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Urn, DHiifMnam; GIOLOGICAL SURVEY B. w. Bboqk, DmMM. , ■^ti.'N;ri''l No. 34, GBOLOGIOAL MCRIB8 The Archaean Geology or Rainy Lake Re -studied BT Andrew C Lftwaoa No. mi ■■m-. h*n I. Seine conglomi-ratc: wrat of M'vthieu, Caiuuliui Northern railK 36570— Frontiipit'ie CANADA DEPARTMENT OP MINES Bom. Loch Coi>.Ma, Miiama: A. F. Low, Dnvn Mirnn.; GEOLOGICAL SURVEY R- W. BaocB, DmmroB. i MEMOIR 4?! No. M, GIOLOGIGAL SERIES The Archaean Geology OP Rainy Lake Re-studied BY Andrew C. Lawton Msro-i OTTAWA OoTiBHmuT Primtino Bvmaio 1013 No. USt ' CONTENTS. r ■ PawMs CHAPTER I. ImaoDi >mT I CHAPTER n. G«olocy Arehmui (•olosy : gsgvnl lUteiiwiit Th* Coutehichinn trtn The Rice Bay mm. The B«w PMMHie an* |{ The KMithern belt M Petrognphinl notee H Chemical compoeitioa 3t Th« Keewatin iprira. .. IS Oeaeral rharaeter and diitributioB IS The northern area M The itnuthem area. . 40 0th * belU ot Kec «atla W Petroiraphiral note*. 4S Cheinieal compoeition 80 The Laurentian rocki 8t The Bad Vermilion Laka sraalte SI Area SI Petrographieal rharaeter SS Relatione to adjoininc rooke S3 The Mud L.kke granite S4 The iheared granite ot Qrauy '''and.. M The Rice Bay crt --gar'n Sft PetroBTaphical n> 87 The Peine KrieK 80 The Se^ iif conglon —e 8t The Hbr..i Lake area 80 E , , . of Hhoal lake 63 T' •• o!<>;loii!srate weito(8hoal lake 07 Pet. .'{(rf.phical notei 72 Other <>ccurrenoea of conglomerate 78 The Sei'ie quartiitea, aericitic aehiita, and elate* 78 Petrographieal notea 78 Lamprophyric rocks 70 Two widely separated periods of plutonic activity in the Arehjsan 80 The Algoman rocks 82 3S570-U iU Pmb Mica lyenite gneiss 82 The Rocky Islet Bay area 83 The Hopkins Bay area 8S The Pukamo Island area 87 The Bear Passage area 89 Petrographical notes 89 Chemical composition 91 Banded biotite granite-gneiss 91 Chemical composition 93 Porphyroid gneiss 93 Other granites and granitoid gneisses 96 The Grassy Island granite-gneiss 97 The Nowhere Island granite-gneiss 97 The Knuckle Island granite 99 The Bear Passage granite 99 The Redgut Bay granite 99 Summary of observations regarding the Plutonic intrusions usually referred to as Laurentian 103 Kaweenawan dykes 109 PaUsoioic rocks HO IRDU 113 ILLUSTRATIONS. Qeologieal map In pocket Plate I. Seine conglomerate west of Mathieu on the Canadian North- em railway Frontispiece. II. A: Coutchiching on the north side of Rice bay; showing stratifi- cation; B: Coutchiching on the west side of Rice bay; showing massive bed interstratified with more fissile schists 6 ni. A: Coutchiching on the north side of Rice bay; showing stratifi- cation; B: Coutchiching on the north side of Rice bay; showing stratification 8 rV. A: Horisontal joints in granite at contact with Coutchiching on Joint bay; B: Contact of granite and Coutchiching on the west side of the entrance to Blind bay 18 V. A: Sheared tacies of anorthosite east end of Seine bay; B: Gran- ite (below) intrusive in anorthosite (above) Finger bay. Bad Vermilion lake 40 VI. A: Exposure of limestone in Keewatin. Golden Star mine at the northeast end of Bad Vermilion lake; B: Another ex- posure of the same limestone at the same locality showing bands of chert and chert fragments in the limestone 44 Faob Plate VII. A: Seine conclomerato. Weat of Uathiea on the Cuadian Northern railway; B: Fanglomerato at the baae o( the Seine conglomerate, near Golden Star mine 00 VIII. A: Seine conglomerate. Island on north side o( Rat-root bay; B: Seine conglomerate, Prospect bay t2 IX. A: Granitic dykes in schists. Showing participation in the deformation of the schists. South side of Prospect, bay; B: Granitic dykes intruded into schists after the deformation and schistification of the latter. South side of Base Line bay 84 Fig. 1. Cross bedding of Seine quartiite, Shoal lake 63 n vtt PREFACE. The present memoir is the result of investigations carried on in northwestern Ontario by Dr. A. C. Lawson during the season of 1911. It will be remembered that in the eighties, Dr. Lawson, then a young geologist on the staff of the Geological Survey, was engaged in a reconnaissance in this region, and that his reports on the district became classical. At that time the district was difficult of access and covered with primeval forest, so that geological work was carried on under great difficulties, and only a recoimaissance was possible. In the interval of time that has elapsed, a vast amoimt of detailed work has been carried on by the United States Geological Survey and the various state surveys to the south of the International Boundary line that has added largely to the knowledge of the Pre-Cam- brian. It was felt that it would be of great interest and value to have Dr. Lawson revisit his old field, and study it under the more favourable conditions now prevailing. Since the principal object is to present Dr. Lawson's position and his mature opinions based on his re-examination and more detailed study of the district, the memoir is printed without alteration as submitted in manuscript by Dr. Lawson. (Signed) R. W. Brock. THE ARCHAEAN GEOLOGY RAINY LAKE RE-STUDIED. OF CHAPTER I. INTRODUCTORY. In a field bo complicated and so extensive as that presented by the Archaean terranes of Canada it is not surprising that as investigation proceeds there should be conflict of opinion. The early records of the earth's history are obscure and difficult to decipher. They are susceptible in their imperfection of more than one interpretation. The acquisition of facts is so slow and laborious that no one geologist can hope to become familiar with the details of more than a very small portion of the entire field. The work to be done is appalling in its magni- tude; yet none shrink from the task. There is so much that is fundamental to the science of geology in the elucidation of the Archsan that everyone interested in this branch of the subject feels constrained to contribute what little he may to the general effort which the vastness of the problem calls for. What cannot be done by the individual shall be done by co- operation. Naturally this co-operation resolves itself into the study of small discrete areas by individual workers and a comparison and discussion of the results there obtained, until eventually we arrive at that consensus of opinion which is commonly accepted as scientific truth. In this discussion, which proceeds slowly through years and decades, conflict of opinion is inevi- table. Owing to the variation of conditions the conclusions which are reached in one area fail of verification in another. Disputes thus arise which can only be settled by a careful restudy of the facts concerned in the question at issue. An interesting case in point is the discussion which has arisen out of my report on the geology of the Rainy Lake region. Up to the time of the publication of my reports on the Lake of the Woods (1885) and Rainy lake (1887) the notions which prevailed almost univerpally regarding the Archsan of North America were quite different from those which have obtained general acceptance since then. The Archcean corjisted of two main divisions known as the Laurentian and Huronian, the latter lying unconformably upon the former on the north- east margin cf the type Huronian area, with a basal conglomer- ate. The Laurentian comprised certain metamorpbic rocks, notably the limestones of the Grenville series, and with these there were associated certain gneisses which were also held to be metamorphic. Below the Grenville series was a vast expanse of granitoid gneiss, sometimes reftrred to as the Ottawa Gneiss or the Fundamental Gneiss, or t..o lower Laurentian. Above the Grenville series was the TTorian series or upper Laurentian consisting of gneissic anorthosite and allied rocks. All of the ^eiss of the Grenville series, and all of the Funda- mental Gneiss as well as the anorthosite of the Norian series were regarded as metamorphic sedimentanr strata. With the progress of reconnaissance mapping it was found t^at the rocks of the type of the Fundamental Gneiss were by lu,t the most extensively distributed throughout Canada, and these rocks came to be designated simply as Laurentian on many maps and in many reports, without any change in the current con- ception of their origin, viz., that they were metamorphic sedi- ments. This practice prevailed not only in Canada but also in the United States, and it extended to various other countries. My reports of 1885 and 1887 showed that these granitoid gneisses of the Fundamental Gneiss type, which form so large an element of the Archsean, Were not metamorphic sediments, but were in reality plutonic igneous rocks, and a new point of departure was thus established for the study of the Archaean. The old notion of the metamorphic origin of these rocks became rapidly obsolete and the interpretation which I advocated was confirmed by observers in other fields and has become generally accepted, with all that it implies as to the extraordinary con- ditions which prevailed in the earth's crust in Archsnan time. In these same papers, particularly in that on Rainy lake, I described and mapped two series of metamorphic rocks as constituent members of the Archsan, which had not hitherto been fully recognized. These were the Keewatin and the Coutchiching. These were both shown to be older than the rocks then commonly called Laurentian. The Fundamental Gneiss thereupon lost its fundamental character from a chrono- loi^cal point of view; for instead of being the basement upon which the Coutchiching and Keewatin were deposited it was found to be an igneous rock intrusive in both. In the recon- naissance maps of hoth Canada and the United States the Keewatin had been confounded with the Huronian. It-? segregation from the latter as a series of rocks quite distinct, from and much older than the Huronian has been fully confirmed by the work of the past 25 years and i" '-me Keewatin has been generally accepted. The Keewatin series has been found to have a wide-spread distribution and persistent character over a large part of the continent. It is made up chiefly of volcanic rocks with sub- ordinate admixture of sedimentary strata. Below the Keewatin on Rainy lake I described and mapped as a series of metamorphic sedimentary strata free from volcanic admixture, the Coutchiching. My views of the geology here, however, have not met with the same favour among geologists as did my interpretation of the Laurentian and my recognition of the Keewatin. The conclusions as to the stratigraphic position of the Coutchiching series set forth in the report of 1887 have been called in question both by officers of the United States Geological Survey and by an international committee of geolo^ts appointed to harmonize as far as possible conflicting usage with regard to the nomenclature of the Archtean. In view of the growing economic importance of the Archsan rocks and the extension of detailed mapping of them in various parts of Canada it seemed to the Director of the Survey that the issues thus raised should be settled if possible. At his request, therefore, I devoted the field season of 1911 to a re- study of the southern portion of Rainy lake with particular reference to the stratigraphic position of the Coutchiching. The result of this investigation has been to confirm the con- clusion reached in 1887 that the Coutchiching underlies the Keewatin. A fuller statement of the facts and the argument in support of this conclusion are set forth in the present report. In the prosecution of this work I have made other observations and reached other conclusions of even more impovtance from a general point of view than this regarding the stratigraphic position of the Coutchiching. Although, since the publication of my reports of 1885 and 1887, the old ideas of the metamorphic origin of the granitoid gneisses have been entirely abandoned and they are now generally recognized as of igneous plutonic origin, yet the term Laurentian was retained for these rocks and it was supposed for many years that they represented but one general period of plutonic activity. This usage of the term laurentian has been confirmed by a decision of the International Committee on Geological Nomenclature. But in recent years it has become apparent to a number of observers that the rocks cle-^sed unde. this term were not all of the same age. I have f ad during my field studies on Rainy lake and the Seine r r in 1911, the most satisfactory evidence that the rocks which aave been usually called Lauren- tian in this region really belong to two widely separated periods of time withta the Archaan. For the older of these periodi I have retained the name Laurentian in accordance with the definition of the term by the International Committee, and for the later period I propose to use the term Algoman, from the old district of Algoma. The full recognition of the dual age of the plutonic rocks hitherto commonly referred to the Laurentian I regwd as a most important step in the elucidation of the Archean of Canada. Two other series of rocks occur in the region examined one known as the Steeprock series, and one which I have named the Seine series and these are probably the correlatives of the two divisions of the Huronian of Lake Huron. In the lower Huronian, or Steeprock series, I was fortunate enough to find well preserved fossil remains which have been described in Memoir No. 28. These appear to be the oldest fossil remains at present known. The only other matter of interest referred to in the report is the discovery of a small outlier of Palaozoio strata near Fort Frances at a point 200 miles distant from the nearest formerly known exposure of these rocks in Manitoba. Dunng the season I was ably assisted in the field by the late lamented Dr. J. D. Trueman, who was exceptionally efficient and well qualified for the work, by Dr. R. C. Wallace of the Umversity of Manitoba, and by Mr. H. C. Cooke. A geological map on a scale of one mile to the incii accom- pames the report. In the preparation of the report no attempt has been made to ^ain discuss the physiography of the region; nor is any effort made to restate the Pleistocene geology; and for information on these matters reference must be made to the report of 1887 ftom a petrographic point of view the rocks of the region are of great mterest, but an exhaustive discussion of this phase of the geology would be a task of great magnitude, beyond the limits of my present opportunities; and I have had to content myself with a microscopic examination of a limited number (1^5 in all) of thm sections of representative specimens of the rocks mapped to determine their character and classification. It seemed to me that the most desirable contribution to the petrography of these rocks would be careful chemical analyses of some of the more important types. I have, therefore, had thirteen analyses made in the laboratory of the Survey and these are mcorporated in the present report. CHAPTER II. GEOLOGY ARCHMAN QEOLOQY: GENERAL STATEMENT The oldest rocks of the Rainy Lake region are a thick series of sedimentary strata, now chiefly metamorpliosed to mica schist and paragneiss, to which in the report of 1887' I gave the name Coutchiching series. This series is free from volcanic admixture. Resting on the Coutchiching series is the Keewatin, a series made up chiefly of volcanic rocks, but com- prising also sedimentary strata mtercalated with these. In- cluded with the Keewatin as belonging to the same general geological period are certain gabbros which are intrusive in that series. Intrusive in both Coutchiching and Keewatin are certain granites and granite-gneisses for which the term Laurentian is retained, in accordance with general present usage. This was followed by a period of erosion which exposed the Laurentian batboUths extensively at the surface. Upon this eroded surface there accumulated the Steeprock series of sediments and vol- canics includin': several hundred feet of fossiliferous limestone. This series is tentatively correlated with the lower Huronian. After an interval of uplift, deformation, and erosion, in which the Steeprock series was extensively denuded, the region was again depressed and there accumulated upon it the Seine series comprising conglomerates, quartzites, and slates. Minor intrus- ions of lamprophyric rocks traverse the conglomerates. The Seine series is tentatively correlated with the upper Huronian (the middle Huronian of some writers), there being only two divisions of the Huronian recogi ized. After the deposition of several thousand feet of Seine strata the region was again invaded by vast batholiths of granite-gneiss and syenite-gneiss. For these post-Huronian plutonic rocks, which have heretofore been commonly confused with the older Laurentian rocks of similar character, the name "Algoman" is here proposed. The next event which it is possible to recognize in the history of the region is a protracted interval of profound erosion which I have elsewhere designated the "Eparchtean Interval." Upon the vast peneplain resulting from degradation during the Epar- chsean Interval were deposited the Animikie sediments. The Animikie is thus separated from the Huronian by an enormous interval of geological time. On the far side of that interval >Geol. and Nat. Hiit. Sunr«y of Can. Ann. Kept., N.S., Vol. Ill, Pt. 1, 1887-88. th« r^H^T'* *" effected by plutonic activitle., involving £Lr.'^*''^"''""!'*^r^'*^'"'»n'l Huronian similaHy. which ?n L 2 i"J^'' ^" "l''" '^°''*''' the Huronian Ih allied S,d i8''r„'W,t"'*A'^.*''*^ the Coutchiching and Keewatin Tfffi COUTCHICHING SERIES, Within the limits of the territory embraced in the accom- panymg map the rocks of the Coutchiching neries occur Tn three Jwtmct areas. The first cf these is aJT annular belt Sh''."*'' fr^"^^°^^otHhe^edgT^te or granite ^hyrJ which 18 well exposed on the shore, of Rice bay. Th- S schists of the Coutchiching completely enclose the gra™S and dip away from it in all directions in the form of an anti! cliiuU dome. The second area is in the form of a broad belt iSmHSi'oT R««^8"t b?y -o"*^^"* '^d west to the STniTn^^ /'f.\"''Pj . ^^'^ ^^^'t « al^o anticlinal in struc- &»; ^- '" '*' (y" ^'^"^"' '« ^««* wPo-e^ in the vicinitrof £t o?^ T^f'^^J^^ "^*"«^ t° «« *»>« B«" parage a n«™h«r > /* '•" northeastern end the belt splits up into a number of tapermg tongres or prongs which extend into £?kST*'«PT °^ ^.^'Pt bay, on the mar^i of a gie!° bathohth. Southwesterly from Bear passage the belt encloses successively three separate batholithic areas of granite or SrS CL T^™"8hout its extent this belt of CoutchicS^ il Sitiph^ «ther Side by Keewatin rocks. The thir 1 a ef of KnirJ^^K *^.°>o»t extensive and is that, occupying a St^ritnV'^^ ¥»!°"f 2,*'' ^oast of Rainy lake and the CaSa; dian territory, south of Bleak bay. Cliff lake, and part of th^ fch-"'";.!*' ""?'*« *° *h« «»>th remaining Undefined ^n THE RICE BAY AREA. ovRl TJiTn'^''"' "•''^r *' °^ ^''"' ^?y °'^'="Py a closed belt of flattened The wiZ ^f *r'l"l^ '^?*'f ™^« ^^ »°t™«^« grnnite-gneiS^ three^fourthi S^ ^"'"i ""^""S ^^"^ '^^^ ^^^ ^alf a mile tfover Hi/,!- ii^ ^r°/u ^ ".''^ ^^ averages about half c mile. The ine dip of the schists is away fum the granite. At several ocahties particularly on the western note of the antS?ne liJ ''^rr*' °^ ^'""^ ^0» to 50°, but on the flanEof th^ antichne the dip is steeper, usually from 60» to 70°. The schists Pl,«T« II. A. Coutchiching on the north side of Rice bay; ihowing atratification. B. Coutchiching on the we»t eidc o( Kice bay; showing massive bed intenttratiticd with more figsile achistg, 36570-p. 8. in many tectloM h..ow evidence of beddinR, apparent in cnntraata of colour uiitl texture, luid the iic)iiHto«ity in in general purallel to the bedding. There are numerous granitic intruaiona in the scbiata. Tnoae which are parallel to the bedding and aohia- toaity are interpreted aa lilla and will be here no dctipated. Thoae in any way tranavene to the bedding and Bchutoeity will be referred to um dykett. Thctie dykeii and ailla are moHt numerous in the vicinity of the central granite-gneiia moMt, and they are regarded aa apophyaes of that moaa, not only from thia fact, but also by reason of their pctropaphical aimilarity to the main intrusion. Besides these panitic sills and dykes there are also in the schists occasional long, narrow belts of hornblende schists which are regarded aa very probably being basic ailb which, originally injected into sedimentary strata, have been reduced to hornblende schists by the same dynamic action which converted those strata into mica schists. There are also some beds interstratified with the mica schists which consist very largely of feldspar, quarts, garnet, and epidote with some pyrite, and which do not fall into the general cate- gory of mica schists. These are regarded as beds which were originally calcareous rather than argillaceous and have conse- quently yielded a different product as a result of metamorphism. Nearly all the rocks of this area, including both the central pranite ^eiss and the annular belt of schists which sunounda it, show m a remarkable degree the effects of intense compression and shearing. The granite-gneiss is somewhat variable in mineralogical composition and this variation is expressed chiefly in tb' development of the orthoclase. The rock is prevail- ingly a very quartzoHc biotite granite and in some of its facies the orthoclase is abundant in large well formed crystals, while in Oiiher cases the orthoclase is much less conspicuous and the quarts is prominent in abimdant large crystals. In other facies neither orthoclase nor quarts are especially prominent and the rnck has more the texture of an ordinary medium grained granite. But whatever its local habit, the rock has been so sheared that it has a distinctly foliated and schistose character. Where either orth -. lose or quarts are porphyritically developed, this shearing gi'...a rise to an au^en-gneiss structure. This is most peiifectly and most commonly developed, however, in those facies which have porphyritic quartzes. The latter are characteristically reduced to very flat lenses, the major diameters of which are not uncommonly an inch and even 2 inches in length. The major diameters of the lenses lie parallel to the dip of the schistosity. The pronounced foliation which has been induced in the central granite mass is parallel to that of the encasing schists, both as to strike and dip. It thus has also an anticlinal disposition and the dip of the planes 8 of foliation at the western end of the anticlinal structure, i.e., in the direction of the anticlinal axis, is as low as 35 . Ihe strike of the foliation of the granite-gneisa here swngs around in perfect conformity with the curve of the outcrop of the schists. The intrusions in the encasing schists, particularly in the sills, iave the same characteristics. They were evidently similar mineralogically and structurally to the central mass, have suffered the same deformation, and have yielded the same results. The dykes which traverse the schists transversely have been contorted due to a shortening in the direction of their strike, which has caused them to double upon themselves in sigmoid curves, which are sometimes rather acute. The com- pression to which they have been subjected has very clearly diminished the width of the sills and the length of the dykes The compression has without doubt similarly reduced the original thickness of the mica schists into which they are intrusive. The compensation for this reduction m thickness has been an elongation, chiefly in the direction of the dip, with a less marked elongation in the direction of the strike. The Present apparent thickness of these schists I estimate to be about 1500 feet. But the original thickness may have been very much greater. The underlying granitic rock which occupies the core of the anticline has displaced the basement upon which the original strata were deposited. In displacing that basement it has also displaced the basal portion of the Coutchichmg series. How much camiot be stated. But it is quite possible that we are dealing here with only the upper part of the series. As to how the displacement was in detail effected, I will not here enter upon the discussion of so large and so interesting a problem, but will simply point out that the extremely quartzose character of the granitic gneiss suggests an enrichment of silica by resorp- tion of the encasing acid rocks; and that the porphyritic devel- opment of the quartz in a plutonic rock mdicates that this enrichment resulted in a super-saturation of silica which caused it to crystallize out first in accordance with the eutectic law. Now it must be evident in view of the facts stated that the compression and shearing have affected both the central Kranite and the encasing schists after the consolidation of the former. This being the case, it follows that this post-granite deformation contributed in no small measure to the appression of the anticline, and that whatever dips the encasmg schists had away from the central granite before the advent ot this deformation, these have been greatly steepened m consequence of that deformation. Indeed this deformation has probably played so large a r61e in the development of the present anticlinal structure of the encasing schists that we must suppose that they at one time rested upon gramte m comparatively Plate III. A. n. Coutchichinf; on the north side of Rice bay; showing stratification. Coutchiohing on the north aide of Rice bay; showing stratification. 36570— p. S flat attitudes. It is this conception of the development of the structure which has led me to interpret the granitic intrus- ions parallel to the bedding of the schists as sills rather than dykes. It is quite evident from this intensely sheared condition that they too were intruded anterior to the period of compres- sion, and, therefore, at a time when the schists were in much flat- ter attitudes than at present. Outside of this annular belt of mica schists and concentric with it is a belt of typical Keewatin rocks comprising chiefly hornblende schists, ellipsoidal greenstones, massive greenstones, greenstone schists, chloritic schists, and gabbros, with subor- dinate intercalations of mica schists, chert, limestone, and con- glomerate. The boundary line between the Keewatin and the Cout- ehiching mica schists skirts the northwestern comer of Lower Rice bay a little back of the shore. Thence following it in a northeasterly direction it lies in the peninsula between Rice bay and Hopkins bay, being on the traverse line shown on the map 17 chains north of the shore at the narrows between Upper and Lower Rice bay and passing through the northeast inlet of Upper Rice bay. The general dip of the mica schists in the numerous exposures along the northwest side of Rice bay varies from 60° to 70° and averages about 65° to the northwest, carrying these schists below the Keewatin, the dip mentioned being true of the bedding as well as the schistosity. Beyond the northeast comer of Rice bay the strike of the contact of the Coutchiching and Keewatin swings around to east and then to southeast. The contact is next intersected on a north-south traverse at a point about 15 chains north of Pocket pond where the rocks strike 123° and dip N.N.E. at from 65° to 70° and again on a parallel traverse 30 chains e-^st of this. It is again intersected on a parallel traverse a mile farther east and again on an east-west traverse 30 chains to the southeast. To the southeast and south, between this point and the Can- adian Northern railway, the position of the boundary line between the two series of rocks was located as mapped on tliree traverse lines at intervals of 30 chains, 55 chains, and 'M; chains respectively. Following the boundary southwesterly it intersects the line of the Canadian Northern railway at a point about midway between miL-posts 212 and 213 and again with a westerly strike at a point on the railway about a fourth of a mile east of mile-post 214. The dip of the schists along the r8''way l.« about vertical. Leaving the railway the boundary line between the two series passes to the north of Nickel lake and was intersected 12 chains north of its north end. It was again intersected a few chains south of the southwest corner of Rice b-.y and again where it crosses the 36570—2 10 Narrows between Rocky Islet bay and Rice bay. North rf the Narrows for about three-fourths of a mile the iV^ew*"" is intermpTed byan intrusive mass of mica syemte-gnejss upon Xch thf Coutchiching schists abut, but this syenite is other- ^^^Sfv^fcrpStlt^^wh^^^^^^^^^^^ from the actuaUine of contact, make it certain that the Rice aH^?£rs^.ie-trs£Ut^ Sts^trf SUf tte Sctch^r. sM- th?|^= BtU holds I have shown that a residual volume of the Cout- lliTi^^^riP^ the lower part of which has disappeared, is foSb^u "wtrS^^^^^^ of granite-gneiss and d ps under „^ ar^a nf Keewatin rocks w^'ch completely encircles it. But the CernatSal . , nimittee on Geologica Nomen- 1 A /ifo n I nPoloBical Survey'^ deny the -existence of Wr,..iH it not be well for these eminent authorities oeiore wiping S;rihe Cou\S^ utterly, to examine the Rice Bay section? THE BEAR PASSAGE AREA. Am ftwav from an intrusive mass of granite gneiss, ine '""8" d amS of thU mass extends southwesterly from Bear diameter uiw shorter diameter transverse to STfs ^bout U nSes" T^fs mass differs from the Rice Bay your. Geol. Vol. 13, 1905. >Mon. UI, 1«11. 