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 BULLETIN OF THE GEOLOGICAL SOCIETY OF AMERICA 
 
 Vol. 9, pp. 223-238 
 
 CLASTIC HURONIAN ROCKS OF WESTERN ONTARIO 
 
 BV 
 
 ARTL. :l P. COLEMAN 
 
 ^^y^^try. 
 
 ROCHESTER 
 
 PUBLISHED BY THE S0CIP:TY 
 
 February, 1898 
 
BULLETIN OF THE GEOLOGICAL SOCIETY OF AMERICA 
 
 VOL. 9, PP. 223-23« FbBRUARV 2., ,«3« 
 
 CLASTIC IICUOMAN RuCKS OK WKSTKIJX ONTARIO 
 
 i!V .virnni! p. coi.kma.n 
 
 {Read hrfore the Snnclij Thrvmhcr J!), 1S!)7) 
 
 (X)NTKNTS 
 
 Ua«iiItH (,f provioiiH work in tlio region. ''"»■"■ 
 
 t;iiissifi,.ati,,ii of (he rofk .-^erioK, .."... "•' 
 
 Huroniiin clustic's ~-^ 
 
 < ioneral .stati'incnf a.s to origin ..'''',\\ "■* 
 
 KiHMvatin rocks —-♦ 
 
 Conch idling rocks , \\ --''' 
 
 Helation of K.>(>watin to Concl, idling' "" 
 
 Tiiickiici^s of till! Hiironian scries "'' 
 
 Field relations of Lanrentian and Hnr.'.niaii "^ 
 
 Sections tliro.igh |.re-ranil.rian .no.intains. "" 
 
 (n'ologicalhistory of the re-ion -•'" 
 
 Comparison with oth-- regions -•'' 
 
 Cause of these mountain structures . -''- 
 
 Kxtent of the hatholitic region -■'•' 
 
 Concluding ohservatioiis ■' ' -•'•"' 
 
 2;!S 
 
 Kksults of |'k,.;vi...-s uokic rx tuk Rk(ii..n 
 
 . The -odes of we.ster.1 Ontario have been more or loss carefullv ex.n» 
 nK.l y several .eolo.ists, sueh as J.,sl>v, Hell, and I^t \^X 
 
 y t' hv"^ r 7T' " "T • ?'" "■'•^ '''''' '' '''' '-'^' ->--^ ^ 
 
 St! V n V T!' "; '" '""' "" '""''^^'"'^ fottndation for the future 
 tn.ly of the Lake ot the Woods and Rainy Lake districts.* Since e 
 a«llo.nn,, .hstncts have been ,nap,.ed hy W. If. r. Smith and Vd 
 ne^ and specuU portions have been studied bv H. L. Sn.^th Winctn 
 and Grant, and the prese.tt writer. The ,eneral eonehtsion ;!' b v 
 Lawson have been eo.nn.only aceepte.l by those who have followed an 1 
 wUHu^ade use of largely in the present paper, though .no o th 
 
 *ii.M,|.Surv,.y„rc,miul,.,lss;^, ,„„•((■(■; un.i [s^.i^i^uy 
 XXXIV-Bn.i.. (iKui.. .s,„. .\.M., V(,i. -J, 1SU7. 
 
 {2L';i) 
 
224 
 
 A. v. COI.KMAN — CI.ASTIC II li« >NI AN KocKS, 
 
 facts cmployiMl lum- Lccn ..l.s,.nT.l l.y tlir writer wl.il.- .■n-ii.inl in lifl.l 
 work for tlic Oiitjirio Hiirciiu of Mines. 
 
 ('l.AS-^Il'IfAIMnN <>:• I'lIK IJotK SkHIKS 
 
 r.awson .les.Tihes tl.c n-ion as wholly Aivhean. and .livi.les the rocks 
 into two i)arls-a lower one, the l.aurcntian, an-l an npi.er (.nc, the Onta- 
 rian, further subdivide.! into the Coucliiching and the Keewalin. 'I he 
 tenn Laurentian is used here in a petroKrai-liic sense, to denote a series 
 of entirely crvstalline, <ienerally acid, rocks, esi-ecially coarse- grained 
 jrueisses and jiranites, in spite of the fact that these rocks have an oruptivo 
 contact with the overly inj: series, and so are later in a-je than the Ontanan. 
 The fouchichinu rocks, found chielly in the southern portion ol the 
 reuMon alon.i,' the boundary of Miiniesota, consist in general <.f nionot- 
 on'ous grav or hrown micaschists and gneisses, sedimentary in origin. 
 
 The"Keewatin. wlii.'h overlies the Couehiching where the latter is 
 present and in other cases rests on the I>aurentian. is largely composed 
 of eruptives and their products-schists resulting from shearing, ash 
 rocks, and aiiglomerates— basic in the lower part, acid in the upper.* 
 
 Lawson d()cs not delinitelv correlate the Couehiching with either the 
 Laurentian or lluronian, but Van 11 ise includes at least part of it in the 
 HasenientCon.plex.t l.awson puts the Keewatin doubttuUy with the 
 lluronian. pointing out numerous dilVerences between it and the original 
 lluronian as described by Logan. In general, however, Canadian geol- 
 ogists .lo not hesitate to class these altered eruptives and the accompany- 
 ing sedimentary rocks as lluronian. and this usage will be followed m the 
 
 present paper. 
 
 In the first place the lluronian clasti<-s will be briefly descrilxxl, and 
 afterwards the relations subsisting l)etween the series of rocks and their 
 causes will be discussed. The term .\rchean will be used to include both 
 Laurentian and lluronian (,or Ontarian), though according to the classi- 
 fication adoi)ted by the United States (ieological Survey the latter would 
 be included in the .Mgonkian. 
 
 lllKOMAN Ci.Asru's 
 
 (iE.\Eirii. ■•^rAri-:Mi-:.\r AS yo o/,'/(,/.v 
 
 As to origin, the .Archean <'lastic rocks of western Ontario are of three 
 kin.ls— pyiH)clastics, autoclastics, and sedimentary rocks proper. 
 
 The pyroclastics. consisting of agglomerates, ash rocks, e tcetera, are of 
 
 *i.r.il. Survi'V 111' (':iii:icla, 1SX7, |>. '.i'A F, »'t<'. 
 
 f 
 
 • ••.», , - • • 
 
oiUfilV. 
 
 •>•>." 
 
