geologic attitude of the beds unfortunately displaces the original average magnetic vector of many outcrops toward the earth's field. However, there is no general tendency formation to show consistent influence for anyone of the present Fig. 11-8 indicates that the geologic correction directions of magnetization together. geologic earth's field. has brought the average Many of the circles of confidence that included the earth's field before correction did not do so after correction. The rejection of several outcrops from the final analysis most of the earth's field influence, although perhaps not all. eliminated Ta.b1eH-1 SEDIMENTARY DEMAGNETIZATION VALUES No. D. M. No. M 5 33-3 35-3 38-4 J 30-1 352 10 354 354 12 5 10 23 9 1 1 4 350 352 328 359 355 40 47 39 22 20 22 13-2 14 3 21 42 44 42 36 32 34 29 24 27 4 27-1 9 1/2 20 1/2 1/2 41 12 2 11 356 359 5 50 48 44 36 44 32 43 40 45 67 1/2 P 8* 62-1 64 60 70 37 41 46 42 47 52 1/2 56 50 347 350 348 336 345 342 44 40 45 21 1/2 25 27 33 29 35 56 95 60 49 4l 47 42 44 46 353 10 2 1/2 15 28 23 31 1/2 25 27 13 1/2 14 15 61 1/2 59 58 59 1/2 51 44 50 45 52 44 1/2 50 42 270 232 205 58 55 40 P 7* 53 D. M. 248 221 206 274 246 228 42 35 25 42 34 17 335 273 266 276 263 256 35 346 271 28 - 8 47 27 2 68 79 64 60 P 12* 96 100 1/2 355 1/2 354 359 12 15 13 17 13 16 20 1/2 2 15 353 349 354 p 5 J 29-1 54 67 J 26 2 16 43 44 39 1/2 28 26 21 2 1/2 7 11 42 45 P 2 2 11 335 340 330 No. 56 P 1 1 7 1 J 72 69 73 56 49 52 65 1/2 56 60 1/2 D. M. P 13 101 102 346 69 297 55 280 26 66 247 251 43 . 10 254 6 284 1/2 283 -13 288 -36 352 358 334 347 345 359 59 54 47 40 32 33 No. P 15* 116 119-1 120 D. M. 250 59 1/2 258 50 263 35 8 1/2 215 208 - 8 194 -22 346 54 1/2 343 54 339 1/2 55 112 No. 19 21 V 3* 22-1 26-1 Md 1 2 4 6 Md 2 10 14 17 353 359 355 352 1/2 2 356 352 1/2 358 357 54 56 45 4247 41 31 1/2 40 29 29-1 V 4* 31 32-2 18 15 17 1 1/2 358 3 13 14 11 32 35 29 20 19 22 26 24 32 35-1 54 57 29 31 V 2 18 19 1/2 16 17 344 1/2 350 351 352 348 355 58 1/2 64 56 29 1/2 27 34 37 1/2 4239 59 V 8* 61 64 8 10 7 35 1/2 40 38 No. 71-1 73-1 76-1 203 191 186 189 186 185 217 1/2 196 178 54 1/2 38 20 28 13 1 27 28 20 205 208 5 45 62 42 358 6 14 20 61 79 57 56 51 67 1/2 55 42- V 7 1/2 358 16 18 21 15 3 1 9 32 1/2 35 27 31 40 39 27 V 12* 69 67 1/2 50 38 154 138 107 69 50 39 56 47 31 49 1/2 49 4267 56 40 281 1/2 302 332 358 358 359 156 126 54 45 54 55 52 1/2 42 31 38 65 66 348 319 282 15 359 336 53 40 37 40 39 24 20 23 352 2 1 22 19 20 28 32 34 31 34 29 35 40 32 V 10* 78 79 60 11 81 84 88-1 94-1 96 22 28 D. 1'-1:. V9* V 7 Md 3 26 2 358 3 4 10 2 D. M. 27 25 29 32 33 39 V 14 101 103-1 282 260 234 316 270 216 - 2 -22 -24 50 1/2 66 54 360 15 2 7 24 5 49 47 54 82 1/2 61 57 No. D. M. V 16 107 III 114 V 17* 117 121 124 V 18* 126 128 131 No. 12 26 34 27 340 1/2 2 2 11 15 2 53 58 54 56 43 49 7 34 37 14 3* .18-1 22-1 NC 154 1/2 - 3 li8 2 85 7 102 17 81 28 60 28 16 -4 8 13 11 22 4* 23-1 32-1 122 1/2 36 27 148 172 19 27 346 67 336 69 194 272 60 1/2 60 222 189 40 29 -10 34 - 6 2 15 22 1/2 -10 24 -15 17 - 4 No. 56 34-1 36-1 5* 38-1 55 1/2 46 32 4l 12 - 8 75 68 48 76 64 42 57-1 60-1 62-1 64-1 68-2 72-1 1* 1-1 3 6-1 187 1/2 35 189 29 16 184 71 1/2 55 110 62 162 46 183 27 1/2 184 19 