The Palmer Gneiss * by Carl A

BULLETIN OF THE GEOLOGICAL SOCIETY OF AMERICA VOL. 46, PP. 1137-1162, PL. 93. 8 FIGS. JULY 31, 1938

THE PALMER GNEISS * BY CARL A. LAMEY (Accepted by the Committee on Publications, 1985) CONTENTS Page Introduction...... 1137 The Palmer area...... 1140 The Palmer gneiss problem...... 1142 The Middle Huronian series...... 1143 General statement...... 1143 Ajibik quartzite...... 1144 The Lower Huronian series...... 1146 General statement...... 1146 Kona dolomite...... 1147 Kona-Mesnard contact...... 1150 Mesnard quartzite...... 1151 Remaining Palmer gneiss belt...... 1155 Region south of the Palmer gneiss belt...... 1157 Structure...... 1158 Conclusions...... 1160

INTRODUCTION The Palmer gneiss was originally described as a part of the Base ment Complex of the Marquette district in northern Michigan.1 This gneiss was thought to consist of Archean rocks intruded by Laurentian granite. More detailed work later disclosed that some of the rocks designated Palmer gneiss are Middle Huronian sediments.2 Also, since these Huronian sediments were found to be extensively intruded by granite, it became evident that this granite must be as late as Middle Huronian and that its intrusion probably gave rise to some of the metamorphism which caused the Huronian sediments to be * Manuscript received by the Secretary of the Society, December 21, 1934. 1C. R. Van His«, W. S. Bayley, and H. L. Smyth: The Marquette iron-bearing district of Michigan, U. S. Geol. Surv., Mon. 28 (1897) p. 149-160, 190-192, 194, 211-220. 2 C. R. Van Hise and C. K. Leith: The geology of the Lake Superior region, U. S. Geol. Surv., Mon. 52 (1911) p. 255-256. (1137)

Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/46/7/1137/3415306/BUL46_7-1137.pdf by guest on 26 September 2021 1138 C. A. LAMEY— THE PALMER GNEISS described as Palmer gneiss.3 During the course of a field study of the relations of this younger granite (the Republic granite) to the Huronian formations, the writer observed outcrops of dolomite, quartzite, and graywacke in the rocks still designated Palmer gneiss. The presence of these sediments, especially the dolomite, and their stratigraphic position below the conglomeratic base of the Middle Huronian series, suggested that at least a part of the remaining Palmer gneiss might well be Lower Huronian formations intruded and metamor phosed by the Republic granite.4 Consequently, a study of the com position and origin of the Palmer gneiss was undertaken, the results of which are presented in this paper. The field work was conducted during the summers of 1930, 1931, and 1932, in connection with the problem of the Republic granite, and completed in the summer of 1934 under a Penrose research grant from the Geological Society of America. It consisted of an examina tion of the rocks previously designated Palmer gneiss, and the making of a geological map, showing the different formations comprising this gneiss. Mapping was done by means of a dial compass, because of magnetic attraction, and by counting paces, care being taken to check on section comers and other known locations as frequently as possible. An airplane map of the region was a valuable aid. As a rule, the Ajibik quartzite, the lowest formation of the Middle Huronian series, was the horizon from which traverses were started, as the base of this formation generally furnished one boundary of the Palmer gneiss. From this established horizon the gneiss belt was subdivided as far as possible—until granite intrusions rendered recognition of its com ponent formations uncertain. Many rock specimens were collected, both from the Palmer gneiss area and from the Huronian areas near Marquette and Negaunee. Thin sections were obtained of those not readily identified by means of a hand lens, and the slides were studied from time to time in the field with a petrographic microscope, put at the writer’s disposal through the courtesy of the Michigan College of Mining and Technology. In this manner it was possible to investi gate more thoroughly any doubtful areas and to obtain additional specimens for more detailed petrographic study wherever necessary. 3 C. A. Lamey: Granite intrusions in the Huronian formations of northern Michigan, Jour. Geol., vol. 39 (1931) p. 291; The intrusive relations of the Republic granite, Jour. Geol., vol. 41 (1933) p. 493-494; Some metamorphic effects of the Republic granite, Jour. Geol., vol. 42 (1934) p. 261-262. 4 C. A. Lamey: What is the Palmer gneiss? Geol. Soc. Am., Pr., 1933 (1934) p. 92. The presence of outcrops of this character, and their probable significance, had been known by A. E. Seaman for some years. Oral communication. See, also, A. C. Lane: Sixth Ann. Report of the State Geologist of Michigan, 1904 (1905) p. 146.

Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/46/7/1137/3415306/BUL46_7-1137.pdf by guest on 26 September 2021 INTRODUCTION 1139 For laboratory study, 194 thin sections were selected from the many specimens collected. Preliminary pétrographie work was conducted during 1933 and 1934 from specimens previously collected, and final study of all thin sections was completed in the fall of 1934. The final 89* 88* 87*

Figtjbe 1.—Index map showing location of the area described and its position with respect to the Marquette synclinorium pétrographie study was made near field headquarters, in order that any doubtful areas could be re-examined before the close of the field season. The writer is greatly indebted to the Geological Society of America for a Penrose bequest research grant which made possible the comple tion of the Palmer gneiss investigation. Also, acknowledgment is due to the Geology Department of Northwestern University for many courtesies extended during the course of this study; to the Michigan College of Mining and Technology for the use of equipment and laboratories; and to Professor A. E. Seaman for much valuable advice and for the use of field equipment.

Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/46/7/1137/3415306/BUL46_7-1137.pdf by guest on 26 September 2021 1140 C. A. LAMEY— THE PALMER GNEISS THE PALMER AREA Geologically, the Palmer area is a part of the Marquette district, which in turn is part of the Lake Superior pre-Cambrian region (Fig. 1). The most recent rock succession for the Marquette district is given by Leith.5 Not all the formations in this succession are repre sented in the Palmer area, due in part to structural conditions. Post Keweenawan Upper Cambrian sandstone Algonkian ------Unconformity------Killamey Granite Acidic intrusives Basic intrusives Keweenawan Huronian Upper Upper Michigamme slates Bijiki iron formation Lower Michigamme slates Clarksburg volcanics Greenwood iron formation Goodrich quartzite ------Unconformity----- Middle Negaunee iron formation Siamo slates Ajibik quartzite ------Unconformity- - - Lower Wewe slate Kona dolomite Mesnard quartzite Algoman Granite Knife Lake (may be Lower Huronian) Archban ------Unconformity------Laurentian Granite Granite, syenite, peridotite Palmer gneiss Keewatin Kitchi schist and Mona schist The rocks in the immediate vicinity of Palmer form a part of the southern limb of the Marquette synclinorium, but a fault of consider able magnitude, north of Palmer, causes the area to appear as a pro jection along the southern side of the synclinorium. This fault, com bined with other features of the local structure, gives the Palmer area the aspect of an independent syncline (Fig. 2B). A fairly consistent relation of topography to structure exists within the area, and gives rise to its basin-like aspect. Northward, a fault 8 C. K. Leith: The pre-Cambrian, Geol. Soc. Am., Pr., 1933 (1934) opposite p. 176, Correlation Chart—Lake Superior Region.

Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/46/7/1137/3415306/BUL46_7-1137.pdf by guest on 26 September 2021 THE PALMER AREA 1141 scarp forms the wall of the basin; eastward, quartzite ridges tend to establish another boundary; granite masses partially block the western end; and ridges of northward-dipping iron formation and quartzite, together with other ridges of dolomite, granite, and gneiss, form the

F ig ure 2.— Geologic map of the Palmer area A, as in U. S. G. S. Monograph 28; B, as in Monograph 52. (Symbol for Mesnard quartzite in B was used for Wewe slate in A.) southern wall. Characteristically there are two sets of southern ridges separated by a narrow valley, the more northern ridge being composed of Ajibik quartzite and the more southern one consisting of Mesnard quartzite, Kona dolomite, granite, and gneiss. In general, this valley between the Ajibik quartzite ridges and the more southerly ridges marks, approximately, the contact between the Ajibik quartzite and the complex heretofore known as Palmer gneiss (Fig. 2B).

Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/46/7/1137/3415306/BUL46_7-1137.pdf by guest on 26 September 2021 1142 C. A. LAMEY— THE PALMER GNEISS THE PALMER GNEISS PROBLEM As originally defined, the Palmer gneiss comprised non-fragmental Archean rocks, presumably mashed parts of the Basement Complex, which, it was clearly shown, had been intruded in many places by a granite, thought to be of Laurentian age.® These rocks were sepa rated from Huronian formations because they were found below well- defined conglomerates or, where no such conglomerates existed, because they were thought to be non-fragmental. Later it was discovered that the Palmer gneiss contains much fragmental material.7 These fragmental rocks represent Ajibik quartzite and Siamo slate, and consequently they were assigned to the Middle Huronian series. The gneiss belt as originally mapped extended east and west for six miles in the vicinity of Palmer (Fig. 2A), but after the discovery that Huronian sediments were included in this area the distribution of the Palmer gneiss was restricted to the eastern part of the Palmer area on a revised map of the region (Fig. 2B). The rocks taken from the Palmer gneiss and assigned to the Middle Huronian contain many granite intrusions (Fig. 3), showing that locally there must be a granite as young as late Middle Huronian. Recent investigation of the relation of the granite of the Southern Complex to the Huronian formations indicates that much if not all of it is of post-Upper Huronian age.8 Further, the writer found that this granite intrudes dolomite, quartzite, graywacke, and slate in that part of the Palmer gneiss which remains after assigning the western part of the gneiss area to the Middle Huronian. Much of this material lies below the base of the Ajibik quartzite, the lowest formation of the Middle Huronian series, and therefore occupies the stratigraphic position of the Lower Huronian series. Heretofore on maps of the Palmer area no Lower Huronian formations have been shown as present south of the Ajibik quartzite (Fig. 2), but the presence of dolomite, which is typical of the Lower Huronian in the Marquette district, together with quartzite and graywacke, indicates the presence of this lower series. Moreover, a study of conditions along the northern side of the Marquette synclinorium, as well as to the north east of Palmer, shows that the area south of Palmer is the normal place in which to find Lower Huronian formations if they are present south of the Ajibik quartzite. If Lower Huronian formations are eC. R. Van Hise, W. S. Bayley, and H. L. Smyth: op. cit,, p. 211-213. 7C. R. Van Hise and C. K. Leith: op. cit., p. 255-256. 8 C. A. Lamey: The intrusive relations of the Republic granite, Jour. Geol., vol. 41 (1933) p. 487-500.

Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/46/7/1137/3415306/BUL46_7-1137.pdf by guest on 26 September 2021 THE PALMER GNEISS PROBLEM 1143 shown to be present there, it follows that the Palmer gneiss may cease to exist as a definite formation. A discussion of all rock formations found in the present Palmer gneiss area, and of all evidence which may shed light upon the com-

F ig u re 3.—Map showing intrusion of granite in Middle Huronian formations The area mapped is in seotion 26, south of the Tilden mine (see Fig. 2), and is part of the original Palmer gneiss belt. position and origin of the gneiss, is presented in the following pages. From this evidence certain conclusions are drawn, which it is hoped may clarify some of the pre-Cambrian geology of the Lake Superior region. THE MIDDLE HURONIAN SERIES GENERAL STATEMENT All the formations of the Middle Huronian series—Negaunee iron formation, Siamo slate, and Ajibik quartzite—are present in the imme diate vicinity of Palmer, but only the oldest of these formations, the

Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/46/7/1137/3415306/BUL46_7-1137.pdf by guest on 26 September 2021 1144 C. A. LAMEY----THE PALMER GNEISS Ajibik quartzite, occurs within the boundary of the Palmer gneiss area. AJIBIK QUARTZITE The base of the Ajibik quartzite has heretofore been regarded as the boundary between Algonkian and Archean rocks in the Palmer area, and was thought to separate the Middle Huronian formations