 'Z^tuli-t ;""""-^=7-'-''"t'-- "-l-iul l.un..,.,n tlH.sul.i..ts 
 
 i— Mn,Ml:n- Mo,.|<,sorn.d< .oul-l hanlly Inv.- 1.....,, Inn-I.-.l int. 1 r 
 
 "•^ '7"''^- ''=^»'-"' • -ti-"^ fansit s l...tw,.,.n a,..lo„u..U,.s , fn ' 
 
 -...lon.eruh.s with ..u...rn p.l.i.les, .,.iH. ...i.hn.u :.. : 
 
 volcaiuc iimtmuls.lr,,,, into thesoa. ' '"""""*-' 
 
 'Hh" a..tn,.|asti,.s a,v not very oxtensiv,. an.l will n.-ivlv 1... Mu-ntion.-l 
 ^^;m.p..odu...Il.ytl.eaaio^..f,.n.hi^,a^.lslH.a^nK^ 
 ' ' ^' tho love) wh.r. prossu.v pn.,!,,.. plastintv, an.l t .iv.a hint 
 
 iiHMitioiuMl, ar.' the 
 
 - .own to nus onntfn, ,1,. .ruptivos alr.a.ly ..,,.,,,, „,, 
 
 n.H..st.,n.. hro,.c..a.s ot St.ep RuHc ia|<o and rortain n.n.lon.erates to L 
 s-n a nule wostof Fort Fran,.c.s. wIum-« in tho sharp lol.Hn. n t 
 
 .. san. ston. ..tw... lay.rs of sH.ist the latt.r has yiH.ir.| p s r 
 
 u loMu.r was i,ro,<.n to fra,nu.nts now ,.n.l.,..,...d , Jpehhlos [^^ 
 
 I 1... ordinary Hashes, tr,.. s,.,|in„.nts, ar. orsp...iai intnvst as .ivin-. 
 e ear ., eas o, the ,.on.liti..ns of ,h.. .inw. an.! so will h. .l..s.ril -.f . ^ 
 at length than the two previous .roups. The Keewatin. tho . v v 
 h -Koly o ernpt^vo origin. ....ntains in.portant s,.lin.en, rv n^ >S 
 and the Loueiuehmg is wholly sedimentary. ' ' 
 
 KKF.WATIS IIOCKS 
 
 The wator-tbrined rlasti<.s ofthe Keewatin areofunvat varietv inelu.l 
 n.g Inuestones. slates, ,uartzites. ,rits. .raywaekes. I.reeeias, a " i p t 
 and houlder eon, .n.erates. The lin.estones are, however of l"' 
 
 U'OL hen,, .nnd ,n any thiekness only at Steep IJoeIc lake. 7,. n U. 
 east ol i.nny lake, wh.re there is a sn,all area dillerin. hoth petro-r., . 
 |-ny and strnetnrally tronMlH. rest or ,h.. .,,i..n/ Tln.s.';ii;;;;^ 
 .ave a very n.odern look, hein, seareely at all erystalline in appearance 
 iKmn, ..herty layers ,n ,ray lin.estone at son.e points an.l lIlLk v^^: 
 •jH ......eeous h.ls at^.,th..,.. One alnu.st exp.^ts to .liseover Ibs^iJ " 
 
 then,, hut none l,av.> h.HM, found. Thev have hee.i fol.le.l in an ext,-vo • 
 <l.na,-y way into an antieline and syneline havin, their axis inelin. H i 
 or moi-e degrees* miMio oi) 
 
 Theslatcsare wi.lesprea.l, passing oCten into phvllites. .Manv ..f then, 
 .'ontan, earhoua.'eous .natte.-, and .son.e exa.nples have a ,raphitie 1... 
 and^.MHlK.Jin,ers. One ot" the,n. n-o.n an u.lab'sis hy i;;. la^^:;^ 
 
•J2»l 
 
 A. r. (OI.KMAN — CLAS'llC III IU»NIAN UO( KS. 
 
 touiid to (•..iitiiiii 7.11 iMT (•(.iit<)rcarlM.n,i\n(l is porous as tliou^'li liydro- 
 carlions liail volatilizi'tl Icaviuf,' roiinl cavilii's.'^ 
 
 'riM'so.arl.oiia.fous slates may l.c company with tlif i)lack hIuIc of the 
 Su.lhury n,-ioM. in wlii.h Dr Kllis has f(.uiul ('..S per (•cut of carhoiMUul 
 whirh was at one time l.ilumiiious. as shown in Halt'our township l.y a 
 larire vein of anthraxolite, once no doiil.t a Ihiid or i.histie petroleum 
 
 product.! 
 The widespread -ray wackes need o.dy h(Mii<'ntioMe<l, since they present 
 
 no points (.1' special interest, and the same may he said of the somewhat 
 unusual qiiartzites and ^rits, hut the con^ilomerates are of more impor- 
 tuuee. Thev are iounil in many localities, hut only one example will lie 
 taken for dJscrij.tion, that of Shoal lake, more thorou-ldy studinl than 
 the others hecause occurrinij: close to a numher of ^old-hearing' veins. 
 
 As .seen on the shore of the lake, it is a Bchist-con^domerate consisting 
 of ^q-een chlorite as a matrix, with well rounded pehhles of all sizes up 
 to two feet in .liameter emhedded in it. That this portion of th« con- 
 glomerate has underjione shearing is slu.wn l.y the llatteninK an.l even 
 tailinji out of .some (.f tne softer pehhles and the hreakin-? and shifliuK 
 of the'i.arts of some of the harder ones. The <-ommonest rock species in 
 {\n- pehhles arc (piartz porphyry and i.orphyrite, felsite,aiid «;reen schists 
 indistinj,niisliid)le from adjoining' Keewatin schists. In addition, there 
 are fra^nnentsof hlackand red (luartzite and of white, pulverulent .sand- 
 stone, of vein (juartz and of anorthosite. No gneiss or granite has heen 
 found after careful search, though some (lua^lz-porphyries having the 
 crystals of felspar and dihexahedra of quartz much crowded, look, at first 
 glance. v.M-y like granite. Most of these pel)l)les are easily matched hy 
 Keewatiii rocks, sometimes, however, many miles distant; a few are 
 evidently t'oucliiching. and none are Laurentian. One rock, a ([uartz- 
 parphvrv. half ma<lc up of heautiful spherulites having feathery inter- 
 growths of .piartz and felspar, has not hitherto hecn recognized in Ontario. 
 Two or three miles north of Shoal lake and some distance across the 
 strike the n.rk hccoiues much less schistose, has a coarse grit as matrix, 
 and might almost he (lescril)ed as a hreccia, since many of the pehhles 
 arc scan'cly rounded. The pehl)les are, however, of the same rock si.ecies 
 as those on the sliore of the lake. 
 