11 granite gneiss in that there is little if any evidence of the com- pression and shearing which have affected that intrusion since its consolidation. The rock is a medium grained fairly homo- geneous biotite granite, with on the whole a feebly developed foliation, although locally the foliation may be pronounced. There arc few pegmatitic or aplitic dykes traversing it; and inclusions of the encasing rocks are scarce except in the immediate vicinity of the intrusive contact. This contact is splendidly exposed at the south end of Bear passage. Here, at the entrance of the strait, on the west side, the prevailing rock is granite with large inclusions of mica schist; on the east side it is mica schist traversed by irregular apophyses of granite, the schist dipping easterly or northeasterly at 30° to 45°. About 14 chains north of the entrance on this side we come to the actual contact of the schist and granite. From this point northerly along the shore or a little back of it there may be seen the roof of the batholith resting upon the granite. The schists lie upon the granite at quite low angles, the angle of dip decreasing as we pass northerly from 45° to 30° at the entrance to from 30° to 25°, and then to from 25° to 20°; and in some places it is as low as from 15° to 10°. These figures give not only the dip of the schists reposing upon the granite but also the attitude of the contact plane between the granite and the schists, this contact being exposed in the face of cliffs having various salients, and re-entrants. In the granite there are numerous quartz veins which extend up to the contact but do not penetrate the overlying schists, except to a very slight extent in an irregular way. In several of these quartz veins tl ^ '"'H-^ct nnrt is at the contact and they taper in width as the> into the granite. It is evident from these relations that "! granite, after consolidation suffered a greater contraction of volume than did the overlying schists, and that this resulted in cracks in general normal to the contact. These cracks became subse- quently the seat of vein deposition. Although these veins are thus so intimately connected with the granite contact, there is nothing to suggest that the deposition of the quartz can be referred to the magmatic waters of the granite. The curvature of the trace of the contact followed northerly carries it below the waters of the strait for about 48 chains, and we next find it on the west side about a mile from the entrance. Here the strike of the contact plane and of the schists has swung around to 258° and the dip is northerly at angles of from 38° to 46°. Beyond this the details of the contact are obscured by forest and marsh. At the sc athwest end of the granite mass in the vicinity of Breeze bay, the encasing mica schists of the Coutchiching series in the bottom of this bay and on its east side at a distance 36570—21 13 of from 20 to 25 chains from the contact, lie at low angles of from 10" to 15" dippinc away from the granite, and are out by dykes of the granite; but close to the granite the dip steepens, and at the contact is nearly vertical. The northern boundary of the granite is located approximately as mapped from data obtained on two northerly traverses from the lake shore. From the facts above described, it is clear that the mica schists of the Coutchiching lie above and upon the granite which invades them from below; and also that the basement upon which the schists were originally deposited as sediments has been displaced by the granite, and that the displacement has involved the lower part of the series so that we have to deal with a residual volume of it; further it is apparent from the map that as we go away from the contact at the strait known as Bear pabsage we come upon typical Keewatin rocks resting upon the Coutchiching mica schists, at a distance of about half a inile. In this distance the dip of the bedding of the mica schists is prevailingly about 30" to the northwest, or away from the granite and towards and under the Keewatin. Locally the dip may be as high as 45",but near the contact with the Keewatin Jt IS as low as 25° to 20". That we are dealing with bedding as well as schistosity in the observation of these dips is apparent from the usual evidence whereby the fact of bedding is estab- lished, viz., the contrasts of colour, weathering, texture, and composition of the different strata. These contrasts are not everywhere apparent but they are well displayed in the vicinity of the contact about 35 chains south of the Canadian Northern railway. Here the contrasts are accentuated by the effect of con- tact metamorphism referable to the granite intrusion. Certain beds, usually less than a foot in thicLness, have had developed in them large numbers of crystals of secondary silicates of alumina which weather out prominently on the surface, while adjacent beds of comparable thickness are devoid of these crystals or neariy so . In consequence of this the rock is distinctly banded and the banding expresses a difference in original composition, which in a sedimentary series must be stratigraphic. There is a rather frequent display of repeated alternations of this sort In sharply marked stratigraphic arrangement in the Coutchiching rocks in proximity to intrusive granites. The line of the contact emerges on the shore in a little bay about 20 chains south of the railway, where the Coutchiching and Keewatin rocks are not more than about a chain apart. Followed in from the shore in a southwest direction for a few chains the two series of rocks may be seen in actual contact, on the face of a steep little slope facing the southeast. In the lower part of this slope are the Coutchiching mica schists and in the upper part, the Keewatin greenstone; and the two are so close 18 together that they may both be toaehed at once, without ■tretching ^e anna. Here the mica schists dip under the green- stone at an angle of about 30* and the suiMrposition of the greenstone upon the schist cannot be questioned. From the utile bay above mentioned where the contact emerges at the shore line, the boundtury between the two series of roclcs may be followed northeasterly for about 2 miles on the west side of Redgut bay. In this stretch, unfortunately, it lies for the most part below the waters of the lake, but owing to the irregularities of the shore line and the disposition of various islands, it can nevertheless be located very closely, and the dip of the Coutch- iching mica schists is very uniformly from 30" to 40° to the northwest or under the Keewatin, the bedding being quite apparent at a number of places. Where the contact line skirts the points of the shore on the west side of Redgut bay the dip of the greenstone schists and hornblende schists above the Coutchiching conforms to that of the latter and iS northwesterly 30° to 45°. The same relation holds for a belt of hornblende schists 15 chains to the west of the contact, where on an island half a mile north of the railway the dip is W.N.W. at an angle of 35° to 40°. Here well within the Keewatin terrane the horn- blende schists are associated with some beds of interstratified mica schists and quartzite, the former, however, difTering some- what from the typical mica schists of the near-by Coutchiching. On another island 30 chains north of this is ar interbedding of rather massive green schists with quartzose mica schists similarly dipping W.N.W. 35° to 40°. For the next mile northerly the contact is below the waters of Redgut bay, and where it again enters the shore at a point about 2} miles north of the railway the strike has swung around to the northwest but the dip is still under the Keewatin or to the southwest at an angle of 60° and away from the area of granite gneiss which has cut away the greater part of the series on the northeast. The facts here recited in regard to this line of contact, par- ticularly near the railway on the shores of Bear passage and the south end of Redgut bay, taken in connexion with the relations of the Coutchiching to the granite, appear to me to prove conclusively the superposition of the Keewatin upon the rocks mapped by me as Coutchiching in the report of 1887. I invite the attention of the International Committee and of the U.S. Geological Survey to this section and challenge them in view of the facts there apparent and easily accessible, to deny the relations of the Keewatin and Coutchiching as I mapped and described them a quarter of a century ago. The fact that these eminent authorities have denied in toto the existence of the Coutchiching series as a constituent member of the Archaean below the Keewatin, without any attempt to verify the very 14 explicit Htatemcnt of the evidence in regard to this section con- tained in tiie report ^i i887', places them in a curious light from the point of view of -jientific method. The evidence above set forth &a to th» t "^r'wsition of the Keewatin upon the (^outch- ichmg is practically the same as that published in 1887. In the course of the work of the past field season this has been sup- pipmented by other observations which support the conclusions then arrived at. The area of Coutchiching mica schists, the western contact of which with the Keewatin I have just been discusising, is an anticlinal fold in the northeastward prolongation of the longer axis of the granite mass exposed so well at Bear passage. The width of the area transverse to its general trend is from 2 miles near the granite to IJ miles on the section through Bear Pass Station. The anticlme is asymmetric, the dips on the east limb being on the whole steeper than on the west, so that the axis of the anticline lies about two-thirds of the width of the belt from its western margin. This position is, however, approximately coincident in direction with the longer axis of the Bear Passage granite mass. The dips of the Coutchiching rocks are well exposed at numerous places on the shores of the south end of Redgut bay, on the shores of Bear passage, and along the line of the Canadian Northern railway between the bridge over Bear passage and Bear Pass Station. At many of these exposures it is apparent that the schistosity is coincident with the bedding. The dips on the west side of the axis are uni- formly westerly or northwesterly at angles ranging generally from 28 to 45 , and on the east side of the axis the dips are uniformly easterly or southeasterly at angles ranging generally from 40° to 60 . Along the line of the axis of the fold the strata are pre- vailingly at very low angles and the fold is here a low buckled arch, and in one of the buckles exposed on the south shore of Redgut bay the strata may be seen dipping in opposite direc- tions in the same clifif-face. The flat dips, however, are best seen perhaps along the cuts of the Canadian Northern railway where, just on the east side of the axis of the anticline, the strata dip southeasterly at 15° for some distance before acquir- ing the steeper dip which characterizes this limb of the fold. At the eastern margin of the anticlinally folded Cout- chiching area the mica schists pass beneath the Keewatin rocks on the line of the railway at an angle of about 60°. The actual contact is well exposed in a rock cut about a mile southwest of Bear Pass Station. Here on the face of the cut the Keewatin greenstone may be seen reposing upon the Coutchiching mica schist. The greenstone is finer grained at the contact than it 'Ann. Rept. p. 103F. 16 is n few feet above it, a phenomenon which MUfUtests a chilling of the butte of a flow. Tlie top of the Coutchiehing in very quartzose and prestntH the appearance of bands of quurtzite interstratified with mica schiot, but the rocks are somewhat obscured by an ochreous deposit due to the oxidation of pyrite in the rocks near the contact. On the Keewatiti side of the con- tact the greenstone gives place in a short space to stratified green schists. There is no conglomerate or other erosional detritus at the contact. The underlying Coutchiehing is some- what crumpled. This contact may be followed for over a mile into tlie brusli north of Bear Pass Station witli the same general features, and for nearly 2 miles to the south, where it comes to the siiore on the north side of Swell bay. Here the chilled margin of the basal bed of the Kecwatin greenstone is well dis- played in immediate contact with the mica schist, Supplementary to this stratigraphic and structural proof of the fact that the Coutchiehing antedates the Keewatin and underlies it is an interesting observation that I made in a rock cut on th-' line of theCanatlian Northern railway 20 chains west of mile-pv.rit 211. Here the Keewatin hornblende-gabbro contains angular inclusions, some several feet in diameter, of mica schist. The mica schist clearly antedates the gabbro and is quite similar in its essential features, particularly as to its composition, to the schists of the Coutchiehing, though it lacks some of the evi- dence of deformation to which the latter have been subjected. With little doubt it represents an altered pre-Keewatin sedi- mentary rock which was caught up by the gabbro magma in its pacsage upward. If there is anything further needed to establish the fact that the Coutchiehing rocks are disposed in an anticline domed around an intrusive mass of granite and that they pass on both flanks of the anticline beneath the Keewatin, I should be very glad to have the International Committee or the U.S. Geological Survey point it out. If there be nothing further needed to complete the proof of this relationship, it would seem to be incumbent upon these eminent authorities that they should recoasider their somewhat dogmatic denial of the existence of such a series of rocks as I have described under the name of the Coutchiehing. North of the south shore of Redgut bay the mile and a half wide belt of Coutchiehing rocks just described encounters another extensive mass of granite, which is locally quite gneis- sic, and in doing so it breaks up into at least three tongues. The middle one of these lies along the axis of the anticline and is exposed on the shores of Moose point. Here, as farther south in the same situation, the Coutchiehing mica schists are almost quite flat over an area of half a mile by a fourth of a mile. 16 But • little north of Moon point the lame iiehmti dip down to the MUtheaat into the granite, in which they are embedded, at anglee varying from 2&' to 30", and the foliation of the gran- ite gneiH haa the same dip. This tongue of achiat is travened by numerouj apophyses of the granite and the neighbouring mam mass of nanite holds numerous inclusions of the invaded "**» • . i '■ *vident that we have here a remnant of the actual roof of the batholith, reposing in flat attitudes upon the granite in the axis of the anticlinal fold which was domed up by and arched over the granite magma at the time of its consolidation. This domed or arched relation of the invaded rocks to the under ying batliolith is characteristic of several of the smaller batholiths of this region. It is noteworthy that it is the same •tnictural relation as that which obtains in the case of lacco- liths. It IS one which must be taken into consideration in any complete account of the mechanics of batholithic intrusion. u--.^u ^a^'e'ly of the three tongues of the Coutchiching belt skirts the east ^lde of Redgut bay in juxtaposition to a similar tongue of the Keewatin and the two together form a point or prong tapering out to nothing in the granite less than a mile north of Bear Pass Station on the Canadian Northern railv^^iy. The westerly tongue is a residual strip of the main Coutchiching belt left between the intrusive granite of the north end of Redgut bay and the Keewatin of the west side of the bay. This tongue swings around so as to enter the shore with a northwesterly strike and a southwesterly dip of from 55" to 60° below the Keewatin. The exploration of the country south of Base-line bay indicates that this tongue is cut out by the granite so as to bring the latter against the Keewatin at a point less than a mile inland. n>^° **?*'. .^°"**^'*^^t'^"d of Bear passage the main belt of Coutchiching mica schists bifurcates and, as has been stated, encloses the granite mass which extendi southwesterly to Tra- verse inlet. The two arms of the bifur-ation coalesce between lYaverse hay and Joint bay and at the latter the belt opens out again to embrace another small batholithic dome of granite, which extends with a major diameter of 3J miles west nearly to Goose island. The greatest north and south diameter is a little over 11 miles. This granite mass may be refer- red to bnefly as the Knuckle Itlznd granite. It is even more homogeneous, less gneissic and freer from pcgmatitic and aplitic dykes than the Bear Passage granite and it also con- tains very few inclusions of the encasing schists except at the immediate contact. The phenomena of intrusion are, however, well displayed at the contact, both by the contact metamor- phism of the^ encasing rocks and by the apophyses from the main mass of the granite cutting the schists. It is the same I'lm IV, I) A. Huriiontal )oint^< in Kruniti> at lontai-t with CoutrhichinK on Joint bay. B. Contact of Kranite and Coutrliiehing on thf west side o( the entrance to Blind bay. 3SS70-P. IS. 17 kind of r*nite m that of the Bew Pmnun k>n» uiri !. w«..k» li3th"tf'"'x«'?*M' '"'r 't •"'^ Tr''lSi^t"i'i „# »k n « "* ** """■ between the MUthweat im«' ''^ds have tWs feature in a ?ykt irthrji^/''^n».°' 't^'' '* ^'together. Numeous ?tVe-norwSS%*h^^-^dvr^^^^ oUhTSJon'Jh; ?" *'^'"«l' «' *»'•' tfJ'islaSd^fu t tuS of th« S c V f '^°'* '^'J"^ *h'' <'°"*»''t « revealed, the strike C and ?^ 4V i th ""'^^ ^'T ^f"''* *h« southwest end of hi or rw»l f *Ji.*'"' °°':*'>«'»t «nd and the dip is southeasterly or away from the granite at 40" to 45°. The contact of thn panite and schist to the north of the bay was intersected bv a traverse made from its middle part at a distanced nrhJ.! aTJ^', '^r- 7.^'' ".*"•'« °f the schists here is 102° anj^he fZt *° ^•'^""'•t':; All .the shores of the bay west of thL con! Iround tKt V *^^V** '^ ^'^'''^y '^'^' '^^^ the schists ^ap fhlT^ * r* y^JJ "htuse east end of the granite mass and that the strike of the schists conforms to the contour of^heTn Se ^1(th "coXT'^' *'V'='''«*'' ?- domed about'the n»uJ*.\ ■ contact the granite contains an abundance of ?h.v S ^'"*' "'"l"y "^^""t * ^°°t °' •««« in width, which whiS i«Li?^i"°** so sharply abut upon the contact m in the casi descrOied at Bear passage, are clearly analogous phenol na. They represent the infilling of shrinkage cracks inTht gramte below the over-arching rSof of schU?* The j^aSte ^s 18 ■J also characterized by a remarkably even and sharply defined horizontal jointagc in the vicinity of the contact. Eastward from the contact along the shore the angle of dip increases to G0° and then to G7° and then gets rapidly lower again in Breeze bay. Southwestward from Joint bay the contact is, for about a mile, below the waters of the lake, and then skirts the outer points of Knuckle island. Here following the contour of that island it swings to the west and enters the main shore about a mile west of Knuckle island. Beyond this point this contact swings to the west-nortliwest and the mica schists dip away from the uitrusive granite at angles varying from '>b° to 75° for an observed stretch of a mile. Beyond Marsh island the contact passes between Ben island and Jolni island and is next observed on the nortliwest side of Noon island, where the mica schist is in immediate contact witli the granite dipping away from it to the north 30°. On the north side of Goose island these mica schists also dip north at angles of 45° to 50°. It is evident from a consideration of the map that, ni the interval between Ben island and Cloose island, the schists have swung sharply ."round the west end of the Knuckle Island granite. TJie northerly dip of the mica schists un Noon island and Goose island at the very moderate angles mentioned, 30° to 50°, is towards and under the Keewatin schists of tlie mainland and these dij) also northerly at about G0°. The mica schists of Noon island are traceable across the head of Duck bay where they as before dip below the Keewatin at 50° and the observed dip of the latter is 00° a little north of the contact. This belt of Coutchiching lying between the granite and the Keewatin tapers out easterly so that it is eventually cut out entirely by the granite and the granite comes against the overlying Keewatin, as may be seen in a section northerly from Blind bay. By way of summary, it may be said that the Knuckle Island granite is in all essential particulars similar to the Bear Passage granite, that it underlies the Coutchiching schists which are domed around it, and that the latter dip away from it below the Keewatin rocks which flank them, which relationship is particularly clear as regards the Keewatin on the north side of the dome. To the southwest of the Knuckle Island granite, the Cout- chiching belt again bifurcates and embraces a mass of intrusive plutonic rocks which extends from Sand Point island westward through Rainy lake in an ever widening area to the western limits of the map. The southern portion of this area is chiefly occupied by biotite granite gneiss which appears to terminate between Last island and the outlet of the lake. The northern part is occupied by mica s\ enite-gneiss, which extends with 19 increasing breadth wostwaril to the west side of the lake and thence indefinitely beyond. Between the granite-gneiss and the syenite-gneiss tliere is a narrow belt of Coutchichiiig mica schists extending from Last island to Nowhere island, a distance of about ;i miles. The widtli of this schist belt is only a few chains. The eastern end of this complex plutonic mass is about one-fourth of a mile west of the northern extremity of Sand Point island. Here the width of the mica scliists sejjarat- ing this ii\trusive mass from the Knuckle Island granite is a little less than one-fourth of a mile. From this point of bifur- cation, the northern arm of the Coutchiching belt extends througli Jolin island, Goose island, Lichen island, and the southern part of the peninsula lying south of (Commissioners bay from Back point nearly to Gash point, where it ends in a point. The southern arm extends through the north part of Sand Point island. Angling island, Red Pine island, Jack- fish island, Stop island, and the south sliore of the lake from Medouganak point to Coutchiching at the outlet of tlie lake and for an indeterminate distance beyond. West of Noon island the contact of the Coutcliiching against the Keewatin which lies to the north of it, is first seen on the shore about 35 chains north of Back point. Here both mica schists and the hornblendic schists of the Keewatin dip northerly at an angle of from 65° to 75°, but a precise line of demarcation between the two series cannot be located in this section. For 200 feet or more across the strike, horn- blende schists idternate with mica schists and it is probable that the conditions of sedimentation which prevailed in Cout- chiching time persisted after the volcanic activity of the Keewatin had set in m neiglibouring parts of the region, this volcanic activity yielding strata of basic material which became intercalated with tlie uppermost beds of the lower series. West of this the contact as mapped is characterized by high dips, about 80° to the north, in both series, and the evidence of the superposition of the Keewatin on the Coutchiching depends upon the continuitj- of the rocks of both series with those farther east, where, as above described, the relations are clear. In the foregoing description of tlie central anticlinal belt of Coutchiching, extending on the map accompanying this report from the middle of Redgut bay to tlie lower end of Rainy lake, attention has been directed chiefly to the relations of the mica schists of that series to the underlying intrusive granites on the one hand and to the Keewatin, which lies above it on the other side of the belt. It remains to describe briefly the southern boundary of this belt and its relations to the Keewatin, which lies to the south of it. 20 The eastern boundary of that portion of the Coutchiching belt exposed in the vicinity of Bear passage has been described as skirting the west side of Finger point half a mile east of the entrance of Bear passage. The belt of Keewatin rocks with which the Coutchiching is here in contact, is, how- ever, narrow and tapering to the south. On the east side of Finger point is another belt of Coutchiching schists which skirts the shore on that side and occupies all of the north and east side of Shelter cove. This belt has a width across the strike of the schists of about half a milr. Between the Bear Passage belt of Coutchiching and the Shelter Cove belt the tongue of Keewatin tapers t'- the south, but includes two small islands ofif the point, ,r.^ is, beyond these, no longer seen on any of the islands. To the north it widens for about 2} miles and then bifurcates about a southwesterly projecting lobe of the large and irregular granite area which extends easterly from Redgut bay. At the point of bifurcation the Keewatin rocks have a breadth across the strike of nearly a mile. Both arms of the bifurcation are apparently cut off by the granite, the west one in about a mile and the east in 2 miles. This area of Keewatin has thus the shape of an acute spearhead, the converging sides of which are bounded on both sides by Coutchiching rocks and the re-entrant base of which abuts upon and partially encloses an intrusive mass of granite. This relationship is interpreted as the tapering end of a synclinal trough sunk in and closely appressed in the underlying Coutchiching, the larger part of the fold having been cut away by the intrusion of the granite. But the dip of the rocks on both sides of the contact on the shores of Shelter cove is southeast at 60° to 70°, so that if we interpret the Keewatin as an appressed syncline we must also regard it as an overturned one. Similarly the Shelter Cove belt of Cout- chiching becomes an overturned anticline since the dip is fairlv uniform across its breadth. The Shelter Cove belt of schists is traceable inland as mapped for about 4 miles, having been intersected by a traverse made northerly from the extreme north part of Swell bay along the west boundary of the Indian Reserve 26a, and again by a traverse from the south end of Little Ottertail lake 1 he rocks of the belt show stratification very plainly at a number of places, particularly on the shores of Shelter cove and the schistosity is parallel with the bedding. Petrographically the rocks of the Shelter Cove belt as ex- posed on the shores of Shelter cove are not identical with those of Bear passage. The differences are, however, clearly ascrib- able to the fact that the sediments are less altered. In general the character of the Coutchiching rocks is in notable degree a 21 function of their distance from the granites which invade them. Near the granite they are typical harsh mica schist homfels with, in some beds, an abundant development of contact minerals particularly cordierite. These weather out on the surface in a wart-like fashion, and where the rock is broken the presence of these crystals gives the rock a nodular appearance, the schis- tosity accommodating itself to their contours. At a distance from the granite these minerals are not developed, but the rock may be a well defined fine grained mica schist. Still farther away some of the beds may be mica schists while others interstrati- fied with them are scarcely more than phyllites, or quartz slates in which the mica is present only on a miToscopic scale. On the basis of mineral composition some might indeed term the latter quartzHes, but this term as usually employed suggests if it does not definitely imply, that the original rock was a sand- stone, whereas the rocks here referred to appear never to have been sandstones but rather extremely fine siliceous silt^i. In their present condition, in view of the poverty of our nomen- clature, they are better termed quartz slates. Now in addition to the mica schists of the Shelter Cove belt there is a consider- able proportion of phyllites and quartz slates, which might easily have become mica schists had they been subjected to more intense metamorphic action. Indeed this same belt if followed about 4 miles along its strike to the vicinity of the granite on the south side of Little Ottertail lake, changes its character and the rocks composing it become well defined mica schists. This only partially metamorphosed facies of the Coutohiching sediments characterizes the southern margin of the main belt of these rocks as traced through the islands of Rainy lake from Shelter cove to Stop island, a distance of about 12 miles. But beyond this along the strike they assume the charac- ters of mica schists; and wherever we pass from the margin towards the granites which occupy the central part of the belt we may observe similar evidence of more intense metamorphism. The mapping of the southern boundary of the main central belt of Coutchiching where it is in contact with the Keewatin to the south is based upon practically continuous tracing as far as the insular nature of the exposures would permit. Besides the exposures observable on the two traverses north from the north side of Swell bay the contact of the two series may be seen on the west side of Wreck point, where the Coutchiching strata, here mica schists, dip under the Keewatin greenstone at an angle of 70°. For the next mile to the southwest it is concealed by the waters of the lake, and then cuts across the south side of Dude island with a strike of 53° and dip of 75° to 80° to the S.E. Three-fourths of a mile beyond this it similarly cuts across the south side of Morton island, the dip here being vertical. 