F ig ure 4.—Distribution of Ajibik quartzite, granite, gneiss, and basic intrusives A. Map showing distribution of Ajibik quartzite within the Palmer gneiss belt. The major part of the Ajibik formation occurs immediately north of this belt. B. Map showing distribution of granite, gneiss, and basic intrusives within Palmer gneiss belt. from the Palmer gneiss (Fig. 2). Most of the Ajibik quartzite does occur north of the boundary of the Palmer gneiss, but some of the quartzite lies within the gneiss area (Fig. 4A). Throughout much of the area the lower part of the Ajibik formation is conglomeratic. This conglomeratic horizon was located in almost every instance where the quartzite occurs within the Palmer gneiss belt and was used to separate the Ajibik formation from the underlying rocks. The best known type of the conglomerate at the base of the Ajibik quartzite occurs in section 32, west of the Platt mine (Fig. 2), where, together with the overlying quartzite, it forms high and some what bare ridges. It contains pebbles and boulders ranging in size

Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/46/7/1137/3415306/BUL46_7-1137.pdf by guest on 26 September 2021 THE MIDDLE HUBONIAN SERIES 1145 from less than an inch to several feet, although the larger boulders are rare and the average size is about 6 inches. The pebbles and boulders consist chiefly of quartzite, jasper, chert, quartz, and some basic material resembling a greenstone, and these are cemented with quartz, sericite, specular hematite, and magnetite. One phase of this conglomerate contains poikiloblastic crystals of chloritoid as much as half an inch across, the chloritoid appearing in the matrix and boulders alike.9 Finer phases which grade into quartzite may contain rounded grains of quartz, chert, and jasper, well-crystallized octa hedrons of magnetite, poikiloblastic chloritoid, tourmaline, and a matrix of sericite and very fine-grained quartz. Again, the rock may consist chiefly of much fractured and strained quartz in a sericitic matrix, the quartz showing evidence of replacement by sericite; or it may consist chiefly of quartz fragments cemented with specular hematite and magnetite. Within the Palmer gneiss belt this same quartzose type of conglom erate occurs in sections 31, 32, 34, and 35 (Fig. 4A). In sections 32 and 34 it is much sheared and locally intruded by granite, and in sections 34 and 35 it rests directly upon the Lower Huronian Mesnard quartzite. A much less known type of the Ajibik conglomerate forms low out crops in a marshy area in the northwestern part of section 33, south of the Richmond pit (Fig. 2). It occurs just outside the Palmer gneiss area and also within the gneiss boundary (Fig. 4A). This conglom erate contains small, rounded pebbles of dolomite, chert, cherty dolo mite, and quartz; more angular fragments of quartzite containing well- rounded quartz grains; rounded to subangular grains of quartz and chert; and angular quartz fragments; all in a slaty, chloritic and seri citic matrix. This type of conglomerate forms low outcrops rather than high cliffs and ridges, and it occurs above and adjacent to Lower Huronian Kona dolomite. The conglomerate at the base of the Ajibik formation apparently is absent in part of the area, its place being taken by a quartzite which is, as a rule, highly ferruginous, or by a rock similar to a lean, quartzitic phase of the Negaunee iron formation. In such cases it is difficult to separate the Ajibik quartzite from the overlying Negau nee iron formation, as the latter is not the true, non-fragmental formation which occurs in the type area, but contains many quartzitic bands. Indeed, it may well be that part of this ferruginous, frag 9See C. R. Van Hise, W. S. Bayley, and H. L. Smyth: op. cit., p. 215*216, for an early description of this conglomerate.

Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/46/7/1137/3415306/BUL46_7-1137.pdf by guest on 26 September 2021 1146 C. A. LAMEY— THE PALMER GNEISS mental material actually represents the Siamo formation, which char acteristically underlies and grades into the Negaunee formation.10 If such is the case, in some places the Ajibik formation is absent, possibly as a result of faulting, and the equivalent of the ferruginous Siamo slate or a lean phase of the Negaunee iron formation occurs just above the gneiss belt. Such conditions apparently exist in the north-central part of section 33. Much of the Ajibik quartzite included within the Palmer gneiss boundaries has been fractured, badly sheared, intruded by granite, and extensively metamorphosed, but there are many outcrops in which the rock shows well-rounded grains and resembles the Ajibik quartzite on the northern limb of the Marquette synclinorium near Negaunee (PI. 93). Sheared, ferruginous phases of the quartzite near granite intrusions, such as may be found in the northern part of section 34 (Fig. 4A), contain well-formed magnetite crystals embedded in a matrix of sericite and quartz; more quartzose phases contain fractured and strained quartz in a sericitic matrix. Such quartzose phases of the quartzite are similar to like phases of the Ajibik formation in section 26, south of the Tilden pits, within the area formerly designated Palmer gneiss. In some parts of the gneiss belt where granite intrusion was extensive and metamorphism severe, as in section 31 (Fig. 4A), the quartzite has been much sericitized and contains both chloritoid and andalusite; in other instances it has become gneissoid and contains microcline and biotite. Both of these latter phases occur in the original Palmer area south of the Tilden pits, and the gnessoid phase occurs also some miles farther west, near Beacon, where granite intrudes the Ajibik quartzite.11 THE LOWER HURONIAN SERIES GENERAL STATEMENT The complete Lower Huronian series for the Marquette district, with thicknesses of formations, is given as follows:12 Feet Wewe slate ...... 0-1,050 Kona dolomite ...... 0- 700 Mesnard quartzite ...... O- 700 This series lies unconformably below the Middle Huronian series. On the northern limb of the Marquette synclinorium the erosion rela 30 This opinion has been expressed several times by A. E. Seaman. Oral communication. 11C. A. Lamey: Some metamorphic effects of the Republic granite, Jour. Geol., vol. 42 (1934) p. 258-261. 18 M. Grace Wilmarth: Tentative correlation of the named geologic units of Michigan, U. S. Geol. Surv., Michigan chart 3 (1929).

Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/46/7/1137/3415306/BUL46_7-1137.pdf by guest on 26 September 2021 THE LOWER HURONIAN SERIES 1147 tions are such that the Middle Huronian Ajibik quartzite in the vicinity of Teal Lake, about 6 miles north of Palmer, rests on Archean schists and then, to the eastward, first on the Mesnard quartzite, next on the Kona dolomite, and finally on the Wewe slate.13 It will thus be seen that there is marked unconformity between the Middle and Lower Huronian series, and the Ajibik quartzite might rest on any one of the Lower Huronian formations. Two of the Lower Huronian formations, the Mesnard quartzite and the Kona dolomite, have been identified within the Palmer gneiss area. The Wewe slate apparently is absent. KONA DOLOMITE Lying beneath the slaty and dolomitic Ajibik conglomerate in the northwestern part of section 33, and extending eastward nearly to the center-line of section 34, is a belt of dolomite that the writer believes to represent the lower part of the Kona formation. These outcrops are wholly within the area previously designated Palmer gneiss (Fig. 5B). Several phases of this dolomitic formation are represented within the gneiss area—cherty dolomite, slate with dolomite lenses, slate with chert “eyes” and lenses, dolomitic slate, and sericitic slate. These phases are similar, lithologically, to the lower part of the Kona formation—approximately the lower 200 feet—on the northern limb of the Marquette synclinorium. Because of this lithological simi larity, and the fact that the formation occurs immediately below con glomeratic Ajibik quartzite and, in part at least, above an older quartzite, there seems little reason to doubt that this material repre sents the uneroded part of the Kona dolomite on the southern side of the Marquette synclinorium. Hereafter this formation will be referred to as the Kona dolomite.- The Kona dolomite is best developed in the eastern part of sec tion 33, south of the Moore mining location (Fig. 2). There, south of Ajibik quartzite, which has some conglomeratic phases, it forms a ridge 30 or 40 feet high. This ridge generally has a steep northern slope. As a rule, cherty dolomite forms the northern face of the ridge, but this cherty phase is best represented near the western end of the ridge, where large blocks of rock containing dolomite bands as much as 4 feet wide form talus at the foot of a steep cliff. Also, the dolomite is well exposed in the face of this cliff. Slate with dolomite lenses varying in width from a few inches to a foot or ** C. R. Van Hise and C. K. Leith: The geology of the Lake Superior region, U. S. Geol. Surv., Mon. 62 (1911) pi. 19.

Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/46/7/1137/3415306/BUL46_7-1137.pdf by guest on 26 September 2021 1148 C. A. LAMEY----THE PALMER GNEISS more occurs in general south of the cherty dolomite, and still farther south occur other slaty phases of the Kona formation. To the eastward, cherty dolomite and slate with relatively large dolomite lenses are well exposed for about half a mile. The formation

F ig u re 5.—Distribution of Mesnard quartzite and Kona dolomite A. Map showing distribution of Mesnard quartzite within Palmer gneiss area. Inset shows areas in sections 22 and 23. B. Same showing distribution of Kona dolomite. is then partly covered for slightly more than a quarter of a mile, but is traceable, and again is fairly well exposed near the eastern end of the dolomite belt, in section 34 (Fig. 5B). In the western part of section 33, the Kona formation is represented by dolomitic slate containing narrow dolomite lenses. This dolomitic slate disappears in the western part of section 32. In the eastern part of this section there are two small outcrops of chert thought to represent the Kona formation. Between these chert outcrops and the slate in section 32 occurs material which may represent the lower part of the Kona formation but which appears more likely to repre sent the upper part of the Mesnard quartzite. Throughout the gneiss belt the cherty dolomite and the slate with relatively large dolomite lenses, although much sheared in many

Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/46/7/1137/3415306/BUL46_7-1137.pdf by guest on 26 September 2021 THE L0 WEK HUKONIAN SERIES 1149 instances, are readily recognized as phases of the Kona formation and were followed in the field without great difficulty. The dolomite bands and lenses weather rusty brown, apparently due to the presence of an iron-bearing carbonate, possibly ankerite, that produces a limo- nitic coating as much as a quarter of an inch thick. Due to differ ential weathering these bands become depressed, whereas the chert

F ig u re 6.—Map of a part of the Kona dolomite within the Palmer gneiss belt Showing granite intrusions in the dolomite. bands and lenses stand out in relief. If broken, the dolomite is characteristically white. The slaty phases of the Kona formation were traced with much more difficulty than were the dolomitic phases. The dolomitic slate is a greenish, chloritic and sericitic rock, which may contain dolomite bands varying in width from a fraction of an inch to about an inch, or which may be devoid of such bands but contain patches of dolo mite. As a rule, this slate contains, also, more or less chert and fine quartz throughout, and compares favorably in texture and com position with the Kona slate near Marquette. The greenish color of the slate causes it to resemble an altered, basic igneous rock, and makes field mapping a matter of considerable difficulty, as some such igneous rocks are present within the dolomite belt. However, in the igneous rocks there is a lack of quartz, and the feldspar crystals, although much altered, are usually recognizable; also, the texture, which is characteristically that of an igneous rock, is partially pre served. In those cherty phases containing chert “eyes” and lenses, differential weathering aids recognition. The sericitic slate has a

Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/46/7/1137/3415306/BUL46_7-1137.pdf by guest on 26 September 2021 1150 C. A. LAMEY— THE PALMER GNEISS yellowish or greenish cast, and resembles certain slaty phases of the Kona formation on the northern limb of the Marquette synclinorium. Irregular masses and dikes of Republic granite, and quartz veins from the granite, have intruded the Kona formation, causing some metamorphism (Fig. 6). In some instances, small masses of dolo mite have been included in the quartz veins. In such cases the dolomite has become coarsely crystalline, and rhombs nearly 2 inches across are present in the veins; other quartz veins contain small dolomite crystals. Near dikes and granite masses the dolomite is coarsely crystalline, and muscovite, phlogopite, and some tourmaline are present. In those instances where the dolomite was included in the granite, the mica plates attained a size of several inches. Throughout the Kona dolomite belt the amphiboles and pyroxenes so characteristic of the metamorphosed Randville dolomite farther south14 are lacking. This might be expected, as the Kona formation occurs along the edge of the granite mass, whereas its southern equivalent, the Randville formation, is practically surrounded by the granite. Apparently a certain degree of silicification of the Kona dolomite has taken place near the granite, and a rock resembling a cherty, dolomitic quartzite has been formed. This silicification may be more apparent than real, as in such instances intrusion of granite may have been into a very cherty phase of the Kona formation. Southward the Kona dolomite gradually merges with a belt of granite and gneiss, except in those cases where a quartzite lies below the dolomite. In some instances the rocks immediately below defi nitely identified dolomite may represent either the lowest, slaty, and fragmental phases of the Kona formation or the highest, somewhat dolomitic phases of the Mesnard quartzite. KONA-MESNARD CONTACT The contact between the Kona dolomite and the Mesnard quartzite is not always definite, as these formations are conformable and the boundary is a gradational one. Thus the lower parts of the Kona forma tion are slaty and cherty as well as dolomitic, and may contain bands ' of well-rounded quartz grains. As a rule, these lower phases also contain iron oxide. On the other hand, the upper part of the Mesnard formation may be very similar to the lower part of the Kona dolomite. It may not always be feasible, therefore, in an area where there has been extensive metamorphism, to separate the Mesnard formation from the Kona dolomite above definitely recognizable quartzite. 14 C. A. Lamey: Some metamorphic effects of the Republic granite, Jour. Geol., vol. 42 (1934) p. 257-258.

Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/46/7/1137/3415306/BUL46_7-1137.pdf by guest on 26 September 2021 THE LOWER HURONIAN SERIES 1151 In sections 31 and 32 there is a belt of rocks with a greenish cast, which might easily be confused with greenstones, but careful exam ination with a hand lens disclosed the presence of much quartz, appar ently as grains, and well-formed octahedrons of magnetite. The frag mental nature of these rocks was verified by microscopic study. Some phases contain subangular to rounded quartz and feldspar grains, together with chlorite, carbonate, some sericite, biotite, and epidote. Again, there are phases which are distinctly banded but in which the clastic nature is well preserved. Some such phases contain quartz grains and magnetite grains and octahedrons, in a matrix of car bonate, chlorite, and sericite. Nearer granite intrusions the rock may be composed chiefly of epidote and quartz; of epidote, quartz, mag netite crystals, and some amphibole; or of quartz, amphibole, magne tite, and some epidote. The amphibole apparently is not an ordinary variety but is a peculiar one associated with iron-rich formations.15 All the rocks in this belt contain large amounts of quartz and show well their fragmental character except in the vicinity of granite intrusions. In these latter instances, fragmental rocks may be traced into these metamorphosed types. The clastic nature of the rocks in this belt indicates their sedimentary origin; their position below conglomeratic Ajibik quartzite, and close association with Kona dolo mite and definite quartzite, make is probable that they belong to either the Kona or the Mesnard formation. Because of the large amount of quartz contained in them, it seems more reasonable to consider them a part of the Mesnard quartzite (Fig. 5A), and they have been so designated on the revised map of the area (Fig. 7). There appears to be no likelihood whatever of these rocks representing the Wewe slate, as in at least one instance they are underlain by a definite, vitreous quartzite. Moreover, only the lower 200 feet of the Kona formation occurs in this vicinity, indicating that the Wewe slate is absent. MESNARD QUARTZITE Lying beneath the belt of intermediate rocks in sections 31 and 32 there are outcrops of more or less vitreous quartzite (Fig. 5A). The quartzite has been intruded by granite in many instances, but in those cases where there is little or no granite the fragmental nature is clearly shown. Thus the rock may be composed of subangular to rounded quartz and feldspar grains in a sericitic matrix, as in section 31; it may contain rounded quartz grains elongated by shearing, in a chlorite and sericite matrix; or it may consist of a 15 Op. cit., p. 254-255.

Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/46/7/1137/3415306/BUL46_7-1137.pdf by guest on 26 September 2021 1152 C. A. LAMEY— THE PALMER GNEISS quartz mosaic throughout which are streaks of sericite. Under the microscope some of these rocks resemble similar phases of the Mes nard formation occurring near Marquette. Indeed, in some instances it would be impossible to separate one from the other. This fact, together with their stratigraphic position, appears to warrant classi fication of these rocks as Mesnard quartzite. Because of the extensive intrusion of the Republic granite, but a few exposures of definitely recognizable clastic rocks are found beneath the Kona dolomite in sections 33 and 34 (Fig. 5). In section 33, underlying the Kona formation, there are a few outcrops of sheared, highly quartzitic rocks apparently of fragmental origin. Farther east, in the western part of section 34, the Kona dolomite is underlain by slaty rocks. The slate, which is greenish, contains angular to sub angular quartz grains sparsely distributed throughout a chloritic and sericitic matrix. It resembles some of the slaty phases near the top of the Mesnard formation near Marquette, and is thought to repre sent the Mesnard quartzite. The slaty phase of the Mesnard formation in section 34 is nearly continuous with a somewhat similar phase just west of the center of section 34, which, however, lies immediately below Ajibik quartzite. Here, again, the Mesnard formation in its least altered parts is repre sented by a greenish, chloritic rock containing rounded to angular quartz fragments, rounded grains of sericite probably representing original feldspar grains, and a matrix of chlorite and carbonate. Both the Mesnard formation and the overlying Ajibik quartzite have been intruded by granite—small stringers, dikes, and knob-like masses— and an amphibole gneiss has been developed near the larger masses of granite. The slaty rocks in the western part of section 34, which give rise to no great topographic expression except where intruded by knob like granite masses, give place eastward to much more quartzitic rocks which form a bold east-west ridge with precipitous southern slope. Farther eastward this ridge trends northeast and gradually decreases in height until it disappears near a marsh. Eastward across this marsh, in section 35, rise bold quartzite ridges with steep western and southern slopes. Both in section 34 and in section 35 the quartzite which forms the ridges lies immediately below the Ajibik formation. In fact, in places the Ajibik quartzite forms parts of the northern and western fronts of the ridges. In some places at the base of the Ajibik formation there is a quartzose conglomerate containing jasper, quartzite and

Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/46/7/1137/3415306/BUL46_7-1137.pdf by guest on 26 September 2021 THE LOWER HUBONIAN SERIES 1153 quartz pebbles as much as 6 inches across, embedded in a matrix of quartz and hematite, or in a matrix consisting chiefly of quartz. At other places the Ajibik formation is represented by a coarse quartzite, which may be gray, white, or pink. The basal part of the formation, however, is always quartzose and not dolomitic as it is farther west, where it overlies the Kona dolomite. The quartzitic rocks beneath the Ajibik formation are thought to represent the Mesnard quartzite (Fig. 5A) and will be so referred to hereafter. The quartzose phases of the Mesnard formation in sections 34 and 35 are singularly free of granite intrusions. Such intrusions were observed in but three places. In most cases in this vicinity these quartzitic rocks are separated from granite by a swamp of considerable proportions. Nevertheless, the quartzite is much altered. In many cases it is extensively cut by quartz veins, some of which contain specular hema tite, and almost all exposures show marked evidence of shearing and shattering. Indeed, in some instances the mashing has proceeded to such a degree that large outcrops are almost wholly brecciated, and in those cases where the formation had been extensively cut by quartz veins the fractured veins produce the effect, at first sight, of a sheared quartz conglomerate. Despite the shearing and brecciation to which the Mesnard forma tion has been subjected in this vicinity, many different phases are still recognizable as quartzite or slate and resemble phases of the Mesnard formation on the northern limb of the synclinorium. Near the north section line of section 35 there is exposed, in a nearly vertical cliff, a much sheared, red- and white-banded quartzitic rock. Under the microscope this was seen to be composed of small quartz fragments in a sericite matrix, the chief difference between the red and the white bands being the presence of an iron-oxide stain in the sericite matrix of the red bands. Other Mesnard exposures, which have the general appearance of a red, altered igneous rock, consist in reality of a rock composed of angular to subangular quartz grains in a matrix of finer quartz, throughout which are streaks of hematite, which impart a red color to the rock, and large plates of chloritoid. This rock is similar to the northern occurrences of Mesnard quartzite except for the presence of chloritoid. This latter mineral, in large poikiloblastic crystals, is present in other outcrops as well, in which the frag mental nature of the rock may be clearly seen, or in which the quartz presents a more or less interlocking aspect. In some instances the quartzite contains both quartz and feldspar fragments in a chloritic

Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/46/7/1137/3415306/BUL46_7-1137.pdf by guest on 26 September 2021 1154 C. A. LAMEY— THE PALMEB GNEISS and sericitic matrix and, near granite intrusions, well-crystallized magnetite octahedrons. In addition to the various exposures of Mesnard quartzite shown to exist in the original Palmer gneiss belt, there are two isolated areas in sections 22 and 23, previously mapped as Palmer gneiss, in which the rocks are chiefly quartzite and slate (Fig. 5A). The rocks in these two areas are surrounded by Mesnard formation (Fig. 2). In some instances these rocks have been intruded by granite, and near such intrusions a gneiss has been produced, but there are many exposures which are practically identical with the surrounding Mes nard formation and with more northern outcrops. In fact, it is possible to identify a number of phases of the Mesnard formation in these two areas—vitreous quartzite, sericitic quartzite, ferruginous quartzite, graywacke, and slate, the latter with bedding well pre served. It seems clear, therefore, that these rocks should be mapped as Mesnard quartzite. As a rule, the various phases of the Mesnard formation in these isolated areas are recognizable as such both in the field and under the microscope, but the fragmental character is partly obscured in some instances because of the deposition of siliceous cement. The sericitic and ferruginous varieties, in which the grains consist of quartz and the matrix consists of sericite and hematite, show very well their fragmental character (PI. 93), as do also the more slaty varieties. The vitreous varieties, however, do not always so clearly show their clastic nature. This is usually revealed by a careful examination under a hand lens, and also by a microscopic inspection. Without the use of the analyzer the outlines of rounded quartz grains may be seen, especially if they are fringed with a small amount of iron oxide, but under crossed nicols these outlines, although observable, are not very apparent, due to the deposition of siliceous cement with the same optical orientation as the original quartz grains, and in some instances there is little indication of original grains. The almost total obliteration of original granular texture is especially noticeable near larger granite intrusions and is due, probably, to the heat to which the rock has been subjected. Nevertheless, on the whole there is little difficulty in establishing the fragmental character of the rocks in these two isolated Palmer gneiss areas and correlating them with the Mesnard formation, by which they are surrounded. It appears evident, from the preceding discussion, that within the Palmer gneiss boundaries there is much fragmental material of quartz itic and slaty nature. These rocks occur (1) just below the Kona

Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/46/7/1137/3415306/BUL46_7-1137.pdf by guest on 26 September 2021 THE LOWER HURONIAN SERIES 1155 dolomite, which itself rests beneath Ajibik quartzite; (2) below the Ajibik quartzite, the base of which, in many instances, is conglom eratic; or (3) surrounded by Mesnard quartzite. From what has been stated previously regarding the relations existing between the Middle and Lower Huronian series, it is apparent that the Mesnard quartzite might be expected beneath the Kona dolomite—the normal, conformable sequence—or unconformably below the Ajibik quartzite. All evidence, therefore, tends to show the existence of a considerable amount of Mesnard formation within the boundaries of the Palmer gneiss area. REMAINING PALMER GNEISS BELT It has been shown that the original Palmer gneiss belt contains both Middle and Lower Huronian rocks—Aj ibik quartzite, Kona dolo mite, and Mesnard quartzite—but after mapping the distribution of these rocks there remain areas in which no sediments have been traced with certainty. In some of these areas there are no outcrops, and in most cases the probable distribution of rocks has been indicated (Figs. 4 and 5). In other areas all observed outcrops are granite, gneiss, somewhat altered diorite older than the granite, and little altered olivine diabase younger than the granite (Fig. 4B). In these areas granite and gneiss are by far the most abundant. Much of the gneiss is characteristically coarse grained, and neither field nor microscopic examination of it yields any clear evidence as to the rock from which it was derived, but indications pointing to the probable origin of at least part of the gneiss are not lacking. Some of the gneiss may have been and probably was derived from diorite as a result of granite intrusion. Again, much of the diorite in this belt is younger than at least some of the Lower Huronian formations, as it intrudes both the Mesnard quartzite and the Kona dolomite, and it probably caused some metamorphism of those forma tions and was thus a contributing factor in producing the gneiss. Also, some of the gneiss may represent metamorphosed Archean rocks, although no such rocks could be identified, as the base of the Lower Huronian series was not found. In a great many instances, however, both the Mesnard formation and the more slaty phases of the Kona formation were traced directly into a gneiss in the vicinity of granite intrusions. Since much of the Palmer gneiss has been shown to be Huronian sediments, and since the Republic granite, in addition to being a younger intrusion than the diorite, has batholithic propor tions, there appears to be good reason to conclude that a large part of the gneiss within the original belt represents Lower Huronian for-

Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/46/7/1137/3415306/BUL46_7-1137.pdf by guest on 26 September 2021 on 26 September 2021 by guest Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/46/7/1137/3415306/BUL46_7-1137.pdf 1156 . . AE—TE AMR GNEISS PALMER THE LAMEY— A. C.

F ig u re 7.—Revised geological map of the Palmer area No changes have been made in Huronian formations younger than the Ajibik quartzite. Compiled from field notes by the writer and from geological maps in United States Geological Survey Monographs 28 and 52. Culture from air survey mosaic prepared by Michigan Geological Survey. REMAINING PALMER GNEISS BELT 1157 mations, much metamorphosed by the intrusion of the Republic granite. This would be in conformity with metamorphism produced elsewhere by this granite. Moreover, evidence from the region south of the original Palmer gneiss belt tends to substantiate this conclusion. REGION SOUTH OF THE PALMER GNEISS BELT The majority of outcrops observed south of the Palmer gneiss belt consist of granite and amphibole or biotite gneiss, but some small outcrops of rock have escaped severe metamorphism, and these patches furnish valuable information regarding the probable origin of some of the gneiss. Certain outcrops, particularly in section 32, have the appearance of graywacke in one part of the outcrop but furnish con tinuous exposure through gneiss into granite. Microscopic examina tion of some of the rocks with the appearance of graywacke shows the presence of subangular to rounded grains of quartz and feldspar in a chloritic matrix and indicates their fragmental nature. A grada tional series of specimens, from apparent graywacke into granite, shows (1) rounded quartz and feldspar grains, some-of the latter much altered, in a chloritic matrix; (2) rounded quartz and feldspar grains, rimmed and partly replaced by epidote, in an amphibole matrix; or (3) subangular to rounded quartz, sericitized feldspar, and an amphi bole matrix; followed by (4) gneiss showing somewhat rounded spots of quartz and feldspar, some of which apparently are newly formed, as well as irregular masses of those materials, and biotite instead of amphibole, or a gneissoid or granitic rock containing rounded spots of sericite, quartz, and feldspar amidst large feldspar crystals. From series such as this it seems apparent that some of the gneiss south of the Palmer gneiss belt has been derived from sedimentary rocks. In view of the fact that but a relatively small part of the total thickness of the Mesnard formation is accounted for in the definitely identified Mesnard quartzite within the Palmer gneiss belt, there is a strong indication that the fragmental material south of the Palmer gneiss area represents the lower part of the Mesnard for mation and that at least part of the gneiss was derived from such material as a result of the intrusion of the Republic granite and the metamorphism thus produced. On a small scale, the disappearance of the Lower Huronian Mesnard quartzite in the Palmer area appears to be analagous with the disappearance of the Huronian formations in Ontario.16 30T. T. Quirke and W. H. Collins: The disappearance of the Huromaa, Geol. Survey, Canada, Mem* 160 (1930).

Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/46/7/1137/3415306/BUL46_7-1137.pdf by guest on 26 September 2021 1158 C. A. LAMEY----THE PALMER GNEISS Although isolated patches of fragmental rocks do occur south of the Palmer gneiss belt, and grade into gneiss, and much of the gneiss within the belt probably was derived from Huronian formations, the difficulty of separating the sediment and gneiss outcrops from the granite and other igneous rocks is so great that it seems advisable to designate as granite everything south of definitely identified Huro nian sediments in more or less continuous belts. This practice has been followed on the revised map of the area (Fig. 7). The Palmer gneiss, as a separate formation, thus disappears from the map of the area, its place being taken by Huronian sediments and by granite of post-Upper Huronian age, the latter including some gneiss, diorite, diabase, sediments, and possibly some Archean rocks, from which it was not feasible to separate it. STRUCTURE It is extremely difficult to trace for any distance and with certainty all structural features within the Palmer gneiss belt, due to the pres ence of a major unconformity, to the obliteration of bedding by shear ing and fracturing, to at least three periods of igneous intrusion— two basic and one granitic, one of the basic intrusions older, the other younger than the granitic intrusion—to close folding, and to faults, some of which may be of considerable magnitude. Throughout much of the region the folding is close and complex, and the dips, especially in the middle and eastern parts of the belt, approach verticality. In a broad, general way, the structure may be said to follow rather consistently the structure of the overlying iron formation, even though the Lower and Middle Huronian series are unconformable. This similarity of structure is due to the fact that both series form part of the southern limb of the Marquette synclinorium. However, the structure departs radically from that of the iron formation in some places, especially near igneous intrusions or near areas in which faulting appears to have been extensive. Minor faults are abundant throughout the area, and it is likely that several major faults exist. No attempt was made to locate the many minor faults observed, as the displacement along them is insig nificant, but conditions shown along a number of them were sketched in order to portray the type of faulting existing in the area and the character of displacement that might be expected along any major fault (Fig. 8). The faults observed in the area trend, in general, in three direc tions—northwest (Fig. 8a), northeast (Fig. 8b), and nearly east-west.

Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/46/7/1137/3415306/BUL46_7-1137.pdf by guest on 26 September 2021 STRUCTURE 1159 All major faulting apparently is along east-west trending lines, such as the large fault forming the northern boundary of the Palmer basin (Fig. 2).17 Each observed fault with this trend dips north more steeply than do the beds, and the character of displacement is such that either repetition or omission of beds might be caused, depending

Figure 8.—Maps and sections showing types of faulting in the Palmer area All sketches drawn to scale, but the scales differ. Displacements are all small—from a few inches to a foot or two. upon the relation between erosion, dip of fault surface, and dip of bedding (Fig. 8e). There are many indications of major faulting in the area, especially near the contact between the Ajibik quartzite and the Palmer gneiss belt. Throughout much of the region this contact is marked by a valley rarely over 150 feet wide and in many places having a width of but 20 or 25 feet. In many places the walls of this valley are steep, the bare rocks are sheared, and surfaces show the presence of 17 A diabase dike, not shown on maps of the area, trends nearly east and west and cuts the Negaunee iron formation. This dike can be traced for several miles and apparently it has suffered no major displacement from cross-cutting faults.

Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/46/7/1137/3415306/BUL46_7-1137.pdf by guest on 26 September 2021 1160 C. A. LAMEY— THE PALMER GNEISS slickensides. Moreover, large blocks of rock, apparently fault blocks, are to be found in some places within the valley. Granite intrusions occur on both sides of the valley, but in some places large masses of relatively pure granite occur on one side of the valley whereas within 50 feet or less, on the other side of the valley, granite appar ently is absent. Many indications along this valley point to faulting of some magnitude, but there is no good horizon marker by means of which the amount can be established, as it apparently occurs close to the base of the Ajibik quartzite, the lowest formation of the Middle Huronian series, which overlies the Lower Huronian series with marked unconformity. Faulting at this horizon, which is a zone of weakness, might well be expected. In addition to the probable faulting near the base of the Ajibik quartzite, a small but fairly persistent fault occurs south of the Palmer gneiss belt, extending in general along the northern side of State road M 35 (Fig. 7), but neither the dip of the fault surface nor the type of displacement could be ascertained. South of this road is the oversized valley of Werner Creek, into which the fault passes to the eastward. This valley was undoubtedly enlarged during glacial time and probably carried off much of the flood water of the region. The question may be raised, however, whether the fault north of this valley may not be a branch of or extend parallel to a much larger fault within the valley. Extensive faulting such as this would not be surprising, in view of the magnitude of faulting along the northern side of the Palmer basin (Fig. 2). Moreover, some miles farther north there is another large fault.18 Between these two northern faults there apparently is a fault block of some magnitude. Conse quently, it may in time be demonstrated that a large fault exists south of the Palmer region, and that this area, which is in a sense a unit, is in reality a fault block. CONCLUSIONS It has been shown that the Palmer gneiss, originally described as part of the Archean Basement Complex cut by Laurentian granite, in reality consists of a variety of Huronian sediments—conglomerates, quartzites, dolomite, graywacke, and slate—intruded by granite which the writer believes to be of post-Upper Huronian age; diorite of post- Lower Huronian age or younger, which intrudes part of the sediments; olivine diabase younger than the granite; gneiss; and possibly some Archean rocks. 18C. R. Van Hise and C. K. Leith: The geology of the Lake Superior region, U. S. Geol. Surv., Mon. 52 (1911) pi. 17.

Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/46/7/1137/3415306/BUL46_7-1137.pdf by guest on 26 September 2021 Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/46/7/1137/3415306/BUL46_7-1137.pdf by guest on 26 September 2021 BULL. GEOL. SOC. AM. VOL. 46, 1935, PL. 93

PHOTOMICROGRAPHS OF AJIBIK QUARTZITE AND MESNARD FORMATION WITHIN PALMER GNEISS BELT COMPARED WITH THE SAME FORMATIONS NEAR NEGAUNEE AND MARQUETTE

Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/46/7/1137/3415306/BUL46_7-1137.pdf by guest on 26 September 2021 CONCLUSIONS 1161 The sediments are thought to belong to two great unconformable series of Middle and Lower Huronian age. The Middle Huronian series is represented by only a small part of the Ajibik quartzite, which contains granite intrusions. The base of this quartzite is conglom eratic and serves as a means of separating the Ajibik quartzite from the underlying formations. The Lower Huronian series is represented by approximately the lower 200 feet of the Kona dolomite and the upper part of the Mesnard quartzite. These two formations lie unconformably beneath the Ajibik quartzite, the latter sometimes resting upon the Kona dolomite and sometimes directly upon the Mesnard quartzite. The Wewe slate apparently is absent. It appears likely that these sediments were earlier designated Palmer gneiss because the granite which intrudes them was thought to be of Laurentian age. Much of the gneiss within the Palmer gneiss area apparently was derived from Middle and Lower Huronian sediments as a result of granite intrusion, as well as great pressure, as such sediments grade into gneiss near granite intrusions, and patches of recognizable sedi ments were observed within the gneissoid area south of the Palmer gneiss belt. Some of the gneiss may have originated from the meta morphism of post-Lower Huronian diorite, and such diorite intru sions themselves may have been a contributing factor in the meta morphism of the sediments. Part of the gneiss may be altered Archean rocks, but no material that could be definitely identified as Archean was observed, as the base of the Lower Huronian series was not found. The structure of the area is complex. The Huronian sediments have been closely folded, much shattered, and sheared. Many minor faults occur, and some major faults are thought to exist.

P late 93— PHOTOMICROGRAPHS OF AJIBIK QUARTZITE AND MESNARD FORMATION WITHIN PALMER GNEISS BELT COMPARED WITH THE SAME FORMA TIONS NEAR NEGAUNEE AND MARQUETTE (A) Ajibik quartzite from Palmer gneiss belt, showing subangular to rounded quartz grains in sericitic matrix. Crossed niçois, X 64. (B) Ajibik quartzite from vicinity of Negaunee. Crossed niçois, X 64. (C) Ajibik quartzite from Palmer gneiss belt, showing rounded quartz grains in hematite cement. Crossed ni cols, X 27. (D) Ajibik quartzite from vicinity of Negaunee, without as much hematite in the cement. Crossed niçois, X 27. (E) A similar phase of the Mesnard formation from the Palmer gneiss area, containing more ^ricite. Without analyzer, X 13. (F) Mesnard formation from vicinity of Marquette. Large and small quartz grains, and sericite. Note similarity to Mesnard formation from Palmer gneiss area. Crossed ni cols, X 13.