 This hand of conglomerate is at least K) miles long and 2 miles wide. 
 Its thickness can hardly he less than a mile and may he almost douhle 
 that, since the dip is steep, hut a covering of sand [.revents very accurate 
 measurements of th(! width. A very similar conglomerate appears on the 
 east shore of I'ppcr .Maniti.u lake, ")(» mil.'s to the north, containing por- 
 
 *(Jfol. Siirvi-y of Ciiimila, 1HH.\ PP- f'". 12+, nnd loO, CC. 
 
 toiiliirio Hun'Mii of Mim^^ U.'lMirl, Iwic, p. I.V.i, <'tc..t..ni. 
 
^ima 
 
 KKKWATIN ASK rn| ( || I( M l\(i ItocKS. 
 
 '>'>: 
 
 J'l.yr.y l,.|sit... .,i,M.f/.it,., ,.tr..tn-a, un.| a (ino ,.xan.|.l,, is fouiul at I{at Per- 
 tu..'.-. tiK. n.atnx ... this ..„•.. I.uuvv.t. Im-!,,. s,.,i..iti,. insfa.! ufrhlnritic 
 Numon.iw other n.stan.u.s a.v fouM.i in various parts of tlu- rcKion. No 
 
 '';: ■ ''"■^ ^;' "•••' ;"" " >"''l'"'l>- ''^"uvntia., l.avo iKMM, reported fron, unv 
 
 '•1 <l'|-'". though ^M'a.nte hoMl.h.rsare rou,nl,as. fur exainph.. near AhranH 
 
 Z'n''n ;'"'''•''''''''"'■■ ''''"•>• ■•-'•"'•'-■''-ly.'n.ptive.ranitoH 
 ..e.ni ^. the Keewat.n „, ..ei.,!.l.orin;. inralities. an.l .iiller in appearanee 
 "■""I the clianieteristie },'raiiite of ih(! Imurentian. 
 
 rnniiiriilMi Iim-K.^ 
 'I'la- ('.......hiehin,!,' rocks are ail lornn.l of san.l or ehivev san-l more or 
 
 U-ss n.etamorph..s.,l. The least ehan,,re.l werefo.nnl hv' the writer on the 
 HlM.re oi I.an.y rn er a n.ile l.eluw Fort Fran,-es a.ul at the Seran.l.le nm.o 
 near Kat I ortaj,'e. Tiiey lorn, thin Ih.Is of yell,.wish or l.rownish soft 
 san.lstone lynifr I.etvveen n.ieaeeons an.l ehloriti.- sehists. I'nder the 
 "Men.seope. hesi.le jrrains of .p.art/, there are partieles of magnetite an.l 
 
 "iMnerons sn.all prisn.s, pro! ly of tren.olite. In .enerul, however, the 
 
 ( ou.h.eh.nfr consists of hiotite sehist or j,meis.s. the .pmrt. showin-^ a 
 castK. or,j,nn. Some of these schists contain sillin.anite; more rarelv 
 
 Ihey appear as tiH.rouuhlycrystalliMejrneiss containing nu,s,.uvite.,niero. 
 cln.e, etcetera. reseml.Iin^ the adjoining Laiircntian and lorming transi- 
 tions toward it. 
 
 The Couchiol.inK inelu.Ies no ..oarse elasti.s and is nowhere separated 
 from he underlyn.fr F.aurentian l.y a i.asal eon^domerate. These rocks 
 luive b,.en mapped l.y F,awson. Snuth, and Mclnness as coverin-^ exten- 
 sive areas in the southern part ..f the re,,ion. l{ocks of a si ar 'kind 
 
 '•••'•ur on Mamtou lake, near the lake of the Woods and at other points, 
 I'lit have not l.eeii separated in the mappinj^. 
 
 IvKl.ATIoN OK KkiaV ATIN To ( 'on II KM l.Nd 
 
 F.iwson su-ests that the Shoal i,ake and otl,, r conulmncratcs repre- 
 sent the hascof the Kccwatin, and so indicate an un,.onforn>itv hetween 
 
 thekccwatmand.lH.Couchichin.-^Muitthclindin.M.fmanvKeewatin 
 peN. es ,n the e,.„glomerates opposes this view. .\ striking, evi.lence 
 
 hat the l.reak represented l.y these conglomerates comes hi,d. up in the 
 ke..wat^.n uistead of at its has,, just ahove the (V.uchichin^ is to he thund 
 at Shoal lake, where a d^sy i.oulders of coarse--i lind anortho:ute found in 
 
 he schist con,i,domerate are exactly like portions of a hoss of an<.rtho.ite 
 two nules away. As this anorthositc. an-a contains masses a.id strips of 
 eharactenstic Keewatin sehist swept olV durin- its eruption, it is evident 
 
 ♦linil. Siirvrv of (mm;!!!,'!, Inst, ;>, si, K, 
 
''2S 
 
 A. I'. «n|.i;.M AN — < I.ASllr ||i litiM AN lioi KS. 
 
 tliat ill) iip.iiiciisc liipst' itf tiiiir s(>|i:ir!Ut's tliP (■oii;,'|<)iii(>nitf iind tli*' un- 
 tlorlyiii;; Kcfwaliii. loiii.' ciioiiu;!! I"i" ii cinirsc-^'niiiicil iiliitunic rock to 
 Hitlidily, |ii'nl>al>ly nt ciiiisidcnililf (lc|itlis. ami tlu>n lot- tlic i-t'^;ioii to lio 
 so |irol'oiiii(lIy irodcil as to inciviilf |ii'l>l»l('s of tlir iiliilnnic rocU on a 
 sfashoi'c. It is prolialtlf that llic Kecwatin coii^loiinTatcs wliicli liavo 
 lu'i'ii rcrcrrfd to ivpri'Sfiit an iiii|»oitaiil iiilcrval of erosion, |M'rlia|is 
 «M|uivaicnt to the one sho'i. n lo cxi- liy \'aii llise and (tthui'rt ludwiion 
 till' ii|i|prr and Iowit lluronian in tin- .stiiU's to the south.* 
 
 Ncvi'i'tliflcss tin' strilvinij, dillri'i'ni'o in tin' cliarai'lfr o|' tlic rocks ol" the 
 two scries, wholly sandy scdinn-nts in the CoiU'liicliinj.', largely dialiasi; 
 and |>or|ihyry and the products of their alteration in the Keewatiu, 
 shows that conditions had greatly chani^cd Iteloris the lat''r series wan 
 I'oi ined. 
 