6 187 40-1 47-2 205 198 189 176 180 183 247 1/2 216 200 33 28 26 39 1/2 31 19 59 52 39 38 1/2 14l 161 32 178 29 1/2 29 1/2 50 1/2 70 52 72 1/2 135 175 48 1/2 190 42 200 33 9 75-1 NC NC 220 20 206 16 12 195 248 1/2 38 1/2 218 4l 192 32 205 1/2 21 1/2 18 195 187 10 72 29 171 70 182 40 8* 65-2 NC - 4 -10 - 2 7* NC NC 37 22 12 289 298 309 227 208 229 65 12 358 D. M. 355 356 358 NC 20-1 352 47 359 40 31 3 12 1/2 46 12 35 10 24 1 1/2 53 7 44 10 36 D. M. 77 81 333 340 342 16 14 19 10 5 9 1/2 2 1/2 5 1/2 -19 1/2 14 1/2 19 1/2 20 11 6 15 NC 6 NC 10 2 49 7 1/2 - 4 -10 348 .2 -12 52 6 1/2 -14 8 -15 5 - 4 4 - 9 6 - 5 7 -15 * Rejected from final analysis With the Massachusetts All of the outcrops sandstones seem to have been influenced Also, the geologic correction displaces away from the average direction probability the situation is very different. by the earth's field. the magnetic vector directly of the other formations. that the iron in the sandstone ,It'inally,the was derived from the Deer- field Diabase further suggest that the magnetization may be later than Triassic. 3. Reduction of Scatter ~ Geologic Correction It has been stated in Parts I and II that the geologic correction has reduced the scatter among the average outcrop directions most of the areas. 95% probability magnetization As evidence of this, the circle of confidence has been calculated for the average direction of the outcrops before and after geologic Only those outcrops which were included been used. for of correction. in the final analysis have This data is given in Table H-2. The lack of significant variations the area tends to minimize scatter. within the influence It is noticed, however, circles of confidence of the corrections but can be inferred on the that the outcrops with the smallest show a better reduction with large circles of confidence. statistics in the strike and dips wi thin in scatter than those This point is not demonstrated from the illustrations ~~th in Part II. In the igneous areas, only Nova Scotia showed an increase in scatter with correction. Pennsylvania sediments. So was the case with the Maryland-vlest However, both of these increases were less than the corresponding areas. decreases of scatter in the other Also, note that the overall influence four areas was a significant reduction of scatter on the sediments in scatter. from the Table B-2 INFLUENCE OlF GEOLOGIC CORRECTION Area Igneous N. S. Mass. - Conn. Pa. - Va. Sed. e95 (Original) 80 8 1/20 7 1/20 Md. - W. Pa. 8 3/40 Avg. (sed.) 8 3/40 16 1/40 13 1/20 N. C. (Corrected) 18 1/20 N. J. - E. Pa Va. e95 90 10 1/20 14 1/20 130 170 12 1/20 90 6 1/20 BIBLIOGRAPHY Since most literature find, the bibliography directly coverage is relatively includes only those articles concerned with this report. particularly worthy of mention, Several Nagata easy to which are selections are however, because of their extensive of a topic or because of their comprehensive They are: Irving on rock magnetism bibliographies. (1953), Watson and Irving (1957), Rimbert (1958), (1959), and Thellier (1959). BIBLIOGRAPHY As, J. A., and J. D. A. Zijderveld, Geophys. Jour. Vol. 1, p. 308, (1958). Beams, J. W., Rev. oci. Instr., Vol. 1, p. 