22 On both Dude island and Mortor island the conditions at the contact are the same. Feebly micaceous schists anil phyl- lite and siliceous slates in which bedding is more or less apparent stand in highly inclined or vertical attitudes in juxtaposition to greenstone schists, travorsing which are bands of chlorite schist. On ^Iorton island the chloiito schist is in contact with the Cout- chiciiing. The schistosity of the Keewatin rocks is parallel to the contact plane. The contact is next seen on the eastern end of Armot island 2] miles to the west-southwest, where it is very iimilar to that on Morton island, but more difficult to locate with precision, owing to tlie evident gradation from one set of rocks into the other. The dark green chlorite material of the Keewatin whether derived from volcanic ashes or from the waste of vol- canic rocks accumulating in the region, is evidently intermixed with t)ie uppermost beds of the Coutchiching and for a space of 100 or 200 feet it would be difficult to say where one series ends and the other begins, although the exposures are excellent. It is evident that there is no erosional break or uncon- formity between the two sets of beds. The schists are in vertical atMtudcs and as we go from the transition zone, we pass on the north side into rocks which have no chlorite and on the .south side into rocks which have o wholly volcanic origin. Quite similar conditions obtain at the section afforded by the Narrows between Armot a id Sand Point islands, and again at the west end of Sand Point island and the south side of Angling, Red Pine, and Red Sucker islands. Throughout this stretch it is practically impossible to locate a definite precise boundary between the two series, although on either side of a transitional zone these two series are strongly contrasted as to physical properties and origin. On the south side of Jackfish island, however, the line of demarcation between the two series appears to be more sharply defined. Here a portion of the shore is occupied by typical Keewatin greenstone schist and to the north of this lie the mica schists of the CoufpliicliinK with a narrow intervening strip of rather fissile chloritic schist. At all of the localities above mentioned from Morton island to Jack- fish island the dips of the schists at \,he contact and the contact plane itself are either vertical or northerly at angles ranging from 90° to 70°, so that little can be certainly inferred as to the question of the superposition of one series on the other. There is, however, nothing in this attitude of the rocks inconsistent wth the view previously expressed as to the anticlinal character of the belt of Coutchiching lying to the north of this contact. The significant facts connected with this line of contact are the mutually confirmatory observations: — ham 23 (1) Tliat there is a transition from one series into the other, which may be explained by basic volcanic ashes having been contributed to the basin in which the last of the CoutchichinR sediments were accumulating, in advance of the outpouring of lavas, and (2) That there is no trace of conglomerate or other evidence of erosional interval between the two series. Beyond Jackfish island the contact lies in the channel north of Grassy island and passes into Rat-root bay where, however, it appears to be cut off at the surface by the trans- gression of the conglomerate wliich occurs there. The relation of this com '.omerate to the Keewatin and the Coutchiching will be discussed in p later part of this report. THE SOUTHERN BELT. The area embraced within the special map accompanying this report includes the .lorthern part of the great body of mica schists mapped as Coutchiching in the report of 1887. The northern edge of this terrane is in contact with the main Keewatin belt of Rainy lake along a line which extends across the map from east to west. It was the examination - this line of contact, particularly in the vicinity of Rat-root bay and at Shoal lake on the Seine river, which led the Interna- tional Committee to conclude that the stratigraphic relations of the Coutchiching and Keewatin were just the reverse of my statement of them contained in the report of 1887. The following paragraph, quoted with approval from the report of the Committee, by the tl. S. Geological Survey' clearly express s the views of my critics : — "In the Rainy Lake distric. ;Ii? parly observed the relations of the several formations along 0"c line of sietii,.. at the cast end of Shn.-*! lake and at a number of other loealities. The party is satisfied that along the line of section most closely studied the relations are clear and distinrt . Tlie Coutchiching schists form the high- est formation. These are a series of micaceous schists graduating downward into grecti hornblenilic and chloritic schists, here mapped by Lawson as Keewatin, which pass into a coni^lomerate known as the Shoal Lake conglomerate. This conglomerate lies upon an area of green schists and granites known as the Bad Vermilion granites. It holds numerous large well-rolled fragments of the underlying rocks, and forma the base of a sedimentary series. It is certain that in this line of section the Cout- chiching is stratigraphically higher than the chloritic schists and conglomerates mapped as Keewatin. On the south aide of Rat-root bay there is also a great conglomerate belt, the dominant fragments of which consist of green schist and greenstone, but which also contain much granite. The party did not visit the main belts coloured by Lawson as Keewatin on the Rainy Lake map, constituting a Urge part of the northern and central parts of Rainy lake. These, however, had been visued by Van Hise in a previous year, and he regards these areivi as largely similar to the green-schist areas intruded by graniteat Bad Vermilion lake, where the schists and granites are the source of the pebbles and bowlders of the conglomerate." The views here expressed are so positive that in the re-ex- amination of the iield I was prepared to find that my early inter- ■Mon. LII, p. 147, 1911. 24 capacity reviewing aSeakewS " ^'^*'''»' deci«ion that the CoutchiSg TeS °m "^v *,^^^ there must be some very convir^in^ .^!f . • *"® Keewatm, of this relationsniD I havp wi *^ and unequivocal evidence All the facts Xh I have Teen S to ofi'"^ *° ^°^ ^^^ P'"^^- ent with the superposiUon of Thrii^ *•"'"' are quite consist- ing established CTh^e^S l^lndrarP^asT^^ ComJJtUTn"?:loi?T?L'''^'*'^''^i " *'" Coutchiching up?n the KeewatinlTr^H ^^P^'-P^ti^'n of the C^ nrrsSFfV^!^^^^^^^^^ base of the Keewatin In thii'f"''^ this conglomerate at the the InternJtitTc^mmitte?i'^\E^toTf! ^^^'^^omj^t th« conglomerate is iviV if!!»!;- • • *"^ conclusion that westerly through Ev UW. /« fu ^*'°^ '?^*' ^^ thence the south of it for h.K . Jle teyond thi. w^JrfSS ?»"»">'.«; 25 1 with one foot on Coutchiching and the other on the Keewatin. There i8 no trace of conglomerate or other evidence of eroKionai unconformity at the contact. The contact plane ia parallel to the Hchistosity of the rocks on either side. This same belt of Keewatin comes to the Seine river just above Wild Potato lake on the south side of Partridge Crop lake (Pinirmiifa lakr) and agam above Sturgeon Falls, with the rocks of the Seine series lymg to the north of it. On the south side of Shoal lake a traverse made by my assistant, Mr. H. C. Cooke, from a point about south of Bell City, encountered this i me belt of Keewatin at from 55 to 70 chains south of the lake sh ire. To the north of tte Keewatin belt he tlie pebbly grits, quartzitos, and greywackes of tlic Seine aT^*' 1 *'°.**^^ ^^^^ ^^'^^' t^*' ™Pa schists of the Coutchiching. About IJ miles east of this another parallel traverse was ma,de by Mr. Cooke, but the place where the Keewatin belt IS due IS occupied by a muskeg with the rocks of the Seine series on the north of it and the mica schists of the Coutchiching on the south. Still another traverse, made by myself 2 miles to the east of thf last, encountered a belt of muskeg and glacial drift, about half a mile wide, between the Seine scries and the Coutchiching, the latter being exposed as typical mica schists with a strike of 73° and a vertical dip at a point about li miles south of the Seine river. At the mouth of the creek which enters the Seine river just east of the portage to Rat river, the Keewatin belt is again ex- posed, with the pebbly grits and quaitzites of the Seine series on the north of it and typical Coutchiching mica schists on the south. The strike of the rocks is east ^nd west and the dip departs little from the vertical. From this point westerly the Keewatin rocks occupy the south side of Grassj lake for a dis- tance of 3 miles and comprise greenstones, greenstone schists, and chloritic schists. Short traverses south from the lake shore reveal the Cuutehiching mica schists immediately to the south of the Keewatin. Nowhere was any conglomerate found at the contact of the two series, but the conglomerates, quartzites, etc., of the Seine series are exposed at a number of places on the north side of Grassy lake to the north of the Keewatin belt. West of thb lower end of Grassy lake, along the Seine river, the exposures are so poor that little informa- tion can be obtained as to the relations of the two series, but it appears that the basal conglomerate of the Seine series, which on Shoal lake lies wholly within the Keewatin area, obliquely crosses to the contact between the Coutchiching and the Kee- ora"; '^^^^ '^ ^*® position for 2 miles along the north side of Cliff lake. This is the only place that I know of where the con- glomerate actually lies between the Coutchiching and Keewatin. 36570—3 26 and the only place at which, taken alone, it m'glit be interpreted as a basal couxlomerate of the CoutchichinR. But this inter- pretation is BO inconsistent with many other sections across the contact of the Coutchiching and Keewatin and with the general distribution of the conglomerates within the Keewatin area, that it is very probable the interpretation suggested is fallacious. The position of tlie conglomerate on Cliff lake may be readily explained on the supposition that a gravelly flood-plain, which for the most part was spread out over t' e Keewatin rocks, at this place covered the contact between be Cuutchiching and Keewatin and subsequently became infolded and schistified at the time of the acute deformation of the region. The conditions under this supposition would then be quite analogous to those at Steeprock lake, where, as I have shown', the basal con- glomerate of the Steepock series was spread across the con- tact between the granitoid gneiss (Laurentian) and the Keewatin and subsequently infolded in vertical attitudes between these two sets of rocks. Smyth- in his description of the geology of Steeprock lake, failed to recognize this infold, included the Keewatin with the later series, and regarded the conglomerate as plunging indefinitely beneath the combined assemblage. A similar misconception of the structure might well arise at Cliff lake if the conditions there were considered without regard to information obtainable in other sections. Another illustration of the infolding of a conglomerate at the contact of two different formations, both older than the conglomerate, is afforded by the Seine conglomerate on Shoal lake, as I shall show on a later page. West of ClitT lake, the conglomerate is not exposed for some miles, but on the east shore of Bleak bay and on some of the islands on the north side of that bay, the Keewatin rocks are succeeded on the south by a dctrital formation which doubt- less represents the conglomerate horizon, and the next rocks observable to the south of this on the shores and islands of Bleak bay are the regular Coutchiching mica schists. Beyond Bleak bay, to the west, the contact of tlie Coutchi- ching and Keewatin is contr iled by the waters of Rainy lake for about 8 miles. It is i,ext observable on the Minnesota coast a little west of the line between St. Louis and Itasca counties, whence westward it skirts the shore for 2^ miles to the entrance of Black bay. Here the condition at the contact of the two series is very much like that on Armot and Sand Point islands and the line mapped as the boundary must be more or less arbitrarily chosen in a transition zone. 'Dfpt. Minrs. Geological Survpy, Mom. 28, 1912. •Structural Geology of Steeprock lake, Am. Jour. Sci. 142, p. 317 et seq. 1891. 27 Soutli of the line adopted, tlie rocks are prevailinRly hiRhlv altered mica schists with an east and west strike and an ar.nrox- imately vertical dip. To the north of this lie alternatinK bods of chloritic schist, groy phyllites, and quartz slates, with Kreen- stone schists on some smaU islands off shore. There is no conglomerate at the contact; but the rocks of the Coutchiching to tlie south are notably more highly crystalline and metam- orphosed than thoxe of the Keewatin to the north and this fact IS made use of in deciding where to draw the lino hetween the two series. Followed westward across the mouth of Black l>ay, the contact lies between a group of three small islands and the mam shore. The islands are composed of typical Keewatm greenstone schists; the rocks of the main shore a few chains to the south are typical Coutchiching mica schists. Half a mile west of the islands the contact intersects the main shore again with the Keewatin schists on the north and the Coutcliiclung on the soutli. Then, is no conglomerate or otrier evidence of erosional unconformity rt the contact. A little ess than an ciglith of a mile to the iiorfi of the contact, beyond the be t of Keewatm, is a conglomerate; but as will be shown later, this lies m a synclinal trough within the Keewatin urea just us It docs at fehoal lake. A mile and a fourth west of this the belt of Keewatin which intervenes between the Coutchi- ching .-.ad the conglomerate is again seen at the bottom of a smalbiy just east of the line between concessions XXII and AAlll ai'd again at the mouth of the creek which f ters the lake just south of (ira.ssy narrows. Westward from this creek the country is low and marshy and other exposures are not known, llic general conclusions arrived at from a consideration of tlie coud.tions which are observable at tlie contact of the mam southern area of the Coutchiching with the Central Rainy Lake belt of Keewatin are:— (1 ) There is no i)roof of the superposition of the Coutchiching upon ihe Keewatin. (2) The post-Keewatin conglomerate which has been supposed to be tlie base of the Coutchiching lies for the most part well withm the Keewatin area and not at the contact ot tJie two series. (3) The conglomerate prior to the last folding of the region lay across the Keewatin and Coutchiching rocks indifferently and tlie occurrence of the conglomerate at the contact on Cliff lake is best explained as an infolded synclire. (4) With this assumption for Cliff lake and at all other points on the contact without such assumption, the conditions are quite consistent with tlie superposition of the Keewatui upon the Coutchiching estabUshed by the Rice Bay and Bear Passage sections. 36570—31 28 A re-exRmiimtion of tho action of the Coutchiching south aiid eoutheftHt of Bloak bay uh fur «s Cormorant l)tty by my awiistant, Dr. R. C. Wallace, confiriiw my interpretation of the structure as given in the report of 1887. On Cliff lake and on the nhores of Hleak bay the dip of the Coutchichinj? rocks diminisheu as we go Houtherly across the ntrike from vertical to 70°N. At Hallelujah point it is SS'N. In the next mile across tho strike it diminishes from this to 35" and from the narrows to Cormorant bay it diminishes to 15° and in places it is almost flat. From Cormorant bay to Deer's Honi point the northerly dip ranges from 20° to 55°. On some of the islands between Deer's Horn point and Vague point is a granite intru- sion and beyond this to the south tlie dips are southerly. In the rejwrt of 1887 I interpreted the line of change of dip as an anticlinal a.tis and I find no reason to change my view. The rocks between this axis and the Seine river occupy structur- ally the northern limb of an anticlinal fold of bedded mica schists and paragneisses and the thickness of the strata involved is about 4} miles. The chief objection that has been urged to this interpretation is the great thickness of the strata. But when we compare it with the 29,000 feet or 5i milej of monoton- ous sandstones and shales in the Cretaceous section of California, I fail to see that excessive thickness can be urged as an argument against my interpretation of the structure. The absence of any valid objection to the plain implication of the observed dips of the Coutcliiching rocks between Bleak bay and Cormorant bay renders unavoidable the recognition of this belt of strata as the north limb of an anticline. Conse- qut itly the Coutchiching rocks underlie the Keewatin This conclusion will be confirmed hy showing on a later page that the structure of the Keewatin L.^lt to the north is synclinal. PETROGRAPHICAL NOTES. t'rom the south side of Lower Rice bay a number of repre- sentative specimens of the Coutchiching mica schists were taken for petrographic examination. One of these is a fine textured grey mici at, with a ponounced sheen on the cleavage surfaces. Microscopically it appears in thin section as a mosaic of quartz and brown biotite in the ratio of three to one, these two minerals making up four-fifths of the rock. The other important mineral is zoisite which occurs rather abundantly, partly in well defined but irregularly terminated prisms and partly as allotriomorphic granules. The mineral thus identified has a very low double refraction, but a high refraction. It is biaxial and is optically positive, with a negative elongation. It shows cleavage parallel 2b ' rlonRfttion an«l the extinction w approximately utraight. Awjociated with the xoiHite there m i\\m some epidote. There are occahional cr>Btali» of apatite, titanite, and pyrite, and trace« of chlorite and caicite. The biotite in diHixMed with itH cleavage parallel to the plane of ttchiutosity, and had itn greatent elongation in that plane. Another Hpecimen pretteutti the Bame general appciirance of a typical grey mica ichist, but the Hpanglee of mica which reflect the light from the cleavage nurfuceM arc larger, and these BurfuccM have a diHtinctly luntrouB appearance. In thin section tluB rock is alBo a mosaic of quartz and biotite, but the latter is olive green rather than brown in positions of maximum absorption. 'Ihe rock contains Borae jsoiMite but not nearly so much as in the last specinien. This «U;liciency of zoisite Ih made up for, however, in the abundance ot pale wine coloured garnet. This mineral bIjows no idiomorphium, but occurs as lenses and elongated granules disposed parallel to the schistosity. The boundaries are allotriomorphic to both quartz and biotite. There are a few granules of pyrite in the rock and an occasional crystal of epidote is observable. Another specimen is a line textured grty schist having a laminated appearance and having wart-like protuberances upon Its weathered surfaces. Examined microscopically the rock presents the appearance of a mosaic consisting chiefly of quartz, fresh feldspar, and brown biotite, with a pronounced parallel structure due to the disposition of the biotite in layers. The feldspar predominates over the quartz and comprises orthoclase, microciine, and albite. Along with the biotite is considerable n.uscovite. (iamet occurs in occasional large anhedrons, and there is a fair sprinkling of magnetite and Jess pyrite. Zoi ite, apatite, and titanite are sparingly represented. The wart like protuberances observed upon the weathered surfaces prove to be nests of cordierite, which in this way makes up p ' "pg 10 per cent of the rock. At the outlet of Rice bay the north side the rock =s a fine grained grey garnetiferous mica schist. Microscopically the rock appears to consist chiefly of quartz and greenish biotite with some feldspar, garnet, and clinozoisitc. The feldspar com- prises both orthoclase and acid plagioclase and some of it is partially kaolinizcd. The garnet occurs in irregular, but usu- ally elongated anhedra and the larger of these have a pro- nounced poikilitic structure due to tlie inclusion of email grains of quartz. The mica plates have a marked parallel orientation and are elongated in the plane of schistosity; but the feldspar and quartz lie in a mosaic showing no elongation. Interstratified with the fine textured grey schists above des- cribed are bands of coarser mica schist in which the spangles of 30 mictt rftiiRo from one to 8«>vcral millimotr.H in diumrttr and give th.. rock u H,m,.K!,.d npiH-araiue on all fracturt. Hurfnro,. NotoH on thrt'*' of tluttc fcillow: — One of the NiM-cimcns rff.'rret<>.a"'» quartz, the latter being sub- ordinate m amount to the micas. The rock in general hvs a coarse texture and the schistose structure is rudely developed but m thm section there appear oval areas half an inch in larger diameter composed of the same minerals with a much finer tex- ture and in addition the mineral chuozoisite in rather large stout prisms. '' Interstratificd with the mVa schists of the south side of tnrTi. . i"'\.'""'" «<^.<''*«'""''l bands of black glistening fine tex- tured hornblende schist, with thin lenses of quartz disposed parallel to - - schi.stosity. One of these in thin section appears as mosaic ,, quartz and green hornblende with a lam mated wZh"''/"",-". '^' 'Alternation of bands rich in hornWende wth bands which are chiefly composed of quartz. W^mJ ''."^y*'"'!'' '« f"r tl'e most part elongated in the plar ^ of^ch istosity, but IS ocmionally transverse to it. Associate, with the hornblende is a little brown biotite. Magnetite in small granules is di-seeminated through the rock ih. ^i •'"'*• ""rth of the outlet of Rice bay on the west shore fi» ?^'?* «*^|"«t« fl?ve interstratificd with them a bed about 10 Sfo r^- f peculiar character, dipping westerly at an angle of w . I his bed 18 distinct from the mica schists above and below M it owiriK ti> its nuiHHivi' or n()n-Hrliif*t«me AHpi'ct, liut is irrf>KU< liirly liimiiiiitcd. Tin- rock Iiuh tlu« tcxtvin- nf uii ijuluratcd HiiiiiNtii,. , iiiul in of i\ (tr.y colour liiotclud with KnTuisli >. llow iluc to the !il)Uiiiliiin'«' of I'piilotc. In nonie j»urfn it appturM to he Ktinu'tiftTouH jind in otlur« pyritifrrouH. Mii-n \h conspic- uouniy ulmrnt. In ttiin M-ction the rock in fouiui to In- hiKlily fclilhpiithif in conipoHitioii. One scctior sIiowh it (o be conipon- «'<1 diicHy of (lUiirtz, fnsli acie nodular bodies rich in cordierite which charac! terue tlie two specimens. In column IV is given the average of Pal'^ozoif ;rf ^T' '"^ '" ^ ''^ f composite analysis of fiftT.^^; Pahiozoic shales for purposes of comparison. In colunm VI is the analysis of the abnormal rock found in the midst of the SiO,... TiO, AltO,. FejO)., FeO... MnO.. taO... BaO... MgO . NaiO.. K,()... H,f)- H^+. PiO... CO, ... 11. SO». 8 .. CI . Cr,0, 8rO.. C .. 59-42 60 19-69 4-94 10 1-96 0-04 .3-84 2-04 2-96 24 2-64 18 58-32 0-69 18 -.SB 1-93 5-71 10 304 01 2 44 3-44 3-10 40 1-73 0-18 III. IV. 0-01 none none •race 0-02 none none 002 101-02 I lOO-M 57-08 108 13-!J2 3-43 7-83 0-09 1-32 0-03 6-84 0-24 5-28 38 2-12 21 0-15 trace none 58-27 0-79 17 37 2-57 6-16 0-10 2-11 0-Ot 4-37 1-91 3-78 0-34 2-16 019 60- 15 0-76 16-45 404 2-90 trace. VI. 006 1-41 0-04 2-32 1 01 3-60 089 3-82 0-15 1-46 0-58 001 0-88 (. 57 0-11 7-66 0-04 0-72 1 60 3 10 0-19 0-32 0-18 0-03 0-10 none 0-04 5 99-60 ' 100-23 100-46 99-63 r'ii'^TdfiPrF^-^^-v^^^^^^ &Tierr^'a!:i.'"*j:'ii"c5o'or'"'^^^ and unnTJ^Tl'"? °/,*^^^ analyses it appears that I, II, and III, and particularly their average, IV, representing as far ^aiUn^ f vn^^ r '™i*t^ ?.«election, th^ compositionTthrpre- vailmg type of > outchichmg rocks, agrees fairly well with the composition of the Paleozoic shales shown in v! The chief 35 difference appears to be in the ratio of Fe203 to FeO; but this dif- ference is in accord with the process of deoxidation which com- monly takes place in the passage of a sedimentary rock into a crystalline schist'. The proportions of silica and total alkalies and the ratio of tlie magnesia to lime accord with the general char- acteristics of sedimentary rocks, as distinguished from granites, mentioned by Adams, ^xhe analysis Vj does not sustain so clearly the suggestion that this rock is also an altered sediment and it is apparent that, if it be a sedimentary rock, as supposed, its original composition was quite different from that of the sediments which, by the same process of metamorphism, gave rise to the normal mica schists. THE KE^^^ATIN SERIES. GENERAL CHARACTER AND DISTRIBUTION The Keewatin rocks of the region examined comprise: (I) fine grained greenstones showing frequently elliiisoidal or amygdaloidal structures or both ; (2) coarser textured green- stones showing neither ellipsoidal nor amygdaloidal structures ; (3) greenstone schists of varying degrees of schistosity ; (4) rather massive chlorite schists; (5) evenly fissile chlorite schists ; (6) irregularly cleaved chlorite schists ; (7) black glistening hornblende schists, usually on the periphery of the Keewatin belts where they come in contact with granitic intrusions; (8) grey felsi.s, sometimes amygdaloidal; (9) sericitic schists ; (10) various stratified greyish green schists probably ash beds ; (II) agglomerates ; (12) grey siliceous slates and schist ; (13) banded cherts ; (14) mica schists ; (15) limestone. Besides these there are certain intrusive rocks which may be conveniently included in the Keewatin, since, although they are of later age than the aggregate of rocks above listed, they are confined so far as is yet kno^oi to the Keewatin areas and were injected into the series beiore its chief deformation and metamorphism. They thus partake of the structural features of the Keewatin belts. These intrusions appear to have been of the nature of thick sills and comprise two types of gabbro, both of very coarse texture. One is highly feldspathic, consisting almost wholly of basic feldspar, and would be classified as an anorthosite. The other is highly homblendic. The two gab- bros are strongly contrasted in colour, the one being whitish and the other very dark. In some of their occurrences they are both thoroughly schistified, but for the most part they are massive and unsheared. •Van Hiw. uses. Mon. XLVII, p. 807. 'A further contribution to our knowledge of the Laurentian. Am. Jour. Sci. Vol. L. p. 65. 