 It must not he assumed, of course, that all oi' the erupti\es tound in 
 the Keewatin were surface Mows of the sanus ui.'<* as' the enclosing rocks. 
 Many of them arc prolialiiy <>( the nature of lac(!(<litic sills like the 
 trap slu'cts in the Aninukie near Thunder iiay. In fact, hut for the un- 
 doul>ted pyroi'lastit: rocks anion;.; the seiliments oiu; mi^iht sus|iect that 
 most of tlcm were injected hetween the sedimentary heds, perhaps at '■: 
 much later dale. <ince no aii'Vi^daloidal varieties have liccn found. In 
 a reirion where there has ix'on so much foldiiii; and shearing' it is rash to 
 make positive statements mi such matters, however. 
 
 % 
 
 'rmcKNKss Ol' TiiK llruoNiAN Skuiks 
 
 I.awson estimates the thickiie-< of the Keewatin at alxiut ') miles, j" and 
 of the CoUclMchiiiL;- at alxiut the same ; I hut W. II. ('. Smith su^'<j;ests for 
 the latter that tlu'rc may lie a iiumlx'r of closely appressed folds.not easily 
 separated, so that the thickness of the ( 'ouchichiiii,' may he very n uch 
 less, thoujih still reaching' S.Odd ,,r '.>.("»() fect.^ 
 
 Kollowiii'.i l.awson's estimate, the two series to^fclher sum up to od.OOO 
 or more feet in thickness, thoU'.:h it is prolial)le that the lowest heds of 
 the ('< uchi<'hini:- have lieeii dissolved liy the iiiolti'ii l.aureiitian rocks 
 lieiieath. since no liasal conglomerate has hccn found ; and also that 
 there has liecii a coiisidci'alile amount of compi'cssiou diirin^j; the sipiecz- 
 in.r underL^one in liie sliar|i synclinal folds, as proved l)y the llattening 
 of soft pelthlcs in tlie conglomerates. 
 
 The Couchichinir. containing some little consolidated sandstonen, can 
 scarcelv he included in the Laurcntian : and as it forms transitions to 
 
 ♦.IninilMl III' lir(p|..L'V. vol. i. No. 2. p. I'JIP. 
 + 1. •■<■!. SlirVl'.V of ( ;lllilllil. INNT, |l. ■'I'l, I'". 
 
 ; Uihi.. pp. nn mh.i \i<:. v. 
 
 '. IImiI,, 1m»i-'',i1, pp. M and .v., (i. 
 
inKKNKSS AM. llM-> I! Kl ATIUX. 
 
 .M 'ii::,,i „: i,,,;;:; ■ .r;;-'™ "■■ '■- ■■■' "■■■ '"■■ '"»•■"■•- -I'-m 
 
 ,- . II .IS III,. .\|.|.iiliicli)iiii,s mid tlic Kockifs. 
 Kii;.... I!i.;i.ATi..Ns n,.- laruKMiAx am. II, ,.,man 
 
 '■'■■I'"'-' V. ,i,. „.,. .,■,.,, ;■ ; ;',.",":;"":'";■■>• ""' '■■■ 
 
 i:;'n^':sJ::;:i:';,;vl"r 7'''-'' "..'-- :;:;::;;;:; 
 
 -■^'■^, -■--.". ''M:;;;;t;::;;:;i:n ;,;:;:;:r:'''-';'''r«" 
 
 "' Si-...iit...|.,- it,,,,,- r,.|»i„. ,.,,,,,,..,11, ,," ,, ■'"'".->' .I.'; Hikes 
 
 11.11 h„. WluT,. tl„. kfl,.,- i ■ k- ll.c «,„,„» „„„ 11,^, 
 
 lllr Iluroiu;;;, Hchist.s haVf ;illUu-|| •.Ki-,,-. , .. i- 
 
 (•..-i.s, H.'!,!,..,, I,.ss il,„„ I,-, ,1, . ,' ■, " """''. ''''■ '"'">■ '""" ll.« 
 i..(....l...l-|.sv,„.,h„. ■ ■""' " '■'■" '■ I ."■- '■'.I.le.l 
 
 .ii.';;:.::':::;:;:':;'';;:;,,';;:::;/;:;;;':;:'':;:-'^' :".-.M...si„ 
 
 '■""" r..n,., ( I .JnnlZZ,'7"- "":'"' "'"""' 
 
 I....R ir...,. ,■;,», „, ,v,.,l ,„„| ,.-, ,,i,|„ , , , „,„,.. •,,"'-"'-\.;"' ","l.«' 
 
 liikf of tlio \\'o(»( 
 
 ,„,.,. '': =""' 111 tlu.lJnm.l,. I'lvs.iu'iU. „r tj... 
 '-i''nnlosnUn,,t!MVoM..ast,owostan.l/.h:;-u;: 
 
 *•"■<. I, Siir\ 
 
 "'■\ "I <'aM!i Im, I.snT, |.. Ill', K. 
 
230 
 
 A. 1'. ( (iI.KMAN — CLASTIC rirUONIAN HOCK'S. 
 
 Ol' the sinallcv arcMs niontioii iiuiy Ue iiiiulc of Sultiina island a tew 
 inilt's iVoin Rat Portajie. I'ainous for its <;()ltl mine. Here a boss of coarse 
 ])or|)hyritie <i;ranitoi(l f^neiss a mile in len<fth by lialf a mihi in width 
 prose '.ts the same eruptive contact witli tlie 1,'reon Keewatin rocks as one 
 finds arounil the laruer masses. Another simih\r boss of coarse Lauren- 
 tian jiranite was found by the writer at Caribou hd<e, east of the lower 
 end of lake Manitou, the area bein^ only about a scjuare mile. Exam- 
 ples of intermediate sizes may be found on the Canadiar. Geological Sur- 
 vey's maps of the region. 
 
 Finer grained granites, generally showing no foliation on the edges of 
 the areas, are common also both in Jluronian strips and in the I.auren- 
 tian; and many more small knobs and bosses tlian were mapped by 
 Lawson in Ins somewhat hurried work will be found from time to time; 
 such as the area of protogine containing so many gol;l-bearing veins at 
 
 lAUfteNTIAfi 
 
 GlIANI TL 
 
 Kna UK. 
 
 ScALt or MiLtt. 
 
 -(iruhi'iiriit Miiji nf I'ait nf W'l stint Oiildriti. 
 
 Shoal lake. So far a.s known, these granite bosses are later than both 
 Keewatin and Laurentian, having penetrate-' both. It is, however, not 
 alwavs easy to say whether a given rock is Laurentian or a later granite, 
 and it is likely that *lie two are connected in origin and might be ar- 
 ranged as a consecutive series. Both Laurentian and other granites send 
 off felsitic dikes into the adjoining rock, and in this way one may often 
 discover the proximity of a gneiss or granite area a ([uarter of a mile 
 before reaching the contact. 
 