667, (1930). Belshe, J. C., (private communication) (1959). Bruckshaw, J. McG., and E. I. Robertson, Jour. Sci. Instr., Vol. 25, p. 444, (1948). _____ , and S. A. Vincenz, M.N.R.A.S., Vol. 6, p. 579, (1954). Chapman, S., and J. Bartels, Geomagnetism, Press, (1940). Geophys. Supp., Vol. I, Oxford Univ. Clegg, J. A., M. Almond, and P. H. S. Stubbs, Phil. Mag., Sere 7, Vol. 45., p. 583, (1954). _____ , E. R. Deutsch, C. W. F. Everi1l, and P. H. S. Stubbs, Phil. Mag. SuPP., Vol. 6, p. 219, (1957). Cox, A. A., Nature, Vol. 179, p. 685, (1957). Creer, K. M., Ann. de Geophys., Vol. 14, p. 373, (1958). Doell, R. R., Ph.D. Thesis, Univ. of Calif., Berkeley, Calif., (1955). _____ " Trans. Arner. Geoph.vs. Union, Vol. 37, p. 156, (1956). DuBois, P. M., E. Irving, N. D. Opdyke, ~. R. Runcorn, and M. R. Banks, Nature, Vol. 180, p. 1186, (1957). Fisher, Sir R. A., Proc. Roy. Soc. !, Vol. 217, p. 295, (1953). Grabovsky, M. A., Ann. de Geophys., Vol. 15, p. 119, (1959). Graham, J. W., Jour. Geophys. Res., Vol. 54, p. 131, (1949). , Ibid, Vol. 59, p. 215, (1954). , Ibid, Vol. 60, p. 329, (1955). _____ , A. ],i'. Buddington, and J. R. BalSley, Ibid, Vol. 62, p. 465, (1957). Graham, K. W. T., and A. L. Hales, Adv. in Phys., Vol. 6, p. 149, (1957). Green, R., Nature, Vol. 182, p. 382, (1958). Haigh, G., Phil. Mag., Vol. 3, p. 267, (1958). Hargrave, R. B., and A. G. ft'ischer,Geophys. Jour., Vol. 2, p. 32, (1959). Hood, P. J., M.A. Thesis, Univ. of Toronto, Toronto, Canada, (1956). Howell, L. G., J. D. Martinez, and E. H. Statham, GeophYs., Vol. 23, p. 285, (1958). Irving, E., Geophys. Jour., Vol. 2, p. 51, (1959).' Johnson, E. A., and A. G. McNish, Terr. Mag., Vol. 43, p. 393, (1938). _____ (1948). " T. Murphy, and O. W. Torreson, Ibid., Vol. 53, p. 349, _____ " T. Murphy, and P. ~'.Michelson, Rev. Sci. Instr., Vol. 20, p. 429, (1949). Kalashinkov, A. G., Ann. de Ueopbys., Vol. 15, p. 67, (1959). Krynine, P. D., Conn. State Geol. and Nat. Hist. Sur., Bull. 73, (1950). McLearn, F. H., G. S. A. Bull., Vol. 64, p. 1205, (1953). Magata, T., Bull. Earthq. Res. Inst. Tokyo, Japan, Vol. 21, p. 1, (1943). _____ , Rock Magnetism, Meruzen & Co., '!'okyo,Japan, (1953). _____ , T. Rikitake, and K. Akasi, Bull. Earthq. Res. Inst., Tokyo, Japan, Vol. 21, p. 276, (1943). Neel, E., Ann. de Ueophys., Vol. 5, p. 99, (1949). _____ , C. R. Acad. Sci. Paris, Vol. 234, p. 1991, (1952). Petrova, G. N., Ann. de GeophYs., Vol. 15, p. 60, (1959). Reeside, Jr., J. B., et ale G. S. A. Bull., Vol. 68, p. 1451, (1957). Reinemund, J. A., U. S. Geo1. Sur. Prof. Paper 246, (1955). Rimbert, !t'., D.Sc. Thesis, Univ. de Paris, (1959). Roberts, J. K., Virginia Geol. Sur., Bull. ~, (1928). Runcorn, S. K., Ann. de Geopnvs., Vol. 15, p. 87, (1959). Serson, P. H., and W. L. "'1.Hannaford, Canada Jour. Tech., Vol. 34, p. 232, (1956). _____ Thellier, ., Canadian Jour. Phys., Vol. 35, p. 1387, (1957). E., and O. Thellier, Ann. de Geophys., Vol. 15, p. 285. (1959). Watson, G. S., and E. Irving, p. 289, (1957). ~l.N .R.A.S., Geophys. Supp., Vol. 7, Willard, 1'-1.E., Bedrock Geology of the Greenfield Quandrangle, i~J.ass., U. S. Geolo. Sur. Geologic Quad. Maps, (1952).

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