36 The distribution of these Keewatin rocks may be best aacertained by a glance at the geological map. There it appears that they occur in two principal areas. One of these extends from Redgut bay to Prospect bay and consists of an annular belt, concentric to and outside of the Rice Bay anticline of Coutchiching strata, and a prolongation westward, in the shape of a fishtail, which terminates in so far as the land area is con- cerned, at Gash and Reef points. It may be referred to as the Northern Area. The other area occupies a belt extending acrosa the quadrangle embraced in the map from its northeast comer near Mine Centre to its southwest comer near Rat-root bay. East of Swell bay this belt is much intermptad by intmsive masses and is irregular in form; but from Swell bay westward It tapers very regularly from a breath of about 6 miles to almost a pomt at Rat-root bay. Besides these two principal areas there are two minor belts, one on the south side of Shoal lake and another on the south side of Grassy lake, both extending eastward beyond the limits of the quadrangle mapped. THE NORTHERN AREA. The first mentioned area of Keewatin, annular about the Rice Bay anticline, is composed chiefly of ellipsoidal Kreen- stones, hornblende schists, and chloritic schists. On tho s^hores of Prospect bay there are some micaceous schists interstrati- fied with the hornblende schists; and on Grassy Portage bay and Nickel lake, there are coarser textured greenstones which are not ellipsoidal. On the line of the Canadian Ntirthem west of Nickel lake are bands of siliceous schists and mica schists and near Nickel lake are banded clierts or quartzites. Beginning at the west, the south boundary of this area of Keewatin intersects the shore between Gash point and the line of the Canadian Northern railway, where it lies in contact with the Coutchiching. It lies to the north of the railway for about a mile and is then south of or coincident with the railway for another mile, partly on the shores of Commissioners bay, the rocks being hornblende schists in nearly vertical attitudes. It then bends slightly to the south away from Commissioners bay and emerges on the shore at a point less than half a mile north of Back point where, as already mentioned, there is an apparent gradation from the Coutchiching to the Keewatin indicated by an interstratification of hornblende schists and mica schists in a narrow transitional zone. The southem boun- dary of the Keewatin is next seen on the shore north of Noon island, the hornblende schists here dipping north away from the Coutchiching at an angle of 60°. At the head of Duck bay It is again seen with similar northerly dip, the Coutchiching HilHi 87 here being a very narrow band between the Keewatin and the granite. On a traverse north from Blind bay the Keewatin is found with northerly dip in in>mediate contact with the granite, the Coutchiching having locally been cut out by the latter. On a tra": ;3e north from Joint bay the southern boundary of the Keewatin was next located, but here with the Coutchiching mica schists again intervening between it and the granite; and a similar relation wa.s established on a section north from the head of Traverse bay. It was next observed where it intersects the shore of Bear passage, about a fourth of a mile south of the Canadian Northern railway. Here as already described the Keewatin lies upon the Coutchiching i»t comparatively low angles. From this point northerly the boundary of the Kee- watin skirts the shore and islands of Redgut bay for about 3 miles as mapped, at all exposures dipping away from the Cout- chiching. On the west side of Redgut bay the boundary of the Keewatin curves from northeast to northwest and intersects the shore at a point about three-fourths of a mile south of the entrance to Base-line bay. But while the strike of the rocks thus curves, the dip of the Keewatin is steadily away from the Coutchiching which adjoins it. The location of the boundary of the Keewatin westward from Redgut bay is determined as mapped by a series of traverses in the woods. Three of these were made from the south shore of Base-line bay ; one from Niv- en's base line south at a point between Black Sturgeon lake and Base-line bay; two southward from Black Sturgeon lake; three north or northwest from Rice bay, one from Hopkins bay to Black Sturgeon lake ; five between Rocky Islet bay and Hop- kins bay, and one between Prospect bay and Hopkins bay. These observations serve to determine with a very fair degree of precision the outer boundary of this Keewatin area and show that it is completely encircled by other rocks. The only other boundary of the area is the inner one of the annular belt where it comes in contact with the Rice Bay anticlinal dome of Coutchiching. Within the area thus enclosed is the intrusion of mica syenite and its basic facies which occupy so large a part of the shores of Rocky Islet bay, as a mass of irreg- ular shape with maximum diameters of nearly 2J and 1 1 miles. A notable feature of this area of Keewatin is the curved or hook-like belts of coarse dark hornblende-gabbro. The larger of these extends from the mouth of Commissioners bay, along the south side of Grassy Portage bay. Thence crossing the Canadian Northern railway between Grassy Portage buy and Redgut bay, it has been traced northward on the shores of the latter and by traverses in the woods to the vicinity of the south shore of Base-line bay. Its width has been determined 38 approximately as mapped by seven completely transverse tra- verses and some partial ones. This belt of gabbro lying enMre- ly with the Keewatin has a length of about 11 miles Its maximum width, about three-fourths of a mile, is in its middle part. At its western extremity it appears to split up into a num- ber of narrow tongues which are injected into the Keewatin rocks parallel to the strike of the latter. The belt curves in general with the strike of the Keewatin so that like the latter it is concentric to the Rice Bay anticline. At its northern ex- tremity it swings around to the northwest, and appears to end in a hook, abutting upon the granite-gneiss south of Base-lin« bay. The second belt of homblende-gabbro extends from a point on the north shore of Grassy Portage bay about a mile from its mouth, along the line of the Canadian Northern railway to Nickel lake. It occupies all the west side of this lake, its eastern boundary making a short curve through tho middle of this narrow body of water and thence striking westerly from its northwest end. An attempt to follow the belt farther by tra- verses in the woods showed that beyond the end of Nickel lake it rapidly tapered to a point. Its northern and western bound- ary was approximately determined by traverses, and particul- arly where it crosses the small lake west of Nickel lake. The belt thus has the configuration of a fishhook. Another narrow belt of the same gabbro is traceable for nearly :! miles along the north side of Grassy Portage bay with Keewatin greenstones on both sides of it part of the way. This, however, is probably a branch from the large belt first referred to. Another small belt half a mile long lies to the north of the railway and east of Nickel lake. Contacts of this gabbro with the Keewatin greenstones and hornblende and chloritic schists are exposed at a number of localities, particularly on the shores of Grassy Portage bay, the cuts on the railway, the shores (f Rcdiiut bay, and the shores of Rainy lake. At the more favourable expo- sures it is perfectly evident that the rock is intrusive in the Keewatin. At some it shows a chilled selvage and at others it contains angular fragments of the Keewatin rocks. On the railway between Grassy Portage bay and Redgut bay it also contains angular fragments of the underlying Coutchiching mica schist. It is evident from the mapping that the intrusion of the gabbro mto the Keewatin partakes of the general deformation which has affected the rocks of that series. That it also par- ticipated in the more intimate structural deformation is evident from the fact that at a number of localities the gabbro is thor- oughly sheared and schistose. The fact that this gabbro is wholly confined to the Keewatin area suggests that the intrusion 39 has the character of a siil, or a series of sills, injected into the Keewatin prior to its deformation. If this be so, then we should expect to find the present disposition of the sill or sills conform to and be expressive of the general structure of the Keewatin belt. Now the disposition of the fishhook like areas of gabbro lymg to the west of Nickel lake is distinctly conformable to the synchnal structure of that portion of the Keewatin belt. The Keewatin rocks south of Rice bay dip south away from the southerly dipping Coutchiching, and on the line of the Canadian Nr them railway between the entrance to Rocky Islet bay and Nickel lake the Keewatin rocks dip north on both sides of the gabbro belt and in the vicinity of mile-post 217 this angle of dip IS as low as 43°. At this exposure, which may be followed at mtervahs for over half a mile, the gabbro may be seen resting with a chilled selvage at its bottom upon the stratified Keewatin rocks which dip under it. The gabbro sheet, itself, therefore, appears to have a northerly dip. In view of these facts there can be no doubt but that the structure of the Keewatin terrane in the section south from Rice bay to mile-post 217 is synclinal and that the gabbro sheet partakes of this same structure. The hook-hke eastern end of the gabbro at Nickel lake may thus safely be interpreted as the nose of the syncline. The axis of the syncline has a nearly east and west trend, passing through the middle of the bend of Nickel lake, and the pitch of the synchne is westward, probably at a very moderate angle. This syncline is the complement of the Rice Bay anticline and con- firms the conclusion previously drawn, that the Keewatin rests upon the Coutchiching. Following this line of section through mile-post 217 to the south of the gabbro the northerly dipping Keewatin rocks have a width of about a fourth of a mile, and south of this we en- counter the larger belt of gabbro with a width of a little less than half a mile, and then another belt of Keewatin extending across the striKe about a fourth of a mile to the contact with the Coutchicliing. Tlie Keewatin rocks on both sides of the large gabbro belt dip northerly and would thus appear to form part of the southern limb of the syncline, the axis of which passes through Nickel lake. It is very probable, however, that the middle belt of Keewatin between the two gabbro belts in this section is a subordinate anticline between two synclines. This interpretation finds support in the fact that the low dips at mile-post 217 become much steeper and are almost vertical on the south side of the Keewatin belt. In this view of the struc- ture the Keewatin belt would be a synclinorium and the two belts of gabbro would be detached portions of the same intrusive sheet, which appears to me to be very probable. 40 At the head of Graasy Portage bay the Keewatin rocka dip Bouthei«t away from the Coutchiching mica schists of the Rice Bay anticline at high angles, about 70'; but on the shores of Redgut bay in the vicinity of the railway and in Bear passage south of the railway, the Keewatin i^'tB northeast at much lower angles, about 30°. We thus have again, in this section, a syncline of Keewatin rocks between the Rice Bay anticline and the Bear Passage anticline. In the middle part of this syncline lies the larger belt of gabbro with a breadth on the line of the railway of about half a mile. In this section there is but one belt of gabbro and no indication of a double syncline. It would, therefore, appear that,of the two synclines indicated for the section south of Rice bay, the northern one spoons out near Nickel lake, while the southern one is the per- sistent fold of the Keewatin belt. It is probable that this syncline persists through Commissioners bay to Prospect bay, and that its axial line is indicated by the small wedge of conglomerate to be later described as occurring on the shores of Prospect bay. In general, then, it may be said that the southern half of the Keewatin belt which encircles the Rice Bay anticline is synclinal in structure and is flunked on the south, southeast, and east by the Coutchiching anticline which is so well revealed in the vicinity of Bear passage. When, however, we turn to the northern part of the Kee- watin annular belt '.tending from the east side of Redgut bay to Reef point, we find that it is flanked to the north throughout this stretch by batholithic intrusives. These comprise the granitoid gneiss of Redgut bay and the mica syenite gneiss of Black Sturgeon jlake and Hopkins bay. The former cuts off the extension of the Keewatin syncline, and the unde/lying Coutchiching in the region south of Base-line bay. The syen- ite gneiss having its margin more nearly coincident with the strike of the Keewatin belt, has wholly displaced the Coutchich- ing on the north side of the Keewatin and has also carried away the greater part of the north limb of the Keewatin syncline. For a distance of 2 miles in the isthmus between Hopkins bay and Rocky Islet bay the margin of the syenite-gneiss is appar- ently nearly coincident with the axis of that syncline, as is indicated by the fact that it comes in contact with a remnant of the Seine conglomerate whicli is regarded as having been an inpinched fold reposing upon the Keewatin. THE SOUTHERN AREA. The second great belt of Keewatin, extending diagonally across the quadrangle as mapped, is of varied stratigrapbic com- position, but it comprises chiefly greenstones, greenstone schists, PtATt V. B A. Shcarrd facics of unorthositc, cast ond of Seine bay. B. Granite (below) intrusive in anorthositc (above); Finger bay, Bad Vermilion lake. 36570-p. 41 41 hornb.endc BchiHtH. and chloritic schistH. In addition to thene there are notable occurrencea of grey felaitcM and felHite achiats and at the (ioiden Star mine near the east en' ' of Bad Vermilion lake there is a bed of limestone. In the lower part of the Heriea there are well utratified grey and greenish grey schists, some mica schists, and some coarse detrital rocks. On its northern side the Keewatin belt is bouidcd by Elutonic intrusives from Little Turtle river to the vicinity of ear Puss Station on the Canadian Northern railway. These intrusives are two in numlier anil are differently related to the Keewatin. From Little Turtle river to a ]mnt alwjut a mile west of tlie west end of Turtle lake the Keewatin lies against the edge of a great batholith of handetl or streakwl gneiss liaving a quartz porjihyry selvage, and for this stretch of 10 miles the boundary of the Keewaiin is comparutivelv straight and even, with an east-west strike. Beyond this point westward to Bear FasM Station, the Keewatin comes against a more granitoid gneiss wliich shows no banding, and this intrusive makes an ex- tensive embavment southerly into the Keewatin belt, robbing the belt locally of a large part of its normal width. Into thia cmbaynient project tapering tongues of the schists into which the granitoid gneiss is intrusive. From the vicinity of Bear Pass Station west-southwest to Rat-root bay the Keewatin is bounded on the north by the Bear Passage anticlinal belt of Coutchich- ing. The southern boundary of the belt from the eastern limits of the quadrangle to the mouth of the Seine river is a mass of granite, sometimes gneissoid, known as the Bad Vermilion granite. But for the first :i miles the contact of the Keewatin and granite is covered by a synclinal trough of Seine conglom- erate. From the mouth of the Seine river to Bleak bay, the Keewatin is flanked on the south by the Coutchiching with a narrow intervening strip of conglomerate on the north side of Chfif lake, which is regarded as an infolded remnant of the Shoal Lake syncline. South of the east end of Dryweed island on the Minnesota coast and thence westward to the vicinity of Rat-root bay the Keewatin belt is in contact on the south with the Coutchiching mica schists. In this belt of Keewatin we may include for convenience the coarse, highly feldspathic gabbro or anorthosite of Bad Vermil- ion lake. This rock is intrusive in the Keewatin, aa ia proved by many dykes cutting the Keewatin greenstones on the shores of Seme bay and by the contact phenomena on the north shore of Bad Vermilion lake; but the intrusion took place at a time anterior to the severe deformatiou of the latter, as is indicatrd by the fact that it is locally intensely sheared and schistose. The area occupied by the anorthoeite has the form of a tadpole : the 36670—4 43 bulging i <'(m1 to the en«t inpludeo mtrnt of thp an-ii of Bad Vermil- ion lake and the long ttlcnder tail exteiidn wratward through Seine Imy into the open part of Rainy lake. The total length of the maw in aliout 18 miles and the maximum width at Bad Vermilion lake Ih about A mileH. On the went Hide of BacI Ver- milion lake it in almotit cut in two at its widest part bv a deep embayment of granite which is continuoun with the more ex- tensive granite area lying to the south of the lake. This granite is intrusive in the anorthosite. It is probable from the areal relations of the Kwwatin, anorthosito and (xraiiite that the basic plutonie mass was intnidid into tin Ke«watin in the form of i< lareolithie lens, tap«'ring westward to a sill or dyke and that later when bot'i Keewatin and anorthosite were in- vaded by the granite, the boUom of the central ])art of the lens was displaced by the granite, either by flominj! or by eiigulfment and resorption, thus appearing ii^ an embayment at the present " rface of erosion. Besicles the anorthosite there are minor ' I'urrences of dark hornblende gabbro similar to that of Grassy Portage bay already described. These occur chiefl m the country north of Seim bay and associated with them are outcroppings of titaniferous magnetite. This iron ore has attracted the atten- tion of prospectors find nn effort is being mnde at tlicpres«nt time to clear-cut and positive that httl,. ro..m Ih h-ft for «loul)t. This evidence con»JHt8 in the recognitidn of the Hrv- weed iNland synciiiu; of Seine connlomerate nnd quanteii already dewribed. Thw Hyncline of Seine rockn i^ no ch.H.Mv upprewed that the conglomerate on lM)th limlm of the f jid ia in vertical attituden. Both the flanking conglomerate and „U i .^ dumquartzite are deeply sunk into the Keewutin, and are wl ollv surroun.le.1 by Keewatin from the ea«t end of Drvweed inland to the itMJUth of Hay creek and beyond. The Seine roeks are an thoroughly HchiHt«»He and otherwiHc dynamicallv metamor- phow'd as are the underlying Keewatin rock«. Iti» perfectly evident and certain that the rocks of the Seine syncline have participated in the major folding and deformation of the Kee- watin. It therefore, follows that the Keewatin belt is also synclinal m structure and rests upon the Coutchichinjf f nrtner east in the Bleak Bay section it has been slu/wn that the ( outchu-hmg r(,ck»< between Bleak bay and Cormorant jH.int have the general structure of the northern limb of a great antichnul fold. Agreeing with this the Keewatin rocks north of Bleak bay dip northerly. On the south side of Seine bay th« jingle of dip IS high but on the north side it is in places an low as .Jo , and ranging from this up to 65°. This northerly dip ^ wars to prevail as far as the south side of Swell bay. a distan. of a little less than 4 n-iles across the strike. From this distance there may be deducted, however, nearly a mile for the space occu- pied by intrusive gabbro and granite. On the south side of hwell bay the prevailing dip is almut 70° nortlu-rly ; on the north- east shore of Swell bay the prevailing dip is 70° southeily. This dip applies to the bedding as well as to the schistosity. Althougli these opposing dips are at angles too high to be relied upon for the location of axes of folds, they nevertlieless suggest a syncliiial structure wHh an axis passing through the southeast eornpr <,f ^well bay. This sugRostion is borne out bv the occur- rence of a small patch of boulder conglomerate at' the south- east corner of Swell bay, which may be fairly regarded as an inpinched remnant of the Seine conglomerate, and therefore, in Itself mduative of a synclin-d axis. In the north-south sci tion through Mine Centre from Turtle Jake to the Golden St.ir mine the KeewatL. belt has a width across the strike of about 2 miles, and in this width the dip is iso- clinal and to the north. On the south the Keewatin lies against the intrusive Bad Vermilion granite, the contact passing below tiie beine conglomerate; and on the north it is in contact with o(i.)70 — 44 44 ^e margin of a great batholith of banded and streaked gneiss, l-hore 18 thus little in the section except the dip to indicate which IS the top and which tlie bottom of the section. Where the dips are at high angles this is not a very safe guide, even whore it is certain, as is tlie case in this section, that the dips apply to the bedding as well as to the schistosity. It may be said however, that on the south margin of the belt the dips are lower than on the north belt. In the immediate vicinity of the Golden btar mine, is a cropping of a bed of cherty limestone 8 feet thick wluch has a stnke of 88° and a northerly dip of 48°. The linieatone is grey in colour, medium grained crystalline in texture, and lias scattered through it crystals of brown mica, which *r*.*'*'i""""*® as t" easily escape observation. In the midst of the lim«'«tone are discontinuous bands of che-t, and in parts of the formation there are numerous small angular fragments of chert projecting like warts above the weathered surface Kesting immediately upon the ILuestone is a 2 foot bed of brecciated chert which grades at the top into a porphyritic. dense felsitic" lava. The phe^iocrysts in this rock are feldspar and ferromagnesian minerals are not apparent. This top layer of chert differs in appearance from the chert inter- banded with the limestone, being greenish in colour. The lime- stone m Its general aspects, particularly in regard to the dis- position of the chert in it, the brecciation of the latter, and the occurrence of small angular fragments of chert embedded in it, resembles in a marked degree many occurrences of freshwater limestone m the late Tertiary of California, some of them occur- nng as lenses, without other associated sedimentary rocks, between sheets of lava. The general appearance of the outcrop 18 shown m Plate VI, in which B shows the alternation of limestone and chert, as measured in the field. The rocks below this limestone bed as well as those above are extremely fine textured or dense porphyritic lavas of dark grey colour, weather- ing whitish, in which the mineralogical composition of the ground-mass cannot be made out. They are rocks that the field geologist generally describes in his notes as "felsites". Inasmuch as the chemical composition of these geologi- cally early limestones is a matter of interest from a theoretical point of view, an analysis by Mr. H. A. Leverin of a sample of the uolden htar limestone is here given: — Inaolubis matter n in Peio, + Ai/1, ;■ J5 Sa-:::;::;:::::;::::;:::;;;;;:;;;;:;;;;;:;;;;;;;;:_^ W'38 PlATI VI. '«>^:^ ^"^ A. ExKjBurp of limc8toni' in K.^watin; Goldrn Star mine, at the northeast end of Bad Vertnihon lake. A, dark urey or black chert; P. limestone with eontin- uous bands of chert; C. chert; D, limestone with discontinuous narrow bands of chert: E. greenisn, finely hreeriatod chert: F. fclsite. B. Another eiposure of the same limestone at the same locality, showinR bands of ,.„„ ,, chert, and chert fragments in the limeatone, W'O— p. 4^ 45 The intercBting feature of the analysis is the very small proportion of magnesium carbonate present. The insoluble matter is probably composed largely of brown mica which doubtless contains magnesia in the form of silicate formed at the expense of the carbonate. This bed of limestoae dipping with the felsites northerly at an angle of 48" with nearly the whole of the KeewaUn section to the north of it suggests that we have here the lower part of the section. But as the belt lies between two different batho- liths of different dates of intrusion this conclusioa is not alto- gether certain. On the south and north sides of the east end of Bad Vermilion lake, the Keewatin rocks consist of various greenstone schists, chlorite schists, and homblendic schists standing at much higher angles. Along the line of the railway, the schists, while still dipping northerly, depart but little from verticality. On the south shore of Turtle lake the dip ranges from 60 to the north to vertical. In general the data is insuf- ficient to determine the upper and lower sides of the Keewatin in this section and this is commonly true of bands of sehists bounded on both sides by plutonic imiptives. OTHER BELTS OF KEEWATIN. *u- Of the two subordinate belts of Keewatin to the south of this which have already been alluded to m the discussion of the heme rocks, it is only necessary to say that the one which lies along the south side of Shoal lake and is exposed for the width of a mile at the east end of the lake, is composed chiefly of ellip- soidal and amygdaloidal greenstones, greenstone schists, and chlontic schists; while the belt which occupies the south side of Grassy lake and extends thence eastward is composed of green- stone schists and chloritic schists. In both of these belts the dip of the schistosity is nearly vertical and little can be made out of their internal structure, although it is clear that the first one is anticlinal with reference to the folding which affected the Seine series and produced the synclinal troughs on each side of it. PETROGRAPHICAL NOTES. . . A limited number of thin sections of the more character- istic Keewatin rocks have been examined microscopically and the results of this examination are here summarized:— ■^^u™"'? massive greenstoues show no remnants of pyrox- ene. This mineral appears to have been first altered to green hornblende and the latter then partially or wholly chloritieed The chloritization, however, in most cases, appears to have left the form and cleavage of the hornblende intact, and even the 46 pleochroism is often pronounced; it is only the prevailine very weak double refraction that shows we are cfealing not with iS blende but with the pscudomorph chlorite. In general the pW- oclase IS fairly well preserved but varies greatly in the propof- sZ.'nM^' '* '''"'T '" tlJe various greenstones examined. Some of these greenstones are chiefly feldspathic in composition and in thin section present a ground-mass of micro-granular foS&ir ""f"^ are embedded blades of fresh or chbritS hornblende. In such rocks zoisite, clinozoisite, titanite, and ilmenite or magnetite usually appear in var>-^ng degrees of • stSr^'- A/"de parallelism in^The orientation of t^e con- stituent minerals may be m some instances detected. ««♦ '" "there of these greenstones an ophitic structure is appar- entjmd there is little doubt but that the rock was originally a dolente or diabase Some of these chloritized diabaL have ^ch titanite m them and this in many instances ^clearly peeudomorphic after ilmenite. Epidote in small granules and occasional larger crystals is commonly observable ,;*; So^ejarieties of these massive greenstones show a porphy- whfch rr."n1; ^^" was particularly observed in one case in Ti^l I 1? Ph^n^crysts of a ferromagnesian mineral, now com- pletely changed to chlorite, were embedded in a ground mass consisting chiefly of a felt of small chlorite blades, with some . alcite, zoisite, and magnetite. In some rather coarse green- stones, sheaves of nearly colourless amphibole, which in some ca^es resemble altered phenocrysts, lie in a ground-mass conTt! mg chiefly of chlorite, zoisite, and feldspar with or without titan- f„. ^A massive whitish green rock of limited occurrence that is found associated with the greenstones of the north side of Seine bay may be here mentioned. It appears in thin section to be composed almost wholly of divergent sheaves of clinozoisite and subordinate zoisite m stout prisms. Tlere is a very small amount of interstitial plagioclase and nests of calcite occur through the slide. -rok/" ?ome of the more feldspathic greenstones there is consid- erable sidente due, doubtless, to the carbonatization of the iron of the ferromagnesian silicates, and this siderite shows all stages of alteration to limonite. * In still other varieties of greenstoce there is but a very small P^2lf «^,/«'dspar present. The rock, which in such cases is exceptionally coarse textured, is composed of an aggregate of large areas of chlorite showing residual cores of hyperathene, or remnants of a well marked diallage structure. Besides the chlorite there is usually considerable secondary hornblende epidote, zoisite, and ilmenite partially altered to titanite. 47 These various greenstones of massive aspect, particularly those of finer texture, very commonly grade into greenstone schists and these cannot be clearly segregated from the less fis- sile varieties of chlorite schist. Such chlorite schists are prob- ably in almost all cases nothing more than greenstones in which, by a process of internal shearing, chlorite has not only been developed at the expense of all other ferromagnesian constit- uents but has been rendered more apparent by its parallel or sub-parallel orientation. The finer textured greenstones and greenstone schists very commonly show a well marked ellipsoidal structure, and less commonly an amygdaloidal structure. The ellipsoidal struct- ure appears to differ in no essential particular from that char- acteristic of many lavas and intrusive rocks of later geological periods. The only amygdaloidal greenstone schist which has been submitted to microscopic examination is one from the east end of Shoal lake. Here the greenstones are very distinctly schis- tose and exhibit at several excellent exposures a well marked ellipsoidal structure. In this section the amygdaloidal rock presents a ground-mass of feldspar and green hornblende, the latter being disposed in parallel orientation. In this ground- mass are numerous well preserved phenocrysts of rather acid plagioclase. The rock is probably an altered andesite. The amygdules are apparent as lenses of quartz in aggregates show- ing a mosaic arrangement in section. At the ends of these flattened amygdules there is usually some calcite. The amyg- dules are, however, much more satisfactorily observable on tho glaciated rock surface and in hand specimens than in thin sect- ions, many of the amygdules being over half an inch in length. The more typical chlorite schists appear to consist chiefly of a felt work of chloritized hornblende with occasional residues of fresh hornblende; the feldspar is usually quite subordinate in amoimt. Zoisite and clinozoisitc arc usually prominent con- stituents. Titanite is also fairly common. Quartz may or may not be present. One or two crystals of pyrite may usually be observed. In some cases, however, feldspar may be abundant as a ground-mass. The hornblende schists in the field are usually easily dis- tinguished from the various phases of greenstone schist and chloritic schist by their black colour, their even cleavage with transverse joints and the glisteninir lustre of the cleavage faces. They occur characteristically in e proximity of granites or granite gneisses intrusive in ; iie J watin, and appear, therefore, to represent the result of contact > -tamorphism upon the green- stones from which they are derived, and into which they pass insensibly away from such irruptive contacts. ««™ii°/*''1"**'*'''° >*'^® ^°^^^ a™ noteworthy for the almost ^^tt'^/M""* °' f^''"^- They are composed of w^n The hornblende w m rather stout prisms and is alwa^ di- quarts) usually form a mosaic which may or mav not show elongationofU.e constituent anhedra. l/sLr?itance^ th^ hornbende greatlj predominates over the feldspar bit b most cases these two mmerals are fairiy equally represented R^^lv the eldspar predominates and the hornbSKdisp,^ J parallel layers or zones in the feldspathic aggregate ^^ nnrfiL f2 ^^'"*^ '^^ ^^'"*« ««»>«»« which occur in some sCroflii! K^P"" P*"^ °^ ^^^. Keewatin, particularly on the shores of Swell bay, are mteresting as showinir the variation in n\trr?c'ks 'tf ' '^""^ ,n'^^ •"'•'« "P the"Llk of thf S^° in these rocks the ongmal character of the lava appears to be better preserved than in the case of the more basi? dows In thm section they show characteristically a fine Kround-mass o? rather variable texture consisting of Juartz and "eldspar in dS^fanl Tuartf ^r " f^^^^ p'enoc?y.«ts of orthodS oligS SV ? 5- • Usually there is some secondary biotite in minute scales disposed in parallel orientation and some chlorite n nSs'U"if^S.'*'"^f.'^ ^r.? *^? ^'^^'^^ ^"'^ •" part occurring in nests as if the result of the alteration of some pre-existin* oisericite <-aIcite is sometimes present n nests. The ouarta phenocrjsts are the cross sections of dihexahedral crystals bu? Some of these felsites are plainly amygdaloidal, the amvir- dules being sometimes quite olump or rounded and sometTmos drawn out into lenses. Some of the amygdules havrSw centres showing that they did not completdy fill the cavtJ theLTtw"; ""■ ^ "^'.'T"^ °^ "^■j*^ ^"^^^ I« thin .secS the quartz of the amygdules resembles vein quartz and is of mich larger grain than the ground-mass. The quai tz agKregate li othe7?it V^^'""^^ r?"^^ ««f ^'""^ thelest of Kock in other cases, lenses of similar quartz occur which arp probaDly also amygdules sqieezed\ut of their nomL Interstratified with the Keewatin rocks of volcanic ori«n ZSI'Ty''^''^''^''.