 It is worthy of note, as observed l>y Lawson, that often the gneiss 
 throws darker and more liasic near the contact with basic Iluronian rocks, 
 as though some of the latter material had been incori)orated in the un- 
 derlying Laurentian. 
 
 The accomjiiuiying map, figure 1. will ilhistrate the geological relati(m- 
 shii)s just mentioned. It has been ]>antogra|»hed from tliree map sheets 
 issued bv tlu! Canadian (biological Survey— the Rainy Lake, Seine River, 
 
I 
 
 I'IKI.I) I.KT.ATroNS AM. SKCTfONs. 
 
 2.'U 
 
 90 
 
 -e,„e,l ,vi„e t„ „ . ,'' ^ l' :'::;?-"''''''' »'■« '■"■"Pli-te.l, it 
 
 B«>l<.sical l,„un<i.„-i,., 'fiV "'l'"»'"l'l'.v »" as „„l t., ,■„„/■„,„ tlie 
 
 a...l .v«t>v„„l,l s «t, . """'';;■"';<»': 'l"'"Bl' tm..t, t„tl,o m.rtl, 
 
 ...■«;l:t.":;::;;,,ji;:::;:'. '7'""' i'«-"""" i--"» « -t ,„. 
 rtir;::;.r-;;;;;S!-::7f"-'r-™™-'^- 
 
 1>«- va„i8l,e,l I,„.„ ," *" "•""":"'""■ ""■ '"'"""> of "« imrt that 
 
 "....,.>et., we ,1'; I 'rix'':;;!'"- ■;.''"'■ '■■■;"■"' "■"""'"»' '"'"» 
 
 v-.vi.,,. rr„,„ I n.ik. t„ r,o „ I .! w , T, ''^ ', """ '" '""""■''^'■'' 
 
 '"»■■» of i„oilo„ ,-ocl< wan l„,,„,l l,a.„,| '""'^""'" ""' "'« "l.-l»«h,i>K 
 
 Wcatiii through which tlicv ri... t .,,. i , •* ' V''*'^'^'^ «^ the kee- 
 
 ortl.o.te bo. ,. the stu„,„ „ra volca„o ,-„,.„U„i,„ t^^ 'l^'jitir* 
 
 (iKf)r,0(;i,-Ar, IIisTouv ,„.- thk R|.:,ii,)N 
 
 IfevHMvin,,. the facts prese.ite.l l,y the n.cks of western Ontari,, «■ r . 
 -^^^i-tHenes^Couchi^^^ 
 
 *<i.,,,l. Sii|-v,,y<,f ('..,„a,|;,, IwT, p. :,7, K. ^" 
 
 XX.W-lliu,. iiK„i,. S,„: Am., \„,.. :,, is;,;. 
 
 m 
 
232 
 
 A. 1'. (Ol.KMAN— 'lASTlc III UONIAN KocKS. 
 
 cU.posit.cl .m a son iK.ttu.n. sinr. entiroly .U.stn.y..l. 'rh. u.ljoiuinK Huul 
 nu.stlKivr pivs.M.UHl an nLundnnce of quurtz-beuriug rucks to lunnsh 
 
 so nianv cuUic luiK's of san«l. 
 
 Vrterat least a mile and a l.alf aiul probably liv(; miles tlucknoss ot 
 tbeso san.ls had been laid down in the soutbern portion ot tiic region, 
 the seeon.l or Keewatin series began, in wl.ieb great eruptions ol basic 
 .,nd acid rocks alternate with clays, grits, and congl...nerates, the latter 
 sometimes a mile thick. It is probable that an important break in ,e 
 series is shown bv the conglomerates. During the later part, il no the 
 whole, of the tinie we may sui.pose that organisms existed, turnishing 
 the lar.'c percentage of carbon found in scmie of the rocks. 
 
 ritimatel V the sinking sea bottom was loaded with an eight or ten iniles 
 thickness ol' sediments and eruptive materials, as in the geosynclinos 
 preparin.'- the wav for later mountain ranges, and th(> slowly nsnig i.so- 
 <reotherms softened or fused the foundation, which rose into domes, tiie 
 hmer i.arts .solidifying as granite, the outer more viscul portions having 
 their constituents dragged into rough parallelism with the adjoining .solid 
 rocks and forming gneiss. 
 
 COMP.VIUSON WITH OTIIKK RkOIONS 
 
 Th.. usual theorv of mountain-building, by lateral thiust <lue to the 
 sinkin..- in of the earth's crust to conform to the shrinkage ol the interior 
 throu'd. loss of heat or of volatile constituents, seems capable ot produc- 
 i„„ ouiv folds: and it is doubtful if thrusts in two directions at right 
 an'des t'o each other couhl pro.luce anything except more complex forms 
 c.f the rame kind. The formation of irregularly placed domes .lemanus 
 
 some other cause. . , ,, , 
 
 One naturallv compares these batholitic^:-- mountains with the lacco- 
 litcs so distinctiv bnmght before the world by Gilbert in his description 
 of the llenrv mountains of Colorado. There also there are oval domes, 
 though not .".ver M or 4 miles in diameter. Larger but more irregular ones 
 •ire described bv Whitman Cross from the adjoining western states. It 
 i. evident, however, that these cake-like masses of erui-tive rock resting 
 on their undisturbe<l lloor of stratilied rock diU'er greatly Ir.mi the Ilamy 
 Lak.' mountain stumps, which are only more elevated portions oi the 
 S-eneral substratum of gneiss on which the sedimentary rocks now rest. 
 The erui)tive masses described by Dawson from the Swi'ct (irass lulls 
 of northern Montana, tilting up "the previously horizontal beds ot the 
 plains," so thai those immediately siin-ounding the igneous m asses rest 
 
 ♦ Hulliylit.' is tlH' foviii (if the vvonl iin'lVir.Ml l.y Oanii :uicl Zirk.'l. 
 
COMl'AKISON WITH „■,„,,;,; liK(U()NS 
 
 233 
 
 l!|.„.l iVii ,• ; V '•"' '""'""*•' "1' ""■ »'""» into ,l,„„cs in Uw 
 
 I;;;;,:;::,';:" ""— «-i"»t.«etiK.,„,eiv«„„r-,i ,g„,.u 
 
 le 
 
 '''''^' ;l'>mo of tlH. l^luH. hills, us re,,r.so„t.,l l-v Kussell j sonns to 
 <'"n,o rlcsest to tlu' l.iitholitic .lo.nes of westcn. Onl-n-io H. .V 1 ! 
 
 iitu.l „.|„.t „n ivl,„so t,ls„» rests tlic ,1 b „f .„,li,m.„ta,v rocks •,, 
 
 :;:;;: \, ;;,;■;■ r' 'r t ""'"-■'*• '""•■'™"^'' '■■'■ » -'■-'•■ !■' -i 
 
 htos .stu,i,,.a „„ to ti,„ ,.,.,™t, a,„i ,1,0 th„. or ti.0 ,„tc,, ,„.,irt ,o„.i, 
 
 Cacsk of tiiksk Mountain Stiu.tuuks 
 
 fJilhert sus,'ests for tl.o laccolites that the asre.ulin. fh.,v of .nolten 
 . nsesonly unt.1 the overlyin, n.ck is U.s dense than itsel.> 
 th U^ ,s pushed up ,uto a dou.e. the ,eneral huv of hydrostatics hein 
 
 tlie- 
 t to 
 
 Whitman Cross, following Dana, does not aoeept the hvdrostatio l 
 -T. tlunkn., that the loree which set the lava in motion is sulH ^^ 
 account for the tacts. || ^ ■^uiinitn 
 
 I.C.Russell su,uu.,,sts "that uplifts which owe their orifrin to the intru- 
 
 :";■"" ;"""'^"" "-- 't. ,herocl<sI.eneaththenM.ete, d - 
 
 '•;'"";";' :;;'^-"f' ■'■'-y'-'vhe,anciedto..ri,inaterron,th"." . 
 
 ;;''^ •"—'""."'— •"'■-n.st.-. Methinks.hatthecooli .a 
 
 .ere.recontracnn,..ustor,l.earU 
 .' ' '"t^-'-'or s,,ueezn„ upwanl the n.olten rode, which nun- either 
 
 ♦li.'ol. Siirv.'v of <Vin,i,|„, |s,s'.'-'s:i--s| p'iTc ~ ' 
 
 f.liMiriialdf (i,.„|,,t-v. v.. I. iv, riu. l. ,,. -i o(p. ' 
 
 ..•"lo,o-.„ ,1,.. II..„ry ,„o,„„Hi„s. Wasl.i,,,,.,',. ,,:;. ,',, I.' ,!;,',';,;; 
 
 ^.'-n, f „„,. ^;,,;;^, ;;!;. :;;■;';■ ' '^"'- ^""' An.o„H-\v„.„i„„„„, ,.,,, ,,, ,„. 
 
 ♦♦ Ibj.l., pp. |;hi. 1:i|. 
 
234 
 
 A. I'. COI.KMAN— «'I.ASTI<' lUUONIAN 1{(»<KS. 
 
 Suass thinks that oruptivos of this sort cannot elevate the roc-l<s ahove, 
 but, on the contrary, can (.nly occupy spaces ah'ea.ly prepared hy ten- 
 sions in tlie earth's crust. ^i= ,. 11 * 4lw> 
 So.ne of tlic methods n^f-rrcl to arc ohv.ously inapplicahle to the 
 ,,„holitic tvpe of n.ountains. Russeirs su-cstion of np^ve l.n^ lavas 
 ur..ea In- a 's^uee/.inu' action of the earth's crust can har.lly he hrouoht 
 to'i.earou a region wlu.v the whole soli.l crust for th.usa.H Is ..square 
 n,i!,.s has l.c.n tosscl into irregular .lonies. In fact it is d.lhcnlt U. see 
 l,nw anv ..ntsi.le force can he applied in such a way as to elevate don.es 
 rxi miles across when the earth's crust a.ljoinin;.- is itselt plastic. We 
 seen, forced to look for so.ne force inherent in tluMnas.es then.se ves 
 If we look at tlu. <'onditions we Hnd that the granites ot these hathohtes 
 w.re prol.ahlv fusel hv.lrothern>ally. hut not excessively hot since 
 hl,K>ks of iKis,;. Huronian rock, readily fus.-d hy a dry heat too low to 
 melt -ranite. often lie in them with unrounde.l ed-es. Kven at a rela- 
 tivelvlow fusion point they nn.st have heen nu.ch hotter and hence 
 (potentiallv)li-hter than the unfused rock ahove. particularly when the 
 latter was i.asic like most mcmhers of the Keewatin series. 1 his rela- 
 tivelv li ..t sili.'ious mauma. prohahly not thoroughly liquid, hut only 
 plastic, f..llowin- the laws of hydrostatics crept upward where the loa.l 
 of overlvin.'- rock was smallest, the heavier lluiH.nian heds meanwhile 
 scttlino- siowlv into svnclines between the risin- balholites. 1 he process 
 n.av he conceived to have -one on very slowly under sufBcient loa. to 
 i.re'vent violent disruptions of the overlyin- strata, since a certain plas- 
 tirity of the heds is shown hy the shearin- ohserved, especially among 
 the softer pehhles of the eon.ulomerates.. _ 
 
 The lar-e porphvritic felspars ohserved in many of the gneisses and 
 ..■nnites -u-.-est two statres in the history of tlu^se rocks-an earlier one, 
 bethre the i.scent he-an. and the later slow consoli.latioii. Augen-neiss 
 around the margin of hatholites proves that th(> crystals existed helore 
 the shcariiii:- uprise was complete. 
 
 Some of th.. la.rolip.s .Irscrihrd by (liUnTt slmw ..nrpnsmgly pcrhrt 
 unl,roi<endonH.sof >tratilicdrock.and the same is true ol the domes 
 elevatc.l hv plutonir plugs; in hoth ca.ses Ine, as suggested hy (ulhert, 
 to there havin- hren load enough to prevent disruption. 1 he amount 
 „f stretching undergonr by the aivhed strata in the instanres describe.! 
 was, however, not very great. 
 
 In the case of the lai-er hatholitic .l..mes of western t)ntario the ex- 
 tension must have heen as a rule much greater. 'I'he (Iran.l I'resqu . e 
 dome may have heen .•omparatively U.w ami llat^sim^' a dq. ot onh^---l 
 
 * Antlitz (ler Erdo, vol. 1, p. ai«, ''to 
 
KXTKXT OK TJIK UKcilOX. 
 