^'"}''''^^ bed3 which are soTneS ^\^ ^•*?. ^^ ^"^^'^y designated cherts. A notable occurrence of this kind IS ut^^the northeast end of Swdl bay. Here the rock 18 distmctly bedded and some of the beds are finely laminSed 49 while others are not. The schistosity is parallel to the beddinR. On one side these siliceous beds are seen in sharp contact with a rather massive green chloritic schist, and the bedding is parallel to the plane of this contact. The chert is of a dark grey colour and varies somewhat in texture. Microscopically it consists of a very fine aggregate of apparently clastic grains of quartz, so fine m parts as to be unresolvable by the higli power of the microscope, the diameter of the grains being much less than the thickness of the slides. In this are nests and lenses of coarser aggregates of quartz and others of calcite. There are minute scales of sericite sparingly distributed, some filmy chlor- ite, and a few crystals of pyrite. Another chert from the extreme east end of Sand Point island is dark grey to black in colour and has small nodules of white quartz in it the size of a pea. These pea-like bodies are disposed in bands separated by bands of chert in which they are absent. Some are drawn out in lenses. They are sometimes crowded together and sometimes well spaced. Tlieir disposi- tion resembles that of spherulites in certain rhyolites; and it is possible though not probable that in this ca.se we have to deal with a thoroughly silicified spherulitic rhyolite. Microscop- ically it consists of a fine aggregate of quartz grains with min- ute scales of biotite, the whole disposed in many irregular lay- ers. These layers wrap around the pea-iike nodules. The latter consist of relatively coarse quartz presenting in this sec- tion the mosaic arrangement of vein quartz. The dark gabbro, which though intrusive in the Keewatin is included with it as belonging to that geological period, is pre- vailingly a co.irsely granular rock of plutonic aspect. In the field the chief constituent minerals hornblende and feldspar are easily identified, tlic former usually predominating. At many localities magnetite may also be recognized on careful inspection. Whenever the rock is encountered there is a strong local variation of the compass. When examined in thin section the rock is found to consist essentially of the three minerals named. The feldsp;ir on opti- cal study proves to be labradorite. The ampliiboh is ordin- ary green hornblende. The magnetite is variable in its distri- bution being abundant in large irregular shaped grains in some cases and almost absent in others. The labradorite is for the most part fresh and shows the usual multiple twinning in broad lamel- la;. Occasionally, however, it is altered to an aggregate of epidote and zoisite. It occurs in large anhedrons allotriomorphic to the hornblende, but is everywhere charged with abundant small prisms of hornblende of an earlier generation. The horn- blende occurs also in large anhedrons which have, however, a pronounced elongation in the direction of the prismatic axis, 50 i i- and thus appears to have a closer approximation to idiomorph- ism than the feldspar. This hornblende Is poikilitic in struct- ure owing to the inclusion within it of numerous small anhed- rons of untwinned feldspar. These are often so abundant as to give the hornblende in cross section the appearance of a sponge. The hornblende in some cases also occurs as aggregates of diverse- ly oriented individuals; and these polysomaUc areas of horn- blende have the same relation to the labradorite that the larger individuals of hornblende have, but in this case interstitial feldspar occurs in small anhedrons between the members of the aggregate. In some cases there is a very small amount of quarta associated with the feldspar. CHEMICAL COMPOSITION. In order to contribute in some small measure to our knowl- edge of the chemical composition of the Keewatin rocks, two specimens were selected for analysis. One of these was taken from the schistose ellipsoidal greenstone which occurs on the first island inside of the entrance to Rocky Islet bay. Its com- position is shown in column I. The other specimen was taken from a black glistening hornblende schist near a granite dyke in the belt between Rice bay and Hopkins bay. Its analysis is shown in column II. SiOt. . TiOt . . AliOi . FcfOi.. FeO... MnO... CbO . . BsO .. MgO .. NaiO.. KK>..., HK)— . H,0+ PiO, . CO, . S CI .. CtK), SrO. 46-28 1-70 14-24 3-93 1IS3 002 U-28 trace. 740 2-48 0-81 005 0-28 15 II. 47 SO 0-58 17 03 415 «' ?"«ny lake. Analyst, M. K. Connor. IV. Bamlt, Ki..;,.«a. Amily^t O. bilvestris (Quoted from Waahingtons Chemical Analyses o. Igneous Rocks. L'.S.G.S. Prof. Paper 14 ) ■<»" cm Ci9..S>- m 51 These analyaes agree fairly well with each other except that there is a defect of uoda in the hornblende gchixt, and that more of the iron is in the ferric condition in that rock than in the green- stone schist. The agreement indicates approximate identity of original composition. Both analyses also agree fairly well with many analyses of basaltic lavas. In colunm III is given an analyses of the hornblende gub- bro which forms so large a feature of the Kcewatin in the cen- tral portion of the territory mapped; and for comparison is given in IV the analysis of the basalt of Kilauea. THE LAVRENTIAN ROCKS. The term Laurentian is here reserved, in accordance with the decision of the International Committee on Geological Nomenclature, for those Archsan granites and granite-gneisses which are of pre-Huronian age. Within the territory covered by the accompanying geo- logical map. there are several areas of granite and granite-gneiss which are referred to the Laurentian in this sernu of the term. These are the Bad Vermilion Lake granite, the Mud Lake granite, the sheared granite of Gra%y island, and the granite- gneiss of Rice bay. All of these are post-Kcewatin. ^me of them are certainly pre-Seine (upper Huronian) in age and others are believed also to be pre-Seine on the basis of their correla- tion with those for reasons set forth in the following account of their occurrence. THE BAD VERMILION LAKE GRANITE. Area. This mass of granite has been found to be more extensive in its surface distribution than was indicated on the map accom- panying the report of 1887. It occupies the shores of the south- west part of Bad Vermilion lake, and this area is in direct continuity with a main curving belt from 1 to 2 miles wide, extending from the Golden Star mine to the vicinity of the mouth of the Seine river, a distance of about 12 miles. On its northern border, including the lobe extending into Bad Ver- milion lake from the main belt, this granite mass is bounded for the greater part of ita extent by the anorthosite (gabbro)of Bad V^ermillion lake, but at its northeastern and southwestern ends it is also in contact with the Keewatin. On the southeast border of the main belt, from the vicinity of the Golden Star mine to the middle of Grassy lake on the Seine river, the gran- ite is flanked by the basal conglomerate of the Seine series; but r™i l^''\^ **•* ^?"**' °'.*'"' ^«»*' ■ ■*'*P o' Keewatin •ppeare to intervene between the granite and the conglomi rate. Petroumphieal Character. The rock composing this mass is prevailingly a medium coarse textured, light coloured, biotite granite.^p^r in bh.tiS and grading by a dimmution of thij constituent into a binary fher^*r/.I «'''«'"*«•. .^rthoclase is the dominant f -ds^r Zt there is also a notable proportion of acid plagioclase. ahd both r^P wS^^'""k^.*'*^,'^T'"?^'''°» P'"^""-*"' including cal- ^ w!;^. V^'' V^ ^ ^"'"^}y. "bundant. tT.c biotite i. n.ore or less n«!Il« ^''k Ki'*''' *"i*^ '•'* """* *"""' '" «*"»'K«1 with slender needles, probably rutde, intersecting ut eO" in the plane of the ceavagp A few plates of muscovite may also be occasionally rnX'r1.ck " ""^ ^ """"^ secondary epidote prcseSt .r^rJa. '*" **!? '^^' **•'" "^"^ °^*"» presents a blenched appearance and near the contact with the overlying Seine con- i^TJ'Jt^uV T""? 'I"'** y/»»wi8h, the yellow ^lour fading U^.^l Padual'y a few hundred feet from the contact of the over- Z^LJ'^ P"u "•• •»?w«ver, no indication of important f^mm Jr?T ^ «*em'Cftl decomposition of the granite where It immediately underlies the Seine strata. Locally the granite obrr^2lH.»i!I!.*?f'"P'^5' ^"t^ *}^'' f« apparently in all cases observed due to deformation by shearing and is not an original structure o the rock. Besides this dominant facies the gSte presents interesting variations in character, particularly on its Hn^ tT;H J*"^ °"*5 '"*"r°'i °^ "'^« '»<=«' raarginnl facies is mL.?Jw '*t?"Ti?*"'" P^'^ fi°" *«'''*"'« and a darker colo.ir. Microscopically the rock is then seen to have a hc.locrystalllne phenocrysts of fel.lspar. The ground-mass also contains chlr.ri- tued bDtite and epidote is usually present. 'I'his facies of the rock in some localities grades into a more basic facies in which it 18 difhcult to detect any quartz with the aid of a lens The basic facies occasionally appears coarser grained as on Reser\e bay, where, at a number of exposures, it has the aspect of a in. ,1- lum coarse diorite which grades into a quartzose granitic rock. A quite different facies, whicli occurs at the contact of the f nH n^w '? ''P"P^y««' «'^"ing the latter, is a very fine grained and light coloured, practically white, rock containing no ferro- magnesi. n constitmnts, but having scattered througlT it rather sparsely, ^e dihexahedrHl phenocrysts of quart/^ some of which are tialf an inch or more across. This marginal facies Obi^hiSlLe.""*"^^^ observable on the north side of There are very few pcgmatitp dykes in the Rrtinitc uiul these »rc all quite Binall. There arc, however, n good nmny quurtf vcinn and itome of thexe have t^ecn mined. ReUUiona to Adjoining Roeka. The Bad ViTmilion I,ake granite it intni-ivo info the anor- thoHJto (gal)l)ro) of liixi\ Vermilion lake. The intru^ivi* relation 18 mIhiwii not only by the marginal rooe seen on the went nide of Finger bay, where a dyke of the granite 20 feet wide cuts squarely across the handed structure of the gabl)ro. On the north side of Obashinsing lake, apophys(>s of modified granite cut the gabbro at numerous places. ()n the west side of the south part of Bad Vermillion lake inclusions of gabbro were olMerved in the dark marginal faeies of the granite. Nowhere was any marginal alteration or modification of the gabbro observed at these contacts. The peculiar distribution of the granite and anor- thositc (gabbro) in the Bad Vermillion Lake district is sug- gestive of a definite structund relation. In the southwest part of the lake there is an obtusely triangular area of granite almost completely surroumied by the anorthosite (gabbro), but connected by a narrow strip with the main Ix-lt of granite. This mapping indicates that the anorthosite existed as thick sill or attenuated laccolith intrusive in the Keewatin. After .solidi- fication, the intrusion of granite magma was inserted Ix^low the anorthosite sill, doming it somewhat in its central part. The truncation of the region has aince pared away the top of the dome, leaving the central mass of granite surrounded by the earlier basic intrusive. It seems fairly certain at least that the contact surface between the anorthosite (gabbro) and the granite is a domed surface and that the granite is beneath the anorthosite. Since, as has been shown, the anorthosite (gabbro) is intru- sive in the Keewatin, it may be positively inferred that the gran- ite is also intrusive in the rocks of that series. This inference is confirmed by direct evidence of the intnisive relation at the contact of the granite with the Keewatin rocks. Near the Gol- den Star mine on the road from Mine Centre Station to Shoal lake, the granite holds angular inclusions of the near-by Kee- watin rocks and on the east side of Island bay there are numerous incIu.iions of greenstone in it. At the west end of the main granite belt, near the mouth of the Seine river, the granite may be seen in intrusive relation to the hornblende schists of the Kee- watin. ■J M Thp relation of th<> granitp to the Srine wrirn of rorks which flanks It on the Kouthetwt i8 plain and unequivoeal. The basal conRlomprafn of that serifH rentH indifferently upon the erodwl •urfnre of th,- granite and the Keewatin. It in eertum thut after th(. intrusion of the p-anite into the Kwwatin and theanortho- ■Ite (gabbro the region wan profoundly degraded and that on the erowonal surface tf.u« e«tablishc were de- posited. Ihe interval l)etween the Keewatin and the !rU>iue •eries 18 a verv long one and is one of the important farts In the historical geology of the Archican. THE MUD LAKE GRANITE. To the north of Seine bay there is a remarkably lin.ar belt of granite which extends from a point ea«t of Wind b.^v to Im>- yond Porcupine lake, a distance of over 10 miles. This granite be t has iKM-n eros.sed by seven traverses into the woods north of Seme bay and its width as thus d<'termined is very uniforml- about half a mile On both sides of the belt are Keewatin rocks. Ihe extension of the Ijelt to the northeast of Porcupine lake is indeterminate, and it may pos.sibly have a greater prolong- ation in that direction than is indicated on the map. Mud lake appears to lie wholly in this granite and it may, therefore be conveniently distinguished by that name ' n.A V Pi^n't^w/'milar in its general characteristics to the ?n^„ Vemihon Lake granite, but is more bleached in appear- ance and IS more commonly sheared and schistose. In many of Its exposures It is apparently devoid of mica and hornblende or so nearly so that it may be called alaskite. It is prev^iSlv very quart.ose and shows no porphyritic structure s^ fa? « observed. Portions o the granite which have been e^cep^o^ ally sheared have a thinly sl.eete.l or slaty structure "^^P""'' thoJof^hrk' ^°''^- ^'**'^*,hi/'h the granite is in contact are those of the Keewatin, and although the contacts are not well ^K .'? ^^^r"^"' «" ^'^o «f th'" traverses which cro8.sed the Sri^iatii """ "^"^'^^'^ ^'^ '"'^« ^"^ intrusive relation to w» i ^'T'"^ appears to be no reason for doubting that this gran- THE SHEARED GRANITE OF GRASSY ISLAND. On Grassy island, near Rat-root bay, there are two very distinct granitic rocks traversing the i.,laAd from northeasltj sheir.T* 'a ^7u ^ *' i'* i^'rtaposition. One of these is g^at J sheared and otherwise altered, the other is not sheared Ind is i^B 65 fmb. It is evident that the iihrwrcd gnuiite ix an intruHivt; maw distinct fron the unshcared ffranito, that it hax !e seen in contact on hare rock urfacen and the older granite is seen to be cut by anophyses of mh- later granite and to occur as angular inclus(K)nH in the latter. In its general field aspect this granite resembles the more sheared portions of the granite of the Bad Vermilion Lake and Mud Lake areas. In some of its exposures it presents a bleached appearance, but for the most part it has a stained appearance varying from pinkish to yellowish. It is in places far more stieiircd than the granite of the Bad Vermilion Lake and Mud l^ake areas and the granitic structure in entirely oblitrratud. From this thoroughly deformed and p«-tro»n"aphically obsj'uri condition, it grades into less sheared facies, where it has* the char- acters of an alaskite or a biotite granite poor in mica. This rwk in turn grades on its southern margin into a dense com- pact microgranite or quartz porphyry, where it comes in con- tact with the Keewatin of the south side of Cirassy island. At the imnndii.lc lontact it presents the phenomena of a chilled cdtri i,|^:iin.-t the rocks into which it is intrusive. The effect oi f-lif Mring s not observable except to a quite limited extent in tlii-« hi.er urnined fiu ies of the intrusive rock near the contact. Tlif ro' k further resembles the granite of Bad Vermilion lake ill the fact that it is traverse*! by quartz veins, some of which have attracted the attention of prospectors. The l)elt of older sheared granite with its marginal quart' porphyry facies ex- tends not only across Graosy island, but part of R#'view island and the small if r.r,. these two. It probably crosses thi < ; vcen Grassy is- •nf,h to Rat-root •I' r!,/> later granite, THE RICE BAY GR KSS. The granite gneiss which occupy •• ' ••- t.atjc of the Rice Bay anticlinal dome, and which is exp- -•. .jcfly on the shores of Rice bay is remarkable for the inteiihiiy of the deformation to which it has been subjected. The deforntation ha.s pro- duced in the rock a very pronounced foliation, which is disposed both as to strike and dip, particularly on the periphery of the mass, in planes parallel to the contact with the overlying and I 56 Burrounding Coutchiching schists. The least deformed facies of the granite is exposed on the southeast side of UpporRico b^ b mk'wltWrfiH*^'"?- "'•'-it^aratherc^rriprphyK in a ^i i ?n* J"* '"?"'"P^"' r*'''*'^" *"*^ orthoclasesrembedded bbUtf T i f °V°^-"»«?8 of quartz and feldspar ^d a little Jini If M faces vanes considerably in the si«e and abund- ion lake Thir/^u^'^ ^r''' °^.*^''. «^^°'*« "^ Bad Vermil- ^H I K ;i. V^ ^."^^ ^'^'^^'^ ■■^'P'd'y into ai awffen gneiss in which both orthoclase and quaitz crystals occur ,is rat h^ plump lenses in parn U-l orientation: and from this condition there"? «. easy gradation into more acutely deformed facies in which the porphyritic crystals have been drawn out into very thin lenses <.f remarkable length, the maximum diameter of th^ lens tSl.T"''^i'-"'"f1 'V^"" ^'P °^ the foliStn Many of .i..nr'''"''*'7'''''y.*h"''^"f the quartz, are over 2 inihcs lonp and appear when viewed with a pocket ens to be a homo! KS ''iw"""".^"'*' ^•'*^ -'treous lustre lid conchS irattuic Ihey are, however, m reality, probably agKreiiates aLXervaS7n^"tf • ^'' ^'^"t Phenom'Lna of';ieS1ttn are observab e in the numerous dykes or sills of this granite which occur in the encasing Coutchiching schists, and it is evf- of the"ro,^U^,''"'*'•^"^"^^' ^^^^ the maximum Iniat'on to the strike '" *^' P''^*' °' *'" '^^' ^ "^ "8ht Ingles ««Ki7!*^i *'^f""°ation to which this intrusive rock has been fJ^te ^1k'"«!f V^^y '*™°K'y that the present ratio of length ns due fn t{,*^' horizontal section of the mass of about 3 tS coS^tituei? .LMT f^^™'"K P™«^« *hich has reduced the constituent crystals to lenses. It was probably originally nearly equidimensional in horizontal section, and wa8 3oubt- edly intruded into the Coutchiching when the latteT^ Sf comparatively little deformed; sine! the grSte itseirrpiS encSsT^ it''"irthT';!i^ '^'llf*^ '" *^" '^P^^* «; the'sSS encasing it. If this be so then we may properly think of the CoS^k'^ ^''T« ^^ •°"»"'^'>' « quiteVt rcSf of the Coutchiching strata over it. Thus the mass may well have inis possibihty is in a measure sustained by the oeculiarlv fni of tf i*°"!?- "T^'**"'^ of cooling. The excessive sS ing of the mass indicates a peculiar susceptibility to this kind ^lit£ ~W?"' r**/** I "" '^^^ perhaps also indicatra lac- StSffK • ""^•'''P*u*° *•"* ^'''"^K ^"'^ rather than that of a Sfii^K ' VJ"''' "*. ^h® ««"«'»■ deformation of the region a 'ac- briuihrSli'"^*'"^f^ H '^' '°l^'"8 •''^d so mor^e^ily ''^ brought into a position favourable for intense compression; 87 whereas a deep rooted batholith would be more stable and might act rather as a buttressed mass against which the sur- rounding rocks would be compressed. The occurrence of num- erous sills of the granite found in the encasing and overlying Coutchiching schists also lends strength to this view. Similar sills of amphibolitic schist may with great probability be inter- preted as intensely sheared and dynamically metamor- phosed baaic rocks, perhaps lamprophyres, satellitic upon the mam intrusive body. The term granite is given to it in a gen- eral sense. In a strict petrographical classification, it would probably be placed with the granite-porphyries. This Rice Bay granite mass, whether it be structurally a batholith or a laccolith, with little doubt belongs to the earlier Archa-an or Laurentian granite-gneiss. The great deforma- tion which it has undergone differentiates it quite sharply from other less deformed granitic rocks, yet to be described in the same region. Its petrographical characteristics as well as its sheared and bleached condition ally it with the granite of Bad Vermilion lake, which has been shown to belong to the earlier period. The fact that it was intruded into the Coutchiching before the latter had been greatly deformed agrees with and supports this conclusion. The mass is, therefore, placed m the same category vrith the Bad Vermilion Lake, Mud Lake, and Grassy Island granites, as belonging to the Laurentian. PETROGRAPHICAL NOTES. A few specimens of the sills or dykes which traverse the Coutchiching mica schists in the vicinity of the Rice Bay granite were examined microscopically. One of these was taken from the north side of the outlet of Rice bay in the narrows leading to Rocky Islet bay. Here an acid sill cuts the mica schists parallel to the schistosity, the dip being S. W. at 45° to 60°. The rock is light grey in colour but is stained locally yellowish by traces of limonite. The rock has a fine grained granular texture and a pencilled structure; that is it has schistosity chiefly parallel to a direction rather than to a plane. In fracture surfaces paral- lel to this direction, the schistosity is marked, while in fractures transverse to this it is scarcely apparent. The direction of pen- cilling is that of the dip. Notwithstanding this general struct- ural characteristic, the rock contains numerous quartz lenses, many times longer and broader than thick, and these determine a cleavage parallel to the plane of the dip. The rock has evi- dently been subjected to great deformation and the quarta lenses are the result of the drawing out or squeezing of large crystals of quartz, and the direction of elongation of the rock as a result of this squeezing has been that of the dip. In the midst of the 36570—5 58 rock there are here and there small neata of molybdenite, and ■ome small stringers of qtiarti traversing the rock also contain molybdenite. In thin section the rock is seen to be composed chiefly of alk- ali feldspar and quarts with a quite subordinate amount of brown biotite in ducrete plates lying in various azimuths. The feldspars which make up the bulk of the rock are fresh, and both these and the quarts are throughout allotriomorphic. The large quarts lenses are seen to be polysomatic. Since the shearing to which it was once subjected the rock has evidently been reconstructed, for little evidence of cataclastic structure remaius. In this respect it is analogous to the adjacent mica schists in which all trace of the original clastic structure has been effaced by the processes of reconstroetion due to meta- morphism. A specimen of a simflar sill fron the south aide of Rice bay shows the same general features in thin section, except that there are bands of finer grain alternating rudely with bands of coarser grain, indicating zones of granulation due to shearing. A few specimens of the basic sills were also tpken for micro- scopic examination. One of these from the west side of Lower Rice bay appears in the field as a band of olack, glistening, hornblende schist, flanked on either side by mica schist, and conforming in dip to the latter. In this section the rock is seen to be composed of nearly equal parts of gree i hornblende and feldspar together with a very considerable amount of ilnien- ite and titanite. The structure is that of an allotriomorphic granular aggregate with a feeble manifestation of parallel struc- ture. The hornblende shows only occasitmally a pronounced elongation in tl» prismatic axis. The feldspar is for the most part unstriated. The occaakiiiai twinned crystals belong to the basic end of the plagioclase series and the unstriated crystals have a higher refractive index than balsam. The ilmenite usually his a border of titanite or is enclosed as residual nuclei in the latter. Another specimen from the north rde n( Lower Rice bay appears as a black hornblende schi.st wit.', glistening cleavage faces and streaks of light yellow colour. (>n r.ijcroscopic exam- inatioo the rock is found to consist chiefly of green hornblende aad Boiaite with some felospar. The hornblende is commonly elnngated in the direction at the prism and disposed in pari>Uel orientation giving the lock a we'l defined schistosity. The yellow streaks are due to the predominance of zoisite and clinozoisite over tlie hornblende, the latter being lacking in certain bands. A specimen from another of these basic sills on the south side of Lower Rice bay is also a black glistening hornblende 59 BchMt, but is compoaed of hornblende, feldspar, quarti, and tit- anite, with a pronouoced parallel arrangement. The titanite 18 in the form of long narrow zones parallel with the schistosity and encloses numerous nuclei of ilmenite. A^i analysis by M. F. Connor of a specimen of one of the acid Bills on th*" south side of Lower Rice bay, which brings out promiiiently the contrast between these intrusive sheets and tbe Coutchiehmg mica schists, is herewith given — 1^' 7000 TiOi 0.20 ^1^1. 1600 FetOi FeO.. IfnO.. c»o. BaO M|0 NaiO. 128 061 0C8 3-30 004 O-IO 8-34 KiO . PK).. 8 ... CI .. CnOi.. 8rO... t-or 06 tnoe. MM. 001 MM a THE SEINE SERIES. » 1^ ^™ "Seine" is here given for temporary convenience to »i pojt-Keewatin series of sedimentary rocks that are typically exposed at many places along the Seine river. The serira doubtless has its correlative in standard sections elsewhere in the . ake Superior region and it will appew fron the discussion in hp sequel that it is very probably the equivalent of the upper Mu.oman, if we exclude the Animikio from the Huronian and regard the latter as made up of but two subdivisions, an upper and lower For the present I prefer to use a local name which may be abandoned later, when the correlation of the Lake Sup- erior Archaean has been finally worked out. The Seine series consists of two parts:— (1) — A basal conglomerate. (2)— A thick volume of quart, ites (oft^^n pebbly), seri- citic schists, grits, greywackes, and clay slates and phyllites. THE SEINE CONGLOMERATE. The Shoal Lake Area. The^ typical exposure of the Seine conglomerate is on the north side of Shoal lake on the Seine river. Here it occupies a well defined synclinal trough with the lower part of the Seine qujirtzites iymg in the middle of the ayncline, the axis of which passes through Old Mine Centre. The axis of the fold has a northeast-south w.st trend; but both to the northeast and to the 3G570— 5i 60 southwest of Shoal lake the axis of the fold curves to a more nearly east-west trend. The strata both of the conglomerate and of the overlying pebbly quartzites are nearly vertical and the schistosity which characterizes both sets of rocks conforms for the most part, though not everywhere, to the stratification. The northwest limb of the syncline rests upon the Bad Vermilion granite, which is well exposed a short distance from the shore of the lake to the north of the Foley Mine landing, and which comes to the shore of the lake southwest of the landing. The southeast limb of the syncline rests upon Keewatin rocks which occupy a belt a mile or more in width at the east end of Shoal lake. The conglomerate is thus clearly spread over the contact between the Keewatin and the Bad Vermilion granite and is sharply infolded between them. The Keewatin rocks on the southeast of the syncline are typical greenstone schists with ellipsoidal and umygduloidal structures abundantly appar- ent; with these are subordinate bands of chloritic schists. The conglomerate contains a large amount of debris derived from the waste of the Keewatin rocks, but the pebbles and boulders, usually well water-worn, consist chiefly of different varieties of granite with a subordinate proportion of pebbles of greenstone, quartz, quartzite, and quartz porphyry, and there are occasional pebbles of chert such as are associated with some of the Keewatin limestone and iron ores. Professor Coleman' records also the occurrence of boulders of coarse grained anor- thosite similar to that of Bad Vermillion lake in this conglom- erate. The well rounded water worn pebbles ran^e in size from that of a marble to diamett^rs of about a foot; but ia other local- ities in this same coi^lomerate may be found occasional boulders of granite as much as 3 feet in diameter. As a general rule the matrix of the conglomerate is of a dark green colour, more or less chloritic in composition and thoroughly wchistified. The schistosity adapts itself to the contours of the pebbles and boulders and it is evident from an inspection of sections afforded by the glaciated surfac*> that the deformatic^ of the rock has caused the matrix to flow around them, and ii«s oriented them with the plane of tb«ir major axes parallel to the schistosity. The granite pebWes a«Bd bwilders art- rarely, if ever, deformed in the tjhoal Lake section of the con|^«aerate ; but in the maie formation a few mil«^ to the northeat^ on the line of the Can- adian Northern railway th*> ixwilders ;.-av<* in many instances been pulkd apart by the flows* of the rofk induced by lateral compression. The resuH of this .nunderii^ of the boulders of the oonglcHnerate is the »,ppcwfmcf trf one wr two or three, or rarelv more, transverse gashes m tf**' ^jonldcr fiied with quarti veina having a columnar t>.t the outlet of Cliff lake and thence westerly it skirts the points of the north shore of that lake for 1) miles. In this stretch the Keewatin lies to the north of the con- glomerate and the waters of the lake, to the south. On the south side of the lake are typical Coutchiching mica schists with northerly dips ranging from 75° to 90°. No section showing \ ^» juxtaposition of conglomerate and Coutchiching could be founu. There is, however, no reason to doubt that the synclinal struct- ure of the conglomerate belt so well displayed on Shoal lake continues through to Cliff lake. Going westward through Rainy lake, the next occurrence of the conglomerate which is worthy of discussion is on the is- lands off the Minnesota coast north of the mouth of Black bay. Here as the ma^ ^hows, the conglomerate occurs as a well defined elongated syncline enclosing a considerable body of quartzites which are usually sericitic and pass into quite fissile sericitic schists. The syncline lies wholly within the Keewatin area and the conglomerate nowhere comes in contact with the great southern belt of Coutchiching. At its western end, however, where the synclinal trough pinches to a very narrow belt and the quartzites are cut out an attenuated band of conglomer- ate probably extends through and connects with the conglom- erate of Rat-root bay, which is probably in contact with the Coutchiching rocks of the north side of the bay. And these are part of the central belt of Coutchiching which in general lies to the north of the Keewatin. The northern limb of this conglomerate syncline at its eastern end is well exposed on the small island immediately east of DryweeJ island. The con- glomerate here is flanked on the north by Keewatin greenstone schists and the sericitic quartzites lie to the south of it. The strike is 90° and the dip is vertical. Westward from this exposure the conglomerate may be traced as a narrow band intervening between the Keewatin and the sericitic quartzites cutting across the northeast point of Dryweed island, and thence skirting the north shore of that island to its western extremity. Ii .