 235 
 
 dc^,^os ,nay ).. ,,l>son-o,l in Hun.niun nc-hist restin. on -n.oi.s at the 
 
 s 
 e 
 
 .St 
 
 eic, l,lle,l „ hull. „„l,.r tl.o ...b,.„ltl,.. li,.tl,oli(,., it is |„,,l„, Hmt tli. 
 
 l...nt. was ,m,cl, l.igl.er, „„.] ll,. strol,.|,i„,.of tl,.. „v,., vi.,- «l -, , 
 
 '""'" " "'"«' "■- ' I- - 1,,,.,,. .i„„„» iik„ ,i,„t ;,"{i.u.yi,r' 
 
 EXTKNT OF THK liATIIOMTIC RwilON 
 
 .V.rtwt""r;rr'?"' J-tory Ik. just lHH.n slcetch.l exton.ls 
 Com the luk . ol th. \\ oods on the wo.st to lac do.s MiHe I.tr.s on the ea«t 
 
 -(» nules. .Mo,st of tin.s ]a.-e extent of country .show.s the .ne.;h stnu- 
 t.Te M, a more or I.ss tyi-ieal way, thou.uh toward lae des MiUe I aes on 
 the east the l.ands of fluronian tend to heon.e parallel, su^^^i 
 approach to the nu.re nonnal lohled n.oun.ain structure ^-ou-W 
 th... whole rejiionthe Laurentian has eruptive contacts witlUheHu 
 n.an,a.Kl notlnn, liUe a hasal con.lon.erate of the Iluronian clul .^ 
 
 It would be unwarranted perhaps to su-est that the relationships de- 
 s<-rd.ed are n<,rn,al lor the Archean, especially when relativelv onl a 
 Muall portion ot the nun.ense extent of the Canadian Archean has I.^Vmi 
 '"jM'P-1 jv.th any detail, yet in a considerable nun.ber of instances sinnlar 
 relationships have been found. 
 
 Drnvling n.aps imperfect mesh-like strips of Huronian about areas of 
 eruptive gnei.s,s and granite from the district of Kcewatin f SO miles 
 north of the lake ot the Woods, and Harlow .states that the underlvim! 
 gneiss has an eniptivec.ontactwiti, the Huronian in the Sudburv region 
 •J . n.h.sto,hceas, of lac des AlilU. Lacs. I )r Hell, however, appea;:: to 
 .1 c. .on. Ins v.cw. ..xplamnig the relation of the two series of rocks 
 at W ahnap.tae lor instance, by assuming a tault,: M v own observations 
 near. Sudbury ami Wahnapitae convince me that at tln.se points the con- 
 tact is eru|,t,ve,^sinc^dike^ oO^^egmatite. etcetera, may be seen passing 
 
 rn:;-^;j::::;:::';:;;-;:;:;;:;:::;y;;;t:;:--— -<■■■• -^.^•m.,:.S,s 
 
 t<l<'"l. Siirvoyof c.innil.n, l,s:il, piirt K. 
 J IM.I., |,S!I(kVi|, |., II, F. 
 
236 
 
 A. 1'. ( nl.KMAN- 
 
 l.ASIir MI KttNlAN i;<)« KS. 
 
 fnim tlic ;j;iii'iss into tlic -rciMi Iluronijin rocks. Tlie lonp;^ so oh a raot er- 
 istic of the iluroiiiMH I'lrtiuT \v<'st arc. however, to l>e seen only indis- 
 tinctly, if at all. on i'.cU's ina|p of the re^'ion. .Vdanis atul Harlow show 
 the same rehilionships l>ctwecn the Hastings and Crenville series of east- 
 ern Ontario and the underlyiuji Ottawa .uneiss.* and Adams maps sim- 
 ilar eurvini,' hands of the (Jrenville crystalline limestones sinkinjr into 
 tlic <:neisscs helow. in his report on tlie Lanrentian area north of the 
 island of Montreal. t Tiicse two scries are prohahly the eastern c(|uiva- 
 lents of the western lluronian. the (ircnville series liavinu' under^'one a 
 more intense metamorphisni than the nsual llnronian. Tlie coii-ilom- 
 erates found hv .\dams prove tliat tliese rocks were undoiil>tedly of sedi- 
 mentary origin. 
 
 Still "farther east, in the great Labrador peninsula. Lowe ilescrihes 
 crystalline limestones and garnetiferous, graphitic gneisses fornung l>ands 
 in the i,aurentian. tliou-h his evidence as to tlie relatit)!) of the ordinary 
 lluronian to the underlying i^aurcnlian is not so conclusive, lie recog- 
 nizes in some of the mica-gneisses seilimentary heds like Lawson's Rainy 
 Lake Conchicliing. luit in other ]ilaees speaks of lluronian roeks as rest- 
 iii'..;- uiiconformaltlv on tlic Laurciitian. though in some cases they are 
 more or less interfoldcd witii tlie Laurciitian.}. 
 
 On the other liand. according to \'aii Hise. Logaifs original lluronian, 
 north of the lake from which it got its name, seems to he of later age 
 than tiic underlying Laurentian. since 1h linds l>asal conglomerates or 
 breccias containing fragments of Laurentian rock at two localities. § Har- 
 low, who has examined the same region, thinks, however, that there also 
 the contact is eruptive. 
 
 From Vail Ilise's admiralilc '• Principles of North American pre-Cani- 
 liriaii (ieoloiiy " one linds that a conglomerate of the lluronian rests dis- 
 cordantly on tiie foliated edges of the I'.asal Complex at many points 
 south o|' lake Supcrior.jl and Dr Dawson informs me that characteristic 
 lluronian lied- rest on an eroded Laurciitian surface in New Hrunswick. 
 l\ inav hi'thal at more southcily points the tliickncs,- of the lluronian 
 series is coiisiilerahly less than in tlietypical Archcan region. and hence 
 that the iloor on which the sediments rested was not softened or fused- 
 as happened fartlier north. ( )ii the other hand, it is not impossihle that 
 in the states south of the lakes n.cks of a somewhat later age. resting on 
 the uptunictl edges of the .\rehean ( including the Uainy Lake HuroniaiO 
 havulieen looked on as lluronian. Van Hise includes miea-sehi.sts, green 
 
 * Am. .Iiiiir. Sri., viil. iii. M;irrli iM'.iT. 
 + iiiM,|. Siirvy of CMiiiiila. is'.i:.. |..irt .1. 
 
 ;(,.■..!. Sin\l\ ..r <;im;,.I;i, Ixi:.. |.:irt I., p. llHi, I'll-. 
 
 i N. Aim. I'r.' I aiiil.|i:iH. l^'.ii'. I'. 777. 
 " II. i. I., \: 7S1. 
 
KX'I'KNT (i|- Till, |!|.:(i|(,\. 
 