^ next observed on the northern extremity of Grindstone island, all the rest of that island to the south being occupied by the sericitic quartzites. The next exposure is on the shore of the mainland about 28 chains west of the west end of Grindstone island, and it occupies this shore for nearly a mile to fVank bay. 69 The flouthern limb of the conglomerate syncline is exposed on the south side of Dryweed island near its eastern end and again nearer the middle part of the island. It occupies an island south of the western end of Dryweed island and is next encountered on the main shore on the south side of Neil point. At Frtmk bay this southern limb of the syncline appears to converge upon t'-e northern limb, for beyond this the quartzites appear to have been pinched out and the conglomerate itself is traceable only by the characteristic appearance of the matrix and is at best a very narrow band. The area thus enclosed by these two belts of conglomerate converging at both ends, has the shape of the cross section of a lens. Its length is about 6 miles and its maximum width about three-fourths of a mile. Within the area thus enclosed lie the sericitic quartzites and sericitic schists. Inasmuch as the con- eomerate is clearly post-Keewatin and rests upon it, there can ) no question as to the correctness of the interpretation of the structure. It is certainly a closely appressed syncline. The conglomerates of this area come nowhere in contact with the Coutchiching mica schists to the south. A. belt of Keewatin rocks intervenes. The sericitic quartzites and schists which lie upon the conglomerate in the middle of the syncline in no way resemble the mica schists of the Coutchiching to the south. There is thus no suggestion in the conditions which obtain here, that the conglomerate is the base of the Coutchiching, and that the latter is superposed upon the Keewatin. On the contrary, the facts are a sufficient proof of sequence as I stated it in 1887. For if the Seine conglomerate and quartzite occupy a closely folded syncline, there appears to be no escape from the conclus- ion that the belt of Keewatin upon which it lies is also synclinal in structure, and that the Coutchiching rocks of the Minn^ota coast, therefore, underlie the Keewatin — a conclusion which is in harmony with that previously reached, that the Coutchiching rocks of the Bear Passage belt are anticlinal and underlie the Keewatin. West of Frank bay well defined conglomerate cannot be traced, but a peculiar schist which serves as a matrix of portions of the conglomerate on the shore between Neil point and Frank bay is found to extend through from Frank bay to the mouth of Hay creek. Beyond this it is lost in marshy ground. Both on Frank bay and'at the mouth of Hay creek, Keewatin green- stones lie to the south of this, as well as to the north. It thus occupies the position of the conglomerate syncline and with little doubt represents the attenuated prolongation of the western tapering end of the synclinal trough. Whether this is continuous below the marsh and timber to Rat-root bay is uncertain, but in the prolongation of this belt on the shores of that bay little 70 III more than a mile distant we find the conglomerate again in excellent exposure. There can be no reasonable doubt but that the Rat-root Bay conglomerate is the same geological forma* tion as that of the Drvweed Island syncline. The trough which IS nearly pmched out between Frank bay and Hay creek, here swells out again. On .he shores of the bay the conglomerate IS exposed on the south side, at the head of the bay and on a small island near the north side. The conglomerate on the south side of the bay lies on the south side of a belt of hornblende schists which in turn flank an intrusive mass of granite gneiss of rather variable composition. This granitic rock occupies the south side of the bay for the first three-fourths of a mile. It is intrusive in the Keewatin and at one locality on the north side of Grassy island, not far from the contact of the Coutchiching and Keewatin, it holds included blocks of typical Coutchiching mica schist. It is. therefore, later than both Keewatin and Coutchiching. The conglomerate is remarkably coarse. It consists in part of a dark green chloritic schist matrix in which are embed- ded large boulders of granite and granite-porphyry, some well rounded and some angular or sub-angular. Several of these measured over a foot in diameter, some over 2 feet, and one over 3 feet. While the matrix shows abundant evidence of shear- ing and stretching, the boulders are not notably deformed and show no transverse gash veins like those observed east of Shoal lake. A few have their longer diameters transverse to the schistosity. Some are quite plump and even spherical in form, but the most of them are elongated oval in shape. The rounded ones have all the appearance of water-worn boulders. The f oi m- ation may fairly be interpreted as a torrential deposit. A little farther west, along the same shore, the boulders are more sporadic ai>d have more of a quartz porphyry facies. With these are some boulders of quartzite. Associated with the boulder beds are others free from boulders or pebbles, which have the character of micaceous schists. The absence or ex- treme scarcity of small waterwom pebbles is a notable feature of this conglomerate. The conglomerate at the head of Rat-root bay and on the island near the north side presents quite a different facies from that just described on the south shore. The pebbles are more abundant and much smaller and are usually well waterwom, though prevailingly elongated rather than round. The matrix of the conglomerate, greenish grey in colour, is generally schis- tose but 18 made up chiefly of quartz, the clastic origin of which IS scarcely if at all masked by the secondary minerals and the schistosity. The pebbles range in size ordinarily from 1 to 4 mches and are mostly about 2X3 inches. Occasionally 71 larKer ones are observed, the maximum diii ..sions being 7X11 inches. The pebbles are mostly a whitish quartiite, but near- ly as many are composed of a grey quartzose rock. I found no pebbles in any way resemblmf; the Keewatin greenstonos. The prey pebbles vary much in fixture. Many aro fine grain- ed micaceous schists, while others ure coarser and show on the weathered surface protuberant grains of quartz. They may very probably represent a sheared granitic rock, such as the older granite of Grassy island. There are also a considerable number of white quartz pebbles and these are for tho most part well waterwom and plump or spherical. In contrast to there the grey pebbles are lenticular in form, a fact which is probably m part due to an original cleavage which determined their shape as pebbles and perhaps in part also to their greater susceptibil- ity to deformation and stretching when the conglomerate was ■chistified. The strike of the schistosity of the conglomerate is 69' and the dip varies from 80° to 90° to the north. Oblique to this schistosity is banded structure, due to bands nearly or quite free from pebbles alternating with others charged with them. The bands vary in width from 6 inches to several feet and are marked by differences of texture observable on the weathered ' uuf ® ^ ***' ** ^^ *^® absence or presence of pebbles. The pebble-free bands are in some cases discontinuous or abruptly *aP«"n« and grade into the pebbly parts of the formation. This banded structure reveals with little question the original bedding of the deposit. The strike of the bedding is 98° and he dip appears to be vertical. The schistosity thus locally makes an angle of 29° with the bedding. Traversing the conglomerate are numerous stringers of quartz, some of which cut across the pebbles and most of which appear to have been affected by the shearing action involved in the schistification. It is of interest to note that this facies of the conglomerate IS apparently in juxtaposition with the Coutchiching of the northern belt which is geologically continuous from Bear '"sageto Coutchiching. Consistently with its unconform- ' f relation to the Keewatin, the Seino conglomerate, having a .e nearly east and west trend than the Keewatin belt, has ed the latter obliquely to the north side, and lies upon the .utchiching where the Keewatin had been removed from it »n the erosional interval immediately preceding the Seine per- iod (rf deposition. The fact that the Keewatin belt, which has a width of about 6 miles in the meridian of Bleak bay, tapers steadily to the west-southwest until in the vicinity of Rat-root V '*J® P''°^*^'y °°* °iore than a fourth of a mile wide, and that the Seine conglomerate, which rests upon it unconform- n m ably and is nynclinallv sunk into it, extends down to the point of this taperinR trough and beyond it so as to come against the Coutchiching of the north side, proves clearly thitt the Keewatin in the vicinity of Kat-root ba> was relatively very thin at the time of the deposition of the Seine conglomerate, and that the lattrr extended out over its edge on to the underlying Coutchiching. Petrouraphieal Notet. A number of the specimens of the conglomerate of Rat-root bay, both pebbles and matrix, were taken for microscopic ex- amination. From this study it appears that the quartz pebbles which are so abundant are pruhuhly chiefly vein quartz. These pebbleH consist practically wholly of quartz showing in section the uf^ual mosaic arrangement of vein quartz with no trace of deformation except perhaps a slight undulatory extinction. In one of these quartz pebbles there was found considerable epi- dote in irregularly shaped grains and some cubes of pyrites with a shell of limonite. Some of the pebbles consist of black chert of dense texture or lack of texture of flint. The material resembles closely certain bands of black chert occurring in the Keewatin on Sand Point and Red Sucker islands. Mi'iroscopically this black chert consists of a mui.{y aggregate of exceedingly fine quartz grains with numerous small elliptical areas which have a clear periphery and murky centre like the general matrix. These elliptical areas are suggestive of organic remains, but whether they are so or not could not be established. One pebble was found t'> be a very quartzose biotite granite composed chiefly of ouartz and partially decomposed orthoclase with some oligoclase, brown biotite, and a few irregular grains of pyrite. The pebbles of grey rock of medium fine grain which are perhaps the most abundant in the conglomerate appear to have the character of alaskite or alaskite-porphyry. They consist chiefly of quartz, orthoclase, and acid plagioclase, with small amounts of biotite, chlorite, epidode and zoisite, and generally some calcite. In some of these rocks there is an interstitial matrix consisting of a finely granular aftgregate of quartz and feldspar, the rock having the character of an alaskite porphyry. In other cases this {rround-mass is absent and the structure is hypidiomorphic granular. In these cases, however, the feld- spars have a strongly marked poikilitic structure as if they had incorporated an incipient ground-mass. These grey alaskite and alaskite-porphyry pebbles resemble certain local f acies of the Bad Vermillion Lake granite (alaskite) . Jb^^ 78 The matrix in which these pcbhJns are rmbedded is a shearad and schistiaed quaitaite, with secondary biotite, chlorite, calcite. pyrite, and magnetite Both the original clastic structure and the cataclastic structure which has been imposed upon it are quite apparent in thin section. A stratum devoid of p'-bblea which lies embcddi'd with the conglomerate appeant under the microscope as a quartz^hlorite schist. The clastic structure is apparent. Scattered through the rock are niiraprous well formed stout hexagonal prisms of some unknown mii.rral now completely replaced by an aggregate of epldote and zoisite. Uesides thcw there e.i a fow grains of pyrite. The large bouldtrs .n the conglomerate on the south side of Kat-root bay appear from three representative specimena CTamined to be rather fine grained granite. They are composed Of a hypidiomorphic granular aggregate of quartz, orthoclase, and plagioclase and biotite. The feldspars are fresh but the biotite, which is not abundant, is often chloritized. A few grains of pyrite occur in the slides. Other Oecurrencea of Conglomerate. •*k-^*r® "® *'*'*® °*^*"' "'OO' occurrences of conglomerate withm the area studied which may be tentatively referred to the Seine series, although their relations are not entirely clear. One of these occupies a portion of the shore of Prospect bay between Gash noint and Reef point, as indicated on tLe nap. It lies m the midst of a Keewatin belt, which for reasons already ■et forth, IS probably synclinal in structure, and it is probable that, the conglomerate is the portion of an inpinched fold ot a deposit resting unconformahly upon the Keewatin. The con- glomerate contains numerous pebbles up to 4 or 5 inches in diameter ard boulders up to a foot in diameter. Nearly all of these are more or less deformed by the compression to which the country has been subjected, so that the pebbles and boulders present the appearance of Uaving been flattened into lenses. This deformation of the pebbles has, however, been differential. Of the two major axes of the lenticular ellipsoid to which each pebble or boulder has been reduced, the longer lies invariably in the direcHon of the dip and the shorter in thv direction of the strike. I. vident that the diminution of the thickness of the formation . to compression has been compensated for by elongation cniefly in the direction of the dip and to a notably less extent in the direction of the strike, an effect which agrees with that observed at many other localities in this region. The pebbles co"atained in this conglomerate comprise: — •*u^l'^- ^'*'** ^^^ medium grained biotite fanite gneiss, with foliation always parallel to the longest axis. This is the 36570 — 6 74 UKMt common tjrpe of rock reprcMiitMl by the pebble* but the de- gree of foliation is quite variable. (2) A dark grey feldspar hornblende rock of dioritic faciea. (3) Homblendite. (4) Porphyritic grey gneisa. (6) A fine grained dark grey gneiu; notably finer textured than No. 1. (6) Whitiiih quarti or quartiite. (7) A fine grained grey quartzotis rock. In the conglomerate are bands nearly or quite free from pebbles. These bands alternating with the pebbly beds nfTord un excellent indication of the bcddinK. The strike is 08° and the dip is vertical. The matrix of the pebbles is thoroughly schistose and the schistosity appears to make a slight angle with the bedding, but this could not be clearlv observed. The con- glomerate is exposed for a distance of from one-eighth to one- to'trtli of a mile along the strike and for a width of about 100 yards. On both sides of thin it is couceal(>d. A careful search was made for the continuation of the conglomerate eastwurd between this locality and Commissioners bay, but it was not found. The conglomerate b cut by several dykes comprising biotite granite gneiss, aplite, and mica syenite. Some of these dykes where they happen to be coincident in strike, or nearly so, with that of the conglomerate, have been pulled apart into dis- crete lenses and have been flattened just as the pebbles in the conglomerate have been. Where the dykes, however, are trans- verse to the strike of the conglomerate they have been doubled upon themselves and more or less plicated. The dykes are wi'.li little doubt apophyses of neighbouring batholithic intrusions of similar rocks, and their deformation thus affords evidence of the interesting fact that a large part of the more intense defor- mation of the region has been subsequent to these intrusions; and the fact that they cut the conglomerate shows clearly enough that some of the intrusions at least occurred in post-Seine time. The second occurrence of conglomerate is located on the northw;8tern margin of the Feewatin belt which lies between Rocky Islet bay and Hopkins bay just where that margin comes against the great mass of porphyritic mica syenite so well exposed on Hopkins bay. This conglomerate is a narrow band, nowhere observed to be more than 100 feet wide, and is ob- scurely expwsed in the timber at intervals for a distance of about 2 miles. The matrix of the conglomerate is a mica schist and associated with t^e conglomerate on the south side of it are similar schists free from pebbles. The pebbles and boulders in the conglomerate range up to a foot in diameter, and as far as could be observed, are all tcr* "^ite. The strike of the beds is from 42° to 48° and the dip > Mcal. The coarse porphyritic mica 78 ■y«nit<. In intruiivc Ir both the conglomrrato and the K.-watin A well defined contact metamorphic lone in locally devoloiwd in the conglomerate where it IIpm ugainHt the syenite. The Kio- watin conglomerate, and syonitc are all throe cut by dyke^ of reddish quartiosc bmary granite or laskite, of «,uite Hmail width, and alHO by dykc« of p<.gmatite. It iH by no meanN certain that thi8 conglomerate w poMt-Kcewiitin, but from analogy with Other conglom. rates already dewrib*^!, nuch Ih probably the cue. If 8o then the narrow belt of Keewatin lying b< t ween tho two area* of mtruMive «yenite, the one on Hopkins buy and the other on Rocky Wet bay, in probably tb- remnant of a Hynclinal trough m the midst of which lies the onglomerate, but the northern limb of which has been carried away oy tin- intrusion on that Bide, leaving the conglomerate locally in contact with the •yenite. This interpretation is, however, more or less con- jectural. The third occurrence of conglomerate is on the shore of Kainy lake at the southeast comer of Swell bay and is briefly referred to in the report of 1887. It is chiefly interesting as m indication of the position of a synclinal axis in the Keewatin belt •t this locality. THE SEINE QUAHTZITES, 8ERICITIC SCHISTS, AND SLATES. *u- .^*"*'°8 "Pon .**>« basal conglomerat • of the Seine scries is a thick volume of sedimentary strata of -omewhat variable charac- ters, the clastic origin of which is everywhere apparent except quite locally where they are highly schistose and are completely reduced to sericitic schists resembling those derived from the acute deformation of quartz porphyries or rhyolites. In their typical and most extensive development along the S< ine river they are well stratified, often distinctly cross-bedded in the coarser strata and characterized at certain horizons b • the pres- ence of pebbles usually of quartz or quartzite. 7 peobles are generally sporadically distributed in the beds in h they occur but are sometimes aggregated in cf.nglomei lenses. Ihe faner textured strata are more thinly hedd.d tlum the coarser and have a more distinct cleavage. They 1 . ve the properties w*' f-^-* u*** V^"^ exceptionally fine, and ' sn an- sometimes phyllitic; but there are all grada< .oh. from the lircst to the coars- est sediments. The cleavage in i! I'aese rocks is parallel to the Deddmg. In the coarser beds at various localities one may Observe, with the aid of a lens, secondary biotite or muscovite or both, but the reconstruction of the rock has never proceeded tar enough to conceal the clastic structure, which is usually ^^'^o^?S^'"*°*, °^ *^® weathered surface of glaciated areas, as oo570 — 65 i : d 76 well as in fragments examined with a lens. The prevailing coloiw of these rocks along the Seine varies fron light grey to greenish Key and the weathered surfaces are generally whitish, or at ut much lighter in colour than the fresh fracture. Where these rocks have been intimately sheared and reduced to schists, however, they are commonly yellowish. The quartzites and sericitic schists of the Dryweed syncline are prevailingly yel- lowish with purplish tints in the more schistose facies. A partial account of the distribution of these rocks has been given in the foregoing description of the basal conglomerate of the series and this may now be supplemented. It has been pointed out that in the Shoal Lake section the Seine quartzites He in the middle of a synclinal trough tapering at both ends, the structure of which is established not only by the symmet- rical disposition of the strata, but more particularly by the cross- bedding of the quartzites, which clearly points to a synchnal axis passing through Old Mine Centre. It has further been glinted out that this trough lies across the contact between the ad Vermilion granite and the Keewatin, the former being on the northwest flank of the syncline and the latter on the south- east flank. These relations at once suggest that the mile-wide Kee- watin belt on the southeast flank is an anticline. This sug- gestion, unfortunately, cannot be directly verified, by an exam- ination of the Keewatin rocks of that belt. These are chiefly greenstone schists with amygdaloidal and ellipsoidal structures in which original depositional planes are difficult to observe and in which the prevailing schistosity is vertical or nearly so. But on the south side of this Keewatin belt we have another belt of Seine rocks in which we find evidence of a synclinal structure. This belt consists chiefly of cross-bedded quartzites, pebbly quartzites, and a subordinate proportion of beds approximately slates in their fineness of texture. It extends along the south side of Shoal lake and Wild Potato lake and thence up the Seine river. To the west it appears to pinch out in Grassy lake, but it may extend a little farther down the Seine, the in- sufiiciency of exposure leaving this somewhat uncertain. This body of Seine quartzites lies between the mile-wide belt of Kee- watin on Shoal lake and another belt of Keewatin which parallels it on the south at a distance of from a mile to less than half a mue. This southern belt of Keewatin occupies the south shore of Grassy lake for about 3 miles from its east end. The synclinal structure of the Seine quartzites between these two belts of Keewatin is not only indicated by its position taken in conjunct- ion with its known superposition upon the Keewatin, but is also proved by independent evidence. 77 On a section made south from a point on the Seine river between Shoal lake and Wild Potato lake, the quartzites are strongly cross-bedded in the northern part of the section, and the curves of this cross-bedding clearly show that the upper side of the nearby vertical beds faces the south. Farther south the croM-bedding is much less m evidence, the rocks beinir finer textured, but at one locality, about a mile south of the river gomg across the strike of the strata, in a group of pebbly quartz- ites the cross-beddmg IS quite plain, and shows that the upper side xJ *^^^ ^f?u *]'.® ^°?*>- "^^^ »*"''«' of *»>« strata here is about 78 and the dip 75° to 80° to the south, the beds being slightly overturned. It is evident from these facts that be- tween this point and the river there is a synclinal axis Again on the south side of Wild Potato lake in a small bay about 2 miles west of the Indian village at the head of the t^ko o o °® °^°^ ^^™* around rather sharply from a strike .u °' u* *° °P^^^ *"^ s°"*'> a^d there is clearly exposed on the shore of the bay the tip of a westerly pitchmg syncline. At the tip of the spoon-shaped structure the beds dip westerly down the synclinal axis at an angle of 30°. The beds are coarse textured and gritty with angular fragments up to a quarter of an inch in diameter. They are also stronRly and generally cross-bedded and the curves of the cross-beddini we concave upward, showing that the beds are not overturned; ine evidence is positive and unmistakable that we have here to do with a synclinal axis; and this axis lies in the middle part of tne Seme belt a little north of midway between the Keewatin belt on the north side of Wild Potato lake and the southern belt of Keewatin which parallels it to the south of the lake. A general conclusion from these observations and deduct- ions IS that the narrow southern Keewatin belt dips under this syncline of Seine strata separating the latter from the still lower and petrographically distinct mica schists of the Coutchichinit In my report of 1887 I failed in this general section to recognize the separate existence of the Seine series and placed part of It m the Keewatin and part in the Coutchiching. That error is doubtless in some measure the cause of the later mis- take of the International Committee and the U.S. Geolowcal Survey in assertmg that the Shoal Lake conglomerate is the base of the Coutchiching and that the latter rests upon the r xu^S *^® ^®'?® 7^*' ^^^"^ Wi'^J Potato lake the quartzites of the Seine series become less pebbly and there is a larger pro- portion of slaty rocks. These rocks are abundantly exposed on the shores of the Seine river and its lake-like expansions Mid m numerous cuts and natural outcrops along the line of the Canadian Northern railway. They have thus been traced c ' ! 