 237 
 
 H. ..sts c.t,.,.t,.n,,,.| UusuM in llH. nas..,n..n( ( o.npl-x. on whos. .ro.!..! 
 
 that .l.stnu. ly <■ ...s,,.. n.Ks, sud. as tl,.. littl.. alCrnl C.nn.lnVi.in. san I 
 
 e ell lor :, small party of A.nonran an.l Cuna.lian ,..olo,ists int.resLl 
 u Iks. .„u.st,onsto,o over n-rtain typical iv^ions to^.ther, sc. as to 
 con e to a nmnnon ba^.s of .■lassili..ation tor tlu.. .liflh.ult lo.n.ations. 
 _ llonvvor It may he in other r.-ions. there is eertainlv a verv lai-earea 
 
 .n.ortlnvest( nUuMo inuhielaluM-elationshetween hatholitJso/;^^^^^ 
 . uul ,ne.ss an.l he selusto.se roeks of llnrouian (Ontarian or Al.otkian 
 age are as , esenhed in the lore.oin, paper. Tens of thousands, i 
 
 u M : ^''••7":'«' "• -l^'--'" il-'l' .1... western Iluronian were 
 oMoe alloat on a plastie .ranitie ma,n,a whieh swelled into .reat huhhle 
 
 .Icomoun.isMvluletheeohlersuWaeeroekste.uledtosinkiutotlK. al 
 be weeu ; and a pheuoiueuon ol stieh wi,le extent deserves earelui s t " 
 whether the explanation ^iven ahove h,. eorreet or n,.t 
 
 It IS worthy of note that in several re-dons wheiv aneient sed-'meuts 
 woresupposnl to rest dise.>rdautly on the Fundamental Complex more 
 detailed s u.ly has proved tliat the eontaet is eruptive. The latest i. - 
 
 tanee ,.s descnhed hy R. A. Daly, who finds hatholitie guei.s. pu.hin. 
 throned, overlym- miea-sehist in New Hampshire f " 
 
 It IS prohahk. that wherever sediments aeeunuilate to a thiekness of 
 4.M...no,. ,o.,,UO ,eet the heds on wdneh they li.. l^eoine i!la!:tie if m! 
 
 ^et w^ 1 tl "■ !''"■;■ " •""•••'■^'"""'^" '•- ''-'•-"' '--'n ..ruptiveeou- 
 •acts Mth the roeks ahove. As this has taken plaee heiieath every great 
 mountain ran.e. perhaps aided hy relief from pressure under antk.Hue^, 
 . Hd I,, no doubt .still akin, plaee where preparations are heing made for 
 the great mountain ehains of the future, a ,so-ealled Fundamental fom- 
 plex IS to be regarded, not as eharaeteristie of great anti-juitv. but as re- 
 .sultii.g Iron, a eert un set of eonditions whieh mav exist Vt an v age 
 I hi' ,.hler mountain ranges, having been more deeplv" eroded, ^dve lu, on- 
 portunity to study these guei.ssic and granitie,.ores, while in later ranges 
 hey are sti 1 lu.ried out of sight. It is likely, however, that a ba.sal sec- 
 t.o.i through our pre.seut mountain rang,.s woiil.i show long bands of 
 gneiss and granite rather than approximately eireular batholites sueh 
 as we hnd in western Ontario. 
 
 If the supposition just made be eorreet, areas of the r.aurentian or 
 
 H.ndamenta Complex do not represent the earth's cr.tarnnu,,/cn,,te 
 
 but are merely portions of the earth's crust, of se.lin.entarv oi- other 
 
 oru^nn, whu^h have been buried deeply enough for hvdrothermal fusion 
 
 * Pre-eiimbrimi {icolotty, p. 7xi 
 
 t.lniirnHl of (i,.„|„^'y, vol. v. n<.. 7. p. ow, vW. 
 
'ins 
 
 A. t'. fOI.KMAN — CLASTIC IK l!i>M AN IKM KS. 
 
 ;,ih1 liMV.' aftcrwiinl l..-..iMli>int(TiTcl l^y l-.n- c.mtiiuUMl .IcMUuliiif,' i'nivcs. 
 (;,Hul t'Xiimpli's ..r wi.k- iirciis ,.1' ^nmitoi.l n-cUs. incr^qiiii at many [.oints 
 into jiiu-iss and liaviii- an cniptivc c.iitart with tlu' ..vcrlyin-; rncl;s. arc 
 t(,l.("loUM(l.acc..nlin.-i- tn Dr Daus.ui. in tli.' C.ast ranucs ar.l Int. nor 
 i.latcan nf I'.ritisli C.ininl.ia,- l.nl hciv tiir I'.asal C.n.pi.'X is ..f Juiassir 
 
 a-iX'. 
 
 CoNCI.I-niNll (^nSKIiVATlONS 
 
 It will ln> ..hs.M'vcMl that the term. Lanivnlian has lurn cini.loy.'d m 
 this paiMTas l.aws..nan.l oth.T ( ana.lian nvnlcjists a,'e acrustoincd to 
 ,.nii.l..vit.inaiK.tn.urai'hi.'alan(l stnictnral sens., forcrystallini' .Lnicissic 
 ,„ ..ranith- rocks undcrlvin- the llun.nian. That thcs.' r.u'Us have ron- 
 
 si)li(latc(l at a later time tlian tlic llnn.ma 
 
 n is evident, and tlierel'ore 
 
 thev have not the position in time which I.oiian supj-osed when the 
 name was -iven. it may he a.lvisahlc to provide another .lesi.onatnm 
 
 for these widespread rocks, which occni.y thesame position stru.'tnral y 
 and are formed of practi.'ally the sam.' mat.'rials as those to the sonth. 
 whose attitude with reference to t'.ie lluronian correspon.ls to Loj;an s 
 
 orijiinal lluronian. 
 
 ll.nv much of the -J.t >()().< 10(1 s.piare ndh'S of the Canadian .\rcl.ean 
 presents the same relath.nships as have l.e.'n .U'scrihed m this pai-er. 
 •uid how much shows the ..rlho,h.x unconformity hetween lluronian 
 and Laurentian can he determined only hy careful Held w..rk. ll the 
 erui.tiv." contact is the normal type and the lluronian whul. rests dis- 
 eordantlvon the I.aurentian turns. ,ut t.. he really later m a,-c than Law- 
 ^..n-sOntarian.wemustl.M.kon the ( ouchichinii- series as presenting the 
 ol.k'st known nu-Us. This wouhl carry hack the ordinary sedimentary 
 deposit of sands and clays to the he-innin- ..f known K^olo.uical tune. 
 
 ♦ .ii'.il. Survey cf CMiiailM. l.xsc., piii-l H, »n.l IWM, y:\rt H. 
 
 i 
 
 1 ( 
 
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n / 
 
 5;