78 -I r. through practically continuously to the eastward of Sabawe lake, with very little variation in their general features and with great constancy of strike and dip. The stratified and clas- tic character of the rocks is everywhere apparent, but in general they appear to become finer textured towards the east and to have a less pronounced and less common cross-bedding. The belt of Keewatin rocks which flanks the Seine series on the south was traced at intervals to a point a little above Sturgeon Falls. Beyond this various attempts were made to determine the rela- tions of the series to the Coutchiching rocks on the south in (he course of a reconnaissance trip up the Seine river, but the act- ual contact was not found in any of the sections examined. Wherever the two sets of rocks were found near each other there was obterved to be a sudden and abrupt change fron the obvious- ly clastic and comparatively little altered Seine rocks to the highly metamorphic mica schists of the Coutchiching with no trace of clastic structure remaining. The sections examined for this purpose comprise one south from the south end of Non- watin lake to Pine lake, one south from Perch lake at the inlet of the creek draining McCauley lake, and a third south from the Seine river, through Jackfish lake to the lake lying to the southeast of it. Near the outlet of Sabawe lake, at Iron Spur on the Can- adian Northern railway, the Seine rocks are cut by an intrusive mass of biotite granite-gneiss, which is doubtless the same as that occupying an extensive area to the south and mapped as Laui'entian on the Seine River sheet. The phenomena of in- trusion and contact metamorphism are well displayed in the rock cuts of the railway, both on the main line and on the spur to the iron mines. Sufficient work has not yet been done to afford a reliable basis for an estimate of the volume of the Seine series, but it is safe to say that it is several thousand feet thick. . Petrographiail Notes. The sericitic quartzite schist of Dryweed island shows abund- ant evidence in thin section of its clastic origin notwithstand- ing the deformation to which it has been subjected. The sec- tions show that it is composed chiefly of grains of quartz with a subordinate quantity of orthoclase and pla^oclase. These grains are in some cases fairly uniform in size, while in others the size varies so that there is a matrix made up of very small grains of quartz and in this there are scattered sparsely or thickly larger grains of quartz and feldspar. In those cases where the grains are of fairly uniform size they are separated by sericite so that the latter is disposed in section like the oord of 79 an irregular net, while the quartz and feldspar grains occupy the holes of the net. The breadth of the sericite varies from a mere film to a third of a millimetre, but is everywhere, of course, composed of an aggregate of minute scales. The borders of the clastic grains of quartz and feldspar have lost their original worn contour and are now very commonly indentate or suture- like. It is evident that they have been subjected to solvent action, and that the sericite has been developed at the expense of the peripheral portions of the clastic grains and replaces them in part. Where the rock is of uneven texture with larger grains embedded in a finer matrix, the sericite is not so systematically disposed and tends more to development in nest. LAMPROPHYRIC ROCKS Associated with the Seine conglomerate both on Shoal lake and on Drjrweed island are certain occurrences of a 1am- Erophyric rock. The rock is composed chiefly of a rather light rown and green hornblende together with some brown biotite, both of which are extensively altered to chlorite. These occur usually in rather large partially idiomorphic crystals, and disposed interstitially is quite a subordinate amount of allot- riomorphic feldspar, which for the most part is unstriated, though occasionally polysjmthetic twinning may be observed. jEpidote is fairly abundant both in rounded granules and in large well formed crystals. Titanite and leucoxene are quite characteristic of the rock but are not &<; a rule idiomorphic. Apatite occurs very sparingly in minute crystals and magne- tite is also represented by sporadic crystals. There is usually present considerable calcite. On the assumption that the unstriated feldspar is ortho- clase the rock would have the mineraJogical composition of vogesite. But as the feldspar has not been satisfactorily identi- fied the rock may be referred to under the more general desig- nation of lamprophyre. The largest area of this lamprophyre is on the northwest side of Shoal lake in the vicinity of the Foley Mine landing. Here it occupies the shore for a fourth of a mile and extends inland for a similar distance The rock is clearly intrusive in the Seine conglomerate and in the granite upon which the latter reposes. The intrusive contact is exposed at a number of places and portions both of the conglomerate and granite occur as inclusions in the eruptive mass. The lamprophyre area intf -- rupts the continuity of the line of contact of the conglomerate and granite and ejctends into the latter. A small islet |in Shoal lake, half a mile northwest of Old Mme Centre, is composed of a somewhat similar rock, but li : ! I 80 when examined in thin section it appears to be more of the nature of a minette, since the brown biotite predominates over the chloritized hornblende. There is also a larger proportion of feldspar. The same lamprophyre occurs on both limbs of the Dry* weed Island syncline. The rock here differs from that at the Foley Mine landing, chiefly in being more thoroughly chlori- tized, in containing more calcite and less epidote, and in having a less proportion of feldspar. On the south side of Diyweed island it occupies the shore for perhaps a fourth of a mile, near the east end of the island. It here appears to have been intruded into the conglomerate at a time when it was an incoherent aggregate ot boulders and pebbles, since the latter occur abundantly as inclusions in the igneous rock, so that it is not easy to draw the line between the intrusion and the conglomerate. The line of contact between the two is extremely irregular. It is possible that here the erup- tive is in part effusive. On the north flank of the syncline the same rock occurs on the south side of a small island lying off the west end of Dryweed island in close proximity to the conglomerate, but not seen in actual contact with it. The fact that this lamprophyre is known only in association with the Seine conglomerate and that on the south side of Dry- weed island it appears to have incorporated numerous boulders and pebbles of the latter while they were still uncemented renders it very probable thai this intrusion occurred in Seine time and it is, therefore, tentatively referred to this place in the geo- logical scale. TWO WIDELY SEPARATED PERIODS OF PLUTONIC ACTIVITY IN THE ARCHMAN. On a previous page four areas of granite or granite-gneiss have been described and referred to the Laurentian. These are probably genetically closely allied and represent a single irruptive event in the history of the region. The granite is post-Keewatin in age. It is also quite certainly pre-Seine in age, since on or near the shores of Bad Vermilion lake and Shoal lake, the basal conglomerate of the 3eine series may be clearly observed resting upon the erod8 of the region into two widely separated periods upon the signif- icanc e and use of the term Laurentian, will be discussed later. Vtraetnnl Geology of Steejprook Utke, Ontario, Am. Jour. Bei. 142, 189L ■MtmoirlB, Owl. Surrej Branch, Dept. of MinM, Canada, 1«12. n u For the present, having restricted the term Laurentian to the older, or pre-Huronian, granite rocks, we may recognize the need of a name for the aimiliar intrusives of po^t-Seine, i. e. post- Huronian, age, and refer to them and to the period in which they were developed as Algoman. THE ALGOMAN POCKS. The Algoman rocks within the territory mapped comprise four areas of mica syenite-gneiss, three areas of banded biotite granite-gneiss, two belts of porphyroid gneiss occurring as a marginal facies of the banded granite-gneiss, and five areas of massive granite and granite-gneiss quite distinct in ch^-kacter from the banded type first mentioned. The mica syenite-gneiss is intrusive in the Seine conglomer- ate and is, therefore, post-Huronian in age. There appears to be little doubt as to the general correlation of the five areas of massive granite and granite-gneiss, one with another; some of these have a marginal facies which grades into the typical mica syenite-gneiss, and they are for that reason believed to belong to the same general period of plutonic activity as the syenite. The banded granite-gneiss and its marginal facies of porphyroid gneiss cut both the syenite-gneiss and the massive granite and granite-gneiss. We thus seem to have good warrant for classing all of the^e plutonic masses as post-Huronian. In the follow- ing pages brief descriptions are given of these Algoman rocks and their relationships area by area. MICA SYENITE GNEISS. There are within the area mapped several notable masses of granitoid gneiss which consist chiefly of orthoclase and biotite, and which, therefore, fall into the class of the syenites rather than the granites. These rocks are prevailingly coarse grained and light coloured or flesh tinted, and have a pronounced porphyritic structure, due to idiomorphic development of orthoclase in large crystals. They grade on the one hand into porphyritic biotite granite, but with quite subordinate quartz, and on the other hand into hornblende syenites, in which case the porphyritic habit is much less pronounced and is often not developed. Besides these gradations, which are usually gradual, there are quite abrupt transitionii from the normal type of mica ^ enite into dark basic facies, such transitions occurring usuuily on the margins of the normal facies. These basic facies in some cases are composed of feldspar and a dark ferromagaesian silicate and have the appearance of very homblendic diorites; in other cases the feldspar is absent, in so far as can be determined by field inspection, and the rock hM the appearance of a medium grained homblendite. The normal light coloured facies of the mica syenite, with its abundant porphyritic crystals of orthoclase and the dark nomhlendic facies, are both regarded as differentiation products of the same intrusive body of magma. Occasionally the basic rock occurs as an isolated dyke, as in the case of that cutting the Coutchiching schists in Bear passage. In other cases it is found in limited belts in the midst of the normal facies of the mica-syenite, not apparently related to the marpin of the mass, as is true of some minor occurrences on the north Bhore of Crow Rock inlet. The normal facies of the mica syenite has almost always a distinct gneissic foliation. In some cases this appears to be due to an original flow movement in the solidifying magma, but in naany cases it is apparent that the rock has suffered deformation since Its solidification which has produced or at least greatly accentuated the gneissic foliation. The basic facies are very commonly perfectly massive, but in other instances they show varying degrees of schistosity. The mica-svenite gneiss has not only a very distinct folia- tion wherever observed, but at many localities it has a streaked or banded appearance, due to the incorporation in the mass of the syenite of elongated lenses of rock which havemany of the features of the basic facies above referred to. Some of these included lenses are fine grained pepper and salt grey rocks in fresh fracture with occasional large porphyritic crystals of orthoclase. These lenses are in some instances which were measured, twelve times as long as they are wide in the horizontal plane. They are dis- posed parallel to the foliation of the syenite and in most cases are sharply delimited from the normal syenite on either side. In other cases the boundary is vague and gradational. There are also other lenses of still darker rock similarly disposed. They are all probably inclusions of the more basic first produc ts of differ- entiation caught up in the later and more acid magma, and, by imperfect assimilation, give the latter a heterogeneous character. The Rocky Islet Bay Area. Perhaps the most interesting, though the smallest of the areas occupied by the mica-syenite and its differentiation pro- ducts IS that of Rocky Islet bay. On the map accompanyinjr the report ot 1887, the basic marginal facies of this intrusive bod- was confounded with the Keewatin and mapped as such. Th- more careful studies of the past season have made it possible to di8»,ingui8h between the two with a fair degree of certainty. The syenite and its basic faces taken together occupy a heait shaped area, in the midst of which lies Rocky Islet bay, the apex w 84 of the heart pointing to the northeast. The more important Spwure. «e on t^shorea and Ulands of the bay. but where necemary for the proper delimiUtion of the area excursiona were made inland from the shores. , _ ..... . The mass is clearly intrusive in both Coutchichmg and Keewatin since it interrupts the continuity oi t^ese 'ocks and shows the usual phenomena due to mtrusion at the contact. The relation of the intrusive mass to the su"oundmg rocks is, however, quite different from that of the neighoourmg R'ce Bay granite^neiss. The latter mass, as has been shown, was m- Suded into the Couchiching before its acute deformation and participated in the deformacion to which these rocks were sub- fected It is evident from the mapping of the Rocky Islet B«or mass that it was intruded into the Coutchiching and Kee- watin at a time subsequent to their main deformation, since the schists of both series abut upon the periphery of the mass and the latter shows little or none of the intensive shearing action so Sent in the Rice Bay mass. The foliation of the mica^yemte gneiss is, moreover, parallel to the elongation of the norm^ Scies of the intrusive mass and tb« if clearly transverse to the elongation of tlae Rice Bay mass. The directions of co^npres- Bion in the two cases were, therefore, widely divergent. For these reasons the mica syenite of Rocky Islet bay is regarded as Llonging to a later Archtean period of batholithic develop- mentthan that represented by the Rice Bay famte gneiss. An interesting feature of the Rocky Islet Bay mass is that the dark basic facies predominates over the normal facies of tbe infcifyeiSto gneiss. TThe lattor is confined to a lenticular area S)Sut 4 milei long and three-eighths of a mile wide at .ts widest part, lying in the east half of the heart-shaped area. This Incomplete ysu^ounded by the bas c facies, but the breadth of this on the west side is from half a mile to a mile, while on the east side it is only from one-eighth to one-fourth of a mile. Ibe total area of the basic facies is between three and four times that of the normal facies. Of course, this apparent excess of the basic Scies over the normal facies may be due to the Posi ion of the accidental section afforded by the present surface, "the mass be regarded as a batholith, then the section may be through its upper part, and a deeper section might reveal a much larger prop^rtio^of the normal type of rock. If the mass, on the other hand^ be regarded as laccolith in type as seems QUite possible then the section may pass through its b^al Partmwluch there might well be an excess of the heavier dif^erentiaticm product On an island on the northern part of Rocky Islet bay the rock is mostly a gabbro. varying from an anorthosite to a p^«- enite. and is in parts very coarse textured and m others medium S^teituM. The coars^t textured rock occurs as dykes cutting I'HTC tX. B A. Gmnitic dykes in si-hists, showinii piirticipiition in thr ilcforniHtion of the sthista ; .xoutli side of I'rosptct buy. B. Granitic dylces intruded into schists after the deforiimtion and sohistification of the latter; south side of Buso-line bay. 36570— p. 8-J 1 1 1 \ ^ i m i 1 Il1 i:r| ■A ;« 85 th« BMdittm t«itured g«bbro. Thb gftbbro in Hi varying Mpecta if prob»Uy an extreme differentiation product of th« magma, which ■olidi&ed normally aa a mica syenite. On another island more nearly in the middle of the bay, a large dyke of quartzose biotite granite-gnclM cuts the syenite. The gneiado foliation ia distinct and appears to be an original structure of the rock. Mineralogically the rock ia composed chiefly of orthodaae, plagioclaiie, both fresh, and quarti. The biotite ia not notably abundant. The rock is in contrast to the mica-syenite, not only in the large proportion of quarta present, but also in the absence of epidote, the abundance of which la characteriaticoftheayenite. . „ ^ .. . . .. There aia alao fairly numeroua dykea of flesh tinted bmary granite or alaskite, cutting the normal facies of the mica-syenite, but rare'y seen in the basic facies. These consist of orthoclase and quarts of medium grained texture, but grading on the one band into coarse pegmatites and on the other hand into aplites. It ia worthy of note that these pegmatitic and aplitio dykes do not show vhe foliation that is so pronounced in the syenite- gneiss. On the northeast of the heart shaped syenite area there is » large dyke of granite, somewhat pegmatitic in character, cutting the Coutchiching schists; and on the southeast of the area ortion of the belt with similar rocks on the Canoe River route to the north of the area mapped is uncertain, the intervening country not yet having been explored. On the map of 1887 the two areus were conjecturally shown as connected. Along the northern border of the stem of the hook, the mica syenite-gneiss is in contact with a well foliated and banded biotite granite-gneiss. On the southern border it is in contact with a much sheared porphyroid gneiss which will be further described on another page. On the outside or convex side of the hook, the syenite- Keiss is in contact with the well foliated and banded gneiss in acdonald inlet, with Keewatin rocks on Cheery island, and with Keewatin rocks for the most part on the southeast side of Hopkins bay. In the territory between Hopkins bay and Rocky Islet bay, however, there is a narrow belt of conglomer- ate, lying against the northwest side of the Keewatin belt and between the latter and the syenite. On a previous paRe this conglomerate has been correlated with the basal conglomerate of the Seine series, the relationship being regarded as that of a portion of a synclinal fold above the Keewatin, the greater part of which has been removed. This removal is in part due to intrusion. If this interpretation be correct, then the mica syenite-gneiss is post-Seine in age, a conclusion which accords with that arrived at from a discussion of the Rocky Islet Bay area of the same rock. In the sequence of events involved "n the development of the Archsean of this region, therefore, the mica-syenite-gneiss appears to belong to the later period of plutonic activity. 87 ^S^^K*'*' Keewatln .re everywhere intrusive, the u,uS contact phenomena beim well exemplified in the form of aoo. fKJT?.°' .*''?. •y/"*** cutting the KeewatinandofincluwoM^ the latter in t » former near the contact. The Ketwatin green- ■tonei near tue contact take on the characters of black horn- blende schirts, aa u usually the case near irruptive masses. -K«« i! conglomerate at the contact with the syenite EK? J marked degree the phenomena of contact metamor- .i-^/Tk""^ "'1°' '^""'"S' *««np'«fied l>«t in the non-pebbly eds of the conglomerate formation. These beds are rendtred S,Sn?y*l*""/'.*°'*u-*J'' ^^1 «^»'"»<:t"- of a rather ma«.ive rstallme hornfels, which grad.-s away from the contact bto caceous schintu containing water worn pebbles ,.. yt^"»">K ».*>o mica-syenite gnei»s there are fairly numer- 0U3 dykes and irregular mtruHions o{ a more granitic type compnwng biotito granite and alaskite. These are the counter^ part of Bimilar occurrences noted in the Rocky Inlet Bay area and are similarly regarded aa later manifestations of the same nrSnl.*" ''t^T *^"'''• 8»v« '>" »<> *»>« "y^'nite as the chief product. The basic facies of the syenite which is so pronounced • feature of Rocky Islet Bay area is quite subordinate in the Z. ** # *l"t.^ '^L**i It appears to be a feature of the inner bor- der of the hook shaped portion of the belt. But even here it la relatively small m amount and non-persistent. Noteworthy ^VYT*^ "Z u *^« /"nt?":* o' the mica syenite-gneisa with the foliated and banded gneiss on the north sid. of Hopkins bay. Black island, Sunday island, entrance to Macdonald inlet anm its occurrence on a group of Wands which he south of the shore between Gash p^int ^d Back p^int. Of this group Pukamo island is one of the largest and the area may, therefore, be referred to as the Pukamo Island area. Almost the entire shore from the vicinity of Gash point M i ^i 88 to Ba^k point is occupied by Coutchiching mka Bchists the onlv exceotioM being two small headlands about li miles wS of B?ck%int, which are composed of t^e mica syemte. ?he islands immediately off shore are c«"?PO«^;/,.*J« >? ""J rock The boundary between the syenite and the Cout- chiching is thus located in the lake just off th.s shore and parallel S it The southern boundary so far as it. is known frori the islands is a narrow belt of Coutchiching "^ica schist extending from the south side of Last island to the north side of Nowhere Lland and probably in continuity with the same schists on Goose £nd This narrow belt of mica schists separates the S syS gndss from the distmctively quartzoseb^^^^^^ wanite-Bneiss of the Nowhere Island area. The two boundar- KftKca syenite-gneiss above indicated as the northerly and southerly converge at a point in the lake south of Back wintS it appears possible that the tapering eastern end of the areTis in tto neighbourhood surrounded by the Coutchich- inl mfca scWsts If this be true, then the narrow belt of mica Mhirts extending from Nowhere island to Last island is a tonSe exteSI out from the main area of Coutchiching on Sen and Goos^e islands. It seems, however, more probable that the schist belt referred to is isolated and that the yenite area continues on as a narrow zone under the waters of She lake to the east of Nowhere island and connects with the area of syenite rocks on the south end of Goose island and the northweTend of Sand Point island, which are clearly but a marginal f acies of the granite gneiss ^ will be shown later^ Westward the syenite gneiss is traceable on the islands be- tween Lobstick island and the mainland, followed by the Canad- Un Northern railway. There is, therefore, no doubt as to the continuity S the Pukamo Island area with the large m^s of the ^me rock at the west end of the lake. Owing to the fact that ShfboSndary of the mica syenite-gneiss lies for the most part in the Uke its contact with the encircling Coutchiching schists s Sservab'le only at a few localities. Wherever this contact is exposed however, as on Last island. Nowhere island, .and on the sCe west of Back point, the syenite is intrusive into the ^''*'' T^he rock of the Pukamo Island area is prevailingly a typi- cal mica syenite-gneiss with orthoclase in large porphyntic development! but associated with this mica syenite-gneiss and SinHnS it are more basic rocks. These m their extreme Cs are massive homblendite and between this and the syen- te the inSmediate gradations comprise d orite, mica diorite, Sd syenrte p™or in orthoclase but rich in biotite ajid hornblende U is very probable that the intermediate gradations include 1j8«^ monzUtic types, but this could not be definitelv ascertained. 89 The Bear Passage Area. wmmmm mile. The dyke is whoWv in ;h r^ f^ -^I"^^ .^'^'"« »«* over a Petrographkal Notes. Whole approtth^^^^^^^^^^ -k as a north\rrnrcfo;'LXnL?"" °' "^""P^^ ^-- the orthoclase and m'croctoe and rlh ^°°^P°«^d chiefly of fresh biotite and green hSwdrn^*-^',""^:?'''^''^"*^ amounts of also titanite^ The "Sfter occuS i?T' "^'■^^' '' ^H"-"'^*^* «« i« 36570-7 ^^^ idiomorphic crystals, i it'll Ul m ii 90 but it is also found in smaller forms with apa«te endo^ in the feldspars. There are also occasional cubic crystals oj Py"^*- In this matrix are embedded the large crystals of orthoclase. The rockis qSte gneissic and in this section shows a pronounced ^n^thersSSen from the west end of Crow Rock inlet nroves to be similar to that last described, but has little or no Cbende inTt« composition. Oligoclase occurs arnong^e feldspars and there is a little quartz present. There is the same abundance of epidote. The biotite is largely altered to chlorrte and with the latter are granules oj.mapetite The rock snows a streaked gneissic appearance and in thm section there is appar pnt a well developed cataclastic structure. -^ * „ ♦!,. '''* YslLcimen of the basic fades of the ^^.^X^ofortSclie north side of Crow Rock inlet is composed chiefly oorthocl^ and microcline with much green hornblende and ^"'^ "^ J^" hiotite There is a great deal of primary epidote, and titaniie and apatite^e all- aLidant, the latter '^ 'f.^^ larj-^^^^^^^^^ There is a sparing amount of quartz locally present, ine ^'""f^^SZ^:^^^ prevailing ba^cfades.crf Rocky Stb^y is composed chiefly of ff.'^^^omblende^with some biotite and subordinate amounts of feldspar in which^ acid plagioclase predominates over orthoclase. There is aoun dant epidote and considerable titanite and a very little quartz. ^'^ rofh^ipeSSsoti^Ro^^^^ bay is a granular aggregaft frSh Pliiodase and hornblende with some zoisite "''^^li^ome cases the basic rock of Rocky Islet bay has been oMAc in the fo- of fine dust and also in nests. Calcite is lairiy ab^da^t A very little original feldspar and quartz may be '^'*' Tht basic dyke in Bear passage is a coarse granular iS'oJl^'^i^-Jsot^i^S^^on^^^^^ numerous indu- pyroxene being changed to green hornblende. 91 Chemical Composition. s the analysis shows PviHo^nJ T ^^ , ^^^ ^'''^ of which III romagnesiaVconSpnr. . ^?^ '^.•°.^'"*' alteration of the fer- the m^e reSrS IS^^^^^^ ^^'f *?• Column II is although ^^ef^reTs^eTZ^'^^iX^^^^^^^^ «^-*^' ,Rociy¥irb^^;'a^f Sty '^^naT;:!* 1^" V'A^- entrance c' .;,.- ,a^,, ^,^. from we8t side of inland in Ro^kv Islet h„v/;?'''T- .,"v ' '-"ies of syeSte '-.ea Of eyenite from northwe^rr^'^', &y^".t"C inai^sri-. ^"cS BANDED BIOTITE GRANITE GNEISS. Within the field defined by the limits nf th^ panying this report ther.. m-wK,„„ . *°^ ™*P accom- commonly streaked or IIh^.kw'^.^'^^' °^ ^^" foliated and these is tU^Se'b'/ilo'rof tKoTf ^^ . 2^' "^ mica syenite-jmeiss- th/Jn^Av . "'^ nook-shaped belt of of theLldinKastemhalf lJ'rh.'K-«^ T**^^™ ^^o^^^r era border in the westSi hllf t^ tbrd lies along the north- 36570-71 "^^ '^* mentioned areas fill mi 92 ES's£rr.rp?„sn=vrs:£^? !„fromlS»S.i»and » the colour varie. t'om very dark to nating f y^^^^j ""V"t„,** rpu —j^de into each other and the arable from the darker They graae i ^^^^ ^^^ ^^^_ nf a few slides of representative specimens. These show that, ■ -fT^iho nprfectlv developed foliation and bandmg, there the same minerals but m different pr- 'O^^; ^ JnJarently an abundance of biotite and ep.dotc he la^^^^^^ apSe'arJalso original constituent of the rocK. iiian j /^^^^^ds. The containing little of that mineral, ^ ^^^ ^ S8 the rock 18 of a nearly uniform light grey colour, a close exami- nation shows that It has a streaked appearance, and in these cases the lines of streaking are very often not straight but are wavy or contorted, sometimes intricately so, and are evidently due to flow movements in the magma prior to its final solidification In some localities the banded gneiss takes on a distinctlv porphyritic appearance due to the development of orthoelase in larg'^ idiomorphic crystals, and these are then disposed in lines or narrow bands. In the banded gneiss of Little Turtle lake, there is a great abundance of inclusions of hornblende schist, both in the form of large tapermg bands and in smaller angular fragments. Chemical Composition. A representative specimen of the banded gneiss from the north side of Hopkins bay, near its contact with the mica syen- ite-gneiss, was analysed by Mr. M. F. Connor with the fol- lowmg results: — BiOi 6882 TiOi. AltOi. FeK),. FeO. . . HnO.. CaO.. BaO.. MgO. NaiO 0'2S 15-70 IM 1-77 007 3 S8 002 1-28 S'08 K,0. . Hi()— .. HtO+.. PjOi... CO, ... S CI ChOi 1 31 010 0-58 10 trace. 03 none. I none. 100- 13 It IS apparent from this analysis that the ratio of NaiOto K,0 suggests that the rock is more properly classed with the soda granites or with the granodiorites than with normal biotite gramte or granitite. It would be rash, however, to assume that this one analysis expresses the general composition of a rock at once so extensive and so heterogeneous as the banded gneiss- and until such time as more elaborate determinations can be made it seems better to refer to the rock as a granite-gneiss. PORPHYROID GNEISS. I- .Traversing the field from east to west, near the northern limits of the area mapped, is a remarkably linear and persistent belt of sheared granitic rock, which will be referred to as the porphyroid gneiss. This belt has been traced in practically continuous exposure from the east end of Liale Turtle lake to Black Sturgeon lake, a distance of 21 miles. It may possibly extend eastward beyond Little Turtle lake and beyond the limits of the map under the marshy flood-plam of the Little Turtle riv»r 94 ll ■I ^\l< The average width of the belt is about a fourth of a mile. Its maximum width at Pine narrows is a little over half a mile. Another similar belt skirts the north side of Cheery island and embraces several islands to the north of it. The length of this belt is about 4 miles within the limits of the map, but it has an indefinite extent beyond its western boundary. The porphyroid gneiss is prevailingly red or flesh coloured but grades into grey. It is characterized mineralogically by being composed chiefly of orthoclase and quartz with little or no ferromagnesian minerals. It is almost always porphyatic, due to the idiomorphic development of an early generation of ortho- clase. It generally shows a foliation which is apparently due to shearing since the porphyritic feldspars are reduced to Augen and are i Irawn out in lines on the surface of the rock. In many cases thi^ foliation is accompanied by a marked schistosity or tendency to cleave indefinitely, while in other cases the rock has a platy structure with no appreciable schistosity within the plates. The examination of ^ few thin sections from represent- ative specimens of this porphyroid gneiss, shows that it has a pronounced cataclastic structure and that the schistosity of the rock is referable to deformation involving shearing of the mass. Even in the platy facies of the porphyroid gneiss, the con- stituent minerals of the rock, chiefly orthoclase, have been broken down and in part reduced to a fine secondary matrix into which the residual large crystals are locked in suture like boundaries. The comminuted material is disposed in bands in which have been developed secondary sericite and chlorite. There is some epidote in the rock, but it is irregularly granular in its occurrence and not in idiomorphic crystals. This belt of porphyroid gneiss grades into the banded gneiss both across the strike and along the strike. From the east end of Little Turtle lake to Farrington on the Canadian Northern railway, the porphyroid gneiss forms the southern border of the large area of banded gneiss in which Little Turtle lake lies. In passing from the typical facies of one rock to the typical facies of the other it is impossible to draw any line at which it can be said: here one ends and the other begins. In approaching the banded gneiss, the porphyroid gneiss loses its red colour, its ground-mass becomes coarser and biotite makes its appearance more and more abundantly, but the rock retains its poiphyritic habit and resembles in the weathered aspect the less sheared portions of the porphyroid gneiss. Finally it loses this porphy- ritic habit and passes into the typical banded gneiss. A quite similar gradation is observable at the west end of the belt, where it crosses Black Sturgeon lake. Where the belt enters the lake from the east it is the typical porphyroid 95 gjieiM with a reddish colour. On the other side of the lake in the line of strike, a mile or so distant, the rocks have lost their red colour but otherwise resemble the porphyroid gneiss except that the ground-mass of the rock is perhaps a little coarser in texture. Here just as on Little Turtle lake the effort, which was constantly made to map the porphyroid gneiss as a thing distinct from the banded gneiss, broke down, and it waspractic- ally impossible to find a dividing line between them. It has been shown that the banded gneiss has no cataclastic structure, that its banding is probably due to viscous flow in a heterogeneous magma and th.it, therofore, there is no evidence of Its having suffered acute deformation since its solidification. Ihe porphyroid gneiss, on the other hand, has been clearly de- formed by a process which involved much shearing and a break- ing down of the original structure of the rock. From the statements thus far made it is evident (1) that the porphyroid gneiss should be regarded as a marginal facies of the great batholithic area of banded gneiss which extends north from Little Turtle lake, (2) that it differs mineralogically from the great mass of the batholith in its poverty of ferromagnesian con- stituents and structurally in the development of a pronounced porphyritic habit, and (3) that it has been deformed, sheared, and schistified, while the main mass of the batholith has not been so affected in so far as observations indicate. By analogy the belt of porphyroid gneiss on the north of l.heery island may be regarded as a marginal facies of the great area of banded and streaked biotite granite gneiss of the northern part of Rainy lake. Where the porphyroid gneiss occurs in the vicinity of the Keewatin rocks, as between Farrington and the east end of Little Turtle lake, it is in several places charged with numerous inclusions of hornblende schist. While the interpretation above presented as to the relation- ship of the porphyroid gneiss to the banded gneiss seems fairly certain, it must be pointed out that there is an important part of the belt occupied by this rock in which it is not marginal to the banded gneiss. This lies between Farrington on the Canadian Northern railway and Black Sturgeon lake, a stretch of about y miles. This portion of the belt of porphyroid gneiss serves as a connecting link between the banded gneiss of Little Turtle lake and the same rock occupying the area enclosed by the hooked end of the belt of mica syenite-gneiss. In this 9 mile stretch the belt of porphyroid gneiss is bordered on the north by m... syenite gneiss and on the south by a large mass of biotite granite showing in general but feeble gneissic foliation. At one end of the stretch referred to, the rock grades into the banded gneiss of Little Turtle lake and at the other into the banded gneiss of a similarly expanding but smaller area of the same rock 96 If 111 III It would appear, therefore, that this portion of tne '*elt of porphyroid gneiss or marffinal facies of the banded (mr'-s is of the nature of a peat dyke. The mapping shows that % iyke cuts across the granite and granitoid gneiss to the south and its in- cluded fragments of Coutchiching and Keewatin schists. That it is also intrusive in the mica syenite-gneiss to the north is shown by the fact that numerous dykes of rather fine grained porphyritio binary granite, resembling closely the porphyroid gnoiss or the transitional rock between the latter and the banded gneiss are found cutting the syenite. There are also bands or elongated fragments of the syenite gneiss enclosed in the handed gneiss near the contact of the two rocks. It seems clear, therefore, that both the banded gneiss and the porphyroid gneiss are intrusive in the syenite gneiss, the two former being but different facies of the same intrusion. Since it has been showTi that the syenite gneiss is mtrusive in the post-Keewatin conglomerate between Hopkins bay and Rocky Islet bay, which has been correlated with the Seine con- glomerate, it follows that in the post-Seine or later Archaean period of plutonic activity there is a definite sequence of irrup- tions, a syenite followed by granitic. Of these, the former was the more homogeneous magma, but was accompanied by quite basic differentiation products. It owes its gneissic foliation in large part to mechanical deformation after solidification. The later irruption was that of a heterogeneous magma which develop- ed a gneissic banding by viscous flow. A marginal and dyke facies of this rock, remarkably free from ferromagnesian con- stituents, was, however, subjected to intense shearing which rendered it either schistose or platy. f I ill OTHER GRANITES AND GRANITOID GNEISSES. Within the field here discussed, there are five areas of granite or granitoid gneiss referable to a later period of intrusion than that which gave rise to the granite extending from Grassy island to Bad Vermilion lake. These areas are: (1) that of the north side of Grassy island and the south side of Rat-root bay; (2) The Nowhere Island area, occupying chiefly the islands of the lake to the south and southeast of Nowhere island; (3) The Knuckle Island area, extending from Noon island to the east side of Joint bay; (4) The Bear Passage area, extending from Traverse inlet to Bear passage; (5) The Redgut Bay area, extending from Base-line bay to the eastward of Barber lake. The granites of these five areas are for the most part normal biotite granite, with usually a rude or feebly developed gneissic foliation, which, however, locally becomes quite pronounced. 97 They usually have a fairly abundant proportion of fresh biotite Ik- u' »<«°P?"t'on. *nd are thus mincralogically distinct from They are free from the shearmg which has affected the older granite, and the contrast between the sheared and the unsheared granite is most pronounced on Grassy island, where both ^nnf «hZ 1'h^ Ki^ ''k':i '^^^'^ y"""*"' «'''"'**'«. moreover, do not exhibit the bleached appearance presented by the older S^'lli^:, "* ^u^ "^^^f " '^a^J.flesh tint or even a distinct pink- ?iw-H^ , • *lf'*V°*'^'u"^ "^y intrusive in the Coutchiching or Keewatin or in both. The evidence of this consists of the usual l!!?-.?f^'' °°1™'^.T*"*^'' "^ abundantly observable, compris- mg. (1) fragments of the encasing rocks enclosed in the granite- (2) apophyses of the granite cutting the encasing rocks; (3) intense metamorphism in the vicinity of the contact of the ^anite with the encasing rock. The Grassy Island Granite-Gneiss. ^.vil!"" '^'^lu'^i ? ^""^ ^^^^^ o^ a*'""* 21 miles and a maximum width of less than a fourth of a mile. It may be IS f ♦f %r ^'l* .lenticular dyke striking with the general trend of the Keewatin belt in which it occurs. It may have LSh'iK° ^ I*"*" ''}"ir \'i^''=at«d, since at both ends it passes beneath the waters of the lake. On the north side of Grassy island It 18 in observable intrusive contact with Keewatin hom- S mil* i!- "'^^"L^*"^ granite contains also angular inclusions of micp. ochis. doubtless derived from the near by Coutchichinjt which here may be at no great depth below the Keewatin. On the south Bide, from Review island to the west end of Grassy island, the p-anite-gneiss is in contact with the older and ereatly Sheared and decomposed granite previously described. On tnis side the gramte-gneiss presents locally a relatively basic facies resembling certain facies of the mica syenite gneiss. On the east end of Review island the older sheared grinite is cut mJ^nfiK^ f*^" darker facies of the later granite and frag- .^ -.! \ *u ^ /"^""^^ ."®. "^'^•"ded in the latter. The difference m age of the two rocks is thus not merely a matter of inference from the contrast in their physical condition, but is also based on the positive evidence revealed at this contact. The Nowhere Island Granite-Gneiss. . This mass extends from the northwest end of Sand Point ^.,tf ♦ ?*^?^ P°"l* '^ ^^^ ^'^^^ between Last island and the outlet of the lake. Its length is probably between 8 and 9 miles 'II I ! f iff It! maximum width is about 21 miles in its middle part. The area thus has the form of an elongated ellipse. It appears, in so far as the insular character of the exposures permits a con- clusion, to be enclosed by the Coutchiching mica schists, but to the southwest of Last island and to the east of Nowhere island the granite-gneiss may come in contact with the mica syenite- gneiss of the Pukamo Island area and may even pousibly grade into that syenite and be continuous with it. The rock is pre- vailingly a medium grained, distinctly quartiose. biotite gran- ite-gneiss, with a little muscovite, the gneissic foliation l>emg generally better developed than in other areas of this typo of rock. At the eastern end of the area, however, the rock becomes deficient in quartz, hornblende accompanies the biotite, and these two minerals are so abundant that the rock becomes dark in colour. In general it takes on the facies of the less porphy- ritic portions of the mica syenite-gneiss. Microscopic exami- nation of several thin sections of this rock shows that it also resembles the syenite-gneiss in the fact that there is consider- able epidote in it. Besides the dominant minerals, orthoclase, biotite, and hornblende, there is some acid plagioclase and a little Suartz. Apatite is present as an accessory. The rock, though istinctly gneissic, shows no cataclastic structure. This more basic or syenite facies of the granite is chiefly developed on the west end of Sand Point island, on the south side of Goose island, and on some of the smaller islands adjacent to these. It appears to grade off insensibly into the biotitc-granite gneiss and the gradation again suggests, as in the case of the same rock on Grassy island, that this granite is genetically closely allied to the mica syenite-gneiss already described. On the map it will be seen that this biotite granite-gneiss is separated from the Pukamo Island area of mica syenite-gneiss by a narrow belt of Coutchiching mica schist extending from Last island to No- where island. In the description of the Pukamo Island area it was pointed out that the north and south boundaries of the mM8 appeared to converge at a point beneath the waters of the lake just south of Back point, and that the tapering east end of the area was perhaps enclosed by the Coutchiching. This, however, is but a conjecture and it is equally possible, and indeed equally probable, that the syenite of the Pukamo Island area may be continuous with the syenite facies of the Nowhere Island gramte- gneiss of Goose island and Sand Point island. In this event, the narrow belt of mica schist extending from Last island to Nowhere island would be an isolated inclusion, and the syenite of the Pukamo Island area and the granite of the Nowhere Island area would constitute a single iiruptive mass, differentiated into two petrographic types. Indeed, the narrow belt of schist separating them is so slight a partition that even if it be regarded 09 «-!)?T* '"'"?/*"' ?»'" r°"*'^»>'«'hlng arpa, it i.<« difficult to th!t l^l"' '^^'^'^A- "".^ «™r^«' «: having any other rrlatio .hS than that juKtrndioatotl 1 Hhail, therefore, tentatively n lopt tha view ami regard the granite gneisses here considered us belonging to the some p«.riod of irruption a« the mica-HVenite' gneisa and derived hv differentiation from the rZe m««nm rnr"!*!?. n'!?,*r'^*^r'''"7 and geogruphieally Hufficiently disTintt Zlt. ^tTr °^ K^*''«8''''''' .'napping. It followH from thi« con- elusion that these Rranitt-gneisHes and granites, being praeticallv th«*rfT°'*'"" i" «"r with the . nite Wii. belong o the post-Seme or later ArchiEun period of Plutonic Activity The Knuckle Island Granite. theNnw},?«Tlf'*i''''"'* f'*''**? °"^' *'>°"K*' Heparated from the Nowhere Island area of granite-gneiss by less than a fourth of a mile of schists, shows none of the basic di«fer«-ntiation facies which is so marked a feature on the southwest side of the separating belt. Minor-.'ogicully the ro.k is identical with that of the prevailing or normal faeies of the Nowhere Island granite- peiss, but It IS nearly devoid of gnei.-Mie foliation and is more homogeneous in character. It is free from basic inclusions and fragments of the encasing mica-schists are limited to the imme- diate vicinity of its contact with the Coutchiching. Apophyses of the granite are similarly confined to a narrow zone on the f,^^ «"i^»'°'' '"^*' °' the contact. It is also remarkably free from aphtic and pegmatitic dykes and later granitic dykes. The contact metamorphism which it has induced in the encas- ing schists 18, however, strongly marked. The Bear Passage Granite. K-n,.Xu T®r ''j**'"***^T*^*°'*® '^ 1""'^ «™''»'' t^ that of the Knuckle Island area. It is a medium grained, fairly homogen- «^«fi!.°V'f- «/'^'*«rth, on the whole, a very feebl? developed gneiss ic foliation. In some localities, this foliation is not dis- cernible, in others it is quite pronounced. There are few apli- tic or pegmatitic dykes cutting it and inclusions of the encasing rocks are practically limited to the vicinity of the contact The contact metamorphism induced in the encasing CoutchichinK iSh ^ ^"^r "^[^ mtensiye than in the case of the Knuckle island granite. The general phenomena displayed at the con- rocL ^^^ described in the discu-ion of the Coutchiching The Redgut Bay Granite. ehinh^L*^^ discussion of the structural relations of the Cout- chiching to the Bear Passage and Knuckle Island granites, it n a 1 1 ! i- ' i I 100 hM been .hown that the 'irnci^Z^^^'(ifj;S\TiXl the encMing rock. l^V'^hf ^^^ cS^dKyrably hold. In Ion of . iMCohth roof. P* "^' ShSg to the combined Nowhere Wand »nd I'uliaroo iBianu ^ piutonit- maw widen. This area w by far the >a'B^^ "' ^ Brained biotite granite in rock ha. the character, oi a med urn B'^'^^^jJ'^bly developed, which gneiK.c »«»'»^'°?„ "XdT^ area i. not only large but may be locally quite »»»'''«'«;. :„p-uiftr in outline. On the but iH qiite a«y"?™«^"V K'^^^narlt Sght ew? and west line north .ide it i. bounded by a near ystr^ghtewia^^ which i. the !^»^J»^«'3?,^'^" bt^^^ ^ois° K marginal or ;j AitoUh^ baSed rnffeut. So,, the granite and ter- "^n ihe «,uth Bide the granite is jn -tact with both the Keewatin and Coutchichmg. This line «>* <^onja[J^„ ^^^^ from the northern boundapr from wesUo east ana ^^^^_ Bharply to the north m ^^'VJi^'f.'yiine oi the Cunu M .n North- ing the northern boundary near the line ot we v.unu ^^^^^^ em railway ^^out 2* mj^^es ^f f^^^^^ is noteworthy for the rema^aWeinte«^^^^^ g ^^^_j.^^ ^^^ ^^ £-StheVMf^^^^^^ and Keewatin rocks which "'^^/^X^fhat in V parts where from bemg a simple dome. " »» '^^"^^Ag-. ^ terranes, that the the granite lobe, e^^tend into the P/J«»f,JJ>,'/;ocks; and that granite magmas rose higher "J^" **>« °X*'^\7e granite terrane, ^here the tongues of «°b'«*Ks7t»^J*?oS that were more these tongues represent portions ol tne rooi vu 101 deeply bunken in the gmnltlc maicma in the faiihion of Daly « roof pendantn. They are roof pendanto that nro itdll connected with the margin of the roof. There are, howi>ver numerous isolated included Mu of Hchistt in the granite which may be interpreted an portions of roof pendants which hnve heen left discrete by the i rosion of the greater part of roof from off the batholith. Thn' they are actually pendantH and not loose pieces that have Ltt'come detached from the roof and sunk into the magma while it was in process of irruption, is indicated by the accoidance of the dip and strike of the schisN in ihcs*- isolated Wits with the structure of neighlwuring portionH of the roof still intact. Such isolated remnants of roof {M-ndunts are exemplified in several occurences along the west side of Rcdgut bay. The largest one observed, however, is in the vicinity of Farrington on the south side of the Canadi.in Northern rail- way, where a belt of schist 2 miles long and t\ fourth of a mile wide occurs sunk into the granite. The schist has an east and west strike and a dip varying from vertical to 70° N. The northern half of this belt consists of Coutchiching mica schists and the southern half of Keewatin hornblende schists, nnd it appears to be in the prolongation ot a similariy dually constituted tongue of schist projecting into the granite at Hear Puss .Stat- ion. On its nortliern side it hcs licen cut off by the later intrus- ion of porphyroid gneiss previously described. Arourd the west end of Base-line bay, there are also rather numerous Ix-lta of schist sunk into the granite, some of which appear to be iso- lated while others are still connected with the main area of Keh,- Bad Vermilion granite the she rr granites of Grassy island and Rice bay, and v "ry prol 4lv Jhe intervening granite of the Mud Lake belt. ^ Pro'>-i"I> the (2) One of these, the granitoid gneiss of Steeorock l-ik-n anteda e.s the Steeprock series, and probably aU of them do ' (6) 1 here are certain other syenite gneisses, granite-eneisscs tTusi^^nlt' "S '" '"''' ♦^"./he^eine sV^ies'anlarr^: trusive in it. These are specifically the granite-gneiss of th^ nr/heTh T'T °^ '^' ^'"'"^ River sheet and the^reater par? of the bhebandowan sheet mapped by the Survey as LaurenS WnLn i;^^^'*^■'^"^^ "^ ^'^'"^ ^^'^' ''- -Pp"d as (4) Associated with this syenite-gneiss are certain areas of granite gneiss which are regarded as practically contemporaneous r"p?i4';rj;S' ^"" "^"^ P™'^"'^ P™^"'*" «f theTmTrr- (5) Later than the syenite-gneiss is the banded gneiss and its marginal facies, the porphyroid gneiss. The interval betweS the syemte gneiss and the banded gneiss is not known aTdi? may be of a minor order. r« t ^\ ^7^ *hu\have in the region at leas ; two groups of nlutonic rocks, both of which are commonly referred tl as Laurentir SSoT order'.'' ''^'"'"^'''^ ''^ ^'^ '"''''•^''^' °^ ^^^'"S''^'-*' ♦i^" «' ^ (7) The interval last referred to embraces — f'nn/.'k; l^"" time necessary for the degradation ot the btruJvete them^'^'^^"*" ^^' *'^ ^^'"^^ P'"^-- — rock^serie?'^ *'"''' required for the deposition of the Steep- erosiS oTtL*'^'' '""""'r''' '■" ^^"^ See Memoir 28, Geological Survey of Canada, 1012. •U.S.G.S. Mon. LII, 1011, p. 147, el teq. Hip. Cil. 105 where emphasized as the Eparchaan Interval*. This, it seems to me, IS ample justification for the view that the Animikie is not m any way connected with the Huronian and that to class it as upper Huronian is to obscure one of the great facts of geolo- gical history, viz., the importance of the break between the Archffian and post-Archaean terranes. It may here be noted that the term Archsean as defined by Dana, and as used by the Survey for many years, includes the Huronian, and the recognition of the fact that many, and probably most, of the rocks classed as Laurentian are post-Huronian, thoroughly justifies that definition as against the proposal to extend the Algonkian downward so as to embrace formations on both sides of the Eparc*'sean Interval. The dual age of the Laurentian granites and gneisses has in recent years become generally recognized and the time seems to have come to mark that recognition as a step in advance in the general solution of the Archtean problem. The International Committee on Geological Nomenclature m its report* of 1905, lent its authority to the current practice of i designating as Laurentian the granite-gneisses of the Archaan notwithstanding diversity of age. But at that time the fact was not fully appreciated that so large a proportion of the rocks of this type were post-Huronian. The diversity of age was ooweyer, clearly recognized in the following paragraph:— "For the granites and gneissoid granites which antedate, or protrude through, the Keewatin, and which are pre-Huronian, the term 'Laurentian' is adopted. In certain cases this term may also be employed, preferably with an explanatory phrase, for associated granites of large extent which cut the Huronian, or whose relations to the Huronian cannot be determined." In 1909, Van Hise and Leith in their paper on the Pre-Cam- bnan geolojn' rf North America call attention' to the anomalous use of it Laurentian. To quote briefly, they say, "A considera f the rocks mapped as ' Lauren tian' is intrusive into the A.e . . (meaning Huronian) but another large part 18 mtrusive v-aiy into the Keewatin. ' Laurentian' as used in the broad sense, becomes a catch-all for Pre-Cambrian gneisses and gramtes of any area where structural relations have not been discrimmated. There is danger that unless the narrower and much more desirable application of the term recommended by the committee be emphasized, the discrimination of the Arch- »an and Algonkian (meaning pre-Huronian and post-Huronian) P"*^^^! so important for structural purposes, will be over- >Bull. Dept. Geo! 'Journal of Oeolos •U.8.G.8. Bull. M 36570—8 -... Vol. 3. No. 3, 1902. r, Vol. XIII, 1«05. pp. 89-104. 106 been included under the term Laurentian " ' °*^ ^^''^ which, together vrith the v^rin^.l "^'l^e.^tary and volcanic, "S T?i2i H **"^?' '' recognized by Van Hise and L??h who sav i-moi, euLioseu in the Jjaurent'an >mpwa "j ti i • compJM. On both of these counts the Huronian is mclnded 'Sheffield, 1910. |:^-S.G.8.Mon.LII, 1911,0.610. 'Addres* Geological Section. B. A. A. S., Sheff -, ISIO. 107 in the Archaean and the Animikie is exchided from it This being the case, it seems best, if the term Algonkian is to be used, K„f «K«' M^i"^ not be made to straddle the Eparcha^an Interval but should be restricted to the group of formations laid dowi^ Cambri ^^*^^^° *'^^ Archaean as above defined and the If now, we assume that the Animikie and Kewemawan mav m this sense properly be designated Algonkian, the geological scale for the Lake Superior region with the present usage of the term Laurentain would appear as follows:— Algonkian /Kewcenawan. lAmmikie. Eparchaean Interval Laurantian granite-gneisses. He. Upper Huronian. Erosion interval. Archffian ^Lower Huronian. Erosion interval. Laurcuiian granite-gneisses, etc. Keewatin. Coutchiching. lonal^/f '^ obviously a use of the term Laurentian that cannot Sfnn nf ?*'°"^'^' t""^ ^^'^ ^''""^^ "« ^ack to the practical question of how we shall dispose of the infelicity arising from the chronologically dual significance of the term. If we reserv" the term Laurentian for the plutonic rock, of one period ar ' Sfffin w ? *^™ ^?'" ^^^ ^™"'^'" '•o^^ks of the other period, thi^ rrS^ ^ ^* ?°'^ ^"''^'•. ^^"^ '° "^"y «=a«e«. where tiie Huronian Li, .1"""*;^°°* P'^^^^' •* ^'" ^"^ q^ite impossible to determine whether the plutonic rock, in question belong to the earlie" or iihlK- P«".°d-. The field geologist in preparing his map for fnH, r*'°°ir'';^ T*^*'' ^^^^ *° «"^«« »« to which of the two per' period, leaving the matter undecided. Judging from the con- di ions which prevaH over the greater part of A^ch^t an Canada this indecision will be a feature of most of the geological maos red to hwrr** altogether, and th.nt the rocks hitherto refer- red to by that name appear on the maps by petroKranhical designations with sv.h approximations to their age as^fSied nrp wvf ■! *^^ ^^'P'l'^^^ions post-Keewatin, etc Th=s proced- Hn;nn?''^ '* u ^^ ^' f*^'"^^ "P°" "« '° those regions where the Huronian rocks are absent, would, however, not best serve the purposes of geology in those important regions that give us the 36570— 8J IM Uounul o( Goology, Vol. XIII. IMS. p. 108. : ! 109 to b?J*fdb JJf "'' " '^' "'"'"^^ °"*''°'°'' °^ *•>•« discussion, ., ,. fKewcenawan. Algonkian i Unconformity. lAnimikie. Eparchsun Interval. AJgoman granites, gneisses, etc. Irruptive contact. Upper Huronian Unconformity. Lower Huronian. Unconformity Laurentian granites, gneisses, etc. Irruptive contact. Keewatin. /-^ . . Coutchiching. (Ontanan. Archaean . KEWEENAWAN DYKES. „f tv,?®7^'''^l '"'^^ ^y^^f °^ diabase traverse the Archasan rocks of the territory mapped. Three of these are represented in the Se'but '.xHh7' '}' T^- '^^'y '•^^« * northwest^outheS rtnke but exhibit a tendency to convergence to the southeast. Their position is of interest as marking in a general way the boundary between a more elevated region in which Rain7lakl n^dff 7k* ^o^^'u^'l'S.''?'' ■■^«^°°' "^a^t'ed with Pleistocene de- posits, through which Rainy river flows to Lake of the Woods idn.trfl '^^^f °^,*u® ^""^ character occurs on the small S „ V?u*^^."*ll'^ °^ *^^ """^^ oP«° P*^ of the lake, but this Aolr-^"}- l^iortheaEt-southwest. These dykes are sufficiently studv the.;,%*^^rP°'^rV^^-^ *°d '^^ ^"«°^Pt ^^ been made to study thena further It has been found, however, that the ro.I: ?887 l^r^ '"^!.°^ ^T^y ^.°^^^ b^y- ''^'''^ 5° the report of s?ve b^U ^hTlf' ^'"''T.L '" in reality a portion of an exten- fi^l -K °f .hornblende gabbro of much greater antiquity. It .wZri^/.r ^.t ^""^ ''y^f represented on the map are identical wh^nWK- • ^^^ ^a°y others occurring throughout the region of f i i^ t '' t P^'^-u ^"^ *^« ^•"'^'ty of the Lake Superio? coa^t *5,3.dy'^«f. have been shown to be a manifestation of the eruptive activity of the Keweenawan, and the diabase dykes of Ramy lake are, therefore, correlated 'with the predicts of ^hat no m\ M PALEOZOIC ROCKS. of pi^*"*^*'"" ^^ °'u*^* township of Croiier, about 6 miles weat ?1 -vf ^™°'^««' tliwe is a small outcrop of creai^colou^ which mantles the region. A shallow pit has been sunk on b^TlrfS 5 ♦ "* ••^V" a southerly direction, which could not »nH f h» ^ rfetermmed owmg to the smallness of the exposures and the uneven character of the stratification. The extent and hickness of the formation could not be ascertained and I could learn of no other similar outcrops in the neighbourhw,d The S ?hat the'^r hif T^'" \^"'^y possible, but quit^improbaUe! drift ThL «ri'*'°.''^'' "P°". " *»"8« «"'^t''^ embedded in the n^ninnl^ f w ""^ }^'i^ erratics in the vicinity and it is my opinion that we have here to deal with an outlier of the PalaozSo MailtobT ''^"°^''°^'y '^^^^ •« the valley of the Red riTeHn .♦ a J^^ ^^^^ resembles that described by Tyrrell and Dowlinir at Stony Mountain and Little Stony Mountain in ManUobf and reterred othe Richmond g.oup' of the upper Ordovician A collection of fossils which I made at the Crozier dhv ro£'ofihl%^'- P-'^yE Raymond, Invertebrati P^Sl lowit m^mtandum"-^ "^^ '^ ""^ '''"^'^ «"PP"«'* *»>« ^o'- hlvXl?dttS^-^^'^''"°°'^> ^««- ^^« ^ollo;LTfo';m'l Rhynchotrema capax, Conrad. Leptema unicosta, Meek and Worthen. rlectambonitea sericeus, Sowerby. Rafinesquina allernata, Emmons. Hebertella, sp. indec. Trochonema umbilicatum, Hall. Holopea, sp. indet. Conularia, sp. indet. Inocaulia canadensis, Whiteaves. Onchometopus susae, Whitfield. tain,'Manitor' '' " "^^"'^ '' ""^'^ "'^ ''''' ^* ^'^^^y ^oun- FrAnli^ t^'^^'^A^. °^ this outlier of Ordovician strata near Fort Frances, at a distance of about 200 miles southeast from the 'Ann. Kept. Geol. Survey, Canada. Vol. XI, Part F. 1898, pp. 88-M. rest ired Irift on is not ires md uld lize )le, the my oic in II n. ty 8B- 31- nt >e IS 111 nearest known exposure at Stony Mountain, sheds an interesting hght upon the former extent of the Ordovician tcrrane in this part of Canada. It ha^ a significance analagous to that of the outher of Niagara at Lalce Timinkaming, and contribute,* to the increasing volume of evidence that the Ordovician and Silurian seas were more widely extended than was once supposed over central Canada, where, by reason of the thinness o^ the forma- tions, the latter have been almost wholly removed by erosion, i he extension of the Ordovician limestone to Rainy lake is also of importance as indicative of the source of the limestone of the grey drift of Minnesota. It may also have an economic im- portance as a local source of supply of lime for constructional or metallurgical purposes. In this connexion the following analyses of the Iin.estone kindly supplied by Mr. G. A.Stethem, of Fort Frances, will be of interest. I. i: III. BiO, 3' 18 1-73 1-43 28-76 18- 14 none, trace. 4S-48 2-93 1-02 9o fil- 44S VtiO, AltO, |2-80 CaO M«0 8, trate, trace. 46-02 p ::::::;::::: LoM on ignition \Hib 04 /CO, 41-78 »9-73 100 04 99 21 I. Analyst. C. A. Graves. Duluth Testing Laboratory II Analvst r A 2r;'6ffi^ciTelS!:«On'.:?r°'^- '"•^-'^" ^.'^'L. ^.^t^-orUl Ill lis INDEX. A '*« Alfomu, Bamft •pplted to Plutonic rorku i ■ im rocka, dsMription o( ' ' 'S Aulyija, acid ■ill, Lower Hire biky.. . S buHledgnein S Coutchkhiastoitu g " (iolden Star limentoM 3 " Keewatin rock< Jz " limeitone ,?? . . ",. . "'.'r» 'yenite (nein ''! ABimikie ndimenU •! B Bad Vermilion Lake granite, area, character, etc.. m Bear Panage area ,- Ji „, . " granite '»• g BioUte granite gnein • JJ C Chemleal oompoution banded biotite granite gnein. ..... ga ' " Coutchiching rocks m ;; ;; Keewatin ro^ki gO _, „ , mica iyenite gnein at Coleman, Prof., itatement respecting Laurentian. . . " loi Cooglomeiste, oiiier occurrences n ".. „ west of Shoal lake S Connor. II. F.. awUyais acid sill, Lower Rice bay » „ " banded biotite Kranite gneiss 93 „ ' Coutohiching rocks '.'.'....'.'." 33 „ Keewatio rocks jq r^ i_ i» ^ - .' . mica syenite gneiss gt Cooke, H. C, Seld assUtant *! Cordierite. '.'.'.'.'.'.'.'.'.'.'.". 2I Coutchiching rooks, chemical composition.. . 13 "ries '.'.'.'.'.'.'.'.'.'.['.y.'.'.'.'.'.'.'.'.'.'x 6, e Eparchaan Interval . .5, lOS Fonila, collection from Crosier tp " oldest known is Staaprock series.. 110 4 113 114 O«ol«i(or. marnu ■Ulemnt Oriiuy jiilaihj " Mud lakK " Uirp bay urunitM nn.l Kraniloid KBoiwes "*'.,'"*'"' K'"""' gneiM . , Or»VM, C. A.. uiUy la oj liinMtoM. O Moa s 51 M M U M 97 M 111 Hopkiiu Bay arm. 83 !li Introductory Iron ore dcpoajt ..... " depoaiti caat ol Shoal'lake. . KMwatin rorka, chemical compooltion aerica " r'.*J["' '■'"»™«t«" «nd diatribution. nortiiern area " other belta .,, „ " Bouthern ares. Kcweenawnn ily kca ' Kunckle laland granite. .......... t U M 10 9. S a» M 4S 40 100 w Sit'- L Latnprophyrin rocki. . . . l^ni^l'^]^;''\,:^^{:T:'^t^' «.don t«v,r«d by the N.tion.1 ColliM. No. 10S9. '>e'ween Lake Nipigon and CUy Uke, Ont. By W. h! dCpS:^ By'lf.r'Elfs'^C n°0? """ '='>•'«»* i»ti" 0, ,h. oa-hal. deporit. Memoir I . Memoir 2. Memoir 3. Memoir 6. Memoir 6. Memoir 7. MEMOIRS-GKOLOGICAL SERIES. Geology of the Nipigon baiia. Ontario. By No. I Geologieal Seriu. Alfred W. G. Wilron. ;-4^c\'X^^\f"^i.J^,^'^i^^^^^^ Hedley Mining a.a,,^Province of OntS^y't^^/, Ma^ /n^d^^^* '"'•Qj^'^^^foA S^ "* '*• «"»° -«»t^- P«>vince of MEMOIRS-TOPOGRAPHICAL SERIES "^""^ " ""• 'io?vKJrk^;i«»^Ty«-ett!sf '•-"- <- V- Memoirs and Reports Publlslied During 1911, REPORTS. from^rse^? t'o'itl'iXlWrX'JiteT'^'Vt „'''''«' ^jest Territories. Report on a p.irt of the North W«.f tCH; • " j " .""?°»- No. 1006. Attowapi,kat rifer;.°'By W. McU^el! ^No'TcSo' ''"""'' "^ '•" *'"''' ""-J ^PPer By MXE"wte"^o.1o«."'" '^'°'""« *'' ""^ «'»<' "f Lake Timiakaming. MEMOIRS-GEOLOGICAL SERIES ^"'D.-B'^feili/'^"- T'"" E<'"'°'"<» «»•' field. Alberta. By ^"■M*,;iS°h'^"'^'^"- ^^""^ '"^ »>««i". Alberta. By G. 3. Memoir 8. Memoir 0. Memoir 10. Memoir 12. Hamoir IS. Memoir IS. Memoir 14. in Ifo. IS.Oeoloaical Sena. The clay and shale depoaita o( Nova Scotia J^ph kS °' ^'^ B™""'"=k- By Heinrl^ Rie. aL^t,^ by MEMOIRS-BIOLOGICAL SERIES. ^''" M«p™i"„'T,"n ^H!"- ^^7 "J^"*' °' '•>•"» collected by Mr. J„l.n ByTu"liS^^£'lit^rd"iikufcrh'. "'""• ^"""^ ^°"'""'"'- Memoir 13 Memoir 21 . n. eAN- LAURENTIAN («r«uilv ami ^^iiiif ^neiaa Sdctlon aloo^ Une AB Scale I aiJe to I Inch Irpnitt Hon. L Coocrri i«' r. stcr] OloioeiCAl m ijlr^iy,-!, if. . , ■ -.iijfclT^^^^^H la i Section along I P tt^ Pis [m WB^ 1 %M 1 t • Miax M 12 f kC' WAek P* Hfprntiiiiiit itf Bints L COOCRHE MlN, A P LowOtPUTrMlNlST CEOlO(>i( VI SURVEY R.Wts - « [JiHtrTOR ) Seetian alanft line Trf Br^ line C-D ""■J* J mile K> 1 ineh ■\ I>T GEOGRAPHY « ■■■■.- ^.-v- r rA ■ Hfraii* ■lint •(■It* I^KMaito aaf lisir ARCH>CAN< LAUMNTIAN OOUTCMKMINO •s- r+-i Horiaaual itma ^ f ' a ,,_,.ji.*u-'^"^-^ - ■ uuaoAiir ask ^BbS^Sr^ A mnmmfmfyMmmtmlf ^ AjC£ .»2»--» .^^ •o » p o ■r-" m ^k '■^■i^V^"^^ /?|^^ iT^ "